The role of MET receptor tyrosine kinase in non-small cell lung cancer and clinical development of targeted anti-MET agents

Abstract

A better understanding of the pathophysiology and evolution of non-small cell lung cancer (NSCLC) has identified a number of molecular targets and spurred development of novel targeted therapeutic agents. The MET receptor tyrosine kinase and its ligand hepatocyte growth factor (HGF) are implicated in tumor cell proliferation, migration, invasion, and angiogenesis in a broad spectrum of human cancers, including NSCLC. Amplification of MET has been reported in approximately 5%-22% of lung tumors with acquired resistance to small-molecule inhibitors of the epidermal growth factor receptor (EGFR). Resistance to EGFR inhibitors is likely mediated through downstream activation of the phosphoinositide 3-kinase /AKT pathway. Simultaneous treatment of resistant tumors with a MET inhibitor plus an EGFR inhibitor can abrogate activation of downstream effectors of cell growth, proliferation, and survival, thereby overcoming acquired resistance to EGFR inhibitors. Development and preclinical testing of multiple agents targeting the HGF-MET pathway, including monoclonal antibodies targeting HGF or the MET receptor and small-molecule inhibitors of the MET tyrosine kinase, have confirmed the crucial role of this pathway in NSCLC. Several agents are now in phase III clinical development for the treatment of NSCLC. This review summarizes the role of MET in the pathophysiology of NSCLC and in acquired resistance to EGFR inhibitors and provides an update on progress in the clinical development of inhibitors of MET for treatment of NSCLC.

Figure 1.

Structure and function of the MET receptor tyrosine kinase.

Figure 2.

MET signal transduction pathways. Abbreviations: EGFR, epidermal growth factor receptor; FAK, focal adhesion kinase; GRB, growth factor receptor-bound protein; HGF, hepatocyte growth factor; MAPK, mitogen-activated protein kinase; MEK, MAPK–extracellular signal related kinase kinase; mTOR, mammalian target of rapamycin; PAK, p21-activated kinase; PI3K, phosphoinositide 3-kinase; PLC, phospholipase C; SHC, SRC homology 2 domain containing transforming protein; SHP, small heterodimer protein; SOS, son of sevenless; STAT, signal transducer and activator of transcription.

Figure 3.

Proposed mechanism for acquired resistance to EGFR inhibitors by MET. (A): In erlotinib-sensitive cells, HER-3 phosphorylation by EGFR and downstream activation of PI3K/AKT is inhibited. (B): MET amplification phosphorylates HER-3 and activates PI3K/AKT in erlotinib-resistant cells. (C): MET inhibition by tivantinib and EGFR by erlotinib prevents phosphorylation of HER-3 and downstream activation of PI3K/AKT. Abbreviations: EGFR, epidermal growth factor receptor; HER human epidermal growth factor receptor; PI3K, phosphoinositide 3-kinase. Adapted from Nat Med 2007;13:675–677, with permission from Macmillan Publishers Ltd. Copyright 2007.