Abstract 3982: Repurposing disulfiram for treatment of relapsed/refractory acute myeloid leukemia

Background Despite toxic treatments, acute myeloid leukemia (AML) continues to have an overall poor prognosis of about 50% in children while significantly less in older adults. For patients with relapsed AML refractory to chemotherapy, there is little chance for survival. Therefore, the need for novel treatment modalities continues to be critically important. Disulfiram (DS) is an aldehyde dehydrogenase (ALDH) inhibitor that has been used for decades for the treatment of alcoholism without major side effects. While DS has been reported to have anticancer cytotoxicity that is in part copper (Cu2+)-dependent, the mechanisms are still not fully elucidated. The goal of the present study was to investigate whether DS has significant cytotoxicity against AML. Methods and Results In the present study the IC50 were determined for DS alone or in combination with 1 µM Cu2+ in a panel of 16 AML cell lines using Cell Titer Glo assay. DS/Cu2+ resulted in significant killing of all cell lines (IC50 between 20-75 nM) while the response to DS alone showed significant variation (IC50 from 20 nM - 7 µM). Cu2+ alone was not toxic. Cytarabine (Ara-C), a key drug in AML treatment, was compared with DS/Cu2+. The AML cell lines THP1 (acute monocytic leukemia), UT7-epo and CMY (acute megakaryoblastic leukemia) were profoundly resistant to Ara-C (IC50 between 1.2-2.4 µM) but showed extreme sensitivity to DS/Cu2+ (IC50 between 31-46 nM). Although DS is an inhibitor of ALDH, we demonstrated that the cytotoxicity of DS or DS/Cu2+ was not directly associated with the level of ALDH or its inhibition. AML cell lines were treated with different doses of DS or DS/Cu2+ and ALDH activity and cell death were determined by flow cytometry. The percentage of cell death was dose-dependent and occurred irrespective of ALDH activity in cell lines with high endogenous ALDH activity (MV-4-11, CMY, CMK and K562) compared to those with low or undetectable ALDH activity (Kasumi-1, Molm-13, NB4 and KG-1a). As DS-mediated cytotoxicity has been associated in previous reports with proteasome inhibition, the effects of DS and DS/Cu2+ were compared to Bortezumib. Western blot analysis showed that DS induced PARP cleavage similar to Bortezumib, suggesting that proteasome inhibition may be contributing to DS or DS/Cu2+ cytotoxicity. Conclusion These data demonstrate that multiple AML cell lines are sensitive to DS and to DS/Cu2+, including some that show extreme resistance to Ara-C, such as CMY from a patient with Down Syndrome. This DS sensitivity may provide a less toxic and efficacious treatment approach to be tested in this group of patients with poor outcome following relapse. The cytotoxic activity of DS does not appear to be solely dependent on ALDH inhibition. Ongoing studies are focusing on determining the mechanisms of cell death, and cytotoxic efficacy in in vitro and xenograft models using patient AML samples, with the goal of developing a clinical trial in patients with relapsed/refractory AML. Citation Format: Eiman A. Aleem, David O. Azorsa, Ranjan Bista, Oliver B. Pepper, David W. Lee, Daniel H. Wai, Robert J. Arceci. Repurposing disulfiram for treatment of relapsed/refractory acute myeloid leukemia. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3982. doi:10.1158/1538-7445.AM2014-3982