Enhanced formation of non-phenolic androgen metabolites with intrinsic oestrogen-like gene transactivation potency in human breast cancer cells: a distinctive metabolic pattern.

Breast cancer is a sex steroid hormone-dependent malignant neoplasia. The role of oestradiol in this malignancy has been well documented; however, the involvement of androgens has remained controversial. To determine the role of nonphenolic androgen metabolites in human breast cancer, we studied the metabolism of [ 14 C] testosterone and [ 14 C] androstenedione in oestrogen-dependent MCF-7 cells and non-oestrogen-dependent MDA-MB 231 cells, at different substrate concentrations (1–10 mM) and time periods (30 min–48 h). Cultured non-oestrogen-dependent HeLa and yeast cells served as controls. Metabolites were identified and quantified by reverse isotope dilution. A distinctive pattern of androgen metabolism was identified in MCF-7 cells, being the 5a-androstane-3a,17b-diol (3a,5a-diol) and its 3b epimer (3b,5a-diol), the major conversion products of testosterone (48$3%), with 5a-dihydrotestosterone as intermediary. The formation of 3a,5a-diol and 3b,5a-diol (diols) was substrate concentration- and time-dependent, and abolished by finasteride. In contrast, very little of any diol formation was observed in MDA-MB 231, HeLa and yeast cell incubations. Additional enzyme gene expression studies revealed an overexpression of 5a-steroid reductase type-1 in MCF-7 cells, as compared with MDA-MB 231 cells. The oestrogen-like activities of diols were assessed in HeLa cells co-transfected with expression vectors for a or b subtypes of the human oestrogen receptor (hER) genes and for an oestrogen-responsive reporter gene. The results show that 3b, 5a-diol and to a lesser extent 3a,5a-diol bind with high relative affinity to hERa and hERb.