Metabolism of the oral contraceptive steroids ethynylestradiol and norgestimate by normal (Huma 7) and malignant (MCF-7 and ZR-75-1) human breast cells in culture.

Human breast cancer cells are used extensively for the study of steroid hormone action. It is known that in both receptor positive and receptor negative cell lines there is considerable metabolism of the natural estrogens, estradiol (E2) and estrone (E1) with interconversion of the two steroids and formation of sulphate and glucuronide conjugates. The aim of the present work was to see if the commonly used oral contraceptive steroids (OCS) ethynylestradiol (EE2) and norgestimate (Ngmate) were metabolized in human breast cancer cell lines (MCF-7 and ZR-75-1) and a normal breast cell line (Huma 7). MCF-7, ZR-75-1 and Huma 7 cells were maintained in Dulbeccos Modified Eagles Medium (DMEM) containing foetal calf serum (FCS) insulin and hydrocortisone. In addition, ZR-75-1 cells required epidermal growth factor (EGF) and E2 while MCF-7 cells required only EGF. On reaching confluence cells were transferred to DMEM containing charcoal-stripped FCS, insulin and hydrocortisone. 48 h later this medium was renewed, radiolabelled steroid ([3H]E1; [3H]E2; [3H]EE2, [3H]Ngmate; [3H]E1-SO4; 1 nM; 0.2 microCi) was added and incubation was for 24 or 48 h. Following incubation, the medium was removed and radioactive steroid extracted with ether. Metabolites were analysed by on-line radiometric HPLC. All the cell lines were able to interconvert E1 and E2; the equilibrium favouring the formation of E2 in MCF-7 and ZR-75-1 and E1 in Huma 7 cells. E1 and E2 also underwent phase II metabolism to form their respective estrogen sulphates, this activity being most marked in the Huma 7 cell line. In addition to sulphotransferase activity, the study with E1 sulphate demonstrated sulphatase activity in both normal and cancer cells. There appeared to be no difference in extent of hydrolysis, with both E1 and E2 formed. With EE2 as substrate there was no evidence of phase I metabolism in any of the cell lines but there was conversion to the presumed 3-sulphate conjugate. The percentage formation of this metabolite was very much greater in Human 7 cells (64.1 +/- 9.6% after 24 h) than in MCF-7 and ZR-75-1 cells (7.4 +/- 5.3% and 10.6 +/- 4.1%, respectively after 24 h). In all the cell lines deacetylation of the progestogen Ngmate to norgestrel oxime was complete within 24 h. In addition there was evidence of loss of the oxime moiety to give norgestrel.(ABSTRACT TRUNCATED AT 400 WORDS)