Richard C. Winneker

The preclinical biology of a new potent and selective progestin: trimegestone

Trimegestone (TMG) is a 19-norpregnane progestin being developed, in combination with an estrogen, for the treatment of postmenopausal symptoms. TMG binds to the human progesterone receptor with an affinity greater than medroxyprogesterone acetate (MPA), norethindrone (NET), and levonorgestrel (LNG). In contrast, TMG binds with low affinity to the androgen, glucocorticoid and mineralocorticoid receptor and has no measurable affinity for the estrogen receptor. Compared to other progestins, TMG demonstrates an improved separation of its PR affinity from its affinity to other classical steroid hormone receptors. In vivo, TMG has potent progestin activity. For example, TMG produces glandular differentiation of the uterine endometrium in rabbits and is about 30 and 60 times more potent than MPA and NET, respectively. In the rat, TMG maintains pregnancy, induces deciduoma formation, inhibits ovulation and has uterine anti-estrogenic activity. With respect to these endpoints, TMG appears to be more potent and selective on uterine epithelial responses than other classical progestin responses. In vivo, TMG does not have significant androgenic, glucocorticoid, anti-glucocorticoid or mineralocorticoid activity but does have anti-mineralocorticoid activity and modest anti-androgenic effects. This overall profile is qualitatively similar to progesterone. When TMG is administered chronically, it antagonizes the effect of estradiol on the uterus but does not antagonize the beneficial bone sparing activity of estradiol. In rat studies evaluating CNS GABAA receptor modulatory activity, TMG is less active on this likely undesirable endpoint than progesterone and norethindrone acetate, which may translate into fewer mood-related side effects. The results indicate that TMG is a potent and selective progestin with a preclinical profile well suited for hormone replacement therapy.

Endocrine profile of win 49596 in the rat: A novel androgen receptor antagonist

Win 49596 is a new orally active, steroidal androgen receptor antagonist. Win 49596 inhibited ventral prostate, seminal vesicle and levator ani weight gain in either 5 alpha-dihydrotestosterone (DHT) or testosterone propionate-treated castrated, immature male rats. In intact, adult male rats, Win 49596 significantly inhibited weight gain by the ventral prostate, dorsal lateral prostate and seminal vesicles, but not the testes at doses as low as 50 mg/kg/day x 14 p.o. However, daily oral administration of equivalent antiandrogenic doses of either Win 49596, ICI 176,334, or flutamide for 14 days to mature, intact male rats resulted in elevations of circulating testosterone of approximately 3-, 2-, and 10-fold, respectively. At doses as high as 400 mg/kg p.o., Win 49596 did not have androgenic, progestational, estrogenic or antiestrogenic activity in rat or rabbit models. However, in the Clauberg assay, Win 49596 did have weak antiprogestational activity at doses of 25-400 mg/kg/day p.o. These data indicate that Win 49596 is a peripherally selective antiandrogen that has minimal effects on circulating testosterone levels and is devoid of hormone agonist activity. Thus, Win 49596 may be useful for the treatment of androgen dependent conditions such as benign prostatic hyperplasia and prostatic cancer.

Studies on the mechanism of action of win 49596: A steroidal androgen receptor antagonist

Win 49596 is an orally active antiandrogen in the rat. This report describes a series of in vitro and in vivo studies which were performed to characterize the mechanism of action of this compound. In vitro competition and Lineweaver-Burk analyses indicate that Win 49596 binds competitively to the rat ventral prostate androgen receptor with a Ki of 2.2 +/- 0.4 microM. Similar to other androgen antagonists, the relative binding affinity (RBA) of Win 49596 was greater after 1 h of incubation with androgen receptor than after an 18 h incubation (RBA of 2.2 versus 0.05, respectively). Win 49596 did not bind to rat cytosolic uterine estrogen or progesterone receptors or thymus glucocorticoid receptors. Furthermore, Win 49596 did not inhibit rat ventral prostate 5 alpha-reductase or 3 alpha-oxidoreductase, rat adrenal 3 beta-hydroxysteroid dehydrogenase or human placental aromatase activity in vitro at concentrations as high as 10 microM. A series of in vivo studies demonstrated that Win 49596 inhibited the uptake of [3H]testosterone as well as testosterone-induced nuclear accumulation of androgen receptor in the rat ventral prostate. Collectively, these results support direct androgen receptor antagonism as the mechanism for the antiandrogenic effects of Win 49596.

Studies on the mechanism of action of danazol and gestrinone (R2323) in the rat: evidence for a masked estrogen component.

The effects of androgen and estrogen receptor antagonists on the action of danazol and gestrinone (R2323) were investigated. The tropic effect of danazol and gestrinone on sex accessory tissues of castrated, immature male rats was inhibited by the antiandrogen flutamide, whereas the uterotropic action of these steroids in immature female and adult ovariectomized rats was not inhibited by flutamide. In contrast, the uterotropic effect of danazol was reduced by the antiestrogen, LY156758. The estrogen-sensitive endpoints, vaginal keratinization and uterine progesterone receptor concentration, were enhanced by treatment with a combination of flutamide and either danazol or gestrinone. These data indicate that danazol and gestrinone have estrogenic activity that is masked by the androgenic component of these drugs.

Danazol Suppression of Luteinizing Hormone in the Rat: Evidence for Mediation by both Androgen and Estrogen Receptors

Abstract Previous studies had indicated that the effects of danazol on rat peripheral tissues were mediated through both androgen and estrogen receptors. The purpose of this study was to examine the role of androgen and estrogen receptors in danazol suppression of luteinizing hormone (LH) in the rat. The estrogen receptor antagonist, LY 156758, partially antagonized the suppressed levels of LH observed 3–5 hr after administration of danazol to ovariectomized rats. In contrast, the androgen receptor antagonist, flutamide, had no effect on suppressed LH levels 3–5 hr after danazol, but did partially reverse the inhibition of LH 24 hr after danazol administration to ovariectomized rats. Danazol also increased pituitary progesterone receptor levels, an estrogen-sensitive end point. These data indicate that the suppressed levels of LH following danazol treatment resulted from the functional activation of both androgen and estrogen receptors.

The interaction of nivazol with the glucocorticoid receptor from rat and rhesus monkey target tissues

Steroid hormone receptor competition techniques were used to evaluate the glucocorticoid receptor binding properties of nivazol and its 11 beta-hydroxy derivative, Win 44577 in rat and monkey target tissues. These agents competitively inhibited the binding of 3H-dexamethasone to the glucocorticoid receptor from the liver and anterior pituitary from both rat and monkey with relative binding affinities of Win 44577 greater than dexamethasone greater than nivazol greater than cortisol in all cases. However, nivazol and Win 44577 had approximately twice the affinity for the anterior pituitary glucocorticoid receptor from both species. Neither compound demonstrated any significant binding to rat estrogen, progestin or androgen receptors. These results are consistent with a glucocorticoid receptor mediated mechanism of action for nivazol and Win 44577; however, the difference in the endocrine profile of nivazol in the rhesus monkey versus the rat does not appear to be due to a species selectivity in the affinity of nivazol for the glucocorticoid receptor from central or peripheral target tissue.

Synthesis and androgen receptor affisity of steroidal methylsulfonylforans and a menthylsulfonylthiophene

Abstract Syntheses of the unsubstituted steroidal [3,2-b]furan ( 3a ), thiophene ( 3b ) and [2,3-b]furan ( 24 ) are described. Lithiation of the THP ethers 18a and 18b followed by the reaction with methyl disulfide and deprotection gave the 5′-methylsulfide derivatives 19a and 19b . Oxidation of the sulfides and ethynylation provided the compounds 2a and 2b . Swern oxidation of the [2,3-b]furan 24 with DMSO/TFAA/diisopropylethylamine resulted in oxidation to the 17-ketone and introduction of a 5′-methylthio group to give 25 . Ethynylation at C-17 followed by oxidation of the sulfide group provided the product 27 . 5′-Methylsulfonyl[3,2-b]furanosteroid 2a bound to the rat ventral prostate androgen receptor. However, the corresponding thiophene 2b and the [2,3-b]furan 27 lacked affinity for the receptor.

Glucocorticoid/antiinflammatory activities of nonsteroidal phenylpyrazoles in the rat

Six nonsteroidal phenylpyrazoles are described that have significant glucocorticoid and antiinflammatory activities. These agents competed with dexamethasone for the glucocorticoid receptor from the rat thymus, suppressed adrenal weight when administered orally to intact female rats, produced liver glycogen deposition and thymolysis when administered orally to adrenalectomized male rats, and reduced cotton granuloma formation when administered in the cotton pellet. In addition, in the latter model, no systemic activity (thymolysis or reduced body weight gain) was seen with doses up to 500 to 5000 times the dose which reduced granuloma formation. At least one compound was more potent than methylprednisolone in three of the four rat assay systems used. The compounds described are structurally different from conventional steroidal glucocorticoids but possessed potent glucocorticoid activities. However, they exhibited antiinflammatory activity without evidence of systemic activity when administered locally.

Chapter 17. Chemical Control of Fertility

Publisher Summary This chapter reviews advances made in the development of agents those interfere with pregnancy by inhibition of progesterone (P) biosynthesis; or by antagonism of P at the receptor level, and of prostaglandins (PGs) with improved properties. The status of research in male contraception is summarized with particular emphasis on the antifertility effects of gossypol. Finally, the antifertility effects of a group of compounds characterized by their structural and mechanistic diversity are described. The chapter discusses antiprogestins, steroidogenesis inhibitors, prostaplandins, male contraception—potential contraceptive agents for the male, their dosages, toxicity level and unaccetable side effects—spermatogenesis—and some miscellaneous drugs assisting in terminating pregnancy—their dosages, reactions and effectiveness. The successful termination of early human pregnancy by the P receptor antagonist mifepristone could be regarded as the most significant development in female fertility control in the last few years. Although preliminary results suggest that this drug may lack sufficient efficacy to compete with existing methods when given alone, the validity of the approach has, nevertheless, been established. In a related and potentially equally important development, epostane, a P biosynthesis inhibitor, caused a fall in plasma P levels in early human pregnancy. Results of definitive pregnancy termination studies are not yet available. The discussion includes menstrual regulation and early post-coital drugs, the immunological approach to fertility control, and long acting contraceptives.