Background: The survival rate for acute myeloid leukemia remains unacceptably low, in large part owing to resistance to chemotherapy and high rates of relapse. There is an urgent need to develop new therapeutic modalities, in particular such that are tolerated by patients over the age of 60 years, who form the bulk of new acute myeloid leukemia diagnoses. Vosaroxin (SNS-595), a second-generation topoisomerase II inhibitor and DNA intercalating agent, shows promising preclinical and clinical activity against acute myeloid leukemia. Venetoclax (ABT-199), a selective Bcl-2 inhibitor, was recently approved for the treatment of acute myeloid leukemia.
Objective: The objective of this study was to determine the anti-leukemic activity and the underlying molecular mechanisms for the combination of venetoclax and vosaroxin in acute myeloid leukemia cell lines and primary patient samples ex vivo.
Patients and methods: Using both acute myeloid leukemia cell lines and primary patient samples, annexin V/propidium iodide staining and flow cytometry analyses were used to quantify apoptosis induced by venetoclax or vosaroxin, alone or in combination, with subsequent western blotting analyses to assess levels of Bcl-2 family proteins. Alkaline comet assays were performed to quantify DNA damage induced by the two agents and to determine the effect of venetoclax on DNA repair. Finally, colony-forming assays were conducted on normal human CD34+ cord blood cells and primary acute myeloid leukemia patient samples to determine the effect of venetoclax and vosaroxin on normal hematopoietic and leukemic progenitor cells.
Results: We found that venetoclax and vosaroxin synergistically induced apoptosis in multiple acute myeloid leukemia cell lines. Although vosaroxin could partially abrogate the increase of Mcl-1 protein induced by venetoclax, it could not abrogate the increased binding of Bim to Mcl-1 induced by venetoclax. Cooperative induction of DNA damage occurred within 8 h of treatment with venetoclax plus vosaroxin. Moreover, repair of DNA damage induced by vosaroxin was significantly attenuated by venetoclax. The combination also synergistically induced apoptosis in primary acute myeloid leukemia patient samples and significantly reduced the colony formation capacity of acute myeloid leukemia progenitor cells, while sparing normal hematopoietic progenitor cells.
Conclusions: Vosaroxin and venetoclax synergistically induce apoptosis in acute myeloid leukemia cells and cooperatively target acute myeloid leukemia progenitor cells while sparing normal hematopoietic progenitor cells. Our results support the clinical testing of vosaroxin in combination with venetoclax for treating patients with acute myeloid leukemia, especially in the elderly population.