Abstract 5456: Preferential targeting of N-Ras mutant and other wild type B-Raf human melanoma cells with c-Met inhibitor: a preclinical promise
Authors: Chattopadhyay Chandrani , Ellerhorst Julie A. , Ekmekcioglu Suhendan , Grimm Elizabeth A. 
Published: February 2011

Melanoma is the deadliest skin cancer known and the incidence continues to rise. The 2009 report from American Cancer Society predicts there would be 68,720 new cases of melanoma this year and deaths amounting to 8650. Melanoma detected early responds well to surgery but metastatic melanoma is highly resistant to conventional radiation and chemotherapy, and most immunotherapy, although this area is improving. Targeted therapies are most attractive as several mutations and altered growth pathways have recently been identified. Approximately 60% of melanoma are known to express mutated B-Raf, about 20% express mutated N-Ras, and the rest a variety of other mutations. The B-Raf mutated tumors are exclusive of the N-Ras, suggesting at least two biologically distinct groups.

The c-Met/HGF growth promoting pathway has recently been identified as active in human cutaneous as well as uveal melanoma, with reports showing that HGF may regulate melanoma cell proliferation, migration and differentiation. However, the activation and functional activities of the HGF receptor, c-Met, has been studied only minimally in melanoma. Our studies report that as high as 90% of melanoma cell lines express c-Met and most of these secrete a detectable level of the ligand HGF. Melanoma cells with different somatic mutations, including the mutually exclusive mutated B-Raf or N-Ras genes and other cells with wild type copies of both genes were directly compared for sensitivity to c-Met inhibition using the small molecule c-Met inhibitor PHA665752 from Pfizer. We have previously reported that the N-Ras mutant melanoma cells (SB2, SK-Mel-2 cell lines) are more sensitive compared to the B-Raf mutated lines (A375, WM35, WM793). Subsequently we observed that the majority of cell lines in the non B-Raf mutated populations (including mutant N-Ras) were positive for phospho-c-Met indicating activation of c-Met pathway.

After analyses of patient tumors by IHC, we report that 12/19 B-Raf wild type melanoma including N-Ras mutated, show activation of the c-Met pathway by detection of phospho-c-met in situ. Using formalin-fixed paraffin embedded primary cutaneous melanoma tumor tissues that had DNA sequencing after laser capture micro-dissection, we found that most B-Raf wild type tumors have activated c-Met. 5 out of 6 tumors with wild type B-Raf and N-Ras show positive staining for phospho-c-Met and about 83% cells are stained. 7 out of 13 tumors with wild type B-Raf and mutant N-Ras show phospho-c-Met with 54% cells staining positive, but in the group of B-Raf mutant tumors, only 1 out of 5 tumors stained positive for phospho-c-Met with staining in 20% cells.

Thus most human melanoma with wild type B-Raf show c-Met activation, as indicated by c-Met phosphorylation, and could be the ideal subgroup for therapeutically targeting c-Met in melanoma.

This work was supported by a Melanoma SPORE grant from the NCI (P50 CA093459).

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5456.