Selenium-Thioredoxin Axis Contributes to Ferroptosis Resistance in Pancreatic Cancer Cells

Pancreatic ductal adenocarcinoma (PDAC) shows substantial heterogeneity in cysteine dependence and ferroptosis sensitivity. We identify two PDAC subtypes distinguished by EMT status: mesenchymal-like cells are highly cysteine-dependent and rapidly undergo ferroptosis upon cystine deprivation or system xc^- inhibition, whereas epithelial-type cells are ferroptosis-resistant. Selenium supplementation protects cells from erastin-induced ferroptosis, and this protection persists even when intracellular glutathione (GSH) is depleted, supporting an additional GPX4-independent protective mechanism. Sepp1 knockdown does not alter sensitivity, indicating that selenium's protective effect is independent of Sepp1. Instead, epithelial-type cells rely on both cytosolic and mitochondrial thioredoxin reductases (TrxR1 and TrxR2) to maintain ferroptosis resistance. Chemical inhibition of thioredoxin reductases abolishes selenium-mediated protection and sensitizes epithelial cells to ferroptosis inducers, while dual genetic suppression of TrxR1 and TrxR2 similarly restores ferroptosis sensitivity. These findings uncover a selenium-thioredoxin redox axis that functions independently of GPX4 and contributes ferroptosis resistance in epithelial-type PDAC cells. Co-targeting cysteine metabolism and thioredoxin reductases may therefore represent a rational strategy to overcome ferroptosis resistance in some PDAC subtypes.