Abstract
Recurrent/metastatic head and neck cancer remains a devastating disease with insufficient treatment options. We investigated the MET receptor tyrosine kinase as a novel target for the treatment of head and neck squamous cell carcinoma (HNSCC). MET/phosphorylated MET and HGF expression was analyzed in 121 tissues (HNSCC/normal) by immunohistochemistry, and in 20 HNSCC cell lines by immunoblotting. The effects of MET inhibition using small interfering RNA/two small-molecule inhibitors (SU11274/PF-2341066) on signaling, migration, viability, and angiogenesis were determined. The complete MET gene was sequenced in 66 head and neck cancer tissue samples and eight cell lines. MET gene copy number was determined in 14 cell lines and 23 tumor tissues. Drug combinations of SU11274 with cisplatin or erlotinib were tested in SCC35/HN5 cell lines. Eighty-four percent of the HNSCC samples showed MET overexpression, whereas 18 of 20 HNSCC cell lines (90%) expressed MET. HGF overexpression was present in 45% of HNSCC. MET inhibition with SU11274/PF-2341066 abrogated MET signaling, cell viability, motility/migration in vitro, and tumor angiogenesis in vivo. Mutational analysis of 66 tumor tissues and 8 cell lines identified novel mutations in the semaphorin (T230M/E168D/N375S), juxtamembrane (T1010I/R988C), and tyrosine kinase (T1275I/V1333I) domains (incidence: 13.5%). Increased MET gene copy number was present with >10 copies in 3 of 23 (13%) tumor tissues. A greater-than-additive inhibition of cell growth was observed when combining a MET inhibitor with cisplatin or erlotinib and synergy may be mediated via erbB3/AKT signaling. MET is functionally important in HNSCC with prominent overexpression, increased gene copy number, and mutations. MET inhibition abrogated MET functions, including proliferation, migration/motility, and angiogenesis. MET is a promising, novel target for HNSCC and combination approaches with cisplatin or EGFR inhibitors should be explored.