Tumor cell death by ferroptosis contributes to an immunosuppressive tumor microenvironment in syngeneic murine models of cancer.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by profound metabolic rewiring and a strongly immunosuppressive tumor microenvironment, both of which contribute to poor therapeutic responses. Immunogenic cell death (ICD) represents a potential strategy to overcome immune suppression by coupling tumor cell death to anti-tumor immune activation. Here, we investigated whether targeting amino acid metabolism in PDAC can induce ICD and promote tumor immunity. Through a focused metabolic screen in a panel of syngeneic mouse cancer cell lines, we identified cysteine restriction as a robust inducer of multiple damage-associated molecular patterns (DAMPs) in vitro, hallmark features of ICD. In addition to driving DAMPs, cystine-deprived tumor cells also promoted dendritic cell phagocytosis, maturation, and proinflammatory cytokine production in vitro. Because cysteine deprivation is a known trigger of ferroptosis, we further demonstrated that pharmacologic inhibition of glutathione peroxidase 4 (GPX4) similarly elicited ICD-associated features, which were reversible by the ferroptosis inhibitor Ferrostatin-1. To define additional immune-modulatory signals associated with ferroptosis, we performed metabolomic and lipidomic profiling of cells undergoing, but not yet committed to, ferroptotic death. These analyses revealed selective release of immunosuppressive metabolites and oxidized phospholipids. Consistent with this, conditioned media from ferroptotic cells impaired CD8