Aim: To investigate the anticancer mechanisms of triptolide, a diterpenoid isolated from the plant Tripterygium wilfordii Hook F, against human breast cancer cells and the involvement of the estrogen receptor-α (ERα)-mediated signaling pathway in particular.
Methods: Human breast cancer ERα-positive MCF-7 cells and ERα-negative MDA-MB-231 cells were tested. PrestoBlue assay was used to evaluate the cell viability. The levels of ERα mRNA and protein were detected with real-time PCR and immunoblotting, respectively. Mouse models of MCF-7 or MDA-MB-231 xenograft tumors were treated with triptolide (0.4 mg·kg(-1)·d(-1), po) or a selective estrogen receptor modulator tamoxifen (mg·kg(-1)·d(-1), po) for 3 weeks, and the tumor weight and volume were measured.
Results: Triptolide (5-200 nmol/L) dose-dependently inhibited the viability of both MCF-7 and MDA-MB-231 cells, with a more potent inhibition on MCF-7 cells. Knockdown of ERα in MCF-7 cells by siRNA significantly attenuated the cytotoxicity of triptolide, whereas overexpression of ERα in MDA-MB-231 cells markedly enhanced the cytotoxicity. Triptolide dose-dependently decreased the expression of ERα in MCF-7 cells and MCF-7 xenograft tumors. Furthermore, treatment of MCF-7 cells with triptolide inhibited the phosphorylation of ERK1/2 in dose- and time-dependent manners. In the mice xenografted with MCF-7 cells, treatment with triptolide or tamoxifen resulted in significant reduction in the tumor weight and volume. Similar effects were not obtained in the mice xenografted with MDA-MB-231 cells.
Conclusion: The anticancer activity of triptolide against ERα-positive human breast cancer is partially mediated by downregulation of the ERα-mediated signaling pathway.