Huaier aqueous extract inhibits proliferation of breast cancer cells by inducing apoptosis

Aqueous extract of Trametes robiniophila murr (Huaier) has been commonly used in China for cancer complementary therapy in recent years; however, the mechanisms of its anticancer effects are largely unknown. In the present study, we aim to investigate its inhibitory effect on both MCF-7 and MDA-MB-231 cells, and explore the possible mechanisms of its anticancer effect. Cell viability and motility were measured by MTT and invasive assays, migration and scratch assays in vitro, respectively. The distribution of cell cycle, PI-Annexin-V staining and Rhodamine 123 assay were analyzed by flow cytometry, and western blot were used to test the apoptotic pathways. We found that Huaier extract could strongly inhibit cell viability of MCF-7 and MDA-MB-231 cells in a time- and dose-dependent manner; however, MDA-MB-231 cells showed more susceptibility to the treatment. Furthermore, cell invasiveness and migration were also suppressed with exposure to Huaier extract. We also indicated that Huaier could induce G0/G1 cell-cycle arrest, p53 accumulation and activation selectively in MCF-7 cells. Inspiringly, the PI-Annexin-V staining assay and western blot analysis confirmed cell apoptosis executed by caspase-3. Decreased mitochondrial membrane potential by Rhodamine 123 assay and down-regulation of Bcl-2 and up-regulation of BCL2-associated X protein (BAX) indicated that Huaier induced apoptosis through the mitochondrial pathway. Caspase activation during Huaier-induced apoptosis was confirmed by pan-caspase inhibitor, Z-VAD-fmk. As expected, the inhibitor decreased Huaier-induced apoptosis in both cell lines. Based on our findings, Huaier can induce cell apoptosis in both ER-positive and ER-negative breast cancer cell lines and is an effective complementary agent for breast cancer treatment. (Cancer Sci 2010; 101: 2375-2383).