Canadian women have a lifetime probability of diagnosis of breast cancer of approximately 1 in 9. Although the current management of breast cancer is effective, significant morbidity and mortality are associated with the disease and its treatments. Fisetin, a phytochemical present in many fruits and vegetables, has demonstrated anticancer activity for both prostate and colon cancer. This study explores fisetin as a possible novel therapeutic modality for breast cancer. Breast cancer cell lines (MDA-MB-468, MDA-MB-231, MCF-7, T47-D, SKBR-3; mitozantrone-resistant (MITX) and paclitaxel-resistant (Tx400) cell lines) were exposed to fisetin and cell survival was assessed by MTT, crystal violet, acid phosphatase, and colony-forming assays. Normal cells (human mammary epithelial cells, fibroblasts, human umbilical vein endothelial cells) were used as negative controls. The mechanism of action of fisetin was explored using cell cycle analysis and assays for apoptosis/necrosis, including Annexin V-propidium iodide staining, DNA fragmentation measured by JAM assay, and LDH-release assay. Apoptosis induction pathways were studied using Western blotting, as well as caspase inhibitors and cell viability assays. Flow cytometry was used to assess mitochondrial membrane stability (DiOC6 staining) and reactive oxygen species (ROS) production (dihydroethidium staining). Fisetin exhibited a dose- and time-dependent cytotoxic effect on breast cancer cell lines (e.g., 100 µM fisetin decreased MDA-MB-468 cell viability by 70% at 72h in both crystal violet and acid phosphatase assays). In contrast, the viability of normal cells was not substantially affected by concentrations of fisetin that killed breast cancer cells. Fisetin-treated breast cancer cells showed cell cycle arrest (MDA-MB-468 cells arrested at G2/M phase; MDA-MB-231 cells arrested in S-phase) and death by apoptosis (e.g., MDA-MB-468 cells showed up to 50% apoptosis and 8% late apoptosis/necrosis by Annexin V-staining; cell cycle analysis and LDH-release assays supported these results). Fisetin-induced apoptosis was associated with mitochondrial membrane permeabilization but did not involve caspase activation since Western blotting showed that caspase-3 was not cleaved in fisetin-treated breast cancer cells and cell viability was not preserved in the presence of a pan-caspase inhibitor. In addition, fisetin did not cause ROS production in MDA-MB-468 or 231 cells, indicating that ROS do not contribute to the cytotoxic effect of fisetin. Together, these findings suggest that fisetin may be useful in the treatment of breast cancer. Ongoing studies are using Zebra fish as a model to explore the in vivo anticancer activity of fisetin.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4215. doi:10.1158/1538-7445.AM2011-4215

©2011 American Association for Cancer Research
2011