Abstract A13: ASCL1 confers tolerance to tyrosine kinase inhibitors in EGFR mutant lung cancer

Abstract

Abstract The majority of EGFR mutant lung adenocarcinomas respond well to EGFR tyrosine kinase inhibitors (TKIs). However, the majority of these responses are partial, with drug-tolerant residual disease remaining even at the time of maximal response. This residual disease serves as a reservoir for the emergence of acquired resistance and tumor relapse, which inevitably occurs in patients treated with TKIs. It is thus critical to understand the biology of residual tumor cells and find out the mechanisms that underlie drug tolerance. Knowledge of such mechanisms could lead to the identification of potential strategies to forestall the emergence of drug resistance. Studies of residual disease have been hampered by the difficulty of studying these persister cells in patient specimens, and most studies to date have relied on analysis of established cell lines in culture. To investigate the cellular and molecular properties of residual tumor cells in vivo, we leveraged patient-derived models of EGFR mutant lung cancer. Three EGFR mutant PDXs were treated with the 3rd-generation TKI osimertinib. Tumors regressed in all cases, but measurable residual tumor remained in 2 out of the 3 PDXs even after 6 weeks of osimertinib treatment. Whole-exome sequencing (WES) of the untreated PDXs compared to the residual tumors revealed an unchanged mutational landscape between the samples, indicating that genetic mechanisms did not account for drug tolerance. Bulk RNA-sequencing, however, revealed extensive transcriptional changes between the untreated PDX and residual disease. In one of the PDXs, we identified upregulation of neuroendocrine lineage transcription factor ASCL1 in residual disease compared to untreated tumors. Using single-cell RNA-sequencing, we found a pre-existing ASCL1hi tumor cell population in untreated tumors, suggesting that these cells, which possessed drug-tolerant properties, were selected for during drug treatment. Depending on the cell line examined, expression of ASCL1 in human mutant EGFR lung cancer cell lines increased the number of persister clones following osimertinib treatment, indicating that the cellular context contributed to ASCL1’s role in conferring drug tolerance. Our studies provide insights into the role of neuroendocrine factor ASCL1 as a potential driver of drug tolerance in mutant EGFR lung cancer, and ongoing work is focused on identifying the mechanistic underpinnings of these findings. Citation Format: Bomiao Hu, Fernando J. de Miguel, Zongzhi Liu, Lok-Hei Chan, Mary Ann Melnick, Qin Yan, Don Nguyen, Rong Fan, Katerina Politi. ASCL1 confers tolerance to tyrosine kinase inhibitors in EGFR mutant lung cancer [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr A13.