R419

R419 is a small molecule inhibitor of mitochondrial complex I (NADH:ubiquinone oxidoreductase) originally developed by Rigel Pharmaceuticals for the treatment of metabolic disorders. By inhibiting mitochondrial respiration, R419 increases the cellular AMP/ATP ratio, which leads to the indirect activation of AMP-activated protein kinase (AMPK), a central regulator of energy homeostasis. Preclinical research has demonstrated that R419-induced energetic stress triggers the integrated stress response and stimulates the expression and secretion of growth differentiation factor 15 (GDF15), a hormone that suppresses food intake and promotes weight loss. R419 reached Phase 1 clinical trials for type 2 diabetes but is no longer listed in Rigel's active development pipeline.