Vemurafenib induces a noncanonical senescence-associated secretory phenotype in melanoma cells which promotes vemurafenib resistance

More than one half melanoma patients have BRAF gene mutation. BRAF inhibitor vemurafenib is an effective medication for these patients. However, acquired resistance is generally inevitable, the mechanisms of which are not fully understood. Cell senescence and senescence-associated secretory phenotype (SASP) are involved in extensive biological functions. This study was designed to explore the possible role of senescent cells in vemurafenib resistance. The results showed that vemurafenib treatment induced BRAF-mutant but not wild-type melanoma cells into senescence, as manifested by positive β-galactosidase staining, cell cycle arrest, enlarged cellular morphology, and cyclin D1/p-Rb pathway inhibition. However, the senescent cells induced by vemurafenib (SenV) did not display DNA damage response, p53/p21 pathway activation, reactive oxygen species accumulation, decline of mitochondrial membrane potential, or secretion of canonical SASP cytokines. Instead, SenV released other cytokines, including CCL2, TIMP2, and NGFR, to protect normal melanoma cells from growth inhibition upon vemurafenib treatment. Xenograft experiments further confirmed that vemurafenib induced melanoma cells into senescence in vivo. The results suggest that vemurafenib can induce robust senescence in BRAF(V600E) melanoma cells, leading to the release of resistance-conferring cytokines. Both the senescent cells and the resistant cytokines could be potential targets for tackling vemurafenib resistance.