Anti-tumor Effect of Osthol Combined with Tumor Necrosis Factor-Related Apoptosis Inducing Ligand on Breast Cancer Stem Cells

OBJECTIVE To investigate the synergistic effect and mechanism of osthole and tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) in breast cancer stem cells.METHODS After treatment of osthole and TRAIL in the MCF-7 cancer stem cells (MCF-7-CSCs) as well as the MCF-7-non-cancer stem cells (MCF-7-non-CSCs), MTT assay was performed to detect the cell viability; flow cytometry analysis was performed to measure the cell apoptosis; Western blot analysis was performed to evaluate the activation of caspase-9 and caspase-3, expression of Apaf-1, and release of cytochrome C; co-immunoprecipitation was performed to detect the interaction with Apaf-1 and pro-caspase-9, respectively.RESULTS The sensitivity of MCF-7-CSCs to TRAIL was significantly lower than the MCF-7-non-CSCs. Addition of osthole significantly increased the inhibitory rate of MCF-7-CSCs treated with TRAIL. The results of Western blot indicated that the treatment of osthole could significantly upregulate the expression of Apaf-1 without changing the release of cytochrome C. Transfection with Apaf-1 siRNA abolished the synergistic effect of osthole and TRAIL in MCF-7-CSCs. In addition, the results of co-immunoprecipitation indicated that the combination of osthole and TRAIL significantly induced the interaction with Apaf-1 and pro-caspase-9, which led to the activation of caspase-9 in MCF-7-CSCs.CONCLUSION Osthole promotes the TRAIL-induced activation of caspase-9 and apoptosis by upregulating the expression of Apaf-1 in the breast cancer stem cells.