R80

R80 is a highly selective small molecule inhibitor of cytidine triphosphate synthase 1 (CTPS1), a rate-limiting enzyme in the de novo nucleotide synthesis pathway that converts uridine triphosphate (UTP) into cytidine triphosphate (CTP). Developed by StepPharma, R80 is designed to target hematological malignancies, particularly B-cell and T-cell lymphomas, which exhibit a high dependency on CTPS1 for cellular proliferation. The drug's mechanism involves the depletion of intracellular CTP pools, leading to impaired DNA synthesis and the induction of apoptosis. Research presented at the EHA Annual Congress 2026 indicates that R80 also disrupts mitochondrial homeostasis and mitophagy by remodeling phospholipid metabolism, specifically through the downregulation of CEPT1. R80 is closely associated with the clinical candidate STP938, which is currently undergoing Phase 1/2 clinical evaluation (NCT05463263) for relapsed or refractory diffuse large B-cell lymphoma (DLBCL) and other lymphoid malignancies.