ErbB3 targeting enhances the effects of MEK inhibitor in wild-type BRAF/NRAS melanoma

MEK-ERK1/2 signaling is elevated in melanomas that are wild-type for both BRAF and NRAS (WT/WT), but patients are insensitive to MEK inhibitors. Stromal-derived growth factors may mediate resistance to targeted inhibitors, and optimizing the use of targeted inhibitors for WT/WT melanoma patients is a clinical unmet need. Here, we studied adaptive responses to MEK inhibition in WT/WT cutaneous melanoma. TCGA dataset and tumor microarray studies of WT/WT melanomas showed that high levels of neuregulin-1 (NRG1) were associated with stromal content and ErbB3 signaling. Of growth factors implicated in resistance to targeted inhibitors, NRG1 was effective at mediating resistance to MEK inhibitors in patient-derived WT/WT melanoma cells. Furthermore, ErbB3-ErbB2 signaling was adaptively upregulated following MEK inhibition. Patient-derived cancer-associated fibroblast studies demonstrated that stromal-derived NRG1 activated ErbB3/ErbB2 signaling and enhanced resistance to MEK inhibitor. ErbB3- and ErbB2-neutralizing antibodies blocked the protective effects of NRG1 in vitro and cooperated with MEK inhibitor to delay tumor growth in both cell line and patient-derived xenograft models. These results highlight tumor microenvironment regulation of targeted inhibitor resistance in WT/WT melanoma and provide a rationale for combining MEK inhibitors with anti-ErbB3/ErbB2 antibodies in WT/WT cutaneous melanoma patients for whom there are no effective targeted therapies options.

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