Abstract 1273: Molecular dynamics prediction of the mechanism of acquired resistance to EGFR inhibitors in EGFR-mutant lung cancer

Abstract

Abstract Background Acquired drug resistance is the most challenging problem in treating nonsmall cell lung cancer (NSCLC) patients with EGFR tyrosine kinase inhibitor (TKI). We evaluated whether resistance cell subclones significantly increased shortly after treatment with EGFR-TKIs could determine the final resistance phenotype for EGFR-TKIs in the tumor with EGFR mutations. Methods We generated 2 EGFR-mutant lung cancer cell lines (PC9GR and HCC827GR) resistant to gefitinib and evaluated the resistance mechanisms in each cell line. In parent cell lines (PC9 and HCC827) the amounts of EGFR T790M mutation and C-MET and VIMENTIN mRNA expression were measured before and after 48 hours treatment with gefitinib or paclitaxel. Using a cell line derived directly from tumors of treatment-naïve NSCLC patient with EGFR mutation, the above tests were repeated. We prospectively collected the bloods from 4 NSCLC patients with EGFR mutations at baseline and eight weeks after EGFR-TKI treatment and measured the level of T790M mutation in circulating tumor DNAs (ctDNA) from their bloods by colourimetric assay. Results EGFR T790M mutation was detected in PC9GR cells whereas C-MET amplification in HCC827GR cells. The proportion of EGFR T790M mutation significantly increased in the PC9 cells treated with gefitinib whereas not in the same cells treated with paclitaxel or not in the HCC827 treated with gefitinib or paclitaxel. The mRNA expression of C-MET was significantly increased in the HCC827 treated with gefitinib. The VIMENTIN mRNA expression was not changed in both cell lines. When we treated the patient-derived cells with gefitnib, the frequency of T790M significantly increased whereas C-MET mRNA expression decreased and VIMENTIN mRNA expression was not changed. In the corresponding resistance tumor tissue, only T790M mutation was detected without C-MET amplification and VIMENTIN overexpression. Two cases whose T790M mutation level in their ctDNAs increased at 8 weeks by more than 50% revealed T790M mutation in their final resistance tumor tissue. But, in other cases without an early surge of T790M mutation in their ctDNAs, T790M mutation was not detected in posttreatment biopsy sample. Conclusions Early-on-treatment quantitative change of resistance-related gene alterations may predict the final mechanism of resistance to EGFR-TKI. Citation Format: Youngjoo Lee, Yu-Ra Choi. Molecular dynamics prediction of the mechanism of acquired resistance to EGFR inhibitors in EGFR-mutant lung cancer [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 1273.