Improving the reproducibility of the MCF-7 cell proliferation assay for the detection of xenoestrogens

Emerging organophosphate ester resorcinol bis(diphenyl phosphate) exerts estrogenic effects via estrogen receptor pathways

Environmental occurrence and human exposure of emerging organophosphate esters (eOPEs) have increased significantly in recent years. Resorcinol bis(diphenyl) phosphate (RDP) is one of the major eOPEs detected in indoor dust, but the knowledge on its toxicities and health risks is rather limited. In this study, we investigated the in vitro estrogenic effects and underlying mechanism of RDP in comparison with a legacy OPE triphenyl phosphate (TPHP). Our results showed that RDP promoted MCF-7 cell proliferation with the lowest effect concentration of 2.5 μM, and the maximum enhancement of 1.6 folds is greater than that of TPHP (1.3 folds). The effect was inhibited completely by an estrogen receptor (ER) antagonist, suggesting that ER activation was responsible for the enhancement. In luciferase reporter gene assays both RDP and TPHP activated ER transcriptional activity at 2.5 μM, but RDP activity was higher than TPHP. Competitive fluorescence binding assays showed that RDP bound to ER with an IC10 of 0.26 μM, which is 20 folds lower than TPHP (5.6 μM). Molecular docking simulation revealed that both RDP and TPHP interacted with ER at the binding pocket of estradiol, although the hydrogen bonds were different. Taken together, RDP exerted stronger estrogenic effects than TPHP through ER-mediated pathways and may pose more health risks.

Disposition of Dietary Polyphenols in Breast Cancer Patients' Tumors, and Their Associated Anticancer Activity: The Particular Case of Curcumin

SCOPE

Some polyphenol-derived metabolites reach human breast cancer (BC) tissues at concentrations that induce cell senescence. However, this is unknown for isoflavones, curcuminoids, and lignans. Here, their metabolic profiling in normal (NT) and malignant (MT) mammary tissues of newly-diagnosed BC patients and the tissue-occurring metabolites' anticancer activity are evaluated.

METHODS AND RESULTS

Patients (n = 26) consumed 3 capsules/day (turmeric, red clover, and flaxseed extracts plus resveratrol; 296.4 mg phenolics/capsule) from biopsy-confirmed diagnosis to surgery (5 ± 2 days) or did not consume capsules (n = 13). NT and MT, blood, and urine are analyzed by UPLC-QTOF-MS using targeted metabolomics. Anticancer activity was tested in MCF-7 and MDA-MB-231 BC cells. Mainly phase-II metabolites were detected (108, 84, 49, and 47 in urine, plasma, NT, and MT, respectively). Total metabolite concentrations reached 10.7 ± 11.1 and 2.5 ± 2.4 µmol L^-1 in NT and MT, respectively. Free curcumin, but not its glucuronide, was detected in the tissues (1.1 ± 1.8 and 0.2 ± 0.2 µmol L^-1 in NT and MT, respectively). Breast tissue-occurring metabolites' antiproliferation was mainly exerted in p53-wild-type MCF-7 cells by curcuminoids through cell cycle arrest, senescence, and apoptosis induction via p53/p21 induction, while isoflavone-derived metabolites exerted estrogenic-like activity.

CONCLUSION

Curcuminoids could be coadjuvants that might help fight BC upon regular consumption.

Natural bioactive 4-Hydroxyisophthalic acid (4-HIPA) exhibited antiproliferative potential by upregulating apoptotic markers in in vitro and in vivo cancer models

There is tremendous scope for identifying novel anti-cancer molecules from the unexplored reserves of plant kingdom. The application of dietary supplementation or medicine derived from such sources is a promising approach towards treatment of cancer. In the present study we have evaluated the antiproliferative potential of 4-hydroxyisophthalic acid (4-HIPA), which is a novel antioxidant compound isolated from the roots of the aqueous extract of Decalepis hamiltonii. 4-HIPA was screened in vitro against human breast cancer cell lines MCF-7, MDA-MB-468 and normal human breast epithelial cell MCF-10, and demonstrated that human breast cancer cell lines, in contrast to MCF-10, are sensitive to 4-HIPA .4-HIPA showed marked reduction in cell viability and short-term proliferation assays in these cells. Results of the long-term colony formation and scratch assay further reaffirmed that 4-HIPA inhibited the growth and proliferation in breast cancer cells. We further conducted in vivo studies using murine Ehrlich Ascites Tumor (EAT) cell model. Our in vivo results established that treatment with 4-HIPA reduced the tumorigenesis by promoting apoptosis in EAT-bearing mice. The results of our molecular docking predictions further warranted our claim. This study is valuable as 4-HIPA exhibits antiproliferative potential that can be exploited in the development of anticancer drugs.

The estrogenic proliferative effects of two alkylphenols and a preliminary mechanism exploration in MCF-7 breast cancer cells

Bisphenol A (BPA) and 4-cumylphenol (4-CP), as estrogen-like chemicals, are ubiquitous in the environment media and associated with the occurrence and development of hormone-dependent tumors. However, the combinatorial effects of these two structurally similar alkylphenols are not well informed. In the present study, the classic breast cancer cell line MCF-7 was used as in vitro model to estimate the estrogenic proliferative effects of BPA and 4-CP. MTT assay, reactive oxygen species, cell apoptosis, cell cycle, and real-time fluorescent quantitative Step One Plus Real-time PCR System (Applied Biosystems, CA, USA) were applied to explore their proliferative mechanisms. MTT results showed that both BPA and 4-CP ranging from 10^-9 to 10^-5 M stimulated cell proliferation in a nonmonotonic dose-response manner. Along with the proliferative effects, cell cycle was progressed from G0/G1 to S and G2/M phase. Meanwhile, the expression levels of ERα, pS2, and Bcl-2 mRNA were also upregulated. In contrast, 4-CP and BPA at high dose (10^-4 M) obviously displayed antiproliferative effects in MCF-7 cells via inducing cell apoptosis and blocking cell cycle in G0/G1 phase. As expected, the relative expression levels of ERα, pS2, and Bcl-2 mRNA were decreased, whereas Bax mRNA was increased. Interestingly, the proliferative or antiproliferative effects of 4-CP were higher than that of BPA. Moreover, coexposure of lower concentrations BPA and 4-CP significantly induced cell proliferation in a synergistic manner. These findings indicated that the potential environmental risks of coexposure of BPA and 4-CP were greater than either of them.

Chlorinated Polyfluoroalkylether Sulfonic Acids Exhibit Stronger Estrogenic Effects than Perfluorooctane Sulfonate by Activating Nuclear Estrogen Receptor Pathways

Chlorinated polyfluoroalkylether sulfonic acids (Cl-PFESAs) have been shown to have potential thyroid hormone (TH) disruption effects. Here, we further investigated their estrogenic effects and underlying mechanisms. In vivo results revealed that exposure of zebrafish to Cl-PFESAs induced disorder of sex hormones during the early embryonic stages and caused histopathological lesions in the gonads of adult zebrafish relative to control groups. To find out whether the estrogen receptor is the molecular target of Cl-PFESAs, the binding interaction between Cl-PFESAs and ERs was investigated using a series of in vitro assays. We found that all tested chemicals could bind directly to ERs and exhibit relatively weak agonistic activity toward ERs, suggesting that the ER-mediated signaling pathway is directly involved in the estrogenic effects of Cl-PFESAs. The internal dose of 8:2 Cl-PFESA was significantly higher than the others, which explained why it obviously displayed an ER agonistic effect despite its weak ER binding affinity. Taken together, these results uncover that, in addition to the TH disruption effect, Cl-PFESAs might also cause estrogenic effects by activating ER pathways.

Physiological Relevance of the Antiproliferative and Estrogenic Effects of Dietary Polyphenol Aglycones versus Their Phase-II Metabolites on Breast Cancer Cells: A Call of Caution

While preclinical studies suggest the breast cancer (BC) chemopreventive effects of dietary polyphenols, the human evidence is still very weak. The huge existing in vitro-in vivo gap is mainly due to the plethora of potential effects reported by in vitro studies that usually assay polyphenols as occurring in the food (beverages, extracts, foods) and/or derived aglycone metabolites with doubtful physiological relevance. Since phase-II metabolites can reach systemic tissues such as malignant breast tumors, we aimed here to compare for the first time the antiproliferative and estrogenic/antiestrogenic effects of dietary polyphenols and microbiota-derived metabolites (i.e., resveratrol, dihydroresveratrol, urolithins (A, B, and Isourolithin A), and the flavanone hesperetin), with those effects exerted by their physiologically relevant glucuronides and sulfates on human BC cell lines (MDA-MB-231 and MCF-7). Results showed that aglycones exerted dose-dependent antiproliferative and estrogenic/antiestrogenic activities, but both their glucuronide and sulfate conjugates lacked these activities. In addition, aglycones underwent phase-II metabolism in BC cells, mainly via sulfation, which determined the cell-dependent differences in the effects observed. Therefore, phase-II metabolism limits the antiproliferative, estrogenic, and antiestrogenic activities of dietary polyphenols on BC cells. Likewise, as a call of caution, enthusiasm should be limited for publishing effects that are not physiologically relevant.

Inhibitory effect of silver nanoparticles on proliferation of estrogen-dependent MCF-7/BUS human breast cancer cells induced by butyl paraben or di-n-butyl phthalate

In this study the effect of silver nanoparticles (AgNPs) on proliferation of estrogen receptor (ER)-positive human breast cancer MCF-7/BUS cells was assessed by means of in vitro assay. The cells were exposed in the absence of estrogens to AgNPs alone or in combination with aluminum chloride (AlCl₃), butyl paraben (BPB) and di-n-butyl phthalate (DBPh). The results revealed that AgNPs at the non-cytotoxic concentrations (up to 2μg/mL) and AlCl₃ (up to 500μM) did not induce proliferation of MCF-7/BUS cells whereas BPB and DBPh showed strong estrogenic activity with the highest effect at 16μM and 35μM, respectively. AgNPs inhibited the proliferation of the cells induced by DBPh, BPB or even with 17β-estradiol (E2) during 6-day incubation in the absence of estrogens. ICI 182,780 (10nM), a known estrogen receptor (ER) antagonist, induced strong inhibitory effect. AgNPs also decreased transcription of the estrogen-responsive pS2 and progesterone receptor (PGR) genes but modulated expression neither of ERα nor ERβ in MCF-7/BUS cells exposed to BPB, DBPh or E2 for 6h. Our results indicate that AgNPs may inhibit growth of breast cancer cells stimulated by E2 or estrogenic chemicals, i.e. BPB and DBPh.

A Chip for Estrogen Receptor Action: Detection of Biomarkers Released by MCF-7 Cells through Estrogenic and Anti-Estrogenic Effects

The fluorescence-based multi-analyte chip platform for the analysis of estrogenic and anti-estrogenic substances is a new in vitro tool for the high throughput screening of environmental samples. In contrast to existing tools, the chip investigates the complex action of xenoestrogens in a human cell model by characterizing protein expression. It allows for the quantification of 10 proteins secreted by MCF-7 cells, representing various biological and pathological endpoints of endocrine action and distinguishing between estrogen- and anti-estrogen-dependent secretion of proteins. Distinct protein secretion patterns of the cancer cell line after exposure to known estrogen receptor agonists ß-estradiol, bisphenol A, genistein, and nonylphenol as well as antagonists fulvestrant and tamoxifen demonstrate the potential of the chip. Stimulation of cells with Interleukin-1ß shifts concentrations of low abundant biomarkers towards the working range of the chip. In the non-stimulated cell culture, Matrix Metalloproteinase 9 (MMP-9) and Vascular Endothelial Growth Factor (VEGF) show differences upon treatment with antagonists and agonists of the estrogen receptor. In stimulated MCF-7 cells challenged with receptor agonists secretion of Monocyte Chemoattractant Protein (MCP-1), Interleukin-6 (IL-6), Rantes, and Interleukin-8 (IL-8) significantly decreases. In parallel, the proliferating effect of endocrine-disrupting substances in MCF-7 cells is assessed in a proliferation assay based on resazurin. Using ethanol as a solvent for test substances increases the background of proliferation and secretion experiments, while using dimethyl sulfoxide (DMSO) does not show any adverse effects. The role of the selected biomarkers in different physiological processes such as cell development, reproduction, cancer, and metabolic syndrome makes the chip an excellent tool for either indicating endocrine-disrupting effects in food and environmental samples, or for screening the effect of xenoestrogens on a cellular and molecular level.

Weight-of-the-evidence evaluation of 2,4-D potential for interactions with the estrogen, androgen and thyroid pathways and steroidogenesis

A comprehensive weight-of-the-evidence evaluation of 2,4-dichlorophenoxyacetic acid (2,4-D) was conducted for potential interactions with the estrogen, androgen and thyroid pathways and with steroidogenesis. This assessment was based on an extensive database of high quality in vitro, in vivo ecotoxicological and in vivo mammalian toxicological studies. Epidemiological studies were also considered. Toxicokinetic data provided the basis for determining rational cutoffs above which exposures were considered irrelevant to humans based on exceeding thresholds for saturation of renal clearance (TSRC); extensive human exposure and biomonitoring data support that these boundaries far exceed human exposures and provide ample margins of exposure. 2,4-D showed no evidence of interacting with the estrogen or androgen pathways. 2,4-D interacts with the thyroid axis in rats through displacement of thyroxine from plasma binding sites only at high doses exceeding the TSRC in mammals. 2,4-D effects on steroidogenesis parameters are likely related to high-dose specific systemic toxicity at doses exceeding the TSRC and are not likely to be endocrine mediated. No studies, including high quality studies in the published literature, predict significant endocrine-related toxicity or functional decrements in any species at environmentally relevant concentrations, or, in mammals, at doses below the TSRC that are relevant for human hazard and risk assessment. Overall, there is no basis for concern regarding potential interactions of 2,4-D with endocrine pathways or axes (estrogen, androgen, steroidogenesis or thyroid), and thus 2,4-D is unlikely to pose a threat from endocrine disruption to wildlife or humans under conditions of real-world exposures.

Oestrogen activity of the serum in adolescents with Type 1 diabetes

AIMS

To assess serum oestrogen levels and oestrogenic activity in adolescents with Type 1 diabetes compared with a healthy control group.

METHODS

We conducted a cross-sectional study that evaluated adolescents with Type 1 diabetes (n = 38) and healthy adolescents (control group; n = 32). Serum oestrogens, urinary oestrogen metabolites and serum oestrogenic activity were assessed. Oestrogenic activity was evaluated in an in vitro cell proliferation assay using a modified E-screen assay with MCF-7/BUS cells.

RESULTS

Adolescents with Type 1 diabetes had lower oestrogenic activity levels in both phases of the menstrual cycle compared with the control group (follicular phase: 76 vs 94%; luteal phase: 97 vs 131%; P < 0.01), even after adjusting for BMI, oestradiol and oestrone levels. Postmenarcheal adolescents with Type 1 diabetes had lower oestradiol levels compared with control subjects in the follicular phase (63.3 pmol/l vs 89.4 pmol/l; P < 0.01) and higher oestrone levels compared with controls in the luteal phase (196 vs 151.9 pmol/l; P < 0.05).

CONCLUSIONS

Adolescents with Type 1 diabetes had lower levels of serum oestrogenic activity, and these were lower than expected based on their serum oestradiol levels. We postulate that changes in the serum milieu of oestrogens in patients with Type 1 diabetes may explain their decreased oestrogenic activity and may play a role in their adverse metabolic profile.

Estrogenic evaluation and organochlorine identification in blubber of North Sea harbour porpoise (Phocoena phocoena) stranded on the North Sea coast

Thirteen individual organochlorine compounds at 3 concentrations (80, 400, and 2000 ng/mL culture medium), as well as mixtures, were assayed for the estrogen receptor (ER) activation or inhibition, using a luciferase reporter gene assay (RGA). None of the PCB 138, 153, or 180 or their mixture induced a response in the RGA. o,p′-DDT was the most potent xenoestrogen from the DDT group, inducing a response already at 80 ng/mL. From the HCH and HCB group, only β-HCH (at 400 and 2000 ng/mL) and δ-HCH (at 2000 ng/mL) displayed estrogenic activities. These 13 organochlorines were determined by GC-MS in 12 samples of North Sea harbor porpoise blubber. The PCBs were the main contaminants. Within each group, PCB 153 (6.0 × 10²~4.2 × 10⁴  μg/kg), p,p′-DDE (5.1 × 10²~8.6 × 10³  μg/kg), and HCB (7.6 × 10¹~1.5 × 10³  μg/kg) were the compounds found in highest concentrations. The hormonal activity of the porpoise blubber samples was also assayed in RGA, where two samples showed estrogenic activity, seven samples showed antiestrogenic activity, and one sample showed both estrogenic and antiestrogenic activity. Our results suggest that the 13 POPs measured by GC-MS in the samples cannot explain alone the estrogenicity of the extracts.

Potential estrogenic effects of phosphorus-containing flame retardants

As the substitute of polybrominated diphenyl ethers (PBDEs), further assessments about the potential ecological safety and health risks of phosphorus-containing flame retardants (PFRs) are required because the worldwide demand for PFRs has been increasing every year. In this study, we examined the agonistic/antagonistic activity of a group of PFRs by three in vitro models (luciferase reporter gene assay, yeast two-hybrid assay, and E-screen assay). Molecule docking was used to further explain the interactions between ERα and PFRs. Data from luciferase reporter gene analysis showed three members of the nine tested PFRs significantly induced estrogenic effects, with the order of TPP > TCP > TDCPP, while TCEP and TEHP have remarkable antiestrogenic properties with calculated REC20 and RIC20 values of 10(-6) M or lower. Results from the luciferase reporter gene method are generally consistent with results obtained from the yeast two-hybrid assay and E-screen, except for the positive estrogenic activity of TBP in E-screen testing. Docking results showed that binding between ligands and ERα was stabilized by hydrophobic interactions. As a proposed alternative for brominated flame retardant, PFRs may have anti/estrogenic activity via ERα at the low dose typical of residue in environmental matrix or animals. PFRs with a short chain, halogen, and benzene ring in the substituent group tend to be estrogenic. Our research suggests that comprehensive evaluations, including health and ecological assessments, are required in determining whether PFRs are preferable as an emerging industrial substitute.

Comparative genomic hybridization (CGH) in genotoxicology

In the past two decades comparative genomic hybridization (CGH) and array CGH have become crucial and indispensable tools in clinical diagnostics. Initially developed for the genome-wide screening of chromosomal imbalances in tumor cells, CGH as well as array CGH have also been employed in genotoxicology and most recently in toxicogenomics. The latter methodology allows a multi-endpoint analysis of how genes and proteins react to toxic agents revealing molecular mechanisms of toxicology. This chapter provides a background on the use of CGH and array CGH in the context of genotoxicology as well as a protocol for conventional CGH to understand the basic principles of CGH. Array CGH is still cost intensive and requires suitable analytical algorithms but might become the dominating assay in the future when more companies provide a large variety of different commercial DNA arrays/chips leading to lower costs for array CGH equipment as well as consumables such as DNA chips. As the amount of data generated with microarrays exponentially grows, the demand for powerful adaptive algorithms for analysis, competent databases, as well as a sound regulatory framework will also increase. Nevertheless, chromosomal and array CGH are being demonstrated to be effective tools for investigating copy number changes/variations in the whole genome, DNA expression patterns, as well as loss of heterozygosity after a genotoxic impact. This will lead to new insights into affected genes and the underlying structures of regulatory and signaling pathways in genotoxicology and could conclusively identify yet unknown harmful toxicants.

Identification of possible genetic alterations in the breast cancer cell line MCF-7 using high-density SNP genotyping microarray

Context:

Cancer cell lines are used extensively in various research. Knowledge of genetic alterations in these lines is important for understanding mechanisms underlying their biology. However, since paired normal tissues are usually unavailable for comparison, precisely determining genetic alterations in cancer cell lines is difficult. To address this issue, a highly efficient and reliable method is developed. Aims: Establishing a highly efficient and reliable experimental system for genetic profiling of cell lines.

Materials and Methods:

A widely used breast cancer cell line, MCF-7, was genetically profiled with 4,396 single nucleotide polymorphisms (SNPs) spanning 11 whole chromosomes and two other small regions using a newly developed high-throughput multiplex genotyping approach.

Results:

The fractions of homozygous SNPs in MCF-7 (13.3%) were significantly lower than those in the control cell line and in 24 normal human individuals (25.1% and 27.4%, respectively). Homozygous SNPs in MCF-7 were found in clusters. The sizes of these clusters were significantly larger than the expected based on random allelic combination. Fourteen such regions were found on chromosomes 1p, 1q, 2q, 6q, 13, 15q, 16q, 17q and 18p in MCF-7 and two in the small regions.

Conclusions:

These results are generally concordant with those obtained using different approaches but are better in defining their chromosomal positions. The used approach provides a reliable way to detecting possible genetic alterations in cancer cell lines without paired normal tissues.

Estrogenic and Acetylcholinesterase-Enhancement Activity of a New Isoflavone, 7,2',4'-Trihydroxyisoflavone-4'-O-beta-D-Glucopyranoside from Crotalaria Sessililflora

A new isoflavone, 7,2',4'-trihydroxyisoflavone-4'-O-beta-D-glucopyranoside has been isolated from the aerial part of Crotalaria sessiliflora. The isoflavone glucoside enhanced the proliferation of the MCF-7 human breast cancer cell line, which possesses estrogen receptor (ER) and responds to estrogen in culture. The estrogenic property of the isoflavone glucoside was blocked by the known ER antagonist tamoxifen, indicating the involvement of the ER. Furthermore, the isoflavone glucoside was found to enhance the acetylcholinesterase (AChE) activity of the rat neuronal cell line PC12 at low concentrations of nerve growth factor (NGF).

Differential effects of a complex organochlorine mixture on the proliferation of breast cancer cell lines

Organochlorine compounds (OCs) are a group of persistent chemicals that accumulate in fatty tissues with age. Although OCs has been tested individually for their capacity to induce breast cancer cell proliferation, few studies examined the effect of complex mixtures that comprise compounds frequently detected in the serum of women. We constituted such an OC mixture containing 15 different components in environmentally relevant proportions and assessed its proliferative effects in four breast cancer cell lines (MCF-7, T47D, CAMA-1, MDAMB231) and in non-cancerous CV-1 cells. We also determined the capacity of the mixture to modulate cell cycle stage of breast cancer cells and to induce estrogenic and antiandrogenic effects using gene reporter assays. We observed that low concentrations of the mixture (100 × 10(3) and 50 × 10(3) dilutions) stimulated the proliferation of MCF-7 cells while higher concentrations (10 × 10(3) and 5 × 10(3) dilutions) had the opposite effect. In contrast, the mixture inhibited the proliferation of non-hormone-dependent cell lines. The mixture significantly increased the number of MCF-7 cells entering the S phase, an effect that was blocked by the antiestrogen ICI 182,780. Low concentrations of the mixture also caused an increase in CAMA-1 cell proliferation but only in the presence estradiol and dihydrotestosterone (p<0.05 at the 50 × 10(3) dilution). DDT analogs and polychlorinated biphenyls all had the capacity to stimulate the proliferation of CAMA-1 cells in the presence of sex steroids. Reporter gene assays further revealed that the mixture and several of its constituents (DDT analogs, aldrin, dieldrin, β-hexachlorocyclohexane, toxaphene) induced estrogenic effects, whereas the mixture and several components (DDT analogs, aldrin, dieldrin and PCBs) inhibited the androgen signaling pathway. Our results indicate that the complex OC mixture increases the proliferation of MCF-7 cells due to its estrogenic potential. The proliferative effect of the mixture on CAMA-1 cells in the presence of sex steroids appears mostly due to the antiandrogenic properties of p,p'-DDE, a major constituent of the mixture. Other mixtures of contaminants that include emerging compounds of interest such as brominated flame retardants and perfluoroalkyl compounds should be tested for their capacity to induce breast cancer cell proliferation.

Performance of the flow cytometric E-screen assay in screening estrogenicity of pure compounds and environmental samples

In vitro estrogenicity screens are believed to provide a first prioritization step in hazard characterization of endocrine disrupting chemicals. When applied to complex environmental matrices or mixture samples, they have been indicated valuable in estimating the overall estrogen-mimicking load. In this study, the performance of an adapted format of the classical E-screen or MCF-7 cell proliferation assay was profoundly evaluated to rank pure compounds as well as influents and effluents of sewage treatment plants (STPs) according to estrogenic activity. In this adapted format, flow cytometric cell cycle analysis was used to allow evaluation of the MCF-7 cell proliferative effects after only 24 h of exposure. With an average EC(50) value of 2 pM and CV of 22%, this assay appears as a sensitive and reproducible system for evaluation of estrogenic activity. Moreover, estrogenic responses of 17 pure compounds corresponded well, qualitatively and quantitatively, with other in vitro and in vivo estrogenicity screens, such as the classical E-screen (R(2)=0.98), the estrogen receptor (ER) binding (R(2)=0.84) and the ER transcription activation assay (R(2)=0.87). To evaluate the applicability of this assay for complex samples, influents and effluents of 10 STPs covering different treatment processes, were compared and ranked according to estrogenic removal efficiencies. Activated sludge treatment with phosphorus and nitrogen removal appeared most effective in eliminating estrogenic activity, followed by activated sludge, lagoon and filter bed. This is well in agreement with previous findings based on chemical analysis or biological activity screens. Moreover, ER blocking experiments indicated that cell proliferative responses were mainly ER mediated, illustrating that the complexity of the end point, cell proliferation, compared to other ER screens, does not hamper the interpretation of the results. Therefore, this study, among other E-screen studies, supports the use of MCF-7 cell proliferation as estrogenicity screen for pure compounds and complex samples.

Responses of PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) in MCF-7 cells are culture condition dependent

To compare the effects of the food toxin 2-amino-1-methyl-6-phenyl-imidazo[4,5-b]pyridine (PhIP) and estradiol in hormone-responsive MCF-7 cells, the cells were exposed to different concentrations of either PhIP or estradiol. The effect of various culture conditions (e.g. phenol red, FBS, vehicle (DMSO/EtOH) and seeding density) on responses was studied. Cells were continuously grown with steroid-containing or -deprived medium, or switched from steroid-containing to -deprived medium for the experiments to minimize the effect of background estrogenicity. Effects of PhIP and estradiol on cell viability and proliferation were determined by ATP analysis and Ki-67 immunocytochemistry. Expression of estrogen receptor alpha, cell stress markers (p53 and ERK) and estrogen responsive proteins (c-myc and ERK) were immunoblotted. All concentrations of estradiol induced cell proliferation, viability and changes in protein expression, typical for estrogenic responses. PhIP, however, increased viability only at low concentrations and depending on culture conditions. No changes in protein expressions by PhIP were noted, not even when switching cells from steroid-containing to -deprived medium which down-regulated the expression of proteins at basal level. Vehicle affected significantly viability, especially after exposure to PhIP, but not protein expression while medium changes affected both. In conclusion, the effects of PhIP and estradiol in MCF-7 cells are dependent on culture conditions. The detected PhIP-induced changes are weaker compared to those induced by estradiol.

1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE) disrupts the estrogen-androgen balance regulating the growth of hormone-dependent breast cancer cells

INTRODUCTION

Estrogen and androgen signalling pathways exert opposing influences on the proliferation of mammary epithelial and hormone-dependent breast cancer cells. We previously reported that plasma concentrations of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE), the main metabolite of the insecticide DDT (1,1,1-trichloro-2,2-bis [p-chlorophenyl]ethane) and a potent androgen antagonist, were associated with tumor aggressiveness in women diagnosed with breast cancer. We sought to examine the biological plausibility of this association by testing the effect of p,p'-DDE on the proliferation of CAMA-1 cells, a human breast cancer cell line that expresses the estrogen receptor alpha (ERalpha) and the androgen receptor (AR), in the presence of physiological concentrations of estrogens and androgens in the cell culture medium.

METHODS

The proliferation of CAMA-1 cells was determined in 96-well plates following a 9-day treatment with p,p'-DDE alone (0.1 to 10 muM) or in combination with 17beta-estradiol (E2) (100 pM) and dihydrotestosterone (DHT) (100, 500, or 1,000 pM). We also assessed p,p'-DDE-induced modifications in cell cycle entry and the expression of the sex-steroid-dependent genes ESR1, AR, CCND1, and TFF1 (pS2) (mRNA and/or protein).

RESULTS

We found that treatment with p,p'-DDE induced a dose-response increase in the proliferation of CAMA-1 cells when cultivated in the presence of physiological concentrations of estrogens and androgens, but not in the absence of sex steroids in the cell culture medium. A similar effect of p,p'-DDE was noted on the proliferation of MCF7-AR1 cells, an estrogen-responsive cell line that was genetically engineered to overexpress the AR. DHT added together with E2 to the cell culture medium decreased the recruitment of CAMA-1 cells in the S phase and the expression of ESR1 and CCND1 by comparison with cells treated with E2 alone. These androgen-mediated effects were blocked with similar efficacy by p,p'-DDE and the potent antiandrogen hydroxyflutamide.

CONCLUSION

Our results suggest that p,p'-DDE could increase breast cancer progression by opposing the androgen signalling pathway that inhibits growth in hormone-responsive breast cancer cells. The potential role of environmental antiandrogens in breast carcinogenesis deserves further investigation.

Soy isoflavones decrease the catechol-O-methyltransferase-mediated inactivation of 4-hydroxyestradiol in cultured MCF-7 cells

The tissue concentrations of the female sex hormone 17beta-estradiol (E2) and its reactive catechol metabolites such as 4-hydroxyestradiol (4-HO-E2) play important roles in hormonal carcinogenesis. They are influenced by the activity of local enzymes involved in the metabolic activation and inactivation of E2. In the mammary gland, catechol estrogens are predominately inactivated by catechol-O-methyltransferase (COMT). Food supplements containing the soy isoflavones genistein and daidzein are consumed because they are believed to protect from breast cancer; however, this proposed benefit is controversial. The aim of the present study was to investigate the influence of soy isoflavones on the gene expression and activity of COMT in cultured human mammary adenocarcinoma MCF-7 cells. Levels of COMT messenger RNA (mRNA) were determined by reverse transcription/competitive polymerase chain reaction and COMT activity was determined by high-performance liquid chromatography analysis of the methylation products of both the model substrate quercetin and the physiological relevant substrate 4-HO-E2. Our study demonstrates for the first time that soy isoflavones at hormonally active concentrations cause a significant reduction of both COMT mRNA levels and COMT activity as well as of the methylation of 4-HO-E2. Experiments using the estrogen receptor (ER) antagonist ICI 182,780 support a role of the ER in the isoflavone-induced down-regulation of COMT expression. Thus, this study not only demonstrates that hormonally active concentrations of soy isoflavones inhibit the detoxification of catechols in this human breast cancer cell line but also implies that diet might influence COMT activity to a greater extent than heretofore recognized.

Investigation of the estrogenic activities of pesticides from Pal-dang reservoir by in vitro assay

Endocrine disruptors, when absorbed into the body, interfere with the normal function by mimicking or blocking the hormone system. To investigate compounds mimicking estrogen in the drinking water source of the residence of Seoul, the Pal-dang reservoir was monitored over a period of 5 years, between 2000 and 2004. Nine kinds of pesticide (carbaryl, DBCP, diazinon, fenitrothion, fenobucarb, flutolanil, iprobenphos, isoprothiolane and parathion) were found to exist in the river water sample. These compounds were detected at low concentrations in the water samples. The total concentration and those of each of these pesticides were below the permissible limits of the National Institute of Environmental Research (NIER), Korea. The estrogenic potencies of the nine pesticides were examined using an E-screen assay with MCF-7 BUS estrogen receptor (ER)-positive human breast cancer cells, with ER-negative MDA MB 231 cell lines also used to compare the results. From this, flutolanil and isoprothiolane were confirmed to have estrogenic activities as shown by the increasing MCF-7 BUS cell growth on their addition. In addition, the estrogen receptor alpha (ERalpha) protein, estrogen receptor-regulated progesterone receptor (PR) and pS2 mRNA levels on the addition of flutolanil and isoprothiolane were measured with MCF-7 BUS cells. It was observed that the levels of ERalpha protein decreased and those of the PR and pS2 genes increased on the addition of either flutolanil or isoprothiolane at concentrations of 10(-4) M, in the same manner as with the addition of 17beta-estradiol, which was used as the positive control. From these results, it was confirmed that flutolanil and isoprothiolane exhibit estrogenic activities, suggesting they might act through estrogen receptors.

Mixture effects of estrogenic compounds on proliferation and pS2 expression of MCF-7 human breast cancer cells

Humans are exposed to a variety of food-borne phytochemicals (PC) as well as synthetic chemicals (SC). Some of these compounds have been reported to have estrogenic or anti-estrogenic properties and are therefore suspected endocrine disruptors. Until now it remains unclear if non-additive effects occur in combinations with endogenous estrogens, such as 17beta-estradiol (E(2)). To investigate such interactions, several PC and SC were tested individually, in mixtures and as combinations of mixtures with E(2) for effects on ERalpha receptor mediated cell proliferation and estrogen regulated pS2 expression level in MCF-7(bus) cells. PCs (coumestrol, genistein, naringenin, catechin, epicatechin, quercetin) or SCs (4-nonylphenol, octylphenol, beta-hexachlorocyclohexane, bisphenol A, methoxychlor, dibutyl phthalate) were mixed (PCmix and SCmix) either in concentrations reflecting human serum concentrations or at equipotent concentrations for estrogenicity. EC(50) values were applied in two approaches of the concentration-addition model (the method of isoboles and the cumulative estrogen equivalency method) to assess mixture effects. In both models PCmix and SCmix or combinations of the mixtures with E(2) showed no departure from additivity. In conclusion, the tested PCs and SCs appeared to act as (full) agonists for the estrogen receptor and interacted in mixtures and with estradiol in an additive way. In addition, it is concluded that the possible contribution of food-borne PCs to the estrogenic effect of xenobiotics is likely to be more significant than that caused by food-borne SCs.

Sample preparation method for the ER-CALUX bioassay screening of (xeno-)estrogenic activity in sediment extracts

The application of bioassays to assess the occurrence of estrogenic compounds in the environment is increasing in both a scientific and statutory context. The availability of appropriate validated methods for sample pre-treatment and analysis is crucial for the successful implementation of bioassays. Here, we present a sample preparation method for the bioassay screening of estrogenic activity in sediment with the in vitro Estrogen Receptor mediated Chemical Activated LUciferase gene eXpression (ER-CALUX) assay. The method makes use of an Accelerated Solvent (ASE) or Soxhlet extraction with a mixture of dichloromethane and acetone (3:1, v/v), followed by clean up of the extract by Gel Permeation Chromatography (GPC). Recoveries of a panel of 17 pollutants differing largely in physical-chemical properties from spiked sediment were determined and appeared to be on average about 86%. Furthermore, the estrogenic potencies of all test compounds were individually assessed by determination of concentration-response relationships in the ER-CALUX assay. Concentration dependent estrogenic potency was found for 14 of the 17 compounds, with potencies of about 10(5) to 10(7) fold lower than the natural estrogenic hormone 17beta-estradiol. Anti-estrogenic potency was assessed by testing combinations of estradiol and individual test compounds, but was found for none of the compounds. The low estrogenic activity of the test compounds in the spiking mixture was well recovered during GPC treatment of the pure mixture, but did not contribute significantly to the background estrogenic activity present in the spiked sediment. Application of the method to field samples showed that estrogenic activity can be found at different types of locations, and demonstrated that levels between locations may vary considerably over relatively short distances.

Activation of estrogen receptor-mediated gene transcription by the equine estrogen metabolite, 4-methoxyequilenin, in human breast cancer cells

4-Methoxyequilenin (4-MeOEN) is an O-methylated metabolite in equine estrogen metabolism. O-methylation of catechol estrogens is considered as a protective mechanism; however, comparison of the properties of 4-MeOEN with estradiol (E(2)) in human breast cancer cells showed that 4-MeOEN is a proliferative, estrogenic agent that may contribute to carcinogenesis. 4-MeOEN results from O-methylation of 4-hydroxyequilenin, a major catechol metabolite of the equine estrogens present in hormone replacement therapeutics, which causes DNA damage via quinone formation, raising the possibility of synergistic hormonal and chemical carcinogenesis. 4-MeOEN induced cell proliferation with nanomolar potency and induced estrogen response element (ERE)-mediated gene transcription of an ERE-luciferase reporter and the endogenous estrogen-responsive genes pS2 and TGF-alpha. These estrogenic actions were blocked by the antiestrogen ICI 182,780. In the standard radioligand estrogen receptor (ER) binding assay, 4-MeOEN showed very weak binding. To test for alternate ligand-ER-independent mechanisms, the possibility of aryl hydrocarbon receptor (AhR) binding and ER-AhR cross talk was examined using a xenobiotic response element-luciferase reporter and using AhR small interfering RNA silencing in the ERE-luciferase reporter assay. The results negated the possibility of AhR-mediated estrogenic activity. Comparison of gene transcription time course, ER degradation, and rapid activation of MAPK/ERK in MCF-7 cells demonstrated that the actions of 4-MeOEN mirrored those of E(2) with potency for classical and nonclassical estrogenic pathways bracketing that of E(2). Methylation of 4-OHEN may not represent a detoxification pathway because 4-MeOEN is a full, potent estrogen agonist.

Enantioselectivity in estrogenic potential and uptake of bifenthrin

Despite the fact that the biological processes of chiral compounds are enantioselective, the endocrine disruption activity and uptake of chiral contaminants with respect to enantioselectivity has so far received limited research. In this study, the estrogenic potential and uptake of the enantiomers of a newer pyrethroid insecticide, bifenthrin (BF), were investigated. Significant differences in estrogenic potential were observed between the two enantiomers in the in vitro human breast carcinoma MCF-7 cell proliferation assay (i.e., the E-SCREEN assay) and the in vivo aquatic vertebrate vitellogenin enzyme-linked immunosorbent assay (ELISA). In the E-SCREEN assay, the relative proliferative effect ratios of 1S-cis-BF and 1R-cis-BF were 74.2% and 20.9%, respectively, and the relative proliferative potency ratios were 10% and 1%, respectively. The cell proliferation induced by the two BF enantiomers may be through the classical estrogen response pathway via the estrogen receptor (ER), as the proliferation induced by the enantiomers could be completely blocked when combined with 10-6 mol/L of the ER antagonist ICI 182,780. Measurement of vitellogenin induction in Japanese medaka (Oryzias latipes) showed that, at an exposure level of 10 ng/mL, the response to 1S-cis-BF was about 123 times greater than thattothe Renantiomer. Significant selectivity also occurred in the uptake of BF enantiomers in the liver and other tissues of J. medaka. These results together suggest that assessment of the environmental safety of chiral insecticides should consider enantioselectivity in acute and chronic ecotoxicities such as endocrine disruption.

Dichlorodiphenyltrichloroethane impairs follicle-stimulating hormone receptor-mediated signaling in rat Sertoli cells

Any toxicant that affects Sertoli cell development can potentially disturb male fertility. So far, the effects of organochlorine compounds have been poorly investigated in male. Here, we studied the effects of dichlorodiphenyltrichloroethane (DDT), an organochloride pesticide, on Sertoli cells. DDT inhibited the cAMP response to follicle-stimulating hormone (FSH), the major endocrine control of Sertoli cell development, and to a beta2-agonist, isoproterenol. DDT exposure decreased the level of FSH binding sites. Direct adenylyl cyclase activation by Forskolin was unaltered by DDT, while the activation of Galphas by cholera toxin was decreased by DDT. The DDT inhibitory effect on the FSH response was also observed in Ser W3 cells, a Sertoli cell-derived immortalized cell line. All these effects were reproduced by the lipophilic aromatic bisphenol A but not by structurally unrelated CisPlatin. In conclusion, these results are a first step in understanding the molecular basis of DDT deleterious effects in spermatogenesis.

Prenylflavonoids as nonsteroidal phytoestrogens and related structure-activity relationships

In the search for estrogen receptor (ER) modulators, a series of prenylflavonoids were found to be widely distributed amongst tonic herbal medicines and to possess estrogen-like activity in MCF-7/BOS cells, as evaluated by an estrogen-screening assay. Cell-cycle analysis revealed that the stimulatory effects of these compounds toward cell proliferation were elicited at the G1-S checkpoint and could significantly increase the S-phase population of MCF-7 cells under hormone-free conditions. ER-responsive gene (PS2, PgR) and protein (PgR) expression was also detected; mRNA and protein-expression levels for PS2 and PgR were up-regulated by the compounds in a dose-dependent manner. These effects could be inhibited by the pure ER antagonist ICI 182,780 ((7alpha-[9-{4,4,5,5,5-pentafluoropentyl}sulfinyl]nonyl)estra-1,3,5(10)-triene-3,17beta-diol). It was therefore concluded that the estrogen-like effects of these prenylflavonoids were mediated primarily through ERs. Furthermore, to explore the structure-activity relationship based on the estrogen receptor and detailed molecular mechanisms among the prenylflavonoids, protein-ligand docking simulations were carried out by using the DS-MODELING software package. The binding affinity of each prenylflavonoid toward ERalpha was scored, and the receptor-ligand interaction was also analyzed to provide the simulation characteristics of virtual molecular recognition mechanisms.

Flow cytometric cell cycle analysis allows for rapid screening of estrogenicity in MCF-7 breast cancer cells

The quantitative measurement of individual cells and their characteristics by means of flow cytometry is already for many years of great value for clinical studies. However, its potential as a tool in (eco)toxicology has only recently been discovered. Analysis of cell cycle kinetics with DNA-staining dyes can offer a valuable alternative to detect effects of chemicals on cell proliferation, an important endpoint in screening estrogen-like properties of chemicals. In the present study, flow cytometric cell cycle analysis in growth arrested MCF-7 cells exposed to five xenoestrogens correspond well with cell proliferation results of the conventionally used E-screen assay. Moreover, re-induction of proliferation in MCF-7 cells, indicated by the percentage of cells in S(ynthesis)-phase, is most pronounced after 24 h exposure, thus allowing a faster screening of xenoestrogens. This flow cytometric proliferation assay confirms that the estrogenic activity of structurally analogous parabens is mediated by the estrogen receptor pathway and is proportional to the alkyl chain length. Moreover, the ER-mediated mode of action of two fluorotelomer alcohols (6:2 FTOH and 8:2 FTOH), recently reported as xenoestrogenic, could be elucidated. These results support the potential of flow cytometric cell cycle kinetics as a screening assay for estrogen-like properties of chemicals.

Biological validation of a sample preparation method for ER-CALUX bioanalysis of estrogenic activity in sediment using mixtures of xeno-estrogens

The combined estrogenic effects of mixtures of environmental pollutants in the in vitro ER-CALUX (chemical activated luciferase gene expression) bioassaywere examined to biologically validate a sample preparation method for the analysis of estrogenic compounds in sediment. The method used accelerated solvent extraction (ASE) and gel permeation chromatography (GPC) and was validated with respect to recovery of biological response taking mixture effects into account. Four mixtures of three to six xenoestrogenic compounds (bisphenol A, 4-nonylphenol, (4,4'-dichlorodiphenyl)trichloroethane, (2,4'-dichlorodiphenyl)trichloroethane, dieldrin, 4-n-octylphenol, alpha-chlordane, dibutylphthalate, (4,4'-dichlorodiphenyl)dichloroethylene, and 2,4,5-trichlorobiphenyl) were prepared. Experimentally determined mixture effects were well described by the concept of concentration addition (CA), as expected for similarly acting compounds. Observed estradiol equivalence factors of the mixtures (on average 1.2 +/- 0.3) agreed very well with the value predicted according to CA. The sample preparation method was then applied to pure mixtures of standards and to sediment spiked with one of the mixtures. Recoveries of estrogenic compounds were estimated by determination of their mixture potencies in ER-CALUX and compared to the mixture effects predicted by CA. Recoveries of estrogenic activity were between 80 and 129%, indicating that the additive behavior of mixtures of xeno-estrogens is well conserved during sample preparation. Together with an average repeatability of 18.3%, low average limit of detection (2.6 +/- 1.8 pg of EEQ/ g), and coefficient of variance (3.5 +/- 3.3%),this demonstrated the suitability of the sample preparation method for the analysis of mixtures of (xeno-)estrogenic compounds in sediment with the ER-CALUX assay.

Urolithins, ellagic acid-derived metabolites produced by human colonic microflora, exhibit estrogenic and antiestrogenic activities

Urolithins A and B (hydroxy-6H-dibenzo[b,d]pyran-6-one derivatives) are colonic microflora metabolites recently proposed as biomarkers of human exposure to dietary ellagic acid derivatives. Molecular models suggest that urolithins could display estrogenic and/or antiestrogenic activity. To this purpose, both urolithins and other known phytoestrogens (genistein, daidzein, resveratrol, and enterolactone) were assayed to evaluate the capacity to induce cell proliferation on the estrogen-sensitive human breast cancer MCF-7 cells as well as the ability to bind to alpha- and beta-estrogen receptors. Both urolithins A and B showed estrogenic activity in a dose-dependent manner even at high concentrations (40 microM), without antiproliferative or toxic effects, whereas the other phytoestrogens inhibited cell proliferation at high concentrations. Overall, urolithins showed weaker estrogenic activity than the other phytoestrogens. However, both urolithins displayed slightly higher antiestrogenic activity (antagonized the growth promotion effect of 17-beta-estradiol in a dose-dependent manner) than the other phytoestrogens. The IC(50) values for the ERalpha and ERbeta binding assays were 0.4 and 0.75 microM for urolithin A; 20 and 11 microM for urolithin B; 3 and 0.02 for genistein; and 2.3 and 1 for daidzein, respectively; no binding was detected for resveratrol and enterolactone. Urolithins A and B entered into MCF-7 cells and were metabolized to yield mainly urolithin-sulfate derivatives. These results, together with previous studies regarding absorption and metabolism of dietary ellagitannins and ellagic acid in humans, suggest that the gut microflora metabolites urolithins are potential endocrine-disrupting molecules, which could resemble other described "enterophytoestrogens" (microflora-derived metabolites with estrogenic/antiestrogenic activity). Further research is warranted to evaluate the possible role of ellagitannins and ellagic acid as dietary "pro-phytoestrogens".

Estrogen-like properties of fluorotelomer alcohols as revealed by mcf-7 breast cancer cell proliferation

We investigated estrogen-like properties of five perfluorinated compounds using a combination of three in vitro assays. By means of an E-screen assay, we detected the proliferation-promoting capacity of the fluorotelomer alcohols 1H,1H,2H,2H-perfluorooctan-1-ol (6:2 FTOH) and 1H,1H,2H,2H-perfluoro-decan-1-ol (8:2 FTOH). The more widely environmentally distributed compounds perfluoro-1-octane sulfonate, perfluorooctanoic acid, and perfluorononanoic acid did not seem to possess this hormone-dependent proliferation capacity. We investigated cell cycle dynamics using flow cytometric analyses of the DNA content of the nuclei of MCF-7 breast cancer cells. Exposure to both fluorotelomer alcohols stimulated resting MCF-7 cells to reenter the synthesis phase (S-phase) of the cell cycle. After only 24 hr of treatment, we observed significant increases in the percentage of cells in the S-phase. In order to further investigate the resemblance of the newly detected xenoestrogens to the reference compound 17beta-estradiol (E2), gene expression of a number of estrogen-responsive genes was analyzed by real-time polymerase chain reaction. With E2, as well as 4-nonylphenol and the fluorotelomer alcohols, we observed up-regulation of trefoil factor 1, progesterone receptor, and PDZK1 and down-regulation of ERBB2 gene expression. We observed small but relevant up-regulation of the estrogen receptor as a consequence of exposures to 6:2 FTOH or 8:2 FTOH. The latter finding suggests an alternative mode of action of the fluorotelomer alcohols compared with that of E2. This study clearly underlines the need for future in vivo testing for specific endocrine-related end points.

Screening estrogenic oxidized by-products by combining ER binding and ultrafiltration

Ozonation and chlorination of 17β-estradiol (E2), 17α-ethynylestradiol (EE2), bisphenol A (BPA), and nonylphenol (NP) were performed to evaluate the estrogenic activity of the by-products of these endocrine disrupting chemicals (EDCs). After 15min oxidation, samples were extracted using solid phase extraction (SPE) cartridges, and tested in vitro to measure the estrogenic activities of the oxidized products. MCF-7 cell proliferation assay showed that chlorinated BPA solution displayed slightly stronger estrogenicity than BPA, while chlorinated NP retained about one-tenth of its bioactivity. The estrogenic mono-, di-, tri-, and tetra-ClBPAs and di-ClNP were screened out from the corresponding chlorinated products by a combined application of estrogen receptor (ER) binding with ultrafiltration and identified by high performance liquid chromatography coupled with mass spectrometry (LC/MS). Ozonation of the above four estrogens and chlorination of E2 and EE2 significantly decreased their estrogenic activities under the applied conditions.

Proliferation-stimulating effects of icaritin and desmethylicaritin in MCF-7 cells

Icariin, icaritin and desmethylicaritin are constituents of Epimedium with a similar structure to genistein and daidzein. Using the modified MCF-7 cell proliferation assay (E-SCREEN assessment system), these compounds were tested for their estrogen-like activities. Icaritin and desmethylicaritin, but not icariin, strongly stimulated the proliferation of MCF-7/BUS cells. Cell cycle analysis revealed that the proliferation stimulatory effect was associated with a marked increase in the number of MCF-7/BUS cells in S phase and a significant increase in the G2/M population, with effects similar to those of estradiol. These actions were dose dependent (range from 1 nM to 10 microM) and could be significantly inhibited by the specific estrogen receptor antagonist ICI 182,780 [7 alpha-[9(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl)-estra-1,3,5(10)-triene-3,17beta-diol)]. The estrogen receptor-regulated progesterone receptor and PS2 mRNA levels were increased by treatment with icaritin or desmethylicaritin within 24 h and the effects were also reversed by ICI 182,780. It was concluded that icaritin and desmethylicaritin are novel phytoestrogens and that the estrogenic effects of icaritin and desmethylicaritin are mediated by the estrogen receptor.

The Bik BH3-only protein is induced in estrogen-starved and antiestrogen-exposed breast cancer cells and provokes apoptosis

Evidence has been accumulating that some estrogen-dependent human breast cancers require estrogen for not only proliferation but also survival. To obtain insights into the molecular mechanisms of apoptosis of breast cancer cells subjected to estrogen starvation or exposed to antiestrogens, we characterized changes in the gene expression profile of MCF-7/BUS human breast cancer cells and revealed a strong induction of Bik, a member of the BH3-only proapoptotic proteins. The Bik mRNA transcript and protein were strongly induced by estrogen starvation or exposure to fulvestrant, a pure antiestrogen that competes with the natural estrogens for binding to the estrogen receptors. This Bik induction preceded apoptotic cell death, which was blocked by zVAD-fmk, a pancaspase inhibitor. Amounts of the Bcl-2-related proteins, such as Bcl-2, Bcl-XL, or Bax, showed only marginal changes in the presence or absence of estrogens or antiestrogens. Suppression of Bik expression by using the small interfering RNA effectively blocked the fulvestrant-induced breast cancer cell apoptosis. These results indicate that Bik is induced in MCF-7/BUS cells in the absence of estrogen signaling and plays a critical role in the antiestrogen-provoked breast cancer cell apoptosis.

Steroidal oxathiazine inhibitors of estrone sulfatase

The presence of estrone sulfatase in breast tumors and the high levels of circulating estrone sulfate may contribute the major portion of estrogen synthesized locally in breast tissues through conversion of estrone sulfate to estrone by the enzyme. Using inhibitors of estrone sulfatase for the treatment of estrogen-dependent (estrogen receptor positive, ER(+)) breast cancer could be a very effective therapeutic strategy for the treatment of estrogen-dependent breast tumors in postmenopausal women. Therefore, we designed and synthesized several steroidal 2',3'-oxathiazines that inhibit estrone sulfatase and have greatly reduced estrogenic side effects. Our in vitro studies indicate that the oxathiazine compounds have inhibitory activity on estrone sulfatase in MCF-7 human breast cancer cells. These estrone sulfatase inhibitors (ESIs) also inhibit the growth of MCF-7 cells induced by estrone sulfate. In addition, our in vivo experiments demonstrate that our ESIs have moderate antitumor activity against MCF-7 breast cancer xenografts in Balb/c athymic nude mice. The synthesis and biological activity of a number of these unique steroidal ESIs are described.

Critical parameters in the MCF-7 cell proliferation bioassay (E-Screen)

The MCF-7 cell proliferation bioassay has grown in popularity as a rapid test for detecting potentially oestrogenic compounds. Several MCF-7 cell sublines with different sensitivities to oestrogens are currently used, with maximal proliferation responses ranging from two- to 10-fold above those of hormone-free controls. In the highly responsive MCF-7 BUS cell line, we evaluated critical assay parameters for test performance, including growth conditions, initial seeding densities and differences in growth stimulation in medium containing human serum or fetal calf serum as well as appropriate solvents for oestrogen-mimicking compounds. Modifications significantly reduced the labour-intensive steps and overall assay costs without affecting the sensitivity of the assay. Using this optimized test regimen, the responsiveness of treated MCF-7 BUS cells was consistently increased up to 11-fold over hormone-free controls. The specificity was characterized by examining the effects of oestradiol-17beta, the anti-oestrogen ICI 182,780, and dieldrin, a recognized xeno-oestrogen. The improved proliferation bioassay will be a useful tool in identifying potential xeno-oestrogens.

Estrogenic effect of leachates and soil extracts from lysimeters spiked with sewage sludge and reference endocrine disrupters

Several experiments were conducted to evaluate the behavior and performance of some potential endocrine disrupters (ECDs). Two in vitro screening assays, one based on MCF7-cell proliferation (E-screen test) and the other on estrogenic receptor activity [enzyme-linked receptor assay (ELRA)], were used for the tests, which were done in lysimeters 80 cm in diameter with depth of 30 cm (shallow) or 90 cm (deep). A sandy soil was used to fill in all lysimeters, which were spiked on the surface with either: (a) a sewage sludge (SS) at a dose equivalent to 20 tons ha-1; (b) a mixture of reference ECDs, comprising 17 alpha- and 17 beta-estradiol (E2), nonylphenol, octylphenol, and bisphenol A at doses 100 times higher than the maximum concentrations respectively found in the applied SS; or (c) a mixture of ECDs and SS. After percolation of the lysimeters with rain and/or artificial water, five leachates were sampled from each lysimeter during a period of 210 days. Immediately after the lysimeter percolation experiments, four and six soil fractions were dissected from, respectively, the 30-cm and 90-cm lysimeters and extracted by water. Both the leachate and soil extract samples were analyzed for their estrogenicity using the assays indicated above. The E-screen assay was highly sensitive only for some leachate and extract samples but gave no response for most leachates and soil extracts. The results of the ELRA assay suggests a significantly higher estrogenicity of leachate samples from shallow lysimeters compared with that of leachates from deep lysimeters. In contrast, the estrogenic effect measured for soil extracts of shallow lysimeters was lower than that measured for soil extracts of deep lysimeters. The results of the E-screen assay suggests the occurrence of a fast mobilization of applied ECDs and a moderate retardation effect of native ECDs contained in applied SS in the sandy soil used in the lysimeters. In lysimeters spiked with a mixture of SS and ECDs, the washing-out effect of ECDs in the first leachate fraction decreased, but the distribution of ECDs in the lysimeters increased. The relatively high estrogenic impact measured for soil water extracts suggests that the ECDs were mostly associated with water-soluble fractions of organic matter and/or water-suspended fractions of the mineral soil matrix. The application of SS to agricultural and forest fields may determine the immobilization of ECDs in soil or their movement to surface and/or groundwater. Therefore, an endocrine risk of exposure exists for the water and soil organisms.

Assaying the estrogenicity of phytoestrogens in cells of different estrogen sensitive tissues

There is currently much concern that a wide range of both synthetic and naturally occurring environmental chemicals may act as endocrine disruptors (ED), and may adversely affect humans and wildlife. We examined the estrogenic effects of the phytoestrogens daidzein (DAI), equol (EQU) and O-desmethylangolensin (O-DMA), two metabolites of DAI, in three different assays. Binding affinity to the estrogen receptor alpha was 1000-10,000-fold lower compared with the endogenous estrogen estradiol. In the receptor positive cell line MCF-7 the phytoestrogens induced the expression of a reporter gene. The E-SCREEN is based on the estrogen-receptor binding induced proliferation of the human breast cancer cell line MCF-7. We also adapted the E-SCREEN for the estrogen-receptor positive human ovarian cancer cell line BG-1. The tested phytoestrogens induced cell proliferation in both cell lines, but not in the receptor negative human breast cancer cell line MDA-MB-231. The phytoestrogen-induced cell proliferation could be blocked by addition of the receptor antagonist 4-hydroxytamoxifen (OHT). Combination treatments with the endogenous estrogen estradiol showed competitive effects in MCF-7 cells. These studies demonstrated that the tested phytoestrogens exerted estrogenic responses in cells derived from two different tissues, breast and ovary. Furthermore, we demonstrated that BG-1 cells are a suitable additional cell system to investigate estrogenicity of test compounds.