Inhibition of glutamine metabolism blocks tumor growth and sensitizes ccRCC to immune checkpoint blockade

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BACKGROUND: Metabolic reprogramming of glutamine plays a pivotal role in the progression of clear cell renal cell carcinoma (ccRCC). Although inhibition of glutamine metabolism has been shown to suppress ccRCC progression, its effect on tumor immune evasion remains poorly understood. METHODS: Bioinformatic analysis and glutamine deprivation assays were performed to investigate the association between glutamine metabolism and clinical outcomes in ccRCC, as well as its effect on tumor cell proliferation. Western blot, flow cytometry, MTT, ELISA, RNA-Seq, immunohistochemistry, and multiplex immunofluorescence were used to evaluate the antitumor effects of the glutamine antagonist DON/DRP-104 and the glutaminase inhibitor CB-839 both in vitro and in vivo, along with their impacts on PD-L1 expression in tumor cells and CD8⁺T cell function. RNA-Seq, Western blot, flow cytometry, and immunofluorescence were further employed to explore the mechanisms by which DON/DRP-104 and CB-839 regulate PD-L1 expression. Finally, in vivo experiments were performed to evaluate the antitumor effects of DRP-104 or CB-839 in combination with an anti-PD-L1 antibody in renal cancer. RESULTS: We demonstrate that pharmacological inhibition of glutamine metabolism with DON/DRP-104 or CB-839 effectively suppressed tumor cell viability in vitro by inhibiting proliferation and inducing apoptosis, and delayed tumor progression in vivo. However, this metabolic inhibition paradoxically impaired CD8+T cell function. Further investigation revealed that inhibition of glutamine metabolism upregulated PD-L1 expression on tumor cells via a reactive oxygen species (ROS)-dependent EGFR/ERK1/2/c-Jun signaling pathway. Consequently, combining DRP-104 or CB-839 with anti-PD-L1 therapy enhanced the efficacy of immune checkpoint inhibitors (ICIs) in mouse models. CONCLUSION: While inhibition of glutamine metabolism blocks renal cancer growth, it concurrently impairs CD8⁺T cell function by upregulating PD-L1 expression on tumor cells via a ROS-dependent EGFR/ERK1/2/c-Jun pathway. Combining DRP-104 or CB-839 with ICIs restores CD8⁺T cell function and improves antitumor immunity.