SELECTIVE RESPONSIVENESS OF HUMAN BREAST-CANCER CELLS TO INDOLE-3-CARBINOL, A CHEMOPREVENTIVE AGENT

Background: Indole-3-carbinol (I3C), a compound found in cabbage, broc coli, and brussels sprouts, inhibits the growth of mammary tumors when fed to certain strains of mice. The chemopreventive and antitumor eff ects of I3C depend on the species and tissue type. The mechanism of ac tion and specific human cell types that respond to I3C are not known. Purpose: Our purpose was to study the mechanism of action of I3C in es trogen-responsive (MCF-7) and estrogen-nonresponsive (MDAMB231) human breast cancer cell lines. Methods: Estrogen responsiveness was determi ned by the ability of estradiol to stimulate the growth of breast canc er cells deprived of estrogen. The effect- of I3C was measured on cell growth, estradiol metabolism, and level of cytochrome P-4501A1. Growt h was measured by cell counts and soft-agar assay, estrogen metabolism was examined by a radiometric assay, and the level of cytochrome P-45 01A1 was measured by Western blots with a polyclonal antibody. Results : I3C inhibits the growth of estrogen-responsive cell line MCF-7 but h as little effect on estrogen-nonresponsive cell line MDA-MB-231. Speci fic C-2 hydroxylation of estrogen and induction of cytochrome P-4501A1 was enhanced by I3C in the MCF-7 but not in the MDA-MB-231 cells. Con clusion: I3C has specific antigrowth effects in human breast cancer ce lls. The inhibitory effects of I3C may involve selective induction of estradiol metabolism and the related cytochrome P-450 system that may be limited to estrogen-sensitive cells.