Oestrogen receptors and selective oestrogen receptor modulators: molecular and cellular pharmacology

New potential selective estrogen receptor modulators in traditional Chinese medicine for treating menopausal syndrome

Women go through several predictable conditions and symptoms during menopause that are caused by age, changes in sex hormone levels, and other factors. Conventional menopause hormone therapy has raised serious concerns about the increased risks of cancers, blood clots, depression, etc. Selective estrogen receptor modulators (SERMs) that can be both agonists and antagonists of estrogen receptors in a tissue-specific manner are being developed to reduce the health concerns associated with menopause hormone therapy. Here, we have searched the Chinese national traditional Chinese medicine (TCM) patent database to identify potential SERM-like compounds with reduced health risks. TCM has been widely used for treating complex symptoms associated with menopause syndrome and thus can be a particularly rich source for pharmaceutical alternatives with SERM properties. After extensive literature review and molecular simulation, we conclude that protopanaxatriol, paeoniflorin, astragalin, catalpol, and hyperoside among others may be particularly promising as SERM-like compounds in treating the menopausal syndrome. Compounds in TCM hold promise in yielding comparable outcomes to hormone therapy but with reduced associated risks, thus presenting promising avenues for their clinical applications.

The G Protein-Coupled Estrogen Receptor (GPER): A Critical Therapeutic Target for Cancer

Estrogens have been implicated in the pathogenesis of various cancers, with increasing concern regarding the overall rising incidence of disease and exposure to environmental estrogens. Estrogens, both endogenous and environmental, manifest their actions through intracellular and plasma membrane receptors, named ERα, ERβ, and GPER. Collectively, they act to promote a broad transcriptional response that is mediated through multiple regulatory enhancers, including estrogen response elements (EREs), serum response elements (SREs), and cyclic AMP response elements (CREs). Yet, the design and rational assignment of antiestrogen therapy for breast cancer has strictly relied upon an endogenous estrogen-ER binary rubric that does not account for environmental estrogens or GPER. New endocrine therapies have focused on the development of drugs that degrade ER via ER complex destabilization or direct enzymatic ubiquitination. However, these new approaches do not broadly treat all cancer-involved receptors, including GPER. The latter is concerning since GPER is directly associated with tumor size, distant metastases, cancer stem cell activity, and endocrine resistance, indicating the importance of targeting this receptor to achieve a more complete therapeutic response. This review focuses on the critical importance and value of GPER-targeted therapeutics as part of a more holistic approach to the treatment of estrogen-driven malignancies.

Effect of Parquetina nigrescens (Afzel.) Leaves on Letrozole-Induced PCOS in Rats: a Molecular Insight into Its Phytoconstituents

Polycystic ovarian syndrome (PCOS) is one of the common causes of female infertility in women of reproductive age. P. nigrescens is a plant used in the treatment of various diseases including menstrual disorders. This study investigated the effect of ethanolic extracts of P. nigrescens leaves on the estrous cycle, fasting blood glucose, and hormonal and lipid profile in letrozole-induced PCOS rats and also evaluated the molecular mechanism of the active constituents using computational methods. After the induction of PCOS with letrozole, rats were treated orally for 14 days with distilled water (1 mg/kg/day), clomiphene citrate (2 mg/kg/day), metformin (7.14 mg/kg/day), and ethanolic extract of P. nigrescens (50 and 100 mg). Thereafter, selected biochemical parameters were assayed to determine the extract's effect on the estrous cycle. Molecular docking and molecular dynamics simulation (MDS) were carried out to determine the binding affinity and relative stability of the ligand-receptor complexes. Letrozole-induced PCOS rats showed irregular estrous cyclicity, elevated (p > 0.05) triglycerides, low-density lipoprotein cholesterol (LDL), total cholesterol, insulin, testosterone, and luteinizing hormone (LH) concentration, low (p > 0.05) progesterone, low follicle-stimulating hormone (FSH), high-density lipoprotein cholesterol (HDL), and high fasting blood glucose concentration compared to that of the control group. The reproductive, biochemical, and structural alterations were reversed by the administration of ethanolic extract of P. nigrescens leaves (50 mg/kg) which restored the estrous cycle after 14 days of treatment. However, the ethanolic extracts of P. nigrescens (100 mg/kg) significantly increased (p > 0.05) FSH, HDL, and progesterone concentrations but decreased the LH, progesterone, and total cholesterol. Of all 44 compounds identified in GCMS analysis of an ethanolic extract of P. nigrescens leaves, only 2-ethylbutyl heptyl ester (CID 91705405) had a higher binding affinity for hormonal receptors and enzymes responsible for hepatic gluconeogenesis compared to standard drugs used in the study. CID 91705405 was also relatively stable over 100 ns of MDS. This compound is therefore revealed to have the potential to modulate both endocrine and metabolic pathways involved in PCOS. The ethanolic extract of P. nigrescens leaves can therefore be considered in the management/treatment of the reproductive and metabolic disorders related to PCOS subject to further experimental validation.

Endocrine resistance and epigenetic reprogramming in estrogen receptor positive breast cancer

Despite the enormous advances during the last three decades, breast cancer continues to be the most frequent type of cancer as well as one of the most frequent cancer-related causes of death in women. Therapeutic management of patients with hormone receptor-positive breast cancer becomes very often a challenge, since de novo or acquired resistance deprives a significant percentage of the patients from the clinical benefit of the well-tolerated hormone therapy. Several molecular mechanisms are implicated in resistance to endocrine therapy, including changes in hormone receptor signaling, activation of parallel signaling pathways, modifications of cell cycle regulators, activation of different transcription factors as well as changes in stem cells activity. In addition, a growing number of studies supports the pivotal role of epigenetic changes not only in the initiation and progression of breast cancer, but also in resistance to endocrine therapy. These changes refer to DNA methylation, histone post-translational modifications as well as to ncRNAs alterations. In this review, we provide an overview of epigenetic mechanisms underlying the endocrine resistance focusing exclusively on breast cancer patients.

Estrogen Receptors in Polycystic Ovary Syndrome

Female infertility is mainly caused by ovulation disorders, which affect female reproduction and pregnancy worldwide, with polycystic ovary syndrome (PCOS) being the most prevalent of these. PCOS is a frequent endocrine disease that is associated with abnormal function of the female sex hormone estrogen and estrogen receptors (ERs). Estrogens mediate genomic effects through ERα and ERβ in target tissues. The G-protein-coupled estrogen receptor (GPER) has recently been described as mediating the non-genomic signaling of estrogen. Changes in estrogen receptor signaling pathways affect cellular activities, such as ovulation; cell cycle phase; and cell proliferation, migration, and invasion. Over the years, some selective estrogen receptor modulators (SERMs) have made substantial strides in clinical applications for subfertility with PCOS, such as tamoxifen and clomiphene, however the role of ER in PCOS still needs to be understood. This article focuses on the recent progress in PCOS caused by the abnormal expression of estrogen and ERs in the ovaries and uterus, and the clinical application of related targeted small-molecule drugs.

Estrogen and estrogen receptors in kidney diseases

Acute kidney injury (AKI) and chronic kidney disease (CKD) are posing great threats to global health within this century. Studies have suggested that estrogen and estrogen receptors (ERs) play important roles in many physiological processes in the kidney. For instance, they are crucial in maintaining mitochondrial homeostasis and modulating endothelin-1 (ET-1) system in the kidney. Estrogen takes part in the kidney repair and regeneration via its receptors. Estrogen also participates in the regulation of phosphorus homeostasis via its receptors in the proximal tubule. The ERα polymorphisms have been associated with the susceptibilities and outcomes of several renal diseases. As a consequence, the altered or dysregulated estrogen/ERs signaling pathways may contribute to a variety of kidney diseases, including various causes-induced AKI, diabetic kidney disease (DKD), lupus nephritis (LN), IgA nephropathy (IgAN), CKD complications, etc. Experimental and clinical studies have shown that targeting estrogen/ERs signaling pathways might have protective effects against certain renal disorders. However, many unsolved problems still exist in knowledge regarding the roles of estrogen and ERs in distinct kidney diseases. Further research is needed to shed light on this area and to enable the discovery of pathway-specific therapies for kidney diseases.

Molecular Signaling Pathways and Essential Metabolic Elements in Bone Remodeling: An Implication of Therapeutic Targets for Bone Diseases

Bone is one of the dynamic tissues in the human body that undergoes continuous remodelling through subsequent actions of bone cells, osteoclasts, and osteoblasts. Several signal transduction pathways are involved in the transition of mesenchymal stem cells into osteoblasts. These primarily include Runx2, ATF4, Wnt signaling and sympathetic signalling. The differentiation of osteoclasts is controlled by M-CSF, RANKL, and costimulatory signalling. It is well known that bone remodelling is regulated through receptor activator of nuclear factor-kappa B ligand followed by binding to RANK, which eventually induces the differentiation of osteoclasts. The resorbing osteoclasts secrete TRAP, cathepsin K, MMP-9 and gelatinase to digest the proteinaceous matrix of type I collagen and form a saucer-shaped lacuna along with resorption tunnels in the trabecular bone. Osteoblasts secrete a soluble decoy receptor, osteoprotegerin that prevents the binding of RANK/RANKL and thus moderating osteoclastogenesis. Moreover, bone homeostasis is also regulated by several growth factors like, cytokines, calciotropic hormones, parathyroid hormone and sex steroids. The current review presents a correlation of the probable molecular targets underlying the regulation of bone mass and the role of essential metabolic elements in bone remodelling. Targeting these signaling pathways may help to design newer therapies for treating bone diseases.

Selective Estrogen Receptor Degraders (SERDs): A Promising Strategy for Estrogen Receptor Positive Endocrine-Resistant Breast Cancer

Estrogen receptor (ER) plays important roles in gene transcription and the proliferation of ER positive breast cancers. Selective modulation of ER has been a therapeutic target for this specific type of breast cancer for more than 30 years. Selective estrogen receptor modulators (SERMs) and aromatase inhibitors (AIs) have been demonstrated to be effective therapeutic approaches for ER positive breast cancers. Unfortunately, 30-50% of ER positive tumors become resistant to SERM/AI treatment after 3-5 years. Fulvestrant, the only approved selective estrogen receptor degrader (SERD), is currently an important therapeutic approach for the treatment of endocrine-resistant breast cancers. The poor pharmacokinetic properties of fulvestrant have inspired the development of a new generation of oral SERDs to overcome drug resistance. In this review, we describe recent advances in ERα structure, functions, and mechanisms of endocrine resistance and summarize the development of oral SERDs in both academic and industrial areas.

G Protein-Coupled Estrogen Receptor, GPER1, Offers a Novel Target for the Treatment of Digestive Diseases

There are gender differences between men and women in many physiological functions and diseases, which indicates that female sex hormones may be important. Traditionally, estrogen exerts its biological activities by activating two classical nuclear estrogen receptors, ESR1 and ESR2. However, the roles of estrogen in the regulation of physiological functions and the pathogenesis of diseases become more complicated with the identification of the G protein-coupled estrogen receptor (GPER1). Although many GPER1-specific ligands have been developed, the therapeutic mechanisms of exclusively targeting GPER1 are not yet well understood. Translational applications and clinical trial efforts for the identified GPER1 ligands have been focused primarily on the reproductive, cardiovascular, nervous, endocrine, and immune systems. More recently, research found that GPER1 may play an important role in regulating the digestive system. Cholesterol gallstone disease, a major biliary disease, has a higher prevalence in women than in men worldwide. Emerging evidence implies that GPER1 could play an important role, independent of the classical ESR1, in the pathophysiology of cholesterol gallstones in women. This review discusses the complex signaling pathways of three estrogen receptors, highlights the development of GPER1-specific ligands, and summarizes the latest advances in the role of GPER1 in the pathogenesis of gallstone formation.

Sex hormones in the cardiovascular system

Gender-associated differences in the development of cardiovascular diseases have been described in humans and animals. These differences could explain the low incidence of cardiovascular disease in women in the reproductive period, such as stroke, hypertension, and atherosclerosis. The cardiovascular protection observed in females has been attributed to the beneficial effects of estrogen on endothelial function. Besides estrogen, sex hormones are able to modulate blood pressure by acting on important systems as cardiovascular, renal, and neural. They can have complementary or antagonistic actions. For example, testosterone can raise blood pressure by stimulating the renin-angiotensin-aldosterone system, whereas estrogen alone or combined with progesterone has been associated with decreased blood pressure. The effects of testosterone in the development of cardiovascular disease are contradictory. Although some researchers suggest a positive effect, others indicate negative actions of testosterone. Estrogens physiologically stimulate the release of endothelium-derived vasodilator factors and inhibit the renin-angiotensin system. Although the cardioprotective effects of estrogen are widely appreciated, little is known about the effects of progesterone, which is commonly used in hormone replacement therapy. Progesterone has both vasodilatory and vasoconstrictive effects in the vasculature, depending on the location of the vessel and the level of exposure. Nevertheless, the mechanisms through which sex hormones modulate blood pressure have not been fully elucidated. Therefore, the characterization of those could lead to a better understanding of hypertension in women and men and perhaps to improved forms of therapy.

Activation of estrogen receptor α enhances bradykinin signaling in peripheral sensory neurons of female rats

Numerous studies have demonstrated that females have a higher risk of experiencing several pain disorders with either greater frequency or severity than males. Although the mechanisms that underlie this sex disparity remain unclear, several studies have shown an important role for sex steroids, such as estrogen, in the modulation of nociception. Receptors for estrogen are present in primary afferent neurons in the trigeminal and dorsal root ganglia, and brief exposure to estrogen increases responses to the inflammatory mediator bradykinin (BK). However, the mechanism for estrogen-mediated enhancement of BK signaling is not fully understood. The aim of the present study was to evaluate the relative contributions of estrogen receptor α (ERα), ERβ, and G protein-coupled estrogen receptor 1 (GPER) to the enhanced signaling of the inflammatory mediator BK by 17β-estradiol (17β-E2) in primary sensory neurons from female rats in culture (ex vivo) and in behavioral assays of nociception in vivo. The effects of 17β-E2 on BK responses were mimicked by ERα-selective agonists and blocked by ERα-selective antagonists and by small interfering RNA knockdown of ERα. The data indicate that ERα is required for 17β-E2-mediated enhancement of BK signaling in peripheral sensory neurons in female rats.

Endocrine-disrupting chemical exposure and the American alligator: a review of the potential role of environmental estrogens on the immune system of a top trophic carnivore

Endocrine-disrupting chemicals (EDCs) alter cellular and organ system homeostasis by interfering with the body's normal physiologic processes. Numerous studies have identified environmental estrogens as modulators of EDC-related processes in crocodilians, notably in sex determination. Other broader studies have shown that environmental estrogens dysregulate normal immune function in mammals, birds, turtles, lizards, fish, and invertebrates; however, the effects of such estrogenic exposures on alligator immune function have not been elucidated. Alligators occupy a top trophic status, which may give them untapped utility as indicators of environmental quality. Environmental estrogens are also prevalent in the waters they occupy. Understanding the effects of these EDCs on alligator immunity is critical for managing and assessing changes in their health and is thus the focus of this review.

Estrogen receptor α and β in the normal immune system and in lymphoid malignancies

Estrogens regulate various normal and pathophysiological processes including cancers. Cellular signaling by estrogens is mediated by estrogen receptor α (ERα) and β (ERβ), respectively. Binding of agonists to the ERs affects gene transcription. The main endogenous estrogen, 17β-estradiol (E2), binds to both ERα and ERβ with similar affinity. However, the ligand-binding pocket of ERα and ERβ are slightly different which has allowed the development of selective ER ligands. Importantly, while estrogens via ERα stimulate proliferation, signaling via ERβ inhibits proliferation and promotes apoptosis. In both normal and cancer cells the ERs are co-expressed with ER splice variants which may modify the transcriptional activity of the wild-type receptors. Estrogens have prominent effects on immune functions and both ERα and ERβ are expressed in immune cells and lymphoid malignancies. With regard to lymphoid malignancies, most show estrogen influence as several epidemiological studies of lymphoid cancers demonstrate gender differences in incidence and prognosis with males being more affected. In line with these findings, recent results generated by us have shown that ERβ selective agonists inhibit growth and induce apoptosis in human and murine lymphomas in vivo in xenograft experiments. This suggests that ERβ selective agonists in the future may be useful in the treatment of lymphomas.

Rapid estrogen receptor signaling mediates estrogen-induced inhibition of vascular smooth muscle cell proliferation

OBJECTIVE

The proliferation of vascular smooth muscle cells (VSMCs) plays a crucial role in vascular diseases, such as atherosclerosis and restenosis, after percutaneous coronary intervention. Many studies have shown that estrogen inhibits VSMC proliferation in response to vascular injury in the mouse carotid injury model. However, the mechanisms that mediate these effects remain unclear. Here, we investigated the mechanisms by which estrogen inhibits VSMC proliferation.

APPROACH AND RESULTS

We established a novel transgenic mouse line, referred to as the disrupting peptide mice, in which rapid estrogen receptor (ER)-mediated signaling is abolished by overexpression of a peptide that prevents the ER from forming a signaling complex necessary for rapid signaling. Carotid artery VSMCs from disrupting peptide mice or littermate wild-type female mice were obtained by the explant method. In VSMCs derived from wild-type mice, estrogen significantly inhibited VSMC proliferation. Phosphorylation levels of Akt and extracellular regulated kinase induced by platelet derived growth factor were significantly inhibited by estrogen pretreatment. Estrogen enhanced complex formation between ERα and protein phosphatase 2A (PP2), and enhanced PP2A activity. The blockade of PP2A activity abolished the estrogen-induced antiproliferative effect on VSMCs. In contrast, none of these effects of estrogen observed in the wild-type VSMCs were observed in VSMCs derived from disrupting peptide mice. These results support that rapid, non-nuclear ER signaling is required for estrogen-induced inhibition of VSMC proliferation, and further that PP2A activation by estrogen mediates estrogen-induced antiproliferative effects.

CONCLUSIONS

These findings support that PP2A activation via rapid, non-nuclear ER signaling may be a novel target for therapeutic approaches to inhibit VSMC proliferation, which plays a central role in atherosclerosis and restenosis.

Discovery of estrogen receptor modulators: a review of virtual screening and SAR efforts

IMPORTANCE OF THE FIELD

Virtual screening (VS) coupled with structural biology is a significantly important approach to increase the number and enhance the success of projects in lead identification stage of drug discovery process. Recent advances and future directions in estrogen therapy have resulted in great demand for identifying the potential estrogen receptor (ER) modulators with more activity and selectivity.

AREAS COVERED IN THIS REVIEW

This review presents the current state of the art in VS and structure-activity relationship of ER modulators in recent discovery, and discusses the strengths and weaknesses of the technology.

WHAT THE READER WILL GAIN

Readers will gain an overview of the current platforms of in silico screening for discovery of ER modulators; they will learn which structural information is significantly correlated with the bioactivity of ER modulators and what novel strategies should be considered for the creation of more effective chemical structures.

TAKE HOME MESSAGE

With the goal of reducing toxicity and/or improving efficacy, challenges to the successful modeling of endocrine agents are proposed, providing new paradigms for the design of ER inhibitors.

Estrogens and selective estrogen receptor modulators regulate gene and protein expression in the mesenteric arteries

Estrogen has both beneficial and detrimental effects on the cardiovascular system. Selective estrogen receptor modulators (SERMs) exhibit partial estrogen agonist/antagonist activity in estrogen target tissues. Gene targets of estrogen and SERMs in the vasculature are not well-known. Thus, the present study tested the hypothesis that estrogens (ethinyl estradiol, estradiol benzoate, and equilin) and SERMs (tamoxifen and raloxifene) cause differential gene and protein expression in the vasculature. DNA microarray and real-time RT-PCR were used to investigate gene expression in the mesenteric arteries of estrogen and SERM treated ovariectomized rats. The genes shown to be differentially expressed included stearoyl-CoA desaturase (SCD), soluble epoxide hydrolase (sEH), secreted frizzled related protein-4 (SFRP-4), insulin-like growth factor-1 (IGF-1), phospholipase A2 group 1B (PLA2-G1B), and fatty acid synthase (FAS). Western blot further confirmed the differential expression of sEH, SFRP-4, FAS, and SCD protein. These results reveal that estrogens and SERMs cause differential gene and protein expression in the mesenteric artery. Consequently, the use of these agents may be associated with a unique profile of functional and structural changes in the mesenteric arterial circulation.

Molecularly targeted endocrine therapies for breast cancer

The identification of the estrogen receptor (ER) provided the first target for antiestrogenic therapeutic agents. Endocrine therapies, either by blocking or downregulating the receptor or by suppressing the estrogen production, inhibit the proliferative effect of estradiol on ER. While the activity on ER is considered a real target-mediated therapy, the effect on enzymatic activity involved in estrogen production (mainly inhibition of aromatase by aromatase inhibitors, AIs, and ovarian ablation) could be considered an "indirect" targeted strategy. In addiction to the direct ligand-ER signal, the complexity of endocrine and non endocrine pathways has led to combination therapies against different targets. Tamoxifen is the widely investigated, most used and representative of drugs blocking the ER and has been introduced in the advanced disease, in neoadjuvant and adjuvant setting and for chemo-prevention of high risk women. Its role has been challenged in the last years by the introduction of third generation aromatase inhibitors that have proven a higher activity than tamoxifen and different toxicity. Several other SERMs (selective estrogen receptor modulators) have been investigated, but none of them was clearly superior to tamoxifen. SERDs (selective estrogen receptor downregulators) act as pure estrogen antagonist. They are used in the treatment of advanced breast cancers and their role in other settings still needs further investigation. Here we discuss the well established data with SERMs, SERDs and AIs, mechanisms underlying resistance and rationale for recycling endocrine compounds and for simultaneously targeting different pathways.

Lasofoxifene: Evidence of its therapeutic value in osteoporosis

INTRODUCTION

Osteoporosis is a skeletal disorder characterized by compromised bone strength and increased risk of fracture. It is a common disorder in elderly subjects and represents a major public health problem, affecting up to 40% postmenopausal women and 15% of men. Among the several therapeutical interventions, hormone replacement therapy (HRT) was traditionally seen as the gold standard for preventing osteoporotic fractures in postmenopausal women, as well as for the management of menopausal symptoms. However HRT, especially if administered long-term, may lead to an increased risk of breast and, when unopposed by progestins, endometrial cancers. Alternative therapies include bisphosphonates and raloxifene, a selective estrogen receptor modulator (SERM). While the former have been associated with suboptimal adherence, the latter was considerably less potent than estrogen and its effect in the prevention of nonvertebral fractures remain uncertain.

AIMS

The purpose of this article is to review the clinical trials of lasofoxifene, a new SERM for the treatment of postmenopausal osteoporosis. The medical literature was reviewed for appropriate articles containing the terms "lasofoxifene" and SERMs".

EVIDENCE REVIEW

There are three (phase II or phase III) clinical trials that clearly demonstrate efficacy and safety of this new SERM in the suppression of bone loss and the prevention of vertebral and nonvertebral fractures. Moreover, lasofoxifene treatment also reduced breast cancer risk and the occurrence of vaginal atrophy.

PLACE IN THERAPY

With its increased potency and efficacy on the prevention of nonvertebral fractures lasofoxifene may be an alternative and cost-effective therapy for osteoporosis in postmenopausal women.

Structural overview of the nuclear receptor superfamily: insights into physiology and therapeutics

As ligand-regulated transcription factors, the nuclear hormone receptors are nearly ideal drug targets, with internal pockets that bind to hydrophobic, drug-like molecules and well-characterized ligand-induced conformational changes that recruit transcriptional coregulators to promoter elements. Yet, due to the multitude of genes under the control of a single receptor, the major challenge has been the identification of ligands with gene-selective actions, impacting disease outcomes through a narrow subset of target genes and not across their entire gene-regulatory repertoire. Here, we summarize the concepts and work to date underlying the development of steroidal and nonsteroidal receptor ligands, including the use of crystal structures, high-throughput screens, and rational design approaches for finding useful therapeutic molecules. Difficulties in finding selective receptor modulators require a more complete understanding of receptor interdomain communications, posttranslational modifications, and receptor-protein interactions that could be exploited for target gene selectivity.

Selective estrogen receptor modulator (SERM) for the treatment of osteoporosis in postmenopausal women: focus on lasofoxifene

Selective estrogen receptor modulators (SERMs) represent a class with a growing number of compounds that act as either estrogen receptor agonists or antagonists in a tissue-specific manner. This article reviews lasofoxifene, a new-generation SERM that has completed phase III development for the prevention and treatment of osteoporosis in postmenopausal women. Consistent with preclinical observations, this new SERM demonstrated improved skeletal efficacy over raloxifene and at an oral dose of 0.5 mg/day was effective in the prevention of both vertebral and nonvertebral fractures in postmenopausal women with osteoporosis. At the same dosage, lasofoxifene treatment also reduced estrogen receptor-positive breast cancer risk and the occurrence of vaginal atrophy, but, like the other SERMs, was associated with hot flushes and an increased risk of venous thromboembolic events. With its increased efficacy on the prevention of nonvertebral fractures than current available SERMs and its positive effects on the vagina, this new compound may represent an alternative and cost-effective therapy for osteoporosis in postmenopausal women.

Molecular mechanism of the inhibition of estradiol-induced endometrial epithelial cell proliferation by clomiphene citrate

We examined the molecular mechanisms of the antiestrogenic effects of clomiphene citrate (CC) in the endometrium using two types of cell lines, Ishikawa and EM-E6/E7/hTERT cells. CC or ICI182780 inhibited 17beta-estradiol (E2)-induced endometrial cell proliferation and transcriptional activation of the estrogen response element (ERE) gene. We directly visualized the ligand-estrogen receptor (ER)alpha interaction using green fluorescent protein (GFP)-tagged ER alpha in a single living cell. Whereas E2 changed the nuclear localization of GFP-ER alpha to a punctate distribution within 5 min, CC or ICI182780 changed the slower and less mobilization of GFP-ER alpha compared with E2. Pretreatment with CC or ICI182780 partly prevented the E2-induced nuclear redistribution of GFP-ER alpha. Fluorescence recovery after photobleaching revealed that GFP-ER alpha mobility treated with E2 was more rapid than that treated by CC or ICI182780. As coactivator recruitment to the ER is essential for ER-dependent transcription, we examined the interaction between ER alpha and steroid receptor coactivator-1 (SRC-1). The complex formation between ER alpha and SRC-1 was significantly increased by E2 but was prevented in the presence of CC or ICI182780 by coimmunoprecipitation. Moreover, the E2-induced colocalization of GFP-ER alpha and SRC-1 was prevented in the presence of CC or ICI182780 according to an immunofluorescence assay. We also observed that the reduction of SRC-1 using small interfering RNA for SRC-1 resulted in the inhibition of E2-induced cell proliferation and transcriptional activation of the ERE gene. Collectively, these results suggest that CC may inhibit E2-induced endometrial epithelial cell proliferation and ERE transactivation by inhibiting the recruitment of SRC-1 to ER alpha.

Effects of raloxifene on platelet functions in patients with postmenopausal osteoporosis

Many studies have addressed the effects of estrogenic compounds on platelet function. Raloxifene is a selective estrogen receptor modulator (SERM), which is currently used for the treatment of postmenopausal osteoporosis. At present, there are no clinical data about the effects of raloxifene on platelet function. The purpose of this study was to determine if raloxifene at therapeutic doses affects platelet function in patients with postmenopausal osteoporosis. The effects of raloxifene on platelet function were investigated using a commercial platelet function analyzer (PFA-100) with collagen epinephrine and collagen adenosine 5'-diphosphate (ADP) cartridges. We studied platelet function of 30 patients with postmenopausal osteoporosis before and 15 days after initiation of raloxifene 60 mg/daily. Closure times did not differ significantly between samples obtained before (117.8 +/- 20.5 s) and after raloxifene therapy (106.5 +/- 25.4 s) in collagen/epinephrine cartridges (P > 0.05). There was also no statistically significant difference in mean closure times with collagen/ADP cartridges at baseline (86.2 +/- 18.5 s) and after raloxifene therapy (84.4 +/- 13.8 s) (P > 0.05). Platelet counts (278.3 +/- 72.9 vs. 262.4 +/- 56.7 109/L, P > 0.05) and mean platelet volumes (8.9 +/- 1 vs. 9.1 +/- 1 fL, P > 0.05) were not different before and after raloxifene therapy. Although estrogen related compounds do affect platelet function, there is suggestive data in our study that raloxifene in therapeutic dose exhibit no effect on platelet function in patients with postmenopausal osteoporosis.

Ligand dissociation from estrogen receptor is mediated by receptor dimerization: evidence from molecular dynamics simulations

Estrogen Receptor (ER) is an important target for pharmaceutical design. Like other ligand-dependent transcription factors, hormone binding regulates ER transcriptional activity. Nevertheless, the mechanisms by which ligands enter and leave ERs and other nuclear receptors remain poorly understood. Here, we report results of locally enhanced sampling molecular dynamics simulations to identify dissociation pathways of two ER ligands [the natural hormone 17beta-estradiol (E(2)) and the selective ER modulator raloxifene (RAL)] from the human ERalpha ligand-binding domain in monomeric and dimeric forms. E(2) dissociation occurs via three different pathways in ER monomers. One resembles the mousetrap mechanism (Path I), involving repositioning of helix 12 (H12), others involve the separation of H8 and H11 (Path II), and a variant of this pathway at the bottom of the ligand-binding domain (Path II'). RAL leaves the receptor through Path I and a Path I variant in which the ligand leaves the receptor through the loop region between H11 and H12 (Path I'). Remarkably, ER dimerization strongly suppresses Paths II and II' for E(2) dissociation and modifies RAL escape routes. We propose that differences in ligand release pathways detected in the simulations for ER monomers and dimers provide an explanation for previously observed effects of ER quaternary state on ligand dissociation rates and suggest that dimerization may play an important, and hitherto unexpected, role in regulation of ligand dissociation rates throughout the nuclear receptor family.

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.

Effects of estrogens and selective estrogen receptor modulators on vascular reactivity in the perfused mesenteric vascular bed

Estrogens and selective estrogen receptor modulators (SERMs), such as raloxifene (RAL) and tamoxifen (TAM), acutely relax arteries, but the long-term effects of estrogens and SERMs on vascular reactivity in the mesenteric vasculature have not been well defined. In this study, we used an isolated, perfused mesenteric vascular bed technique to investigate the effect of chronic treatment of estrogens and SERMs on vascular reactivity of the mesenteric bed. Ovariectomized female Sprague-Dawley rats were treated by gavage with vehicle (control, 2-hydroxypropyl-β-cyclodextrin), ethinyl estradiol, estradiol benzoate, equilin (EQ), TAM, or RAL for 3 wk. EQ and TAM increased vasoconstriction in response to all three vasoconstrictors tested (KCl, norepinephrine, and 5-HT). Ethinyl estradiol increased vasoconstriction in response to KCl and 5-HT, whereas responses to estradiol benzoate and RAL were less consistent. Only EQ (134 ± 4 mmHg) and TAM (104 ± 4 mmHg) changed mean arterial blood pressure compared with control (117 ± 4 mmHg). These data demonstrate that 3-wk gavage treatment with estrogens and SERMs affects vascular reactivity in the mesenteric vascular bed. However, the three formulations of estrogen did not produce equivalent effects, and the effects of the SERMs were different from those of the estrogens.

Estrogen receptor activation and estrogen-regulated gene expression are unaffected by methylseleninic acid in LNCaP prostate cancer cells

Prostate cancer is the most frequently diagnosed cancer and a leading cause of cancer deaths in American men. High dietary intake and status of the essential trace element selenium (Se) have been consistently correlated with reduced risk for prostate cancer. One molecular mechanism by which Se may reduce prostate cancer risk is by catalyzing disulfide bond formation or, otherwise, complexing with reactive sulfhydryl groups in transcription factors, thus altering their binding to DNA and regulation of gene expression. Estrogen plays a role in the etiology of prostate cancer. Estrogen receptors contain cysteines in zinc fingers that are susceptible to oxidation and internal disulfide bond formation, which can prevent DNA binding. We hypothesized that Se alteration of estrogen receptor (ER) binding to DNA and estrogen-regulated gene expression may be one mechanism by which it exerts its chemopreventive effects. LNCaP human prostate cancer cells were treated with 0.05 mumol/L (control) or 5.0 mumol/L (high) Se as methylseleninic acid (MSA). Electrophoretic mobility shift assays showed that binding of ER-beta to the estrogen response element was a nonsignificant 14% lower in cells treated with high MSA. Run-on transcription assays showed no significant changes in transcription rates for estrogen-regulated genes, and steady-state mRNA levels for those genes, assayed by reverse transcription-polymerase chair reaction, were likewise unaffected by MSA. These results suggest that the well-documented chemopreventive effects of Se against prostate cancer may be mediated by mechanisms other than inhibition by monomethylated Se compounds of ER-beta activation or estrogen-regulated gene expression.

Quantitative structure-activity relationships for a series of selective estrogen receptor-beta modulators

The estrogen receptor-beta subtype (ERbeta) is an attractive drug target for the development of novel therapeutic agents for hormone replacement therapy. Hologram quantitative structure-activity relationships (HQSAR) were conducted on a series of 6-phenylnaphthalene and 2-phenylquinoline derivatives, employing values of ERbeta binding affinity. A training set of 65 compounds served to derive the models. The best statistical HQSAR model (q(2) = 0.73 and r(2) = 0.91) was generated using atoms, bonds, connections and donor and acceptor as fragment distinction parameters, and fragment size default (4-7) with hologram length of 199. The model was used to predict the binding affinity of an external test set of 16 compounds, and the predicted values were in good agreement with the experimental results. The final HQSAR model and the information obtained from 2D contribution maps should be useful for the design of novel ERbeta modulators having improved affinity.

Estrogen and CD4+ T cells

PURPOSE OF REVIEW

Many autoimmune rheumatic autoimmune disorders predominantly affect women. Sex hormones, in particular estrogen, can influence CD4 T-helper development and function. We highlight recent studies that begin to provide insights into the mechanisms by which estrogen modulates CD4 T-cell development and function, and thus potentially contribute to disease pathogenesis.

RECENT FINDINGS

High levels of estrogen can lead to thymic atrophy. Recent studies showed that this phenomenon results from effects of estrogen at multiple stages in early T-cell development. Estrogen is also known to affect mature CD4 T-cell function, and, in particular, their ability to produce selected cytokine profiles. The mechanisms by which estrogen can exert these effects were also recently explored and shown to include effects on expression of critical molecules known to be involved in these processes.

SUMMARY

Dissecting the molecular pathways employed by estrogen to modulate CD4 T cells will be critical in elucidating the manner by which estrogen exerts its effects on this compartment. Given that cell type specific differences underlie the ability of many hormonal therapies to exert tissue-specific estrogenic or antiestrogenic activities, this knowledge will be crucial to further exploitation of hormonal therapies in rheumatic autoimmune diseases.

Lasofoxifene: a third-generation selective estrogen receptor modulator for the prevention and treatment of osteoporosis

This article reviews lasofoxifene, a new-generation selective estrogen receptor modulator (SERM) that is currently in Phase III development for the prevention and treatment of osteoporosis in postmenopausal women. This compound selectively binds to both of the estrogen receptors with a high affinity and a median inhibitory concentration that is similar to that seen with estradiol and > or = 10-fold higher than those reported for other SERMs (raloxifene and tamoxifen). Lasofoxifene has a remarkably improved oral bioavailability with respect to other SERMs due to increased resistance to intestinal wall glucuronidation. In both preclinical and short-term studies, the compound showed a favourable safety profile and demonstrated a proven efficacy in preventing bone loss and lowering cholesterol levels. Dose modelling from Phase II studies allowed the selection of lasofoxifene 0.25 mg/day as the lowest fully effective dose.

Pathogenesis of degenerative temporomandibular joint arthritides

Over the past decade, remarkable progress has been made in the study of molecular mechanisms involved in degenerative temporomandibular joint arthritides. Based on recent findings, models of degenerative temporomandibular joint disease predict that mechanical loads trigger a cascade of molecular events leading to disease in susceptible individuals. These events involve the production or release of free radicals, cytokines, fatty acid catabolites, neuropeptides, and matrix-degrading enzymes. Under normal circumstances, these molecules may be involved in the remodeling of articular tissues in response to changing functional demands. However, if functional demands exceed the adaptive capacity of the temporomandibular joint or if the affected individual is susceptible to maladaptive responses, then a disease state will ensue. An individual's susceptibility to degenerative temporomandibular joint disease may be determined by several factors, including genetic backdrop, sex, age, and nutritional status. It is hoped that, by furthering our understanding of the molecular events that underlie degenerative temporomandibular joint diseases, improved diagnostics and effective therapies for these debilitating conditions will be developed.

Harnessing Hormonal Signaling for Cardioprotection

Cardiovascular disease is the leading cause of death in women in the Western world and is predominant among the elderly. A large body of evidence suggests that hormonal signaling plays a critical role in the regulation of cardioprotective mechanisms, as premenopausal women are at significantly lower risk of heart disease compared with men, but the risk greatly increases with the onset of menopause. This association indicates that estrogen may protect the heart from cardiovascular disease. Whereas a number of analyses of the effects of hormone replacement therapy (HRT) on postmenopausal women supported the idea that estrogen is a cardioprotective factor, the findings of the more recent Women's Health Initiative (WHI) study suggested that HRT may actually increase the risk of cardiovascular events. These conflicting reports have left both patients and clinicians reluctant to continue using current HRT regimes. The WHI findings do not, however, negate the epidemiological link between menopause and increased cardiovascular risk. Hence, the identification of the specific actions of estrogen that promote cardioprotective pathways without enhancing deleterious vascular mechanisms may provide novel estrogen-based alternatives to current HRT strategies. In this Review, we outline the known actions of estrogen on the cardiovascular system, focusing on cardioprotective mechanisms that may be targeted for the development of new therapeutic approaches.