CYD-4-61 Suppresses Gastric Tumor Growth by Targeting SOX9–CDK4–Driven Oncogenic Programs and Enhances Anti-PD-1 Therapy

Gastric adenocarcinoma (GAC), particularly with peritoneal carcinomatosis, remains highly lethal and therapeutically refractory. We investigated the anti-tumor activity and mechanisms of CYD-4-61, a small-molecule BAX activator, with emphasis on the SOX9–CDK4 oncogenic axis and tumor immune microenvironment. CYD-4-61 efficacy was evaluated using in vitro GAC models and in vivo xenograft, genetically engineered, and syngeneic mouse models. Bulk, single-cell, and spatial transcriptomics, along with molecular and functional assays, were used to define apoptotic, cell-cycle, and immune-related mechanisms. CYD-4-61 induced BAX-dependent apoptosis and suppressed proliferation, stem-like properties, and tumor growth across multiple GAC models. Transcriptomic analyses revealed inhibition of SOX9-dependent programs, including CDK4, and activation of apoptotic and inflammatory pathways. CYD-4-61 destabilized SOX9 via caspase-dependent cleavage, inhibited cell-cycle progression, activated STING signaling, and enhanced response to PD-1 blockade in immunocompetent models. CYD-4-61 exerts potent anti-tumor effects in GAC by targeting SOX9–CDK4–driven oncogenic programs and modulating immune signaling, supporting its development as a therapeutic agent alone or in combination with immunotherapy.