Propranolol induced G0/G1/S phase arrest and apoptosis in melanoma cells via AKT/MAPK pathway

Both preclinical and epidemiology studies associate beta-adrenoceptors-blockers (beta-blockers) with activity against melanoma. However, the underlying mechanism is still unclear, especially in acral melanoma. In this study, we explored the effect of propranolol, a non-selective beta-blocker, on the A375 melanoma cell line, two primary acral melanoma cell lines (P-3, P-6) and mice xenografts. Cell viability assay demonstrated that 50 mu M-400 mu M of propranolol inhibited viability in a concentration and time dependent manner with an IC50 ranging from 65.33 mu M to 148.60 mu M for 24h -72h treatment, but propranolol (less than 200 mu M) had no effect on HaCaT cell line. Western blots showed 100 mu M propranolol significantly reduced the expression of Bcl-2 while increasing the expressions of Bax, cytochrome c, cleaved capase-9 and cleaved caspase-3, and down-regulated the levels of p-AKT, p-BRAF, p-MEK1/2 and p-ERK1/2 in melanoma cells, after a 24h incubation. The in vivo data confirmed the isolation results. Mice received daily ip. administration of propranolol at the dose of 2 mg/kg for 3 weeks and the control group was treated with the same volume of saline. The mean tumor volume at day 21 in A375 xenografts was 82.33 +/- 3.75mm(3)vs. 2044.67 +/- 54.57mm(3) for the propranolol-treated mice and the control group, respectively, and 31.66 +/- 4.67 mm(3) vs. 1074.67 +/- 32.17 mm(3) for the P-3 xenografts. Propranolol also reduced Ki67, inhibited phosphorylation of AKT, BRAF, MEK1/2 and ERK1/2 in xenografts. These are the first data to demonstrate that propranolol might inhibit melanoma by activating the intrinsic apoptosis pathway and inactivating the MAPK and AKT pathways.