Abstract 575: Disulfiram plus copper synergizes with etoposide for the treatment of Merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine skin cancer with limited treatment options. Currently two immunotherapies are approved for the treatment of MCC, the PD-L1 inhibitor avelumab and the PD-1 inhibitor pembrolizumab. Unfortunately, these treatments only have durable benefit for less than half of patients that can be treated with immunotherapy. Therefore, new and effective treatments are needed for MCC. To address this, we conducted a high-throughput drug screening of ~4,000 small molecules. Our drug screen identified disulfiram (DSF), an aldehyde dehydrogenase inhibitor used in the treatment of alcoholism, as an agent that selectively reduced MCC cell viability. Recent studies suggest that DSF complexed with copper can have anti-cancer effects. Consistent with this, the addition copper at physiological levels increased the potency of DSF in MCC cells lines. Next, we demonstrated that disulfiram combined with copper synergized with the topoisomerase II inhibitor etoposide, lowering the effective dose of etoposide required to reduce MCC cell viability. Mechanistically, combining DSF, copper and etoposide was cytotoxic but did not induce apoptosis in MCC cell lines. This combination increased the formation of double stranded DNA breaks while disulfiram plus copper induced autophagy, which could mechanistically be an indication of immunogenic cell death signaling. Taken together, our data suggest that disulfiram combined with copper and etoposide could be repurposed for the effective treatment of advanced MCC. One strong advantage of this combination is that all agents can be given orally and at dosages with minimal adverse effects. Citation Format: Natasha Tremayne Hill, Tara Gelb, Dan Urban, Tyler Kellenberger, Matthew Hall, Isaac Brownell. Disulfiram plus copper synergizes with etoposide for the treatment of Merkel cell carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 575.