Abstract 3405: Targeting HGF-mediated resistance to vemurafenib in V600E BRAF mutant melanoma cell lines.

Background: Resistance to targeted therapies represents a key hurdle in the treatment of cancer. Preclinical data suggest that resistance is frequently driven by redundant growth factor signaling. For example, HGF has been reported to mediate resistance to BRAF inhibitors in V600E BRAF mutant melanoma. Furthermore, clinical data support these findings as circulating and tumor HGF levels have been shown to correlate with outcome in BRAF mutant melanoma patients treated with vemurafenib. In this study, we evaluated the ability of HGF / MET signaling to attenuate the effects of BRAF and MEK inhibitors in the context of V600E BRAF and NRAS mutant cell lines. Our data suggest that combined blockade of MET and MAPK pathway signaling may be required for a robust and durable clinical response in melanoma. Methods: To confirm the ability of HGF to rescue V600E BRAF mutant melanoma cell lines from the effects of vemurafenib, G361 and SKMEL5 cells were treated with vemurafenib alone or in combination with HGF. Time lapse imaging, viability assays and cell cycle analysis were used to measure treatment effects. Analogous experiments were performed with the selective MEK inhibitor PD0325901. Combinations of a potent and selective MET inhibitor (Compound A) with vemurafenib or PD0325901 were tested to evaluate their ability to attenuate the HGF-mediated resistance. To identify other cell lines rescued by HGF, thirteen V600E BRAF mutant melanoma cell lines were treated with a dose response matrix of vemurafenib and HGF. The ability of six additional growth factors to rescue cells from the effects of vemurafenib was also tested. Three NRAS mutant melanoma cell lines were also screened for HGF-mediated resistance to PD0325901. Results: Nine of thirteen V600E BRAF mutant melanoma cell lines were rescued from the effects of vemurafenib by co-treatment with HGF. Detailed analysis of G361 and SKMEL5 cells revealed that HGF was also capable of rescuing the cells from the effects of PD0325901. This HGF-mediated rescue was attenuated by treatment with combinations of vemurafenib + compound A or PD0325901 + compound A. Mechanistic cell cycle analysis of the HGF-mediated rescue of vemurafenib in G361 cells revealed an increase in proliferating cells and a reduction in growth arrested cells, whereas rescue of PD0325901 treatment occurred through a reduction in the percentage of dead or dying cells. Of the seven growth factors tested, HGF was the predominate growth factor capable of conferring resistance to vemurafenib. Furthermore, HGF rescued one of three NRAS mutant melanoma cell lines from the effects of PD0325901, highlighting the breadth of HGF-mediated resistance in melanoma cell lines. Conclusion: These findings demonstrate the potential role for HGF / MET signaling in mediating resistance to BRAF and MEK inhibitors in melanoma, and support the clinical evaluation of MET kinase inhibitors and neutralizing antibodies to HGF in this setting. Citation Format: Sean Caenepeel, Elaina Cajulis, Rick Kendall, Angela Coxon, Paul Hughes. Targeting HGF-mediated resistance to vemurafenib in V600E BRAF mutant melanoma cell lines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3405. doi:10.1158/1538-7445.AM2013-3405