Encorafenib (LGX818), a potent BRAF inhibitor, induces senescence accompanied by autophagy in BRAFV600E melanoma cells

Encorafenib (LGX818) is a new-generation BRAF inhibitor that is under evaluation in clinical trials. However, the underlying mechanism remains to be elucidated. Here we show that LGX818 potently decreased ERK phosphorylation and inhibited proliferation in BRAFV600E melanoma cell lines. Moreover, LGX818 downregulated CyclinD1 in a glycogen synthase kinase 3 beta-independent manner and induced cell cycle arrest in the G1 phase, Surprisingly, LGX818 triggered cellular senescence in BRAFV600E melanoma cells, as evidenced by increased beta-galactosidase staining, while no appreciable induction of apoptosis was detected, as determined by Annexin V and propidium iodide staining and immunoblot analysis of caspase-3 processing and poly (ADP-ribose) polymerase cleavage. Increased p27KIP1 expression and retinoblastoma protein activation were detected during LGX818-induced senescence. Additionally, inhibition of dual-specificity tyrosine phosphorylation-regulated kinase 1B by AZ191 reversed LGX818-induced CyclinD1 turnover and senescence. Interestingly, autophagy is triggered through inhibition of the mTOR/7056K pathway during LGX818-induced senescence. Moreover, autophagy inhibition by pharmacological and genetic regulation attenuates LGX818-induced senescence. Notably, combining LGX818 with autophagy modulators has anti-proliferative effect in LGX818-resistant BRAF mutant melanoma cells. Altogether, we uncovered a mechanism by which LGX818 exerts its anti-tumor activity in BRAFV600E melanoma cells. (C) 2015 Elsevier Ireland Ltd. All rights reserved.