Abstract 4865: Mechanisms of EGFR inhibitor sensitivity and resistance in chordoma

Abstract

Abstract Target discovery studies have identified EGFR inhibition as a promising therapeutic strategy in chordoma, motivating ongoing clinical trials. Yet EGFR is not mutated in chordoma, leaving the mechanisms associated with EGFR inhibitor (EGFRi) sensitivity and resistance unclear. In this study, we profiled a panel of over 10 chordoma cell lines to categorize their sensitivity to afatinib, a second-generation EGFRi with potency against the wild-type receptor. Several cell lines, including U-CHCF365, UM-Chor1, MUG-Chor1, and U-CH1, were highly sensitive to afatinib in cell viability assays, with absolute IC50 values below 50 nanomolar. In contrast, other chordoma cell lines, including UM-Chor5C and U-CHCF359B, exhibited limited response to EGFRi at concentrations exceeding 1 micromolar. Among sensitive cell lines, we found that afatinib promoted cell death in some cases (e.g., U-CH1) whereas in others it induced a profound cell cycle arrest. Moreover, in U-CH1 cells, acute afatinib treatment enriched a population of drug-tolerant persister cells with a fusiform morphology, potentially indicative of an epithelial-mesenchymal transition. Ongoing studies are focused on understanding the mechanisms of afatinib-induced cell death, drug tolerance, and acquired resistance, with a view to designing rational combination strategies capable of enhancing the magnitude and duration of therapeutic response. In cell lines with matched xenograft models, in vitro responses to afatinib were consistent in vivo. In a panel of 12 chordoma patient-derived xenograft (PDX) models treated with afatinib or cetuximab, differential sensitivity to EGFRi was recapitulated - with EGFRi promoting complete or negligent tumor growth inhibition in sensitive or resistant models, respectively. Finally, we combined drug sensitivity profiling of chordoma cell lines and PDXs with whole-exome and whole-transcriptome sequencing to identify genomic and transcriptomic features associated with sensitivity and resistance to EGFRi in chordoma. Collectively, our data identify a striking degree of differential sensitivity to EGFRi in chordoma, and begin to shed light on factors associated with primary and acquired resistance. These results provide a framework for guiding patient selection and identifying potential combination therapy regimens to improve EGFRi efficacy and address resistance. Citation Format: Nindo Punturi, Lee Dolat, Joan Levy, Josh Sommer, Daniel M. Freed. Mechanisms of EGFR inhibitor sensitivity and resistance in chordoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4865.