Association of activated c‐Met with NRAS ‐mutated human melanomas

Abstract

Cutaneous melanomas can be divided into three mutually exclusive genetic subsets: tumors with mutated BRAF , tumors with mutated NRAS and tumors wild type at both loci (wt/wt). Targeted therapy for melanoma has been advancing with agents directed to mutated BRAF, accounting for 50% of melanoma patients. The c‐Met pathway is known to play a role in melanoma tumorigenesis and preliminary data from our laboratory suggested that this pathway is preferentially activated in NRAS ‐mutated tumors. The objective of this study was to test the hypothesis that melanomas carrying the mutated NRAS genotype are uniquely sensitively to c‐Met inhibition, thus providing rationale for therapeutic targeting of c‐Met in this patient cohort. Using primary human melanomas with known BRAF / NRAS genotypes, we observed greater immunostaining for phosphorylated (activated) c‐Met in NRAS ‐mutated and wt/wt tumors, compared to BRAF ‐mutated tumors. NRAS ‐mutated and wt/wt cell lines also demonstrated more robust c‐Met activation in response to hepatocyte growth factor (HGF). Knock‐down of mutated N‐Ras, but not wild type N‐Ras, by RNA interference resulted in decreased c‐Met phosphorylation. Compared to BRAF mutants, NRAS ‐mutated melanoma cells were more sensitive to pharmacologic c‐Met inhibition in terms of c‐Met activation, Akt phosphorylation, tumor cell proliferation, migration and apoptosis. This enhanced sensitivity was observed in wt/wt cells as well, but was a less consistent finding. On the basis of these experimental results, we propose that c‐Met inhibition may be a useful therapeutic strategy for melanomas with NRAS mutations, as well as some tumors with a wt/wt genotype.