Sodium Aurothiomalate Induces Ferroptosis by Targeting GPX4 via Gold-Dependent Thiomalate Covalent Modification

Ferroptosis, an iron-dependent form of oxidative cell death, is predominantly regulated by glutathione peroxidase 4 (GPX4), making it a promising target for cancer therapy. However, the majority of GPX4 inhibitors, most of which contain a chloroacetamide moiety such as RSL3, are limited by poor pharmacokinetic properties and off-target effects, hindering their preclinical translation. Utilizing a range of interdisciplinary methodologies, we show that sodium aurothiomalate (ATM), a drug approved by many agencies, induces ferroptosis by covalently targeting GPX4 via formation of a selenenylsulfide bond. In preclinical models of neuroblastoma and acute myeloid leukemia (AML), ATM combined with ferric ammonium citrate (FAC) yields a synergistic effect, resulting in a significant reduction in tumor growth. Mechanistically, ATM disrupts GPX4 activity by covalently binding thiomalate to the active site selenocysteine, while modification of specific cysteine residues leads to destabilization of the protein and impaired binding to phospholipids. We propose that these covalent modifications are achieved through a unique reaction mechanism, in which the gold component of ATM acts as a thiol-masking carrier and is only transiently present, being subsequently displaced and allowing the reaction of the thiomalate moiety with the target selenocysteine or cysteine. Our data lay the foundation for development of novel, drug-like thiol-based GPX4 inhibitors.