Green tea’s effect on anti-estrogen treatment

Proc Amer Assoc Cancer Res, Volume 47, 2006 2251 We observed that green tea increases the inhibitory effect of tamoxifen on the proliferation of multiple ER (estrogen receptor-α)-positive human breast cancer cells in vitro. The ID50 (inhibitory dose 50) for tamoxifen alone were as follows: 10.2 μM for MCF-7, 7.2 μM for ZR-75, and 8.4 μM for T47-D. We then demonstrated that the addition of 5 μg/ml of green tea extract decreased the ID50 of tamoxifen to 200 nM for MCF-7, 36 nM for ZR-75 and 30 nM for T47-D. It thus appears that green tea can add to tamoxifen’s effectiveness on ER-positive breast cancer cells. Further experiments showed that green tea did not affect substrate binding to the estrogen receptor. However, green tea decreased the level of estrogen receptors, blocked ER-dependent transcription, as well as estradiol-induced phosphorylation and nuclear localization of mitogen activated protein kinase (MAPK). The addition of green tea to tamoxifen potentiated these ER-dependent activities. These results suggest that consumption of green tea during tamoxifen treatment may be beneficial for breast cancer patients.