The combination of targeted therapy with BRAF and MEK inhibitors has become the standard of care in patients with BRAF (V600E) mutant melanoma, but responses are not durable. In addition, the impressive clinical benefits with anti-PD-1 and anti-PD-L1 antibodies (Ab) in patients with heavily pretreated metastatic melanoma and the synergistic effect of dabrafenib, trametinib and anti-PD-1 compared with single therapy alone groups support the idea that combining dabrafenib, trametinib and immunotherapy based on PD-1 blockade could be an interesting approach in the treatment of metastatic melanoma. With our mouse model of syngeneic BRAF (V600E) driven melanoma (SM1), we tested whether the addition of an immunostimulatory Ab targeting CD137 (4-1BB) and/or CD134 (OX40) would enhance the antitumor effect of dabrafenib, trametinib and anti-PD-1 or anti-PD-L1 therapy. In vitro studies showed that the combination group of dabrafenib, trametinib and anti-PD-1 increases CD8(+) tumor infiltrating lymphocytes (TILs), as well as CD4(+) T cells and tumor-associated macrophages (TAMs). An upregulation of PD-L1 was observed in the combination of dabrafenib, trametinib and anti-PD-1 therapy. Combination of dabrafenib, trametinib and anti-PD-1, with either anti-CD137 or anti-CD134, showed a superior antitumor effect, but the five-agent combination was not superior to the four-agent combinations. In conclusion, the combination of dabrafenib, trametinib, anti-PD1 or anti-PD-L1 therapy results in robust antitumor activity, which is further improved by adding the immune-stimulating Ab anti-CD137 or anti-CD134. Our findings support the testing of these combinations in patients with BRAF (V600E) mutant metastatic melanoma.
Keywords: PD-1; checkpoint blockade; immunotherapy; melanoma; targeted therapy.