PRMT3 Drives IDO1-Dependent Radioresistance and Immunosuppression by Promoting Kynurenine Metabolism in Non-Small Cell Lung Cancer

Radioresistance is one of the primary causes of treatment failure in non-small cell lung cancer (NSCLC). In this study, we identified PRMT3 within tumors as a critical mediator impairing both radiotherapy sensitivity and T-cell anti-tumor activity. In tumor cells, PRMT3 mediated arginine methylation of transcription factor TFAP2A, enhancing its binding to the IDO1 promoter. Methylated TFAP2A exhibited a prolonged half life, increased nuclear localization, and enhanced dimer formation, which ultimately led to heightened IDO1 expression that enhanced synthesis of kynurenine (Kyn). The elevated Kyn production boosted radioresistance in tumor cells and suppressed the infiltration and function of CD8+ T cells by activating aryl hydrocarbon receptors (AhR). Interestingly, combined pharmacological inhibition of PRMT3 and IDO1 effectively disrupted the TFAP2A-IDO1-Kyn axis, overcoming radioresistance, activating anti-tumor immunity, and ultimately eradicating tumors. In conclusion, these findings delineate PRMT3-mediated Kyn metabolism as a mechanism of radioresistance and immune evasion in NSCLC, offering valuable insights for potential interventions for treating lung cancer patients.