Inhibition of human placental progesterone synthesis and aromatase activity by synthetic steroidogenic inhibitors in vitro

The 3beta-hydroxysteroid dehydrogenase inhibitor trilostane shows antidepressant properties in mice

Changes in neuro(active)steroid levels are involved in depressive states and mood disorders. For instance, dehydroepiandrosterone or pregnenolone sulfate showed anti-stress and antidepressant activity in rodents and regulation of allopregnanolone levels appeared to be one of the consequence of an effective antidepressant therapy in patients. 4alpha,5-Epoxy-17beta-hydroxy-3-oxo-5alpha-androstane-2alpha-carbonitrile (trilostane) inhibits the activity of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) that, in particular, converts pregnenolone into progesterone. We examined whether systemic administration of trilostane affects the response to stress and depression. An acute treatment with trilostane (6.3-50mg/kg SC injected twice -16 and -2h before the measure) increased 3beta-HSD mRNA levels in the hippocampus and adrenals, but had little effect on protein levels. The trilostane treatment failed to affect open-field, locomotor or exploratory behaviors, but significantly reduced the immobility duration in the forced swimming test, measuring antidepressant-like activity, and increased the time spent in open arm in the elevated plus-maze, measuring anxiety response. The antidepressant-like effect of trilostane was effective after a repeated treatment (2.5-20mg/kgSC twice-a-day during 7 days) or in mice submitted to a restraint stress during 21 days and showing several behavioral and physiological parameters of depression (decreased body weight, increased adrenal glands weight and anhaedonia). Trilostane also reduced stress-induced increase in plasma corticosterone and ACTH levels, showing direct effect on HPA axis activity. These observations suggest that the 3beta-HSD inhibitor trilostane present antidepressant-like activity, putatively by regulating brain and peripheral levels of neuroactive steroids.

Trilostane in advanced breast cancer

Antiestrogens, principally tamoxifen, and aromatase inhibitors have been used as the first- and second-line therapy in patients with advanced postmenopausal breast cancer for many years. However, some patients acquire resistance to these treatments and, at present, further endocrine treatment is achieved by merely substituting the current medication with a different antiestrogen or aromatase inhibitor. Trilostane offers an alternative endocrine treatment due to its unique mode of action. It is an allosteric modulator of the estrogen receptor and targets both the estrogen- and growth factor-dependent pathways through which estradiol stimulates cell proliferation. In clinical trials, trilostane has been shown to be an effective treatment for breast cancer in patients who have relapsed after receiving treatment with one or more forms of endocrine therapy. Ongoing and future clinical trials are examining the potential for the use of trilostane in premenopausal breast cancer, as well as in other malignancies such as prostate cancer.

Non-competitive steroid inhibition of oestrogen receptor functions

Currently available antioestrogens, such as tamoxifen, are competitive inhibitors that bind to the ligand binding sites of oestrogen receptors, ERalpha and ERbeta. The search for alternative anti-hormone therapies is prompted by the need for drugs that are effective when tumours become tamoxifen resistant. The existence of different receptor isoforms also raise the possibility of improving selectivity. Earlier use of the 3beta-hydroxysteroid dehydrogenase inhibitor, trilostane (4alpha,5- epoxy-17beta-hydroxy-3-oxo-5alpha-androstane-2alpha-carbonitrile), suggested that it had beneficial actions in breast cancer that were only partially attributable to inhibition of steroidogenesis. The present studies on the interactions of trilostane with oestrogen receptors show that it (i) inhibits oestrogen-stimulated proliferation in MCF-7 breast cancer cells, (ii) enhances the affinity of oestradiol binding to ER in rat uteri and specifically increases oestradiol binding to an ERbeta-like isoform, (iii) inhibits ERalpha and ERbeta binding to the classical vitellogenin gene oestrogen response element (ERE) and (iv) inhibits oestrogen-stimulated gene transcription in ERE-linked reporter systems in MCF-7 cells. The results demonstrate a novel, presumably allosteric, mode of antioestrogen action. The beneficial actions of trilostane in breast cancer may be attributed to the combination of this antioestrogen effect with its well documented suppression of steroidogenesis.

Differential effects of trilostane and cyanoketone on the 3 beta-hydroxysteroid dehydrogenase-isomerase reactions in androgen and 16-androstene biosynthetic pathways in the pig testis

3 beta-Hydroxysteroid dehydrogenase-isomerase (3 beta-HSD-I) activity in the pig testis is responsible for the conversion of dehydroepiandrosterone (DHA) to 4-androstenedione and also for the conversion of 5,16-androstadien-3 beta-ol (andien-beta) to 4, 16-androstadien-3-one (dienone). Therefore, 3 beta-HSD-I plays an essential role in the biosynthesis of hormonally and pheromonally active steroids. Previous studies from this laboratory have suggested that the 3 beta-HSD-I reactions in the androgen and 16-androstene biosynthetic pathways may be catalysed by different enzymes with selective substrate specificities [3, 4]. The aim of the present studies was to investigate the reactions further by examining the effects of two classical steroidal inhibitors of 3 beta-HSD-I, trilostane (WIN 24540) and cyanoketone (WIN 19578), on the kinetic parameters of the 3 beta-HSD-I reactions in immature (< 3 weeks) pig testis microsomes. In kinetic analyses of the conversion of DHA to 4-androstenedione, both trilostane and cyanoketone caused increases in the Km(app) for DHA which at the highest concentration used, were 15-fold the control Km(app) of 1.4 mumol/l. No effect on the Vmax(app) (6.55 +/- 0.74 nmol/h/mg protein) was observed, demonstrating that competitive inhibition was evident. Slope and intercept replots confirmed the competitive nature of the inhibition and Ki(app) values of 0.16 mumol/l for trilostane and 0.20 mumol/l for cyanoketone were respectively 9 and 7-fold lower than the Km(app) value. In contrast, trilostane and cyanoketone had no effect on the Km(app) for andien-beta (0.26 mumol/l). The Vmax(app) (1.12 nmol/h/mg protein) was decreased by 40-50% only by trilostane at the highest concentration used, demonstrating a very low affinity for the andien-beta active site. Ki(app) values for trilostane and cyanoketone, obtained from slope and intercept replots were, respectively 1.1 and 1.6 mumol/l, which were 4 and 6-fold greater than the Km(app) for andien-beta. Therefore, trilostane and cyanoketone were powerful competitive inhibitors of the conversion of DHA to 4-androstenedione but were weak non-competitive inhibitors of the conversion of andien-beta to dienone. The selective effects of trilostane and cyanoketone on the 3 beta-HSD-Is involved in the androgen and 16-androstene biosynthetic pathways strongly suggest that the reactions are catalysed by separate enzymes, or at least separate, non-interacting active sites on a single enzyme.

Plasma protein changes induced by two orally administered androgen derivatives

Epostane is a synthetic 17 alpha-alkylated 5 beta-androstane derivative, active following oral administration and devoid of any apparent androgenic, estrogenic or antiestrogenic potency. Circulating concentrations of 13 different plasma proteins were measured in eight women before and after 2 and 4 weeks of daily oral intake of 600 mg of epostane. The results were compared with those previously found during administration of the same daily dose of danazol, a synthetic 17 alpha-alkylated androgen derivative with known androgenic/anabolic activity. Epostane significantly suppressed serum levels of sex hormone-binding globulin, pregnancy zone protein and thyroxin-binding globulin and increased the levels of transthyretin. Haptoglobins, plasminogen and transferrin showed minor and/or transient changes and the levels of high density lipoproteins, alpha2-macroglobulin, albumin, C1-esterase inactivator, C3 complement and transcortin remained unaffected. The pattern of changes in plasma proteins was almost identical to that induced by administration of danazol, although the effects of epostane were somewhat weaker. Thus epostane is capable of inducing substantial changes in the pattern of steroid-sensitive plasma proteins in an androgen-like fashion despite its apparent lack of androgenic activity. The capacity of a steroid to induce such changes thus seems to be tied to the chemical structure rather than to the intrinsic hormonal activity of the molecule.

Multicentre cross-over study of aminoglutethimide and trilostane in advanced postmenopausal breast cancer

Trilostane and aminoglutethimide, both given with a physiological replacement dose of hydrocortisone, were randomly allocated to 112 eligible patients with postmenopausal advanced breast cancer. Following treatment failure on either drug the patient continued with the other, if they were in a suitable clinical condition. Sixty-three patients initially received trilostane, of whom 33 subsequently received aminoglutethimide; 49 patients initially had aminoglutethimide and 14 of these then received trilostane. Both groups of patients were comparable in all respects. There was no difference in the response rate to either drug or in the average time to disease progression for the two drugs. Of the 47 patients who received both drugs, nine (19%) showed a response to both, indicating no cross-resistance. Side effects were seen to both drugs in approximately half the patients; these were mainly gastrointestinal symptoms with trilostane and rashes and drowsiness with aminoglutethimide. There was no evidence of cross-over patient susceptibility to side effects.

Potentiating effect of epostane on pregnancy terminating activity of RU 486 in the rat

The effectiveness of a combination of RU 486, an antiprogestin, and epostane, a 3 beta-hydroxysteroid dehydrogenase inhibitor, for termination of pregnancy in female rats was determined. Epostane administered at doses ranging from 8 to 48 mg/Kg/day on days 7, 8, and 9 of pregnancy did not influence the progress of the pregnancy. RU 486 in doses of 1, 2, and 4 mg/Kg/day terminated pregnancy in 0, 40, and 100% of rats, respectively. The combination of epostane (48 mg/Kg/day) plus RU 486 (1 and 2 mg/Kg/day) terminated pregnancy with complete resorption of fetuses in all treated animals. Unexpectedly, the drug combination that terminated pregnancy used a dose of epostane that was not highly effective in lowering serum progesterone levels when epostane was administered alone. Thus, in the rat, the synergistic action of epostane plus RU 486 may not be dependent upon reduced progesterone secretion plus receptor blockage as anticipated. The present results suggest that the combination of epostane plus RU 486 is effective for pregnancy termination.

Metabolism of the contraceptive steroid desogestrel by human liver in vitro

The metabolism of the progestogen oral contraceptive desogestrel (Dg) has been studied in vitro using human liver microsomes. Metabolites have been separated using radiometric high performance liquid chromatography and identified by co-chromatography with authentic standards and by mass spectrometry. All the livers examined (n = 6) were able to form 3-keto desogestrel as the main identifiable metabolite and also the presumed intermediates 3 alpha-hydroxydesogestrel (3 alpha-OHDg) and 3 beta-hydroxydesogestrel (3 beta-OHDg). In addition, a large polar heterogenous peak was evident on the radiochromatograms which did not co-chromatograph with any known metabolites of desogestrel. Inter-individual variability in metabolite formation was seen. A number of drugs were examined for their propensity to inhibit desogestrel metabolism. Primaquine was the most potent tested having an IC50 value (inhibitory concentration reducing overall metabolite production by 50%) of 30 microM. Cimetidine, trilostane and levonorgestrel failed to inhibit at 250 microM. With 3 alpha-OHDg as substrate, 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSDH) activity was 1.0 +/- 0.3 nmol min-1 mg-1 protein which was five times greater than the activity of the 3 beta-HSDH towards 3 beta-OHDg. Miconazole was the most potent inhibitor tested having IC50 values of 14 and 95 microM for 3 alpha- and 3 beta-HSDH respectively. Surprisingly, trilostane was without inhibitory effect on either enzyme, which contrasts with other data involving 3 beta-HSDH in steroidogenic tissue. Our observations with trilostane may reflect tissue differences in the enzyme and/or differences in endogenous vs exogenous steroids (i.e. in the conversion of 3 beta-OHDg to 3-ketodesogestrel there is no requirement for isomerization). Kinetic parameters of 3 alpha-HSDH were also determined.

The use of prostaglandins and antiprogestins for pregnancy termination

Although vacuum aspiration could be regarded as a simple procedure, complications do occur and attempts have been made to develop non-surgical procedures for termination of pregnancy during the first 3-4 weeks following the first missed menstrual period. A variety of prostaglandin (PG) analogs have been developed which are equally effective as vacuum aspiration to induce abortion during early pregnancy. However, the widespread acceptance of PG treatment is limited by a relatively high incidence of gastrointestinal side effects and uterine pain. Treatment with presently available antiprogestins alone is not sufficiently effective to compete with vacuum aspiration. However, administration of these compounds induces uterine contractions and increases the sensitivity of the myometrium to prostaglandin. These effects allow the development of sequential treatment with RU 486 and a low dose of PG analogs administered intramuscularly or vaginally which is highly effective and is seemingly associated with a lower frequency of side effects than if PG analogs are used alone. It can be concluded that this medical abortion method has the capacity to compete with vacuum aspiration for termination of early pregnancy. Randomized studies comparing the two procedures are, however, needed to confirm this statement.

Epostane in nonpregnant females: effects on progesterone, 17 alpha-hydroxyprogesterone, and 17 beta-estradiol of two dose levels given for one month

So far, the use of epostane, a relatively new inhibitor of 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase enzyme system (3 beta-HSD), has been confined to short-term interference with luteal and placental function. This study explored whether epostane treatment from the beginning of the cycle for approximately 1 month would also inhibit ovarian follicular function. Twenty females with regular cycles received epostane 150 mg/day (ten healthy volunteers) or 600 mg/day (ten patients with endometriosis). Blood samples were drawn three times per week during control and treatment cycles. At 150 mg/day the mean total area under the serum concentration curve (AUC) of estradiol (E2) was somewhat higher than during the control cycles, despite apparently lower preovulatory E2 surges. During medication the highest value of E2 was found during the luteal phase. The mean AUC of progesterone (P) and 17 alpha-hydroxyprogesterone (17-OHP) during the luteal surge was decreased by approximately 45% each. At 600 mg/day all evaluable patients had lower AUC of E2 than during the control cycle. The mean decrease in AUC of P and 17-OHP was much more pronounced than in the lower dose group. Six of the ten patients showed no hormonal signs of follicular development and, consequently, anovulation. The capacity of epostane to modulate or inhibit, depending on the dose, ovarian follicular steroidogenesis and ovulation may prove valuable in a variety of clinical conditions.

Effect of epostane, a competitive inhibitor of the 3beta-hydroxysteroid dehydrogenase enzyme, in cyclic sows

The effect of epostane, a 3beta-hydroxysteroid dehydrogenase (3beta-HSD) inhibitor, on the levels of plasma cortisol and progesterone and on the length of the estrous cycle in sows was examined. Epostane was administered orally on Days 0 to 2 (n = 3), Days 4 to 6 (n = 3), Days 10 to 12 (n = 2) or Days 17 to 19 (n = 3) of the estrous cycle, or subcutaneously on Day 0 (n = 3), Day 4 (n = 3), Day 10 (n = 4) or Day 17 (n = 3). Eleven days after the first dose of epostane, the treatments were repeated. One group of sows (n = 3) that was bled during a single estrous cycle served as controls. Cortisol levels in each of the eight groups of sows that received epostane did not differ (P>0.05) from those in control sows. In contrast, progesterone was lowered (P<0.01) when epostane was given by injection on Day 4, 10 or 17, or when given orally on Days 4 to 6 and 10 to 12. Although epostane reduced progesterone levels, the estrous cycle was not shortened. The interestrous interval for the sows (n = 14) that completed their experimental estrous cycle before they were sacrificed at approximately one week after the last dose of epostane was 21.6 +/- 2.71 d. It was concluded that epostane, as administered in this study, lowered progesterone levels but did not shorten the estrous cycle.

Anti-progesterones for the interruption of pregnancy

Therapeutic abortion can be performed effectively and safely by vacuum aspiration of the uterus up to 12 weeks of amenorrhoea. Although the operative procedure could be regarded as simple, complications do occur and attempts have been made to develop non-surgical means of terminating pregnancy in the first 3-4 weeks following the first missed menstrual period. A variety of PG analogues have been developed which induce abortion in over 90% of women when given by vaginal pessary or intramuscular injections (see Bygdeman, 1984). In a large multicentre study (WHO, 1987) 0.5 mg sulprostone, administered three times with 3 h intervals, was recently found to be equally as effective as vacuum aspiration for termination of early pregnancy. The frequencies of complete abortion were 91 and 94%, respectively. However, the widespread acceptance of PG treatment is limited by a relatively high incidence of gastrointestinal side-effects and uterine pain. Treatment with antiprogesterones, both mifepristone and epostane, effectively induces abortion during early pregnancy, but the frequency of complete abortion is too low to be clinically acceptable. It remains to be demonstrated if other antiprogesterones such as ZK 98.734 and ZK 98.299, currently under development, may change this conclusion. Administration of mifepristone induces uterine contractions and increases the sensitivity of the myometrium to prostaglandins. These effects allowed the development of sequential treatment with a low dose of mifepristone and PG analogues administered vaginally or intramuscularly. The combined therapy has been shown to be highly effective (frequency of complete abortion between 95 and 100%) and is seemingly associated with a lower frequency of side-effects than if PG analogues are used alone. Whether this medical abortion method will be a realistic alternative to vacuum aspiration during the first 8 weeks of pregnancy depends on the outcome of further clinical trials, including randomized studies comparing the two procedures. It has been shown that mifepristone crosses the placenta (Frydman et al, 1985). An important factor which needs to be verified in future studies is therefore the possible embryotoxicity of this type of compound. The risk that pregnancy continues in spite of treatment can never be excluded.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of progesterone synthesis in normal and transformed human placental cells by tight binding inhibitors of 3 beta-hydroxysteroid dehydrogenase

The biosynthesis of progesterone from [3H]pregnenolone was curvilinear over a 6 h time course in human placenta cytotrophoblasts and in human placenta choriocarcinoma cells (JEG-3 cells). Mass measurements determined independently by radioimmunoassay indicate that the progesterone synthesized by cytotrophoblasts (21.0 +/- 5.20 ng/6 h/mg protein) is substantially higher than that synthesized by the JEG-3 cells (4.48 +/- 0.56 ng/6 h/mg protein). Two tight binding inhibitors of 3 beta-hydroxysteroid dehydrogenase (2 alpha-cyanoprogesterone I and cyanoketone II), and a potent inhibitor of the microsomal conversion of pregnenolone to progesterone (2 alpha-bromo-5 alpha-androstan-3-one-17 beta-acetate III) were compared as inhibitors of progesterone synthesis in the two cell-types. Compounds I and II were very potent inhibitors yielding IC50 values of between 10 and 20 nM. At higher concentrations (100 nM - 1,000 nM) compound I promoted a complete cessation of progesterone synthesis which could be reversed by washing the cells free of inhibitor. By contrast compound III was ineffectual as an inhibitor yielding an IC50 value greater than 10 microM. This 1,000-fold difference in inhibitory potency suggests that 2 alpha-cyano-substituted steroids display an unusual capacity to inhibit progesterone biosynthesis and secretion in normal and transformed human cells.

Endocrine effects of Trilostane: in vitro and in vivo studies

Trilostane (4-alpha-5-epoxy-17 beta-hydroxy-3-oxo-5-alpha-androstan-2-carbonitrile) is a modified steroidal molecule. In vitro and in vivo studies in rats have shown that it inhibits adrenal, ovarian and placental steroid synthesis. It seems to act by exerting a selective blockade on 3 beta-hydroxysteroid dehydrogenase. In this study, we investigated whether this molecule interacts with hormone receptors for estrogen, androgen or progesterone. We also tried to demonstrate the effect which Trilostane may have on cellular cultures of human mammary carcinoma (MCF-7 Evsa-T). We also studied hormonal modifications in a series of 12 patients treated with different doses of Trilostane, since this drug is supposed to inhibit the production by the adrenal glands of mineralocorticoids, of glucocorticoids and of the precursors of estrogens. Our results indicate that Trilostane does not react with any of the main hormonal sex steroid receptors, nor does it interfere with cultures of human mammary cancer cells either containing estrogen receptors and therefore allegedly hormone-dependent (MCF-7 line), or estrogen receptor-negative cells, presumably independent of hormonal manipulations (Evsa-T cell line). Finally, endocrine studies on postmenopausal women with advanced breast cancer show that Trilostane significantly reduces the plasma levels of estrone and of its major androgen precursor (androstenedione). However, the latter inhibition is no different from that exerted by hydrocortisone acetate administered alone at a dose of 40 mg/day. The results of clinical trials comparing hydrocortisone alone with hydrocortisone plus Trilostane are awaited.

Early pregnancy termination with antiprogestins: a comparative clinical study of RU 486 given in two dose regimens and Epostane

Mifepristone, (RU 486, Roussel Uclaf, Romainville, France), a progesterone (P) receptor blocking agent, and Epostane, (WIN 32,729, Sterling-Winthrop, Guildford, United Kingdom), a P synthesis inhibitor, were compared for their ability to terminate early human pregnancy. Seventy-eight healthy women, with a gestational length of less than 49 days from the last menstrual period and who requested termination of pregnancy, were recruited to the study. The patients were randomly allocated to three treatment regimens: (1) Mifepristone 25 mg bid for 7 days; (2) Mifepristone 50 mg bid for 7 days; and (3) Epostane 200 mg qid for 7 days. The results of the study confirmed that both compounds are potent abortifacients in early human pregnancy. No difference in efficacy was seen between the two dose regimens of Mifepristone, which both resulted in 61% complete abortions. Seventy-three percent aborted completely in the Epostane group. Subjective side effects, especially nausea, were more common in the women treated with Epostane, but no serious side effects were seen.

Termination of early human pregnancy with epostane

Fifty-six healthy women, with a gestational length of less than 49 days from the last menstrual period, who requested termination of pregnancy were treated with Epostane, a progesterone synthesis inhibitor. Epostane, which competitively inhibits the 3 beta-hydroxy steroid dehydrogenase enzyme system, was given in the dose 200 mg X 4 for seven days. Physical examination, routine laboratory screening and determination of hCG, progesterone, estradiol and cortisol was performed on days 0, 7 and 14. The treatment resulted in 84% complete abortions (90% among women completing therapy). Two women experienced vaginal bleeding only, while 7 were non-responders. Among subjective side effects nausea dominated totally and was also the reason for discontinuation in 4 cases. The average length of bleeding among women with complete abortions was 10.7 days and the decrease in hemoglobin and hematocrit was very slight. Routine laboratory values remained within the normal range. Cortisol levels were elevated on day 7 compared to days 0 and 14, but all single values were within the normal limits.

Effects of Epostane on progesterone synthesis in early human pregnancy

Healthy women requiring abortion in early normal pregnancy were recruited to study the abortifacient effects of different doses of Epostane, an inhibitor of 3 beta-hydroxy steroid dehydrogenase, that previously has been shown to interfere with progesterone production in the luteal phase of humans and to have abortifacient effects in animals. A single dose of 100 mg resulted in decreasing progesterone and estradiol, which rapidly recovered, and none of the women started to bleed. Repeated doses of 50 or 100 mg during one day resulted in a more pronounced decrease in both progesterone and estradiol, but no bleeding. When treatment was prolonged over several days with 100 mg X 4 for five days and 400 mg X 2 for four days, respectively, a suppression of progesterone and estradiol was found and two out of four and eight out of ten women started to bleed and subsequently aborted. The treatment was well tolerated by most of the women. Routine laboratory parameters remained unaltered throughout treatment. Cortisol levels remained within the normal range.

Hormonal changes in postmenopausal women with breast cancer treated with trilostane and dexamethasone

Postmenopausal women with metastatic breast cancer were treated with trilostane, initially 240 mg daily increasing after 3 days to 480 mg daily and after a further three days to 960 mg daily. After 3 days at this dose dexamethasone 1 mg daily was added and this combination was continued until disease progression occurred. Partial remission was seen in 26% and stabilization of previously progressive disease in a further 13% of the first twenty-three patients studied. During therapy with trilostane alone significant increases in DHEAS, androstenedione, 17-hydroxypregnenolone, progesterone, testosterone and oestradiol were seen. A significant fall in oestrone concentration occurred at the same time. After dexamethasone was added the elevated steroid concentrations fell back to the baseline while oestrone remained depressed below this and testosterone was also significantly lowered. No change was seen in cortisol or ACTH concentration while patients were on trilostane alone but cortisol levels were undetectable after dexamethasone was added though, in most patients, ACTH remained detectable. There was no change in the ratio of delta 5:delta 4 steroids at any stage of therapy but a highly significant increase in the androstenedione: oestrone ratio was seen. We conclude that in long-term use in vivo it is difficult to demonstrate that trilostane inhibits 3 beta-hydroxysteroid dehydrogenase but it may produce inhibition of aromatase.

Inhibition of luteal phase progesterone levels in the rhesus monkey by epostane

This study examined the effect of epostane, a new antifertility drug, on normal and hCG-stimulated progesterone production during the luteal phase of the menstrual cycle in rhesus monkeys. When administered once each day for five days, epostane inhibited normal luteal phase progesterone levels in a dose-related fashion. Epostane also reduced the elevated luteal phase progesterone levels of animals treated with hCG indicating that the drug acts directly on the corpus luteum. These data suggest that epostane interferes with corpus luteum function in a primate and that the drug would be effective as an interceptive agent during early pregnancy.

Inhibition of human placental progesterone synthesis by danazol in vitro

In vitro, danazol showed a slight dose-dependent inhibition of the mitochondrial cholesterol side chain cleavage enzyme isolated from early gestational (8th to 12th week of gestation) placenta. In the presence of 100 microM danazol, the enzyme activity was 65% of controls. Danazol inhibits dose-dependently the mitochondrial 3 beta-hydroxysteroid dehydrogenase (I50 = 3.1 microM; Ki = 1 microM) (noncompetitive inhibition) and the cytoplasmic 20 alpha-hydroxysteroid dehydrogenase (I50 = 1.4 microM; Ki = 2.6 microM) (competitive inhibition). The inhibition of human placental progesterone synthesis by danazol in vitro is a further example for the direct interference of danazol with steroidogenesis.