Estrogen receptor β ligands: Recent advances and biomedical applications

Activation of estrogen receptor induces differential proteomic responses mainly involving migration, invasion, and tumor development pathways in human testicular embryonal carcinoma NT2/D1 cells

The aims of the present study were to investigate the global changes on proteome of human testicular embryonal carcinoma NT2/D1 cells treated with 17β-estradiol (E2), and the effects of this hormone on migration, invasion, and colony formation of these cells. A quantitative proteomic analysis identified the presence of 1230 proteins in both E2-treated and control cells. The analysis revealed 75 differentially abundant proteins (DAPs), out of which 43 proteins displayed a higher abundance and, 30 proteins showed a lower abundance in E2-treated NT2/D1 cancer cells. Functional analysis using IPA highlighted some activation processes such as migration, invasion, metastasis, and tumor growth. Interestingly, the treatment with E2 and ERβ-selective agonist DPN increased the migration of NT2/D1 cells. On the other hand, ERα-selective agonist PPT did not modify cell migration, indicating that ERβ is the upstream receptor involved in this process. The activation of ERβ increased the invasion and anchorage‑independent growth of NT2/D1 cells more intensely than ERα. ERα and ERβ may play overlapping roles on invasion and colony formation of these cells. Further studies are required to clarify the mechanism underlying these effects. The molecular mechanisms revealed by proteomic and functional studies might also guide the development of potential targets for a better understanding of the biology of these cells and novel treatments for non-seminoma in the future.

Oestrogens, adipose tissues and environmental exposures influence obesity and diabetes across the lifecycle

Endogenous oestrogens regulate essential functions to include menstrual cycles, energy balance, adipose tissue distribution, pancreatic β-cell function, insulin sensitivity and lipid homeostasis. Oestrogens are a family of hormones which include oestradiol (E2), oestrone (E1) and oestriol (E3). Oestrogens function by binding and activating oestrogen receptors (ERs). Phytoestrogens are plant-derived compounds which exhibit oestrogenic-like activity and can bind to ERs. Phytoestrogens exert potential oestrogenic-like benefits; however, their effects are context-dependent and require cautious consideration regarding generalised health benefits. Xenoestrogens are synthetic compounds which have been determined to disrupt endocrine function through binding to ERs. Xenoestrogens enter the body through various routes and given their chemical structure they can accumulate, posing long-term health risks. Xenoestrogens interfere with endogenous oestrogens and their functions contributing to conditions like cancer, infertility, and metabolic disorders. Understanding the interplay between endogenous and exogenous oestrogens is critical in order to determine their potential health consequences and requires further investigation. This manuscript provides a summary of the role endogenous oestrogens have in regulating metabolic functions. Additionally, we discuss the impact phytoestrogens and synthetic xenoestrogens have on biological systems across various life stages. We highlight their mechanisms of action, potential benefits, risks and discuss the need for further research to bridge gaps in understanding and mitigate exposure-related health risks.

A novel ERβ high throughput microscopy platform for testing endocrine disrupting chemicals

In this study we present an inducible biosensor model for the Estrogen Receptor Beta (ERβ), GFP-ERβ:PRL-HeLa, a single-cell-based high throughput (HT) in vitro assay that allows direct visualization and measurement of GFP-tagged ERβ binding to ER-specific DNA response elements (EREs), ERβ-induced chromatin remodeling, and monitor transcriptional alterations via mRNA fluorescence in situ hybridization for a prolactin (PRL)-dsRED2 reporter gene. The model was used to accurately (Z' = 0.58-0.8) differentiate ERβ-selective ligands from ERα ligands when treated with a panel of selective agonists and antagonists. Next, we tested an Environmental Protection Agency (EPA)-provided set of 45 estrogenic reference chemicals with known ERα in vivo activity and identified several that activated ERβ as well, with varying sensitivity, including a subset that is completely novel. We then used an orthogonal ERE-containing transgenic zebrafish (ZF) model to cross validate ERβ and ERα selective activities at the organism level. Using this environmentally relevant ZF assay, some compounds were confirmed to have ERβ activity, validating the GFP-ERβ:PRL-HeLa assay as a screening tool for potential ERβ active endocrine disruptors (EDCs). These data demonstrate the value of sensitive multiplex mechanistic data gathered by the GFP-ERβ:PRL-HeLa assay coupled with an orthogonal zebrafish model to rapidly identify environmentally relevant ERβ EDCs and improve upon currently available screening tools for this understudied nuclear receptor.

An overview on Estrogen receptors signaling and its ligands in breast cancer

Estrogen governs the regulations of various pathological and physiological actions throughout the body in both males and females. Generally, 17β-estradiol an endogenous estrogen is responsible for different health problems in pre and postmenopausal women. The major activities of endogenous estrogen are executed by nuclear estrogen receptors (ERs) ERα and ERβ while non-genomic cytoplasmic pathways also govern cell growth and apoptosis. Estrogen accomplished a fundamental role in the formation and progression of breast cancer. In this review, we have hyphenated different studies regarding ERs and a thorough and detailed study of estrogen receptors is presented. This review highlights different aspects of estrogens ranging from receptor types, their isoforms, structures, signaling pathways of ERα, ERβ and GPER along with their crystal structures, pathological roles of ER, ER ligands, and therapeutic strategies to overcome the resistance.

Sex differences in cognition following variations in endocrine status

Spatial memory, mediated primarily by the hippocampus, is responsible for orientation in space and retrieval of information regarding location of objects and places in an animal's environment. Since the hippocampus is dense with steroid hormone receptors and is capable of robust neuroplasticity, it is not surprising that changes in spatial memory performance occur following a variety of endocrine alterations. Here, we review cognitive changes in both spatial and nonspatial memory tasks following manipulations of the hypothalamic-pituitary-adrenal and gonadal axes and after exposure to endocrine disruptors in rodents. Chronic stress impairs male performance on numerous behavioral cognitive tasks and enhances or does not impact female cognitive function. Sex-dependent changes in cognition following stress are influenced by both organizational and activational effects of estrogen and vary depending on the developmental age of the stress exposure, but responses to gonadal hormones in adulthood are more similar than different in the sexes. Also discussed are possible underlying neural mechanisms for these steroid hormone-dependent, cognitive effects. Bisphenol A (BPA), an endocrine disruptor, given at low levels during adolescent development, impairs spatial memory in adolescent male and female rats and object recognition memory in adulthood. BPA's negative effects on memory may be mediated through alterations in dendritic spine density in areas that mediate these cognitive tasks. In summary, this review discusses the evidence that endocrine status of an animal (presence or absence of stress hormones, gonadal hormones, or endocrine disruptors) impacts cognitive function and, at times, in a sex-specific manner.

Synthesis and Evaluation of (1,4-Disubstituted)-1,2,3-triazoles as Estrogen Receptor Beta Agonists

Estrogen receptors (ER) are nuclear hormone receptors which are responsible for sex hormone signaling in women. A series of (1,4-disubstituted)-1,2,3-triazoles 5–21 were prepared by reaction of azidophenols with terminal alkynes under Fokin reaction conditions. The products were purified by column chromatography or recrystallization and characterized by NMR and HRMS. The compounds were tested for binding to ERβ via a ligand displacement assay, and 1-(4-hydroxyphenyl)-α-phenyl-1,2,3-triazole-4-ethanol (21) was found to be the most potent analog (EC50 = 1.59 μM). Molecular docking of 5–21 within the ligand binding pocket of ERβ (pdb 2jj3) was performed and the docking scores exhibited a general qualitative trend consistent with the measured EC50 values.

A Role for ER-Beta in the Effects of Low-Density Lipoprotein Cholesterol and 27-Hydroxycholesterol on Breast Cancer Progression: Involvement of the IGF Signalling Pathway?

Cholesterol-in particular, high levels of low-density lipoprotein (LDL) and its metabolite, 27-hydroxycholesterol (27-OHC)-is correlated with increases in the risks of breast cancer and obesity. Although the high expression of LDL/27-OHC has been reported in breast cancer, its effects and mechanism of action remain to be fully elucidated. In this study, we found that the effects of LDL on cell proliferation were mediated by the activation of the cytochrome P450 enzyme, sterol 27 hydroxylase, and cholesterol 27-hydroxylase (CYP27A1) in both ER-α-positive and ER-α-negative breast cancer cells. We found that treatment with 27-OHC only increased cell growth in oestrogen receptor-α (ER-α)-positive breast cancer cells in an ER-α-dependent manner, but, interestingly, the effects of 27-OHC on cell migration and invasion were independent of ER-α. Using ER-α-negative MDA-MB-231 cells, we found that 27-OHC similarly promoted cell invasion and migration, and this was mediated by oestrogen receptor β (ER-β). These results suggest that 27-OHC promotes breast cancer cell proliferation in ER-α-positive breast cancer cells via ER-α, but migration and invasion are mediated via ER-β in ER-α positive and negative cell lines. The addition of LDL/27OHC increased the production of IGF-I and the abundance of IGF-IR in TNBC. We further found that modulating ER-β using an agonist or antagonist increased or decreased, respectively, levels of the IGF-I and EGF receptors in TNBC. The inhibition of the insulin-like growth factor receptor blocked the effects of cholesterol on cell growth and the migration of TNBC. Using TCGA and METABRIC microarray expression data from invasive breast cancer carcinomas, we also observed that higher levels of ER-beta were associated with higher levels of IGF-IR. Thus, this study shows novel evidence that ER-β is central to the effects of LDL/27OHC on invasion, migration, and the IGF and EGF axes. Our data suggest that targeting ER-β in TNBC could be an alternative approach for downregulating IGF/EGF signalling and controlling the impact of LDL in breast cancer patients.

Estrogen Receptor β Contributes to Both Hypertension and Hypothalamic Plasticity in a Mouse Model of Peri-Menopause

Hypertension susceptibility in women increases at the transition to menopause, termed perimenopause, a state characterized by erratic estrogen fluctuation and extended hormone cycles. Elucidating the role of estrogen signaling in the emergence of hypertension during perimenopause has been hindered by animal models that are confounded by abrupt estrogen cessation or effects of aging. In the present study, accelerated ovarian failure (AOF) in estrogen receptor β (ERβ) reporter mice was induced by 4-vinylcyclohexene diepoxide in young mice to model early-stage ovarian failure (peri-AOF) characteristic of peri-menopause. It was found that administering ERβ agonists suppressed elevated blood pressure in a model of neurogenic hypertension induced by angiotensin II (AngII) in peri-AOF, but not in age-matched male mice. It was also found that ERβ agonist administration in peri-AOF females, but not males, suppressed the heightened NMDAR signaling and reactive oxygen production in ERβ neurons in the hypothalamic paraventricular nucleus (PVN), a critical neural regulator of blood pressure. It was further shown that deleting ERβ in the PVN of gonadally intact females produced a phenotype marked by a sensitivity to AngII hypertension. These results suggest that ERβ signaling in the PVN plays an important role in blood pressure regulation in female mice and contributes to hypertension susceptibility in females at an early stage of ovarian failure comparable to human perimenopause.

Predicting Potential Endocrine Disrupting Chemicals Binding to Estrogen Receptor α (ERα) Using a Pipeline Combining Structure-Based and Ligand-Based in Silico Methods

The estrogen receptors α (ERα) are transcription factors involved in several physiological processes belonging to the nuclear receptors (NRs) protein family. Besides the endogenous ligands, several other chemicals are able to bind to those receptors. Among them are endocrine disrupting chemicals (EDCs) that can trigger toxicological pathways. Many studies have focused on predicting EDCs based on their ability to bind NRs; mainly, estrogen receptors (ER), thyroid hormones receptors (TR), androgen receptors (AR), glucocorticoid receptors (GR), and peroxisome proliferator-activated receptors gamma (PPARγ). In this work, we suggest a pipeline designed for the prediction of ERα binding activity. The flagged compounds can be further explored using experimental techniques to assess their potential to be EDCs. The pipeline is a combination of structure based (docking and pharmacophore models) and ligand based (pharmacophore models) methods. The models have been constructed using the Environmental Protection Agency (EPA) data encompassing a large number of structurally diverse compounds. A validation step was then achieved using two external databases: the NR-DBIND (Nuclear Receptors DataBase Including Negative Data) and the EADB (Estrogenic Activity DataBase). Different combination protocols were explored. Results showed that the combination of models performed better than each model taken individually. The consensus protocol that reached values of 0.81 and 0.54 for sensitivity and specificity, respectively, was the best suited for our toxicological study. Insights and recommendations were drawn to alleviate the screening quality of other projects focusing on ERα binding predictions.

Establishment of evaluation criteria for the development of high quality ERα-targeted fluorescent probes

ERα-targeted fluorescent probes are important tools for ERα study. In order to develop high quality ERα-targeted probes, a sound and complete evaluation system is essential but has not been established yet. Herein, we set up a series of evaluation criteria for ERα-targeted fluorescent probes including ERα binding affinity, fluorescence quantum yield, cytotoxicity, ERα tracking capacity, ERα selectivity and ERα labeling ability. To verify the practicability of the evaluation criteria, we designed and synthesized two ERα-targeted fluorescent probes and fully characterized their properties based on the proposed evaluation criteria. It showed that the probes exhibited better performance. Moreover, we applied the probes in MCF-7 cells to study the ERα motion characteristics for the first time. We hope that our evaluation criteria could be helpful for the establishment of a complete evaluation system for ERα-targeted fluorescent probes.

Stable Isotope Tracing Metabolomics to Investigate the Metabolic Activity of Bioactive Compounds for Cancer Prevention and Treatment

A major hallmark of cancer is the metabolic reprogramming of cancer cells to fuel tumor growth and proliferation. Various plant-derived bioactive compounds efficiently target the metabolic vulnerabilities of cancer cells and exhibit potential as emerging therapeutic agents. Due to their safety and common use as dietary components, they are also ideal for cancer prevention. However, to render their use as efficient as possible, the mechanism of action of these phytochemicals needs to be well characterized. Stable isotope tracing is an essential technology to study the molecular mechanisms by which nutraceuticals modulate and target cancer metabolism. The use of positionally labeled tracers as exogenous nutrients and the monitoring of their downstream metabolites labeling patterns enable the analysis of the specific metabolic pathway activity, via the relative production and consumption of the labeled metabolites. Although stable isotope tracing metabolomics is a powerful tool to investigate the molecular activity of bioactive compounds as well as to design synergistic nutraceutical combinations, this methodology is still underutilized. This review aims to investigate the research efforts and potentials surrounding the use of stable isotope tracing metabolomics to examine the metabolic alterations mediated by bioactive compounds in cancer.

Insights into the Role of Estrogen Receptor β in Triple-Negative Breast Cancer

Estrogen receptors (ERα and ERβ) are ligand-activated transcription factors that play different roles in gene regulation and show both overlapping and specific tissue distribution patterns. ERβ, contrary to the oncogenic ERα, has been shown to act as an oncosuppressor in several instances. However, while the tumor-promoting actions of ERα are well-known, the exact role of ERβ in carcinogenesis and tumor progression is not yet fully understood. Indeed, to date, highly variable and even opposite effects have been ascribed to ERβ in cancer, including for example both proliferative and growth-inhibitory actions. Recently ERβ has been proposed as a potential target for cancer therapy, since it is expressed in a variety of breast cancers (BCs), including triple-negative ones (TNBCs). Because of the dependence of TNBCs on active cellular signaling, numerous studies have attempted to unravel the mechanism(s) behind ERβ-regulated gene expression programs but the scenario has not been fully revealed. We comprehensively reviewed the current state of knowledge concerning ERβ role in TNBC biology, focusing on the different signaling pathways and cellular processes regulated by this transcription factor, as they could be useful in identifying new diagnostic and therapeutic approaches for TNBC.

Induced osteoblast differentiation by amide derivatives of stilbene: The possible osteogenic agents

A series of amide derivatives of stilbene was synthesized and investigated for osteogenic activity. Out of sixteen, seven compounds viz19c, 19g, 19i, 24b, 25a, 25c and 26a showed significant osteoblast differentiation within 1 pM-1 µM concentrations. Amongst all, 26a was identified as most active molecule which presented effective mineralization of osteoblasts and expression of mRNA of osteogenic marker gene such as BMP-2, ALP, and Runx-2 at 1 pM. In estrogen-deficient balb/c mice, 26a showed significant osteogenic activity at 5 mg-kg^-1 body weight dose. The protein expression study for estrogen receptors α and β (ER-α & ER-β) using mouse calvarial osteoblasts (MCOs) and molecular docking analyses showed preferential expression of ER-β by 26a indicating the possibility of ER-β mediated osteogenic activity of 26a.

Design, synthesis and biological evaluation of novel dual-acting modulators targeting both estrogen receptor α (ERα) and lysine-specific demethylase 1 (LSD1) for treatment of breast cancer

Breast cancer is a multi-factor disease, thus more and more drug combination therapies are applied in the treatment. However, there are undeniable disadvantages in drug combination therapy. Therefore, the development of new dual-targeting drugs has become a new strategy. In this study, we have developed a series of dual-acting agents targeting both estrogen receptor α (ERα) and histone demethylase based on a privileged OBHS pharmacophore scaffold developed previously by our laboratory. These novel OBHS-LSD1i conjugates showed excellent ERα binding affinity and selectivity, and exhibited potent inhibitory activity against lysine specific demethylase 1 (LSD1). Several conjugates showed higher antiproliferative efficacy in MCF-7 breast cancer cell line compared to 4-hydroxytamoxifen in vitro. Among them, the best compound 11g displayed potent inhibitory activity against LSD1 and MCF-7 cells with IC₅₀ values of 1.55 μM and 8.79 μM, respectively. Flow cytometry analysis of apoptosis of 11g suggested that the effect of this type compounds on MCF-7 cells is partly caused by inducing apoptosis. Moreover, the molecular docking of 11g with ERα and the active site of LSD1/CoREST complex provides practical way for understanding the dual mechanism actions of this kind of compounds with the targets. As such, these compounds have shown potential to become promising leads for the development of highly efficient dual-acting modulators for breast cancer therapies.

Optimisation of estrogen receptor subtype-selectivity of a 4-Aryl-4H-chromene scaffold previously identified by virtual screening

4-Aryl-4H-Chromene derivatives have been previously shown to exhibit anti-proliferative, apoptotic and anti-angiogenic activity in a variety of tumor models in vitro and in vivo generally via activation of caspases through inhibition of tubulin polymerisation. We have previously identified by Virtual Screening (VS) a 4-aryl-4H-chromene scaffold, of which two examples were shown to bind Estrogen Receptor α and β with low nanomolar affinity and <20-fold selectivity for α over β and low micromolar anti-proliferative activity in the MCF-7 cell line. Thus, using the 4-aryl-4H-chromene scaffold as a starting point, a series of compounds with a range of basic arylethers at C-4 and modifications at the C3-ester substituent of the benzopyran ring were synthesised, producing some potent ER antagonists in the MCF-7 cell line which were highly selective for ERα (compound 35; 350-fold selectivity) or ERβ (compound 42; 170-fold selectivity).

Construction of benzofuranone library via a metal-free, one-pot intermolecular condensation, and their application as efficient estrogen receptor β modulators

Facile synthesis of benzofuranone was achieved through a metal-free, one-pot intermolecular condensation between α-hydroxy aryl ketones and resorcinol derivatives. A library of 20 compounds with moderate to good overall yields was prepared. These compounds showed strong binding toward estrogen receptors along with good selectivity for ERβ (>190-fold over ERα). Anti-proliferative activity on DU-145, U-87, and MCF-7 cells gave inhibition IC₅₀ values in the low μM range, which suggested the promising potential therapeutic applications of these new classes of benzofuranones.

LARMD: integration of bioinformatic resources to profile ligand-driven protein dynamics with a case on the activation of estrogen receptor

Protein dynamics is central to all biological processes, including signal transduction, cellular regulation and biological catalysis. Among them, in-depth exploration of ligand-driven protein dynamics contributes to an optimal understanding of protein function, which is particularly relevant to drug discovery. Hence, a wide range of computational tools have been designed to investigate the important dynamic information in proteins. However, performing and analyzing protein dynamics is still challenging due to the complicated operation steps, giving rise to great difficulty, especially for nonexperts. Moreover, there is a lack of web protocol to provide online facility to investigate and visualize ligand-driven protein dynamics. To this end, in this study, we integrated several bioinformatic tools to develop a protocol, named Ligand and Receptor Molecular Dynamics (LARMD, http://chemyang.ccnu.edu.cn/ccb/server/LARMD/ and http://agroda.gzu.edu.cn:9999/ccb/server/LARMD/), for profiling ligand-driven protein dynamics. To be specific, estrogen receptor (ER) was used as a case to reveal ERβ-selective mechanism, which plays a vital role in the treatment of inflammatory diseases and many types of cancers in clinical practice. Two different residues (Ile373/Met421 and Met336/Leu384) in the pocket of ERβ/ERα were the significant determinants for selectivity, especially Met336 of ERβ. The helix H8, helix H11 and H7-H8 loop influenced the migration of selective agonist (WAY-244). These computational results were consistent with the experimental results. Therefore, LARMD provides a user-friendly online protocol to study the dynamic property of protein and to design new ligand or site-directed mutagenesis.

Crystal structure of 1-benzyl-3-cyano-6-phenyl-1,2-dihydropyridine, C19H16N2

C19H16N2, orthorhombic, P212121 (no. 19), a = 7.5177(10) Å, b = 12.4761(16) Å, c = 16.118(2) Å, V = 1511.7(3) Å3, Z = 4, R gt(F) = 0.0424, wR ref(F 2) = 0.0967, T = 293(2) K.

Analogues of ERβ ligand chloroindazole exert immunomodulatory and remyelinating effects in a mouse model of multiple sclerosis

Pharmaceutical agents currently approved for the treatment of multiple sclerosis reduce relapse rates, but do not reverse or prevent neurodegeneration nor initiate myelin repair. The highly selective estrogen receptor (ER) β ligand chloroindazole (IndCl) shows particular promise promoting both remyelination while reducing inflammatory cytokines in the central nervous system of mice with experimental autoimmune encephalomyelitis. To optimize these benefits, we developed and screened seven novel IndCl analogues for their efficacy in promoting primary oligodendrocyte (OL) progenitor cell survival, proliferation, and differentiation in vitro by immunohistochemistry. Two analogues, IndCl-o-chloro and IndCl-o-methyl, induced proliferation and differentiation equivalent to IndCl and were selected for subsequent in vivo evaluation for their impact on clinical disease course, white matter pathology, and inflammation. Both compounds ameliorated disease severity, increased mature OLs, and improved overall myelination in the corpus callosum and white matter tracts of the spinal cord. These effects were accompanied by reduced production of the OL toxic molecules interferon-γ and chemokine (C-X-C motif) ligand, CXCL10 by splenocytes with no discernable effect on central nervous system-infiltrating leukocyte numbers, while IndCl-o-methyl also reduced peripheral interleukin (IL)−17. In addition, expression of the chemokine CXCL1, which is associated with developmental oligodendrogenesis, was upregulated by IndCl and both analogues. Furthermore, callosal compound action potential recordings from analogue-treated mice demonstrated a larger N1 component amplitude compared to vehicle, suggesting more functionally myelinated fibers. Thus, the o-Methyl and o-Chloro IndCl analogues represent a class of ERβ ligands that offer significant remyelination and neuroprotection as well as modulation of the immune system; hence, they appear appropriate to consider further for therapeutic development in multiple sclerosis and other demyelinating diseases.

The promiscuous estrogen receptor: Evolution of physiological estrogens and response to phytochemicals and endocrine disruptors

Many actions of estradiol (E2), the principal physiological estrogen in vertebrates, are mediated by estrogen receptor-α (ERα) and ERβ. An important physiological feature of vertebrate ERs is their promiscuous response to several physiological steroids, including estradiol (E2), Δ⁵-androstenediol, 5α-androstanediol, and 27-hydroxycholesterol. A novel structural characteristic of Δ⁵-androstenediol, 5α-androstanediol, and 27-hydroxycholesterol is the presence of a C19 methyl group, which precludes the presence of an aromatic A ring with a C3 phenolic group that is a defining property of E2. The structural diversity of these estrogens can explain the response of the ER to synthetic chemicals such as bisphenol A and DDT, which disrupt estrogen physiology in vertebrates, and the estrogenic activity of a variety of plant-derived chemicals such as genistein, coumestrol, and resveratrol. Diversity in the A ring of physiological estrogens also expands potential structures of industrial chemicals that can act as endocrine disruptors. Compared to E2, synthesis of 27-hydroxycholesterol and Δ⁵-androstenediol is simpler, leading us, based on parsimony, to propose that one or both of these steroids or a related metabolite was a physiological estrogen early in the evolution of the ER, with E2 assuming this role later as the canonical estrogen. In addition to the well-studied role of the ER in reproductive physiology, the ER also is an important transcription factor in non-reproductive tissues such as the cardiovascular system, kidney, bone, and brain. Some of these ER actions in non-reproductive tissues appeared early in vertebrate evolution, long before the emergence of mammals.

Synthesis and Discovery of Estra-1,3,5(10),6,8-pentaene-2,16α-diol

A metallacycle-centered approach to the assembly of partially aromatic synthetic steroids was investigated as a means to prepare a boutique collection of unique steroidal agents. The synthesis and discovery of estra-1,3,5(10),6,8-pentaene-2,16α-diol (VII) is described, along with structure-activity relationships related to its cytotoxic properties. Overall, VII was found to have a GI50 = 0.2 μg/mL (∼800 nM) in MDA-MB-231 human breast cancer cells, be an efficacious estrogen receptor agonist with potency for ERβ > ERα (ERβ EC50 = 21 nM), possess selective affinity to the cdc-2-like kinase CLK4 (Kd = 350 nM), and be phenotypically related to paclitaxel by an unbiased panel assessment.

A high-affinity subtype-selective fluorescent probe for estrogen receptor β imaging in living cells

Estrogen receptor β (ERβ) has recently been identified as a pharmaceutical target in hormone replacement therapy for breast cancers. However, the biological function of ERβ in disease progression remains unclear. A highly ERβ-selective fluorescent probe (FPNM) was discovered exhibiting nanomolar affinity for ERβ with an ERβ/ERα selectivity as high as 80, which allowed specific labeling of intracellular ERβ. Moreover, distinct ERβ dynamics in various cellular bio-settings such as prostate cancer (DU-145) or triple-negative breast cancer (MDA-MB-231) cells were directly observed for the first time viaFPNM staining.

Increase in chemokine CXCL1 by ERβ ligand treatment is a key mediator in promoting axon myelination

Estrogen receptor β (ERβ) ligands promote remyelination in mouse models of multiple sclerosis. Recent work using experimental autoimmune encephalomyelitis (EAE) has shown that ERβ ligands induce axon remyelination, but impact peripheral inflammation to varying degrees. To identify if ERβ ligands initiate a common immune mechanism in remyelination, central and peripheral immunity and pathology in mice given ERβ ligands at peak EAE were assessed. All ERβ ligands induced differential expression of cytokines and chemokines, but increased levels of CXCL1 in the periphery and in astrocytes. Oligodendrocyte CXCR2 binds CXCL1 and has been implicated in normal myelination. In addition, despite extensive immune cell accumulation in the CNS, all ERβ ligands promoted extensive remyelination in mice at peak EAE. This finding highlights a component of the mechanism by which ERβ ligands mediate remyelination. Hence, interplay between the immune system and central nervous system may be responsible for the remyelinating effects of ERβ ligands. Our findings of potential neuroprotective benefits arising from the presence of CXCL1 could have implications for improved therapies for multiple sclerosis.

27-Hydroxycholesterol Is an Estrogen Receptor β-Selective Negative Allosteric Modifier of 17β-Estradiol Binding

Estrogens bind to two nuclear estrogen receptor (ER) subtypes, ERα and ERβ, which are expressed in differing amounts in various tissues. The endogenous estrogen, 17β-estradiol (E2), binds to both subtypes with nearly equal affinity and is the prototypical agonist. Selective estrogen receptor modulators (SERMs) may bind to both subtypes with equivalent affinities but have agonist activities in some tissues while having antagonist activities in others. In the present study, we demonstrate that the first reported endogenous SERM, 27-hydroxycholesterol (27-OHC), binds preferentially (>100-fold) to ERβ over ERα. Furthermore, 27-OHC is not able to fully compete with E2 binding, suggesting the two may bind at different sites. We provide an allosteric ternary complex model for the simultaneous binding of 27-OHC and E2 to ERβ, which accurately describes the binding data we have observed. We conclude that 27-OHC is a negative allosteric modifier of E2 binding, with an inhibitor constantof 50 nM and cooperativity factor (α) of 0.036. We also propose an in silico three-dimensional model of the simultaneous binding to guide future experiments. Further study of this unique binding model may allow for the discovery of novel ERβ-selective ligands and potentially explain the lack of effectiveness of ERβ-selective agonists in humans vs preclinical models.

Synthesis and biological evaluation of novel cyclopropyl derivatives as subtype-selective ligands for estrogen receptor

Objectives

Tamoxifen is the most commonly used selective estrogen receptor modulators (SERMs); however, patients often develop the acquired drug resistance on tamoxifen therapy. The aim of this study was to develop new SERMs.

Methods

Several novel cyclopropyl derivatives were designed and synthesized. The binding affinities of these compounds as well as the selectivity on subtype of estrogen receptor (ER) were assessed by fluorescence polarization. The antagonistic activity was also evaluated by dual-luciferase reporter assay.

Key findings

Our data identified five compounds (9a, 9b, 9d, 9e and 9f) with a higher selectivity on ERα than ERβ subtype, warranting further development as a subtype-selective ER modulator. The study of antiestrogen activity also demonstrated that compounds 9a, 9c-f acted as full functional antagonists for ERα. These compounds had no or very low cytotoxicity.

Conclusions

Although these cyclopropyl derivatives showed lower binding affinities on ERs compared to 17β-estradiol, five of these compounds exhibited binding to ERα only and therefore might serve as a promising lead compound for further development of novel subtype-selective SERMs.

The in vitro estrogenic activity of the crude drugs found in Japanese herbal medicines prescribed for menopausal syndrome was enhanced by combining them

BACKGROUND

Japanese herbal medicines can be used as alternatives to estrogen therapy and are sometimes prescribed for menopausal syndrome because they have fewer side effects and are associated with better compliance than estrogen therapy, but little is known about the pharmacological mechanisms of such treatments. This study aimed to explore the mechanisms responsible for the estrogen-like effects of five widely prescribed Japanese herbal medicines (unkeito, kamishoyosan, nyoshinsan, keishibukuryogan, and tokishakuyakusan).

METHODS

We evaluated the estrogenic activity of these five Japanese herbal medicines and their metabolites using an estrogen receptor (ER)-dependent cell proliferation bioassay and an ER-dependent reporter assay. We also investigated the estrogenic activity of the crude drugs within the medicines and attempted to detect inter-crude drug synergistic effects using the ER-dependent reporter assay.

RESULTS

We found that unkeito, kamishoyosan, and nyoshinsan exhibited estrogenic activity, and they displayed stronger estrogenic activity after being metabolized. Then, we focused on investigating the estrogenic activity of the crude drugs present within unkeito. We found that glycyrrhizae radix, cinnamomi cortex, evodiae fructus, and zingiberis rhizoma demonstrated ERβ-dependent estrogenic activity. The combined use of evodiae fructus and glycyrrhizae radix, or evodiae fructus and cinnamomi cortex produced synergistic ERβ-dependent estrogenic activity.

CONCLUSION

It was suggested that unkeito, kamishoyosan, and nyoshinsan exert estrogenic activity, and hence, might be useful for treating menopausal syndrome. Furthermore, synergistic estrogenic effects were detected between some of the crude drugs present within unkeito.

Risks and benefits related to alimentary exposure to xenoestrogens

Xenoestrogens are widely diffused in the environment and in food, thus a large portion of human population worldwide is exposed to them. Among alimentary xenoestrogens, phytoestrogens (PhyEs) are increasingly being consumed because of their potential health benefits, although there are also important risks associated to their ingestion. Furthermore, other xenoestrogens that may be present in food are represented by other chemicals possessing estrogenic activities, that are commonly defined as endocrine disrupting chemicals (EDCs). EDCs pose a serious health concern since they may cause a wide range of health problems, starting from pre-birth till adult lifelong exposure. We herein provide an overview of the main classes of xenoestrogens, which are classified on the basis of their origin, their structures and their occurrence in the food chain. Furthermore, their either beneficial or toxic effects on human health are discussed in this review.

Update on the therapeutic significance of estrogen receptor beta in malignant gliomas

Malignant glioma is the most fatal of the astrocytic lineage tumors despite therapeutic advances. Men have a higher glioma incidence than women, indicating that estrogen level differences between men and women may influence glioma pathogenesis. However, the mechanism underlying the anticancer effects of estrogen has not been fully clarified and is complicated by the presence of several distinct estrogen receptor types and the identification of a growing number of estrogen receptor splice variants. Specifically, it is generally accepted that estrogen receptor alpha (ERα) functions as a tumor promoter, while estrogen receptor beta (ERβ) functions as a tumor suppressor, and the role and therapeutic significance of ERβ signaling in gliomas remains elusive. Thus, a deeper analysis of ERβ could elucidate the role of estrogens in gender-related cancer incidence. ERβ has been found to be involved in complex interactions with malignant gliomas. In addition, the prognostic value of ERβ expression in glioma patients should not be ignored when considering translating experimental findings to clinical practice. More importantly, several potential drugs consisting of selective ERβ agonists have exhibited anti-glioma activities and could further extend the therapeutic potential of ERβ-selective agonists. Here, we review the literature to clarify the anti-glioma effect of ERβ. To clarify ERβ-mediated treatment effects in malignant gliomas, this review focuses on the potential mechanisms mediated by ERβ in the intracellular signaling events in glioma cells, the prognostic value of ERβ expression in glioma patients, and various ERβ agonists that could be potential drugs with anti-glioma activities.

Strategies to Target Glucose Metabolism in Tumor Microenvironment on Cancer by Flavonoids

The imbalance between glucose metabolism and cancer cell growth in tumor microenvironment (TME), which are closely related with the occurrence and progression of cancer. Accumulating evidence has demonstrated that flavonoids exert many biological properties, including antioxidant and anticarcinogenic activities. Recently, the roles and applications of flavonoids, particularly in relation to glucose metabolism in cancers, have been highlighted. Thus, the identification of flavonoids targeting alternative glucose metabolism pathways in TME may represent an attractive approach to the more effective therapeutic strategies for cancer. In this review, we will focus on the roles of flavonoids in regulating glucose metabolism and cancer cell growth in TME, such as proliferation advantage, cell mobility, and chemoresistance to cancer, as well as modifiers of thermal sensitivity. Not only have such large-scale endeavors been useful in providing fundamental insights into natural and synthesized flavonoids that can prevent and treat cancer, but also have led to the discovery of potential targets for cancer therapy.

Estrogen Receptor β as a Pharmaceutical Target

A major issue in clinical endocrinology today is how to use hormones to achieve the health benefits that they clearly can provide but avoid the negative side effects, that is, how to develop more precise medicines. This problem of how to use hormones is pervasive in clinical endocrinology. It is true for estrogen, progesterone, androgen, vitamin D, and thyroid hormone, and the problem is amplified in the case of new ligands for the more recently discovered nuclear receptors. Selective targeting of hormone receptor subtypes is one attractive way to harness the beneficial effects of hormones while reducing unwanted side effects. Here, we focus on estrogen receptor (ER)β, which has promise as a selective target in hormone replacement therapy, and in breast and prostate cancers.

Synthesis and Evaluation of the Estrogen Receptor β-Selective Radioligand 2-18F-Fluoro-6-(6-Hydroxynaphthalen-2-yl)Pyridin-3-ol: Comparison with 16α-18F-Fluoro-17β-Estradiol

Estrogen receptors (ERs) are targets for endocrine treatment of estrogen-dependent cancers. The ER consists of 2 isoforms, ERα and ERβ, which have distinct biologic functions. Whereas activation of ERα stimulates cell proliferation and cell survival, ERβ promotes apoptosis. PET of ERα and ERβ levels could provide more insight in response to hormonal treatment. 16α-¹⁸F-fluoro-17β-estradiol (¹⁸F-FES) is a PET tracer for ER with relative selectivity for ERα. Here we report the synthesis and evaluation of a potential ERβ-selective PET tracer: 2-¹⁸F-fluoro-6-(6-hydroxynaphthalen-2-yl)pyridin-3-ol (¹⁸F-FHNP). Methods:¹⁸F-FHNP was synthesized by fluorination of the corresponding nitro precursor, followed by acidic removal of the 2-methoxyethoxymethyl protecting group. In vitro affinity of ¹⁸F-FHNP and ¹⁸F-FES for ER was evaluated in SKOV3 ovarian carcinoma cells. PET imaging and ex vivo biodistribution studies with ¹⁸F-FHNP and ¹⁸F-FES were conducted in athymic nude mice bearing a SKOV3 xenografts. Results:¹⁸F-FHNP had nanomolar affinity for ERs, with a 3.5 times higher affinity for ERβ. ¹⁸F-FHNP was obtained in 15%-40% radiochemical yield (decay-corrected), with a specific activity of 279 ± 75 GBq/μmol. ¹⁸F-FHNP had a dissociation constant of 2 nM and maximum binding capacity of 18 fmol/10⁶ cells, and ¹⁸F-FES had a dissociation constant of 3 nM and maximum binding capacity 83 fmol/10⁶ SKOV3 cells. Both ¹⁸F-FHNP and ¹⁸F-FES PET could clearly visualize the tumor in male mice bearing a SKOV3 xenograft. Biodistribution studies showed similar distribution of ¹⁸F-FHNP and ¹⁸F-FES in most peripheral organs. ¹⁸F-FES showed a 2-fold-higher tumor uptake than ¹⁸F-FHNP. The tumor-to-plasma ratio of ¹⁸F-FES decreased 55% (P = 0.024) and 8% (P = 0.68) when administered in the presence of estradiol (nonselective) and genistein (ERβ-selective), respectively. The tumor-to-plasma ratio of ¹⁸F-FHNP decreased 41% (P = 0.004) and 64% (P = 0.0009) when administered with estradiol and genistein, respectively. Conclusion: The new PET tracer ¹⁸F-FHNP has suitable properties for imaging and shows relative selectivity for ERβ.

Synthesis and structure-activity relationships of 1-benzylindane derivatives as selective agonists for estrogen receptor beta

The estrogen receptor beta (ERβ) selective agonist is considered a promising candidate for the treatment of estrogen deficiency symptoms in ERβ-expressing tissues, without the risk of breast cancer, and multiple classes of compounds have been reported as ERβ selective agonists. Among them, 6-6 bicyclic ring-containing structures (e.g., isoflavone phytoestrogens) are regarded as one of the cyclized analogues of isobutestrol 5b, and suggest that other cyclized scaffolds comprising 5-6 bicyclic rings could also act as selective ERβ ligands. In this study, we evaluated the selective ERβ agonistic activity of 1-(4-hydroxybenzyl)indan-5-ol 7a and studied structure-activity relationship (SAR) of its derivatives. Some functional groups improved the properties of 7a; introduction of a nitrile group on the indane-1-position resulted in higher selectivity for ERβ (12a), and further substitution with a fluoro or a methyl group to the pendant phenyl ring was also preferable (12b, d, and e). Subsequent chiral resolution of 12a identified that R-12a has a superior profile over S-12a. This is comparable to diarylpropionitrile (DPN) 5c, one of the promising selective ERβ agonists and indicates that this indane-based scaffold has the potential to provide better ERβ agonistic probes.

Cyclic Ketoximes as Estrogen Receptor β Selective Agonists

The development of estrogen receptor β (ERβ)-selective agonists represents a therapeutic strategy against several kinds of cancers, but the high homology between the two receptor subtypes, ERα and ERβ, makes the achievement of this goal very challenging. In the past, we developed salicylaldoxime- and salicylketoxime-based molecules that proved to bind well to ERβ. In this paper, further structural evolution of the salicylketoximes is presented: two of the newly synthesized five-membered cyclic ketoximes bind with nanomolar affinities to ERβ, and they show selectivity for this subtype over ERα. Their agonist character was confirmed by cell-free coactivator recruitment assays, in which we demonstrated the ability of these compounds to form an active complex with ERβ capable of recruiting coactivator proteins; this indicated their efficacy as agonists. Finally, their potency and selectivity for ERβ binding were rationalized by molecular-modeling studies.

Prediction of selective estrogen receptor beta agonist using open data and machine learning approach

Background

Estrogen receptors (ERs) are nuclear transcription factors that are involved in the regulation of many complex physiological processes in humans. ERs have been validated as important drug targets for the treatment of various diseases, including breast cancer, ovarian cancer, osteoporosis, and cardiovascular disease. ERs have two subtypes, ER-α and ER-β. Emerging data suggest that the development of subtype-selective ligands that specifically target ER-β could be a more optimal approach to elicit beneficial estrogen-like activities and reduce side effects.

Methods

Herein, we focused on ER-β and developed its in silico quantitative structure-activity relationship models using machine learning (ML) methods.

Results

The chemical structures and ER-β bioactivity data were extracted from public chemogenomics databases. Four types of popular fingerprint generation methods including MACCS fingerprint, PubChem fingerprint, 2D atom pairs, and Chemistry Development Kit extended fingerprint were used as descriptors. Four ML methods including Naïve Bayesian classifier, k-nearest neighbor, random forest, and support vector machine were used to train the models. The range of classification accuracies was 77.10% to 88.34%, and the range of area under the ROC (receiver operating characteristic) curve values was 0.8151 to 0.9475, evaluated by the 5-fold cross-validation. Comparison analysis suggests that both the random forest and the support vector machine are superior for the classification of selective ER-β agonists. Chemistry Development Kit extended fingerprints and MACCS fingerprint performed better in structural representation between active and inactive agonists.

Conclusion

These results demonstrate that combining the fingerprint and ML approaches leads to robust ER-β agonist prediction models, which are potentially applicable to the identification of selective ER-β agonists.

Anticancer agents interacting with membrane glucose transporters

The altered metabolism observed in cancer cells generally consists in increased glucose uptake and glycolytic activity. This is associated with an overexpression of glucose transporter proteins (GLUTs), which facilitate glucose uptake across the plasma membrane and play a crucial role in the survival of cancer cells. Therefore GLUTs are considered as suitable targets for the treatment of cancer. Herein we review some of the most relevant GLUT inhibitors that have been recently developed as prospective anticancer agents.

Optimization of the alkyl side chain length of fluorine-18-labeled 7α-alkyl-fluoroestradiol

INTRODUCTION

Several lines of evidence suggest that 7α-substituted estradiol derivatives bind to the estrogen receptor (ER). In line with this hypothesis, we designed and synthesized (18)F-labeled 7α-fluoroalkylestradiol (Cn-7α-[(18)F]FES) derivatives as molecular probes for visualizing ERs. Previously, we successfully synthesized 7α-(3-[(18)F]fluoropropyl)estradiol (C3-7α-[(18)F]FES) and showed promising results for quantification of ER density in vivo, although extensive metabolism was observed in rodents. Therefore, optimization of the alkyl side chain length is needed to obtain suitable radioligands based on Cn-7α-substituted estradiol pharmacophores.

METHODS

We synthesized fluoromethyl (23; C1-7α-[(18)F]FES) to fluorohexyl (26; C6-7α-[(18)F]FES) derivatives, except fluoropropyl (C3-7α-[(18)F]FES) and fluoropentyl derivatives (C5-7α-[(18)F]FES), which have been previously synthesized. In vitro binding to the α-subtype (ERα) isoform of ERs and in vivo biodistribution studies in mature female mice were carried out.

RESULTS

The in vitro IC50 value of Cn-7α-FES tended to gradually decrease depending on the alkyl side chain length. C1-7α-[(18)F]FES (23) showed the highest uptake in ER-rich tissues such as the uterus. Uterus uptake also gradually decreased depending on the alkyl side chain length. As a result, in vivo uterus uptake reflected the in vitro ERα affinity of each compound. Bone uptake, which indicates de-fluorination, was marked in 7α-(2-[(18)F]fluoroethyl)estradiol (C2-7α-[(18)F]FES) (24) and 7α-(4-[(18)F]fluorobutyl)estradiol (C4-7α-[(18)F]FES) (25) derivatives. However, C1-7α-[(18)F]FES (23) and C6-7α-[(18)F]FES (26) showed limited uptake in bone. As a result, in vivo bone uptake (de-fluorination) showed a bell-shaped pattern, depending on the alkyl side chain length. C1-7α-[(18)F]FES (23) showed the same levels of uptake in uterus and bone compared with those of 16α-[(18)F]fluoro-17β-estradiol.

CONCLUSIONS

The optimal alkyl side chain length of (18)F-labeled 7α-fluoroalkylestradiol was the shortest: C1-7α-[(18)F]FES. Our results indicate that shorter chain lengths within the 4-Å ligand binding cavities of ERα are suitable for 7α-fluoroalkylestradiol derivatives.

Nudging oligodendrocyte intrinsic signaling to remyelinate and repair: Estrogen receptor ligand effects

Demyelination in multiple sclerosis (MS) leads to significant, progressive axonal and neuronal degeneration. Currently existing immunosuppressive and immunomodulatory therapies alleviate MS symptoms and slow, but fail to prevent or reverse, disease progression. Restoration of damaged myelin sheath by replenishment of mature oligodendrocytes (OLs) should not only restore saltatory axon conduction, but also provide a major boost to axon survival. Our previous work has shown that therapeutic treatment with the modestly selective generic estrogen receptor (ER) β agonist diarylpropionitrile (DPN) confers functional neuroprotection in a chronic experimental autoimmune encephalomyelitis (EAE) mouse model of MS by stimulating endogenous remyelination. Recently, we found that the more potent, selective ERβ agonist indazole-chloride (Ind-Cl) improves clinical disease and motor performance. Importantly, electrophysiological measures revealed improved corpus callosal conduction and reduced axon refractoriness. This Ind-Cl treatment-induced functional remyelination was attributable to increased OL progenitor cell (OPC) and mature OL numbers. At the intracellular signaling level, transition of early to late OPCs requires ERK1/2 signaling, and transition of immature to mature OLs requires mTOR signaling; thus, the PI3K/Akt/mTOR pathway plays a major role in the late stages of OL differentiation and myelination. Indeed, therapeutic treatment of EAE mice with various ERβ agonists results in increased brain-derived neurotrophic factor (BDNF) and phosphorylated (p) Akt and p-mTOR levels. It is notable that while DPN's neuroprotective effects occur in the presence of peripheral and central inflammation, Ind-Cl is directly neuroprotective, as demonstrated by remyelination effects in the cuprizone-induced demyelination model, as well as immunomodulatory. Elucidating the mechanisms by which ER agonists and other directly remyelinating agents modulate endogenous OPC and OL regulatory signaling is critical to the development of effective remyelinating drugs. The discovery of signaling targets to induce functional remyelination will valuably contribute to the treatment of demyelinating neurological diseases, including MS, stroke, and traumatic brain and spinal cord injury.

ERβ in CD4+ T Cells Is Crucial for Ligand-Mediated Suppression of Central Nervous System Autoimmunity

The development of therapies for multiple sclerosis targeting pathogenic T cell responses remains imperative. Previous studies have shown that estrogen receptor (ER) β ligands could inhibit experimental autoimmune encephalomyelitis. However, the effects of ERβ-specific ligands on human or murine pathogenic immune cells, such as Th17, were not investigated. In this article, we show that the synthetic ERβ-specific ligand 4-(2-phenyl-5,7-bis[trifluoromethyl]pyrazolo[1,5-a]pyrimidin-3-yl)phenol (PHTPP) reversed established paralysis and CNS inflammation, characterized by a dramatic suppression of pathogenic Th responses as well as induction of IL-10-producing regulatory CD4(+) T cell subsets in vivo. Moreover, administration of PHTPP in symptomatic mice induced regulatory CD4(+) T cells that were suppressive in vivo. PHTPP-mediated experimental autoimmune encephalomyelitis amelioration was canceled in mice with ERβ-deficient CD4(+) T cells only, indicating that expression of ERβ by these cells is crucial for the observed therapeutic effect. Importantly, synthetic ERβ-specific ligands acting directly on CD4(+) T cells suppressed human and mouse Th17 cells, downregulating Th17 cell signature gene expression and expanding IL-10-producing T cells among them. TGF-β1 and aryl hydrocarbon receptor activation enhanced the ERβ ligand-mediated expansion of IL-10-producing T cells among Th17 cells. In addition, these ERβ-specific ligands promoted the induction and maintenance of Foxp3(+) T regulatory cells, as well as their in vitro suppressive function. Thus, ERβ-specific ligands targeting pathogenic Th17 cells and inducing functional regulatory cells represent a promising subset of therapeutic agents for multiple sclerosis.

Estrogen Receptor Ligands: A Review (2013-2015)

Estrogen receptors (ERs) are a group of compounds named for their importance in both menstrual and estrous reproductive cycles. They are involved in the regulation of various processes ranging from tissue growth maintenance to reproduction. Their action is mediated through ER nuclear receptors. Two subtypes of the estrogen receptor, ERα and ERβ, exist and exhibit distinct cellular and tissue distribution patterns. In humans, both receptor subtypes are expressed in many cells and tissues, and they control key physiological functions in various organ systems. Estrogens attract great attention due to their wide applications in female reproductive functions and treatment of some estrogen-dependent cancers and osteoporosis. This paper provides a general review of ER ligands published in international journals patented between 2013 and 2015. The broad physiological profile of estrogens has attracted the attention of many researchers to develop new estrogen ligands as therapeutic molecules for various clinical purposes. After the discovery of the ERβ receptor, subtype-selective ligands could be used to elicit beneficial estrogen-like activities and reduce adverse side effects, based on the different distributions and relative levels of the two ER subtypes in different estrogen target tissues. Therefore, recent literature has focused on selective estrogen ligands as highly promising agents for the treatment of some types of cancer, as well as for cardiovascular, inflammatory, and neurodegenerative diseases. Estrogen receptors are nuclear transcription factors that are involved in the regulation of many complex physiological functions in humans. Selective estrogen ligands are highly promising targets for treatment of some types of cancer, as well as for cardiovascular, inflammatory and neurodegenerative diseases. Extensive structure-activity relationship studies of ER ligands based on small molecules indicate that many different structural scaffolds may provide high-affinity compounds, provided that some basic structural requirements are present.

Induction of targeted osteogenesis with 3-aryl-2H-benzopyrans and 3-aryl-3H-benzopyrans: Novel osteogenic agents

Development of target oriented chemotherapeutics for treatment of chronic diseases have been considered as an important approach in drug development. Following this approach, in our efforts for exploration of new osteogenic leads, substituted 3-aryl-2H-benzopyran and 3-aryl-3H-benzopyran derivatives (19, 20a-e, 21, 22a-e, 26, 27, 28a-e, 29, 31a-b, 32 and 33) have been characterized as estrogen receptor-β selective osteogenic (bone forming) agents. The synthesized compounds were evaluated for osteogenic activity using mouse calvarial osteoblast cells. Four compounds viz20b, 22a, 27and 32 showed significant osteogenic activity at EC50 values 1.35, 34.5, 407 and 29.5pM respectively. Out of these, 20b and 32 were analyzed for their bone mineralization efficacy and osteogenic gene expression by qPCR. The results showed that 20b and 32 significantly increased mineral nodule formation and the transcript levels of BMP-2, RUNX-2 and osteocalcin at 100pM concentrations respectively. Further mechanistic studies of 20b and 32 using transiently knocked down expression of ER-α and β in mouse osteoblast (MOBs) showed that 20b and 32 exerts osteogenic efficacy via activation of estrogen receptor-β preferentially. Additionally, compounds showed significant anticancer activity in a panel of cancer cell lines within the range of (IC50) 6.54-27.79μM. The most active molecule, 22b inhibited proliferation of cells by inducing apoptosis and arresting cell cycle at sub-G0 phase with concomitant decrease in cells at S phase.

Estrogen Receptor β in Melanoma: From Molecular Insights to Potential Clinical Utility

Cutaneous melanoma is an aggressive tumor; its incidence has been reported to increase fast in the past decades. Melanoma is a heterogeneous tumor, with most patients harboring mutations in the BRAF or NRAS oncogenes, leading to the overactivation of the MAPK/ERK and PI3K/Akt pathways. The current therapeutic approaches are based on therapies targeting mutated BRAF and the downstream pathway, and on monoclonal antibodies against the immune checkpoint blockade. However, treatment resistance and side effects are common events of these therapeutic strategies. Increasing evidence supports that melanoma is a hormone-related cancer. Melanoma incidence is higher in males than in females, and females have a significant survival advantage over men. Estrogens exert their effects through estrogen receptors (ERα and ERβ) that affect cancer growth in an opposite way: ERα is associated with a proliferative action and ERβ with an anticancer effect. ERβ is the predominant ER in melanoma, and its expression decreases in melanoma progression, supporting its role as a tumor suppressor. Thus, ERβ is now considered as an effective molecular target for melanoma treatment. 17β-estradiol was reported to inhibit melanoma cells proliferation; however, clinical trials did not provide the expected survival benefits. In vitro studies demonstrate that ERβ ligands inhibit the proliferation of melanoma cells harboring the NRAS (but not the BRAF) mutation, suggesting that ERβ activation might impair melanoma development through the inhibition of the PI3K/Akt pathway. These data suggest that ERβ agonists might be considered as an effective treatment strategy, in combination with MAPK inhibitors, for NRAS mutant melanomas. In an era of personalized medicine, pretreatment evaluation of the expression of ER isoforms together with the concurrent oncogenic mutations should be considered before selecting the most appropriate therapeutic intervention. Natural compounds that specifically bind to ERβ have been identified. These phytoestrogens decrease the proliferation of melanoma cells. Importantly, these effects are unrelated to the oncogenic mutations of melanomas, suggesting that, in addition to their ERβ activating function, these compounds might impair melanoma development through additional mechanisms. A better identification of the role of ERβ in melanoma development will help increase the therapeutic options for this aggressive pathology.

Neural-Network Scoring Functions Identify Structurally Novel Estrogen-Receptor Ligands

The magnitude of the investment required to bring a drug to the market hinders medical progress, requiring hundreds of millions of dollars and years of research and development. Any innovation that improves the efficiency of the drug-discovery process has the potential to accelerate the delivery of new treatments to countless patients in need. "Virtual screening," wherein molecules are first tested in silico in order to prioritize compounds for subsequent experimental testing, is one such innovation. Although the traditional scoring functions used in virtual screens have proven useful, improved accuracy requires novel approaches. In the current work, we use the estrogen receptor to demonstrate that neural networks are adept at identifying structurally novel small molecules that bind to a selected drug target, ultimately allowing experimentalists to test fewer compounds in the earliest stages of lead identification while obtaining higher hit rates. We describe 39 novel estrogen-receptor ligands identified in silico with experimentally determined Ki values ranging from 460 nM to 20 μM, presented here for the first time.