Estrogen synthesis in human colon cancer epithelial cells

Epidemiological and experimental data suggest an involvement of estrogen in the development and progression of colorectal cancer. In order to determin e whether local synthesis of estrogen occurred in human colonic cancer cell s, two colorectal cancer cell lines, HCT8 and HCT116, were evaluated for ge ne expression and enzyme activity of cytochrome P450 aromatase. In addition , the effect on aromatase expression of charcoal-stripped fetal calf serum, of quercetin and genistein and of tamoxifen and raloxifene was investigate d in both cell lines. RT-PCR analysis revealed that colorectal adenocarcino ma cell lines contain aromatase as a major component. The conversion of [H- 3]-androstenedione to estrone and labeled water was dose-dependently inhibi ted by 4-hydroxyandrostenedione and obeyed Michaelis-Menten kinetic with ap parent Ken values of similar to 20 nM and V-max values of approx. 200 and 5 00 fmol/mg protein/h for HCT8 and HCT116 cells, respectively. After 24 h in cubation, genistein (1 mu M) significantly increased aromatase activity in HCT8 cells, with no effect on HCT116 cells. In accord with previous observa tion in reproductive tissues, quercetin (1 mu M) significantly inhibited th e enzyme activity in both cell lines. Also tamoxifen (100 nM) acted as inhi bitor, while raloxifene (10 nM) decreased the enzyme activity only in HCT11 6 cells. The aromatase gene expression modulation by these effective agents was consistent with their effects on enzyme activity. These findings demon strate for the first time that colorectal adenocarcinoma cell lines express aromatase. Interestingly, the enzyme activity was inhibited by quercetin, one major dietary flavonoid, by tamoxifen, a hormonal therapeutic agent for breast cancer, and by raloxifene, used in the prevention of postmenopausal osteoporosis. (C) 2000 Elsevier Science Ltd. All rights reserved.