Metabolism of the oral contraceptive steroids ethynylestradiol, norgestimate and 3-ketodesogestrel by a human endometrial cancer cell line (HEC-1A) and endometrial tissue in vitro.

Human endometrial cancer cells and human endometrial tissue have been extensively used to study steroid hormone action and metabolism. The natural estrogens estradial (E2) and estrone (E1) are known to be metabolized by both cells and tissue with the interconversion of the two steroids and the formation of sulphate conjugates. The aim of the present work was to see if the commonly used oral contraceptive steroids ethynylestradiol (EE2), norgestimate (Ngmate) and 3-ketodesogestrel (3-KDG) were metabolized by a human endometrial cancer cell line (HEC-1A) and human endometrial tissue in vitro. Metabolites were analysed by on-line radiometric HPLC. Endometrial tissue was obtained from women undergoing dilation and curettage or hysterectomy operations. In preliminary studies with endogenous estrogens, HEC-1A cells were able to interconvert E1 and E2; the equilibrium favouring the formation of E2. Normal endometrial tissue extensively converted E2 to E1, tumour tissue appeared to catalyse this reaction much less avidly. In addition sulphate conjugates were formed by normal tissue from some patients. Cell line and endometrial tissue was able to hydrolyse estrone 3-sulphate. With EE2 as substrate there was no evidence of phase I metabolism by cell line or tissue. However, conversion to the presumed 3-sulphate conjugate was observed following incubation with normal tissue from some women. Deacetylation of the progestogen Ngmate to norgestrel oxime (NgOx) was complete within 24 h. There was also some loss of the oxime moiety to give norgestrel (Ng) following incubation with HEC-1A cells. Metabolism of Ngmate was also complete within 24 h following incubation with endometrial tissue. There were both qualitative and quantitative differences in metabolite formation between tissue obtained from different women. In contrast, 3-KDG was relatively resistant to metabolism by cell line and tissue. The major metabolite formed by HEC-1A cells accounted for only 3.3 +/- 0.4% of total added radiolabelled steroid and co-chromatographed with 3 alpha-hydroxydesogestrel. Smaller amounts of other radiometabolites were formed. No phase I metabolites of 3-KDG were formed by normal endometrial tissue, however small amounts of radiometabolites appeared to be formed by malignant tissue. These studies have provided evidence to suggest that the oral contraceptives EE2, Ngmate and 3-KDG are metabolized in the human endometrium. Knowledge of the metabolism of these in target tissues such as the endometrium may be pertinent considering the possibility that metabolites may exert specific effects.