The Role of the Tumor Microenvironment in Resistance to Oncogenic KRAS Inhibition in Lung Cancer - PROJECT SUMMARY Inhibitors against mutant KRAS—the oncogene once deemed undruggable—are impressively showing tumor control in preclinical testing, entering the clinic for testing in various malignancies, and in the case of the KRASG12C inhibitor Sotorasib, gaining FDA approval. MRTX1133, a KRASG12D inhibitor now entering phase 1 clinical testing, represents hope for patients bearing other KRAS mutations, including a significant number of never smokers with non-small cell lung cancer (NSCLC), 56% of whom have a KRASG12D-mutant cancer. MTRX1133 will likely result in a paradigm shift for these NSCLC patients. Moreover, NSCLC responds well to immunotherapy, and thus, the efficacy of combining KRAS inhibition with immune checkpoint immunotherapy (ICI) is expected to be even greater. However, for many molecularly targeted therapies, resistance, and therefore relapse, is common. This has been observed in patients treated with Sotorasib, and there is concern that resistance to MRTX1133 and other KRAS inhibitors will also develop. Resistance is often linked to the remodeling of the tumor microenvironment (TME), and thus, an imperative need has emerged to understand this remodeling process during intervention and tumor recurrence to guide development of future therapeutic treatment paradigms with long-term responses. Our analysis of the TME in a unique KrasG12D inducible and reversible mouse model of NSCLC using single cell RNA sequencing data shows KrasG12D-dependent control of the TME. Upon initiating KrasG12D, the expression of PDL1 decreased in a subset of myeloid cells, potentially indicating that patients with mutant KrasG12D are unlikely to respond to immune checkpoint therapy using PD1/PDL1 inhibitors. Interestingly, when KrasG12D was turned OFF, the expression of PDL1 increased, providing strong rationale for co-treatment of KRAS inhibitors with ICI for these patients. Thus, we hypothesize that a) inactivation of oncogenic KrasG12D in advanced tumors sensitizes lung cancer to anti-PDL1 antibodies and b) therapeutic interventions targeting KrasG12D will result in remodeling of the tumor microenvironment. To test our hypothesis, we will determine tumor regression and survival benefit of KrasG12D inhibition wherein oncogenic KRAS is inhibited either genetically or by MRTX1133 in combination with anti-PDL1. Importantly, we will also study tumor recurrence in NSCLC due to therapeutic resistance in our model (Aim 1). To address the urgent needs to devise effective treatments with long-term responses and understand the interaction between oncogenic KRAS expressing cells and the surrounding TME during treatment and relapse, we will thoroughly evaluate fibroblasts and immune status in relapsed KrasG12D-driven lung cancer in these mice. The intricate mechanisms of a KRASG12D-regulated TME, particularly fibroblast cells, will also be scrutinized in patient derived organoid models using MRTX1133 in co-cultures with matching fibroblasts (Aim 2). Successful completion of this proposal will provide actionable biomarkers and therapeutic targets in relapsed tumors for developing long-term therapeutic solutions.
