Arsenic Trioxide Synergistically Enhances the Antileukemia Activity of Bcl-2 Inhibitor ABT-199 in Acute Myeloid Leukemia
Authors: Liu Sha , Chen Lin , Wang Xiaojiao , Mi Ruihua , Yin Qingsong , Fan Ruihua , Wei Xudong 
Published: November 2019

Background Acute myeloid leukaemia (AML) is a malignancy derived from haematopoietic stem cells in which maturation and apoptosis are blocked and proliferation is uncontrolled during differentiation. With the optimization of chemotherapy regimens, the emergence of new drugs and the development of haematopoietic stem cell transplantation technology, the complete remission (CR) rate and long-term survival of AML patients have significantly improved, but 20-40% of patients still have difficulty achieving a CR. Furthermore, approximately 60% of patients eventually relapse after a CR. Patients who are unable to obtain a CR and who relapse after remission are more likely to develop refractory AML. For patients with refractory/relapsed AML, there is no standard rescue therapy, and general chemotherapy drugs have limited efficacy. It is of great significance to explore new salvage treatment options.
Venetoclax (ABT-199) is an effective oral inhibitor of Bcl-2. ABT-199 has been used to treat various in vitro and in vivo tumour models, including AML models, and these experiments have shown its effectiveness as a single agent. However, its efficacy is very limited in refractory/relapsed AML, Mcl-1 play important roles in ABT-199 resistance. As an ancient pro-apoptotic drug, arsenic trioxide (ATO) has been shown to induce apoptosis in vivo and in vitro. ATO can downregulate the expression of Mcl-1, thereby inducing apoptosis.
objective To explore not only the synergistic pro-apoptotic effects of the Bcl-2 inhibitor ABT-199 and ATO on AML cell lines and AML primary cells, but also the clinical effects on refractory/relapsing AML patients.
Methods 1. Bcl-2 and Mcl-1 mRNA and protein levels in AML cell lines (MOLM13, MV4-11, THP-1, OCI-AML3, U937) were detected by real-time PCR and Western blot, respectively; 2.Apoptosis rates of AML cell lines after treatment with different concentrations of ABT-199 or ATO alone or in combination were measured by flow cytometry; 3. The transcriptomes of THP-1 and OCI-AML3 cells before and after treatment with ABT-199 or ATO alone or in combination were analysed; 4. Western blot, co-immunoprecipitation, cell cycle assay ABT-199, ATO effect on oci-AML3 cells; 5. ABT-199 combined with ATO in the treatment of patients with relapsed and refractory AML, the specific program is: ABT-199 100mg d1, 200mg d2, 400mg d3-28, oral 30 minutes after breakfast, ATO 6mg/m2, d1-28, daily intravenous infusion for 6 hours, review the effect of bone marrow aspiration on the 28th day.
Results 1.MOLM13, MV4-11, THP-1, OCI-AML3 and U937 cells expressed both Bcl-2 and Mcl-1. The sensitivity of AML cell lines to ABT-199 was positively correlated with the Bcl-2 protein expression level; 2.In AML cell lines whether ABT-sensitive or ABT-resistant and primary AML cells, ABT-199 and ATO synergistically promoted apoptosis in a time- and concentration-dependent manner; 3. ABT-199 up-regulated the expression of Mcl-1 in ABT-resistant OCI-AML3 cells, ATO down-regulated the expression of p-AKT, p-GSK3β, and Mcl-1, and the expression of Mcl-1 decreased after the combination of the two drugs. Bim and Mcl-1 protein binding decreased after treatment OCI-AML3 cells with the combination of the two drugs for 24h; 4. ATO promotes DNA damage, and the effect is further enhanced when combinated with ABT-199; 5. A total of 7 patients with relapse were treated with ABT-ATO combined regimen. Four of the 7 patients had multiple relapses and 3 patients had short-term recurrence after remission, with an average age of 49 years. On the 28th day, the bone marrow was reviewed. Two of them achieved CRi, one case with Leukemia-free state (MLFS), two cases with PR, one case with SD, and one case with PD.
Conclusion We demenstrated ATO could reverse AML resistance to ABT-199 and the synergistic effects of the combination of ATO and ABT-199, which may provide a new and probably more effective treatment strategy for refractory/relapsed AML .
Key Words Bcl-2 inhibitor; ABT-199; arsenic trioxide; Mcl-1; AKT; apoptosis

Disclosures
No relevant conflicts of interest to declare.