Abstract 7255: Novel anti-PD(L)1 resistance models for post-anti-PD(L)1 drug development

Abstract Although cancer immunotherapy utilizing blockade of the PD-1/PD-L1 checkpoint has revolutionized the treatment of a wide variety of malignancies, leading to durable therapeutic responses, it is ineffective in many patients who developed drug resistance after initial response. Therefore, the establishment of robust preclinical anti-PD-1 resistance models is of paramount importance for unraveling drug resistance mechanisms and developing novel treatment strategies. The mechanisms of anti-PD-1/anti-PD-L1 resistance include insufficient presentation of tumor antigens, downregulation of MHC class I molecules, dysregulated IFN-γ signaling pathways, and the immunosuppressive tumor microenvironment. GemPharmatech has established 3 models of anti-PD-1 resistance. (1) Drug induced model: BALB/c-hPD1 mice were subcutaneously transplanted with CT26 cells and treated with anti-PD-1 (KEYTRUDA®) twice weekly. Non-responsive tumors were excised, dissociated, cultured, and then re-implanted into naïve mice for anti-PD-1 treatment to maintain screening pressure. The induced model of anti-PD-1 resistance was obtained after repeated screening cycles. (2) Genetically engineered model: Engineered anti-PD-1 resistant models were established by knocking out either B2M or STK11 in CT26, which are known to confer specific genetic alterations to anti-PD-1 resistance. (3) Primary resistance model. CT26 cells acquired anti-PD-1 resistance after a series of KEYTRUDA treatment and re-implantation demonstrated a stable anti-PD-1 resistant phenotype. Compared with parental cell lines, drug-resistant CT26 cell showed a significantly faster tumor growth kinetics in vivo. RNA sequencing data revealed a set of genes disregulated between the resistant and parental cell lines, providing insight into the resistance mechanism to anti-PD-1 therapy. In the engineered PD-1-resistant CT26 model, knocking out STK11 dampen CT26's response towards anti-PD-1 treatment. After ablation of STK11, CD8+ cytotoxic T lymphocyte infiltration was decreased, and myeloid-derived suppressor cells (MDSCs) significantly accumulated in the tumor microenvironment. Additionally, STK11 deletion was associated with reduced PD-L1 expression in tumor cells, suggesting that immunosuppressive microenvironment contributed to the development of resistance. In conclusion, preclinical anti-PD-1 resistance models are valuable tools for researchers to dissect the complexity of anti-PD-1 resistance mechanisms and provide important guidance for the biomarker discovery as well as development of innovative therapeutic strategies. Citation Format: Hongyan Sun, Yan Wang, Zhu Fang, Jianming Xu, Xiang Gao, Jun Wang. Novel anti-PD(L)1 resistance models for post-anti-PD(L)1 drug development [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 7255.