Potent ferroptosis agent RSL3 induces cleavage of Pyroptosis-Specific gasdermins in Cancer cells

Ferroptosis is a form of iron-dependent cell death of interest for the development of novel anti-cancer therapies. Ferroptosis research uses a process of elimination based on assumed ferroptosis-specific inducers and inhibitors; these molecules however have off-target effects and cannot provide a comprehensive picture of overlapping pathways. We investigated whether pyroptosis-a form of inflammatory cell death-is initiated in cancer cells following treatment with the ferroptosis inducer RSL3. We treated 6 cancer cell lines with RSL3 alone or in combination with inhibitors of ferroptosis (Ferrostatin-1), caspases (zVADfmk), necroptosis (Necrostatin-1), BID (BI-6C9), or STING (H-151). Biomarkers of pyroptosis and ferroptosis were assessed using our novel quantitative multiplex immunoassay. Increased secretion of pyroptosis-associated cytokines (IL-1α, IL-1β, IL-18), and gasdermin D and E (GSDMD/E) cleavage with parallel loss of respective full-length proteins-both hallmarks of pyroptosis-were recorded in 5/6 cell lines following RSL3 treatment. RSL3 cytotoxicity was blocked by Ferostatin-1; BID and STING inhibitors also prevented GSDMD/E cleavage. We conclude that the ferroptosis-inducer RSL3 triggers pyroptosis in cancer cells; further work is required to elucidate the role of mitochondria in this process. Measurement of pathway-specific protein biomarkers is therefore necessary to identify the exact mechanism of action of novel cytotoxic agents.