Abstract 4668: Characterization of fourth-generation EGFR inhibitors in binding experiments with C797S mutant EGFR and cell-based assays with osimertinib-resistant non-small cell lung cancer cell lines

Abstract Osimertinib is a third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor that inhibits the EGFR kinase domain by irreversible binding of the cysteine-797 residue (C797). Osimertinib was originally designed to target the T790M mutation, which is clinically the most frequently observed resistance mechanism to treatment with first- or second-generation EGFR inhibitors. Osimertinib has a high selectivity for the classical EGFR driver mutations (exon 19 deletion and L858R) compared to wild-type EGFR. Due to this favorable selectivity profile, osimertinib has become the standard first-line therapy for non-small cell lung cancer (NSCLC). Common resistance mechanisms following osimertinib treatment are MET oncogene amplification, and cysteine-to-serine substitution at position 797 (C797S) of EGFR, which precludes binding of osimertinib. Fourth-generation EGFR inhibitors and combinations with other targeted agents are potential strategies to overcome osimertinib resistance or to increase its efficacy. Three fourth-generation EGFR inhibitors were profiled in biochemical and cell-based assays: BDTX-1535, BLU-945, and JBJ-09-063. The binding kinetics for wild-type and C797S mutant EGFR were determined in surface plasmon resonance binding experiments on a Biacore 1S+ (Cytiva). The effect on osimertinib-resistant cells, generated using two different approaches, was studied in cell viability assays. In the first model, subclones of the NSCLC cell line PC-9, harboring an exon 19 deletion activating EGFR mutation, were selected for osimertinib resistance by in vitro drug selection [1]. In the second model, the EGFR C797S mutation was introduced into the NSCLC cell line NCI-H1975, which expresses both the L858R activating mutation and the T790M resistance mutation, by gene-editing with CRISPR-Cas9. Synergies with fourth-generation EGFR inhibitors were determined by profiling combinations in a 6-by-6 matrix, and quantifying synergistic effects using the Excess over Bliss score. We will present a detailed comparison of the binding kinetics of the three fourth-generation EGFR inhibitors on wild-type and C797S-mutant EGFR, and their ability to compete with osimertinib for binding to the kinase domain of EGFR. The different fourth-generation inhibitors show various selectivities for the various EGFR mutants and differences in their ability to spare wild-type EGFR. Profiling results of the three fourth-generation EGFR inhibitors in the osimertinib-resistant cell lines and on a panel of more than one hundred human cancer cell lines will be presented. Reference: [1] Bertran-Alamillo et al. Nature Communications 10, 1812; 2019 Citation Format: Janneke J. Melis, Kirsten Kevenaar, Jeffrey J. Kooijman, Yvonne Grobben, Jacob Ytsma, Jordi Bertran-Alamillo, Miguel-Angel Molina-Vila, Nicole Willemsen-Seegers, Guido J. Zaman. Characterization of fourth-generation EGFR inhibitors in binding experiments with C797S mutant EGFR and cell-based assays with osimertinib-resistant non-small cell lung cancer cell lines [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(6_Suppl):Abstract nr 4668.