Estradiol an aromatized C18 steroid with hydroxyl group at 3-beta- and 17-beta-position. Estradiol-17-beta is the most potent form of mammalian estrogenic steroids. In humans, it is produced primarily by the cyclic ovaries and the placenta. It is also produced by the adipose tissue of men and postmenopausal women. The 17-alpha-isomer of estradiol binds weakly to estrogen receptors (receptors, estrogen) and exhibits little estrogenic activity in estrogen-responsive tissues. Estradiol enters target cells freely (e.g., female organs, breasts, hypothalamus, pituitary) and interacts with a target cell receptor. When the estrogen receptor has bound its ligand it can enter the nucleus of the target cell, and regulate gene transcription which leads to formation of messenger RNA. The mRNA interacts with ribosomes to produce specific proteins that express the effect of estradiol upon the target cell. Estradiol is used for the treatment of urogenital symptoms associated with post-menopausal atrophy of the vagina (such as dryness, burning, pruritus and dyspareunia) and/or the lower urinary tract (urinary urgency and dysuria). Estradiol is marketed under the brand name Climara (among others), indicated for: the treatment of moderate to severe vasomotor symptoms due to menopause, treatment of symptoms of vulvar and vaginal atrophy due to menopause, treatment of hypoestrogenism due to hypogonadism, castration or primary ovarian failure and prevention of postmenopausal osteoporosis.

Progesterone is indicated in amenorrhea and abnormal uterine bleeding due to hormonal imbalance in the absence of organic pathology, such as submucous fibroids of uterine cancer. Progesterone, converted from pregnenolone, also serves as an intermediate in the biosynthesis of gonadal steroid hormones and adrenal corticosteroids. Progesterone is a naturally occurring steroid that is secreted by the ovary, placenta, and adrenal gland. In the presence of adequate estrogen, progesterone transforms a proliferative endometrium into a secretory endometrium. Progesterone is necessary to increase endometrial receptivity for implantation of an embryo. Once an embryo is implanted, progesterone acts to maintain a pregnancy. Progesterone shares the pharmacological actions of the progestins. Progesterone binds to the progesterone and estrogen receptors. Target cells include the female reproductive tract, the mammary gland, the hypothalamus, and the pituitary. Once bound to the receptor, progesterone will slow the frequency of release of gonadotropin releasing hormone (GnRH) from the hypothalamus and blunt the pre-ovulatory LH (luteinizing hormone) surge. In women who have adequate endogenous estrogen, progesterone transforms a proliferative endometrium into a secretory one. Progesterone is metabolized primarily by the liver largely to pregnanediols and pregnanolones. Pregnanediols and pregnanolones are conjugated in the liver to glucuronide and sulfate metabolites. Progesterone metabolites that are excreted in the bile may be deconjugated and may be further metabolized in the gut via reduction, dehydroxylation, and epimerization. Common progesterone side effects may include: drowsiness, dizziness; breast pain; mood changes; headache; constipation, diarrhea, heartburn; bloating, swelling in your hands or feet; joint pain; hot flashes; or vaginal discharge.

Vilaprisan, a small molecule progesterone receptor antagonist is being developed by Bayer HealthCare Pharmaceuticals (formerly Bayer Schering Pharma) for the treatment of endometriosis and uterine leiomyoma. Hormonal imbalance observed in women with endometriosis is a potential target for treating endometriosis. Vilaprisan is a highly selective steroidal progesterone receptor modulator (SPRM). It is a partial agonist of progesterone receptor, which means that the drug activates progesterone receptors to a certain degree upon binding. This triggers a cascade of biochemical reactions that result in the suppression of prostaglandin production. This, in turn, relieves symptoms such as pain and bleeding. Modulating progesterone by taking vilaprisan might help in treating endometriosis over the long term. Phase I and II studies give encouraging results on the efficacy of vilaprisan at different doses. Like other SPRMs, vilaprisan induces benign changes of endometrium (PR modulator-associated endometrial changes, PAECs). These disappear as treatment is discontinued. Unlike GnRHa treatment, neither UPA nor vilaprisan induce hypoestrogenism and associated symptoms. Phase III studies are ongoing to confirm efficacy and safety of vilaprisan in long-term treatment of symptomatic fibroids.

Telapristone acetate, a selective progesterone receptor modulator (SPRM), was developed for the long-term treatment of symptoms associated with endometriosis and uterine fibroids. It is known, that the progesterone is a steroid hormone that plays an important role in the breast. Deregulation of the progesterone-signaling pathway is implicated in the formation, development, and progression of breast cancer. Thus, the telapristone acetate is studied in phase II clinical trial in stage I-II primary breast cancer. Besides, telapristone acetate participated in phase III clinical trials in pre-menopausal anemic women with symptomatic uterine fibroids. However, FDA terminated these studies because of the safety.

Toripristone has a high inhibiting activity against the cortisol receptors. Toripristone enhanced the antibacterial activities of the sparfloxacin in combination with ethambutol in the treatment of M. avium complex infections. Also, toripristone is a glucocorticoid type II receptor and progesterone receptor antagonist. Toripristone treatment was estimated to selectively occupy approximately 50% of glucocorticoid receptors in rat brain.

Aglepristone (RU 46534) is a competitive progesterone antagonist; it binds to progesterone receptors (PRs) without inducing the molecular cascade associated with progesterone. Its affinity to PRs is higher than progesterone (3.12, 3.8, and 9.26 times greater in the bitch, doe rabbit,and queen, respectively). Aglepristone can therefore beused in various progesterone-dependent physiological orpathologic conditions, with the aim of blocking the action of progesterone. Aglepristone has proven to be an effective and safe means of inducing pregnancy termination or parturition in a large number of domestic species. In domestic species, aglepristone is routinely used for the treatment of pyometra and feline mammary fibroadenomatous hyperplasia, both of which are progesterone dependent. Aglepristone is marketed under the brand name Alizin used as the treatment option for unwanted mating and pregnancy in dogs

Lonaprisan is an orally bioavailable pentafluoroethyl derivative of a mifepristone-related steroid with antiprogestagenic activity. Lonaprisan is a pure, highly receptor-selective progesterone receptor (PR) antagonist (both PR isoforms PR-A and PR-B); binding of this agent to PRs inhibits PR activation and the associated proliferative effects. Lonaprisan showed limited efficacy as second-line endocrine therapy in postmenopausal women with PR-positive metastatic breast cancer. Lonaprisan had been in phase II clinical trials by Bayer for the treatment of breast cancer and dysmenorrhea. However, this research has been discontinued.

Lilopristone (ZK 98.734) has a high affinity for progesterone receptors. The progesterone antagonistic effects of ZK 98.734 could be a result of the decrease in progesterone synthesis by the corpus luteum and/or placenta in addition to the interference with the progesterone binding to its cellular receptors in the target organ. ZK 98.734 has potential for fertility regulation. It is a very potent abortifacient in the common marmosets. Lilopristone could significantly suppress the proliferation of ectopic stromal cells in a time- and dose-dependent manner in vitro. The action mechanisms may be associated with the suppression of expression of NF-kappaB P65 mRNA and NF-kappaB P65.

Asoprisnil (J867) is a novel selective steroid receptor modulator that shows unique pharmacodynamic effects in animal models and humans. Asoprisnil, its major metabolite J912, and other structurally related compounds represent a new class of progesterone receptor (PR) ligands that exhibit partial agonist and antagonist activities in vivo. Asoprisnil demonstrates a high degree of receptor and tissue selectivity, with a high-binding affinity for PR, moderate affinity for glucocorticoid receptor (GR), low affinity for androgen receptor (AR), and no binding affinity for estrogen or mineralocorticoid receptors. This compound was recently in clinical trials for the treatment of uterine fibroids and endometriosis, but those studies were discontinued.

Epostane (WIN-32729) a pure competitive inhibitor of 3-beta-hydroxysteroid dehydrogenase. Epostane blocks progesterone synthesis during the luteal phase and in pregnancy in women and has strong anti-steroidogenic effect in endocrine tissues. Epostane is an abortifacient agent in early human pregnancy. It inhibits ovarian follicular steroidogenesis and ovulation.