Estradiol as an anti-aromatase agent in human breast cancer cells

Estradiol (E2) is an important risk factor in the development and progression of breast cancer. However, a “direct effect” of E2 in breast cancerization has not yet been demonstrated. The estrogen receptor complex can mediate the activation of oncogens, proto-oncogens, nuclear proteins and other target genes that can be involved in the transformation of normal to cancerous cells. Breast cancer cells possess all the enzymes (sulfatase, aromatase, 17β-hydroxysteroid dehydrogenase (17β-HSD)) necessary for the local bioformation of E2. In the last years, many studies have shown that treatment of breast cancer patients using anti-aromatase agents has beneficial therapeutic effects.The aromatase activity is very low in most breast cancer cells but was significantly increased in a hormone-dependent breast cancer cell line: the MCF-7aro, using the aromatase cDNA transfection and G-418 (neomycin) selection. In the present study, we explore the effect of E2 on the aromatase activity of this cell line.The MCF-7aro cell line was a gift from Dr. S. Chen (Beckman Research Institute, Duarte, U.S.A.). For experiments the cells were stripped of endogenous steroids and incubated with physiological concentrations of [3H]-testosterone (5 × 10−9 mol/l) alone or in the presence of E2 (5 × 10−5, 5 × 10−7 and 5 × 10−9 mol/l) for 24 h at 37 °C. The cellular radioactivity uptake was determined in the ethanolic supernatant and the DNA content in the remaining pellet. [3H]-E2, [3H]-estrone ([3H]-E1) and [3H]-testosterone were characterized by thin layer chromatography and quantified using the corresponding standard.It was observed that [3H]-testosterone is converted mainly into [3H]-E2 and not to E1, which suggests very low or absence of oxidative 17β-HSD (type 2) activity in these experimental conditions. The aromatase activity, corresponding to the conversion of [3H]-testosterone to [3H]-E2 after 24 h, is relatively high, since the concentration of E2 was 2.74 ± 0.11 pmol/mg DNA in the non-treated cells. E2 inhibits this conversion by 77, 57 and 21%, respectively, at the concentrations of 5 × 10−5, 5 × 10−7 and 5 × 10−9 mol.In previous studies, it was demonstrated that E2 exerts a potent anti-sulfatase activity in the MCF-7 and T-47D breast cancer cells. The present data show that E2 can also block the aromatase activity.The dual inhibition of the aromatase and sulfatase activities, two crucial enzymes for the biosynthesis of E2 by E2 itself in breast cancer add interesting and attractive information for the use of estrogen therapeutic treatments.