Ravi Salgia, MD, PhD
Despite a strong rationale for targeting the tyrosine kinase receptor MET, drug development has proved fraught with challenges. Finding biomarkers that allow optimal patient selection is likely to be the key to success.MET
exon 14 skipping mutations are emerging as a particularly promising biomarker, at least in the context of lung cancer. First discovered over a decade ago, more than 100 different mutations resulting in exon 14 skipping have been described.
These mutations occur in the sites at which splicing takes place during the processing of precursor messenger RNA (mRNA) into mature mRNA and, in the MET
gene, they result in exon 14 being spliced out—hence, “skipping” the protein region encoded by this exon.
Activation of the MET receptor is tightly controlled, in part by negative regulation through degradation of the protein. Exon 14 encodes the juxtamembrane region of the MET protein, which contains a tyrosine residue that recruits the ubiquitin ligase Cbl. Cbl tags the MET receptor for degradation in the lysosome, the digestive organelle; therefore, exon 14 skipping means the activated MET receptor fails to be properly degraded.
These types of mutations occur predominantly in tumors with adenocarcinoma histology, in an estimated 3%-4% of patients.1
They are found in both the presence and absence of MET
gene amplification, another promising biomarker. Unlike EGFR
, and ALK
alterations, which tend to occur in light- or never-smokers, MET
exon 14 deletions are found in both never-smokers and ever-smokers. They also uniquely tend to occur in older patients. Importantly, several recent studies have demonstrated that these are actionable events in lung cancer and that patients harboring these mutations can experience clinical benefit when treated with MET inhibitors.
Three different MET inhibitors have shown single-agent activity against MET
exon 14 deletions, displaying durable partial responses, leading some researchers to suggest that it may provide a new route to MET inhibitor approval in lung cancer. These agents include crizotinib (Xalkori), cabozantinib (Cabometyx; Cometriq), and the novel small molecule capmatinib (INC280).
In an interview with OncologyLive
, Ravi Salgia, MD, PhD, emphasized the importance of biomarker identification in meeting the potential of MET-targeting therapy. Salgia is the Arthur & Rosalie Kaplan Chair in Medical Oncology and associate director for clinical sciences at City of Hope’s Comprehensive Cancer Center in California. He was part of the original team that discovered MET
exon 14 deletion mutations.
OncologyLive: How has our understanding of the role of the MET pathway in cancer evolved?
: MET’s come a long way. Obviously, since its discovery in 1984, a lot of basic science has gone on. Then, with the discovery of small-molecule inhibitors in 2002-2003 and ultimately clinical trials around 2005, we’ve learned a lot. It has become an important issue to say are we going to inhibit c-MET through tyrosine kinase inhibition like a small-molecule inhibitor or antibody inhibition, and those are all coming to fruition and have come to fruition. We have learned from what has worked, but we have also learned from what has not worked.
What have we learned from phase III failures of MET-targeting drugs?
What we’ve learned is that not the right biomarkers were potentially chosen. The anti-MET or the anti-HGF trials and selection criteria were based on immunohistochemistry, but it depended on one antibody versus another antibody, so it really depended on the epitope. But the activated form of MET
was not looked at, nor was the amplification of MET
, nor mutations of MET
So we’ve learned from, for example, in the EGFR world or the ALK
translocation world for non–small cell lung cancer, that we really need to be able to drill down to the molecular genetics and then come back and ask whether the therapy will work or not.