AML-137: Preclinical Evaluation of Cytarabine and Venetoclax in Secondary AML

Abstract

Context Novel treatment approaches for patients with secondary acute myeloid leukemia (AML) are urgently needed. Secondary AML constitutes about 25-30% of AML and it has been observed that patients with secondary AML have worse responses rates to chemotherapy, increased rates of relapse, and worse overall survival compared to patients with de novo AML. Objective Our long-term goal is to develop more effective therapeutic options for patients with secondary AML. Our objectives in this study are: (i) to demonstrate synergy between cytarabine and venetoclax in secondary AML cell lines and patient-derived samples, (ii) to elucidate the mechanism of this synergy, (iii) functional characterization of Bcl-2 family proteins by BH3 profiling performed on secondary AML cell lines and patient samples. Results Synergy was demonstrated between cytarabine and venetoclax in secondary AML and de novo AML cell lines (Molm13, MV4;11, SKM-1; ML-2) using both an MTT cell viability assay and a flow-cytometry based Annexin-V assay, quantified by the computer software Compusyn. BH3 profiling of these cell lines indicated a dependence on both Bcl-2 and Mcl-1. Interestingly, SKM-1 showed sole dependence on Mcl-1. In SKM-1 cells, western blotting showed increased expression of Mcl-1 after treatment with venetoclax for 8 hrs and decreasing Mcl-1 expression with time (8hrs–72hrs) after treatment with cytarabine. Combination treatment for 24-48 hrs led to Mcl-1 expression that was similar to or less than Mcl-1 expression in control cells. Synergy between cytarabine and venetoclax was confirmed in patient samples. Importantly, BH3 profiling showed that patient samples exhibited dependence on Bcl-2 or both Mcl-1 and Bcl-2. Conclusions There is significant synergy between cytarabine and venetoclax in both de novo and secondary AML cell lines as well as patient samples. One of the potential mechanisms of this synergy is abrogation of Mcl-1 upregulation. Secondary AML exhibits variable functional dependence on Mcl-1 and Bcl-2. These findings support the clinical investigation of cytarabine and venetoclax in patients with secondary AML as well as the use of BH3 profiling as a potential predictive biomarker. Acknowledgements This work was supported by the NIH R01 CA-217141 and AACR Bayer Innovation and Discovery Award to Z. Nikolovska-Coleska.