OBJECTIVE:To investigate the effects of ophiopogonin D on human breast cancer MCF-7 cells.METHODS:Cell viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and colony formation experiments.Cell cycle was measured with cell cycle fl ow cytometry and a living cell assay.Apoptosis and terminal deoxynucleoitidyl transferase-mediated d UTP nick end labeling assays were performed to detect the apoptosis of MCF-7 cells induced by ophiopogonin D.Finally,Western blotting was used to explore the mechanism.RESULTS:Exposure of cells to ophiopogonin D resulted in marked decreases in viable cells and colony formation with a dose-dependent manner.Treatment of these cells with ophiopogonin D also resulted in cell cycle arrest at the G_2/M phase,and increased apoptosis.Mechanistically,ophiopogonin D-induced G_2/M cell cycle arrest was associated with down-regulation of cyclin B1.Furthermore,activation of caspase-8 and caspase-9 was involved in ophiopogonin D-induced apoptosis.CONCLUSION:The data suggested that ophiopogonin D inhibits MCF-7 cell growth via the induction of cell cycle arrest at the G_2/M phase.