LAUSR

Overall, some 30% of human cancers are driven by mutant RAS proteins, which have proven relatively difficult to target. While immunotherapy is effective for NRAS-mutant melanoma, no options exist for resistant disease, and mutant KRAS-driven lung and pancreatic carcinomas are much less responsive overall. Oncogenic pathways are often key targets for inhibition. However, pathway agonism has not been systematically explored as a therapeutic approach. BRAF-mutant melanomas respond to BRAF inhibitors (BRAFi) due to decreased ERK signaling. They can recover signaling by acquiring activating RAS/MEK mutations, but exhibit decreased proliferation in the absence of inhibitor, suggesting that supraphysiologic ERK signaling also compromises fitness. In line with this, we observed that increasing ERK hyperactivation in RAS-mutant cancers, particularly in those with a high ERK activity, might elevate ERK signaling to a degree to induce senescence and also create an inflammatory tumor microenvironment. We have shown that a majority of RAS-mutant cancer cell lines we tested undergo senescence-like arrest following exposure to all FDA-approved BRAF inhibitors at clinically relevant doses. Simultaneous MEK or ERK inhibition allows the cells to recover proliferation, and a BRAFi which does not induce ERK activation fails to have any effect, confirming that ERK hyperactivation is the key driver of this response. Importantly, these findings generalize across NRAS-mutant and KRAS-mutant cancer cell lines including in fresh human pancreatic adenocarcinoma explants. Finally, our data in two novel genomically-characterized, immunocompetent models of NRAS-mutant melanoma and KRAS-mutant pancreatic adenocarcinoma support our in-vitro findings. Both RAS-mutant murine models demonstrate that anti-PD1 therapy is substantially more efficacious when mice are additionally treated with BRAFi. Molecular profiling of the tumor microenvironment reveals the expression of cytokines related to senescence and marked infiltration of activated CD8+ T-cells. In order to implement more potentially effective immunotherapies, we have analyzed the expression of different immune-checkpoint molecules and we have observed a high expression of LAG3 and TIM3 in the melanoma NRAS-mutant model. We will further analyze the effect of those checkpoints in combination with BRAFi to potentiate the anti-tumoral responses and tumor regression. We propose that oncogenic pathway agonism is a novel, effective, and untested strategy to induce proliferation arrest and sensitization to immunotherapy. The impact of this data is in the ability to broadly sensitize RAS-mutant cancers to immunotherapy in the settings of de-novo and acquired resistance. The direct connection between a tumor cell signaling vulnerability to immunotherapy response is a major point of novelty and provides a clear molecular rationale for pursuing combined targeted and immune-based therapy. Citation Format: Alvaro de Mingo Pulido, Charles Adelmann, Brittney Sell, Karol Prieto, Kimberly Nguyen, Cynthia Dixey, Ivannie Ortiz-Rivera, Marco Napoli, Elsa Flores, Jason Fleming, Karen Mann, Christin Burd, Kenneth Y. Tsai. Using oncogenic pathway agonism to sensitize RAS-mutant cancers to immunotherapy [abstract]. In: Proceedings of the AACR Special Conference: Targeting RAS; 2023 Mar 5-8; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Res 2023;21(5_Suppl):Abstract nr A010.