Abstract: Objective: To investigate the effects of geraniol (GOH) combined with oridonin (ORI) on the viability, apoptosis, intracellular reactive oxygen species (ROS) level, mitochondrial membrane potential and cell cycle in human breast cancer MCF-7 cells. Methods: The cells were divided into a control group, a GOH group (102.81 μg/mL), an ORI group (4.32 μg/mL) and a GOH (102.81 μg/mL) + ORI (4.32 μg/mL) group. The methylthiazolyldiphenyl-tetrazolium bromide (MTT) method was used to detect the effects of GOH and ORI on the survival rate of MCF-7 cells. Chou-Talalay median effect analysis was adopted to evaluate the synergy of GOH combined with ORI. ROS levels, mitochondrial membrane potential change, apoptotic rate and cell cycle were measured by flow cytometry, the expression level of cytochrome c, an apoptosis-related protein, was evaluated by Western blot, and the activation of caspase-9 and caspase-3 was determined by spectrophotometry. Results: GOH and ORI alone could significantly inhibit the growth of MCF-7 cells, while their combination was more effective, giving combination index less than 1. The combination treatment increased the ROS level in cancer cells by 27.03 folds compared with the control group, reduced the mitochondrial membrane potential, blocked the cell cycle in the S phase, increased the release of cytochrome c by 3.01 folds compared with the control group, activated caspase-9 and downstream caspase-3, and induced the apoptosis of MCF-7 cells. Conclusion: The combination of GOH and ORI can significantly promote the apoptosis of MCF-7 cells mainly through increasing the ROS level in the cells to trigger mitochondrial dysfunction, release cytochrome c and activate apoptosis-related proteins, and thereby induce the apoptosis of MCF-7 cells via the mitochondrial pathway.

Key words: geraniol; oridonin; synergistic effect; apoptosis; cell cycle