Comparison of the effects of 17alpha-ethinylestradiol and 17beta-estradiol on the proliferation of human breast cancer cells and human umbilical vein endothelial cells.

Objective: Little is known about the direct comparison between 17α-ethinylestradiol (EE2) and 17β-estradiol (E2) on pre-existing breast cancer cells and on their angiogenetic effects. In this study we investigated the effect of both estrogens on the proliferation of MCF-7 cells, a human breast cancer cell model, and on human umbilical vascular endothelial cells (HUVECs). Methods: The steroids were tested in the concentration range of 10 - 1 0 to 10 - 5 M. The proliferation of MCF-7 and HUVEC cells was measured after five and six days by the crystal violet staining technique. Results: In the concentration range from 10 - 1 0 to 10 - 5 M both estrogens showed a proliferative effect in the MCF-7 cells, E2 having a gradually declining effect on proliferation with increasing concentration while EE2 showed a constant proliferative effect over a large concentration range. At the highest concentration tested E2 had no effect on proliferation while EE2 even inhibited growth. In the HUVEC cells both estrogens showed a slightly significant stimulatory effect at the lowest concentration, and no significant effect at the remaining concentrations. EE2 again inhibited cell growth at the highest concentration. Conclusions: At the serum concentrations seen in hormone replacement therapy, EE2 appears to have less proliferative effect on breast cancer cells compared with E2, while both estrogens appear to have similar effects on endothelial cells.