Active notch protects MAPK activated melanoma cell lines from MEK inhibitor cobimetinib.

The crosstalk between Notch and MAPK pathway plays a role in MEK inhibitor resistance in BRAFV600E metastatic melanoma (MM) and promotes migration in GNAQQ209L uveal melanoma (UM) cells. We determined the cytotoxicity of combinatorial inhibition of MEK and Notch by cobimetinib and γ-secretase inhibitor (GSI) nirogacestat, in BRAFV600E and BRAF wt MM and GNAQQ209L UM cells displaying different Erk1/2 and Notch activation status, with the aim to elucidate the impact of Notch signaling in the response to MEK inhibitor. Overall the combination was synergic in BRAFV600E MM and GNAQQ209L UM cells and antagonistic in BRAF wt one. Focusing on UM cells, we found that cobimetinib resulted in G0/G1 phase arrest and apoptosis induction, whereas the combination with GSI increased treatment efficacy by inducing a senescent-like state of cells and by blocking migration towards liver cancer cells. Mechanistically, this was reflected in a strong reduction of cyclin D1, in the inactivation of retinoblastoma protein and in the increase of p27KIP1 expression levels. Of note, each drug alone prevented Notch signaling activation resulting in inhibition of c-jun(Ser63) and Hes-1 expression. The combination achieved the strongest inhibition on Notch signaling and on both c-jun(Ser63) and Erk1/2 activation level. In conclusion we unveiled a coordinate action of MAPK and Notch signaling in promoting proliferation of BRAFV600E MM and GNAQQ209L UM cells. Remarkably, the simultaneous inhibition of MEK and Notch signaling highlighted a role for the second pathway in protecting cells against senescence in GNAQQ209L UM cells treated with the MEK inhibitor.

Porcelli L ，Mazzotta A ，Garofoli M ，Di Fonte R ，Guida G ，Guida M ，Tommasi S ，Azzariti A ... -  《-》

The protein kinase C inhibitor enzastaurin exhibits antitumor activity against uveal melanoma.

Wu X ，Zhu M ，Fletcher JA ，Giobbie-Hurder A ，Hodi FS ... -  《PLoS One》

Combination small molecule MEK and PI3K inhibition enhances uveal melanoma cell death in a mutant GNAQ- and GNA11-dependent manner.

Khalili JS ，Yu X ，Wang J ，Hayes BC ，Davies MA ，Lizee G ，Esmaeli B ，Woodman SE ... -  《-》

Impact of combined mTOR and MEK inhibition in uveal melanoma is driven by tumor genotype.

Ho AL ，Musi E ，Ambrosini G ，Nair JS ，Deraje Vasudeva S ，de Stanchina E ，Schwartz GK ... -  《PLoS One》

Combination with γ-secretase inhibitor prolongs treatment efficacy of BRAF inhibitor in BRAF-mutated melanoma cells.

Oncogenic triggering of the MAPK pathway in melanocytes results in senescence, and senescence escape is considered as one critical step for melanocytic transformation. In melanoma, induction of a senescent-like state by BRAF-inhibitors (BRAFi) in a fraction of treated cells - instead of killing - contributes to the repression of tumor growth, but may also provide a source for relapse. Here, we demonstrate that NOTCH activation in melanocytes is not only growth-promoting but it also protects these cells against oncogene-induced senescence. In turn, treatment of melanoma cells with an inhibitor of the NOTCH-activating enzyme γ-secretase led to induction of a senescent-like status in a fraction of the cells but overall achieved only a moderate inhibition of melanoma cell growth. However, combination of γ-secretase inhibitor (GSI) with BRAFi markedly increased the treatment efficacy particularly in long-term culture. Moreover, even melanoma cells starting to regrow after continuous BRAFi treatment - the major problem of BRAFi therapy in patients - can still be affected by the combination treatment. Thus, combining GSI with BRAFi increases the therapeutic efficacy by, at least partially, prolonging the senescent-like state of treated cells.

Zhu G ，Yi X ，Haferkamp S ，Hesbacher S ，Li C ，Goebeler M ，Gao T ，Houben R ，Schrama D ... -  《-》