In vitro antiprogestational/antiglucocorticoid activity and progestin and glucocorticoid receptor binding of the putative metabolites and synthetic derivatives of CDB-2914, CDB-4124, and mifepristone

Abstract

In determining the biological profiles of various antiprogestins, it is important to assess the hormonal and antihormonal activity, selectivity, and potency of their proximal metabolites. The early metabolism of mifepristone is characterized by rapid demethylation and hydroxylation. Similar initial metabolic pathways have been proposed for CDB-2914 (CDB: Contraceptive Development Branch of NICHD) and CDB-4124, and their putative metabolites have been synthesized. We have examined the functional activities and potencies, in various cell-based assays, and relative binding affinities (RBAs) for progesterone receptors (PR) and glucocorticoid receptors (GR) of the putative mono- and didemethylated metabolites of CDB-2914, CDB-4124, and mifepristone and of the 17α-hydroxy and aromatic A-ring derivatives of CDB-2914 and CDB-4124. The binding affinities of the monodemethylated metabolites for rabbit uterine PR and human PR-A and PR-B were similar to those of the parent compounds. Monodemethylated mifepristone bound to rabbit thymic GR with higher affinity than monodemethylated CDB-2914 or CDB-4124. T47D-CO cells were used to assess inhibition of R5020-stimulated endogenous alkaline phosphatase activity and transactivation of the PRE 2-thymidine kinase (tk)-luciferase (LUC) reporter plasmid in transient transfections. The antiprogestational potency was as follows: mifepristone/CDB-2914/CDB-4124/monodemethylated metabolites (IC 50’s∼10 −9 M) > aromatic A-ring derivatives (IC 50’s∼10 −8 M) > didemethylated/17α-hydroxy derivatives (IC 50’s∼10 −7 M). Antiglucocorticoid activity was determined by inhibition of dexamethasone-stimulated transcriptional activity in HepG2 cells. The mono- and didemethylated metabolites of CDB-2914 and CDB-4124 had less antiglucocorticoid activity (IC 50’s∼10 −6 M) than monodemethylated mifepristone (IC 50∼10 −8 M) or the other test compounds. At 10 −6 M in transcription assays, none of these compounds showed progestin agonist activity, whereas mifepristone and its monodemethylated metabolite manifested slight glucocorticoid agonist activity. The reduced antiglucocorticoid activity of monodemethylated CDB-2914 and CDB-4124 was confirmed in vivo by the thymus involution assay in adrenalectomized male rats. The aromatic A-ring derivatives-stimulated transcription of an estrogen-responsive reporter plasmid in MCF-7 and T47D-CO human breast cancer cells but were much less potent than estradiol. Taken together, these data suggest that the proximal metabolites of mifepristone, CDB-2914, and CDB-4124 contribute significantly to the antiprogestational activity of the parent compounds in vivo. Furthermore, the reduced antiglucocorticoid activity of CDB-2914 and CDB-4124 compared to mifepristone in vivo may be due in part to decreased activity of their putative proximal metabolites.