Combined with Gefitinib Overcomes Immunosuppression Induced by long-term Glutamine blockade in Bladder Cancer

Glutamine is a major energy source for tumor cells and blocking glutamine metabolism is being investigated as a promising strategy for cancer therapy. However, the antitumor effect of glutamine blockade in bladder cancer remains unclear, necessitating further investigation. Here, we demonstrated that glutamine metabolism was involved in the malignant progression of bladder cancer. Treatment with the glutamine antagonist 6-Diazo-5-oxo-L-norleucine (DON) inhibited bladder cancer cells in vitro in several ways. In addition, we observed a remarkable inhibition of tumor growth in bladder cancer-bearing mice using JHU083, a prodrug that was designed to prevent DON-induced toxicity. However, the antitumor immune effect of T cells changed from activation to inhibition as the administrated time extended. We found that both in vitro treatment with DON and in vivo prolonged administration of JHU083 led to the upregulation of PD-L1 in bladder cancer cells. Mechanistically, glutamine blockade up-regulates PD-L1 expression in bladder cancer cells by accumulating ROS, subsequently activating the EGFR/ERK/C-Jun signaling pathway. Combinatorial treatment with JHU083 and gefitinib reversed the up-regulation of PD-L1 in bladder cancer cells induced by prolonged glutamine blockade. This reversal resulted in the alleviation of T-cell immunosuppression and a significant improvement in therapeutic outcome. These preclinical findings suggested that broad targeting of glutamine metabolism could represent a viable therapeutic strategy for bladder cancer, with the potential for further enhancement through combined treatment with gefitinib.