Abstract 330: High-throughput drug screens in osimertinib-resistant NSCLC cell lines, using continuous high-content imaging, identify potential co-targets to overcome acquired resistance

INTRODUCTION: Oncogenic mutations in EGFR are found in 15-30% of non-small cell lung cancers (NSCLC). Patients with EGFR -mutant NSCLC derive clinical benefit from EGFR tyrosine kinase inhibitors (TKIs), such as erlotinib and afatinib. Recently, a 3 rd -generation EGFR TKI, osimertinib, was approved for first-line treatment of metastatic EGFR -mutant NSCLC based on improved progression-free survival compared to earlier EGFR TKIs. Unfortunately, resistance to osimertinib and other EGFR TKIs invariably develops. While secondary mutations in EGFR are a common resistance mechanism, resistance also frequently arises independent of EGFR alterations. We hypothesize that “bypass” signaling pathways are responsible for much of this off-target drug resistance. Moreover, we hypothesize that these bypass signaling pathways are pharmacologically targetable. DESIGN: Osimertinib-resistant cell lines were developed for 6 months and characterized via Western blot, CellTiter Blue, and RNA-seq. Drug screens were conducted with nine matched isogenic osimertinib-sensitive and -resistant cell lines, using continual imaging and cell counting on an automated high-content imaging microscope, in the presence and absence of osimertinib. The drug-induced proliferation (DIP) rate metric was used to generate time-resolved analyses of drug effect while minimizing effect of deviations in plating density. A library of 1176 compounds was selected based on: (1) published bioactivity/safety data; (2) prior clinical investigation; (3) target diversity; (4) minimized chemical redundancy. RESULTS: No de novo secondary EGFR alterations were found in any osimertinib-resistant cell line. Clear evidence of epithelial-to-mesenchymal transition was apparent in 4 of 9 resistant lines, which correlated with decreased EGFR and ErbB-family protein expression. FGFR1 mRNA expression was elevated in 8 of 9 resistant lines, and protein expression increased in 4 of 9 osimertinib-resistant lines. Initial drug screens have identified candidate “hits” which are more efficacious in an osimertinib-resistant cell line than its matched parental line. CONCLUSION: These results suggest that acquired osimertinib resistance, relying on certain “bypass” signaling pathways, arise independently in multiple cell culture models. Secondly, these results suggest that such “bypass”-mediated resistance can be identified and is pharmacologically targetable. Lastly, screening data demonstrates the utility and robustness of the DIP rate metric in image-based high-throughput drug screens. Citation Format: David Westover, Yun-Kai Zhang, Yingjun Yan, Stephen Himmelberg, Darren R. Tyson, Joshua A. Bauer, Christine M. Lovly. High-throughput drug screens in osimertinib-resistant NSCLC cell lines, using continuous high-content imaging, identify potential co-targets to overcome acquired resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 330.