Abstract B014: Leveraging T cell anti-tumor immunity to enhance the efficacy of Ras inhibition in pancreatic cancer

Abstract The advent of Ras inhibitors has revolutionized the treatment paradigm for pancreatic ductal adenocarcinoma (PDAC). However, preclinical models and early clinical results have shown that Ras inhibitor monotherapy is insufficient to produce durable anti-tumor responses. Thus, there is a great need to design rational combination therapies that can increase the effect of Ras inhibitors. Oncogenic K-Ras is known to drive the profoundly immunosuppressive tumor immune microenvironment (TIME) that is characteristic of PDAC tumors. Downstream signaling reshapes the TIME by recruiting and activating immunosuppressive cell populations such as regulatory T cells and myeloid-derived suppressor cells. This immunosuppressive milieu acts to prevent the infiltration and activity of anti-tumor T cells. Given the complex interaction between cancer cells and the TIME, we employ two mouse models of PDAC to dissect the effects of Ras inhibition on the T cell compartment. An orthotopic model of PDAC is used to study the short-term immunomodulatory effects of Ras inhibition. As a complementary model, we utilize the KPC genetically engineered mouse model to study the long-term effects of treatment on tumor response and survival. Importantly, the KPC mouse is a preclinical model that can be used to predict clinical response. Using the orthotopic model, we showed that Ras inhibition promotes the infiltration of CD4 T cells and cytotoxic CD8 T cells into the tumor. Thus, we hypothesize that enhancing the activity of these newly expanded T cell populations will improve the durability and increase the robustness of the anti-tumor response compared to monotherapy Ras inhibition. Immunohistochemical analysis of treated tumors revealed that these T cells express a range of co-stimulatory and exhaustion markers that are attractive options for combinatory regimens. In the KPC model, we used single cell-RNA sequencing to characterize differences in the T cell population at various timepoints during treatment. Compared to vehicle-treated tumors, we found that T cells in 1-week treated tumors show higher expression of transcription factors and other genes associated with T cell activation. Furthermore, when comparing T cells from endpoint tumors to tumors treated for one week, we demonstrated that this activated state is downregulated at endpoint. Strikingly, we also noted a significant downregulation of genes associated with long-term T cell memory in endpoint tumors. This suggests immune escape could be a contributing factor to tumor outgrowth at later timepoints. We are currently investigating adding T cell-stimulating immunotherapy to provoke stronger and longer-lasting anti-tumor immunity compared to monotherapy Ras inhibition. In summary, we are employing our mouse models of PDAC to delineate changes to the TIME in response to Ras inhibition over time. We aim to develop a combination therapy that incorporates T cell stimulation to enhance anti-tumor immunity, establish immunological memory, and improve the preclinical efficacy of Ras inhibition. Citation Format: Tanner Dalton, Urszula Wasko, Alvaro Curiel- Garcia, Stephen Sastra, Carmine Palermo, Marie Hasselluhn, Kenneth Olive. Leveraging T cell anti-tumor immunity to enhance the efficacy of Ras inhibition in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr B014.