A nonsteroidal glucocorticoid receptor antagonist

Small-Molecule Induction Promotes Corneal Endothelial Cell Differentiation From Human iPS Cells

Purpose: Corneal endothelial cells (CECs) serve as a barrier and foothold for the corneal stroma to maintain the function and transparency of the cornea. Loss of CECs during aging or disease states leads to blindness, and cell replacement therapy using either donated or artificially differentiated CECs remains the only curative approach.

Methods: Human induced pluripotent stem cells (hiPSCs) that were cultured in chemically defined medium were induced with dual-SMAD inhibition to differentiate into neural crest cells (NCCs). A small-molecule library was screened to differentiate the NCCs into corneal endothelial-like cells. The characteristics of these cells were identified with real-time PCR and immunofluorescence. Western blotting was applied to detect the signaling pathways and key factors regulated by the small molecules.

Results: We developed an effective protocol to differentiate hiPSCs into CECs with defined small molecules. The hiPSC-CECs were characterized by ZO-1, AQP1, Vimentin and Na⁺/K⁺-ATPase. Based on our small-molecule screen, we identified a small-molecule combination, A769662 and AT13148, that enabled the most efficient production of CECs. The combination of A769662 and AT13148 upregulated the PKA/AKT signaling pathway, FOXO1 and PITX2 to promote the conversion of NCCs to CECs.

Conclusion: We established an efficient small molecule-based method to differentiate hiPSCs into corneal endothelial-like cells, which might facilitate drug discovery and the development of cell-based therapies for corneal diseases.

Onapristone Extended Release: Safety Evaluation from Phase I-II Studies with an Emphasis on Hepatotoxicity

Introduction

Antiprogestins have demonstrated promising activity against breast and gynecological cancers, but liver-related safety concerns limited the advancement of this therapeutic class. Onapristone is a full progesterone receptor antagonist originally developed as an oral contraceptive and later evaluated in phase II studies for metastatic breast cancer. Because of liver enzyme elevations identified during clinical studies, further development was halted. Evaluation of antiprogestin pharmacology and pharmacokinetic data suggested that liver enzyme elevations might be related to off-target or metabolic effects associated with clinical drug exposure.

Objective

We explored whether the use of a pharmaceutic strategy targeting efficacious systemic dose concentrations, but with diminished peak serum concentrations and/or total drug exposure would mitigate hepatotoxicity. Twice-daily dosing of an extended-release formulation of onapristone was developed and clinically evaluated in light of renewed interest in antiprogestin therapy for treating progesterone receptor-positive breast and gynecologic cancers. The hepatotoxic potential of extended-release onapristone was assessed from two phase I–II studies involving patients with breast, ovarian, endometrial, and prostate cancer.

Results

Among the 88 patients in two phase I–II studies in progesterone receptor-positive malignancies treated with extended-release onapristone, elevated alanine aminotransferase/aspartate aminotransferase levels were found in 20% of patients with liver metastases compared with 6.3% without metastases. Of five patients with grade 3 or higher alanine aminotransferase elevations with or without bilirubin elevations (four with breast cancer and one with endometrial cancer), four were assessed as unrelated to extended-release onapristone by the safety data review committee. Furthermore, while the fifth patient’s liver enzyme elevations were considered possibly drug related by the study investigator, they were adjudicated as unlikely to be related (< 25% likelihood) by a subsequent independent hepatologist.

Conclusions

These results suggest that the extended-release formulation by reducing drug exposure may be associated with a reduced risk of hepatotoxicity, and supports the continued clinical evaluation of extended-release onapristone for treating progesterone receptor-positive cancers.

Targeting IL-17A/glucocorticoid synergy to CSF3 expression in neutrophilic airway diseases

IL-17A plays a critical role in the pathogenesis of steroid-resistant neutrophilic airway inflammation, which is a hallmark of severe asthma and chronic obstructive pulmonary disease (COPD). Through RNA sequencing analysis of transcriptomes of human airway smooth muscle cells treated with IL-17A, dexamethasone (DEX, a synthetic glucocorticoid drug), alone or in combination, we identified a group of genes that are synergistically induced by IL-17A and DEX, including the neutrophil-promoting cytokine CSF3. In type-17 (Th17/IL-17Ahi) preclinical models of neutrophilic severe asthma (acute and chronic) and COPD, although DEX treatment was able to reduce the expression of neutrophil-mobilizing CXCL1 and CXCL2 in lung tissue, CSF3 expression was upregulated by DEX treatment. We found that DEX treatment alone failed to alleviate neutrophilic airway inflammation and pathology, and even exacerbated the disease phenotype when CSF3 was highly induced. Disruption of the IL-17A/DEX synergy by IL-17A inhibition with anti-IL-17A mAb or cyanidin-3-glucoside (C3G, a small-molecule IL-17A blocker) or depletion of CSF3 effectively rendered DEX sensitivity in type-17 preclinical models of neutrophilic airway diseases. Our study elucidates what we believe is a novel mechanism of steroid resistance in type-17 neutrophilic airway inflammation and offers an effective steroid-sparing therapeutic strategy (combined low-dose DEX and C3G) for treating neutrophilic airway diseases.

The contraceptive medroxyprogesterone acetate, unlike norethisterone, directly increases R5 HIV-1 infection in human cervical explant tissue at physiologically relevant concentrations

The intramuscular progestin-only injectable contraceptive, depo-medroxyprogesterone acetate (DMPA-IM), is more widely used in Sub-Saharan Africa than another injectable contraceptive, norethisterone enanthate (NET-EN). Epidemiological data show a significant 1.4-fold increased risk of HIV-1 acquisition for DMPA-IM usage, while no such association is shown from limited data for NET-EN. We show that MPA, unlike NET, significantly increases R5-tropic but not X4-tropic HIV-1 replication ex vivo in human endocervical and ectocervical explant tissue from pre-menopausal donors, at physiologically relevant doses. Results support a mechanism whereby MPA, unlike NET, acts via the glucocorticoid receptor (GR) to increase HIV-1 replication in cervical tissue by increasing the relative frequency of CD4+ T cells and activated monocytes. We show that MPA, unlike NET, increases mRNA expression of the CD4 HIV-1 receptor and CCR5 but not CXCR4 chemokine receptors, via the GR. However, increased density of CD4 on CD3+ cells was not observed with MPA by flow cytometry of digested tissue. Results suggest that DMPA-IM may increase HIV-1 acquisition in vivo at least in part via direct effects on cervical tissue to increase founder R5-tropic HIV-1 replication. Our findings support differential biological mechanisms and disaggregation of DMPA-IM and NET-EN regarding HIV-1 acquisition risk category for use in high risk areas.

Drug design strategies for Cushing's syndrome

INTRODUCTION

Cushing's syndrome (CS) is a metabolic disorder caused by chronic hypercortisolism. CS is associated with cardiovascular, metabolic, skeletal and psychological dysfunctions and can be fatal if left untreated. The first-line treatment for all forms of CS is a surgery. However, medical therapy has to be chosen if surgical resection is not an option or is deemed ineffective. Currently available therapeutics are either not selective and have side effects or are only available as an injection (pasireotide). Areas covered: The authors discuss the recent drug developments for the medical treatment of CS through two validated molecular targets. Specifically, the authors look at selective inhibitors of CYP11B1 that reduce cortisol production by inhibiting steroid 11beta-hydroxylase and glucocorticoid receptor (GR) antagonists that interrupt cortisol-mediating transcriptional regulation of related genes. Expert opinion: Patients with CS have limited treatment options; indeed, there is an unmet need for new compounds that target CYP11B1 selectively versus several steroidogenic enzymes and/or GR-signaling pathways. The complexity of steroid biosynthesis and signaling requires the application of structure-based drug discovery techniques that use molecular targets and highly similar off-targets. Significant differences in steroidogenesis between humans and other species necessitates caution over the choice of in vivo model for the preclinical evaluation of future potential compounds.

Basal glucocorticoid receptor activation induces proliferation and inhibits neuronal differentiation of human induced pluripotent stem cell-derived neuronal precursor cells

Glucocorticoids (GC) have first been shown to originate from the adrenal glands where synthesis and release is controlled by the hypothalamic-pituitary-adrenal (HPA) axis. Recently, it was shown that GC and other steroid hormones are also synthesized in the central nervous system, so-called neurosteroids. GC bind to specific GC receptors (GR) which function as ligand-activated transcription factors. GR are expressed in nearly all cell types in the brain, and therefore GC have a strong impact on neuronal development. Most knowledge of the influence of GC on neurodevelopment has been obtained from animal research. Recent advances in stem cell technology made it possible to generate neuronal precursor cells (NPCs) and neurons from human induced pluripotent stem cells (hiPSCs). To explore the cellular mechanism of GC affecting human neuronal development, we quantified the proliferation and differentiation of hiPSCs-derived NPCs in the absence and presence of the selective high-affinity GR agonist dexamethasone and the selective GR antagonist mifepristone, respectively. Our results show that inhibition of GR significantly reduced proliferation of NPCs and promoted differentiation whereas GR activation suppressed neuronal differentiation. This implies that neuronal GC must be present in NPCs for proliferation. Consequently we identified the presence of 11-β-hydroxylase CYP11B1, which hydroxylates the respective steroid precursors to bioactive GC, in NPCs. We propose that hiPSC technology offers an ideal system to get more insight into the synthesising and regulatory pathways in steroidogenesis in human neurons and to differentiate between the mechanism by which adrenal GC and neuronal GC impact on neurodevelopment.

The study of progesterone action in human myometrial explants

STUDY HYPOTHESIS

Myometrial explants represent a superior model compared with cell culture models for the study of human myometrial progesterone (P4) signalling in parturition.

STUDY FINDING

Gene expression analysis showed myometrial explants closely resemble the in vivo condition and the anti-inflammatory action of P4 is not lost with labour onset.

WHAT IS KNOWN ALREADY

Circulating P4 levels decline before the onset of parturition in most animals, but not in humans. This has led to the suggestion that there is a functional withdrawal of P4 action at the myometrial level prior to labour onset. However, to date, no evidence of a loss of P4 function has been provided, with studies hampered by a lack of a physiologically relevant model.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Myometrial biopsies obtained at Caesarean section were dissected into explants after a portion was immediately snap frozen (t = 0). Microarray analysis was used to compare gene expression of t = 0 with paired (i) explants, (ii) passage 4 myometrial cell cultures or (iii) the hTERT myometrial cell line. Western blotting and chemokine/cytokine assays were used to study P4 signalling in myometrial explants.

MAIN RESULTS AND THE ROLE OF CHANCE

Gene expression comparison of t = 0 to the three models demonstrated that explants more closely resemble the in vivo status. At the protein level, explants maintain both P4 receptor (PR) and glucocorticoid receptor (GR) levels versus t = 0 whereas cells only maintain GR levels. Additionally, treatment with 1 µM P4 led to a reduction in interleukin-1 (IL-1) β-driven cyclooxygenase-2 in explants but not in cells. P4 signalling in explants was PR-mediated and associated with a repression of p65 and c-Jun phosphorylation. Furthermore, the anti-inflammatory action of P4 was maintained after labour onset.

LIMITATIONS/REASONS FOR CAUTION

There is evidence of basal inflammation in the myometrial explant model.

WIDER IMPLICATIONS OF THE FINDINGS

Myometrial explants constitute a novel model to study P4 signalling in the myometrium and can be used to further elucidate the mechanisms of P4 action in human labour.

LARGE SCALE DATA

Data deposited at http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?token=gvmpggkurbgxfqf&acc=GSE77830.

STUDY FUNDING AND COMPETING INTEREST

This work was supported by grants from the Joint Research Committee of the Westminster Medical School Research Trust, Borne (No. 1067412-7; a sub-charity of the Chelsea and Westminster Health Charity) and the Imperial NIHR Biomedical Research Centre. The views expressed are those of the author(s) and not necessarily those of the NHS or the Department of Health. The authors have no conflict of interest.

High Physiological Concentrations of Progesterone Reverse Estradiol-Mediated Changes in Differentiation and Functions of Bone Marrow Derived Dendritic Cells

Female sex steroids, estradiol (E2) and progesterone (P4), play a key role in regulating immune responses in women, including dendritic cell (DC) development, and functions. Although the two hormones co-occur in the body of women throughout the reproductive years, no studies have explored their complex combinatorial effects on DCs, given their ability to regulate each other’s actions. We examined murine bone marrow derived dendritic cells (BMDC) differentiation and functions, in the presence of a wide range of physiological concentrations of each hormone, as well as the combination of the two hormones. E2 (10⁻¹² to 10^-8M) enhanced the differentiation of CD11b⁺CD11c⁺ DCs from BM precursor cells, and promoted the expression of CD40 and MHC Class-II, in a dose-dependent manner. In contrast, P4 (10⁻⁹ to 10^-5M) inhibited DC differentiation, but only at the highest concentrations. These effects on BMDCs were observed both in the presence or absence of LPS. When both hormones were combined, higher concentrations of P4, at levels seen in pregnancy (10^-6M) reversed the E2 effects, regardless of the concentration of E2, especially in the absence of LPS. Functionally, antigen uptake was decreased and pro-inflammatory cytokines, IL-12, IL-1 and IL-6 production by CD11b⁺CD11c⁺ DCs, was increased in the presence of E2 and these effects were reversed by high concentrations of P4. Our results demonstrate the distinct effects of E2 and P4 on differentiation and functions of bone marrow myeloid DCs. The dominating effect of higher physiological concentrations of P4 provides insight into how DC functions could be modulated during pregnancy.

Noncanonical mechanisms to regulate nuclear receptor signaling

Nuclear receptor (NR)-targeted therapies comprise a large class of clinically employed drugs. A number of drugs currently being used against this protein class were designed as structural analogs of the endogenous ligand of these receptors. In recent years, there has been significant interest in developing newer strategies to target NRs, especially those that rely on mechanistic pathways of NR function. Prominent among these are noncanonical means of targeting NRs, which include selective NR modulation, NR coactivator interaction inhibition, inhibition of NR DNA binding, modulation of NR cellular localization, modulation of NR ligand biosynthesis and downregulation of NR levels in target tissues. This article reviews each of these promising emerging strategies for NR drug development and highlights some of most significant successes achieved in using them.

Relaxin improves TNF-α-induced endothelial dysfunction: the role of glucocorticoid receptor and phosphatidylinositol 3-kinase signalling

AIMS

Human relaxin-2 influences renal and cardiovascular functions. We investigated its effects on experimental endothelial dysfunction.

METHODS AND RESULTS

Acetylcholine-mediated vasodilation of rat aortic rings, impaired by 48 h tumour necrosis factor-α (TNF-α) treatment, was dose-dependently improved by relaxin co-incubation, an effect sensitive to phosphatidylinositol 3-kinase (PI3K) inhibition and the glucocorticoid receptor (GR) antagonist RU-486. TNF increased endothelial nitric oxide synthase (eNOS) phosphorylation at Thr495 and decreased total eNOS expression and both basal and stimulated eNOS activity. Relaxin co-incubation did not affect eNOS expression but improved its activity via PI3K-dependent Thr495 dephosphorylation and Ser1177 phosphorylation, and additional Ser633 phosphorylation. Via GR, relaxin attenuated the TNF-related stimulation of endothelin-1 expression, superoxide and nitrotyrosine formation, and arginase II expression. Relaxin restored, via GR-CCAAT/enhancer-binding protein-β (c/EBP-β)-mediated promoter stimulation, the compromised expression of superoxide dismutase-1 (SOD1). In rat aortic endothelial cells, relaxin activated protein kinase B (Akt) and repressed TNF-induced nuclear factor-κB and activator protein-1. Finally, the relevance of the different findings to the model used was proved by pharmacological interventions.

CONCLUSION

Relaxin improved endothelial dysfunction by promoting eNOS activity, suppressing endothelin-1 and arginase-II expression, and up-regulating SOD1 via GR, GR-c/EBP-β, and PI3K-Akt pathways. This corroborates the notion that it functions as an endogenous and potentially therapeutic vasoprotector.

On the trail of the glucocorticoid receptor: into the nucleus and back

The glucocorticoid receptor (GR) belongs to the superfamily of steroid receptors and is an important regulator of physiological and metabolic processes. In its inactive state, GR is unbound by ligand and resides in the cytoplasm in a chaperone complex. When it binds glucocorticoids, it is activated and translocates to the nucleus, where it functions as a transcription factor. However, the subcellular localization of GR is determined by the balance between its rates of nuclear import and export. The mechanism of GR nuclear transport has been extensively studied. Originally, it was believed that nuclear import of GR is initiated by dissociation of the chaperone complex in the cytoplasm. However, several studies show that the chaperone machinery is required for nuclear transport of GR. In this review, we summarize the contribution of various chaperone components involved in the nuclear transport of GR and propose an updated model of its nuclear import and export. Moreover, we review the importance of ligand-independent nuclear transport and compare the nuclear transport of GR with that of other steroid receptors.

Differential regulation of endogenous pro-inflammatory cytokine genes by medroxyprogesterone acetate and norethisterone acetate in cell lines of the female genital tract

BACKGROUND

Medroxyprogesterone acetate (MPA) and norethisterone (NET) and its derivatives are widely used in female reproductive therapy, but little is known about their mechanisms of action via steroid receptors in the female genital tract. MPA used as a contraceptive has been implicated in effects on local immune function. However, the relative effects of progesterone (Prog), MPA and norethisterone acetate (NET-A) on cytokine gene expression in the female genital tract are unknown.

STUDY DESIGN

Using two epithelial cell lines generated from normal human vaginal (Vk2/E6E7) and ectocervical (Ect1/E6E7) cells as in vitro cell culture model systems for mucosal immunity of the female cervicovaginal environment, we investigated steroid receptor expression and activity as well as regulation of cytokine/chemokine genes by MPA and NET-A, as compared to the endogenous hormone Prog.

RESULTS

We show that the Prog, androgen, glucocorticoid and estrogen receptors (PR, AR, GR and ER, respectively) are expressed in both the Vk2/E6E7 and Ect1/E6E7 cell lines, and that the GR and AR are transcriptionally active. This study is the first to show ligand-, promoter- and cell-specific regulation of IL-6, IL-8 and RANTES (regulated-upon-activation, normal T cell expressed and secreted) gene expression by Prog, MPA and NET-A in these cell lines. Moreover, we show that the repression of the TNF-α-induced RANTES gene by MPA in the Ect1/E6E7 cell line is mediated by the AR.

CONCLUSION

Collectively, these data demonstrate that cell lines from different anatomical sites of the female genital tract respond differently to Prog and the synthetic progestins, most likely due to differential actions via different steroid receptors. The results highlight the importance of choice of progestins for immune function in the cervicovaginal environment. They further suggest that choice of progestins in endocrine therapy may have implications for women's risk of susceptibility to infections due to differential actions on genes involved in inflammation and immune function.

Progesterone stimulates mitochondrial activity with subsequent inhibition of apoptosis in MCF-10A benign breast epithelial cells

The effects of progesterone on breast epithelial cells remain poorly defined with observations showing both proliferative and antiproliferative effects. As an example, progesterone levels correlate with increased epithelial cell proliferation, but there is discordance between the dividing cells and the cells with nuclear progesterone receptor expression. The release of paracrine growth factors from nuclear receptor-positive cells has been postulated as a mechanism, since in vitro studies show a lack of growth effect by progesterone in breast epithelial cells lacking nuclear receptors. This study examined possible nongenomic effects of progesterone in breast epithelia by using MCF-10A cells known to lack nuclear progesterone receptor expression. Treatment for 30-60 min with progesterone or the progestin, R5020, increased mitochondrial activity as shown by an increase in mitochondrial membrane potential (hyperpolarization) with a concordant increase in total cellular ATP. The reaction was inhibited by a specific progesterone receptor antagonist and not affected by the translation inhibitor cycloheximide. Progestin treatment inhibited apoptosis induced by activation of the FasL pathway, as shown by a decrease in sub-G(1) cell fraction during fluorescence-activated cell sorting and a decrease in caspase 3/7 levels. Progestin treatment did not alter the cell cycle over 48 h. Our study demonstrates a nongenomic action of progesterone on benign breast epithelial cells, resulting in enhanced cellular respiration and protection from apoptosis.

Ligand-selective transactivation and transrepression via the glucocorticoid receptor: role of cofactor interaction

The mechanisms that determine ligand-selective transcriptional responses by the glucocorticoid receptor (GR) are not fully understood. Using a wide panel of GR ligands, we investigated the relationships between the potency and maximal response for transactivation via a glucocorticoid response element (GRE) and transrepression via both nuclear factor small ka, CyrillicB (NFsmall ka, CyrillicB) and activator protein-1 (AP-1) sites, relative binding affinity for the GR, as well as interaction with both coactivators and corepressors. The results showed ligand-selective differences in potency and efficacy for each promoter, as well as for a particular ligand between the three promoters. Ligand potency correlated with relative affinity for the GR for agonists and partial agonists in transactivation but not for transrepression. Maximal response was unrelated to relative affinity of ligand for GR for both transactivation and transrepression. A good and significant correlation between full length coactivator binding in two-hybrid assays and efficacy as well as potency of different receptor-steroid complexes for both transactivation and transrepression supports a major role for coactivator recruitment in determination of ligand-selective transcriptional activity. Furthermore, ligand-selective GR binding to GRIP-1, as determined by both two-hybrid and DNA pull down assays, correlated positively with ligand-selective efficacy for transactivation of both a synthetic GRE reporter with expressed GR as well as of an endogenous gene via endogenous GR. The receptor interacting domain of the corepressor SMRT exhibited strong interaction with both agonists and partial agonists, similar to the results for coactivators, suggesting a possible role for SMRT in activation of transcription. However, there was no correlation between ligand affinity for the GR and cofactor interaction. These results provide strong quantitative biochemical support for a model in which GR-mediated ligand-selective differential interaction with GRIP-1, SRC-1A, NCoR and SMRT is a major determinant of ligand-selective and promoter-specific differences in potency and efficacy, for both transactivation and transrepression.

RXFP1-inactive relaxin activates human glucocorticoid receptor: further investigations into the relaxin-GR pathway

The relaxin peptide family regulates diverse biological functions (central nervous processes, reproduction, cardiovascular and kidney function, and connective tissue composition) through different G protein-coupled receptors. We reported earlier that human relaxin-2 and porcine relaxin additionally interact with the human glucocorticoid receptor (GR) in an agonistic manner. Here we investigated whether the membrane receptor RXFP1 is critically involved in this pathway. We used chemically modified porcine relaxin which was biologically inactive at RXFP1. Native porcine relaxin, but not the modified peptide affected RXFP1-dependent and GR-independent readouts: ERK-1/2 and Akt phosphorylation as well as up-regulation of Akt and endothelin type-B receptor. In contrast, relaxin and modified relaxin inhibited endotoxin-stimulated secretion of TNF-alpha and IL-6 by human macrophages, an effect sensitive to the glucocorticoid receptor antagonists RU-486 and D-06. Both relaxins caused Ser(211) phosphorylation of GR, a biomarker of agonist-related receptor activation. Relaxin-induced accumulation of Ser(211)-phosphorylated GR was found in the cytoplasm and nucleus of HeLa cells, in endothelial cells, and in transfected HT-29 cells. In AP-1-luciferase assays, relaxin and modified relaxin inhibited endotoxin-induced activation of AP-1, a transcription factor essentially involved in endotoxin signaling. This study suggests that the inability of relaxin to interact with its membrane receptor does not interfere with its ability to activate GR.

Minireview: nuclear receptors and breast cancer

Until recently, the study of nuclear receptor (NR) function in breast cancer biology has been largely limited to estrogen and progesterone receptors. The development of reliable gene expression arrays, real-time quantitative RT-PCR, and immunohistochemical techniques for studying NR superfamily members in primary human breast cancers has now revealed the presence and potential importance of several additional NRs in the biology of breast cancer. These include receptors for steroid hormones (including androgens and corticosteroids), fat-soluble vitamins A and D, fatty acids, and xenobiotic lipids derived from diet. It is now clear that after NR activation, both genomic and nongenomic NR pathways can coordinately activate growth factor signaling pathways. Advances in our understanding of both NR functional networks and epithelial cell growth factor signaling pathways have revealed a frequent interplay between NR and epithelial cell growth factor family signaling that is clinically relevant to breast cancer. Understanding how growth factor receptors and their downstream kinases are activated by NRs (and vice-versa) is a central goal for maximizing treatment opportunities in breast cancer. In addition to the estrogen receptor, it is predicted that modulating the activity of other NRs will soon provide novel prevention and treatment approaches for breast cancer patients.

Discovery of a functional glucocorticoid receptor beta-isoform in zebrafish

In humans, two glucocorticoid receptor (GR) splice variants exist: GRalpha and GRbeta, which are identical between amino acids 1-727 and then diverge. Whereas GRalpha (the canonical GR) acts as a ligand-activated transcription factor, GRbeta does not bind traditional glucocorticoid agonists, lacks GRalpha's transactivational activity, and acts as a dominant-negative inhibitor of GRalpha. It has been suggested that this receptor isoform is involved in the induction of glucocorticoid resistance in asthma patients. Unfortunately, a GR beta-isoform has been detected in only humans, and therefore, an animal model for studies on this isoform is lacking. In the present study, we demonstrate that in zebrafish a GR isoform exists that diverges from the canonical zebrafish GR at the same position as human GRbeta from human GRalpha. The zebrafish GR beta-isoform acts as a dominant-negative inhibitor in reporter assays, and the extent of inhibition and the effective GRalpha/GRbeta ratio is similar to studies performed with the human GR isoforms. In addition, the subcellular localization of zebrafish GRbeta is similar to its human equivalent. Finally, expression levels of GRalpha and GRbeta were determined in adult zebrafish tissues and at several developmental stages. Both receptor isoforms were detected throughout the body, and GRbeta mRNA levels were relatively low compared with GRalpha mRNA levels, as in humans. Thus, for the first time, a GR beta-isoform has been identified in a nonhuman animal species, shedding new light on the relevance of this GR splice variant and providing a versatile animal model for studies on the GR system.

Glucocorticoid receptor binding: a biphasic dependence on molecular size as revealed by the bilinear LinBiExp model

For corticosteroids, receptor-binding affinity (RBA) at the glucocorticoid receptor (GR) is a major determinant of therapeutic potential. Here, the results of a comprehensive quantitative analysis of relative RBA (rRBA) data obtained from more than a hundred active structures are reported. Because of a clear biphasic size-dependence, the recently introduced linearized biexponential (LinBiExp) model provided very good fit: for steroids that satisfy the main binding criteria at the GR, it accounts for close to 80% of the variability in the free energy of binding DeltaG0 (or logrRBA) data by using only two descriptors: calculated molecular volume and an indicator variable for the presence of 6alpha/9alpha-halogen or cyclic 16,17-acetal moieties. Accordingly, binding is strongest for corticosteroids close to an ideal size that is large enough to provide as large nonspecific (van der Waals-type) interactions as possible, but is not too large to have difficulty fitting due to size-limitations at the binding site. Binding affinity is dramatically increased by 6alpha- or 9alpha-halogenation or introduction of a cyclic 16,17-acetal moiety (in average, about 7-fold), but there is no significant increase after the first substitution. Known highly active glucocorticoids, such as betamethasone 17-monopropionate, fluticasone propionate, or mometasone furoate, indeed satisfy both of these criteria. For small-enough structures, the obtained size-dependency (slope) of the free energy of binding suggest that, as long as only nonspecific interactions are involved, addition of a methylene-sized non-hydrogen atom to the ligand structure increases DeltaG0 on average by about 1.5 kJ/mol, corresponding to an almost doubling of the binding affinity.

Glucocorticoid action and the development of selective glucocorticoid receptor ligands

Glucocorticoids are important endocrine regulators of a wide range of physiological systems ranging from respiratory development, immune function to responses to stress. Glucocorticoids in cells activate the cytoplasmic glucocorticoid receptor (GR) that dimerizes, translocates to the nucleus and functions as a ligand-dependent transcriptional regulator. Synthetic glucocorticoids such as dexamethasone and prednisolone have for decades been the cornerstone for the clinical treatment of inflammatory diseases, such as rheumatoid arthritis and asthma, and in some lymphoid cancers, yet its prolonged use has undesirable side effects such as obesity, diabetes, immune suppression and osteoporosis. Detailed knowledge on the mechanism of GR action has led to the development of novel selective glucocorticoid receptor modulators (SGRMs) that show promise of being efficacious for specific treatments of disease but with fewer side effects. SGRMs promote specific recruitment of transcriptional co-regulators that elicit specific gene responses and show promise of greater efficacy and specificity in treatment of inflammatory diseases and type-2 diabetes.

Mood stabilizers target cellular plasticity and resilience cascades: implications for the development of novel therapeutics

Bipolar disorder is a devastating disease with a lifetime incidence of about 1% in the general population. Suicide is the cause of death in 10 to 15% of patients and in addition to suicide, mood disorders are associated with many other harmful health effects. Mood stabilizers are medications used to treat bipolar disorder. In addition to their therapeutic effects for the treatment of acute manic episodes, mood stabilizers are useful as prophylaxis against future episodes and as adjunctive antidepressant medications. The most established and investigated mood-stabilizing drugs are lithium and valproate but other anticonvulsants (such as carbamazepine and lamotrigine) and antipsychotics are also considered as mood stabilizers. Despite the efficacy of these diverse medications, their mechanisms of action remain, to a great extent, unknown. Lithium's inhibition of some enzymes, such as inositol monophosphatase and glycogen synthase kinase-3, probably results in its mood-stabilizing effects. Valproate may share its anticonvulsant target with its mood-stabilizing target or may act through other mechanisms. It has been shown that lithium, valproate, and/or carbamazepine regulate numerous factors involved in cell survival pathways, including cyclic adenine monophospate response element-binding protein, brain-derived neurotrophic factor, bcl-2, and mitogen-activated protein kinases. These drugs have been suggested to have neurotrophic and neuroprotective properties that ameliorate impairments of cellular plasticity and resilience underlying the pathophysiology of mood disorders. This article also discusses approaches to develop novel treatments specifically for bipolar disorder.

α-Methyltryptamine sulfonamide derivatives as novel glucocorticoid receptor ligands

Alpha-methyltryptamine sulfonamides were identified as human glucocorticoid receptor (hGR) ligands in an ultra high throughput screening (UHTS) campaign. Described will be the hit-to-lead activities, including parallel and single point analog synthesis to map the scaffold. Ligands were identified that exhibited 30 nM binding to hGR. The SAR and selectivity of these compounds will be discussed.

Cross-talk between nuclear receptors and nuclear factor kappaB

A variety of studies have shown that some activated nuclear receptors (NRs), especially the glucorticoid receptor, the estrogen receptor and peroxisome proliferator-activated receptor, can inhibit the activity of the transcription factor nuclear factor kappaB (NF-kappaB), which plays a key role in the control of genes involved in inflammation, cell proliferation and apoptosis. This review describes the molecular mechanisms of cross-talk between NRs and NF-kappaB and the biological relevance of this cross-talk. The importance and mechanistic aspects of selective NR modulation are discussed. Also included are future research prospects, which will lead to a new era in the field of NR research with the aim of specifically inhibiting NF-kappaB-driven gene expression for anti-inflammatory, anti-tumor and immune-modulatory purposes.

Discovery of 6-N,N-Bis(2,2,2-trifluoroethyl)amino- 4-trifluoromethylquinolin-2(1H)-one as a Novel Selective Androgen Receptor Modulator

The androgen receptor is a member of the extended family of nuclear receptors and is widely distributed throughout the body. Androgen therapy is used to compensate for low levels of the natural hormones testosterone (T) and dihydrotestosterone and consists of administration of T, prodrugs thereof, or synthetic androgens. However, currently available androgens have many drawbacks. We identified 6-dialkylamino-4-trifluoromethylquinolin-2(1H)-ones as orally available tissue-selective androgen receptor modulators.

Insight into the molecular mechanisms of glucocorticoid receptor action promotes identification of novel ligands with an improved therapeutic index

Glucocorticoids are highly effective in the therapy of inflammatory and autoimmune disorders. Their beneficial action is restricted because of their adverse effects upon prolonged usage. Topical glucocorticoids that act locally have been developed to significantly reduce systemic side effects. Nonetheless, undesirable cutaneous effects such as skin atrophy persist from the use of topical glucocorticoids. There is therefore a high medical need for drugs as effective as glucocorticoids but with a reduced side-effect profile. Glucocorticoids function by binding to and activating the glucocorticoid receptor that positively or negatively regulates the expression of specific genes. Several experiments suggest that the negative regulation of gene expression by the glucocorticoid receptor accounts for its anti-inflammatory action. This occurs through direct or indirect binding of the receptor to transcription factors such as activator protein-1, nuclear factor-kappaB or interferon regulatory factor-3 that are already bound to their regulatory sites. The positive action of the receptor occurs through homodimer binding of the receptor to discrete nucleotide sequences and this possibly contributes to some of the adverse effects of the hormone. Glucocorticoid receptor ligands that promote the negative regulatory action of the receptor with reduced positive regulatory function should therefore show improved therapeutic potential. A complete separation of the positive from the negative regulatory activities of the receptor has so far not been possible because of the interdependent nature of the two regulatory processes. Nevertheless, considerable improvement in the therapeutic action of glucocorticoid receptor ligands is being achieved through the use of key molecular targets for screening novel glucocorticoid receptor ligands.

New and improved glucocorticoid receptor ligands

The therapeutic and prophylactic use of glucocorticoids is widespread due to their powerful anti-inflammatory, antiproliferative and immunomodulatory activity. However, long-term use of these drugs can result in severe dose-limiting side effects. One of the most critical and debilitating side effects is osteoporosis, which leads to increased risk of fractures. Glucocorticoids damage bone through several different mechanisms. The search for novel glucocorticoids that have reduced side effects in bone and other tissues is being driven by the identification of new mechanisms of action of the glucocorticoid receptor. This may facilitate the detection of new, safer therapies with efficacies equivalent to currently prescribed steroids.

Adrenocortical hypertension

Primary aldosteronism, congenital adrenal hyperplasia, Cushing's syndrome, glucocorticoid-remediable aldosteronism, and corticotropin-dependent forms of adrenal pathology can cause hypertension by excessive production of adrenocortical hormones. Although traditional biochemical assays continue to be used, genetic testing has simplified the diagnosis of glucocorticoid-remediable aldosteronism. Also new interventional radiologic approaches for the diagnosis and treatment of corticotropin-dependent forms of Cushing's syndrome are available. Medical and surgical approaches, however, still remain viable options for treatment.

A fully dissociated compound of plant origin for inflammatory gene repression

The identification of selective glucocorticoid receptor (GR) modifiers, which separate transactivation and transrepression properties, represents an important research goal for steroid pharmacology. Although the gene-activating properties of GR are mainly associated with undesirable side effects, its negative interference with the activity of transcription factors, such as NF-kappaB, greatly contributes to its antiinflammatory and immune-suppressive capacities. In the present study, we found that Compound A (CpdA), a plant-derived phenyl aziridine precursor, although not belonging to the steroidal class of GR-binding ligands, does mediate gene-inhibitory effects by activating GR. We demonstrate that CpdA exerts an antiinflammatory potential by down-modulating TNF-induced proinflammatory gene expression, such as IL-6 and E-selectin, but, interestingly, does not at all enhance glucocorticoid response element-driven genes or induce GR binding to glucocorticoid response element-dependent genes in vivo. We further show that the specific gene-repressive effect of CpdA depends on the presence of functional GR, displaying a differential phosphorylation status with CpdA as compared with dexamethasone treatment. The antiinflammatory mechanism involves both a reduction of the in vivo DNA-binding activity of p65 as well as an interference with the transactivation potential of NF-kappaB. Finally, we present evidence that CpdA is as effective as dexamethasone in counteracting acute inflammation in vivo and does not cause a hyperglycemic side effect. Taken together, this compound may be a lead compound of a class of antiinflammatory agents with fully dissociated properties and might thus hold great potential for therapeutic use.

Synthetic progestins used in HRT have different glucocorticoid agonist properties

The synthetic progestins, medroxyprogesterone acetate (MPA) and norethisterone acetate (NET-EN or NET-A), are widely used as female contraceptive agents and in hormone replacement therapy (HRT). Competitive binding revealed that MPA displays a higher relative binding affinity than NET-A and progesterone (prog) for the human GR (Kd of 4.2 nM for dexamethasone (dex) and Ki's of 10.8, 270 and 215 nM for MPA, NET-A and prog, respectively). Furthermore, MPA displays much greater glucocorticoid (GC) transactivation agonist potency than NET-A or prog (EC50s of 1.1, 7.2, >1000 and 280 nM for dex, MPA, NET-A and prog, respectively) and much greater GC agonist potency for transrepression than NET-A or prog (EC50s of 0.21, 2.7, >100 and 26 nM for dex, MPA, NET-A and prog, respectively). In addition, MPA induces phosphorylation of the GR at Ser 211 to a much greater extent than NET-A or prog and protects the GR from partial trypsin digestion in vitro to a much greater extent than NET-A or prog at saturating concentrations. Together these results suggest that the differences in biological activity of the progestins are not merely due to differences in their affinity for the GR but also due to the induction of different conformational changes in the liganded-GR. MPA and NET-A therefore display very different GC-like properties compared to each other and to prog, and are likely to exhibit different side effects via the GR.

The search for safer glucocorticoid receptor ligands

Steroidal glucocorticoids are commonly used due to their powerful antiinflammatory activity. However, despite their excellent efficacy, severe side effects frequently limit the use of these drugs. The search for novel glucocorticoids with reduced side effects has been intensified by the discovery of new molecular details regarding the function of the glucocorticoid receptor. These new insights may pave the way for novel, safer therapies that retain the efficacy of currently prescribed steroids.

Progesterone antagonizes the permissive action of estradiol on tumor necrosis factor-alpha-induced apoptosis of anterior pituitary cells

We previously reported that TNF-alpha-induced apoptosis of lactotropes is estrogen dependent and predominant at proestrus. Here we observed that TNF-alpha (50 ng/ml) failed to induce apoptosis of anterior pituitary cells from ovariectomized rats cultured in the presence of progesterone (10(-6) m). However, progesterone blocked the apoptotic effect of TNF-alpha in anterior pituitary cells and lactotropes cultured with 17beta-estradiol (10(-9) m). In addition, 17beta-estradiol induced apoptosis of somatotropes and triggered the proapoptotic action of TNF-alpha in these cells, effects completely blocked by ICI 182 780 (10(-6) m), an estrogen receptor antagonist. Progesterone reverted the permissive effect of 17beta-estradiol on TNF-alpha-induced apoptosis of somatotropes. TNF-alpha induced apoptosis of somatotropes from rats killed at proestrus but not at diestrus. The antiprogestine ZK 98,299 (10(-6) m) completely inhibited the protective action of progesterone on TNF-alpha-induced apoptosis of anterior pituitary cells, lactotropes, and somatotropes. Although progesterone can interact with glucocorticoid receptors, dexamethasone (10(-6) m) had no effect on TNF-alpha-induced apoptosis of anterior pituitary cells, lactotropes, and somatotropes. Our results show that progesterone, by interacting with progesterone receptors, antagonizes the permissive action of estrogens on TNF-alpha-induced apoptosis of lactotropes and somatotropes. These observations suggest that the steroid milieu may modulate the apoptotic response of anterior pituitary cells during the estrous cycle.

Selective glucocorticoid receptor nonsteroidal ligands completely antagonize the dexamethasone mediated induction of enzymes involved in gluconeogenesis and glutamine metabolism

Glucocorticoids (GCs) are vital multi-faceted hormones with recognized effects on carbohydrate, protein and lipid metabolism. Previous studies with the steroid antagonist, RU486 have underscored the essential role of GCs in the regulation of these metabolic pathways. This article describes the discovery and characterization of novel GRalpha selective nonsteroidal antagonists (NSGCAs). NSGCAs 2 and 3 are spirocyclic dihydropyridine derivatives that selectively bind the GRalpha with IC(50s) of 2 and 1.5 nM, respectively. Importantly, these compounds are full antagonists of the induction by dexamethasone (Dex) of marker genes for glucose and glutamine metabolism; the tyrosine amino transferase (TAT) and glutamine synthetase (GS) enzymes, respectively. In contrast, GC-dependent transcriptional repression of the collagenase 1 (MMP-1) enzyme, an established GRalpha responsive proinflammatory gene; is poorly antagonized by these compounds. These NSGCAs might have useful applications as tools in metabolic research and drug discovery.

Glucocorticoid receptor antagonists: new tools to investigate disorders characterized by cortisol hypersecretion

Increased cortisol levels have been observed in patients suffering from a number of metabolic and psychiatric disorders. In some of these disorders a causal relationship has been suggested between the increased cortisol secretion and the observed clinical phenomena. Glucocorticoid receptor antagonists which block cortisol effects might have a benefit in both the diagnosis and treatment of these disorders. Selective glucocorticoid receptor antagonists with in vivo potency have not been described thus far, partly due to the similarity between the glucocorticoid and progesterone receptors. In the present studies, we report on three different chemical classes derived from the glucocorticoid/progestagen antagonist RU486. Selected compounds from the classes 11-monoaryl steroids, 11,21-bisaryl steroids and 11-aryl, 16-hydroxy steroids proved to be selective glucocorticoid receptor binders with in vivo antagonistic activity. Most compounds were able to pass the blood-brain barrier. These compounds offer the opportunity to investigate and possibly treat patients with a disturbed hypothalamus-pituitary-adrenal axis without side effects caused by an antiprogestagenic action.

Modulatory Effects of l-Carnitine on Glucocorticoid Receptor Activity

L-carnitine (3-hydroxy-4-N,N,N-trimethylaminobutyrate) is a conditionally essential nutrient with a major role in cellular energy metabolism. It is available in the United States as both a prescription drug and an over-the-counter nutritional supplement. Accumulating evidence from both animal and human studies indicates that pharmacologic doses of L-carnitine (LCAR) have immunomodulatory effects resembling those of glucocorticoids (GC). On the other hand, in contrast to GC, which cause bone loss, LCAR seems to have positive effects on bone metabolism. To explore the molecular bases of this GC-like activity of LCAR, we investigated its effects on glucocorticoid receptor (GR)-modulated cytokine release ex vivo, and on the transcriptional activity, intracellular trafficking, and binding of GR in vitro. At high noncytotoxic doses, LCAR (a) suppressed the lipopolysaccharide-stimulated release of tumor necrosis factor alpha and interleukin-12 from primary human monocytes in a GC-like fashion, (b) stimulated the transcriptional activity of GR on the GC-responsive promoters, (c) triggered nuclear translocation of green fluorescent protein (GFP)-fused GR, and (d) reduced the whole cell binding of [(3)H]-dexamethasone to GR. These results suggest that LCAR is a "nutritional modulator" of the GR, by acting as an agonist-like compound. Since LCAR appears to have positive effects on bone metabolism, in contrast to GC, LCAR may share some of the therapeutic properties of GC, particularly on the immune system, but not their deleterious side effects on some of other organs/tissues. Thus, LCAR is potentially a useful alternative compound of GC in particular therapeutic situations. The clinical and therapeutic implications of these findings, as well as a better understanding of their mechanisms, warrant further research.

Emerging experimental therapeutics for bipolar disorder: clues from the molecular pathophysiology

Bipolar affective disorder (manic-depressive illness) is a common, severe, chronic, and often life-threatening illness, associated with significant comorbidity. The recognition of the significant morbidity and mortality of patients with bipolar disorder, as well as the growing appreciation that a high percentage of patients respond poorly to existing treatments, has made the task of discovering new therapeutic agents, that are both efficacious and have few side effects increasingly more important. Most recent agents introduced into the pharmacopeia for the treatment of bipolar disorder have been anticonvulsants and atypical antipsychotics. We propose that novel treatments developed specifically for bipolar disorder will arise from (1) understanding more precisely the molecular mechanisms of treatments that are clearly efficacious or (2) developing medications based on the knowledge obtained of the underlying pathophysiology of bipolar disorder. Knowledge with regard to the underlying pathophysiology of bipolar disorder is increasing at a rapid pace, including alterations in intracellular signaling cascades as well as impairments of cellular plasticity and resilience in critical neuronal circuits. We propose that therapeutics designed to enhance cellular plasticity and resilience and that counter maladaptive stress-responsive systems may have considerable utility for the treatment of bipolar disorder. Therapeutic strategies designed to address cellular resilience and plasticity include the regulation of neurotrophic pathways, glucocorticoid signaling, phosphodiesterase activity, and glutamatergic throughput and mitochondrial function. While the task of developing novel medications for bipolar disorder is truly daunting, these and similar approaches will ultimately lead to better medications for the millions who suffer from this devastating illness.

Synthesis, activity, metabolic stability, and pharmacokinetics of glucocorticoid receptor modulator–statin hybrids

The synthesis, activity, metabolic stability, and pharmacokinetics of steroidal and nonsteroidal glucocorticoid receptor modulator-statin hybrids is reported. Potent steroidal antagonist-statin hybrids like 22 (h-GR binding IC(50)=7 nM) and nonsteroidal modulator hybrids like 16 (h-GR binding IC(50)=2 nM) were discovered. Appending a 'statin'-like diol-acid group to the modulators dramatically improved metabolic stability (and in some cases hepatocyte activity), but did not impart hepatoselectivity.

Adrenocortical hypertension

Primary aldosteronism, congenital adrenal hyperplasia, Cushing's syndrome, glucocorticoid-remediable aldosteronism, and corticotropin-dependent forms of adrenal pathology can cause hypertension by excessive production of adrenocortical hormones. Although traditional biochemical assays continue to be used, genetic testing has simplified the diagnosis of glucocorticoid-remediable aldosteronism. Also, new interventional radiologic approaches for the diagnosis and treatment of corticotropin-dependent forms of Cushing's syndrome are available. Medical and surgical approaches, however, still remain viable options for treatment.

The interplay between the glucocorticoid receptor and nuclear factor-kappaB or activator protein-1: molecular mechanisms for gene repression

The inflammatory response is a highly regulated physiological process that is critically important for homeostasis. A precise physiological control of inflammation allows a timely reaction to invading pathogens or to other insults without causing overreaction liable to damage the host. The cellular signaling pathways identified as important regulators of inflammation are the signal transduction cascades mediated by the nuclear factor-kappaB and the activator protein-1, which can both be modulated by glucocorticoids. Their use in the clinic includes treatment of rheumatoid arthritis, asthma, allograft rejection, and allergic skin diseases. Although glucocorticoids have been widely used since the late 1940s, the molecular mechanisms responsible for their antiinflammatory activity are still under investigation. The various molecular pathways proposed so far are discussed in more detail.