Abstract: The aim of this study was to investigate the anti-tumor effect of procyanidin B2 (PCB2) on human breast cancer MCF-7 cells and the underlying mechanism. The methyl thiazolyl tetrazolium method was used to measure the effect of PCB2 at different concentrations and treatment times on the survival rate of MCF-7 cells. The changes in Ca2+ concentrations in cells and the apoptotic morphology after Hoechst 33342 staining were observed by confocal laser microscopy. The effects of PCB2 on the apoptosis rate, cell cycle, reactive oxygen species (ROS) level and mitochondrial membrane potential of MCF-7 cells were detected by a flow cytometer. Western blot was employed to determine the effect of PCB2 on the expression levels of apoptosis-related proteins in MCF-7 cells. The results indicated that PCB2 could significantly reduce the survival rate of MCF-7 cells in a dose-dependent manner when the concentration of PCB2 was in the range of 10–80 μmol/L. The IC50 for the survival rate of MCF-7 cells at 24, 48 and 72 h were 114.82, 57.15 and 55.64 μmol/L, respectively. PCB2 could remarkably increase the apoptosis rate, ROS level and nuclear fluorescence intensity of MCF-7 cells, destroy the Ca2+ balance, dramatically decrease the mitochondrial membrane potential, and block the cell cycle in the G0/G1 phase to induce apoptosis. PCB2 could up-regulate the relative expression levels of Bax, cytochrome c, caspase-12 and caspase-3 proteins, and down-regulate the relative expression level of Bcl-2. In conclusion, PCB2 has antitumor effect, and the underlying mechanism is related to the activation of apoptosis pathway mediated by mitochondria and endoplasmic reticulum, cell cycle arrest and an increase of intracellular ROS levels.

Key words: procyanidin B2; MCF-7 cell; apoptosis; mechanism