Abstract 3602: Cross-resistance to 1st, 2nd, and 3rd generation EGFR tyrosine kinase inhibitors in vitro is characterized by MET amplification and PTEN loss

Abstract

Abstract Reversible EGFR tyrosine kinase inhibitors (TKIs) such as erlotinib and gefitinib offer significant clinical benefit to patients with EGFR mutation positive non-small cell lung cancer (NSCLC) compared to chemotherapy alone, but high rates of resistance especially at EGFR T790M (50-60% of resistant cases) underscore the need for better targeted treatments for NSCLC patients. Third generation irreversible TKIs–AZD9291 and CO-1686–were developed for efficacy in the T790M setting. However, resistance to the new class of EGFR TKIs is inevitable, prompting us to investigate the relationship between erlotinib and AZD9291 resistance mechanisms and explore novel ones. NSCLC cell lines harboring activating EGFR mutations with (NCI-H1975) or without T790M (HCC4006, HCC827, and PC-9) were exposed to erlotinib, dacomitnib, or AZD9291 at IC 75 or greater for three months to generate resistance. We observed cross-resistance to other EGFR TKIs in nearly all resistant lines, suggesting that T790M was not the main driver of resistance in the erlotinib-treated lines and that a common mechanism might account for resistance in each cell line set. An epithelial to mesenchymal transition (EMT) was observed and a corresponding increase in vimentin staining was seen in resistant lines, consistent with cross-resistance. Previous studies showed that MET amplification caused erlotinib resistance in HCC827; our data suggest MET amplification also accounted for the AZD9291 and dacomitnib resistance in HCC827. In AZD9291-resistant HCC4006 and H1975 lines, PTEN levels were substantially reduced compared to the parental line, with a corresponding increase in PIK3 pathway markers. Whole exome sequencing data support homozygous deletion of PTEN loss as a mechanism of acquired resistance to AZD9291 in NCI-H1975. The PTEN null line NCI-H1650 was found to be resistant to all three TKIs without long-term drug exposure, implicating PTEN loss as a mechanism of de novo resistance. An analysis of EGFR mutation status, PTEN status, MET expression, and the kinetics of acquired resistance will be presented and clinical implications will be discussed. Citation Format: Sarah M. Paul, Dorothee Nickles, Xioafen Ye, Robert L. Yauch, David S. Shames. Cross-resistance to 1st, 2nd, and 3rd generation EGFR tyrosine kinase inhibitors in vitro is characterized by MET amplification and PTEN loss. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3602. doi:10.1158/1538-7445.AM2015-3602