<?xml version="1.0" encoding="utf-8"?>
<!--Generated by DFIN XBRL Instance Document - http://www.dfinsolutions.com/ - Version R3.0 - on 04-February-2021 [08:31:52] {AM}-->
<linkbase xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:xbrldt="http://xbrl.org/2005/xbrldt">
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#CondensedBalanceSheets" roleURI="http://www.meipharma.com/role/CondensedBalanceSheets" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#CondensedBalanceSheetsParenthetical" roleURI="http://www.meipharma.com/role/CondensedBalanceSheetsParenthetical" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#CondensedStatementsOfOperations" roleURI="http://www.meipharma.com/role/CondensedStatementsOfOperations" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#CondensedStatementsOfStockholdersEquity" roleURI="http://www.meipharma.com/role/CondensedStatementsOfStockholdersEquity" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#CondensedStatementsOfCashFlows" roleURI="http://www.meipharma.com/role/CondensedStatementsOfCashFlows" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#TheCompanyAndSummaryOfSignificantAccountingPolicies" roleURI="http://www.meipharma.com/role/TheCompanyAndSummaryOfSignificantAccountingPolicies" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#FairValueMeasurements" roleURI="http://www.meipharma.com/role/FairValueMeasurements" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#LicenseAgreements" roleURI="http://www.meipharma.com/role/LicenseAgreements" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#BeigeneCollaboration" roleURI="http://www.meipharma.com/role/BeigeneCollaboration" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#NetLossPerShare" roleURI="http://www.meipharma.com/role/NetLossPerShare" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#CommitmentsAndContingencies" roleURI="http://www.meipharma.com/role/CommitmentsAndContingencies" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ShortTermInvestments" roleURI="http://www.meipharma.com/role/ShortTermInvestments" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#StockholdersEquity" roleURI="http://www.meipharma.com/role/StockholdersEquity" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ShareBasedCompensation" roleURI="http://www.meipharma.com/role/ShareBasedCompensation" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#TheCompanyAndSummaryOfSignificantAccountingPoliciesPolicies" roleURI="http://www.meipharma.com/role/TheCompanyAndSummaryOfSignificantAccountingPoliciesPolicies" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#TheCompanyAndSummaryOfSignificantAccountingPoliciesTables" roleURI="http://www.meipharma.com/role/TheCompanyAndSummaryOfSignificantAccountingPoliciesTables" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#FairValueMeasurementsTables" roleURI="http://www.meipharma.com/role/FairValueMeasurementsTables" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#NetLossPerShareTables" roleURI="http://www.meipharma.com/role/NetLossPerShareTables" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ShareBasedCompensationTables" roleURI="http://www.meipharma.com/role/ShareBasedCompensationTables" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#TheCompanyAndSummaryOfSignificantAccountingPoliciesAdditionalInformationDetail" roleURI="http://www.meipharma.com/role/TheCompanyAndSummaryOfSignificantAccountingPoliciesAdditionalInformationDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#TheCompanyRevenueAssociatedWithTheFollowingLicenseAgreementsDetail" roleURI="http://www.meipharma.com/role/TheCompanyRevenueAssociatedWithTheFollowingLicenseAgreementsDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#TheCompanyScheduleOfChangesInContractAssetsAndContractLiabilitiesDetail" roleURI="http://www.meipharma.com/role/TheCompanyScheduleOfChangesInContractAssetsAndContractLiabilitiesDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ScheduleOfFinancialInstrumentsMeasuredAtFairValueOnRecurringBasisDetail" roleURI="http://www.meipharma.com/role/ScheduleOfFinancialInstrumentsMeasuredAtFairValueOnRecurringBasisDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ScheduleOfAssumptionsUsedToCalculateFairValueOfWarrantLiabilityDetail" roleURI="http://www.meipharma.com/role/ScheduleOfAssumptionsUsedToCalculateFairValueOfWarrantLiabilityDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ScheduleOfChangesInEstimatedFairValueOfWarrantLiabilityDetail" roleURI="http://www.meipharma.com/role/ScheduleOfChangesInEstimatedFairValueOfWarrantLiabilityDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#LicenseAgreementsAdditionalInformationDetail" roleURI="http://www.meipharma.com/role/LicenseAgreementsAdditionalInformationDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#NetLossPerShareAdditionalInformationDetail" roleURI="http://www.meipharma.com/role/NetLossPerShareAdditionalInformationDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ScheduleOfLossPerShareBasicAndDilutedDetail" roleURI="http://www.meipharma.com/role/ScheduleOfLossPerShareBasicAndDilutedDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#AntidilutiveSecuritiesDetail" roleURI="http://www.meipharma.com/role/AntidilutiveSecuritiesDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#CommitmentsAndContingenciesAdditionalInformationDetail" roleURI="http://www.meipharma.com/role/CommitmentsAndContingenciesAdditionalInformationDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#LeasesAdditionalInformationDetail" roleURI="http://www.meipharma.com/role/LeasesAdditionalInformationDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ShortTermInvestmentsAdditionalInformationDetail" roleURI="http://www.meipharma.com/role/ShortTermInvestmentsAdditionalInformationDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#StockholdersEquityAdditionalInformationDetail" roleURI="http://www.meipharma.com/role/StockholdersEquityAdditionalInformationDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ShareBasedCompensationAdditionalInformationDetail" roleURI="http://www.meipharma.com/role/ShareBasedCompensationAdditionalInformationDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ShareBasedCompensationExpenseForStockAwardsDetail" roleURI="http://www.meipharma.com/role/ShareBasedCompensationExpenseForStockAwardsDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#SummaryOfStockOptionActivityDetail" roleURI="http://www.meipharma.com/role/SummaryOfStockOptionActivityDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#FairValueOfStockOptionsWeightedAverageAssumptionsUsedDetail" roleURI="http://www.meipharma.com/role/FairValueOfStockOptionsWeightedAverageAssumptionsUsedDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#CoverPage" roleURI="http://www.meipharma.com/role/CoverPage" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#Leases" roleURI="http://www.meipharma.com/role/Leases" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#LeasesTables" roleURI="http://www.meipharma.com/role/LeasesTables" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ScheduleOfFutureMinimumRentalPaymentsDetail" roleURI="http://www.meipharma.com/role/ScheduleOfFutureMinimumRentalPaymentsDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ScheduleOfTotalOperatingCostsDetail" roleURI="http://www.meipharma.com/role/ScheduleOfTotalOperatingCostsDetail" />
<roleRef xlink:type="simple" xlink:href="meip-20201231.xsd#ScheduleOfSupplementalCashFlowInformationRelatedToOperatingLeasesDetail" roleURI="http://www.meipharma.com/role/ScheduleOfSupplementalCashFlowInformationRelatedToOperatingLeasesDetail" />
<arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" />
<arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" />
<arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" />
<arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" />
<arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" />
<arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/notAll" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#notAll" />
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/CondensedBalanceSheets">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_27" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaap_AssetsAbstract_22" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_27" xlink:to="loc_us-gaap_AssetsAbstract_22" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_32" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_22" xlink:to="loc_us-gaap_Assets_32" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="loc_us-gaap_AssetsCurrentAbstract_23" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_22" xlink:to="loc_us-gaap_AssetsCurrentAbstract_23" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaap_AssetsCurrent_37" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_23" xlink:to="loc_us-gaap_AssetsCurrent_37" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_33" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_23" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_33" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashCashEquivalentsAndShortTermInvestments" xlink:label="loc_us-gaap_CashCashEquivalentsAndShortTermInvestments_35" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_23" xlink:to="loc_us-gaap_CashCashEquivalentsAndShortTermInvestments_35" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_36" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_23" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_36" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShortTermInvestments" xlink:label="loc_us-gaap_ShortTermInvestments_34" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_23" xlink:to="loc_us-gaap_ShortTermInvestments_34" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ReceivableForForeignTaxWithholding" xlink:label="loc_meip_ReceivableForForeignTaxWithholding_765429" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_23" xlink:to="loc_meip_ReceivableForForeignTaxWithholding_765429" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_31" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_22" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_31" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_765674" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_22" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_765674" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_25" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_27" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_25" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="loc_us-gaap_CommitmentsAndContingencies_41" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_25" xlink:to="loc_us-gaap_CommitmentsAndContingencies_41" use="optional" order="13" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Liabilities" xlink:label="loc_us-gaap_Liabilities_40" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_25" xlink:to="loc_us-gaap_Liabilities_40" use="optional" order="14" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_42" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_25" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_42" use="optional" order="15" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_26" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_25" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_26" use="optional" order="16" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="loc_us-gaap_AccountsPayableCurrent_43" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_26" xlink:to="loc_us-gaap_AccountsPayableCurrent_43" use="optional" order="17" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_44" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_26" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_44" use="optional" order="18" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredRevenueCurrent" xlink:label="loc_us-gaap_DeferredRevenueCurrent_45" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_26" xlink:to="loc_us-gaap_DeferredRevenueCurrent_45" use="optional" order="19" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="loc_us-gaap_LiabilitiesCurrent_46" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_26" xlink:to="loc_us-gaap_LiabilitiesCurrent_46" use="optional" order="20" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseLiabilityCurrent" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_765678" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_26" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_765678" use="optional" order="21" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="loc_us-gaap_StockholdersEquityAbstract_29" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_25" xlink:to="loc_us-gaap_StockholdersEquityAbstract_29" use="optional" order="22" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdditionalPaidInCapitalCommonStock" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_49" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_29" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_49" use="optional" order="23" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockValue" xlink:label="loc_us-gaap_CommonStockValue_48" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_29" xlink:to="loc_us-gaap_CommonStockValue_48" use="optional" order="24" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PreferredStockValue" xlink:label="loc_us-gaap_PreferredStockValue_47" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_29" xlink:to="loc_us-gaap_PreferredStockValue_47" use="optional" order="25" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_50" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_29" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_50" use="optional" order="26" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_51" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_29" xlink:to="loc_us-gaap_StockholdersEquity_51" use="optional" order="27" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WarrantsNotSettleableInCashFairValueDisclosure" xlink:label="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_39" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_25" xlink:to="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_39" use="optional" order="28" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredRevenueNoncurrent" xlink:label="loc_us-gaap_DeferredRevenueNoncurrent_311823" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_25" xlink:to="loc_us-gaap_DeferredRevenueNoncurrent_311823" use="optional" order="29" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_765679" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_25" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_765679" use="optional" order="30" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_28" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_27" xlink:to="loc_us-gaap_StatementTable_28" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="31" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_24" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_28" xlink:to="loc_dei_LegalEntityAxis_24" use="optional" order="32" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_38" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_24" xlink:to="loc_dei_EntityDomain_38" use="optional" order="33" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_38_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_24" xlink:to="loc_dei_EntityDomain_38_default" use="optional" order="34" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/CondensedBalanceSheetsParenthetical">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_55" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_61" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_55" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_61" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_62" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_55" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_62" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="loc_us-gaap_CommonStockSharesIssued_63" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_55" xlink:to="loc_us-gaap_CommonStockSharesIssued_63" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_64" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_55" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_64" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_58" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_55" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_58" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_59" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_55" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_59" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_60" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_55" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_60" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_56" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_55" xlink:to="loc_us-gaap_StatementTable_56" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_54" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_56" xlink:to="loc_dei_LegalEntityAxis_54" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_57" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_54" xlink:to="loc_dei_EntityDomain_57" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_57_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_54" xlink:to="loc_dei_EntityDomain_57_default" use="optional" order="11" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/CondensedStatementsOfOperations">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_72" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CostsAndExpensesAbstract" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_67" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_72" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_67" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CostOfGoodsAndServicesSold" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_75" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_67" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_75" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CostsAndExpenses" xlink:label="loc_us-gaap_CostsAndExpenses_78" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_67" xlink:to="loc_us-gaap_CostsAndExpenses_78" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_77" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_67" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_77" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_76" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_67" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_76" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareAbstract" xlink:label="loc_us-gaap_EarningsPerShareAbstract_89" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_72" xlink:to="loc_us-gaap_EarningsPerShareAbstract_89" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareBasic" xlink:label="loc_us-gaap_EarningsPerShareBasic_90" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_89" xlink:to="loc_us-gaap_EarningsPerShareBasic_90" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="loc_us-gaap_EarningsPerShareDiluted_91" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_89" xlink:to="loc_us-gaap_EarningsPerShareDiluted_91" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLossAbstract" xlink:label="loc_us-gaap_NetIncomeLossAbstract_69" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_72" xlink:to="loc_us-gaap_NetIncomeLossAbstract_69" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_80" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAbstract_69" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_80" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_81" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAbstract_69" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_81" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NonoperatingIncomeExpenseAbstract" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_70" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_72" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_70" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_82" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_70" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_82" use="optional" order="13" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentIncomeInterestAndDividend" xlink:label="loc_us-gaap_InvestmentIncomeInterestAndDividend_83" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_70" xlink:to="loc_us-gaap_InvestmentIncomeInterestAndDividend_83" use="optional" order="14" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_85" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_70" xlink:to="loc_us-gaap_NetIncomeLoss_85" use="optional" order="15" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_765439" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_70" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_765439" use="optional" order="16" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaap_OperatingIncomeLoss_88" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_72" xlink:to="loc_us-gaap_OperatingIncomeLoss_88" use="optional" order="17" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_86" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_72" xlink:to="loc_us-gaap_Revenues_86" use="optional" order="18" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_73" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_72" xlink:to="loc_us-gaap_StatementTable_73" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="19" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_68" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_73" xlink:to="loc_dei_LegalEntityAxis_68" use="optional" order="20" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_79" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_68" xlink:to="loc_dei_EntityDomain_79" use="optional" order="21" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_79_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_68" xlink:to="loc_dei_EntityDomain_79_default" use="optional" order="22" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_74" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_72" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_74" use="optional" order="23" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_93" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_74" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_93" use="optional" order="24" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_92" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_74" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_92" use="optional" order="25" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/CondensedStatementsOfStockholdersEquity">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_409054" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_409046" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_409054" xlink:to="loc_us-gaap_StatementTable_409046" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_409047" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_409046" xlink:to="loc_dei_LegalEntityAxis_409047" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_409048" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_409047" xlink:to="loc_dei_EntityDomain_409048" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_409048_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_409047" xlink:to="loc_dei_EntityDomain_409048_default" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_409049" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_409046" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_409049" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_409050" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_409049" xlink:to="loc_us-gaap_EquityComponentDomain_409050" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_409050_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_409049" xlink:to="loc_us-gaap_EquityComponentDomain_409050_default" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_409051" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_409050" xlink:to="loc_us-gaap_CommonStockMember_409051" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_409052" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_409050" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_409052" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember_409053" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_409050" xlink:to="loc_us-gaap_RetainedEarningsMember_409053" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_478153" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_409046" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_478153" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_478154" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_478153" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_478154" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_478154_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_478153" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_478154_default" use="optional" order="13" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_478156" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_409046" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_478156" use="optional" order="14" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingencyNatureDomain" xlink:label="loc_us-gaap_LossContingencyNatureDomain_478157" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_478156" xlink:to="loc_us-gaap_LossContingencyNatureDomain_478157" use="optional" order="15" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingencyNatureDomain" xlink:label="loc_us-gaap_LossContingencyNatureDomain_478157_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_478156" xlink:to="loc_us-gaap_LossContingencyNatureDomain_478157_default" use="optional" order="16" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_409058" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409054" xlink:to="loc_us-gaap_StockholdersEquity_409058" use="optional" order="17" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_409059" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409054" xlink:to="loc_us-gaap_NetIncomeLoss_409059" use="optional" order="18" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_409062" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409054" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_409062" use="optional" order="19" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_409064" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409054" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_409064" use="optional" order="20" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_409068" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409054" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_409068" use="optional" order="21" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/CondensedStatementsOfCashFlows">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_102" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_123" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_102" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_123" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_122" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_102" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_122" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_99" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_102" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_99" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_115" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_99" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_115" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromStockOptionsExercised" xlink:label="loc_us-gaap_ProceedsFromStockOptionsExercised_112" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_99" xlink:to="loc_us-gaap_ProceedsFromStockOptionsExercised_112" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_765455" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_99" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_765455" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ProceedsFromPreviouslyIssuedCommonStock" xlink:label="loc_meip_ProceedsFromPreviouslyIssuedCommonStock_765456" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_99" xlink:to="loc_meip_ProceedsFromPreviouslyIssuedCommonStock_765456" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_100" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_102" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_100" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_119" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_100" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_119" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_116" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_100" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_116" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireShortTermInvestments" xlink:label="loc_us-gaap_PaymentsToAcquireShortTermInvestments_117" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_100" xlink:to="loc_us-gaap_PaymentsToAcquireShortTermInvestments_117" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfShorttermInvestments" xlink:label="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfShorttermInvestments_118" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_100" xlink:to="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfShorttermInvestments_118" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_101" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_102" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_101" use="optional" order="13" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_96" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_101" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_96" use="optional" order="14" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DepreciationDepletionAndAmortization" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_106" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_96" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_106" use="optional" order="15" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_104" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_96" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_104" use="optional" order="16" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="loc_us-gaap_ShareBasedCompensation_105" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_96" xlink:to="loc_us-gaap_ShareBasedCompensation_105" use="optional" order="17" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_NonCashLeaseExpense" xlink:label="loc_meip_NonCashLeaseExpense_765686" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_96" xlink:to="loc_meip_NonCashLeaseExpense_765686" use="optional" order="18" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_97" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_101" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_97" use="optional" order="19" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayableTrade" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayableTrade_108" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_97" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayableTrade_108" use="optional" order="20" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_109" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_97" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_109" use="optional" order="21" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerLiability" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_110" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_97" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_110" use="optional" order="22" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_107" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_97" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_107" use="optional" order="23" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_IncreaseDecreaseInOperatingLeaseLiabilitiesCurrent" xlink:label="loc_meip_IncreaseDecreaseInOperatingLeaseLiabilitiesCurrent_765685" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_97" xlink:to="loc_meip_IncreaseDecreaseInOperatingLeaseLiabilitiesCurrent_765685" use="optional" order="24" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_IncreaseOrDecreaseInReceivableForForeignTaxWithholding" xlink:label="loc_meip_IncreaseOrDecreaseInReceivableForForeignTaxWithholding_810778" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_97" xlink:to="loc_meip_IncreaseOrDecreaseInReceivableForForeignTaxWithholding_810778" use="optional" order="25" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_121" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_101" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_121" use="optional" order="26" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_120" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_101" xlink:to="loc_us-gaap_ProfitLoss_120" use="optional" order="27" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_103" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_102" xlink:to="loc_us-gaap_StatementTable_103" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="28" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_98" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_103" xlink:to="loc_dei_LegalEntityAxis_98" use="optional" order="29" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_111" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_98" xlink:to="loc_dei_EntityDomain_111" use="optional" order="30" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_111_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_98" xlink:to="loc_dei_EntityDomain_111_default" use="optional" order="31" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_478166" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_102" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_478166" use="optional" order="32" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeTaxesPaidNet" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_478167" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_478166" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_478167" use="optional" order="33" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability" xlink:label="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_765687" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_478166" xlink:to="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_765687" use="optional" order="34" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/TheCompanyAndSummaryOfSignificantAccountingPolicies">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_402" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureAndSignificantAccountingPoliciesTextBlock" xlink:label="loc_us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureAndSignificantAccountingPoliciesTextBlock_405" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_402" xlink:to="loc_us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureAndSignificantAccountingPoliciesTextBlock_405" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_403" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_402" xlink:to="loc_us-gaap_StatementTable_403" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_401" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_403" xlink:to="loc_dei_LegalEntityAxis_401" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_404" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_401" xlink:to="loc_dei_EntityDomain_404" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_404_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_401" xlink:to="loc_dei_EntityDomain_404_default" use="optional" order="5" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/FairValueMeasurements">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_430" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueDisclosuresTextBlock" xlink:label="loc_us-gaap_FairValueDisclosuresTextBlock_433" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_430" xlink:to="loc_us-gaap_FairValueDisclosuresTextBlock_433" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_431" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_430" xlink:to="loc_us-gaap_StatementTable_431" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_429" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_431" xlink:to="loc_dei_LegalEntityAxis_429" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_432" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_429" xlink:to="loc_dei_EntityDomain_432" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_432_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_429" xlink:to="loc_dei_EntityDomain_432_default" use="optional" order="5" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/LicenseAgreements">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_446" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionsDisclosureTextBlock" xlink:label="loc_us-gaap_RelatedPartyTransactionsDisclosureTextBlock_449" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_446" xlink:to="loc_us-gaap_RelatedPartyTransactionsDisclosureTextBlock_449" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_447" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_446" xlink:to="loc_us-gaap_StatementTable_447" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_445" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_447" xlink:to="loc_dei_LegalEntityAxis_445" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_448" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_445" xlink:to="loc_dei_EntityDomain_448" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_448_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_445" xlink:to="loc_dei_EntityDomain_448_default" use="optional" order="5" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/BeigeneCollaboration">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_453" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CollaborativeArrangementDisclosureTextBlock" xlink:label="loc_us-gaap_CollaborativeArrangementDisclosureTextBlock_456" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_453" xlink:to="loc_us-gaap_CollaborativeArrangementDisclosureTextBlock_456" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_454" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_453" xlink:to="loc_us-gaap_StatementTable_454" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_452" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_454" xlink:to="loc_dei_LegalEntityAxis_452" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_455" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_452" xlink:to="loc_dei_EntityDomain_455" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_455_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_452" xlink:to="loc_dei_EntityDomain_455_default" use="optional" order="5" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/NetLossPerShare">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_460" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareTextBlock" xlink:label="loc_us-gaap_EarningsPerShareTextBlock_463" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_460" xlink:to="loc_us-gaap_EarningsPerShareTextBlock_463" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_461" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_460" xlink:to="loc_us-gaap_StatementTable_461" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_459" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_461" xlink:to="loc_dei_LegalEntityAxis_459" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_462" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_459" xlink:to="loc_dei_EntityDomain_462" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_462_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_459" xlink:to="loc_dei_EntityDomain_462_default" use="optional" order="5" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/CommitmentsAndContingencies">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_475" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:label="loc_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_478" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_475" xlink:to="loc_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_478" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_476" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_475" xlink:to="loc_us-gaap_StatementTable_476" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_474" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_476" xlink:to="loc_dei_LegalEntityAxis_474" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_477" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_474" xlink:to="loc_dei_EntityDomain_477" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_477_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_474" xlink:to="loc_dei_EntityDomain_477_default" use="optional" order="5" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/ShortTermInvestments">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_482" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock" xlink:label="loc_us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock_485" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_482" xlink:to="loc_us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock_485" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_483" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_482" xlink:to="loc_us-gaap_StatementTable_483" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_481" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_483" xlink:to="loc_dei_LegalEntityAxis_481" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_484" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_481" xlink:to="loc_dei_EntityDomain_484" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_484_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_481" xlink:to="loc_dei_EntityDomain_484_default" use="optional" order="5" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/StockholdersEquity">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_489" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_490" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_489" xlink:to="loc_us-gaap_StatementTable_490" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_488" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_490" xlink:to="loc_dei_LegalEntityAxis_488" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_491" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_488" xlink:to="loc_dei_EntityDomain_491" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_491_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_488" xlink:to="loc_dei_EntityDomain_491_default" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquityNoteDisclosureTextBlock" xlink:label="loc_us-gaap_StockholdersEquityNoteDisclosureTextBlock_492" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_489" xlink:to="loc_us-gaap_StockholdersEquityNoteDisclosureTextBlock_492" use="optional" order="5" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/ShareBasedCompensation">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_496" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" xlink:label="loc_us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_499" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_496" xlink:to="loc_us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_499" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_497" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_496" xlink:to="loc_us-gaap_StatementTable_497" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_495" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_497" xlink:to="loc_dei_LegalEntityAxis_495" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_498" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_495" xlink:to="loc_dei_EntityDomain_498" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_498_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_495" xlink:to="loc_dei_EntityDomain_498_default" use="optional" order="5" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/TheCompanyAndSummaryOfSignificantAccountingPoliciesPolicies">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_409" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:label="loc_us-gaap_BasisOfAccountingPolicyPolicyTextBlock_413" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409" xlink:to="loc_us-gaap_BasisOfAccountingPolicyPolicyTextBlock_413" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ClinicalDevelopmentProgramsPolicyTextBlock" xlink:label="loc_meip_ClinicalDevelopmentProgramsPolicyTextBlock_412" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409" xlink:to="loc_meip_ClinicalDevelopmentProgramsPolicyTextBlock_412" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CompensationRelatedCostsPolicyTextBlock" xlink:label="loc_us-gaap_CompensationRelatedCostsPolicyTextBlock_417" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409" xlink:to="loc_us-gaap_CompensationRelatedCostsPolicyTextBlock_417" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeTaxPolicyTextBlock" xlink:label="loc_us-gaap_IncomeTaxPolicyTextBlock_418" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409" xlink:to="loc_us-gaap_IncomeTaxPolicyTextBlock_418" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResearchAndDevelopmentExpensePolicy" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpensePolicy_416" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpensePolicy_416" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRecognitionPolicyTextBlock" xlink:label="loc_us-gaap_RevenueRecognitionPolicyTextBlock_415" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409" xlink:to="loc_us-gaap_RevenueRecognitionPolicyTextBlock_415" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_410" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_409" xlink:to="loc_us-gaap_StatementTable_410" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_408" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_410" xlink:to="loc_dei_LegalEntityAxis_408" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_411" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_408" xlink:to="loc_dei_EntityDomain_411" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_411_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_408" xlink:to="loc_dei_EntityDomain_411_default" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UseOfEstimates" xlink:label="loc_us-gaap_UseOfEstimates_414" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409" xlink:to="loc_us-gaap_UseOfEstimates_414" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_LiquidityPolicyTextBlock" xlink:label="loc_meip_LiquidityPolicyTextBlock_481048" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409" xlink:to="loc_meip_LiquidityPolicyTextBlock_481048" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LesseeLeasesPolicyTextBlock" xlink:label="loc_us-gaap_LesseeLeasesPolicyTextBlock_765461" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_409" xlink:to="loc_us-gaap_LesseeLeasesPolicyTextBlock_765461" use="optional" order="13" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/TheCompanyAndSummaryOfSignificantAccountingPoliciesTables">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_423" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerAssetAndLiabilityTableTextBlock" xlink:label="loc_us-gaap_ContractWithCustomerAssetAndLiabilityTableTextBlock_426" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_423" xlink:to="loc_us-gaap_ContractWithCustomerAssetAndLiabilityTableTextBlock_426" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_424" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_423" xlink:to="loc_us-gaap_StatementTable_424" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_422" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_424" xlink:to="loc_dei_LegalEntityAxis_422" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_425" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_422" xlink:to="loc_dei_EntityDomain_425" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_425_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_422" xlink:to="loc_dei_EntityDomain_425_default" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ScheduleOfRevenueAssociatedWithLicenseAgreementTableTextBlock" xlink:label="loc_meip_ScheduleOfRevenueAssociatedWithLicenseAgreementTableTextBlock_311933" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_423" xlink:to="loc_meip_ScheduleOfRevenueAssociatedWithLicenseAgreementTableTextBlock_311933" use="optional" order="6" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/FairValueMeasurementsTables">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_437" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_FairValueOfWarrantLiabilityAssumptionsTableTextBlock" xlink:label="loc_meip_FairValueOfWarrantLiabilityAssumptionsTableTextBlock_441" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_437" xlink:to="loc_meip_FairValueOfWarrantLiabilityAssumptionsTableTextBlock_441" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ScheduleOfChangesInFairValueOfWarrantLiabilityTableTextBlock" xlink:label="loc_meip_ScheduleOfChangesInFairValueOfWarrantLiabilityTableTextBlock_442" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_437" xlink:to="loc_meip_ScheduleOfChangesInFairValueOfWarrantLiabilityTableTextBlock_442" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_440" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_437" xlink:to="loc_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_440" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_438" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_437" xlink:to="loc_us-gaap_StatementTable_438" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_436" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_438" xlink:to="loc_dei_LegalEntityAxis_436" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_439" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_436" xlink:to="loc_dei_EntityDomain_439" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_439_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_436" xlink:to="loc_dei_EntityDomain_439_default" use="optional" order="7" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/NetLossPerShareTables">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_467" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock_470" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_467" xlink:to="loc_us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock_470" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_468" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_467" xlink:to="loc_us-gaap_StatementTable_468" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_466" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_468" xlink:to="loc_dei_LegalEntityAxis_466" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_469" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_466" xlink:to="loc_dei_EntityDomain_469" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_469_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_466" xlink:to="loc_dei_EntityDomain_469_default" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_765487" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_467" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_765487" use="optional" order="6" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/ShareBasedCompensationTables">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_503" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisclosureOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTextBlock" xlink:label="loc_us-gaap_DisclosureOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTextBlock_507" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_503" xlink:to="loc_us-gaap_DisclosureOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTextBlock_507" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock_506" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_503" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock_506" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_508" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_503" xlink:to="loc_us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_508" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_504" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_503" xlink:to="loc_us-gaap_StatementTable_504" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_502" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_504" xlink:to="loc_dei_LegalEntityAxis_502" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_505" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_502" xlink:to="loc_dei_EntityDomain_505" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_505_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_502" xlink:to="loc_dei_EntityDomain_505_default" use="optional" order="7" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/TheCompanyAndSummaryOfSignificantAccountingPoliciesAdditionalInformationDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TargetedOrTrackingStockStockLineItems" xlink:label="loc_us-gaap_TargetedOrTrackingStockStockLineItems_128" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_NumberOfClinicalStageCandidates" xlink:label="loc_meip_NumberOfClinicalStageCandidates_131" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockLineItems_128" xlink:to="loc_meip_NumberOfClinicalStageCandidates_131" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_133" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockLineItems_128" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_133" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TargetedOrTrackingStockStockTable" xlink:label="loc_us-gaap_TargetedOrTrackingStockStockTable_129" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockLineItems_128" xlink:to="loc_us-gaap_TargetedOrTrackingStockStockTable_129" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_127" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockTable_129" xlink:to="loc_dei_LegalEntityAxis_127" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_130" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_127" xlink:to="loc_dei_EntityDomain_130" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_130_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_127" xlink:to="loc_dei_EntityDomain_130_default" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaap_TypeOfArrangementAxis_311913" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockTable_129" xlink:to="loc_us-gaap_TypeOfArrangementAxis_311913" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_311916" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_311913" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_311916" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_311916_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_311913" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_311916_default" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis" xlink:label="loc_srt_RangeAxis_478189" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockTable_129" xlink:to="loc_srt_RangeAxis_478189" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="loc_srt_RangeMember_478190" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_478189" xlink:to="loc_srt_RangeMember_478190" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="loc_srt_RangeMember_478190_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_478189" xlink:to="loc_srt_RangeMember_478190_default" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_478193" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockTable_129" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_478193" use="optional" order="13" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_478194" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_478193" xlink:to="loc_us-gaap_TypeOfAdoptionMember_478194" use="optional" order="14" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_478194_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_478193" xlink:to="loc_us-gaap_TypeOfAdoptionMember_478194_default" use="optional" order="15" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_AgreementAxis" xlink:label="loc_meip_AgreementAxis_765465" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockTable_129" xlink:to="loc_meip_AgreementAxis_765465" use="optional" order="16" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_AgreementDomain" xlink:label="loc_meip_AgreementDomain_765466" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_meip_AgreementAxis_765465" xlink:to="loc_meip_AgreementDomain_765466" use="optional" order="17" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_AgreementDomain" xlink:label="loc_meip_AgreementDomain_765466_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_meip_AgreementAxis_765465" xlink:to="loc_meip_AgreementDomain_765466_default" use="optional" order="18" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_HelsinnLicenseAgreementMember" xlink:label="loc_meip_HelsinnLicenseAgreementMember_765467" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_AgreementDomain_765466" xlink:to="loc_meip_HelsinnLicenseAgreementMember_765467" use="optional" order="19" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_KkcCommercializationAgreementAndTheHelsinnLicenseAgreementMember" xlink:label="loc_meip_KkcCommercializationAgreementAndTheHelsinnLicenseAgreementMember_810790" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_AgreementDomain_765466" xlink:to="loc_meip_KkcCommercializationAgreementAndTheHelsinnLicenseAgreementMember_810790" use="optional" order="20" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_KkcAgreementsandHelsinnLicenseAgreementMember" xlink:label="loc_meip_KkcAgreementsandHelsinnLicenseAgreementMember_811812" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_AgreementDomain_765466" xlink:to="loc_meip_KkcAgreementsandHelsinnLicenseAgreementMember_811812" use="optional" order="21" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredRevenueArrangementTypeAxis" xlink:label="loc_us-gaap_DeferredRevenueArrangementTypeAxis_810802" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockTable_129" xlink:to="loc_us-gaap_DeferredRevenueArrangementTypeAxis_810802" use="optional" order="22" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredRevenueArrangementTypeDomain" xlink:label="loc_us-gaap_DeferredRevenueArrangementTypeDomain_810803" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DeferredRevenueArrangementTypeAxis_810802" xlink:to="loc_us-gaap_DeferredRevenueArrangementTypeDomain_810803" use="optional" order="23" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredRevenueArrangementTypeDomain" xlink:label="loc_us-gaap_DeferredRevenueArrangementTypeDomain_810803_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DeferredRevenueArrangementTypeAxis_810802" xlink:to="loc_us-gaap_DeferredRevenueArrangementTypeDomain_810803_default" use="optional" order="24" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_UsLicenseMember" xlink:label="loc_meip_UsLicenseMember_810804" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementTypeDomain_810803" xlink:to="loc_meip_UsLicenseMember_810804" use="optional" order="25" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ExUsLicenseMember" xlink:label="loc_meip_ExUsLicenseMember_810805" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementTypeDomain_810803" xlink:to="loc_meip_ExUsLicenseMember_810805" use="optional" order="26" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnrecognizedTaxBenefits" xlink:label="loc_us-gaap_UnrecognizedTaxBenefits_136" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockLineItems_128" xlink:to="loc_us-gaap_UnrecognizedTaxBenefits_136" use="optional" order="27" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_RevenuePerformanceObligationAmount" xlink:label="loc_meip_RevenuePerformanceObligationAmount_311934" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockLineItems_128" xlink:to="loc_meip_RevenuePerformanceObligationAmount_311934" use="optional" order="28" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_481044" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockLineItems_128" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_481044" use="optional" order="29" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_CashAndCashEquivalentsshortTermInvestmentsAndCommonStockProceedsReceivable" xlink:label="loc_meip_CashAndCashEquivalentsshortTermInvestmentsAndCommonStockProceedsReceivable_481046" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockLineItems_128" xlink:to="loc_meip_CashAndCashEquivalentsshortTermInvestmentsAndCommonStockProceedsReceivable_481046" use="optional" order="30" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerAsset" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerAsset_810786" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockLineItems_128" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerAsset_810786" use="optional" order="31" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerAssetNetCurrent" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_810792" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockLineItems_128" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_810792" use="optional" order="32" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_810809" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockLineItems_128" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_810809" use="optional" order="33" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredRevenueRevenueRecognized1" xlink:label="loc_us-gaap_DeferredRevenueRevenueRecognized1_811818" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TargetedOrTrackingStockStockLineItems_128" xlink:to="loc_us-gaap_DeferredRevenueRevenueRecognized1_811818" use="optional" order="34" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/TheCompanyRevenueAssociatedWithTheFollowingLicenseAgreementsDetail">
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_RecognizedRevenueAssociatedWithTheFollowingLicenseAgreementsLineItems" xlink:label="loc_meip_RecognizedRevenueAssociatedWithTheFollowingLicenseAgreementsLineItems_311880" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_RecognizedRevenueAssociatedWithTheFollowingLicenseAgreementsTable" xlink:label="loc_meip_RecognizedRevenueAssociatedWithTheFollowingLicenseAgreementsTable_311877" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_meip_RecognizedRevenueAssociatedWithTheFollowingLicenseAgreementsLineItems_311880" xlink:to="loc_meip_RecognizedRevenueAssociatedWithTheFollowingLicenseAgreementsTable_311877" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaap_TypeOfArrangementAxis_311881" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_meip_RecognizedRevenueAssociatedWithTheFollowingLicenseAgreementsTable_311877" xlink:to="loc_us-gaap_TypeOfArrangementAxis_311881" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_311882" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_311881" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_311882" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_311882_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_311881" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_311882_default" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_KkcAgreementsMember" xlink:label="loc_meip_KkcAgreementsMember_311883" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_311882" xlink:to="loc_meip_KkcAgreementsMember_311883" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_HelsinnLicenseAgreementMember" xlink:label="loc_meip_HelsinnLicenseAgreementMember_311892" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_311882" xlink:to="loc_meip_HelsinnLicenseAgreementMember_311892" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TimingOfTransferOfGoodOrServiceAxis" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_481081" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_meip_RecognizedRevenueAssociatedWithTheFollowingLicenseAgreementsTable_311877" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_481081" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_481082" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_481081" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_481082" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_481082_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_481081" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_481082_default" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransferredOverTimeMember" xlink:label="loc_us-gaap_TransferredOverTimeMember_481084" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_481082" xlink:to="loc_us-gaap_TransferredOverTimeMember_481084" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_311885" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_RecognizedRevenueAssociatedWithTheFollowingLicenseAgreementsLineItems_311880" xlink:to="loc_us-gaap_Revenues_311885" use="optional" order="11" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/TheCompanyScheduleOfChangesInContractAssetsAndContractLiabilitiesDetail">
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ContractWithCustomerAssetAndLiabilityLineItems" xlink:label="loc_meip_ContractWithCustomerAssetAndLiabilityLineItems_139" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_AccountsReceivableNetBeginningBalance" xlink:label="loc_meip_AccountsReceivableNetBeginningBalance_142" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_ContractWithCustomerAssetAndLiabilityLineItems_139" xlink:to="loc_meip_AccountsReceivableNetBeginningBalance_142" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_AccountsReceivableNetEndingBalance" xlink:label="loc_meip_AccountsReceivableNetEndingBalance_144" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_ContractWithCustomerAssetAndLiabilityLineItems_139" xlink:to="loc_meip_AccountsReceivableNetEndingBalance_144" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ContractWithCustomerAssetAndLiabilityTable" xlink:label="loc_meip_ContractWithCustomerAssetAndLiabilityTable_140" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_meip_ContractWithCustomerAssetAndLiabilityLineItems_139" xlink:to="loc_meip_ContractWithCustomerAssetAndLiabilityTable_140" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_141" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_meip_ContractWithCustomerAssetAndLiabilityTable_140" xlink:to="loc_dei_LegalEntityAxis_141" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_151" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_141" xlink:to="loc_dei_EntityDomain_151" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_151_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_141" xlink:to="loc_dei_EntityDomain_151_default" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerAssetNetCurrent" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_145" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_ContractWithCustomerAssetAndLiabilityLineItems_139" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_145" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerLiability" xlink:label="loc_us-gaap_ContractWithCustomerLiability_148" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_ContractWithCustomerAssetAndLiabilityLineItems_139" xlink:to="loc_us-gaap_ContractWithCustomerLiability_148" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerAsset" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerAsset_146" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_ContractWithCustomerAssetAndLiabilityLineItems_139" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerAsset_146" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerLiability" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_149" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_ContractWithCustomerAssetAndLiabilityLineItems_139" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_149" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInReceivables" xlink:label="loc_us-gaap_IncreaseDecreaseInReceivables_143" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_ContractWithCustomerAssetAndLiabilityLineItems_139" xlink:to="loc_us-gaap_IncreaseDecreaseInReceivables_143" use="optional" order="11" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/ScheduleOfFinancialInstrumentsMeasuredAtFairValueOnRecurringBasisDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_154" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByBalanceSheetGroupingTable" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_155" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_154" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_155" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_156" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_155" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_156" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_159" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_156" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_159" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_159_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_156" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_159_default" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_168" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_159" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_168" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_157" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_155" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_157" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_158" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_157" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_158" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_158_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_157" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_158_default" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_166" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_158" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_166" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_160" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_155" xlink:to="loc_dei_LegalEntityAxis_160" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_169" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_160" xlink:to="loc_dei_EntityDomain_169" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_169_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_160" xlink:to="loc_dei_EntityDomain_169_default" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosure" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_165" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_154" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_165" use="optional" order="13" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WarrantsNotSettleableInCashFairValueDisclosure" xlink:label="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_164" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_154" xlink:to="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_164" use="optional" order="14" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/ScheduleOfAssumptionsUsedToCalculateFairValueOfWarrantLiabilityDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_172" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_173" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_172" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_173" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_174" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_173" xlink:to="loc_dei_LegalEntityAxis_174" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_180" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_174" xlink:to="loc_dei_EntityDomain_180" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_180_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_174" xlink:to="loc_dei_EntityDomain_180_default" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_175" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_173" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_175" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_176" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_175" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_176" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_176_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_175" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_176_default" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MeasurementInputExpectedDividendRateMember" xlink:label="loc_us-gaap_MeasurementInputExpectedDividendRateMember_184" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_176" xlink:to="loc_us-gaap_MeasurementInputExpectedDividendRateMember_184" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MeasurementInputExpectedTermMember" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_182" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_176" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_182" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MeasurementInputPriceVolatilityMember" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_183" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_176" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_183" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_181" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_176" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_181" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MeasurementInputExercisePriceMember" xlink:label="loc_us-gaap_MeasurementInputExercisePriceMember_478745" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_176" xlink:to="loc_us-gaap_MeasurementInputExercisePriceMember_478745" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_478746" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_172" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_478746" use="optional" order="13" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/ScheduleOfChangesInEstimatedFairValueOfWarrantLiabilityDetail">
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_FairValueMeasurementsSignificantUnobservableInputsLineItems" xlink:label="loc_meip_FairValueMeasurementsSignificantUnobservableInputsLineItems_191" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_198" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_FairValueMeasurementsSignificantUnobservableInputsLineItems_191" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_198" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_FairValueMeasurementsSignificantUnobservableInputsTable" xlink:label="loc_meip_FairValueMeasurementsSignificantUnobservableInputsTable_192" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_meip_FairValueMeasurementsSignificantUnobservableInputsLineItems_191" xlink:to="loc_meip_FairValueMeasurementsSignificantUnobservableInputsTable_192" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_187" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_meip_FairValueMeasurementsSignificantUnobservableInputsTable_192" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_187" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_190" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_187" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_190" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_190_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_187" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_190_default" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_195" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_190" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_195" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_188" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_meip_FairValueMeasurementsSignificantUnobservableInputsTable_192" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_188" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_189" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_188" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_189" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_189_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_188" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_189_default" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_194" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_189" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_194" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_193" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_meip_FairValueMeasurementsSignificantUnobservableInputsTable_192" xlink:to="loc_dei_LegalEntityAxis_193" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_200" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_193" xlink:to="loc_dei_EntityDomain_200" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_200_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_193" xlink:to="loc_dei_EntityDomain_200_default" use="optional" order="13" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WarrantsNotSettleableInCashFairValueDisclosure" xlink:label="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_196" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_FairValueMeasurementsSignificantUnobservableInputsLineItems_191" xlink:to="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_196" use="optional" order="14" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/LicenseAgreementsAdditionalInformationDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_211" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_AgreementTerminationNoticePeriod" xlink:label="loc_meip_AgreementTerminationNoticePeriod_236" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_AgreementTerminationNoticePeriod_236" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DueToRelatedPartiesCurrentAndNoncurrent" xlink:label="loc_us-gaap_DueToRelatedPartiesCurrentAndNoncurrent_232" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_us-gaap_DueToRelatedPartiesCurrentAndNoncurrent_232" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_PaymentForLicenseAgreement" xlink:label="loc_meip_PaymentForLicenseAgreement_234" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_PaymentForLicenseAgreement_234" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_PercentageOfPurchasesFromMajorSuppliers" xlink:label="loc_meip_PercentageOfPurchasesFromMajorSuppliers_235" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_PercentageOfPurchasesFromMajorSuppliers_235" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_PotentialMilestonePaymentsPayable" xlink:label="loc_meip_PotentialMilestonePaymentsPayable_233" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_PotentialMilestonePaymentsPayable_233" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_PotentialMilestonePaymentsReceivable" xlink:label="loc_meip_PotentialMilestonePaymentsReceivable_226" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_PotentialMilestonePaymentsReceivable_226" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromLicenseFeesReceived" xlink:label="loc_us-gaap_ProceedsFromLicenseFeesReceived_225" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_us-gaap_ProceedsFromLicenseFeesReceived_225" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_213" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_213" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_205" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_213" xlink:to="loc_dei_LegalEntityAxis_205" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_204" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_205" xlink:to="loc_dei_EntityDomain_204" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_204_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_205" xlink:to="loc_dei_EntityDomain_204_default" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_KyowaKirinCoMember" xlink:label="loc_meip_KyowaKirinCoMember_218" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_204" xlink:to="loc_meip_KyowaKirinCoMember_218" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis" xlink:label="loc_srt_RangeAxis_206" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_213" xlink:to="loc_srt_RangeAxis_206" use="optional" order="13" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="loc_srt_RangeMember_207" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_206" xlink:to="loc_srt_RangeMember_207" use="optional" order="14" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="loc_srt_RangeMember_207_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_206" xlink:to="loc_srt_RangeMember_207_default" use="optional" order="15" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember" xlink:label="loc_srt_MaximumMember_219" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_207" xlink:to="loc_srt_MaximumMember_219" use="optional" order="16" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_209" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_213" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_209" use="optional" order="17" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_210" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_209" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_210" use="optional" order="18" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_210_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_209" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_210_default" use="optional" order="19" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_IncrementalPaymentMember" xlink:label="loc_meip_IncrementalPaymentMember_223" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_210" xlink:to="loc_meip_IncrementalPaymentMember_223" use="optional" order="20" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_PotentialPaymentsOnAchievementOfDevelopmentRegulatoryAndCommercialMilestonesMember" xlink:label="loc_meip_PotentialPaymentsOnAchievementOfDevelopmentRegulatoryAndCommercialMilestonesMember_224" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_210" xlink:to="loc_meip_PotentialPaymentsOnAchievementOfDevelopmentRegulatoryAndCommercialMilestonesMember_224" use="optional" order="21" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_212" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_213" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_212" use="optional" order="22" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_208" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_212" xlink:to="loc_us-gaap_RelatedPartyDomain_208" use="optional" order="23" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_208_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_212" xlink:to="loc_us-gaap_RelatedPartyDomain_208_default" use="optional" order="24" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_PresageBiosciencesIncMember" xlink:label="loc_meip_PresageBiosciencesIncMember_221" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_208" xlink:to="loc_meip_PresageBiosciencesIncMember_221" use="optional" order="25" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaap_TypeOfArrangementAxis_214" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_213" xlink:to="loc_us-gaap_TypeOfArrangementAxis_214" use="optional" order="26" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_203" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_214" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_203" use="optional" order="27" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_203_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_214" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_203_default" use="optional" order="28" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_HelsinnLicenseAgreementMember" xlink:label="loc_meip_HelsinnLicenseAgreementMember_215" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_203" xlink:to="loc_meip_HelsinnLicenseAgreementMember_215" use="optional" order="29" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_PresageLicenseAgreementMember" xlink:label="loc_meip_PresageLicenseAgreementMember_216" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_203" xlink:to="loc_meip_PresageLicenseAgreementMember_216" use="optional" order="30" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_KkcAgreementsMember" xlink:label="loc_meip_KkcAgreementsMember_765471" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_203" xlink:to="loc_meip_KkcAgreementsMember_765471" use="optional" order="31" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductOrServiceAxis" xlink:label="loc_srt_ProductOrServiceAxis_765476" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_213" xlink:to="loc_srt_ProductOrServiceAxis_765476" use="optional" order="32" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srt_ProductsAndServicesDomain_765477" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_765476" xlink:to="loc_srt_ProductsAndServicesDomain_765477" use="optional" order="33" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srt_ProductsAndServicesDomain_765477_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_765476" xlink:to="loc_srt_ProductsAndServicesDomain_765477_default" use="optional" order="34" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ExUsLicenseMember" xlink:label="loc_meip_ExUsLicenseMember_765478" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_765477" xlink:to="loc_meip_ExUsLicenseMember_765478" use="optional" order="35" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_DevelopmentServicesMember" xlink:label="loc_meip_DevelopmentServicesMember_765483" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_765477" xlink:to="loc_meip_DevelopmentServicesMember_765483" use="optional" order="36" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_EventAxis" xlink:label="loc_meip_EventAxis_765700" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_213" xlink:to="loc_meip_EventAxis_765700" use="optional" order="37" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_EventDomain" xlink:label="loc_meip_EventDomain_765702" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_meip_EventAxis_765700" xlink:to="loc_meip_EventDomain_765702" use="optional" order="38" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_EventDomain" xlink:label="loc_meip_EventDomain_765702_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_meip_EventAxis_765700" xlink:to="loc_meip_EventDomain_765702_default" use="optional" order="39" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_UpdationOfInitialAssessmentMember" xlink:label="loc_meip_UpdationOfInitialAssessmentMember_765704" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_EventDomain_765702" xlink:to="loc_meip_UpdationOfInitialAssessmentMember_765704" use="optional" order="40" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_UpFrontPayment" xlink:label="loc_meip_UpFrontPayment_228" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_UpFrontPayment_228" use="optional" order="41" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_TotalUpfrontPaymentReceivableForGrantOfRights" xlink:label="loc_meip_TotalUpfrontPaymentReceivableForGrantOfRights_765468" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_TotalUpfrontPaymentReceivableForGrantOfRights_765468" use="optional" order="42" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_TotalTransactionPriceInRespectOfColloborationRevenue" xlink:label="loc_meip_TotalTransactionPriceInRespectOfColloborationRevenue_765470" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_TotalTransactionPriceInRespectOfColloborationRevenue_765470" use="optional" order="43" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ExpectedMilestonePaymentReceivable" xlink:label="loc_meip_ExpectedMilestonePaymentReceivable_765472" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_ExpectedMilestonePaymentReceivable_765472" use="optional" order="44" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_EstimatedDevelopmentCostSharingRecoverableThroughEarnings" xlink:label="loc_meip_EstimatedDevelopmentCostSharingRecoverableThroughEarnings_765473" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_EstimatedDevelopmentCostSharingRecoverableThroughEarnings_765473" use="optional" order="45" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredRevenue" xlink:label="loc_us-gaap_DeferredRevenue_765474" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_us-gaap_DeferredRevenue_765474" use="optional" order="46" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_765475" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_765475" use="optional" order="47" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_LicenseObligationAccountTransactionPriceAllocated" xlink:label="loc_meip_LicenseObligationAccountTransactionPriceAllocated_765480" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_LicenseObligationAccountTransactionPriceAllocated_765480" use="optional" order="48" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_765481" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_765481" use="optional" order="49" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ProfitsAndCostsSharingRatio" xlink:label="loc_meip_ProfitsAndCostsSharingRatio_766229" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_ProfitsAndCostsSharingRatio_766229" use="optional" order="50" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_IncreaseOrDecreaseInReceivableForForeignTaxWithholding" xlink:label="loc_meip_IncreaseOrDecreaseInReceivableForForeignTaxWithholding_766231" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_211" xlink:to="loc_meip_IncreaseOrDecreaseInReceivableForForeignTaxWithholding_766231" use="optional" order="51" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/NetLossPerShareAdditionalInformationDetail">
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_PotentiallyDilutiveSecuritiesOutstandingLineItems" xlink:label="loc_meip_PotentiallyDilutiveSecuritiesOutstandingLineItems_240" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_241" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_meip_PotentiallyDilutiveSecuritiesOutstandingLineItems_240" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_241" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_239" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_241" xlink:to="loc_dei_LegalEntityAxis_239" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_242" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_239" xlink:to="loc_dei_EntityDomain_242" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_242_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_239" xlink:to="loc_dei_EntityDomain_242_default" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesCommonStockSubjectToRepurchaseOrCancellation" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesCommonStockSubjectToRepurchaseOrCancellation_243" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_PotentiallyDilutiveSecuritiesOutstandingLineItems_240" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesCommonStockSubjectToRepurchaseOrCancellation_243" use="optional" order="5" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/ScheduleOfLossPerShareBasicAndDilutedDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_247" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_250" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_247" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_250" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_252" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_247" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_252" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_248" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_247" xlink:to="loc_us-gaap_StatementTable_248" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_246" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_248" xlink:to="loc_dei_LegalEntityAxis_246" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_249" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_246" xlink:to="loc_dei_EntityDomain_249" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_249_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_246" xlink:to="loc_dei_EntityDomain_249_default" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_DilutiveSecuritiesEffectOnBasicEarningsPerShareChangeInFairValueOfWarrantLiability" xlink:label="loc_meip_DilutiveSecuritiesEffectOnBasicEarningsPerShareChangeInFairValueOfWarrantLiability_766234" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_247" xlink:to="loc_meip_DilutiveSecuritiesEffectOnBasicEarningsPerShareChangeInFairValueOfWarrantLiability_766234" use="optional" order="7" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/AntidilutiveSecuritiesDetail">
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_PotentiallyDilutiveSecuritiesOutstandingLineItems" xlink:label="loc_meip_PotentiallyDilutiveSecuritiesOutstandingLineItems_478237" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_478229" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_meip_PotentiallyDilutiveSecuritiesOutstandingLineItems_478237" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_478229" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_478230" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_478229" xlink:to="loc_dei_LegalEntityAxis_478230" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_478231" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_478230" xlink:to="loc_dei_EntityDomain_478231" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_478231_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_478230" xlink:to="loc_dei_EntityDomain_478231_default" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_478232" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_478229" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_478232" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_478233" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_478232" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_478233" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_478233_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_478232" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_478233_default" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_478234" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_478233" xlink:to="loc_us-gaap_EmployeeStockOptionMember_478234" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_478235" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_478233" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_478235" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WarrantMember" xlink:label="loc_us-gaap_WarrantMember_478236" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_478233" xlink:to="loc_us-gaap_WarrantMember_478236" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_478238" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_PotentiallyDilutiveSecuritiesOutstandingLineItems_478237" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_478238" use="optional" order="11" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/CommitmentsAndContingenciesAdditionalInformationDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:label="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentLineItems_271" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_AccruedMilestonePayments" xlink:label="loc_meip_AccruedMilestonePayments_284" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentLineItems_271" xlink:to="loc_meip_AccruedMilestonePayments_284" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_MilestonePaymentsMaximumAmount" xlink:label="loc_meip_MilestonePaymentsMaximumAmount_285" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentLineItems_271" xlink:to="loc_meip_MilestonePaymentsMaximumAmount_285" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_PercentageOfPurchasesFromMajorSuppliers" xlink:label="loc_meip_PercentageOfPurchasesFromMajorSuppliers_286" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentLineItems_271" xlink:to="loc_meip_PercentageOfPurchasesFromMajorSuppliers_286" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PurchaseCommitmentExcludingLongtermCommitmentTable" xlink:label="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentTable_272" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentLineItems_271" xlink:to="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentTable_272" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaap_TypeOfArrangementAxis_273" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentTable_272" xlink:to="loc_us-gaap_TypeOfArrangementAxis_273" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_267" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_273" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_267" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_267_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_273" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_267_default" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_CydexLicenseAgreementMember" xlink:label="loc_meip_CydexLicenseAgreementMember_276" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_267" xlink:to="loc_meip_CydexLicenseAgreementMember_276" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_PresageLicenseAgreementMember" xlink:label="loc_meip_PresageLicenseAgreementMember_274" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_267" xlink:to="loc_meip_PresageLicenseAgreementMember_274" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_SbioPurchaseAgreementMember" xlink:label="loc_meip_SbioPurchaseAgreementMember_275" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_267" xlink:to="loc_meip_SbioPurchaseAgreementMember_275" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherCommitmentsAxis" xlink:label="loc_us-gaap_OtherCommitmentsAxis_478582" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PurchaseCommitmentExcludingLongtermCommitmentTable_272" xlink:to="loc_us-gaap_OtherCommitmentsAxis_478582" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherCommitmentsDomain" xlink:label="loc_us-gaap_OtherCommitmentsDomain_478583" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_OtherCommitmentsAxis_478582" xlink:to="loc_us-gaap_OtherCommitmentsDomain_478583" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherCommitmentsDomain" xlink:label="loc_us-gaap_OtherCommitmentsDomain_478583_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_OtherCommitmentsAxis_478582" xlink:to="loc_us-gaap_OtherCommitmentsDomain_478583_default" use="optional" order="13" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/LeasesAdditionalInformationDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_765501" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_765500" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_765501" xlink:to="loc_us-gaap_StatementTable_765500" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_765502" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_765500" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_765502" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_765503" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_765502" xlink:to="loc_us-gaap_TypeOfAdoptionMember_765503" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_765503_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_765502" xlink:to="loc_us-gaap_TypeOfAdoptionMember_765503_default" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountingStandardsUpdate201602Member" xlink:label="loc_us-gaap_AccountingStandardsUpdate201602Member_765505" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_765503" xlink:to="loc_us-gaap_AccountingStandardsUpdate201602Member_765505" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_StatementGeographicalAxis" xlink:label="loc_srt_StatementGeographicalAxis_765506" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_765500" xlink:to="loc_srt_StatementGeographicalAxis_765506" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_SegmentGeographicalDomain" xlink:label="loc_srt_SegmentGeographicalDomain_765507" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_765506" xlink:to="loc_srt_SegmentGeographicalDomain_765507" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_SegmentGeographicalDomain" xlink:label="loc_srt_SegmentGeographicalDomain_765507_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_765506" xlink:to="loc_srt_SegmentGeographicalDomain_765507_default" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_SanDiegoCaliforniaMember" xlink:label="loc_meip_SanDiegoCaliforniaMember_765508" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_765507" xlink:to="loc_meip_SanDiegoCaliforniaMember_765508" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_NumberOfSquareFeetUnderLease" xlink:label="loc_meip_NumberOfSquareFeetUnderLease_765509" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_765501" xlink:to="loc_meip_NumberOfSquareFeetUnderLease_765509" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LeaseExpirationDate1" xlink:label="loc_us-gaap_LeaseExpirationDate1_765511" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_765501" xlink:to="loc_us-gaap_LeaseExpirationDate1_765511" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseLiability" xlink:label="loc_us-gaap_OperatingLeaseLiability_765708" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_765501" xlink:to="loc_us-gaap_OperatingLeaseLiability_765708" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_InitialRecognitionOfOperatingLeaseRightOfUseAsset" xlink:label="loc_meip_InitialRecognitionOfOperatingLeaseRightOfUseAsset_813724" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_765501" xlink:to="loc_meip_InitialRecognitionOfOperatingLeaseRightOfUseAsset_813724" use="optional" order="13" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/ShortTermInvestmentsAdditionalInformationDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_290" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_291" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_290" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_291" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_289" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_291" xlink:to="loc_dei_LegalEntityAxis_289" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_292" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_289" xlink:to="loc_dei_EntityDomain_292" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_292_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_289" xlink:to="loc_dei_EntityDomain_292_default" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShortTermInvestments" xlink:label="loc_us-gaap_ShortTermInvestments_293" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_290" xlink:to="loc_us-gaap_ShortTermInvestments_293" use="optional" order="5" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/StockholdersEquityAdditionalInformationDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockLineItems" xlink:label="loc_us-gaap_ClassOfStockLineItems_296" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_307" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_296" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_307" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_312" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_296" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_312" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_NumberOfSharesAgreedToBeSoldUnderAgreement" xlink:label="loc_meip_NumberOfSharesAgreedToBeSoldUnderAgreement_314" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_296" xlink:to="loc_meip_NumberOfSharesAgreedToBeSoldUnderAgreement_314" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_SaleOfSharesAndWarrantsUnderAgreement" xlink:label="loc_meip_SaleOfSharesAndWarrantsUnderAgreement_313" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_296" xlink:to="loc_meip_SaleOfSharesAndWarrantsUnderAgreement_313" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_301" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_296" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_301" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_297" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_301" xlink:to="loc_dei_LegalEntityAxis_297" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_316" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_297" xlink:to="loc_dei_EntityDomain_316" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_316_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_297" xlink:to="loc_dei_EntityDomain_316_default" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis" xlink:label="loc_srt_RangeAxis_298" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_301" xlink:to="loc_srt_RangeAxis_298" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="loc_srt_RangeMember_299" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_298" xlink:to="loc_srt_RangeMember_299" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="loc_srt_RangeMember_299_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_298" xlink:to="loc_srt_RangeMember_299_default" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember" xlink:label="loc_srt_MaximumMember_317" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_299" xlink:to="loc_srt_MaximumMember_317" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_302" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_301" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_302" use="optional" order="13" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_300" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_302" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_300" use="optional" order="14" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_300_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_302" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_300_default" use="optional" order="15" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_AtTheMarketSaleAgreementMember" xlink:label="loc_meip_AtTheMarketSaleAgreementMember_318" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_300" xlink:to="loc_meip_AtTheMarketSaleAgreementMember_318" use="optional" order="16" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_TwoThousandAndTwentyAtTheMarketSaleAgreementMember" xlink:label="loc_meip_TwoThousandAndTwentyAtTheMarketSaleAgreementMember_810883" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_300" xlink:to="loc_meip_TwoThousandAndTwentyAtTheMarketSaleAgreementMember_810883" use="optional" order="17" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_478572" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_301" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_478572" use="optional" order="18" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_478573" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_478572" xlink:to="loc_us-gaap_RelatedPartyDomain_478573" use="optional" order="19" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_478573_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_478572" xlink:to="loc_us-gaap_RelatedPartyDomain_478573_default" use="optional" order="20" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaap_TypeOfArrangementAxis_478574" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_301" xlink:to="loc_us-gaap_TypeOfArrangementAxis_478574" use="optional" order="21" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_478576" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_478574" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_478576" use="optional" order="22" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_478576_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_478574" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_478576_default" use="optional" order="23" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_766237" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_301" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_766237" use="optional" order="24" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_766238" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_766237" xlink:to="loc_us-gaap_EquityComponentDomain_766238" use="optional" order="25" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_766238_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_766237" xlink:to="loc_us-gaap_EquityComponentDomain_766238_default" use="optional" order="26" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WarrantMember" xlink:label="loc_us-gaap_WarrantMember_766239" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_766238" xlink:to="loc_us-gaap_WarrantMember_766239" use="optional" order="27" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ShelfRegistrationStatementValue" xlink:label="loc_meip_ShelfRegistrationStatementValue_315" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_296" xlink:to="loc_meip_ShelfRegistrationStatementValue_315" use="optional" order="28" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_304" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_296" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_304" use="optional" order="29" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WarrantsNotSettleableInCashFairValueDisclosure" xlink:label="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_309" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_296" xlink:to="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_309" use="optional" order="30" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_478548" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_296" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_478548" use="optional" order="31" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_UnsoldSecuritiesSharesAndWarrantsUnderAgreement" xlink:label="loc_meip_UnsoldSecuritiesSharesAndWarrantsUnderAgreement_765537" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_296" xlink:to="loc_meip_UnsoldSecuritiesSharesAndWarrantsUnderAgreement_765537" use="optional" order="32" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_AggregateValueOfSecuritiesAvailableUnderAgreement" xlink:label="loc_meip_AggregateValueOfSecuritiesAvailableUnderAgreement_766236" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_296" xlink:to="loc_meip_AggregateValueOfSecuritiesAvailableUnderAgreement_766236" use="optional" order="33" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/ShareBasedCompensationAdditionalInformationDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_339" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_339" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_338" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_338" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_NumberOfSharesToBeReceived" xlink:label="loc_meip_NumberOfSharesToBeReceived_341" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_meip_NumberOfSharesToBeReceived_341" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_326" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_326" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_322" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_326" xlink:to="loc_us-gaap_AwardTypeAxis_322" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_328" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_322" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_328" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_328_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_322" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_328_default" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_345" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_328" xlink:to="loc_us-gaap_EmployeeStockOptionMember_345" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_346" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_328" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_346" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis" xlink:label="loc_srt_RangeAxis_323" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_326" xlink:to="loc_srt_RangeAxis_323" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="loc_srt_RangeMember_478618" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_323" xlink:to="loc_srt_RangeMember_478618" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="loc_srt_RangeMember_478618_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_323" xlink:to="loc_srt_RangeMember_478618_default" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember" xlink:label="loc_srt_MaximumMember_478619" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_478618" xlink:to="loc_srt_MaximumMember_478619" use="optional" order="13" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember" xlink:label="loc_srt_MinimumMember_478620" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_478618" xlink:to="loc_srt_MinimumMember_478620" use="optional" order="14" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_324" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_326" xlink:to="loc_us-gaap_PlanNameAxis_324" use="optional" order="15" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_325" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_324" xlink:to="loc_us-gaap_PlanNameDomain_325" use="optional" order="16" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_325_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_324" xlink:to="loc_us-gaap_PlanNameDomain_325_default" use="optional" order="17" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_TwoThousandAndEightOmnibusPlanMember" xlink:label="loc_meip_TwoThousandAndEightOmnibusPlanMember_332" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_325" xlink:to="loc_meip_TwoThousandAndEightOmnibusPlanMember_332" use="optional" order="18" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_TitleOfIndividualAxis" xlink:label="loc_srt_TitleOfIndividualAxis_329" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_326" xlink:to="loc_srt_TitleOfIndividualAxis_329" use="optional" order="19" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_330" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_329" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_330" use="optional" order="20" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_330_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_329" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_330_default" use="optional" order="21" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_DirectorMember" xlink:label="loc_srt_DirectorMember_347" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_330" xlink:to="loc_srt_DirectorMember_347" use="optional" order="22" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_EmployeesMember" xlink:label="loc_meip_EmployeesMember_348" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_330" xlink:to="loc_meip_EmployeesMember_348" use="optional" order="23" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VestingAxis" xlink:label="loc_us-gaap_VestingAxis_765757" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_326" xlink:to="loc_us-gaap_VestingAxis_765757" use="optional" order="24" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_765759" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_765757" xlink:to="loc_us-gaap_VestingDomain_765759" use="optional" order="25" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_765759_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_765757" xlink:to="loc_us-gaap_VestingDomain_765759_default" use="optional" order="26" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_765760" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_765759" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_765760" use="optional" order="27" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_336" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_336" use="optional" order="28" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_335" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_335" use="optional" order="29" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_340" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_340" use="optional" order="30" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_342" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_342" use="optional" order="31" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_337" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_337" use="optional" order="32" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_333" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_333" use="optional" order="33" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_334" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_334" use="optional" order="34" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited_765779" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited_765779" use="optional" order="35" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_765780" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_765780" use="optional" order="36" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_765781" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_765781" use="optional" order="37" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_NumberOfSharesForEachUnitOfRestrictedStock" xlink:label="loc_meip_NumberOfSharesForEachUnitOfRestrictedStock_765782" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_327" xlink:to="loc_meip_NumberOfSharesForEachUnitOfRestrictedStock_765782" use="optional" order="38" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/ShareBasedCompensationExpenseForStockAwardsDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_351" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_355" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_351" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_355" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_352" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_355" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_352" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_353" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_352" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_353" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_353_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_352" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_353_default" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_358" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_353" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_358" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_357" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_353" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_357" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_354" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_355" xlink:to="loc_dei_LegalEntityAxis_354" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_359" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_354" xlink:to="loc_dei_EntityDomain_359" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_359_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_354" xlink:to="loc_dei_EntityDomain_359_default" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="loc_us-gaap_ShareBasedCompensation_356" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_351" xlink:to="loc_us-gaap_ShareBasedCompensation_356" use="optional" order="10" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/SummaryOfStockOptionActivityDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_365" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_363" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_365" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_363" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_362" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_363" xlink:to="loc_dei_LegalEntityAxis_362" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_369" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_362" xlink:to="loc_dei_EntityDomain_369" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_369_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_362" xlink:to="loc_dei_EntityDomain_369_default" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract_364" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_365" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract_364" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_371" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract_364" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_371" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_370" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract_364" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_370" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_372" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_365" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_372" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_366" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_365" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_366" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_376" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_366" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_376" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_374" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_366" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_374" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_373" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_366" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_373" use="optional" order="12" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_375" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_366" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_375" use="optional" order="13" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_367" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_365" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_367" use="optional" order="14" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_385" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_367" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_385" use="optional" order="15" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_379" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_367" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_379" use="optional" order="16" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_381" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_367" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_381" use="optional" order="17" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_382" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_367" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_382" use="optional" order="18" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_380" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_367" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_380" use="optional" order="19" />
<loc xlink:type="locator" xlink:href="meip-20201231.xsd#meip_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" xlink:label="loc_meip_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_368" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_365" xlink:to="loc_meip_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_368" use="optional" order="20" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_387" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_368" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_387" use="optional" order="21" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_386" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_meip_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_368" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_386" use="optional" order="22" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://www.meipharma.com/role/FairValueOfStockOptionsWeightedAverageAssumptionsUsedDetail">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_392" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_391" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_392" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_391" xbrldt:contextElement="segment" xbrldt:closed="true" use="optional" order="1" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_390" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_391" xlink:to="loc_dei_LegalEntityAxis_390" use="optional" order="2" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_393" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_390" xlink:to="loc_dei_EntityDomain_393" use="optional" order="3" />
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_393_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_390" xlink:to="loc_dei_EntityDomain_393_default" use="optional" order="4" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_311943" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_391" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_311943" use="optional" order="5" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_311944" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_311943" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_311944" use="optional" order="6" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_311944_default" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_311943" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_311944_default" use="optional" order="7" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_397" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_392" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_397" use="optional" order="8" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_395" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_392" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_395" use="optional" order="9" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_396" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_392" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_396" use="optional" order="10" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_394" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_392" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_394" use="optional" order="11" />
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_398" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_392" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_398" use="optional" order="12" />
</definitionLink>
</linkbase>
