Everolimus together with AR-A014418 induces apoptosis of A375 melanoma cells

Abstract

Objective To evaluate effects of simultaneous inhibition of mammalian target of rapamycin complex 1 (mTORC1) kinase and glycogen synthase kinase-3β (GSK-3β) on phosphorylation of 4E-binding protein-1 (4EBP1), cap-dependent translation, as well as survival and apoptosis of melanoma cells. Methods Cultured A375 cells were classified into several groups to be treated with dimethyl sulfoxide (DMSO group), the mTORC1 kinase inhibitor everolimus at a concentration of 5 nmol/L (everolimus group), the GSK - 3β kinase inhibitor AR - A014418 at a concentration of 10 μmol/L (AR-A014418 group), or 5 nmol/L everolimus and 10 μmol/L AR-A014418 (combined treatment group). After additional culture, Western - blot analysis was performed to measure protein expressions of phosphorylated 4EBP1 (p4EBP1) and survivin in A375 cells, m7GTP pull down assay to estimate interaction between eukaryotic initiation factor-4E (eIF4E) and eIF4G, cell counting kit 8 (CCK8) assay to evaluate cell proliferation, and flow cytometry to detect cell apoptosis. Results Both everolimus and AR-A014418 had inhibitory effects on 4EBP1 phosphorylation and survivin expression. The expressions of p4EBP1-65 and survivin were both significantly decreased in the everolimus group (0.74 ± 0.05 and 0.71 ± 0.06 respectively), AR-A014418 group (0.62 ± 0.06 and 0.58 ± 0.07 respectively) and combined treatment group (0.14 ± 0.04 and 0.09 ± 0.05 respectively) compared with the DMSO group (1.00 ± 0.07 and 1.00 ± 0.06, respectively, all P< 0.001), with the most significant decrease observed in the combined treatment group. As m7GTP pull-down assay showed, the everolimus group, AR-A014418 group and combined treatment group all showed significantly lower relative expression levels of eIF4G (0.72 ± 0.04, 0.67 ± 0.05 and 0.12 ± 0.05 vs. 1.00 ± 0.06, all P< 0.001), but significantly higher relative expression levels of 4EBP1 (1.98 ± 0.16, 2.32 ± 0.17 and 7.58 ± 0.25 vs. 1.00 ± 0.08, all P< 0.001) than the DMSO group, and the combined treatment group showed the lowest eIF4G expression but highest 4EBP1 expression. After 24-hour culture, the proliferation of A375 cells was inhibited by 18.5% ± 1.3% in the everolimus group, 19.8% ± 1.8% in the AR-A014418 group, and 61.2% ± 2.1% in the combined treatment group compared with the DMSO group, with the strongest inhibition noted in the combined treatment group. The inhibitory effects of everolimus and AR-A014418 on cell proliferation increased over time, and showed the same trend at 48 hours. Flow cytometry showed that the apoptosis of A375 cells was accelerated by the 24-hour treatments with everolimus and AR-A014418 alone or in combination, with the apoptosis rate being 14.28% ± 2.18%, 14.57% ± 2.35% and 55.18% ± 6.27% in the everolimus group, AR-A014418 group and combined treatment group respectively, and the combined treatment showed the strongest accelerating effect. Conclusion The combined treatment with everolimus and AR-A014418 can evidently inhibit 4EBP1 phosphorylation and eIF4F complex formation in A375 cells, which then suppress cap-dependent translation and promote apoptosis of melanoma cells. Key words: Melanoma, experimental; Apoptosis; Glycogen synthase kinase 3; Survivin; Everolimus; 4E-binding protein-1; Cap-dependent translation