Abstract 2143: Sequential anti-folate (pemetrexed) and anti-PD-L1 (avelumab) combination therapy in patients with previously treated MTAP-deficient advanced urothelial cancer: Clinical outcomes and immune correlative analyses

Abstract MTAP-deficiency in urothelial cancer is associated with poor clinical outcomes but correlates with sensitivity to antifolate chemotherapy. This single-arm phase 2 trial (N=15) assessed the clinical and biological effects of a sequential combination therapy using the immune modulating antifolate agent pemetrexed and anti-PD-L1 agent avelumab in patients with advanced urothelial cancer resistant to prior chemotherapy and/or immunotherapy. The combination regimen treatment resulted in an overall response rate (ORR) of 20% (95% CI: 5%, 42%), a disease control rate (DCR) of 47% (95% CI: 23%, 71%), a median progression-free survival (PFS) of 2.3 months (95% CI: 1.9, 5.5), and a median overall survival (OS) of 13.5 months (95% CI: 3.2. 22.4). To investigate the relationship between clinical outcomes and tumor microenvironment (TME), single-cell RNA sequencing was performed on tumor samples collected from 15 patients at three time points: baseline, after pemetrexed monotherapy (cycle 2, day 1), and following combined treatment (cycle 4, day 1). This analysis profiled 49, 161 cells spanning nine major cell types, including T cells, B cells, plasma cells, myeloid cells, epithelial cells, fibroblasts, and endothelial cells. Correlating TME composition with clinical outcomes revealed that higher proportions of T and NK cells at baseline were positively associated with PFS and clinical benefit. Conversely, elevated levels of proliferating myeloid cells and macrophages correlated with poorer responses to therapy. Pemetrexed monotherapy notably reshape the immune landscape, promoting increased infiltration of type-2 conventional dendritic cells (cDC2). Furthermore, patients with augmented B and plasma cell infiltration following pemetrexed treatment exhibited better clinical outcomes. Resistance to treatment was associated with increased adenosine signaling, suggesting a potentially targetable pathway to enhance treatment efficacy. Preclinical data suggest that targeting adenosine signaling pathway may further enhance the therapeutic effects of pemetrexed and anti-PD-L1 for MTAP-deficient bladder cancer. Additionally, urine methylthioadenosine (MTA), which accumulates due to MTAP deficiency, emerged as a promising biomarker for treatment monitoring. These discoveries unveil the link between TME of MTAP-deficient tumors and response for this clinical trial, suggest potential targetable mechanism to improve efficacy, which better the understanding of MTAP-deficient tumors and design promising strategies to improv clinical translation. These findings underscore the intricate link between the TME and treatment response in MTAP-deficient tumors, offering insights into resistance mechanisms to optimize clinical outcomes in MTAP-deficient urothelial cancer. Citation Format: Amishi Y. Shah, Xinmiao Yan, Rebecca S. Tidwell, Jianfeng Chen, Arlene O. Siefker-Radtke, Sangeeta Goswami, Omar Alhalabi, Yuxue Zhang, Ying Mei, Charles Guo, Miao Zhang, Ana C. Adriazola, Abu Hena Kamal, Nagireddy Putluri, Mark A. Titus, Bogdan Czerniak, Matthew T. Campbell, Linghua Wang, Jianjun Gao. Sequential anti-folate (pemetrexed) and anti-PD-L1 (avelumab) combination therapy in patients with previously treated MTAP-deficient advanced urothelial cancer: Clinical outcomes and immune correlative analyses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2143.