SLC5A11 mediates metformin-induced PD-L1 suppression to enhance cancer immunotherapy through AMPK-IRF1 signaling.

Metformin exhibits immunomodulatory properties in cancer treatment, but the underlying mechanisms remain elusive. Using genome-wide CRISPR screening, we identified SLC5A11 as an essential mediator of metformin sensitivity. Molecular docking and dynamics simulations revealed direct metformin-SLC5A11 binding at the pocket containing Asn78 and Glu102 residues. Metformin suppressed PD-L1 expression across multiple cancer models through SLC5A11-dependent activation of AMPK and subsequent JAK2-STAT1-IRF1 downregulation. SLC5A11 knockout abolished these effects, while reconstitution restored metformin responsiveness. In syngeneic mouse models of lung and pancreatic cancer, combining metformin with anti-PD1 therapy produced synergistic antitumor effects, enhanced T cell infiltration, and potentiated immunotherapy efficacy. Metformin pretreatment significantly enhanced PBMC-mediated cytotoxicity against tumor cells and patient-derived organoids in ex vivo co-culture systems. Our findings establish the SLC5A11-AMPK-PD-L1 axis as a novel mechanism linking metformin to tumor immunity, providing a molecular rationale for combining metformin with checkpoint inhibitors in cancer immunotherapy.