Green tea increases the effectiveness of tamoxifen

5182

Current breast cancer prevention surgical or medical strategies for high risk women are traumatic, and involve serious side effects. Therefore, it is crucial to identify alternative methods to prevent breast cancer or reduce risk. Studies in our laboratory have provided evidence that green tea extract inhibits breast cancer growth via a direct anti-proliferative effect on the tumor cells, as well as an indirect suppressive effect on the endothelial cells. Recently we investigated whether green tea would increase the effectiveness of the commonly used chemopreventive drug tamoxifen. In vitro proliferation assays showed that green tea extract decreased the ED50 (50% effective dose) of tamoxifen in both estrogen-receptor positive human breast cancer cell line MCF-7 and in HUVEC (human umbilical vein endothelial cells). Green tea also increased the TUNEL-positive apoptosis exerted by tamoxifen on MCF-7 cells. In mouse experiments, the combination of green tea and tamoxifen suppressed breast cancer xenograft growth more efficiently than either agent alone. This combination decreased the overall vessel density in treated mouse tumors (16.5 ± 1.5 vessels per high power field), compared to the control group (30.7 ± 2.2 vessels per high power field). Treated tumor specimens also showed less Estrogen receptor alpha, and more TUNEL-positive apoptosis. Further studies may lead to the adaptation of combination regimens that are more effective and less toxic.