Discovery of a Small-Molecule mTORC1 Pathway Activator that Enhances Adoptive T-Cell Therapy via Immuno-metabolic Reprogramming of CD8+ T Cells

Adoptive cell therapy (ACT) has transformed cancer immunotherapy; however, its clinical efficacy remains limited by progressive T cell dysfunction and inadequate metabolic fitness acquired during ex vivo expansion and within the tumor microenvironment. Here, we report the discovery of AS-3, a first-in-class small-molecule activator that enhances the therapeutic competence of CD8 T cells through RAPTOR-dependent mTORC1 activation. Identified by phenotypic screening of an in-house library of pharmacologically relevant scaffolds and subsequent medicinal chemistry optimization, AS-3 markedly increased effector cytokine production while preserving T cell viability. Mechanistically, AS-3 enhanced phosphorylation of mTORC1 downstream effectors, promoted glycolytic and mitochondrial metabolism, and sustained pathway activity under rapamycin-mediated inhibition. Transcriptomic profiling of activated human CD8 T cells revealed coordinated enrichment of mTORC1 signalling, oxidative phosphorylation, glycolysis, proliferative programs, and cytotoxic effector gene networks, consistent with comprehensive immunometabolic reprogramming. Genetic silencing of RAPTOR attenuated both mTORC1 signalling and cytokine induction, establishing pathway dependency. Ex vivo conditioning with AS-3 significantly improved antitumor efficacy in two independent adoptive T-cell therapy models, accompanied by enhanced persistence, reduced exhaustion, and superior effector function. Together, these findings establish pharmacological activation of the RAPTOR-mTORC1 axis as a strategy to generate metabolically resilient T cells and provide a clinically translatable approach to improving the durability and efficacy of next-generation ACT.