Inhibitory effects of tamoxifen and tanshinone, alone or in combination, on the proliferation of breast cancer cells via activation of p38 MAPK signalling pathway

Purpose: To investigate the effects of tamoxifen and tanshinone administered individually or in combination, on the proliferation of breast cancer (BC) cells, and the underlying mechanism(s) of action. Methods: Human breast cancer cell lines (SNU-306, SNU-334 and SNU-1528), and normal primary mammary epithelial cell line (HMEC) were cultured at 37 °C in Dulbecco's modified Eagle's medium (DMEM) supplemented with 5 % fetal bovine serum (FBS), l glutamine (2 mM), penicillin (100 U/ml) and streptomycin (100 μg/ml) in a humidified incubator containing 5 % CO2. Cell proliferation was determined using MTT assay, while real-time quantitative polymerase chain reaction (qRT-PCR) was used to determine the expressions of apoptosis-related genes. The expressions of p38 mitogenactivated protein kinases (p38 MAPK) were determined by Western blotting. Results: There were only few viable cells in tamoxifen- and tanshinone-treated wells, and cell viability was concentration-dependently reduced. Treatment of SNU-306 cells with tamoxifen (30 µM) or tanshinone (20 µM) alone significantly reduced the expression of Wip1 after 72 h of incubation, and the level of expression was significantly reduced in SNU-306 cells treated with combination of tamoxifen and tanshinones, relative to those treated with tamoxifen or tanshinone alone (p < 0.05). The extent of apoptosis was significantly higher in SNU-306 cells treated with tamoxifen or tanshinone alone or in combination than in control cells (p < 0.05). Expressions of Bax, caspase 3 and p53 were significantly higher in SNU-306 cells than in control cells, and were significantly higher in SNU-306 cells treated with combination of tamoxifen and tanshinone than in those treated with tamoxifen or tanshinone alone (p < 0.05). The level of expression of MAPK was significantly higher in SNU-306 cells treated with tamoxifen or tanshinone alone, and in combination treatment, than in control cells (p < 0.05). Conclusion: Tamoxifen and tanshinone administered alone or in combination promote apoptosis in BC cells via mechanisms involving the up-regulation and phosphorylation of MAPK.