MET amplification occurs with or without T790M mutations in EGFR mutant lung tumors with acquired resistance to gefitinib or erlotinib

Abstract

PR-10 Somatic mutations in exons encoding the tyrosine kinase domain of the epidermal growth factor receptor (EGFR) are found in about 10 and 25% of non-small cell lung cancers (NSCLCs) from the United States and east Asia, respectively. Nearly 90% of these mutations occur as either multi-nucleotide in-frame deletions in exon 19 that eliminate four amino acids (LREA), or as single missense mutations that result in substitution of arginine for leucine at position 858 (L858R). Both mutations are associated with increased sensitivity of lung adenocarcinomas to the selective EGFR kinase inhibitors, gefitinib and erlotinib. Unfortunately, patients with drug-sensitive EGFR mutations whose tumors initially respond to gefitinib or erlotinib eventually develop acquired resistance. In about half of cases of acquired resistance to the EGFR inhibitors, a second-site point mutation leading to substitution of methionine for threonine at position 790 (T790M) occurs. To identify additional or alternative genetic alterations that contribute to acquired resistance to EGFR inhibitors and to disease progression, we performed high-resolution genomic analysis (array-based comparative genomic hybridization; aCGH) of tissue samples from 12 patients who initially responded but subsequently progressed while on these drugs. Results were compared to those obtained from genomic analysis of EGFR mutant lung adenocarcinomas resected from 38 patients who were never treated with kinase inhibitors. Among three loci found to be differentially altered in the acquired resistance set, one containedthe MET proto-oncogene. Subsequent quantitative PCR analysis from three independent patient cohorts collectively revealed that MET was amplified in tumors from nine of 43 (21%) patients with acquired resistance vs two of 62 untreated patients (3%) (p = 0.007, Fisher’s Exact Test). Among 10 resistant tumors from the nine patients with MET amplification, four also harbored the EGFRT790M mutation. We also found that an existing EGFR mutant cell line, NCI-H820, harbors both a T790M mutation and MET activation. Growth inhibition studies with these cells demonstrate that they are resistant to erlotinib and an irreversible EGFR inhibitor (CL-387,785) but sensitive to a multi-kinase inhibitor with potent activity against MET (XL880). Furthermore, functional analysis reveals that ERBB3 and other downstream growth signalling is largely dependent on MET, and not EGFR, in these cells. Collectively, these data suggest that MET activation occurs independently of EGFRT790M mutations and that MET may be a clinically relevant therapeutic target for some patients with acquired resistance to gefitinib or erlotinib.
 This work was funded in part by the Thomas G. Labrecque Foundation.