Microbial transformation of oral contraceptive ethisterone by Aspergillus niger and Cunninghamella blakesleeana

Ethisterone (17α-ethynyl-17β-hydroxyandrost-4-en-3-one) (1) is a synthetic steroidal estrogen. It is extensively used as an oral contraceptive. The current study involves the structural transformation of ethisterone (1) by Aspergillus niger, and Cunninghamella blakesleeana. Fermentation of 1 with C. blakesleeana afforded two new polar metabolites, 17α-ethynyl-6β,15β,17β-trihydroxyandrost-4-en-3-one, and 17α-ethynyl-7β,15β,17β-trihydroxyandrost-4-en-3-one, while transformation of ethisterone with A. niger yielded a new metabolite, 17α-ethynyl-6α,17β-dihydroxyandrost-4-en-3-one, along with a known metabolite, 17α-ethynyl-11α,17β-dihydroxyandrost-4-en-3-one. Modern spectroscopic techniques were used to characterize the structures of all transformed products.

Structure-activity relationships of synthetic progestins in a yeast-based in vitro androgen bioassay

The recent identification of tetrahydrogestrinone (THG), a non-marketed designer androgen used for sports doping but previously undetectable by established mass spectrometry-based urine drug screens, and its production by a facile chemical modification of gestrinone has raised concerns about the risks of developing designer androgens from numerous marketed progestins. We therefore have used yeast-based in vitro androgen and progesterone bioassays to conduct a structure-activity study assessing the intrinsic androgenic potential of commercially available progestins and their derivatives, to identify those compounds or structures with the highest risk of forming a basis for such misapplication. Progestins had a wide range of androgenic bioactivity that was not reliably predicted for individual steroids by their progestin bioactivity. 17alpha-Hydroxyprogesterone and 19-norprogesterone derivatives with their bulky 17beta-substituents were strong progestins but generally weak androgens. 17alpha-Ethynylated derivatives of testosterone, 19-nortestosterone and 18-methyl-19-nortestosterone such as gestrinone, ethisterone, norethisterone and norgestrel had the most significant intrinsic androgenicity of all the commercially marketed progestins. Facile chemical modification of the 17alpha-ethynyl group of each of these progestins produces 17alpha-methyl, ethyl and allyl derivatives, including THG and norbolethone, which further enhanced androgenic bioactivity. Thus by using the rapid and sensitive yeast bioassay we have screened a comprehensive set of progestins and associated structures and identified the ethynylated testosterone, 19-nortestosterone and 18-methyl-19-nortestosterone derivatives as possessing the highest risk for abuse and potential for conversion to still more potent androgens. By contrast, modern progestins such as progesterone, 17alpha-hydroxyprogesterone and 19-norprogesterone derivatives had minimal androgenic bioactivity and pose low risk.

[Advances in the study of steroidogenic acute regulatory protein]

The steroidogenic acute regulatory (StAR) protein is an essential component in the regulation of steroid biosynthesis in adrenal and gonadal cells. The StAR protein has a high tissue specificity, located on the mitochondrial membranes of some relative cells. It regulates the transfer of cholesterin from extracellular into intracellular and plays a dominant role in steroidogenic synthesis. Recent studies have also shown that the transcription and expression of StAR are modulated not only through the cAMP-PKA dependent pathway, but also by multiple hormones and cytokines, which contributes to the regulation of cholesterin synthesis.

Microbial transformation of 17alpha-ethynyl- and 17alpha-ethylsteroids, and tyrosinase inhibitory activity of transformed products

The microbial transformation of the 17alpha-ethynyl-17beta-hydroxyandrost-4-en-3-one (1) (ethisterone) and 17alpha-ethyl-17beta-hydroxyandrost-4-en-3-one (2) by the fungi Cephalosporium aphidicola and Cunninghamella elegans were investigated. Incubation of compound 1 with C. aphidicola afforded oxidized derivative, 17alpha-ethynyl-17beta-hydroxyandrosta-1,4-dien-3-one (3), while with C. elegans afforded a new hydroxy derivative, 17alpha-ethynyl-11alpha,17beta-dihydroxyandrost-4-en-3-one (4). On the other hand, the incubation of compound 2 with the fungus C. aphidicola afforded 17alpha-ethyl-17beta-hydroxyandrosta-1,4-dien-3-one (5). Two new hydroxylated derivatives, 17alpha-ethyl-11alpha,17beta-dihydroxyandrost-4-en-3-one (6) and 17alpha-ethyl-6alpha,17beta-dihydroxy-5alpha-androstan-3-one (7) were obtained from the incubation of compound 2 with C. elegans. Compounds 1-6 exhibited tyrosinase inhibitory activity, with compound 6 being the most potent member (IC(50)=1.72 microM).

5alpha-reduction of norethisterone enhances its binding affinity for androgen receptors but diminishes its androgenic potency

Norethisterone (NET), a 19-nor synthetic progestin, undergoes enzyme-mediated 5alpha-reduction and exerts potent androgenic effects in target organs. To investigate its mode of androgenic action we examined, in a comparative manner, the in vitro metabolism of NET and testosterone (T), as well as the binding affinities to androgen receptors (AR) and the androgenic potency of NET, T, and their 5alpha-reduced derivatives. Bioconversion of [3H]-NET and [3H]-T was studied in rat prostate homogenates, AR binding affinity was assessed in rat ventral prostates using [3H]-mibolerone as the radioligand, and the androgenic potency was evaluated by the increase of beta-glucuronidase activity in the mouse kidney, and by the growth of accessory sex organs in castrated male rats. The results demonstrated that 5alpha-NET displayed a higher AR binding affinity but a significantly lower androgenic potency than unchanged NET. The bioconversion studies indicated that the metabolism of NET was similar to that of T, although to a lesser extent, thus ruling out the possibility that the synthetic progestin metabolizes rapidly into less active derivatives. To investigate the nature of the paradoxical effect of 5alpha-reduction upon the NET molecule, the interaction with AR and the androgenic potency of T, 19-nortestosterone (19norT), 17alpha-ethynyl testosterone (ET) and their 5alpha-reduced derivatives were examined. The results of AR binding studies revealed that 5alpha-reduction of T and ET significantly enhanced their affinities, and that the 5alpha-derivative of 19norT displayed a similar binding affinity to that exhibited by 19norT. In terms of biological activity, the results showed that 5alpha-reduction of T and 19norT significantly increased their androgenic potency, whereas 5alpha-reduction of ET resulted in a significant diminution of its androgenicity in a manner similar to that observed with the 5alpha-reduction of NET. When NET and 19norT were simultaneously administered with 5alpha-dihydrotestosterone they exhibited a potent synandrogenic activity, an effect that was cancelled by their 5alpha-reduction. Interestingly, ET displayed an antiandrogenic activity, an effect that was also suppressed by its 5alpha-reduction. The overall results demonstrated a distinctive, paradoxical effect of 5alpha-reduction upon the NET molecule, which was different from that seen in naturally occurring androgens, and which suggests that the presence of the 17alpha-ethynyl group plays a key role in this phenomenon. The data provided further evidence that the metabolism of synthetic contraceptive progestins modulates the expression of their hormone-like actions.

Identification of progesterone binding sites in the plasma membrane of the filamentous fungus Cochliobolus lunatus

Plasma membrane associated binding sites for progesterone have been identified in the filamentous fungus Cochliobolus lunatus (C. lunatus). The Kd for progesterone determined by Scatchard analysis was 13.9 +/- 5.7 nM and the Bmax was 250-360 fmol/mg protein. A broad ligand specificity of these binding sites is suggested by the observation that all tested steroids, regardless of their capability to act as inducers of the 11 beta-steroid hydroxylase, competed at 250-fold excess with [3H]progesterone binding. A biological role of these plasma membrane associated steroid binding sites is nevertheless suggested since in protoplasts which were devoid of them, 11 beta-steroid hydroxylase could not be induced. Progesterone binding sites were present in the plasma membrane as well as in the cytosol and were detected in this fraction, in contrast to the plasma membrane fraction, only under special experimental conditions in respect to redox state. Kd and Bmax of cytosol binding sites were of the same order of magnitude compared to the plasma membrane progesterone binding sites. Ethisterone and 4-cholesten-3-one which cannot induce 11 beta-hydroxylase competed efficiently for plasma membrane binding sites; ethisterone, however also competed for cytosol binding sites and acted, in contrast with 4-cholesten-3-one, as antagonist in the induction of 11 beta-steroid hydroxylase in C. lunatus. On the basis of presented evidence we concluded that C. lunatus contains binding sites for steroids in the plasma membrane and in the cytosol and that both types of binding site are involved in the process of induction of enzymes which transform steroids in this fungus.

A comparison of the effects of danazol and gestrinone on testosterone binding to sex hormone binding globulin in vitro and in vivo

Danazol and gestrinone are both effective agents in the treatment of endometriosis. Their mechanism of action is unknown but may be related to their androgenic activity, which is at least partly dependent on increases in the proportion of testosterone which circulates unbound to plasma protein. We have quantified these increases in patients on treatment, and by experimentation in vitro have demonstrated the relative importance of the reduction of sex hormone binding globulin (SHBG) binding capacity and competition with testosterone for SHBG binding sites by the drugs and some of their metabolites. The mean SHBG binding capacity in patients treated with danazol (400 mg/d, n = 7) and gestrinone (5 mg/week, n = 7) fell from 66.9 and 56.4 nmol/l to 36.1 and 28.1 nmol/l, after 1 week's treatment and to 11.1 and 7.1 nmol/l after 4 weeks respectively. Despite the similarity between the falls in SHBG binding capacity there was a significantly greater increase in % free testosterone in plasma samples from patients treated with danazol than in those from patients treated with gestrinone at 1 week. Experiments in vitro suggest that this was largely due to ethisterone (a major metabolite of danazol) competing with testosterone for SHBG binding sites. After 4 weeks on treatment there was a similar, near maximal reduction in SHBG binding of testosterone in both treatment groups. At the low levels of SHBG binding capacity reached by this time the extra effect of any competition for binding sites was much reduced.

Interaction of contraceptive progestins and related compounds with the oestrogen receptor. Part II: Effect on (3H)oestradiol binding to the rat uterine receptor in vitro

Incubation of the 105 000 times g supernatant of rat uterus homogenate with (3H)oestradiol resulted in an oestrogen specific binding of limited capacity to a macromolecule sedimenting in the 8-9S region after density gradient centrifugation. The contraceptive progestins of the 19-nortestosterone series were able to interfere with oestradiol binding in contrast to the hydroxyprogesterone derivatives chlormadinone, medroxyprogesterone and megestrol. The interaction appeared to be competitive. The strongest inhibition of oestradiol binding was observed in the presence of ethinodiol, followed by northinodrel, lynestrenol and norethindrone respectively. Norgestrel was almost inactive. Of the related structures tested oestrenol displayed more activity than norethindrone, nortestosterone and ethisterone were less active and 6alpha-methyllynestrenol showed only border line activity. In comparison with norethinodrel and norethindrone, lynestrenol and oestrenol appeared in vitro to be stronger competitors for oestradiol than in vivo (Part I; Van Kordelaar et al. 1975). This may be due to the great difference in lipophilic character, which is reflected in the RM values of these compounds. From the results obtained it may be concluded, that the presence of a 17alpha-ethynyl substituent promotes receptor binding, whereas the introduction of methyl substituents in the position 6, 10 and 18 causes the opposite effect. The relationship between the various ring A structures and the affinity to the receptor is discussed.