Abstract B015: Wildtype RAS activity and PI3K signaling as new vulnerabilities in cells with acquired resistance to sotorasib

Abstract Purpose: Sotorasib (AMG510) has demonstrated remarkable response in lung cancer patients with tumors driven by oncogenic KRASG12C mutation. However, recently published clinical data identified acquired mutations in RAS and other genomic alterations as potential mechanisms of resistance. The cause of resistance in more than half of the patient cohort was undetermined with genomic sequencing. We hypothesize that rewiring of signaling networks could be the newly acquired vulnerabilities in cells progressing after sotorasib treatment. Experimental Design: We performed whole exome sequencing, transcriptomic profiling, and mass spectrometry-based proteomics/phosphoproteomics of the parental and sotorasib resistant isogenic line of LU65 (LU65-AMGR). The omics analyses were integrated with functional screens to prioritize a set of druggable targets/pathways. Results: We did not observe obvious acquired mutations that drive resistance to sotorasib in LU65-AMGR cells. To investigate compensatory signaling critically important for the survival/growth of LU65-AMGR cells, we studied signaling perturbations using mass spectrometry-based phosphoproteomics approach. We identified 430 and 1,574 phosphosites differentially expressed in resistant cells (± 1.5-fold & p < 0.05) with phosphotyrosine (pY) and global phosphoproteome (pS/T/Y) enrichment, respectively. Analysis of phosphoproteomics data identified increased phosphorylation of multiple RTKs including EGFR, HER2, HER3, IGF1R, AXL and PDGFRA, including others. RAS-GTP pull-down show increased levels of RAS-GTP and NRAS-GTP in the resistant cells. RAS isoform quantification using parallel reaction monitoring (MRM) mass spectrometry further confirmed increased activity of NRAS in pull-down samples. Transcriptomic analysis revealed elevated genes responsible for anti-apoptosis pathways mediated by PI3K/AKT signaling. Enrichment of transcription factors such as AP1 and AP-2A could drive enhanced EGF expression and EGFR phosphorylation in sotorasib resistant cells. Consistent with enhanced RTK and RAS activity, Western blots confirmed higher phosphorylation of ERK and AKT in LU65-AMGR cells. We show higher EGFR phosphorylation in resistant cells when compared to the parental counterpart. While LU65 cells viability is reduced markedly by sotorasib combination with afatinib, an irreversible HER family inhibitor, resistant cells showed lesser effect on cell viability with afatinib combination. Consistent with our in vitro observations, the sotorasib and afatinib combination treatment significantly regressed tumor growth only in LU65 xenografts, but not in LU65-AMGR xenografts. Conclusions: Our data suggest that activation of multiple RTKs maintains RAS activity and PI3K signaling in LU65-AMGR cells. Thus, dual pan-RAS and PI3K inhibition could serve as promising strategy of treatment in relapsed tumors identified with WT RAS and PI3K signaling activation. Citation Format: Denis Imbody, Hitendra S. Solanki, Bina Desai, Paul A. Stewart, Yaakov Stern, Ryoji Kato, Anurima Majumder, Liznair Bridenstine, Aobuli Xieraili, Bin Fang, Lancia Darville, Fumi Kinose, John M. Koomen, Uwe Rix, Andriy Marusyk, Eric B. Haura. Wildtype RAS activity and PI3K signaling as new vulnerabilities in cells with acquired resistance to sotorasib [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 B015.