Abstract LB-241: HGF promotes resistance to MET inhibitor AMG337 in MET-amplified gastric cancer cells

Abstract

The MET oncoprotein is a tyrosine kinase that is the only known receptor for its ligand, HGF (Hepatocyte Growth Factor). In approximately 5% of gastric cancers, MET is activated by focal amplification, rendering it constitutively active and ligand independent. MET-amplified cancer cell lines and xenografts are typically dependent on MET signaling for proliferation or survival. To test this dependency in patients, a number of small molecule MET inhibitors, including AMG337, are currently undergoing clinical evaluation for the treatment of MET-amplified tumors.Here we characterize resistance mechanisms to MET inhibitor AMG337 in vitro. We show that under standard culture conditions, resistance does not readily arise in MET-amplified gastric cell lines SNU620 and MKN45 treated with a therapeutic dose (>IC90) of AMG337. Surprisingly however, exogenous recombinant human HGF enables resistance to readily appear, with emergent cultures possessing resistance mutations in the MET activation loop at positions D1228 and Y1230. Phosphoprotein analysis shows that HGF increases autophosphorylation and activation of mutant MET sufficiently to drive cell proliferation even in the presence of AMG337.Notably, deep sequencing and clonal analysis of individually barcoded cells show that pre-existing mutant clones are likely present in cultures prior to drug treatment. However, such clones are unable to robustly proliferate in drug-containing media unless HGF is present. Based on copy number analysis, we propose that a single or small number of pre-existing mutant MET alleles in an individual cell is sufficient to drive resistance in the presence of exogenous HGF. In contrast, in HGF-negative media, a single mutant MET allele is insufficient and thus resistance does not readily arise unless gradual drug dose escalation protocols that select for increased mutant MET copy number are employed.Our results identify a key mechanism by which HGF can promote resistance to MET inhibitors in MET-amplified cancer cell lines. Because HGF is present in tumor microenvironments, combining anti-HGF antibodies with maximally-tolerated doses of small molecule MET inhibitors such as AMG337 may be beneficial in preventing resistance and in promoting durable responses. Citation Format: Marcia Gordon, Alexandra Croft, Chi-Ming Li, Sean Taylor, Sean R. Caenepeel, Kim Quon. HGF promotes resistance to MET inhibitor AMG337 in MET-amplified gastric cancer cells. [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 LB-241. doi:10.1158/1538-7445.AM2015-LB-241