Cancer persister cells are sensitized to copper-mediated death

Drug-tolerant cancer persister cells survive drug treatments and contribute to acquired resistance. Elimination of persister cells may increase the durability of treatment responses but there are currently no clinically approved therapies targeting persister cells. We previously showed cancer persister cells which survive oncogene-targeted therapy are selectively vulnerable to ferroptosis induced by GPX4 inhibition. While nontoxic bioavailable GPX4 inhibitors have yet to be developed, the recent emergence of bioavailable FSP1 inhibitors allows for induction of ferroptosis in FSP1-dependent tumor cells in vivo. However, we recently found persister cells are more dependent on GPX4 than FSP1 in cell culture and it remains to be determined whether FSP1 inhibition alone is sufficient to kill persister cells in vivo. Here, we considered other clinically available drugs which may selectively kill persister cells. It was previously reported that persister cells are sensitized to disulfiram, an FDA-approved treatment for alcohol use disorder based on disulfiram's aldehyde dehydrogenase (ALDH) inhibition activity. However, we found disulfiram-mediated persister cell killing is independent of ALDH inhibition. Disulfiram also depletes glutathione and we found glutathione replenishment protects persister cells from disulfiram, but glutathione depletion alone is insufficient to kill persister cells because near complete inhibition of glutathione biosynthesis with buthionine sulfoximine is not consistently toxic to persister cells. Furthermore, we found that persister cells are variably rescued from disulfiram treatment by soluble antioxidants or caspase inhibition, and are not rescued by anti-ferroptosis lipophilic antioxidants. However, in all tested persister cell models, disulfiram-induced killing is inhibited by treatment with copper chelator tetrathiomolybdate. Indeed, disulfiram is also a copper ionophore recently demonstrated to induce cuproptosis. We found another clinically tested copper ionophore elesclomol also selectively kills persister cells. Furthermore, other groups have previously shown that co-treatment of EGFR mutant non-small cell lung cancer tumors with disulfiram or elesclomol improves response durability. Therefore, though disulfiram and elesclomol have failed to produce robust clinical benefit when paired with genotoxic chemotherapies or radiation in treatment-refractory tumors, no prior trials have applied either drug to targeted therapy treated tumors or minimal residual disease. Our observations support repurposing copper ionophores to target minimal residual disease in the context of oncogene-targeted therapy treatments.