Chemotherapeutic Potential of G1 Cell Cycle Inhibitor Indole-3-Carbinol and Its More Potent N-Alkoxy Derivatives in Human Breast Cancer Xenografts in Mice

Consumption of cruciferous vegetables has been shown to be associated with decreased incidence of many cancers, including cancer of the breast. Indole-3-Carbinol (I3C), one of the active compounds derived from cruciferous vegetables, has been shown to arrest the growth of hormone responsive and unresponsive breast cancer cells. I3C also has been found to cause increased growth arrest of MCF7 breast cancer cells in the presence of tamoxifen, an anti-estrogen known to cause cell cycle arrest in MCF7 cells. The authors report here that I3C causes a decrease in levels of functional ER alpha, without altering levels of ER beta. Treatment with I3C causes a transcriptional down regulation of ER alpha. It also causes an inhibition of estradiol-inducible gene expression, as well as estrogen-inducible total ERE activity. The authors also demonstrate that levels, subcellular localization, and ERE binding of ER beta remain unaltered.