Molecular and Pharmacological Properties of a Potent and Selective Novel Nonsteroidal Progesterone Receptor Agonist Tanaproget

Palladium-catalyzed synthesis of 4-sila-4H-benzo[d][1,3]oxazines by intramolecular Hiyama coupling

A palladium-catalyzed synthesis of 4-sila-4H-benzo[d][1,3]oxazines, silicon-switched analogs of biologically relevant 4H-benzo[d][1,3]oxazines, was developed by the intramolecular Hiyama coupling of 3-amido-2-(arylsilyl)aryl triflates.

Progestogens exhibit progestogen-, promoter- and isoform-specific effects via the progesterone receptor

Hormonal contraceptives (HCs) and hormone replacement therapy (HRT) are therapies designed to target the progesterone receptor (PR) to prevent unwanted pregnancy and to alleviate the symptoms of menopause, respectively, in women. Although these therapies are widely used globally, few studies have investigated in parallel how the transcriptional responses of the progestogens used in these therapies compare to each other via the PR isoforms (PR-A and PR-B). Using dose-response promoter-reporter and endogenous gene expression assays, we compared the transcriptional responses of six widely-used progestogens via each PR isoform. The present study shows that progestogens exhibit progestogen-specific potencies and efficacies via both PR isoforms. In addition, the endogenous gene expression data reveals that progestogens exhibit promoter-specific effects. Furthermore, this study reveals that progestogen responses via PR-A are significantly more potent and less efficacious than those observed via PR-B, and that this is unlikely due to differences in PR protein levels. Correlation analysis revealed that there is no detectable correlation between potency or efficacy of progestogens for PR-B or PR-A versus reported relative binding affinity (RBA) of progestogens for the PR, consistent with complex mechanisms of PR regulation. Taken together, our data show that it cannot be assumed that all progestogens have similar transcriptional responses on all genes. Since the PR plays a role in cognition, regulation of inflammation, mitochondrial function, neurogenesis, female reproduction and disease, the data suggest that these important physiological functions could be differentially affected depending on progestogen, promoter, and ratios of PR isoforms.

Expedient Access to Cyanated N-Heterocycles by Direct Flow-Electrochemical C(sp2 )-H Activation

Nitriles are recurring motifs in bioactive molecules and versatile functional groups in synthetic chemistry. Despite recent progress, direct introduction of a nitrile moiety in heteroarenes remains challenging. Recent developments in electrochemical reactions pave the way to more practical cyanation protocols. However, currently available methods typically require hazardous cyanide sources, expensive mediators, and often suffer from narrow substrate scope and laborious reaction set-up. To address the limitations of current synthetic methods, herein, an effective, sustainable, and scalable procedure for the direct C(sp² )-H cyanation of aromatic N-heterocycles with a user-friendly flow-electrochemical set-up is reported. Furthermore, high substrate and functional-group tolerance is demonstrated, allowing late-stage functionalization of drug-like scaffolds, such as natural products and pharmaceuticals.

Involvement of progesterone and estrogen receptors in the ram sperm acrosome reaction

The steroid hormones 17-β estradiol (E2) and progesterone (P4) can regulate capacitation, hyperactive motility, and the acrosome reaction (AR) during the sperm transit through the female tract. Moreover, exogenous P4 and E2 can induce the AR in ovine spermatozoa, and progesterone receptor (PR) and estrogen receptors (ERα and ERβ) are present in these cells. Thus, to investigate whether the effects both steroid hormones in ram sperm capacitation and AR are receptor-mediated, we incubated them with receptor agonists (tanaproget 1 μM and 5 μM for PR or resveratrol 5 μM and 10 μM for ER) or antagonists (mifepristone 4 μM and 40 μM for PR or tamoxifen 5 μM and 10 μM for ER) in capacitating conditions. The addition of receptor modulators did not affect sperm viability or total motility, although changes in progressive motility were detected. The incubation with both receptor agonists increased the percentage of acrosome-reacted spermatozoa, evaluated by chlortetracycline staining, when compared with the capacitated nontreated sample (Cap-C, P < 0.001). Moreover, the ER agonist resveratrol 10 μM provoked a greater AR than E2 (P < 0.01). Furthermore, the incubation with the receptor antagonists prevented the induction of the AR by P4 or E2, as the antagonists-treated spermatozoa presented a similar CTC pattern to that of Cap-C. In conclusion, these results confirm that P4 and E2 can induce the AR in ram spermatozoa and that this effect is receptor-mediated.

Characterisation of progestins used in hormonal contraception and progesterone via the progesterone receptor

Different progestogens are widely used in hormonal therapy and mediate their therapeutic actions via the progesterone receptor (PR). Little published data exist on their relative efficacies and potencies via the PR, while those available may be confounded by off-target receptors, different methodologies and model systems. We performed dose-response analysis to investigate the efficacies and potencies for transcription of progesterone and several progestins widely used in contraception via the B isoform of human PR (PR-B). We compared responses using three different cell lines and two different transient transfection conditions. Results show that in vitro biological responses via PR-B for the select progestogens can vary significantly in biocharacter, rank order and absolute values for efficacies and potencies, depending on the cell line and transfection condition. Progestogen rank orders for published relative binding affinities are mostly different to those for relative efficacies and potencies. These in vitro differences suggest that rank orders and absolute values of the efficacies and potencies of the progestogens are likely to vary in vivo in a cell-specific and progestogen-specific manner, and cannot easily be extrapolated from in vitro data, as is usually the practice. While obtaining such data in vivo is not possible, these in vitro data show proof of concept for likely significant cell- and progestogen-specific PR-B effects.

Structural Reassignment of rel-(3'Z,3R,6R,7R,3a'R,6'R)-3,8-Dihydrodiligustilide and the Activity of Diligustilide and 3,8-Dihydro- and 3,8,7',7a'-Tetrahydrodiligustilides as Progestins

Several phthalides were semisynthesized, including a 3,8-dihydrodiligustilide with progesterone-like activity, previously isolated from Ligusticum chuanxiong, the structure of which was earlier assigned to a semisynthetic product with nonidentical spectroscopic constants. The structure of this natural phthalide was reassigned with a proposal of its absolute configuration. Phthalides acted as progestins in cell viability assays, immunofluorescence microscopy, and docking analysis. Therefore, the structures for natural and semisynthetic phthalides with potential use in hormone-related therapies were reassigned.

Ligand Binding Induces Agonistic-Like Conformational Adaptations in Helix 12 of Progesterone Receptor Ligand Binding Domain

Progesterone receptor (PR) is a member of the nuclear receptor (NR) superfamily and plays a vital role in the female reproductive system. The malfunction of it would lead to several types of cancers. The understanding of conformational changes in its ligand binding domain (LBD) is valuable for both biological function studies and therapeutically intervenes. A key unsolved question is how the binding of a ligand (agonist, antagonist, or a selective modulator) induces conformational changes of PR LBD, especially its helix 12. We applied molecular dynamics (MD) simulations to explore the conformational adaptations of PR LBD with or without a ligand or the co-repressor peptides binding. From the simulations, both the agonist progesterone (P4) and the selective PR modulator (SPRM) asoprisnil induces agonistic-like helix 12 conformations (the "closed" states) in PR LBD and the complex of LBD-SPRM is less stable, comparing to the agonist-liganded PR LBD. The results, therefore, explain the partial agonism of the SPRM, which could induce weak agonistic effects in PR. We also found that co-repressor peptides could be stably associated with the LBD and stabilize the LBD in a "semi-open" state for helix 12. These findings would enhance our understanding of PR structural and functional relationships and would also be useful for future structure and knowledge-based drug discovery.

Colorectal tumor prevention by the progestin medroxyprogesterone acetate is critically dependent on postmenopausal status

The large randomized placebo controlled trials of the Women’s Health Initiative have shown that the combination of estrogen and progestin medroxyprogesterone acetate (MPA) protects from colorectal cancer in postmenopausal women. No effect was observed in women treated with estrogen alone. This suggests that progesterone, or more specifically the progestin MPA may have chemopreventive activity. The effect of MPA on colorectal carcinogenesis has been difficult to study in animal models. Most models are not affected by either depleting female hormones by ovariectomy or treatment with MPA. Importantly, an ovariectomy fails to reproduce one of the hall marks of the postmenopausal state in women with intact ovaries. That is, the continued production of androgens by the atrophic postmenopausal ovaries. Here we show that adenoma incidence is increased in the vinyl cylcohexene diepoxide (VCD) mouse model of the menopause compared to age matched fertile female mice. Treatment with MPA protected VCD treated mice from adenomagenesis, but had no effect on adenoma numbers in age-matched fertile female mice. Our data show that the protective effect of MPA depends on the postmenopausal state and suggest that MPA monotherapy may be studied as a chemopreventive agent in postmenopausal women.

Identification of Morpholino-2H-pyrido[3,2-b][1,4]oxazin-3(4H)-ones as Nonsteroidal Mineralocorticoid Antagonists

A novel series of morpholine-based nonsteroidal mineralocorticoid receptor antagonists is reported. Starting from a pyrrolidine HTS hit 9 that possessed modest potency but excellect selectivity versus related nuclear hormone receptors, a series of libraries led to identification of morpholine lead 10. After further optimization, cis disubstituted morpholine 22 was discovered, which showed a 45-fold boost in binding affinity and corresponding functional potency compared to 13. While 22 had high clearance in rat, it provided sufficient exposure at high doses to favorably assess in vivo efficacy (increased urinary Na⁺/K⁺ ratio) and safety. In contrast to rat, the dog and human MetID and PK profiles of 22 were adequate, suggesting that it could be suitable as a potential clinical asset.

Perturbation Approaches for Exploring Protein Binding Site Flexibility to Predict Transient Binding Pockets

Simulations of the long-time scale motions of a ligand binding pocket in a protein may open up new perspectives for the design of compounds with steric or chemical properties differing from those of known binders. However, slow motions of proteins are difficult to access using standard molecular dynamics (MD) simulations and are thus usually neglected in computational drug design. Here, we introduce two nonequilibrium MD approaches to identify conformational changes of a binding site and detect transient pockets associated with these motions. The methods proposed are based on the rotamerically induced perturbation (RIP) MD approach, which employs perturbation of side-chain torsional motion for initiating large-scale protein movement. The first approach, Langevin-RIP (L-RIP), entails a series of short Langevin MD simulations, each starting with perturbation of one of the side-chains lining the binding site of interest. L-RIP provides extensive sampling of conformational changes of the binding site. In less than 1 ns of MD simulation with L-RIP, we observed distortions of the α-helix in the ATP binding site of HSP90 and flipping of the DFG loop in Src kinase. In the second approach, RIPlig, a perturbation is applied to a pseudoligand placed in different parts of a binding pocket, which enables flexible regions of the binding site to be identified in a small number of 10 ps MD simulations. The methods were evaluated for four test proteins displaying different types and degrees of binding site flexibility. Both methods reveal all transient pocket regions in less than a total of 10 ns of simulations, even though many of these regions remained closed in 100 ns conventional MD. The proposed methods provide computationally efficient tools to explore binding site flexibility and can aid in the functional characterization of protein pockets, and the identification of transient pockets for ligand design.

Identification of spirooxindole and dibenzoxazepine motifs as potent mineralocorticoid receptor antagonists

Mineralocorticoid receptor (MR) antagonists continue to be a prevalent area of research in the pharmaceutical industry. Herein we report the discovery of various spirooxindole and dibenzoxazepine constructs as potent MR antagonists. SAR analysis of our spirooxindole hit led to highly potent compounds containing polar solubilizing groups, which interact with the helix-11 region of the MR ligand binding domain (LBD). Various dibenzoxazepine moieties were also prepared in an effort to replace a known dibenzoxepane system which interacts with the hydrophobic region of the MR LBD. In addition, an X-ray crystal structure was obtained from a highly potent compound which was shown to exhibit both partial agonist and antagonist modes of action against MR.

Carbon-11 radiolabelling of organosulfur compounds: (11) C synthesis of the progesterone receptor agonist tanaproget

Herein a new (11) C radiolabelling strategy for the fast and efficient synthesis of thioureas and related derivatives using the novel synthon, (11) CS2 , is reported. This approach has enabled the facile labelling of a potent progesterone receptor (PR) agonist, [(11) C]Tanaproget, by the intramolecular reaction of the acyclic aminohydroxyl precursor with (11) CS2 , which has potential applications as a positron emission tomography radioligand for cancer imaging.

Water Soluble Components of 'Osteocare' Promote Cell Proliferation, Differentiation, and Matrix Mineralization in Human Osteoblast-Like SaOS-2 Cells

Osteocare, a herbal formulation, has been found to be very effective in bone mineralization and support of the microstructure of bone tissue. The water-soluble components of Osteocare (WSCO) induced osteogenic activity in human osteoblast-like SaOS-2 cells. The addition of WSCO (100 μg/ml) to SaOS-2 cells was effective in increasing the cell proliferation by 41.49% and DNA content by 1.9-fold. WSCO increased matrix mineralization in SaOS-2 cells by increased alkaline phosphatase levels and calcium-rich deposits as observed by Alizarin red staining. WSCO markedly increased mRNA expression for osteopontin (OPN), osteocalcin (OCN), type I collagen (Col I) in SaOS-2 cells, and it down-regulated IL-6 mRNA levels in SaOS-2 cells. The present study showed that WSCO plays an important role in osteoblastic bone formation through enhanced activities of ALP, Col I, bone matrix proteins such as OPN and OCN, down-regulation of cytokines like IL-6, as well as promoting mineralization in SaOS-2 cells.

Looking at nuclear receptors from a new angle

While the structures of the DNA- and ligand-binding domains of many nuclear receptors have been determined in great detail; the mechanisms by which these domains interact and possibly 'communicate' is still under debate. The first crystal structures of receptor dimers bound to ligand, DNA and coactivator peptides provided new insights in this matter. The observed binding modes revealed exciting new interaction surfaces between the different nuclear receptor domains. Such interfaces are proposed to be the route through which allosteric signals from the DNA are passed on to the ligand-binding domain and the activating functions of the receptor. The structural determinations of DNA-bound receptor dimers in solution, however, revealed an extended structure of the receptors. Here, we discuss these apparent contradictory structural data and their possible implications for the functioning of nuclear receptors.

Progesterone receptor targeting with radiolabelled steroids: an approach in predicting breast cancer response to therapy

Steroid receptors have demonstrated to be potentially useful biological targets for the diagnosis and therapy follow-up of hormonally responsive cancers. The over-expression of these proteins in human cancer cells as well as their binding characteristics provides a favourable mechanism for the localization of malignant tumours. The need for newer and more selective probes to non-invasively assess steroid receptor expression in hormone-responsive tumours has encouraged the synthesis and the biological evaluation of several steroidal derivatives labelled with positron and gamma emitters. The physiological effects of the steroid hormone progesterone are mediated by the progesterone receptor (PR). Since PR expression is stimulated by the oestrogen receptor (ER), PR status has been considered as a biomarker of ER activity and its value for predicting and monitoring therapeutic efficacy of hormonal therapy has been studied. Imaging of PR-expressing breast cancer patients under hormonal therapy may be advantageous, since the response to therapy can be more accurately predicted after quantification of both ER and PR status. Thus, ligands for PR targeting, although much less explored than ER ligands, have gained some importance lately as potential PET and SPECT tumour imaging agents. In this review, we present a brief survey of explored approaches for progesterone targeting using radiolabelled progestins as potential clinical probes to predict responsiveness to breast cancer therapy. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Nuclear receptors and their selective pharmacologic modulators

Nuclear receptors are ligand-activated transcription factors and include the receptors for steroid hormones, lipophilic vitamins, sterols, and bile acids. These receptors serve as targets for development of myriad drugs that target a range of disorders. Classically defined ligands that bind to the ligand-binding domain of nuclear receptors, whether they are endogenous or synthetic, either activate receptor activity (agonists) or block activation (antagonists) and due to the ability to alter activity of the receptors are often termed receptor "modulators." The complex pharmacology of nuclear receptors has provided a class of ligands distinct from these simple modulators where ligands display agonist/partial agonist/antagonist function in a tissue or gene selective manner. This class of ligands is defined as selective modulators. Here, we review the development and pharmacology of a range of selective nuclear receptor modulators.

Structural basis for computational screening of non-steroidal androgen receptor ligands

IMPORTANCE OF THE FIELD

Deep structural and chemical understanding of the protein target and computational methods for detection of receptor-selective ligands are important for the early drug discovery in the steroid receptor field.

AREAS COVERED IN THIS REVIEW

This review focuses on the use of currently available structural information of the androgen receptor (AR) and known AR ligands to make computational strategies for the discovery of AR ligands in order to offer new chemical platforms for drug development.

WHAT THE READER WILL GAIN

AR is a challenging target for drug discovery and modeling even if there is a wealth of experimental data available. First, only the active structure of AR is currently known, which hampers the design of AR antagonists. Second, the structural similarity between the ligand-binding sites of AR and its mutated forms and closely related steroid receptors (SRs) such as progesterone receptors presents challenges for the development of drugs with receptor-selective function.

TAKE HOME MESSAGE

Research indicates that a very small chemical change in the structure of a non-steroidal ligand can cause a complete change in its activity. One source of this effect arises from binding to similar binding sites in related SRs and other proteins in the signaling pathway. Currently, computational methods are not able to predict the subtle differences between AR ligand activities but modeling does offer the possibility of generating new lead structures that might have the desired properties.

Discovery of BAY 94-8862: a nonsteroidal antagonist of the mineralocorticoid receptor for the treatment of cardiorenal diseases

Aldosterone is a hormone that exerts manifold deleterious effects on the kidneys, blood vessels, and heart which can lead to pathophysiological consequences. Inhibition of the mineralocorticoid receptor (MR) is a proven therapeutic concept for the management of associated diseases. Use of the currently marketed MR antagonists spironolactone and eplerenone is restricted, however, due to a lack of selectivity in spironolactone and the lower potency and efficacy of eplerenone. Several pharmaceutical companies have implemented programs to identify drugs that overcome the known liabilities of steroidal MR antagonists. Herein we disclose an extended SAR exploration starting from cyano-1,4-dihydropyridines that were identified by high-throughput screening. Our efforts led to the identification of a dihydronaphthyridine, BAY 94-8862, which is a potent, selective, and orally available nonsteroidal MR antagonist currently under investigation in a clinical phase II trial.

X-ray structures of progesterone receptor ligand binding domain in its agonist state reveal differing mechanisms for mixed profiles of 11β-substituted steroids

We present here the x-ray structures of the progesterone receptor (PR) in complex with two mixed profile PR modulators whose functional activity results from two differing molecular mechanisms. The structure of Asoprisnil bound to the agonist state of PR demonstrates the contribution of the ligand to increasing stability of the agonist conformation of helix-12 via a specific hydrogen-bond network including Glu(723). This interaction is absent when the full antagonist, RU486, binds to PR. Combined with a previously reported structure of Asoprisnil bound to the antagonist state of the receptor, this structure extends our understanding of the complex molecular interactions underlying the mixed agonist/antagonist profile of the compound. In addition, we present the structure of PR in its agonist conformation bound to the mixed profile compound Org3H whose reduced antagonistic activity and increased agonistic activity compared with reference antagonists is due to an induced fit around Trp(755), resulting in a decreased steric clash with Met(909) but inducing a new internal clash with Val(912) in helix-12. This structure also explains the previously published observation that 16α attachments to RU486 analogs induce mixed profiles by altering the binding of 11β substituents. Together these structures further our understanding of the steric and electrostatic factors that contribute to the function of steroid receptor modulators, providing valuable insight for future compound design.

Pharmacology and clinical use of sex steroid hormone receptor modulators

Sex steroid receptors are ligand-triggered transcription factors. Oestrogen, progesterone and androgen receptors form, together with the glucocorticoid and mineralocorticoid receptors, a subgroup of the superfamily of nuclear receptors. They share a common mode of action, namely translating a hormone-i.e. a small-molecule signal-from outside to changes in gene expression and cell fate, and thereby represent "natural" pharmacological targets.For pharmacological therapy, these receptors have originally been addressed by hormones and synthetic hormone analogues in order to overcome pathologies related to deficiencies in the natural ligands. Another major use for female sex hormone receptor modulators is oral contraception, i.e. birth control.On the other side, blocking the activity of sex steroid receptors has become an established way to treat hormone-dependent malignancies, such as breast and prostate cancer.In this review, we will discuss how the experience gained from the classical pharmacology of these receptors and their molecular similarities led to new options for the treatment of gender-specific diseases and highlight recent progress in medicinal chemistry of sex hormone-modulating drugs.

Structural basis for agonism and antagonism for a set of chemically related progesterone receptor modulators

The progesterone receptor is able to bind to a large number and variety of ligands that elicit a broad range of transcriptional responses ranging from full agonism to full antagonism and numerous mixed profiles inbetween. We describe here two new progesterone receptor ligand binding domain x-ray structures bound to compounds from a structurally related but functionally divergent series, which show different binding modes corresponding to their agonistic or antagonistic nature. In addition, we present a third progesterone receptor ligand binding domain dimer bound to an agonist in monomer A and an antagonist in monomer B, which display binding modes in agreement with the earlier observation that agonists and antagonists from this series adopt different binding modes.

Discovery of a novel mechanism of steroid receptor antagonism: WAY-255348 modulates progesterone receptor cellular localization and promoter interactions

WAY-255348 is a potent nonsteroidal progesterone receptor (PR) antagonist previously characterized in rodents and nonhuman primates. This report describes the novel mechanism by which WAY-255348 inhibits the activity of progesterone. Most PR antagonists bind to and block PR action by inducing a unique "antagonist" conformation of the PR. However, WAY-255348 lacks the bulky side chains or chemical groups that have been associated with the conformation changes of helix 12 that lead to functional antagonism. We show that WAY-255348 achieves antagonist activity by binding to and subsequently preventing progesterone-induced nuclear accumulation, phosphorylation and promoter interactions of the PR. This effect was concentration dependent, as high concentrations of WAY-255348 alone are able to induce nuclear translocation, phosphorylation and subsequent promoter interactions resulting in partial agonist activity at these concentrations. However, at lower concentrations where nuclear accumulation and phosphorylation are prevented, the progesterone-induced DNA binding is blocked along with PR-dependent gene expression. Analysis of the PR conformation induced by WAY-255348 using a limited protease digestion assay, suggested that the WAY-255348 bound PR conformation was similar to that of a progesterone agonist-bound PR and distinct from steroidal antagonist-bound PR conformations. Furthermore, the recruitment and binding of peptides derived from nuclear receptor co-activators is consistent with WAY-255348 inducing an agonist-like conformation. Taken together, these data suggest that WAY-255348 inhibits PR action through a novel molecular mechanism that is distinct from previously studied PR modulators and may be a useful tool to further understanding of PR signaling pathways. Development of therapeutic molecules with this 'passive' antagonism mechanism may provide distinct advantages for patients with reproductive disorders or PR positive breast cancers.

Intestinal tumorigenesis is not affected by progesterone signaling in rodent models

Clinical data suggest that progestins have chemopreventive properties in the development of colorectal cancer. We set out to examine a potential protective effect of progestins and progesterone signaling on colon cancer development. In normal and neoplastic intestinal tissue, we found that the progesterone receptor (PR) is not expressed. Expression was confined to sporadic mesenchymal cells. To analyze the influence of systemic progesterone receptor signaling, we crossed mice that lacked the progesterone receptor (PRKO) to the Apc^Min/+ mouse, a model for spontaneous intestinal polyposis. PRKO-Apc^Min/+mice exhibited no change in polyp number, size or localization compared to Apc^Min/+. To examine effects of progestins on the intestinal epithelium that are independent of the PR, we treated mice with MPA. We found no effects of either progesterone or MPA on gross intestinal morphology or epithelial proliferation. Also, in rats treated with MPA, injection with the carcinogen azoxymethane did not result in a difference in the number or size of aberrant crypt foci, a surrogate end-point for adenoma development. We conclude that expression of the progesterone receptor is limited to cells in the intestinal mesenchyme. We did not observe any effect of progesterone receptor signaling or of progestin treatment in rodent models of intestinal tumorigenesis.

SM-368229, a novel selective and potent non-steroidal mineralocorticoid receptor antagonist with strong urinary Na+ excretion activity

Mineralocorticoid receptor (MR) antagonists, such as spironolactone (SPI) and eplerenone (EPL), are useful for the treatment of hypertension and heart failure. However, the use of these two agents has been limited due to endocrine disturbance (SPI) and poor drug action (EPL). In our search for safer and more effective MR antagonists, we identified SM-368229 as a novel non-steroidal MR antagonist. SM-368229 showed strong MR inhibitory activity with IC(50) values of 0.021 and 0.13 µM in the binding assay and reporter-gene assay, respectively. The selectivity of SM-368229 for MR was 18-fold higher than that for other steroid receptors, such as androgen, progesterone, and glucocorticoid receptors. SM-368229 dose-dependently increased urinary Na(+)/K(+) ratio with an ED(50) value of 5.6 mg/kg in adrenalectomized rats treated with deoxycorticosterone acetate, and its efficacy was superior to that of SPI (ED(50) = 14 mg/kg) or EPL (ED(50) = 147 mg/kg). Moreover, even at high doses of 100 and 300 mg/kg, SM-368229 showed very weak anti-androgenic effect in methyltestosterone-treated male rats and no progestagenic effect in estrus cycle synchronized female rats. These findings indicate that SM-368229 may offer a new promising therapeutic option for the treatment of hypertension and heart failure.

Development of [F-18]fluorine-substituted Tanaproget as a progesterone receptor imaging agent for positron emission tomography

The level of progesterone receptors (PRs) in breast tumors can be used to guide the selection of endocrine therapies for breast cancer patients. To this end, we have prepared a fluorine-18 labeled analogue of Tanaproget, a nonsteroidal progestin with very high PR binding affinity and low affinity for androgen and glucocorticoid receptors, and have studied its tissue distribution in estrogen-primed rats to evaluate its potential for imaging PR levels by positron emission tomography. 4-[(18)F]Fluoropropyl-Tanaproget ([(18)F]9, FPTP) was prepared in three steps, within 140 min at an overall decay-corrected yield of 5% and effective specific activity of >550 Ci/mmol. In biodistribution studies, [(18)F]9 uptake was high in target tissues at both 1 and 3 h (uterus, 4.55 and 5.26%ID/g; ovary, 2.32 and 2.20%ID/g, respectively) and was cleanly blocked by coinjection of excess unlabeled compound. Uterus to blood and muscle activity ratios were 9.2 and 5.2 at 1 h and 32 and 26 at 3 h, respectively. The biodistribution of [(18)F]9 compares favorably to that of previously prepared F-18 labeled steroidal progestins, FENP and FFNP. Its high target tissue uptake efficiency and selectivity, and prolonged retention, suggest that it has excellent promise as a PET imaging agent for PR-positive breast tumors.

Imaging progesterone receptor in breast tumors: synthesis and receptor binding affinity of fluoroalkyl-substituted analogues of tanaproget

The progesterone receptor (PR) is estrogen regulated, and PR levels in breast tumors can be used to predict the success of endocrine therapies targeting the estrogen receptor (ER). Tanaproget is a nonsteroidal progestin agonist with very high PR binding affinity and excellent in vivo potency. When appropriately radiolabeled, it might be used to image PR-positive breast tumors noninvasively by positron emission tomography (PET). We describe the synthesis and PR binding affinities of a series of fluoroalkyl-substituted 6-aryl-1,4-dihydrobenzo[d][1,3]oxazine-2-thiones, analogues of Tanaproget. Some of these compounds have subnanomolar binding affinities, higher than that of either Tanaproget itself or the high affinity PR ligand R5020. Structure-binding affinity relationships can be rationalized by molecular modeling of ligand complexes with PR, and the enantioselectivity of binding has been predicted. These compounds are being further evaluated as potential diagnostic PET imaging agents for breast cancer, and enantiomerically pure materials of defined stereochemistry are being prepared.

Recent patent trends in the field of progesterone receptor agonists and modulators

BACKGROUND

Progesterone receptor agonists are used in female contraception, hormone replacement therapy or some gynecological conditions like endometriosis. The interest for antagonists or selective progesterone receptor modulators (SPRMs) is growing. Recent reports on this class of compounds indicate that they could become the next generation of therapeutics in gynecological treatments.

OBJECTIVE

This overview summarizes the work on progesterone receptor agonists, SPRMs and antagonists reported in the patent literature in the past 4 years.

METHODS

The focus of the article is the examination of patents, primarily published as WO, EU or US patents since 2005. In some cases, additional data from the public literature is included into the discussion. These data are of substantial interest as the available biological data disclosed in patents are usually limited for new compound classes.

RESULTS/CONCLUSION

Some highly active clusters of compounds have been disclosed in the past 4 years. The current research seems to focus on SPRMs and progesterone receptor antagonists.

Molecular docking screens using comparative models of proteins

Two orders of magnitude more protein sequences can be modeled by comparative modeling than have been determined by X-ray crystallography and NMR spectroscopy. Investigators have nevertheless been cautious about using comparative models for ligand discovery because of concerns about model errors. We suggest how to exploit comparative models for molecular screens, based on docking against a wide range of crystallographic structures and comparative models with known ligands. To account for the variation in the ligand-binding pocket as it binds different ligands, we calculate "consensus" enrichment by ranking each library compound by its best docking score against all available comparative models and/or modeling templates. For the majority of the targets, the consensus enrichment for multiple models was better than or comparable to that of the holo and apo X-ray structures. Even for single models, the models are significantly more enriching than the template structure if the template is paralogous and shares more than 25% sequence identity with the target.

Met909 plays a key role in the activation of the progesterone receptor and also in the high potency of 13-ethyl progestins

Many progestins have been developed for use in contraception, menopausal hormone therapy, and treatment of gynecological diseases. They are derived from either progesterone or testosterone, and they act by binding to the progesterone receptor (PR), a hormone-inducible transcription factor belonging to the nuclear receptor superfamily. Unlike mineralocorticoid, glucocorticoid, and androgen receptors, the steroid-receptor contacts that trigger the switch of the ligand-binding domain from an inactive to an active conformation have not yet been identified for the PR. With this aim, we solved the crystal structure of the ligand-binding domain of the human PR complexed with levonorgestrel, a potent testosterone-derived progestin characterized by a 13-ethyl substituent. Via mutagenesis analysis and functional studies, we identified Met909 of the helix 12 as the key residue for PR activation by both testosterone- and progesterone-derived progestins with a 13-methyl or a 13-ethyl substituent. We also showed that Asn719 contributes to PR activation by testosterone-derived progestins only, and that Met759 and Met909 are responsible for the high potency of 19-norprogestins and of 13-ethyl progestins, respectively. Our findings provide a structural guideline for the rational synthesis of potent PR agonist and antagonist ligands that could have therapeutic uses in women's health.

Hormonal influences on seizures: basic neurobiology

There are sex differences and effects of steroid hormones, such as androgens, estrogens, and progestogens, that influence seizures. Androgens exert early organizational and later activational effects that can amplify sex/gender differences in the expression of some seizure disorders. Female-typical sex steroids, such as estrogen (E2) and progestins, can exert acute activational effects to reduce convulsive seizures and these effects are mediated in part by the actions of steroids in the hippocampus. Some of these anticonvulsive effects of sex steroids are related to their formation of ligands which have agonist-like actions at gamma-aminobutyric acid (GABAA) receptors or antagonist actions at glutamatergic receptors. Differences in stress, developmental phase, reproductive status, endocrine status, and treatments, such as anti-epileptic drugs (AEDs), may alter levels of these ligands and/or the function of target sites, which may mitigate differences in sensitivity to, and/or tolerance of, steroids among some individuals. The evidence implicating sex steroids in differences associated with hormonal, reproductive, developmental, stress, seizure type, and/or therapeutics are discussed.

Global gene expression profiling of progesterone receptor modulators in T47D cells provides a new classification system

Progesterone receptor modulators (PRMs) play an important role in women's health. They are widely used in oral contraception or hormone therapy, and provide an attractive treatment approach for gynecological disorders such as uterine leiomyomas, endometriosis or breast cancer. Due to the broad range of activities, various studies were conducted to assess progesterone receptor antagonists (PAs) and selective progesterone receptor modulators (SPRMs) with respect to progesterone receptor (PR) agonistic and antagonistic activities in vivo. These properties are not always adequately reflected in classical in vitro models, especially differences in the agonistic potential of SPRMs, such as asoprisnil, J1042, and J912, and mixed antagonists, such as mifepristone, are not sufficiently substantiated. The effects of PRMs upon gene expression in progesterone target tissues such as breast epithelium and uterus are poorly understood. This study compares the properties of PR ligands using mammalian two-hybrid assays and gene expression profiling. The protein-protein interaction analyses in HeLa cells provide for specific ligand-induced PR conformations, whereas Affymetrix GeneChip HG-U133Plus2.0 analyses in T47D breast cancer cells indicate the transcriptional activity on the level of target genes. The analyses comprise the pure agonist R5020, the non-steroidal PR modulator PRA-910, SPRMs (J1042, asoprisnil, J912), the mixed antagonist mifepristone, classical antagonists (onapristone, ZK 137316) and the pure antagonist lonaprisan to consider all types of ligands described before. Marginal differences were identified in coactivator interaction profiles at all, but significant differences between SPRMs and PR antagonists (PAs) were observed in recruiting the LXXLL-motif containing peptide (LX-H10), very similar to in vivo activities in endometrial transformation in the rabbit (McPhail test). Global gene expression profiles demonstrated progesterone-independent effects for all PR modulators examined and emphasised similarities of asoprisnil and J1042 compared to J912 and all types of PR antagonists. In summary, the data support the popular concept of PR modulator classification in agonists, selective progesterone receptor modulators, mixed and pure antagonists. It further refines previous classification models and accentuates unique effects for each PR modulator.

New drugs in development for the treatment of endometriosis

Endometriosis is a common and enigmatic disease causing pelvic pain and infertility. Current treatment is mainly based on the use of surgery and ovarian suppressive agents. There is in particular the need for new therapeutic options able to allow a normal menstrual cycle to occur and also consent pregnancy. In the present review, we aimed to give a concise and practical overview in order to allow the clinician to clearly understand the level of development of these drugs. We have presented only treatments supported by in vivo researches with a special attention to studies in humans. Results show appealing new possibilities are emerging from agents counteracting the endometriosis-associated inflammation. Recent data also suggests that there is still the opportunity to refine the use of already available agents.

Compound profiling using a panel of steroid hormone receptor cell-based assays

A major focus in the current discovery of drugs targeting nuclear receptors (NRs) is identifying drugs with reduced side effects by improving selectivity, not only from other receptors but also by selective modulation of the NR of interest. Cellular assays not only provide valuable information on functional activity, potency, and selectivity but also are ideally suited for differentiating partial agonists and antagonists. The ability to partially activate a receptor is believed to be closely tied to the ability to selectively modulate the NR, resulting in expression of a subset of the normally regulated genes. To this end, the authors have built a complete panel of cell-based steroid hormone receptor assays for the androgen receptor, estrogen receptor alpha, estrogen receptor beta, glucocorticoid receptor, mineralocorticoid receptor, and progesterone receptor by stably engineering a Gal4 DNA-binding domain/nuclear receptor ligand-binding domain fusion protein into an upstream activation sequence beta-lactamase reporter cell line. Each assay was validated with known agonists and antagonists for correct pharmacology and high-throughput compatibility. To demonstrate the utility of these assays, the authors profiled 35 pharmacologically relevant compounds in a dose-response format against the panel in both agonist and antagonist modes. The results demonstrated that selective estrogen receptor modulators can be identified and differentiated, as well as mixed and partial agonists and antagonists easily detected in the appropriate assays. Importantly, a comparison of the chimeric assays with full-length reporter gene assay data from the literature shows a good degree of correlation in terms of selectivity and pharmacology of important ligands. Taken together, these steroid hormone receptor assays provide good selectivity, sensitivity, and appropriate pharmacology for high-throughput screening and selectivity profiling of modulators of steroid hormone receptors.

Investigational developments for the treatment of progesterone-dependent diseases

BACKGROUND

Clinical evidence has shown that conditions such as uterine fibroids, endometriosis and breast cancer are progesterone-dependent diseases. Therefore, progesterone receptor (PR) antagonists and selective PR modulators (SPRMs) are under development for the treatment of these conditions. However, the first PR antagonists that became available exhibit insufficient selectivity or tolerability for the chronic administration required to treat these conditions. Despite initial setbacks, development of second-generation PR antagonists with better selectivity continues forward.

OBJECTIVE

In this review we would like to summarise prospects for using PR antagonists for the treatment of uterine fibroids, endometriosis and breast cancer, and to give an overview of the development of new steroidal and non-steroidal PR antagonists.

METHOD

Available preclinical and clinical data and publications have been reviewed with the focus on scientific background and use in the three mentioned indications.

RESULTS/CONCLUSION

Preclinical and clinical evidence demonstrated that PR antagonists and SPRMs are effective for the treatment of progesterone-dependent diseases. Future development will demonstrate if they can become important drugs.