In vitro andin vivo modulation of growth regulation in the human breast cancer cell line MCF-7 by estradiol metabolites

Background  The natural estrogen 17β-estradiol (E₂) functions as a potent tumor promoter during tumorigenic transformation of the mammary gland. From amongst the various pathways of E₂ metabolism upregulation of C16α-hydroxylation of E₂ has been associated with carcinogenesis. In the present studyin vitro andin vivo experiments were performed on estrogen receptor positive human breast cancer MCF-7 cells to examine whether the natural estrogen E₂ and its metabolites 16α-hydroxyestrone (16α-OHEi) and 2-hydroxyestrone (2-OHE₁) function as modulators of tumor cell growth. Methods  An anchorage-independent growth assay was used forin vitro study by counting the number of tri-dimensional colonies formed by MCF-7 cells suspended in 0.33% agar.In vivo experiments examined the effect of implanting metabolite material pellets into female nude mice. Results  In the anchorage-independent growth assay (AIG), continuous 14-day exposure to E₂ and to 16α-OHE₁ at 200 ng/ml induced a 59.4% and a 105.9% increase (P=0.001) respectively in the number of colonies of MCF-7 cells. Identical treatment with 2-OHE₁, however, failed to increase AIG relative to that seen in the solvent treated control cultures. In thein vivo tumorigenicity assay, treatment of nude mice with 1.5 mg E₂ or 16α-OHE₁ resulted in a 335.4% and a 384.1% increase (P<0.0002) in tumor growth, while identical treatment with 2-OHE₁ failed to exhibit any increase relative to the control group. Conclusions  These results suggest that the 16α- and 2-hydroxylated metabolites of E₂ may directly affectin vitro growth of MCF-7 cells via an autocrine mechanism andin vivo growth via paracrine mechanisms. Thus, E2-mediated growth regulation in MCF-7 cells may in part be due to distinct effects of specific E₂ metabolites on the breast cancer cells.