Synergetic Activity And Molecular Mechanisms Of Vosaroxin Or IACS-010759 In Combination With Venetoclax In Acute Myeloid Leukemia

Acute myeloid leukemia(AML)is an aggressive malignancy characterized by explosive clonal proliferation of immature myeloid precursor cells and escapse of apoptosis.Survival in pediatric and adult patients remains dismal,with the five-year overall survival rate of 27.4%.For more than 40 years,the standard induction therapy for AML has been a 7 + 3 regimen(7 days of cytarabine plus 3 days of an anthracycline,such as daunorubicin).The consolidation therapies followed include high dose cytarabine-based chemotherapy or allogeneic hematopoietic stem cell transplantation.However,for many patients over 60 years old or those with comorbidities,the 7 + 3 regimen cannot be used.Due to the relatively quiescent cell cycle,AML stem cells are difficult to eradicate with cell cycle-dependent traditional chemotherapeutic drugs,making AML prone to relapse.Once relapsed,AML cells could lose sensitivity to chemotherapeutic drugs,resulting in many patients,especially those over 60 years of age,dying from drug resistant or relapsed disease.Therefore,it is urgent to find an anti-AML regimen with low toxicity and potenti efficacy in the elderly to prolong the survival,and ultimately improve the cure rate.The first part of this disseration focuses on the activity and molecular mechanism of the combination of Venetoclax(ABT-199)and Vosaroxin(SNS-595)against AML.Venetoclax,an oral selective Bcl-2 inhibitor,was approved by the US FDA on November 21,2018,in combination with low-dose cytarabine or hypomethylating agents as first-line treatment for patients over 75 years of age or those who cannot tolerate high-intensity chemotherapy.Previous studies in our laboratory have shown that Venetoclax can release the pro-apoptotic protein Bim from Bcl-2,while the anti-apoptotic protein Mcl-1 will bind to the released Bim and prevent it from inducing apoptosis,resulting in Venetoclax resistance.In addition,our previous studies also demonstrate that Venetoclax could enhance DNA strand breaks induced by DNA damaging agents,resulting in synergistic antileukemic activity against AML.Vosaroxin is a topoisomerase II inhibitor and DNA intercalator,which is well tolerated and effective in elderly patients but seems not sufficient as a monotherapy.We hypothesized that combining Vosaroxin with Venetoclax would result in well-tolerated synergistic antileukemic effects through DNA damage and inhibition of Bcl-2.The results show that the combination of Venetocalx and Vosaroxin has synergistic anti-leukemic activity in a series of AML cell lines and primary samples derived from patients with AML.Venetoclax increases DNA damage induced by Vosaroxin and interferes with the repair of DNA damage in AML cells.Besides,the combination of the two drugs successfully inhibits the colony-forming capacity of AML progenitor cells but spares normal hematopoietic progenitor cells.The second part of this disseration focuses on the antitumor activity of Venetoclax in combination with IACS-010759 in AML cell lines,clinical samples from patients with de novo AML,and NSG mouse xenograft models.IACS-010759 is a selective small molecule inhibitor of mitochondrial electron transport chain complex I,which shows antileukemic activity by inhibiting oxidative phosphorylation(OXPHOS)in vitro as well as in AML xenograft models.However,complex I deficiency has been reported to inhibit the release of cytochrome c and apoptosis-inducing factor(AIF),thereby inhibiting apoptosis.Cytochrome c release is tightly regulated by the Bcl-2 family proteins and Venetoclax has also been reported to target OXPHOS in vitro.Therefore,we hypothesized that the combination of IACS-010759 with Venetoclax could synergistically induce apoptosis by inhibiting OXPHOS and/or releasing cytochrome c in AML.Results from this part of the disseration show that IACS-010759 is able to cause cytochrome c accumulation in OXPHOS-dependent AML cell lines and OXPHOS-independent AML cell lines after replacing glucose with galactose in the culture medium.Meanwhile,Venetoclax increases cytochrome c release,thereby overcoming resistance to IACS-010759,resulting in synergistic induction of intrinsic apoptosis.Further,the two agents cooperate in inhibiting colony formation of AML progenitor cells.Fianlly,the combination of IACS-010759 and Venetoclax significantly prolonged the survival of AML cell line-derived xenograft mouse models.In summary,the findings of this disseration form a theoretical and experimental foundation for the clinical evaluation of Venetoclax with Vosaroxin or IACS-010759 in the treatment of AML.