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<!-- Created by Toppan Merrill --> |
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<!-- Based on XBRL 2.1 --> |
<!-- Created on: 5/15/2020 11:53:51 AM --> |
<!-- Modified on: 5/15/2020 11:53:51 AM --> |
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| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RelatedPartyDomain" xlink:to="us-gaap_MajorityShareholderMember" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="us-gaap_RelatedPartyTransactionLineItems"/> |
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| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty" xlink:label="us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty" priority="1" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountsPayableRelatedPartiesCurrentAndNoncurrent" xlink:label="us-gaap_AccountsPayableRelatedPartiesCurrentAndNoncurrent"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_AccountsPayableRelatedPartiesCurrentAndNoncurrent" priority="1" use="optional"/> |
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| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis"/> |
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| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain"/> |
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| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain_637251404302309259" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="ontx-20200331.xsd#ontx_SecondaryPublicOfferingMember" xlink:label="ontx_SecondaryPublicOfferingMember"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="ontx_SecondaryPublicOfferingMember" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_StatementTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/> |
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| | <loc xlink:type="locator" xlink:href="ontx-20200331.xsd#ontx_H.c.WainwrightCoLlcMember" xlink:label="ontx_H.c.WainwrightCoLlcMember"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="ontx_H.c.WainwrightCoLlcMember" priority="1" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="ontx-20200331.xsd#ontx_CertainInstitutionalAndAccreditedInvestorsMember" xlink:label="ontx_CertainInstitutionalAndAccreditedInvestorsMember"/> |
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| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_ClassOfWarrantOrRightAxis" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightDomain" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="ontx-20200331.xsd#ontx_CommonStockWarrantsMember" xlink:label="ontx_CommonStockWarrantsMember"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="ontx_CommonStockWarrantsMember" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsidiarySaleOfStockLineItems" xlink:label="us-gaap_SubsidiarySaleOfStockLineItems"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/> |
| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="1" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" priority="1" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="ontx-20200331.xsd#ontx_PercentageOfCashFeeOnGrossProceeds" xlink:label="ontx_PercentageOfCashFeeOnGrossProceeds"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="ontx_PercentageOfCashFeeOnGrossProceeds" priority="1" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="ontx-20200331.xsd#ontx_PercentageOfManagementFee" xlink:label="ontx_PercentageOfManagementFee"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="ontx_PercentageOfManagementFee" priority="1" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="ontx-20200331.xsd#ontx_PaymentOfNonAccountableExpenses" xlink:label="ontx_PaymentOfNonAccountableExpenses"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="ontx_PaymentOfNonAccountableExpenses" priority="1" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="ontx-20200331.xsd#ontx_PaymentOfClearingFees" xlink:label="ontx_PaymentOfClearingFees"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="ontx_PaymentOfClearingFees" priority="1" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="ontx-20200331.xsd#ontx_WarrantsIssuedToPurchaseOfCommonStock" xlink:label="ontx_WarrantsIssuedToPurchaseOfCommonStock"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="ontx_WarrantsIssuedToPurchaseOfCommonStock" priority="1" use="optional"/> |
| | <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromIssuanceOfWarrants" xlink:label="us-gaap_ProceedsFromIssuanceOfWarrants"/> |
| | <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_ProceedsFromIssuanceOfWarrants" priority="1" use="optional"/> |
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