A molecular dynamics perspective into estrogen receptor inhibition by selective flavonoids as alternative therapeutic options.

Zearalenone is an estrogenic mycotoxin which is a common food contaminant and has been implicated in increasing the incidence of carcinogenesis and other reproductive health ailments through the estrogen receptor alpha (ERα) pathway. Competitive ERα blockers such as 4-Hydroxytamoxifen (OHT), are synthetic FDA approved drugs which, albeit being an effective anticancer agent, induces life altering side effects. For this reason, there is an increased interest in the use of naturally occurring medicinal plant products such as flavonoids. This study aimed to identity flavonoid ERα inhibitors and provide insights into the mechanism of inhibition using computational techniques. The Molecular Mechanics/Generalized Born Surface Area calculations revealed that quercetrin, hesperidin, epigallocatechin 3-gallate and kaempferol 7-O-glucoside out of 14 flavonoids had higher binding affinity for ERα than OHT. The structural analysis revealed that the binding of the compounds to the receptor lead to dynamic alterations, which induced conformational shift in the structure and orientation of the receptor resulting in stabilised, compact and low energy systems. The results of this study provide imperative information that supports the use of flavonoids in the inhibition of ERα to prevent or ameliorate the consequential adverse effects associated with zearalenone exposure.Communicated by Ramaswamy H. Sarma.

Protein druggability assessment for natural products using in silico simulation: A case study with estrogen receptor and the flavonoid genistein.

Traditional herbal medicine (THM) comprises a vast number of natural compounds. Most of them are metabolized into different structures after administration, which makes the clarification of THM's mode of action more complicated. To evaluate the biological activities of those components and metabolites, in silico simulation technology is helpful. We focused on mixed-solvent molecular dynamics (MD) simulation for druggability assessment of natural products. Mixed-solvent MD is an in silico simulation method for the exploration of ligand-binding sites on target proteins, which uses water and an organic molecule mixture. The selection of organic small molecules is an important factor for predicting the characteristics of natural products. In this study, we used the known crystal structure of estrogen receptors with genistein as a test case and explored fragments reflecting the characteristics of natural products. We found that structures with a 4-pyrone structure are more often included in the natural products database compared with the DrugBank database, and we selectively detected the known-binding sites of estrogen receptor α and ß. The results indicate that the 4-pyrone structure might be promising for predicting the protein druggability of flavonoids. Additionally, mixed-solvent MD simulation discriminates the selectivity of genistein between estrogen receptor ß and α, indicating that the simulation can be evaluated using indices that differ from those of traditional ligand docking. Although this approach is still in its early stages, it has the potential to provide valuable information for understanding the diverse biological activities of natural products.

Food flavonoid ligand structure/estrogen receptor-α affinity relationships - toxicity or food functionality?

In silico molecular modelling is used to study interactions between flavonoid phytoestrogens and estrogen receptor (ER)α. Twenty flavonoids from foods were studied; e.g., genistein from soy, naringenin from grapefruit, phloretin from pears, chrysin from oyster mushrooms. These potential ligands' molecular attributes and their spatial arrangements that favour binding to the ligand binding cleft (LBC) of ERα are identified, and Docking Scores calculated. The Docking Score order is the same as the estrogenicity order for 8 of the flavonoids studied in detail. The number and position of flavonoid ring hydroxyls influence the Docking Scores which might relate to ERα's bio-activity. Hydrophobic interactions between ligands and ERα are also important; the number of rotatable CC bonds in ligands likely affects the magnitude of hydrophobic interactions and ligand fit. Our findings suggest that flavonoids with diverse structural features could have different binding energies and binding affinities with ERα, which might confer different functionalities and toxicities.

The Multiple Biological Targets of Hops and Bioactive Compounds.

Botanical dietary supplements for women's health are increasingly popular. Older women tend to take botanical supplements such as hops as natural alternatives to traditional hormone therapy to relieve menopausal symptoms. Especially extracts from spent hops, the plant material remaining after beer brewing, are enriched in bioactive prenylated flavonoids that correlate with the health benefits of the plant. The chalcone xanthohumol (XH) is the major prenylated flavonoid in spent hops. Other less abundant but important bioactive prenylated flavonoids are isoxanthohumol (IX), 8-prenylnaringenin (8-PN), and 6-prenylnaringenin (6-PN). Pharmacokinetic studies revealed that these flavonoids are conjugated rapidly with glucuronic acid. XH also undergoes phase I metabolism in vivo to form IX, 8-PN, and 6-PN. Several hop constituents are responsible for distinct effects linked to multiple biological targets, including hormonal, metabolic, inflammatory, and epigenetic pathways. 8-PN is one of the most potent phytoestrogens and is responsible for hops' estrogenic activities. Hops also inhibit aromatase activity, which is linked to 8-PN. The weak electrophile, XH, can activate the Keap1-Nrf2 pathway and turn on the synthesis of detoxification enzymes such as NAD(P)H-quinone oxidoreductase 1 and glutathione S-transferase. XH also alkylates IKK and NF-κB, resulting in anti-inflammatory activity. Antiobesity activities have been described for XH and XH-rich hop extracts likely through activation of AMP-activated protein kinase signaling pathways. Hop extracts modulate the estrogen chemical carcinogenesis pathway by enhancing P450 1A1 detoxification. The mechanism appears to involve activation of the aryl hydrocarbon receptor (AhR) by the AhR agonist, 6-PN, leading to degradation of the estrogen receptor. Finally, prenylated phenols from hops are known inhibitors of P450 1A1/2; P450 1B1; and P450 2C8, 2C9, and 2C19. Understanding the biological targets of hop dietary supplements and their phytoconstituents will ultimately lead to standardized botanical products with higher efficacy, safety, and chemopreventive properties.

Isoamericanoic Acid B from Acer tegmentosum as a Potential Phytoestrogen.

Phytoestrogens derived from plants have attracted the attention of the general public and the medical community due to their potentially beneficial role in relieving menopausal symptoms. The deciduous tree Acer tegmentosum Maxim (Aceraceae) has long been utilized in Korean folk medicine to alleviate many physiological disorders, including abscesses, surgical bleeding, and liver diseases. In order to explore structurally and/or biologically new constituents from Korean medicinal plants, a comprehensive phytochemical study was carried out on the bark of A. tegmentosum. One new phenolic compound with a 1,4-benzodioxane scaffold, isoamericanoic acid B (1), as well as with nine known phenolic compounds (2⁻10), were successfully isolated from the aqueous extracts of the bark of A. tegmentosum. A detailed analysis using 1D and 2D NMR spectroscopy, electronic circular dichroism (ECD) spectral data, and LC/MS afforded the unambiguous structural determination of all isolated compounds, including the new compound 1. In addition, compounds 2, 4, 5, and 9 were isolated and identified from the bark of A. tegmentosum for the first time. All isolated compounds were tested for their estrogenic activities using an MCF-7 BUS cell proliferation assay, which revealed that compounds 1, 2, and 10 showed moderate estrogenic activity. To study the mechanism of this estrogenic effect, a docking simulation of compound 1, which showed the best estrogenic activity, was conducted with estrogen receptor (ER) -α and ER-ß, which revealed that it interacts with the key residues of ER-α and ER-ß. In addition, compound 1 had slightly higher affinity for ER-ß than ER-α in the calculated Gibbs free energy for 1:ER-α and 1:ER-ß. Thus, the present experimental evidence demonstrated that active compound 1 from A. tegmentosum could be a promising phytoestrogen for the development of natural estrogen supplements.

Beyond the Antioxidant Activity of Dietary Polyphenols in Cancer: the Modulation of Estrogen Receptors (ERs) Signaling.

The potential "health benefits" of dietary polyphenols have been ascribed to their direct antioxidant activity and their impact on the regulation of cell and tissue redox balance. However, because of the relative poor bioavailability of many of these compounds, their effects could not be easily explained by the antioxidant action, which may occur only at high circulating and tissue concentrations. Therefore, many efforts have been put forward to clarify the molecular mechanisms underlining the biological effect of polyphenols in physiological and pathological conditions. Polyphenols' bioavailability, metabolism, and their effects on enzyme, membrane, and/or nuclear receptors and intracellular transduction mechanisms may define the overall impact of these compounds on cancer risk and progression, which is still debated and not yet clarified. Polyphenols are able to bind to estrogen receptor α (ERα) and ß (ERß), and therefore induce biological effects in human cells through mimicking or inhibiting the action of endogenous estrogens, even at low concentrations. In this work, the role and effects of food-contained polyphenols in hormone-related cancers will be reviewed, mainly focusing on the different polyphenols' mechanisms of action with particular attention on their estrogen receptor-based effects, and on the consequences of such processes on tumor progression and development.

Toxicity and non-harmful effects of the soya isoflavones, genistein and daidzein, in embryos of the zebrafish, Danio rerio.

Based on the assumed oestrogenic and apoptotic properties of soya isoflavones (genistein, daidzein), and following the current OECD test-guidelines and principle of 3Rs, we have studied the potential toxicity of phytochemicals on the zebrafish embryos test (ZFET). For this purpose, zebrafish embryos at 2-3 h post-fertilisation (hpf) were exposed to both soya isoflavones (from 1.25 mg/L to 20 mg/L) and assayed until 96 hpf. Lethal and sub-lethal endpoints (mortality, hatching rates and malformations) were estimated in the ZFET, which was expanded to potential gene expression markers, determining the lowest observed effect (and transcriptional) concentrations (LOEC, LOTEC), and the no-observable effect (and transcriptional) concentrations (NOEC, NOTEC). The results revealed that genistein is more toxic (LC50-96 hpf: 4.41 mg/L) than daidzein (over 65.15 mg/L). Both isoflavones up-regulated the oestrogen (esrrb) and death receptors (fas) and cyp1a transcript levels. Most thyroid transcript signals were up-regulated by genistein (except for thyroid peroxidase/tpo), and the hatching enzyme (he1a1) was exclusively up-regulated by daidzein (from 1.25 mg/L onwards). The ZFET proved suitable for assessing toxicant effects of both isoflavones and potential disruptions (i.e. oestrogenic, apoptotic, thyroid, enzymatic) during the embryogenesis and the endotrophic larval period.

Identification by Molecular Docking ofHomoisoflavones from Leopoldia comosa as Ligands of Estrogen Receptors.

The physiological responses to estrogen hormones are mediated within specific tissues by at least two distinct receptors, ER and ER. Several natural and synthetic molecules show activity by interacting with these proteins. In particular, a number of vegetal compounds known as phytoestrogens shows estrogenic or anti-estrogenic activity. The majority of these compounds belongs to the isoflavones family and the most representative one, genistein, shows anti-proliferative effects on various hormone-sensitive cancer cells, including breast, ovarian and prostate cancer. In this work we describe the identification of structurally related homoisoflavones isolated from Leopoldia comosa (L.) Parl. (L. comosa), a perennial bulbous plant, potentially useful as hormonal substitutes or complements in cancer treatments. Two of these compounds have been selected as potential ligands of estrogen receptors (ERs) and the interaction with both isoforms of estrogen receptors have been investigated through molecular docking on their crystallographic structures. The results provide evidence of the binding of these compounds to the target receptors and their interactions with key residues of the active sites of the two proteins, and thus they could represent suitable leads for the development of novel tools for the dissection of ER signaling and the development of new pharmacological treatments in hormone-sensitive cancers.

In silico binding of 4,4'-bisphenols predicts in vitro estrogenic and antiandrogenic activity.

Bisphenols, anthropogenic pollutants, leach from consumer products and have potential to be ingested and are excreted in waste. The endocrine disrupting effects of highly manufactured bisphenols (BPA, BPS, and BPF) are known, however the activities of others are not. Here, the estrogenic and androgenic activities of a series of 4,4'-bisphenols that vary at the inter-connecting bisphenol bridge were determined (BPA, BPB, BPBP, BPC2, BPE, BPF, BPS, and BPZ) and compared to in silico binding to estrogen receptor-alpha and the androgen receptor. Bioassay results showed the order of estrogenicity (BPC2 (strongest) > BPBP > BPB > BPZ > BPE > BPF > BPA > BPS, r2 = 0.995) and anti-androgenicity (BPC2 (strongest) > BPE, BPB, BPA, BPF, and BPS, r2 = 0.996) correlated to nuclear receptor binding affinities. Like testosterone and the anti-androgen hydroxyflutamide, bisphenol fit in the ligand-binding domain through hydrogen-bonding at residues Thr877 and Asn705, but also interacted at either Cys784/Ser778 or Gln711 through the other phenol ring. This suggests the 4,4'-bisphenols, like hydroxyflutamide, are androgen receptor antagonists. Hydrogen-bond trends between ERα and the 4,4'-bisphenols were limited to residue Glu353, which interacted with the -OH of one phenol and the -OH of the A ring of 17ß-estradiol; hydrogen-bonding varied at the -OH of ring D of 17ß-estradiol and the second phenol -OH group. While both estrogen and androgen bioassays correlated to in silico results, conservation of hydrogen-bonding residues in the androgen receptor provides a convincing picture of direct antagonist binding by 4,4'-bisphenols.

Antiestrogens: structure-activity relationships and use in breast cancer treatment.

About 70% of breast tumors express estrogen receptor alpha (ERα), which mediates the proliferative effects of estrogens on breast epithelial cells, and are candidates for treatment with antiestrogens, steroidal or non-steroidal molecules designed to compete with estrogens and antagonize ERs. The variable patterns of activity of antiestrogens (AEs) in estrogen target tissues and the lack of systematic cross-resistance between different types of molecules have provided evidence for different mechanisms of action. AEs are typically classified as selective estrogen receptor modulators (SERMs), which display tissue-specific partial agonist activity (e.g. tamoxifen and raloxifene), or as pure AEs (e.g. fulvestrant), which enhance ERα post-translational modification by ubiquitin-like molecules and accelerate its proteasomal degradation. Characterization of second- and third-generation AEs, however, suggests the induction of diverse ERα structural conformations, resulting in variable degrees of receptor downregulation and different patterns of systemic properties in animal models and in the clinic.

The treatment effects of flaxseed-derived secoisolariciresinol diglycoside and its metabolite enterolactone on benign prostatic hyperplasia involve the G protein-coupled estrogen receptor 1.

Secoisolariciresinol diglucoside (SDG), a lignan extracted from flaxseed, has been shown to suppress benign prostatic hyperplasia (BPH). However, little is known about the mechanistic basis for its anti-BPH activity. The present study showed that enterolactone (ENL), the mammalian metabolite of SDG, shared the similar binding site of G1 on a new type of membranous estrogen receptor, G-protein-coupled estrogen eceptor 1 (GPER), by docking simulations method. ENL and G1 (the specific agonist of GPER) inhibited the proliferation of human prostate stromal cell line WPMY-1 as shown by MTT assay and arrested cell cycle at the G0/G1 phase, which was displayed by propidium iodide staining following flow cytometer examination. Silencing GPER by short interfering RNA attenuated the inhibitory effect of ENL on WPMY-1 cells. The therapeutic potential of SDG in the treatment of BPH was confirmed in a testosterone propionate-induced BPH rat model. SDG significantly reduced the enlargement of the rat prostate and the number of papillary projections of prostatic alveolus and thickness of the pseudostratified epithelial and stromal cells when comparing with the model group. Mechanistic studies showed that SDG and ENL increased the expression of GPER both in vitro and in vivo. Furthermore, ENL-induced cell cycle arrest may be mediated by the activation of GPER/ERK pathway and subsequent upregulation of p53 and p21 and downregulation of cyclin D1. This work, in tandem with previous studies, will enhance our knowledge regarding the mechanism(s) of dietary phytochemicals on BPH prevention and ultimately expand the scope of adopting alternative approaches in BPH treatment.

Artonin E and Structural Analogs from Artocarpus Species Abrogates Estrogen Receptor Signaling in Breast Cancer.

The increasing rate of mortality ensued from breast cancer has encouraged research into safer and efficient therapy. The human Estrogen receptor α has been implicated in the majority of reported breast cancer cases. Molecular docking employing Glide, Schrodinger suite 2015, was used to study the binding affinities of small molecules from the Artocarpus species after their drug-like properties were ascertained. The structure of the ligand-binding domain of human Estrogen receptor α was retrieved from Protein Data Bank while the structures of compounds were collected from PubChem database. The binding interactions of the studied compounds were reported as well as their glide scores. The best glide scored ligand, was Artonin E with a score of -12.72 Kcal when compared to other studied phytomolecules and it evoked growth inhibition of an estrogen receptor positive breast cancer cells in submicromolar concentration (3.8-6.9 µM) in comparison to a reference standard Tamoxifen (18.9-24.1 µM) within the tested time point (24-72 h). The studied ligands, which had good interactions with the target receptor, were also drug-like when compared with 95% of orally available drugs with the exception of Artoelastin, whose predicted physicochemical properties rendered it less drug-like. The in silico physicochemical properties, docking interactions and growth inhibition of the best glide scorer are indications of the anti-breast cancer relevance of the studied molecules.

Evaluation of the Biological Activity of Opuntia ficus indica as a Tissue- and Estrogen Receptor Subtype-Selective Modulator.

Phytoestrogens are selective estrogen receptor modulators (SERMs) with potential for use in hormone replacement therapy (HRT) to relieve peri/postmenopausal symptoms. This study was aimed at elucidating the molecular mechanisms underlying the SERM properties of the extract of Korean-grown Opuntia ficus-indica (KOFI). The KOFI extract induced estrogen response element (ERE)-driven transcription in breast and endometrial cancer cell lines and the expression of endogenous estrogen-responsive genes in breast cancer cells. The flavonoid content of different KOFI preparations affected ERE-luciferase activities, implying that the flavonoid composition likely mediated the estrogenic activities in cells. Oral administration of KOFI decreased the weight gain and levels of both serum glucose and triglyceride in ovariectomized (OVX) rats. Finally, KOFI had an inhibitory effect on the 17ß-estradiol-induced proliferation of the endometrial epithelium in OVX rats. Our data demonstrate that KOFI exhibited SERM activity with no uterotrophic side effects. Therefore, KOFI alone or in combination with other botanical supplements, vitamins, or minerals may be an effective and safe alternative active ingredient to HRTs, for the management of postmenopausal symptoms. Copyright © 2016 John Wiley & Sons, Ltd.

Inhibitory effect of cadmium on estrogen signaling in zebrafish brain and protection by zinc.

The present study was conducted to assess the effects of Cd exposure on estrogen signaling in the zebrafish brain, as well as the potential protective role of Zn against Cd-induced toxicity. For this purpose, the effects on transcriptional activation of the estrogen receptors (ERs), aromatase B (Aro-B) protein expression and molecular expression of related genes were examined in vivo using wild-type and transgenic zebrafish embryos. For in vitro studies, an ER-negative glial cell line (U251MG) transfected with different zebrafish ER subtypes (ERα, ERß1 and ERß2) was also used. Embryos were exposed either to estradiol (E2 ), Cd, E2 +Cd or E2 +Cd+Zn for 72 h and cells were exposed to the same treatments for 30 h. Our results show that E2 treatment promoted the transcriptional activation of ERs and increased Aro-B expression, at both the protein and mRNA levels. Although exposure to Cd, does not affect the studied parameters when administered alone, it significantly abolished the E2 -stimulated transcriptional response of the reporter gene for the three ER subtypes in U251-MG cells, and clearly inhibited the E2 induction of Aro-B in radial glial cells of zebrafish embryos. These inhibitory effects were accompanied by a significant downregulation of the expression of esr1, esr2a, esr2b and cyp19a1b genes compared to the E2 -treated group used as a positive control. Zn administration during simultaneous exposure to E2 and Cd strongly stimulated zebrafish ERs transactivation and increased Aro-B protein expression, whereas mRNA levels of the three ERs as well as the cyp19a1b remained unchanged in comparison with Cd-treated embryos. In conclusion, our results clearly demonstrate that Cd acts as a potent anti-estrogen in vivo and in vitro, and that Cd-induced E2 antagonism can be reversed, at the protein level, by Zn supplement. Copyright © 2016 John Wiley & Sons, Ltd.

Structural changes of 6a-hydroxy-pterocarpans upon heating modulate their estrogenicity.

The isoflavonoid composition of an ethanolic extract of fungus-treated soybean sprouts was strongly altered by a combined acid/heat treatment. UHPLC-MS analysis showed that 6a-hydroxy-pterocarpans were completely converted to their respective, more stable, 6a,11a-pterocarpenes, whereas other isoflavonoids, from the isoflavone and coumestan subclasses, were affected to a much lesser extent (loss of ∼15%). Subsequently, mixtures enriched in prenylated 6a-hydroxy-pterocarpans (pools of glyceollin I/II/III and glyceollin IV/VI) or prenylated 6a,11a-pterocarpenes (pools of dehydroglyceollin I/II/III and dehydroglyceollin IV/VI) were purified, and tested for activity on both human estrogen receptors (ERα and ERß). In particular, the response toward ERα changed, from agonistic for glyceollins to antagonistic for dehydroglyceollins. Toward ERß a decrease in agonistic activity was observed. These results indicate that the introduction of a double bond with the concomitant loss of a hydroxyl group in 6a-hydroxy-pterocarpans extensively modulates their estrogenic activity.

Interactions of isoflavones and other plant derived estrogens with estrogen receptors for prevention and treatment of breast cancer-considerations concerning related efficacy and safety.

Phytoestrogens are natural endocrine disruptors that interfere with estrogenic pathways. They insert directly within the hormone-binding domain of ERα and ß, with a preference for the ß isoform of which the concentration predominates in the normal mammary epithelium. Since ERß antagonizes the growth promoting effect of ERα, which is mainly expressed in estrogen-sensitive tumor cells, a potential protective action against breast cancer incidence has been ascribed to phytoestrogens. The fact that Asian women living in far-east countries who consume isoflavone-rich food are less subjected to breast cancer emergence than their congeners in the USA as well as Caucasian women has been advocated to justify such a concept. Overview of data concerning the mechanism of action phytoestrogens reveals that such a view is an oversimplification: Such compounds interfere with a huge panel of regulatory proteins, giving rise to both promoting and antagonizing carcinogenic effects. Moreover, various physiological and pathological factors able to amplify these effects are not often sufficiently taken into account, which increases the difficulty to interpret data. Nevertheless, this overview of data established that chemical structures and concentrations modulate such effects: at the micromolar level, isoflavones activate ERα-mediated transcription and breast cancer cell proliferation while flavones fail to induce any significant promoting effects. At higher doses, both classes of compounds may display an antitumor activity. Reasons for such distinct behaviors as well as their potential impact in therapeutic applications are analyzed here. Ability of isoflavones and flavones to antagonize the association of calmodulin to ERα, which is required for its enhanced transcriptional activity is evoked to justify the antitumor activity ascribed to some flavones. Finally, a suspicion that peculiar classes of phytoestrogens may adopt a SERM-like conformation is addressed in a context of selection and synthesis of compounds with non-equivocal therapeutic value. This article is part of a Special Issue entitled "Phytoestrogens".

Discovery and structure-activity analysis of selective estrogen receptor modulators via similarity-based virtual screening.

A number of selective estrogen receptor modulators (SERMs) were discovered from the SPECS database via a simple protocol. Based on two reference SERMs we identified via structure-based virtual screening previously, ligand-based similarity search and molecular docking filtering were conducted to identify novel SERMs from SPECS library. Among the 36 purchased compounds, 21 were confirmed to be active by in vitro assays, and 10 showed dual profile properties, namely as antagonists of ERα and agonists of ERß. The anti-proliferative potency of these ligands was also evaluated against MCF-7 cell lines. Further investigation of the anti-proliferative mechanism of compound 3a suggested that it induced a G1 cell cycle arrest in ERα positive MCF-7 cell through ERα mediated cyclin D1 down-regulation.

Estrogenicity of outer scales of onion on uteri of immature mice.

We aimed to investigate the estrogen-like activities of the outer scales of onion and garlic on the uteri of immature mice. This work compared the estrogenic effects induced by estradiol with the effects of plant extract (onion, garlic) in models of immature mice (n = 72). The animals were divided into 6 groups, with 12 animals in each group, as follows: Group I (control group), Group II (estradiol-treated group), Group III (onion extract treated group), Group IV (onion extract treated group after blockage of estrogen receptors), Group V (garlic extract treated group), and Group VI (garlic extract treated group after blockage of estrogen receptors). Uterine wet weight/body mass ratios were determined. Uterotrophic bioassay, immunohistochemical assay for estrogen receptor and proliferative marker Ki67, uterine contractility, and serum estrogen levels were investigated. Onion extract induced proliferative changes in the uterus, it also increased the uterine mass and epithelial cell height. Also, the frequency and amplitude of myometrial contractility were significantly increased in the group treated with onion extract. This estrogenic activity could be attributed to the quercetin and daidzein content, and activation of estrogenic receptors, as these effects disappeared after blockage of E2 receptors. Our results support the possible estrogenic properties of the onion extract, which could be attributed to quercetin and daidzein, but not that of garlic extract.

QSAR study of natural estrogen-like isoflavonoids and diphenolics from Thai medicinal plants.

Two species of Thai medicinal plants, Dalbergia parviflora R. (Leguminosae) and Belamcanda chinensis L. (Iridaceae), used traditionally for the regulation of menstrual disorders, have been found to contain a large number of potential estrogen-like compounds. A set of some 55 isolated isoflavonoids and diphenolics showed a wide range of estrogen activity as determined in breast cancer MCF-7 and T47D cell proliferation assays. This set of compounds was studied by means of computational techniques including quantitative structure-activity relationships (QSAR) and molecular modeling. It was found that the estrogenic potencies of the studied compounds depend mainly upon the presence/absence of hydroxyl groups attached to 3' and 5' positions of B ring of the isoflavone scaffold and the inter-atomic distance between the hydroxyl groups attached to the outer terminal positions 7 of A ring and 4' of B ring. In a QSAR model employing ligand-receptor interaction energy descriptors, the LigScore scoring function of Cerius(2) virtual screening module, which describes the receptor affinities of simultaneous binding to estrogenic receptors α and ß (ER(α) and ER(ß)), led to the best correlation between the observed estrogenic activities and computed descriptors. Consideration of independent binding to ER(α) and ER(ß) did not result in statistically significant QSAR models. It was thus concluded that simultaneous and possibly competitive interaction of the compounds with the ER(α) and ER(ß) receptors, in which the presence of hydroxyl groups at the abovementioned positions of the isoflavonoids and diphenolics molecular scaffold plays a dominant role, may determine the estrogenic potency of the considered phytochemicals.

Endocrine disrupting chemicals targeting estrogen receptor signaling: identification and mechanisms of action.

Many endocrine disrupting chemicals (EDCs) adversely impact estrogen signaling by interacting with two estrogen receptors (ERs): ERα and ERß. Though the receptors have similar ligand binding and DNA binding domains, ERα and ERß have some unique properties in terms of ligand selectivity and target gene regulation. EDCs that target ER signaling can modify genomic and nongenomic ER activity through direct interactions with ERs, indirectly through transcription factors such as the aryl hydrocarbon receptor (AhR), or through modulation of metabolic enzymes that are critical for normal estrogen synthesis and metabolism. Many EDCs act through multiple mechanisms as exemplified by chemicals that bind both AhR and ER, such as 3-methylcholanthrene. Other EDCs that target ER signaling include phytoestrogens, bisphenolics, and organochlorine pesticides, and many alter normal ER signaling through multiple mechanisms. EDCs can also display tissue-selective ER agonist and antagonist activities similar to selective estrogen receptor modulators (SERMs) designed for pharmaceutical use. Thus, biological effects of EDCs need to be carefully interpreted because EDCs can act through complex tissue-selective modulation of ERs and other signaling pathways in vivo. Current requirements by the U.S. Environmental Protection Agency require some in vitro and cell-based assays to identify EDCs that target ER signaling through direct and metabolic mechanisms. Additional assays may be useful screens for identifying EDCs that act through alternative mechanisms prior to further in vivo study.