Paradoxical effect of estradiol: it can block its own bioformation in human breast cancer cells

Abstract

The great majority of breast cancers are in their early stage hormone-dependent and it is well accepted that estradiol (E 2) plays an important role in the genesis and evolution of this tumor. Human breast cancer tissues contain all the enzymes: estrone sulfatase, 17β-hydroxysteroid dehydrogenase (17β-HSD), aromatase, involved in the last steps of E 2 bioformation in this tissue. Quantitative data show that the ‘sulfatase pathway’, which transforms estrogen sulfates into the bioactive unconjugated E 2, is 100–500 times higher than the ‘aromatase pathway’ which converts androgens into estrogens. In this paper we explore the effect of E 2 on the sulfatase activity using two hormone-dependent human breast cancer cells: MCF-7 and T-47D. The action of E 2 on the sulfatase activity was evaluated by the conversion of estrone sulfate (E 1S) into E 2. The cells were incubated in Minimal Essential Medium (MEM) containing 5% steroid-depleted fetal calf serum and incubated with physiological concentrations of [ 3H]E 1S (5×10 −9 M) alone (control) or in the presence of E 2 (5×10 −10 to 5×10 −5 M) for 24 h at 37° C. It was found that E 2 is a potent inhibitory agent of the estrone sulfatase activity in both cell lines. A low concentration of E 2: 5×10 −9 M decreases the sulfatase activity by 67% in MCF-7 cells and 57% in T-47D cells. More than 80% of the decrease in the formation of E 2 was obtained with the dose of 5×10 −7 M in both cell lines. It is concluded that this paradoxical effect of E 2 adds a new biological response of this hormone and could be related to estrogen replacement therapy in which it was observed to have either no effect or to decrease breast cancer mortality in postmenopausal women. Preliminary results are indicated in the Proceedings of the 14th International Symposium of the Journal of Steroid Biochemistry & Molecular Biology (Quebec, Canada, 24–27 June 2000) [J. Steroid Biochem. Molec. Biol. 76 (2001) 95–104] 1 1 [1]cited in abstract. and presented at the 83rd Annual Meeting of the Endocrine Society (Denver, USA, 20–23 June 2001 (abstract no. P2-615).