Tamoxifen and epigallocatechin gallate are synergistically cytotoxic to MDA-MB-231 human breast cancer cells

High concentrations of specific catechins [epigallocatechin gallate (EGCG), epigallocatechin (EGC) and epicatechin gallate (ECG)] inhibit the proliferation of many different cancer cell lines. The aim of this work was to determine if low concentrations of catechins with and without 4-hydroxytamoxifen (4-OHT) co-treatment would cause significant cytotoxicity in estrogen receptor-positive (ERα) and -negative (ERα) human breast cancer cells. Therefore, MCF-7, T47D, MDA-MB-231 and HS578T cells were incubated with EGCG, EGC or ECG (5–25 μM) individually and in combination with 4-OHT for 7 days. Cell number was determined by the sulforhodamine B cell proliferation assay. As single agents, none of the catechins were cytotoxic to T47D cells, while only EGCG (20 μM) elicited cytotoxicity in MCF-7 cells. Additionally, no benefit was gained by combination treatment with 4-OHT. ERα human breast cancer cells were more susceptible as all three catechins were significantly cytotoxic to HS578T cells at concentrations of 10 μM. In this cell line, combination with 4-OHT did not increase cytotoxicity. However, the most striking results were produced in MDA-MB-231 cells. In this cell line, EGCG (25 μM) produced a greater cytotoxic effect than 4-OHT (1 μM) and the combination of the two resulted in synergistic cytotoxicity. In conclusion, low concentrations of catechins are cytotoxic to ERα human breast cancer cells, and the combination of EGCG and 4-OHT elicits synergistic cytotoxicity in MDA-MB-231 cells.