Abstract LB124: Oncogenic KRAS inhibition leverages senescence machinery to confer anti-tumor immunity in pancreatic ductal adenocarcinoma

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) is a deadly cancer with a five-year survival rate of just 12 percent. KRAS mutations are the main drivers of PDAC, primarily occurring at the 12th codon, with the KRASG12D mutation present in over 30% of cases. MRTX1133, a small molecule derived from the KRASG12C inhibitor, has shown notable efficacy in PDAC preclinical models. These KRAS inhibitors can enhance anti-tumor immunity, especially when combined with FDA-approved immune checkpoint therapies. Although the induction of MHC-I and FAS receptors on tumor cells contributes to this immune response, the mechanisms are not fully understood. Our study reveals that KRAS inhibition activates senescence pathways to promote FAS and MHC-I expression, enhancing anti-tumor immunity through therapy-induced senescence. Methods: Murine pancreatic ductal adenocarcinoma (PDAC) cell lines harboring the KRASG12D mutation were treated in vitro with 500 nM of MRTX1133 for 48 hours to investigate cell death pathways. Additionally, a propidium iodide assay was performed to assess cell cycle parameters after 24 hours of treatment. For in vivo studies, C57BL6 mice aged 4 to 6 weeks were implanted with the 7160c5 PDAC cell line and randomly assigned to receive either a vehicle or 15 mg per kg of MRTX1133 via intraperitoneal injection every other day for a total of six doses. After the treatment period, the mice were euthanized, and the tumors were harvested for further analysis. Results: To investigate the effects of KRAS inhibition on cell death pathways, we performed in vitro assays to assess apoptosis, autophagy, and senescence. Immunoblot analyses revealed a significant increase in p16 protein levels following treatment with the KRAS inhibitor (MRTX1133). This treatment resulted in reduced expression of CDK4, CDK2, and MYC, while levels of p21 and p27 remained stable, along with a decrease in phosphorylated RB levels. Additionally, KRAS inhibition elevated FAS receptor expression in PDAC cell lines and induced G0-G1 phase arrest. These findings suggest that KRAS inhibition activates p16, promoting cell cycle arrest and replicative senescence. Flow cytometry analysis indicated increased frequencies of activated NK cells, T NK cells, and both CD4+ and CD8+ T cells within the tumor immune microenvironment (TiME). Furthermore, KRAS inhibition reprogrammed infiltrating macrophages into a pro-inflammatory phenotype characterized by enhanced MHC-II expression. Immunohistochemistry confirmed that p16 expression was significantly higher in the treatment group than in the vehicle group, along with elevated numbers of CD8+ T cells, F480+ macrophages, and increased MHC-II expression on macrophages following KRAS inhibition when compared to CD206. Conclusion: Overall, our data suggests that the anti-tumor immunity conferred following treatment with a KRAS inhibitor (MRTX1133) is due to the activation of cellular senescence machinery via the p16-RB pathway. Citation Format: Sujith Sarvesh, Dhana Sekar Reddy Bandi, Purnachandra Nagaraju Ganji, Bassel F. El-Rayes. Oncogenic KRAS inhibition leverages senescence machinery to confer anti-tumor immunity in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB124.