Cytotoxic activity of soy phytoestrogen coumestrol against human breast cancer MCF-7 cells: Insights into the molecular mechanism.

Coumestrol is a phytoestrogen present in soybean products and recognized as potential cancer therapeutic agent against breast cancer. However, the clear molecular mechanism of anticancer-activity of coumestrol in breast carcinoma has not been reported. It is well established that copper levels are elevated in different malignancies. Therefore, the objective of this study was to investigate the copper-dependent cytotoxic action of coumestrol in human breast cancer MCF-7 cells. Results showed that coumestrol inhibited proliferation and induced apoptosis in MCF-7 cells, which was prevented by copper chelator neocuproine and ROS scavengers. Coumestrol treatment induced ROS generation coupled to DNA fragmentation, up-regulation of p53/p21, cell cycle arrest at G1/S phase, mitochondrial membrane depolarization and caspases 9/3 activation. All these effects were suppressed by ROS scavengers and neocuproine. These results suggest that coumestrol targets elevated copper for redox cycling to generate ROS leading to DNA fragmentation. DNA damage leads to p53 up-regulation which directs the cell cycle arrest at G1/S phase and promotes caspase-dependent apoptosis of MCF-7 cells. In conclusion, copper targeted ROS-mediated p53-dependent mechanism better explains the cytotoxic action of coumestrol in MCF-7 cells. Thus, targeting elevated copper levels might be a potential therapeutic strategy for selective cytotoxic action against malignant cells.