Structure-activity relationships for a large diverse set of natural, synthetic, and environmental estrogens

Surrogate docking: structure-based virtual screening at high throughput speed

Structure-based screening using fully flexible docking is still too slow for large molecular libraries. High quality docking of a million molecule library can take days even on a cluster with hundreds of CPUs. This performance issue prohibits the use of fully flexible docking in the design of large combinatorial libraries. We have developed a fast structure-based screening method, which utilizes docking of a limited number of compounds to build a 2D QSAR model used to rapidly score the rest of the database. We compare here a model based on radial basis functions and a Bayesian categorization model. The number of compounds that need to be actually docked depends on the number of docking hits found. In our case studies reasonable quality models are built after docking of the number of molecules containing approximately 50 docking hits. The rest of the library is screened by the QSAR model. Optionally a fraction of the QSAR-prioritized library can be docked in order to find the true docking hits. The quality of the model only depends on the training set size - not on the size of the library to be screened. Therefore, for larger libraries the method yields higher gain in speed no change in performance. Prioritizing a large library with these models provides a significant enrichment with docking hits: it attains the values of approximately 13 and approximately 35 at the beginning of the score-sorted libraries in our two case studies: screening of the NCI collection and a combinatorial libraries on CDK2 kinase structure. With such enrichments, only a fraction of the database must actually be docked to find many of the true hits. The throughput of the method allows its use in screening of large compound collections and in the design of large combinatorial libraries. The strategy proposed has an important effect on efficiency but does not affect retrieval of actives, the latter being determined by the quality of the docking method itself.

Metabolism of glycitein (7,4'-dihydroxy-6-methoxy-isoflavone) by human gut microflora

Gut microbial disappearance and metabolism of the soy isoflavone glycitein, 7,4'-dihydroxy-6-methoxyisoflavone, were investigated by incubating glycitein anaerobically with feces from 12 human subjects. The subjects' ages ranged from 24 to 53 years with a body mass index (BMI) of 20.9-25.8 kg/m(2) (mean BMI = 24.0 +/- 1.1 kg/m(2)). Glycitein disappearance followed an apparent first-order rate loss. Fecal glycitein disappearance rates for the subjects segregated into three different groups described as high (k = 0.67 +/- 0.14/h), moderate (k = 0.34 +/- 0.04/h), and low (k = 0.15 +/- 0.07/h) glycitein degraders (p < 0.0001). There was no dose effect on the disappearance rates for each subject from 10 to 250 microM glycitein (average k = 0.32 +/- 0.03/h, p > 0.05). Four putative glycitein metabolites, characterized by liquid chromatography-mass spectrometry (electrospray ionization using positive ionization mode), were dihydroglycitein, dihydro-6,7,4'-trihydroxyisoflavone, and 5'-O-methyl-O-desmethylangolensin. Two subjects produced a metabolite tentatively identified as 6-O-methyl-equol, and one subject produced daidzein as an additional metabolite of glycitein. These results show that glycitein is metabolized by human gut microorganisms and may follow metabolic pathways similar to other soy isoflavones.

Soy processing affects metabolism and disposition of dietary isoflavones in ovariectomized BALB/c mice

Soy foods and nutritional supplements are widely consumed for potential health benefits. It was previously shown that isoflavone-supplemented diets, which contained equal genistein equivalents, differentially stimulated mammary tumor growth in athymic mice based on the degree of processing. This paper reports plasma pharmacokinetic analysis and metabolite identification using the parental mouse strain fed the same diets, which contained genistin, mixed isoflavones, Novasoy, soy molasses, or soy flour plus mixed isoflavones. Whereas the degree of soy processing did affect several parameters reflecting isoflavone bioavailability and gut microflora metabolism of daidzein to equol, stimulation of tumor growth correlated significantly with only the plasma concentration of aglycon genistein produced by the diets. This conclusion is consistent with the known estrogen agonist activity of genistein aglycon on mammary tumor growth. Conversely, plasma equol concentration was inversely correlated with the degree of soy processing. Although antagonism of genistein-stimulated tumor growth by equol could explain this result, the very low concentration of aglycon equol in plasma (12-fold lower relative to genistein) is inconsistent with any effect. These findings underscore the importance of food processing, which can remove non-nutritive components from soy, on the pharmacokinetics and pharmacodynamics of isoflavones. Such changes in diet composition affect circulating, and presumably target tissue, concentrations of genistein aglycon, which initiates estrogen receptor-mediated processes required for the stimulation of tumor growth in a mouse model for postmenopausal breast cancer.

Preparative monohydroxyflavanone syntheses and a protocol for gas chromatography-mass spectrometry analysis of monohydroxyflavanones

We describe a facile efficient, and preparative approach for monohydroxyflavanone syntheses. Using this protocol, a hydroxyl is regio-selectively introduced at one carbon of a flavanone A- or B-ring per synthesis. The seven possible isomers were each synthesized from the corresponding monomethoxymethoxylated 2'-hydroxychalcones in acidic solution. These monohydroxyflavanones were characterized using a gas chromatography-mass spectrometry (GC-MS) system that incorporated a DB-5 capillary column. Ours is the first report of a preparative synthetic method during which a single hydroxyl can be selectively added to a flavanone A- or B-ring at any position. We are also the first to develop a procedure that separates the seven isomers by GC and characterizes the mass spectra of the isomers. Both the synthetic method and the GC-MS conditions may become important tools during future flavanone metabolism and oxidation studies.

An in silico ensemble method for lead discovery: decision forest

Recent progress in combinatorial chemistry and parallel synthesis has radically changed the approach to drug discovery in the pharmaceutical industry. At present, thousands of compounds can be made in a short period, creating a need for fast and effective in silico methods to select the most promising lead candidates. Decision forest is a novel pattern recognition method, which combines the results of multiple distinct but comparable decision tree models to reach a consensus prediction. In this article, a decision forest model was developed using a structurally diverse training data set containing 232 compounds whose estrogen receptor binding activity was tested at the U.S. Food and Drug Administration (FDA)'s National Center for Toxicological Research (NCTR). The model was subsequently validated using a test data set of 463 compounds selected from the literature, and then applied to a large data set with 57,145 compounds as a screening example. The results show that the decision forest method is a fast, reliable and effective in silico approach, which could be useful in drug discovery.

Evidence that 17alpha-estradiol is biologically active in the uterine tissue: antiuterotonic and antiuterotrophic action

BACKGROUND

17alpha-Estradiol has been considered as the hormonally inactive isomer of 17beta-estradiol. Recently, nongenomic (smooth muscle relaxation) and genomic (light estrogenic activity) effects of 17alpha-estradiol have been reported, but no reports have yet determined its possible antiestrogenic activity. Therefore, this study investigated: the nongenomic action of 17alpha-estradiol on uterine contractile activity and its potential agonist-antagonist activity on uterine growth.

METHODS

Uterine rings from rats were isometrically recorded. Different concentrations (0.2-200 microM) of 17alpha-estradiol were tested on spontaneous contraction and equimolarly compared with 17beta-estradiol. To examine the mechanism of 17alpha-estradiol action, its effect was studied in presence of beta2-antagonist (propranolol), antiestrogens (tamoxifen and ICI 182,780) or inhibitors of protein synthesis (cycloheximide) and transcription (actinomycin D). Moreover, contractions induced by high potassium (KCl) solution or calcium in depolarized tissues by KCl-calcium free solution were exposed to 17alpha-estradiol. Collaterally, we performed an uterotrophic assay in adult ovariectomized rats measuring the uterine wet weight. The administration for three days of 0.3 microM/day/Kg 17beta-estradiol was equimolarly compared with the response produced by 17alpha-estradiol. Antiuterotrophic activity was assayed by administration of 0.3 microM/day/Kg 17beta-estradiol and various doses ratios (1:1, 1:3, 1:5, and 1:100) of 17alpha-estradiol.

RESULTS

The estradiol isomers elicited an immediate relaxation, concentration-dependent and reversible on spontaneous contraction. 17alpha-Estradiol presented lower potency than 17beta-estradiol although it did not antagonize 17beta-estradiol-induced relaxation. Relaxation to 17alpha-estradiol was not inhibited by propranolol, tamoxifen, ICI 182,780, cycloheximide or actinomycin D. The KCl contractions were also sensitive to 17alpha-estradiol-induced relaxation and calcium contractions in depolarized tissues were markedly prevented by 17alpha-estradiol, implying a reduction of extracellular calcium influx through voltage-operated calcium channels (VOCCs). Uterotrophic assay detected significant increase in uterine weight using 17alpha-estradiol, which was significantly minor as compared with 17beta-estradiol. 17alpha-Estradiol, at all doses ratios, significantly antagonized the hypertrophic response of 17beta-estradiol.

CONCLUSION

17alpha-Estradiol induces a relaxing effect, which may be independent of the classical estrogen receptor, nongenomic action, apparently mediated by inactivation of VOCCs. 17alpha-Estradiol is also a weak estrogen agonist (uterotrophic response); likewise, 17alpha-estradiol may act as an antiestrogen (antiuterotrophic response). The overall data document a nongenomic relaxing action and a novel antiestrogenic action of 17alpha-estradiol, which are relevant in estrogen-mediated uterine physiology.

ERbeta ligands. 3. Exploiting two binding orientations of the 2-phenylnaphthalene scaffold to achieve ERbeta selectivity

The 2-phenylnaphthalene scaffold was explored as a simplified version of genistein in order to identify ER selective ligands. With the aid of docking studies, positions 1, 4, and 8 of the 2-phenylnaphthalene template were predicted to be the most potentially influential positions to enhance ER selectivity using two different binding orientations. Both orientations have the phenol moiety mimicking the A-ring of genistein. Several compounds predicted to adopt orientations similar to that of genistein when bound to ERbeta were observed to have slightly higher ER affinity and selectivity than genistein. The second orientation we exploited, which was different from that of genistein when bound to ERbeta, resulted in the discovery of several compounds that had superior ER selectivity and affinity versus genistein. X-ray structures of two ER selective compounds (i.e., 15 and 47) confirmed the alternate binding mode and suggested that substituents at positions 1 and 8 were responsible for inducing selectivity. One compound (i.e., 47, WAY-202196) was further examined and found to be effective in two models of inflammation, suggesting that targeting ER may be therapeutically useful in treating certain chronic inflammatory diseases.

Evaluation of estrogenic activities of hydroxylated polycyclic aromatic hydrocarbons in cigarette smoke condensate

Estrogenic activities of cigarette smoke condensates obtained from the extraction of particulate matters from mainstream and sidestream cigarette smoke with benzene/ethanol were evaluated by using a yeast two-hybrid assay system expressing human estrogen receptor alpha (hERalpha). To identify the constituents of the cigarette smoke condensate which are responsible for the estrogenic activity, the condensate was fractionated into eleven fractions by liquid-liquid extractions. Among these fractions, the neutral fractions of mainstream and sidestream smoke showed the strongest estrogen receptor-mediated activity by the yeast two-hybrid assay. Then the neutral fractions were fractionated by medium-pressure liquid chromatography with silica gel column. In the fractions that showed strong estrogenic activity, 2-hydroxyfluorene (2-OHFle), 2- and 3-hydroxyphenanthrene (2- and 3-OHPhe), 1-hydroxypyrene (1-OHPyr) and n-propyl-p-hydroxybenzoate (n-PHB) were identified by LC- and GC-MS and HPLC with fluorescence detection. 2-OHFle, 2-OHPhe and n-PHB exhibited estrogenic activity, whereas weak activity was observed with 3-OHPhe and 1-OHPyr. Several other hydroxylated polycyclic aromatic hydrocarbons having no activity were also identified. This is a first study to identify estrogenic hydroxylated PAHs in cigarette smoke condensate. The present findings points out the necessity for detailed investigation of exposure to aerosols containing apparently estrogenic compounds.

Understanding the selectivity of genistein for human estrogen receptor-beta using X-ray crystallography and computational methods

We present X-ray crystallographic and molecular modeling studies of estrogen receptors-alpha and -beta complexed with the estrogen receptor-beta-selective phytoestrogen genistein, and coactivator-derived NR box peptides containing an LXXLL motif. We demonstrate that the ligand binding mode is essentially identical when genistein is bound to both isoforms, despite the considerably weaker affinity of this ligand for estrogen receptor-alpha. In addition, we examine subtle differences between binding site residues, providing an explanation for why genistein is modestly selective for the beta isoform. To this end, we also present the results of quantum chemical studies and thermodynamic arguments that yield insight to the nature of the interactions leading to estrogen receptor-beta selectivity. The importance of our analysis to structure-based drug design is discussed.

The impact of variable selection on the modelling of oestrogenicity

Many oestrogenic chemicals exert their activity via specific interactions with the oestrogen receptor (ER). The objective of the present study was to identify significant descriptors associated with the ER binding affinities of a large and diverse set of compounds to drive quantitative structure-activity relationships (QSARs). To this end, a variety of statistical methods were employed for variable selection. These included stepwise regression and partial least squares (PLS) analyses, as well as a non-linear recursive partitioning method (Formal Inference-based Recursive Modelling). A total of 157 molecular descriptors including quantum mechanical, graph theoretical, indicator variables and log P were used in the study. Furthermore, cluster analysis of variables was performed to identify groups of descriptors representing similar molecular features. Hierarchical PLS analyses were performed, where the scores of the significant components of either PLS or principle component analysis (PCA), performed separately on each cluster, were used as the variables for the top model. This reduced the number of the variables representing the larger clusters, leading to a similar number of descriptors for each distinct molecular feature. The results showed that the most important molecular properties for stronger ER binding affinity are molecular size and shape, the presence of a phenol moiety as well as other aromatic groups, hydrophobicity and presence of double bonds. The best PLS model obtained, in terms of predictive ability, was a hierarchical PLS model. However, a rigorous validation study showed that the MLR model using descriptors selected by stepwise regression has greater predictive power than the PLS models.

Examination of the in vitro (anti)estrogenic, (anti)androgenic and (anti)dioxin-like activities of tetralin, indane and isochroman derivatives using receptor-specific bioassays

Molecules derived from tetralin, indane and isochroman are often used in the synthesis of fragrance materials. The two polycyclic musk fragrances AHTN (6-acetyl-1,1,2,4,4,7-hexamethyltetralin), HHCB (1,2,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta-gamma-2-benzopyran) and ADBI (4-acetyl-1,1-dimethyl-6-tert-butylindane) are derived from tetralin, isochroman and indane, respectively. In previous studies, AHTN and HHCB have been shown to antagonize estrogen receptors (ERs), both in vitro and in vivo. Here, we used two newly developed reporter gene assays, to examine the agonistic and antagonistic properties of several indane, tetralin and isochroman derivatives towards the human androgen receptor (AR) and aryl hydrocarbon receptor (AhR). Additionally, we also assessed (anti)estrogenicity of these compounds. A number of compounds showed weak estrogenic activity towards the human ER alpha. Several compounds showed (anti)estrogenic effects, starting at a concentration of 0.1 microM. Surprisingly, almost all compounds were found to be AR antagonists, starting at 0.1 microM. None of the compounds tested, showed either agonism or antagonism towards the AhR. Non-specific effects via crosstalk of the AhR and the ER or AR can therefore be ruled out. As far as we are aware, molecules derived from indane, tetralin and isochroman showing direct interaction with the ER and AR have not been reported previously.

Oestrogenic activity ofp-hydroxybenzoic acid (common metabolite of paraben esters) and methylparaben in human breast cancer cell lines

This paper addresses the question of whether p-hydroxybenzoic acid, the common metabolite of parabens, possesses oestrogenic activity in human breast cancer cell lines. The alkyl esters of p-hydroxybenzoic acid (parabens) are used widely as preservatives in consumer products to which the human population is exposed and have been shown previously to possess oestrogenic activity and to be present in human breast tumour tissue, which is an oestrogen-responsive tissue. Recent work has shown p-hydroxybenzoic acid to give an oestrogenic response in the rodent uterotrophic assay. We report here that p-hydroxybenzoic acid possesses oestrogenic activity in a panel of assays in human breast cancer cell lines. p-Hydroxybenzoic acid was able to displace [(3)H]oestradiol from cytosolic oestrogen receptor of MCF7 human breast cancer cells by 54% at 5 x 10(6)-fold molar excess and by 99% at 10(7)-fold molar excess. It was able to increase the expression of a stably integrated oestrogen responsive reporter gene (ERE-CAT) at a concentration of 5 x 10(-4) M in MCF7 cells after 24 h and 7 days, which could be inhibited by the anti-oestrogen ICI 182 780 (Faslodex, fulvestrant). Proliferation of two human breast cancer cell lines (MCF7, ZR-75-1) could be increased by 10(-5) M p-hydroxybenzoic acid. Following on from previous studies showing a decrease in oestrogenic activity of parabens with shortening of the linear alkyl chain length, this study has compared the oestrogenic activity of p-hydroxybenzoic acid where the alkyl grouping is no longer present with methylparaben, which has the shortest alkyl group. Intrinsic oestrogenic activity of p-hydroxybenzoic acid was similar to that of methylparaben in terms of relative binding to the oestrogen receptor but its oestrogenic activity on gene expression and cell proliferation was lower than that of methylparaben. It can be concluded that removal of the ester group from parabens does not abrogate its oestrogenic activity and that p-hydroxybenzoic acid can give oestrogenic responses in human breast cancer cells.

QSAR Studies with E-State Index: Predicting Pharmacophore Signals for Estrogen Receptor Binding Affinity of Triphenylacrylonitriles

In connection to developing non-steroidal estrogen analogs, the present study explores the pharmacophore of triphenylacrylonitriles (Fig. 1) for binding affinity to estrogen receptor using Electrotopological State (E-State) indices of constituting atoms. The analysis shows the efficacy of E-State index in developing statistically acceptable model, which defines the electronic environment and topological states of diverse atoms in a molecule. The investigation concluded that electrophilic substitutions at C6 and C18 of the phenyl rings (A and C rings respectively) attached to C2 and C1 of ethylenic moiety, along with presence of hydroxyl substitution at C12 (ring B) and no. of non-hydrogen free terminal atoms of the molecule have influence on the binding affinity to the estrogen receptor.

In silico tools to aid risk assessment of endocrine disrupting chemicals

In silico or computational tools could be used more effectively in endocrine disruptor risk assessment for prescreening potential endocrine disruptors, improving experimental in vitro screening assay design and facilitating more thorough data analyses. The in silico tools reviewed here are three-fold and include the use of: (1) nuclear receptor (NR) crystal structures and homology models to examine potential modes of ligand binding by different representative compounds; (2) multivariate principal component analyses (PCA) techniques to select best predicted cell lines for endocrine disrupting chemicals (EDC) risk assessment purposes; (3) NR quantitative structure-activity relationships (QSARs) that can be constructed from varied biological data sources, using multivariate partial least squares (PLS) techniques and specific descriptors. The cytosolic and NR examples discussed here include the Ah receptor, (AhR), the human oestrogen receptor alpha (hERalpha) and the human pregnane X receptor (PXR). The varied biological data sets can be compared to give a more integrated dimension to receptor cross talk mechanisms, with further support from molecular modelling studies.

Unequivocal estrogen receptor-binding affinity of phthalate esters featured with ring hydroxylation and proper alkyl chain size

The effect of plasticizers phthalate esters (PEs) on health is a controversial subject. PEs are likely to be estrogenic, but the results on the potency obtained by many investigators are still inconsistent and the endocrine disrupting mechanism remains to be clarified. Here, we show that PEs acquire unequivocal binding affinities for human estrogen receptors (ERs) through ring hydroxylation that is possible in the environment and through metabolism. Unexpectedly, the acquired affinities of hydroxylated PEs (PEs-OH) were enhanced by elongation and branching of the ester alkyl chains. PEs-OH with alkyl chains more than six carbons may grope for a new binding site, which is inaccessible to PEs-OH with short chains. The strongest ER-binding affinity among the tested PEs-OH was close to that of diethylstilbestrol, the most potent synthetic ER-binder. Ring hydroxylation would be a new clue to the clarification of the endocrine disruption mechanism of PEs.

Isoflavones in soy infant formula: a review of evidence for endocrine and other activity in infants

Soy infant formulas are widely used, but few studies have evaluated long-term safety or examined specific forms of toxicity, such as to the endocrine or immune systems. This review focuses on newer experimental studies of the effects on estrogen activity, immune function, and thyroid economy of genistein and daidzein, two isoflavones in soy infant formula, and existing human studies of soy formula use. In order to judge the likelihood that an endpoint seen in laboratory studies might occur in soy-fed infants, we examined the doses and the resulting serum or plasma concentrations from the laboratory studies and compared them with doses and concentrations seen in soy-fed infants. We also summarized the estimates of the potency of the isoflavone compounds relative to estradiol. Given the scarcity and inconsistency of existing human data and the substantial laboratory evidence of hormonal and other activity at doses relevant to the soy-fed infant, we conclude that more clinical and epidemiological study is warranted.

Prenatal exposure of Long-Evans rats to 17alpha-ethinylestradiol modifies neither latent inhibition nor prepulse inhibition of the startle reflex but elicits minor deficits in exploratory behavior

Prenatal administration of synthetic estrogens in humans as well as lower mammals was reported to alter behavior in adulthood. The alterations remain to be characterized according to specific pathophysiological hypotheses. In this study, three common behavioral models of schizophrenia were tested, i.e., latent inhibition (LI), prepulse inhibition of the startle response (PPI) and hyperlocomotion under amphetamine. Female Long-Evans rats were injected i.p. with a solution of 17alpha-ethinylestradiol (15 microg kg(-1)) everyday from day 9 to 14 of pregnancy, and behavioral characteristics of their offspring, raised by Wistar foster mothers, were compared to those of rats born from dams injected with the vehicle only, over the same gestation period. LI was tested in a conditioned taste aversion and a conditioned passive avoidance paradigm followed by a parametric study of PPI and an evaluation of locomotion in an open field under saline or amphetamine (1.5 mg kg(-1)). Histological brain measurements were also carried out in a subset of the same rats. Neither LI nor PPI was altered using methods that had proven sensitive in previous pharmacological studies. Treated rats' locomotion was impaired, but amphetamine did not elicit a differential enhancement. A thinner Amon's horn layer was observed in their hippocampus. This indicates that standard models of schizophrenia did not fit to the behavioral abnormalities found by others and confirmed in this study. They were not due to the abnormal maternal care to pups elicited by the treatment.

Synthesis, in vitro and in vivo activity of benzophenone-based inhibitors of steroid sulfatase

Steroid sulfatase (STS) is an important new therapeutic target in oncology. Attempts to design nonsteroidal STS inhibitors, because of the oestrogenicity of the original lead oestrone 3-O-sulfamate in rodents, have led to the discovery of benzophenone-4,4'-O,O-bis-sulfamate (BENZOMATE, 3). The nonfused bicyclic BENZOMATE is a highly potent STS inhibitor in vitro, inhibiting STS activity in intact MCF-7 breast cancer cells by > 70% at 0.1 microM and in placental microsomes by > 98% at 10 microM. When MCF-7 cells were pre-treated with 3 at 1 microM and then washed to remove unbound inhibitor, the initial 94% inhibition was reduced to 89% suggesting that 3, like other sulfamate-based STS inhibitors, inhibits the enzyme irreversibly. This agent also inhibits rat liver STS activity by 84% and 93% respectively 24 h after a single dose of 1 or 10 mg/kg, demonstrating that BENZOMATE possesses similar in vivo potency to the established potent nonsteroidal inhibitor 667COUMATE. Several modifications were made to BENZOMATE structurally and effects on in vitro activity were examined. These structure-activity relationship studies show that its carbonyl and bis-sulfamate groups are pivotal for activity, although conformational flexibility is not required. Two rigid anthraquinone-based sulfamate derivatives however showed inhibitory activity significantly better than BENZOMATE in the MCF-7 cell assay. BENZOMATE and related analogues therefore represent an important class of non-steroidal STS inhibitor and lead compounds for future drug design.

Xenoestrogens and the induction of proliferative effects in breast cancer cells via direct activation of oestrogen receptor alpha

Environmental contamination with a variety of industrial products has been associated with developmental and reproductive abnormalities in wildlife species. Increasing evidence has suggested that bisphenol A (BPA) and 4-nonylphenol (NPH), two major endocrine-disrupting chemicals, might be responsible for adverse effects on humans as a consequence of ubiquitous use together with potential oestrogen-like activity. To provide insight into the oestrogen-like nature of BPA and NPH, their ability to activate a reporter gene construct via an oestrogen response element in the hormone-dependent breast cancer cell lines MCF7 and T47D was ascertained. Both compounds transactivated the endogenous oestrogen receptor (ER) alpha in a direct fashion since the anti-oestrogen 4-hydroxytamoxifen abolished the response. In addition, using steroid-receptor-negative HeLa cells engineered to express ERalpha and ERbeta and the hormone-binding domains of both ERalpha and ERbeta, BPA and NPH confirmed the direct transcriptional activity. Interestingly these properties were supported in MCF7 cells by the ability to autoregulate ERalpha expression as well as to induce its nuclear compartmentalization. We therefore evaluated by reverse transcriptase polymerase chain reaction the expression of oestrogen-controlled genes such as cathepsin D and TFF1 (formerly pS2), which were increased by both chemicals tested. The agonistic effects exhibited in all assays performed prompted the evaluation of a more complex biological response such as the proliferation of MCF7 and T47D cells. The same concentration of xenoestrogens eliciting substantial transcriptional activity significantly stimulated the proliferation of both breast cancer cell lines, although with a reduced effectiveness with respect to the natural hormone 17beta-oestradiol. The results indicate that the biological action of environmental oestrogen such as BPA and NPH should be taken into account for the potential impact on human disease-like hormone-dependent breast cancer. However, further studies are needed to clarify their bioavailability and metabolism as well as whether compound mixtures could produce noticeable effects by synergistic activity.

Identification of a minimal subset of receptor conformations for improved multiple conformation docking and two-step scoring

Docking and scoring are critical issues in virtual drug screening methods. Fast and reliable methods are required for the prediction of binding affinity especially when applied to a large library of compounds. The implementation of receptor flexibility and refinement of scoring functions for this purpose are extremely challenging in terms of computational speed. Here we propose a knowledge-based multiple-conformation docking method that efficiently accommodates receptor flexibility thus permitting reliable virtual screening of large compound libraries. Starting with a small number of active compounds, a preliminary docking operation is conducted on a large ensemble of receptor conformations to select the minimal subset of receptor conformations that provides a strong correlation between the experimental binding affinity (e.g., Ki, IC50) and the docking score. Only this subset is used for subsequent multiple-conformation docking of the entire data set of library (test) compounds. In conjunction with the multiple-conformation docking procedure, a two-step scoring scheme is employed by which the optimal scoring geometries obtained from the multiple-conformation docking are re-scored by a molecular mechanics energy function including desolvation terms. To demonstrate the feasibility of this approach, we applied this integrated approach to the estrogen receptor alpha (ERalpha) system for which published binding affinity data were available for a series of structurally diverse chemicals. The statistical correlation between docking scores and experimental values was significantly improved from those of single-conformation dockings. This approach led to substantial enrichment of the virtual screening conducted on mixtures of active and inactive ERalpha compounds.

Equol, a natural estrogenic metabolite from soy isoflavones: convenient preparation and resolution of R- and S-equols and their differing binding and biological activity through estrogen receptors alpha and beta

Equol is a metabolite produced in vivo from the soy phytoestrogen daidzein by the action of gut microflora. It is known to be estrogenic, so human exposure to equol could have significant biological effects. Equol is a chiral molecule that can exist as the enantiomers R-equol and S-equol. To study the biological activity of racemic (+/-)-equol, as well as that of its pure enantiomers, we developed an efficient and convenient method to prepare (+/-)-equol from available isoflavanoid precursors. Furthermore, we optimized a method to separate the enantiomers of equol by chiral HPLC, and we studied for the first time, the activities of the enantiomers on the two estrogen receptors, ERalpha and ERbeta. In binding assays, S-equol has a high binding affinity, preferential for ERbeta (K(i)[ERbeta]=16 nM; beta/alpha=13 fold), that is comparable to that of genistein (K(i)[ERbeta]=6.7 nM; beta/alpha=16), whereas R-equol binds more weakly and with a preference for ERalpha (K(i)[ERalpha]=50 nM; beta/alpha=0.29). All equol isomers have higher affinity for both ERs than does the biosynthetic precursor daidzein. The availability and the in vitro characterization of the equol enantiomers should enable their biological effects to be studied in detail.

A Genetically Encoded Fluorescent Indicator Capable of Discriminating Estrogen Agonists from Antagonists in Living Cells

A genetically encoded fluorescent indicator was developed for the detection and characterization of estrogen agonists and antagonists. Two different color mutants of green fluorescent protein were joined by a tandem fusion domain composed of LXXLL (L = leucine, X = any amino acid) motif from the nuclear receptor-box II of steroid receptor coactivator 1, a flexible linker sequence, and the estrogen receptor alpha ligand binding domain (ERalpha LBD). Monitoring real-time ligand-induced conformational change in the ERalpha LBD to recruit the LXXLL motif allowed screening of natural and synthetic estrogens in single living cells using fluorescence resonance energy-transfer technique. The indicator was named SCCoR (single cell-coactivator recruitment). The high sensitivity of the present indicator made it possible to distinguish between estrogen strong and weak agonists in a dose-dependent fashion, immediately after adding ligand to live cells. Discrimination of agonists from antagonists was efficiently achieved using the present study. The approach described here can be applied to develop biosensors for other hormone receptors as well.

Performance of (consensus) kNN QSAR for predicting estrogenic activity in a large diverse set of organic compounds

A novel method (in the context of quantitative structure-activity relationship (QSAR)) based on the k nearest neighbour (kNN) principle, has recently been introduced for the derivation of predictive structure-activity relationships. Its performance has been tested for estimating the estrogen binding affinity of a diverse set of 142 organic molecules. Highly predictive models have been obtained. Moreover, it has been demonstrated that consensus-type kNN QSAR models, derived from the arithmetic mean of individual QSAR models were statistically robust and provided more accurate predictions than the great majority of the individual QSAR models. Finally, the consensus QSAR method was tested with 3D QSAR and log P data from a widely used steroid benchmark data set.

Enantioselective recognition of mono-demethylated methoxychlor metabolites by the estrogen receptor

Metabolites of methoxychlor such as 2-(p-hydroxyphenyl)-2-(p-methoxyphenyl)-1,1,1-trichloroethane (mono-OH-MXC) and 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (bis-OH-MXC), have estrogenic activity. Mono-OH-MXC is a chiral compound in which the carbon atom bridging two benzene rings is the chiral centre. In previous studies the estrogenic activity of racemic mono-OH-MXC has been measured, and the activity of each enantiomer of this compound has not yet been elucidated. In this study, we evaluated the estrogen receptor-binding activity of each enantiomer of mono-OH-MXC to clarify the enantioselective recognition by the estrogen receptor. (S)-mono-OH-MXC showed 3-fold higher binding activity than that of the (R) enantiomer. The activity of bis-OH-MXC was only 1.7-fold higher than that of (S)-mono-OH-MXC. This result suggests that the one hydroxy group and the orientation of the CCl3 group of mono- and bis-OH-MXCs are important for the interaction with the estrogen receptor. The result also points out the estrogenic activity of methoxychlor after metabolic activation in vivo, which predominantly produces the (S)-mono-OH-MXC, may be higher than estimated from the in vitro activity of racemic mixtures.

Molecular determinants of ER alpha and ER beta involved in selectivity of 16 alpha-iodo-7 beta estradiol

The two known estrogen receptors, ER alpha and ER beta, are hormone inducible transcription factors that have distinct roles in regulating cell proliferation and differentiation. The natural ligand, 17 beta-estradiol (E2), binds with high affinity to both ER alpha and ER beta. However, a close analogue, 16 alpha-iodo-17 beta-estradiol (16 alpha IE2) showed about 10-fold selectivity for ER alpha over ER beta. From X-ray studies, it has been shown that the ligand-binding domains (LBD) of the two receptors are strikingly similar, and that only two changes fall within the binding cavity (ER alpha Leu384 to ER beta Met336, and ER alpha Met421 to ER beta Ile373). To understand the molecular basis for the ER alpha selectivity of 16 alpha IE2, mutants and chimeras of ER alpha and ER beta were generated, and ligand-binding and transactivation functions were studied. The ER alpha Leu384 Met mutant behaved like ER alpha WT in the presence of 16 alpha IE2; whereas the profile of the ER alpha Met421 Ile mutant was similar to that of ER beta WT. The ER beta mutant Ile373 Met behaved like ER alpha with 16 alpha IE2. The results clearly demonstrate the role of ER alpha Met421 in the ER alpha selectivity of 16 alpha IE2.

Analysis of Multiple Endocrine Disruptors in Environmental Waters via Wide-Spectrum Solid-Phase Extraction and Dual-Polarity Ionization LC-Ion Trap-MS/MS

An analytical method for the determination of 35 endocrine disrupting chemicals (EDCs) present in the aquatic environment was developed and validated. The procedure includes an off-line solid-phase extraction of 500-mL water samples using wide-spectrum polymer packing material combined with two LC-ESI-MS/MS runs, in negative and positive ionization modes. Limits of quantitation were established between 0.1 and 20.0 ng/L. Satisfactory recoveries were obtained ranging from 80.1 to 110.2%. Calibration, using deuterated internal standardization, was performed by linear regression analysis. Linearity (R(2) > 0.99) was demonstrated over individually specified ranges using seven calibration points for each analyte. Intrabatch and interbatch precision, as well as accuracy (n = 5), were investigated at low, medium, and high concentrations. Precision for all compounds, expressed as the RSD, proved to be less than 17.8 and 20.0%, respectively, for intra- and interbatch. Accuracy, expressed as the mean recovery, was between 83.1 and 108.4% at all concentrations. Stability experiments showed no significant loss or deterioration for any of the analytes. Finally, the method was applied on real samples.

Genotoxic activity of four metabolites of the soy isoflavone daidzein

Products containing phytoestrogens are increasingly promoted as the "natural" alternative to estrogen replacement therapy. In the present study, we have used the in vitro micronucleus assay in L5178Y mouse lymphoma cells to investigate the genotoxic potential of the isoflavone daidzein, and of four daidzein metabolites known to be formed in humans. Whereas no induction of micronuclei was observed with daidzein up to the limit of solubility (100 microM), all four daidzein metabolites, i.e. equol (2.3-fold induction at 100 microM), O-desmethylangolensin (6.2-fold induction at 10 microM), 4',6,7-isoflavone (6.7-fold induction at 100 microM) and 3',4',7-isoflavone (8.2-fold induction at 100 microM) induced micronuclei in a concentration-dependent manner. Thus, both reductive and oxidative metabolites of the soy isoflavone daidzein exhibit genotoxic potential in vitro.

The food contaminants bisphenol A and 4-nonylphenol act as agonists for estrogen receptor alpha in MCF7 breast cancer cells

Xenoestrogens are chemically distinct industrial products potentially able to disrupt the endocrine system by mimicking the action of endogenous steroid hormones. Among such compounds, the ubiquitous environmental contaminants bisphenol A (BPA) and 4-nonylphenol (NPH) may promote adverse effects in humans triggering estrogenic signals in target tissues. Following a research program on human exposure to endocrine disruptors, we found contamination of fresh food by BPA and NPH. More important, these contaminants were found to display estrogen-like activity using as a model system the estrogen-dependent MCF7 breast cancer cells (MCF7wt); its variant named MCF7SH, which is hormone-independent but still ERalpha-positive, and the steroid receptor-negative human cervical carcinoma HeLa cells. In transfection experiments BPA and NPH activated in a direct manner the endogenous ERalpha in MCF7wt and MCF7SH cells, as the antiestrogen hydroxytamoxifen was able to reverse both responses. Moreover, only the hormone-binding domains of ERalpha and ERbeta expressed by chimeric proteins in HeLa cells were sufficient to elicit the transcriptional activity upon BPA and NPH treatments. Transfecting the same cell line with ERalpha mutants, both contaminants triggered an estrogen-like response. These transactivation properties were interestingly supported in MCF7wt cells by the autoregulation of ERalpha which was assessed by RT-PCR for the mRNA evaluation and by immunoblotting and immunocytochemistry for the determination of protein levels. The ability of BPA and NPH to modulate gene expression was further confirmed by the upregulation of an estrogen target gene like pS2. As a biological counterpart, concentrations of xenoestrogens eliciting transcriptional activity were able to stimulate the proliferation of MCF7wt and MCFSH cells. Only NPH at a dose likely too high to be of any physiological relevance induced a severe cytotoxicity in an ERalpha-independent manner as ascertained in HeLa cells. The estrogenic effects of such industrial agents together with an increasing widespread human exposure should be taken into account for the potential influence also on hormone-dependent breast cancer disease.

Comparative molecular field analysis (CoMFA) model using a large diverse set of natural, synthetic and environmental chemicals for binding to the androgen receptor

A large number of natural, synthetic and environmental chemicals are capable of disrupting the endocrine systems of experimental animals, wildlife and humans. These so-called endocrine disrupting chemicals (EDCs), some mimic the functions of the endogenous androgens, have become a concern to the public health. Androgens play an important role in many physiological processes, including the development and maintenance of male sexual characteristics. A common mechanism for androgen to produce both normal and adverse effects is binding to the androgen receptor (AR). In this study, we used Comparative Molecular Field Analysis (CoMFA), a three-dimensional quantitative structure-activity relationship (3D-QSAR) technique, to examine AR-ligand binding affinities. A CoMFA model with r2 = 0.902 and q2 = 0.571 was developed using a large training data set containing 146 structurally diverse natural, synthetic, and environmental chemicals with a 10(6)-fold range of relative binding affinity (RBA). By comparing the binding characteristics derived from the CoMFA contour map with these observed in a human AR crystal structure, we found that the steric and electrostatic properties encoded in this training data set are necessary and sufficient to describe the RBA of AR ligands. Finally, the CoMFA model was challenged with an external test data set; the predicted results were close to the actual values with average difference of 0.637 logRBA. This study demonstrates the utility of this CoMFA model for real-world use in predicting the AR binding affinities of structurally diverse chemicals over a wide RBA range.

Fluorescent cellular sensors of steroid receptor ligands

Steroid hormone receptors comprise a major class of therapeutic drug targets that control gene expression by binding steroid hormone ligands. These small molecule-protein interactions are typically characterized in living cells by quantification of ligand-mediated reporter gene expression. As an alternative, non-transcriptional approach, we constructed fluorescent cellular sensors by expressing yellow fluorescent protein (YFP) fused to the ligand binding domains (LBDs) of estrogen receptor-alpha (ERalpha), estrogen receptor-beta (ERbeta), androgen receptor (AR), and the glucocorticoid receptor (GR). These proteins were tethered through a short two amino acid linker and expressed in S. cerevisiae yeast. Recombinant yeast treated with cognate steroid receptor ligands exhibited dose-dependent fluorescence enhancements that were correlated with known relative receptor binding affinity values. These effects generally paralleled ligand-mediated receptor dimerization quantified with analogous yeast two-hybrid transcriptional assays, suggesting that the majority of the observed fluorescence enhancements were conferred by conformational changes coupled with receptor dimerization, such as ligand-mediated stabilization of protein folding. Remarkably, certain interactions such as the binding of cortisol, progesterone, and dexamethasone to the GR were undetectable with yeast two-hybrid assays. However, these interactions were detected with the fluorescent cellular sensors, indicating the sensitivity of this system to subtle ligand-induced conformational effects. These sensors provide a novel, non-transcriptional, and high-throughput method to identify and analyze ligands of nuclear hormone receptors.

Estrogenicity and acute toxicity of selected anilines using a recombinant yeast assay

Suspected estrogen modulators include industrial organic chemicals (i.e., xenoestrogens), and have been shown to consist of alkylphenols, bisphenols, biphenylols, and some hydroxy-substituted polycyclic aromatic hydrocarbons. The most prominent structural feature identified to be important for estrogenic activity is a polar group capable of donating hydrogen bonds (i.e., hydroxyl) on an aromatic system. The present study was undertaken to explore the estrogenic activity and acute toxicity of chemicals containing a weaker hydrogen bond donor group on aromatic systems, i.e., the amino substituent. There is a great deal of chemical similarity between aromatic amines (anilines) and aromatic alcohols (phenols). The chemicals chosen for the current study contained an amino-substituted benzene ring with hydrophobic constituents varying in size and shape. Thus, 37 substituted aromatic amines were assayed for estrogenic activity EC50 and acute toxicity LC50 using the Saccharomyces cerevisiae recombinant yeast assay. While the EC50 of 17-beta-estradiol occurs at the 10(-10) range, the aniline with the greatest activity had an EC50 of 10(-6) M. Thus, anilines, in general, are capable only of very weak estrogenic activity in this assay. A comparison of estrogenic potency between the present group of anilines and a set of previously tested analogous phenols indicated that anilines are consistently less estrogenic than phenols. A comparison of hazard indices (EC50/LC50) of these chemicals revealed that, for the vast majority of anilines, the EC50 and LC50 were in the same order of magnitude. More specifically, estrogenic activity of para-substituted alkylanilines increases with alkyl group size up to 5 carbons in length, after which the acute toxicity of the larger alkyl-substituents precluded the ability of the compound to induce the estrogenic response.

Molecular quantum similarity analysis of estrogenic activity

The main objective of this study was to evaluate the capability of 120 aromatic chemicals to bind to the human alpha estrogen receptor (hER alpha) by the use of quantum similarity methods. The experimental data were segregated into two categories, i.e., those compounds with and without estrogenicity activity (active and inactive). To identify potential ligands, semiquantitative structure-activity relationships were developed for the complete set correlating the presence or lack of binding affinity to the estrogen receptor with structural features of the molecules. The structure-activity relationships were based upon molecular similarity indices, which implicitly contain information related to changes in the electron distributions of the molecules, along with indicator variables, accounting for several structural features. In addition, the whole set was split into several chemical classes for modeling purposes. Models were validated by dividing the complete set into several training and test sets to allow for external predictions to be made.

Screening of high production volume chemicals for estrogen receptor binding activity (II) by the MultiCASE expert system

A structurally and functionally diverse and cross-validated quantitative structure-activity knowledge database generated by the MultiCASE expert system was used to screen 2526 high production volume chemicals (HPVCs) for their estrogen receptor binding activity. 73 HPVCs were found to contain structural features or biophores that have been documented as having the ability to bind to the estrogen receptor. Potential chemicals were ranked according to their quantitatively predicted ER binding potential and the details of the biophores found in them are discussed.

Structure-activity relationship study of a diverse set of estrogen receptor ligands (I) using MultiCASE expert system

The MultiCASE expert system was used to construct a quantitative structure-activity relationship model to screen chemicals with estrogen receptor (ER) binding potential. Structures and ER binding data of 313 chemicals were used as inputs to train the expert system. The training data set covers inactive, weak as well as very powerful ER binders and represents a variety of chemical compounds. Substructural features associated with ER binding activity (biophores) and features that prevent receptor binding (biophobes) were identified. Although a single phenolic hydroxyl group was found to be the most important biophore responsible for the estrogenic activity of most of the chemicals, MultiCASE also identified other biophores and structural features that modulate the activity of the chemicals. Furthermore, the findings supported our previous hypothesis that a 6 A distant descriptor may describe a ligand-binding site on an ER. Quantitative structure-activity relationship models for the chemicals associated with each biophore were constructed as part of the expert system and can be used to predict the activity of new chemicals. The model was cross validated via 10 x 10%-off tests, giving an average concordance of 84.04%.

A screening method for estrogens using an array-type DNA glass slide

A new screening assay was described for the determination of endocrine disrupting chemicals (EDCs), such as synthetic estrogens, with an array-type DNA glass slide having characteristics of 1) a high sample throughput, 2) a compact size allowing a small sample volume, and 3) a sensitive determination based on the estrogen-dependent binding of the human estrogen receptor a (hERalpha) with its estrogen responsive element (ERE; Vit. A2 gene promoter). We devised a glass slide on which a thin agarose gel was mounted. Avidin was then covalently immobilized on each well of the glass slide after the gel was activated by a NaIO4 solution. Also, the biotinylated ERE as a DNA probe was immobilized on the gel layer through avidin-biotin binding. After the estrogen-dependent binding of a yellow fluorescent protein-fused hERalpha (YFP-hERalpha) to ERE on the gel layer, the fluorescence intensity of YFP-hERalpha quantitatively extracted into the gel was directly determined with a fluorescence microplate reader. Pre-incubation of YFP-hERalpha with estrogen at 37 degrees C for 30 min enhanced the estrogen-dependent hERalpha-ERE binding. The determined hormonal activities of estrogens on the interaction of YFP-hERalpha with ERE were as follows in their decreasing order: diethylstilbestrol (DES) > 17beta-estradiol (E2) <==> ethynylestradiol (EE2) > 4-hydroxy tamoxifen (OHT) > clomiphene (Clo). The present method provides a sensitive estrogen-dependent dose-response curve down to approximately 10(-13) M in the case of DES. This method will become a competitive alternative to the conventional in vitro assays, such as a DNA-binding assay using radioisotopes.

Decision forest: combining the predictions of multiple independent decision tree models

The techniques of combining the results of multiple classification models to produce a single prediction have been investigated for many years. In earlier applications, the multiple models to be combined were developed by altering the training set. The use of these so-called resampling techniques, however, poses the risk of reducing predictivity of the individual models to be combined and/or over fitting the noise in the data, which might result in poorer prediction of the composite model than the individual models. In this paper, we suggest a novel approach, named Decision Forest, that combines multiple Decision Tree models. Each Decision Tree model is developed using a unique set of descriptors. When models of similar predictive quality are combined using the Decision Forest method, quality compared to the individual models is consistently and significantly improved in both training and testing steps. An example will be presented for prediction of binding affinity of 232 chemicals to the estrogen receptor.

Sonic spray ionization applied to liquid chromatography/mass spectrometry analysis of endocrine-disrupting chemicals in environmental water samples

A sonic spray ionization liquid chromatography/mass spectrometry (LC/SSI-MS) procedure combined with off-line solid-phase extraction was optimized for the analysis of 20 endocrine-disrupting chemicals (EDCs) in water samples. Method development included a comparison of the novel sonic spray ionization (SSI) with more traditional ion sources, i.e. pneumatically assisted electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). It was demonstrated that SSI and ESI spectra were very similar, but were more prone to the formation of solvent cluster ions as compared with APCI spectra. This phenomenon was most prominent for SSI and resulted in an increased chemical background in full-scan mass spectra. However, this chemical noise did not affect the overall sensitivity of SSI and ESI. After optimization of LC and MS parameters, the LC/SSI-MS method was validated. Recoveries ranged from 76.3 up to 113.4% for all compounds. Limits of detection (LOD) and quantitation (LOQ) were established between 3.0 and 11.5 ng/L and 9.9 and 38.0 ng/L, respectively. Within-day (n = 5) and between-day (n = 5) reproducibility were investigated at three levels and ranged from 3.3-16.5% and 7.6-19.2%, respectively. Eight-point calibration curves were established and showed linearity for all compounds (r(2) > 0.987) over a linear dynamic range of 10-10 000 ng/L.

Oestrogenic activity of benzylparaben

Previous work has demonstrated that the alkyl esters of p-hydroxybenzoic acid (parabens) possess oestrogenic activity, which increases with length of alkyl chain from methylparaben to n-butylparaben and with branching in the alkyl chain from n-butylparaben to isobutylparaben. This study reports on the oestrogenic activity of benzylparaben in a variety of assays in vitro and in vivo. Benzylparaben was able to displace [(3)H]oestradiol from cytosolic oestrogen receptor (ER) of MCF7 human breast cancer cells by 22% at 1000-fold molar excess, by 40% at 10,000-fold molar excess, by 57% at 100 000-fold molar excess and by 100% at 1,000,000-fold molar excess. It was able to increase expression of a stably transfected oestrogen responsive reporter gene (ERE-CAT) in MCF7 cells after 24 h at 10(-5)M/10(-4)M and after 7 days at 10(-6)M/10(-5)M/10(-4)M. Proliferation of MCF7 cells could be increased by 10(-6)M/10(-5)M benzylparaben and this could be inhibited by 10(-7)M pure anti-oestrogen ICI 182,780, indicating that growth effects were ER mediated. Further evidence for ER-mediation was provided from the ability of benzylparaben to increase the growth of a second oestrogen-dependent human breast cancer cell line ZR-75-1, but not the oestrogen-insensitive MDA-MB-231 cell line. When tested in the presence of 10(-10)M 17beta-oestradiol, benzylparaben gave no antagonist response on the growth of either MCF7 or ZR-75-1 cells. Finally, benzylparaben could increase uterine weight in the immature mouse following topical application of three daily doses of 33 mg to dorsal skin. These results demonstrate that the oestrogenicity of methylparaben can be increased by the addition of an aryl group as well as by lengthening or branching the alkyl grouping.

Nongenomic activity and subsequent c-fos induction by estrogen receptor ligands are not sufficient to promote deoxyribonucleic acid synthesis in human endometrial adenocarcinoma cells

Estrogen 17beta-estradiol (E2) rapidly modulates several signaling pathways related to cell growth, preservation, and differentiation. The physiological role of these nongenomic effects with regard to downstream outcomes, and the relationship with transcriptional estrogen activity are unclear. Furthermore, the ability of selective estrogen receptor modulators (SERMs) to trigger nongenomic actions is largely unknown. To determine whether estrogen receptor (ER) ligands exert nongenomic activity in endometrial adenocarcinoma cells, and whether this activity affects transcription and DNA synthesis, we challenged human Ishikawa cells with E2 or partial ER agonists 4-hydroxytamoxifen (OHT) and raloxifene (ral). Serum-starved Ishikawa cells exposed for 5 min to 0.1 nM E2 showed induced phosphorylation of MAPK (ERK1/2). Ral and 4-OHT each at 1 nM also stimulated ERK in a rapid transient manner. E2 and 4-OHT induced proto-oncogene c-fos mRNA expression in Ishikawa cells within 30 min, but ral had no effect. In contrast to nongenomic action, only E2 stimulated expression of an estrogen response element (ERE)-driven luciferase (LUC) reporter gene. To examine DNA synthesis, [(3)H]-thymidine incorporation was measured in serum-starved cultures exposed to E2 or partial agonists for 2 d. E2 at 1 nM stimulated thymidine uptake in an ERK-dependent manner, but 1 nM 4-OHT, 1 nM ral, and 0.1-nM concentrations of E2 had no significant effects. Taken together, these data indicate that both nongenomic and direct transcriptional ER effects are likely required to promote DNA synthesis.

Scientific issues associated with the validation of in vitro and in vivo methods for assessing endocrine disrupting chemicals

The assays required to assess the potential of chemicals to act as endocrine disrupting (ED) agents are either in place or are under current development. However, the validation and utilisation of these assays is currently being hampered by uncertainties regarding their purpose and required sensitivity, and uncertainties as to the intrinsic variability of the parameters being measured. This article discusses these several sources of uncertainty and the intrinsic variability of many of the key assay parameters. It is concluded that current uncertainties regarding the use of ED assays, and the extrapolation of rodent effects to humans, are due to the absence of an extensive agreed rodent control database for the developmental parameters under study, coupled to the established intrinsic variability of these parameters between strains/species of test animals and test protocols. Only when these factors are generally accepted, well studied and controlled for, will it be possible to employ ED assays with confidence and to relate assay data to effects likely to be seen in humans.

A binary screening assay for pro-oestrogens in food: metabolic activation using hepatic microsomes and detection with oestrogen sensitive recombinant yeast cells

An assay, employing microsomes prepared from rat liver and a recombinant cell bioassay (RCBA) expressing the human oestrogen receptor (alpha) linked to a reporter gene, was evaluated for the detection of pro-oestrogens in food using methoxychlor and mestranol as model compounds. Bio-activation of the hop phytoestrogen isoxanthohumol to the potent oestrogen 8-prenylnaringenin was also investigated. The oestrogenic potency values for reference standards determined with the RCBA (17beta-oestradiol = 100%) were: methoxychlor 0.0025%, mestranol 1.3%, isoxanthohumol 0.001%, and for their potential respective metabolites were: bishydroxymethoxychlor 0.015%, 17alpha-ethynyl oestradiol 69% and 8-prenylnaringenin 0.4%. Incubation of methoxychlor and mestranol (10 microM) with microsomes prepared from the liver of rats treated with Aroclor 1254 significantly increased (p < 0.001) their oestrogenic potency from 0.0021 and 2.4% to 0.015 and 8.3%, respectively. In contrast, the potency of the hop phytoestrogen isoxanthohumol was unchanged. Metabolites were identified by UV-HPLC-MS/MS as monohydroxy methoxychlor and HPTE from methoxychlor, and the major metabolite of mestranol was 17alpha-ethynyl oestradiol. There was no evidence for the metabolism of isoxanthohumol. Mestranol was also activated by microsomes induced with saline (control), beta-napthoflavone, 3-methylcholantherene, isoniazid or pregnenolone-16alpha-carbonitrile, but not phenobarbitone. These studies demonstrate the principle for use of a binary assay system for the detection of pro-oestrogens and indicate the potential value for risk assessment of endocrine disrupting chemicals.

Estrogenic and antiproliferative activities of isoliquiritigenin in MCF7 breast cancer cells

Licorice root contains chemically diverse compounds that exhibit estrogenic effects in vitro and in vivo. The chalcone isoliquiritigenin (ISL) is a component of licorice extract exhibiting either antitumorigenic activity or estrogen receptor (ER) alpha-dependent growth promoting effects on breast cancer cells. In order to contribute to a better understanding of this apparent paradox, we synthesized and ascertained the estrogenic properties of ISL using, as model systems, the hormone-sensitive MCF7 breast cancer cells and the steroid-independent HeLa cells. Transfection experiments reveal that ISL is able to transactivate the endogenous ER alpha in MCF7 cells and this is supported by the capability to induce down-regulation of ER alpha protein levels and up-regulation of pS2 mRNA. Moreover, by using chimeric proteins consisting of the hormone binding domains of ER alpha and ER beta fused to the Gal4 DNA binding domain, we have determined that ISL is an estrogenic agonist of both ER isoforms. As a biological counterpart, low and intermediate ISL concentrations that induce substantial transcriptional activity stimulate the proliferation of MCF7 cells. However, high levels of ISL become cytotoxic even in steroid-receptor negative HeLa cells. Thus, the activity of ISL and the balance between risk or chemopreventive factor for estrogen-dependent breast cancer may depend on dietary intake.

Steroid and sterol 7-hydroxylation: ancient pathways

B-ring hydroxylation is a major metabolic pathway for cholesterols and some steroids. In liver, 7 alpha-hydroxylation of cholesterols, mediated by CYP7A and CYP39A1, is the rate-limiting step of bile acid synthesis and metabolic elimination. In brain and other tissues, both sterols and some steroids including dehydroepiandrosterone (DHEA) are prominently 7 alpha-hydroxylated by CYP7B. The function of extra-hepatic steroid and sterol 7-hydroxylation is unknown. Nevertheless, 7-oxygenated cholesterols are potent regulators of cell proliferation and apoptosis; 7-oxygenated derivatives of DHEA, pregnenolone, and androstenediol can have major effects in the brain and in the immune system. The receptor targets involved remain obscure. It is argued that B-ring modification predated steroid evolution: non-enzymatic oxidation of membrane sterols primarily results in 7-oxygenation. Such molecules may have provided early growth and stress signals; a relic may be found in hydroxylation at the symmetrical 11-position of glucocorticoids. Early receptor targets probably included intracellular sterol sites, some modern steroids may continue to act at these targets. 7-Hydroxylation of DHEA may reflect conservation of an early signaling pathway.

Absolute bioavailability of [14C] genistein in the rat; plasma pharmacokinetics of parent compound, genistein glucuronide and total radioactivity

The systemic plasma pharmacokinetics of genistein were determined in rats to evaluate the absolute oral bioavailability and make comparison with similar data in the literature derived from humans subjects. The plasma concentrations of genistein, genistein glucuronide and carbon-14 were determined by LC-MS/MS and liquid scintillation counting following oral and intravenous dosing with [14C]genistein (4 mg kg(-1) body weight). The absorption of total radioactivity from the gut, (parent compound and metabolites), was 56 and 111% in male and female rats, respectively. In contrast, the absolute oral bioavailability of genistein in male and female rats was 7 and 15%. There was a significant (P<0.001) difference between Cmax of genistein after intravenous (6921 and 4392 ng/ml) and oral (21 and 22 ng/ml) dosing in male and female rats, respectively. After oral administration, the concentration profile of genistein glucuronide in plasma greatly exceeded that of parent compound during the absorption/distribution phase suggesting extensive first pass metabolism, and provided evidence of entero-hepatic circulation. Selective plasma analysis by LC-MS/MS, without prior enzymatic hydrolysis, enabled ready discrimination between parent and conjugated metabolites and prevented gross overestimation of genistein bioavailability. Pharmacokinetic parameters Cmax, Tmax and AUC were similar to those reported in humans, which supports the use of the rat model for genistein toxicity studies.