Abstract 1945: Mechanisms of acquired resistance to EGFR tyrosine kinase inhibitor osimertinib and KRAS-G12C inhibitor sotorasib in lung cancer

Abstract A series of molecular targeted drugs have been developed for the treatment of non-small cell lung cancer (NSCLC) harboring driver gene alterations. Although the use of these drugs has substantially improved the clinical outcomes of patients with the genetically altered NSCLC, these patients ultimately develop resistance to the drugs. Various molecular mechanisms of resistance to the molecular target therapies have been reported, it is still a crucial challenge to overcome the drug resistance. Osimertinib, the most used third-generation EGFR tyrosine kinase inhibitor to target both common EGFR mutations and secondary T790M mutation, and sotorasib, a recently developed KRAS inhibitor to target KRAS G12C mutation, are no exception. In this study, we aimed to investigate the mechanisms of acquired resistance to osimertinib and sotorasib in NSCLC by profiling drug-resistant lung cancer cell lines, which were established from EGFR-mutant HCC827 (del E756A750) and KRAS G12C-mutant H23 through exposure to each of the molecular targeted drugs. Phospho-RTK array and western blot analyses revealed MET overexpression and phosphorylation in the osimertinib-resistant HCC827 (HCC827OR) as previous studies reported. Notably in our study, HCC827OR cells were incompletely sensitive to a selective MET inhibitor savolitinib without osimertinib, suggesting that HCC827OR partially lost its dependency on mutant EGFR and got addiction to MET signaling. When sotolasib was administered to the sotolasib-resistant H23 (H23SR) cells, KRAS-GTP, and the downstream ERK and AKT phosphorylation were suppressed. To identify novel mechanisms of the resistance, we performed epigenomic profiling of active enhancer in those cells and found a candidate transcription factor, at whose gene locus H3K27 acetylation signal was increased in H23SR cells compared to parent H23 cells. Immunoblotting showed that protein expression of the gene was indeed higher in H23SR cells than the parent cells. To confirm the involvement of this gene to the resistance, further investigation is warranted. Citation Format: Yuri Yagami, Takashi Sato, Hiroki Yamamoto, Masayuki Shirasawa, Yoshiro Nakahara, Watanabe Hideo, Naoki Katsuhiko. Mechanisms of acquired resistance to EGFR tyrosine kinase inhibitor osimertinib and KRAS-G12C inhibitor sotorasib in lung cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1945.