Abstract 1103: MET gene amplification is a mechanism of resistance to entrectinib in ROS1+ NSCLC

Abstract ROS1 TKIs entrectinib and crizotinib have significantly improved outcomes for ROS1+ lung adenocarcinoma patients. However, drug resistance inevitably develops, leading to disease progression. Approximately 1/3 of patients resistant to ROS1 TKIs demonstrate ROS1 kinase domain (KD) mutations (Dziadziuszko et al. ESMO 2019), but the mechanism of resistance in most patients is unknown or poorly characterized. To model and characterize acquired resistance to ROS1 TKIs, we used patient-derived cell line CUTO28 (TPM3-ROS1) to generate an entrectinib-resistant derivative (CUTO28-ER) in vitro. We utilized several techniques to probe the mechanisms driving resistance: DNA and RNA sequencing (seq), fluorescence in-situ hybridization (FISH), cell proliferation assays, and western blotting. DNA seq of the ROS1 KD in CUTO28-ER failed to reveal mutations. CUTO28-ER cells displayed sensitivity to MET-selective TKIs in proliferation assays, and MAPK and AKT pathways were inhibited only with MET-selective TKI. RNA seq and western blot showed MET overexpression, and interphase FISH confirmed MET amplification compared to parental cells (MET:CEP7 ratio 4.2 vs 1.0). We substantiated in vitro findings in patient tissue, utilizing tumor samples at 2 different points of a single CD74-ROS1 NSCLC patient’s tumor progression. The first tumor sample did not display MET amplification while on ROS1 TKI (MET:CEP7 ratio 0.9, 3.4 copies of MET). However, the second tumor sample collected 5 months later displayed a MET:CEP7 ratio of 2.5 (9.5 copies of MET), indicating progression on ROS1 TKI was likely MET-driven. To determine prevalence of MET amplification in entrectinib-resistant ROS1+ NSCLC, we analyzed circulating tumor DNA (ctDNA) by FoundationOne Liquid CDx from patients with ROS1+ NSCLC in the STARTRK-2 entrectinib trial. Of 105 ROS1+ NSCLC patients with ctDNA analysis both at enrollment and progression, 2 (1.9%) displayed copy number amplification (CNA) of MET. Of these, 1 patient had no detectible CNA at study baseline but MET CNA gain by day 166 of entrectinib therapy and the other had detectable MET CNA gains both at baseline and at progression only 28 days later. Both received 3 lines of therapy prior to entrectinib, none of which targeted ROS1 or MET. In conclusion, we demonstrated MET gene amplification as a potential mechanism of resistance to ROS1 TKI entrectinib. The prevalence of MET amplification at resistance was 2 of 105, but may be greater than was detected in STARTRK-2 due to the sensitivity of ctDNA assays and challenges of measuring CNA in ctDNA. Utilization of the ROS1/MET TKI crizotinib or combination of entrectinib with capmatinib should be explored in patients with ROS1+ NSCLC that display MET CNA to overcome MET-driven resistance following entrectinib. Citation Format: Logan C. Tyler, Anh T. Le, Hala Nijmeh, Liming Bao, Timothy R. Wilson, Brian Simmons, David Chen, Robert C. Doebele. MET gene amplification is a mechanism of resistance to entrectinib in ROS1+ NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1103.