Enzymatic control of estrogen production in human breast cancer: relative significance of aromatase versus sulfatase pathways

Structures and Functions of Human Placental Aromatase and Steroid Sulfatase, Two Key Enzymes in Estrogen Biosynthesis

Cytochrome P450 aromatase (AROM) and steroid sulfatase (STS) are the two key enzymes for the biosynthesis of estrogens in human, and maintenance of the critical balance between androgens and estrogens. Human AROM, an integral membrane protein of the endoplasmic reticulum, is a member of the cytochrome P450 superfamily. It is the only enzyme to catalyze the conversion of androgens with non-aromatic A-rings to estrogens characterized by the aromatic A-ring. Human STS, also an integral membrane protein of the endoplasmic reticulum, is a Ca²⁺-dependent enzyme that catalyzes the hydrolysis of sulfate esters of estrone and dehydroepiandrosterone to the unconjugated steroids, the precursors of the most potent forms of estrogens and androgens, namely, 17β-estradiol, 16α,17β-estriol, testosterone and dihydrotestosterone. Expression of these steroidogenic enzymes locally within organs and tissues of the endocrine, reproductive, and central nervous systems is the key for maintaining high levels of the reproductive steroids. The enzymes have been drug targets for the prevention and treatment of diseases associated with steroid hormone excesses, especially in breast, endometrial and prostate malignancies. Both enzymes have been the subjects of vigorous research for the past six decades. In this article, we review the important findings on their structure-function relationships, specifically, the work that began with unravelling of the closely guarded secrets, namely, the 3-D structures, active sites, mechanisms of action, origins of substrate specificity and the basis of membrane integration. Remarkably, these studies were conducted on the enzymes purified in their pristine forms from human placenta, the discarded and their most abundant source. The purification, assay, crystallization, and structure determination methodologies are described. Also reviewed are their functional quaternary organizations, post-translational modifications and the advancements made in the structure-guided inhibitor design efforts. Outstanding questions that still remain open are summarized in closing.

Structure of human placental steroid sulfatase at 2.0 angstrom resolution: Catalysis, quaternary association, and a secondary ligand site

Human placental estrone (E1)/dehydroepiandrosterone (DHEA) sulfatase (human placental steroid sulfatase; hSTS) is an integral membrane protein of the endoplasmic reticulum. This Ca²⁺-dependent enzyme catalyzes the hydrolysis of sulfate esters of E1 and DHEA to yield the respective unconjugated steroids, which then act as precursors for the biosynthesis of 17β-estradiol (E2) and dihydrotestosterone (DHT), respectively, the most potent forms of estrogens and androgens. hSTS is a key enzyme for the local production of E2 and DHT in the breast and the prostate. The enzyme is known to be responsible for maintaining high levels of estrogens in the breast tumor cells. The crystal structure of hSTS purified from human placenta has previously been reported at 2.6 Å resolution. Here we present the structure of hSTS determined at the superior 2.0 Å resolution bringing new clarity to the atomic architecture of the active site. The molecular basis of catalysis and steroid-protein interaction are revisited in light of the new data. We also reexamine the enzyme's quaternary association and its implication on the membrane integration. A secondary ligand binding pocket at the intermolecular interface and adjacent to the active site access channel, buried into the gill of the mushroom-shaped molecule, has been identified. Its role as well as that of a phosphate ion bound to an exposed histidine side chain are examined from the structure-function perspective. Higher resolution data also aids in the tracing of an important loop missing in the previous structure.

The phytochemical curcumin inhibits steroid sulfatase activity in rat liver tissue and NIH-3T3 mouse fibroblast cells

Curcumin is a phytochemical derived from the spice turmeric that is reported to have therapeutic effects. We are studying the enzyme steroid sulfatase (STS), which removes the sulfate group from inactive steroid hormones in peripheral tissues and we were interested in the effect of curcumin on STS activity due to its structural composition (polyphenolic). We sought to determine if curcumin affects STS activity in two model systems, rat liver and NIH-3T3 mouse fibroblast cells. STS assays were performed on tissue extracts of rat liver, and on NIH-3T3 microsomes and cells, with and without curcumin. Male and female rat liver extracts contained substantial amounts of STS activity, with males averaging higher (4-11 %) levels. Estradiol inhibited STS activity in livers of both sexes at 20 and 10 µM. Curcumin acted as a competitive inhibitor of STS activity in rat liver extracts, with a Ki of 19.8 µM in males and 9.3 µM in females. Curcumin also inhibited STS activity in NIH-3T3 microsomes at both 20 µM and 10 µM, and in whole NIH-3T3 cells at 20 µM. These data are the first to demonstrate STS inhibition by curcumin. Inhibition of STS results in lower active steroid hormone (estrogens and androgens) levels in tissues, possibly altering modulation of immune responses by these steroids.

Impaired redox regulation of estrogen metabolizing proteins is important determinant of human breast cancers

Estrogen evidently involves critically in the pathogenesis of gynaecological-cancers. Reports reveal that interference in estrogen-signalling can influence cell-cycle associated regulatory-processes in female reproductive-organs. The major determinants that influence E2-signallings are estrogen-receptor (ER), estrogen-sulfotransferase (SULT1E1), sulfatase (STS), and a formylglycine-generating-enzyme (FGE) which regulates STS activity. The purpose of this mini review was to critically analyze the correlation between oxidative-threats and redox-regulation in the process of estrogen signalling. It is extensively investigated and reported that oxidative-stress is linked to cancer. But no definite mechanism has been explored till date. The adverse effects of oxidative-threat/free-radicals (like genotoxic-effects, gene-regulation, and mitochondrial impairment) have been linked to several diseases like diabetes/cardiovascular-syndrome/stroke and cancer. However, a significant correlation between oxidative-stress and gynaecological-cancers are repeatedly reported without pointing a definite mechanism. For the first time in our study we have investigated the relationship between oxidative stress and the regulation of estrogen via estrogen metabolizing proteins. Reports reveal that ER, SULT1E1, STS and FGE are target-molecules of oxidative-stress and may function differently in oxidizing and reducing environment. In addition, estrogen itself can induce oxidative-stress. This fact necessitates identifying the critical connecting events between oxidative-stress and regulation of estrogen-associated-molecules (ER, SULT1E1, STS, and FGE) that favors tumorigenesis/carcinogenesis. The current review focus is on unique redox-regulation of estrogen and its regulatory-molecules via oxidative-stress. This mechanistic-layout may identify new therapeutic-targets and open further scopes to treat gynecological-cancers more effectively.

Homologue gene of bile acid transporters ntcp, asbt, and ost-alpha in rainbow trout Oncorhynchus mykiss: tissue expression, effect of fasting, and response to bile acid administration

Bile acid transporters belonging to the SLC10A protein family, Na+ taurocholate cotransporting polypeptide (NTCP or SLC10A1), apical sodium-dependent bile salt transporter (ASBT or SLC10A2), and organic solute transporter alpha (Ost-alpha) have been known to play critical roles in the enterohepatic circulation of bile acids in mammals. In this study, ntcp, asbt, and ost-alpha-1/-2 cDNA were cloned, their tissue distributions were characterized, and the effects of fasting and bile acid administration on their expression were examined in rainbow trout Oncorhynchus mykiss. The structural characteristics of Ntcp, Asbt, and Ost-alpha were well conserved in trout, and three-dimensional structure analysis showed that Ntcp and Asbt were similar to each other. Tissue distribution analysis revealed that trout asbt was primarily expressed in the hindgut, while ntcp expression occurred in the brain, and ost-alpha-1/-2 was mainly expressed in the liver or ovary. Although asbt and ost-alpha-1 mRNA levels in the gut increased in response to fasting for 4 days, ost-alpha-1 expression in the liver decreased. Similarly, bile acid administration increased asbt and ost-alpha-1 expression levels in the gut, while those of ntcp and ost-alpha-2 in the liver decreased. These results suggested that the genes asbt, ntcp, and ost-alpha are involved in bile acid transport in rainbow trout.

Steroid derivatives as inhibitors of steroid sulfatase

Sulfated steroids function as a storage reservoir of biologically active steroid hormones. The sulfated steroids themselves are biologically inactive and only become active in vivo when they are converted into their desulfated (unconjugated) form by the enzyme steroid sulfatase (STS). Inhibitors of STS are considered to be potential therapeutics for the treatment of steroid-dependent cancers such as breast, prostate and endometrial cancer. The present review summarizes steroid derivatives as inhibitors of STS covering the literature from the early years of STS inhibitor development to October of 2012. A brief discussion of the function, structure and mechanism of STS and its role in estrogen receptor-positive (ER+) hormone-dependent breast cancer is also presented. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Inhibition of dehydroepiandosterone sulfate action in androgen-sensitive tissues by EM-1913, an inhibitor of steroid sulfatase

Steroid sulfatase (STS) plays an important role in the formation of estrogens and androgens by allowing the conversion of inactive circulating sulfated steroids into active hormones. These steroids support the development and growth of a number of hormone-dependent cancers, including prostate cancer. Here, we tested a non-estrogenic and non-androgenic inhibitor of steroid STS, namely EM-1913, with special attention to its potential use in the treatment of prostate cancer. After determining the required dosage of dehydroepiandrosterone sulfate (DHEAS) needed to stimulate the ventral prostate and seminal vesicles in castrated rats, we measured that EM-1913 partially (26%) and almost entirely blocked (81%) the stimulating effect of DHEAS on ventral prostates and seminal vesicles, respectively. In addition, the homogenization of these two tissues allowed us to confirm that they were completely deprived of STS activity following a treatment with EM-1913. This effect is also reflected in blood, since the plasma level of DHEAS was increased in animals treated with EM-1913, whereas the levels of dehydroepiandrosterone (DHEA) and dihydrotestosterone (DHT), two DHEAS metabolites, meanwhile decreased. From these results, we concluded that STS inhibitor EM-1913 is a good candidate for additional preclinical studies.

Estradiol 17β and its metabolites stimulate cell proliferation and antagonize ascorbic acid-suppressed cell proliferation in human ovarian cancer cells

Estradiol 17β (E2β) and ascorbic acid (AA) have been implicated in cancer progression. However, little is known about the actions of biologically active metabolites of E2β, 2-hydroxyestradiol (2OHE2), 4-hydroxyestradiol (4OHE2), 2-methoxyestradiol (2ME2), and 4-methoxyestradiol (4ME2) synthesized sequentially by cytochrome P450, family 1, subfamily A (CYP1A1) and B (CYP1B1), polypeptide 1, and catechol-O-methyltransferase (COMT) on ovarian cancer. Herein, we examined the expression of CYP1A1, CYP1B1, COMT, and estrogen receptor α (ERα) and β (ERβ) in human ovarian surface epithelial (IOSE-385) and cancer cell lines (OVCAR-3, SKOV-3, and OVCA-432). We also investigated the roles of E2β, 2OHE2, 4OHE2, 2ME2, and 4ME2 in cell proliferation, and their interactive effects with AA on ovarian cells. We found the expression of CYP1A1, CYP1B1, COMT, ERα, and ERβ in most cell lines tested. Treating cells with physiological concentrations of E2β and its metabolites promoted (13%-42% of the control) IOSE-385 and OVCAR-3 proliferation. The ER blockade inhibited IOSE-385 (∼76%) and OVCAR-3 (∼87%) proliferative response to E2β but not to its metabolites. The ERα blockade inhibited (∼85%) E2β-stimulated OVCAR-3 proliferation, whereas ERβ blockade attenuated (∼83%) E2β-stimulated IOSE-385 proliferation. The AA at ≥250 μmol/L completely inhibited serum-stimulated cell proliferation in all cell lines tested; however, such inhibition in IOSE-385, OVCAR-3, and OVCA-432 was partially (∼10%-20%) countered by E2β and its metabolites. Thus, our findings indicate that E2β and its metabolites promote cell proliferation and antagonize the AA-suppressed cell proliferation in a subset of ovarian cancer cells, suggesting that blocking the actions of E2β and its metabolites may enhance AA's antiovarian cancer activity.

The pharmacogenomics of sex hormone metabolism: breast cancer risk in menopausal hormone therapy

With women in western countries spending nearly one-third of their lifetime beyond menopause and a substantial number of these women facing severe menopausal symptoms, the goal of sex hormone pharmacogenomics is to promote the safe use of hormone replacement therapy (HRT). This could be achieved by providing molecular predictors for the upfront stratification of women in need of relief from menopausal symptoms into those with a likely benefit from HRT and those with a contraindication due to an HRT-associated breast cancer risk or other adverse effects. An increasing knowledge base of sex hormone metabolism and its variability, HRT outcomes and breast cancer susceptibility, as well as emerging examples of pharmacogenomic predictors, underscore the potential relevance of genetic variations for HRT outcome. The genes responsible for the metabolism, signaling and action of sex hormones are at the heart of this research; however, pharmacogenomic investigation of their therapeutic effects due to the enormous complexity of the biological pathways involved is still in its infancy. This article discusses the current knowledge, challenges and potential future directions towards the goal of genotype-guided safer HRT use.

Dual roles of estrogen metabolism in mammary carcinogenesis

A female hormone, estrogen, is linked to breast cancer incidence. Estrogens undergo phase I and II metabolism by which they are biotransformed into genotoxic catechol estrogen metabolites and conjugate metabolites are produced for excretion or accumulation. The molecular mechanisms underlying estrogen-mediated mammary carcinogenesis remain unclear. Cell proliferation through activation of estrogen receptor (ER) by its agonist ligands and is clearly considered as one of carcinogenic mechanisms. Recent studies have proposed that reactive oxygen species generated from estrogen or estrogen metabolites are attributed to genotoxic effects and signal transduction through influencing redox sensitive transcription factors resulting in cell transformation, cell cycle, migration, and invasion of the breast cancer. Conjuguation metabolic pathway is thought to protect cells from genotoxic and cytotoxic effects by catechol estrogen metabolites. However, methoxylated catechol estrogens have been shown to induce ER-mediated signaling pathways, implying that conjugation is not a simply detoxification pathway. Dual action of catechol estrogen metabolites in mammary carcinogenesis as the ER-signaling molecules and chemical carcinogen will be discussed in this review.

Analysis of multiplex endogenous estrogen metabolites in human urine using ultra-fast liquid chromatography-tandem mass spectrometry: a case study for breast cancer

A rapid, sensitive, specific and accurate analytical method of ultra-fast liquid chromatography combined with tandem mass spectrometry (UFLC-MS/MS) was established for simultaneous quantitative analysis of 16 distinct endogenous estrogens and their metabolites (EMs) in postmenopausal female urine. The quantitative method utilized a hydrolysis/extraction/derivatization step and a UFLC system to achieve separation in 16 min. The lower limit of quantitation for each estrogen metabolite was 2 pg mL(-1) with the percent recovery of a known added amount of estrogen at 93.2-109.3%. The intra-batch accuracy and precision for all analytes were 87.5-107.7% and 0.6-11.7%, respectively, while inter-batch accuracy and precision were 87.0-105.8% and 1.2-10.2%, respectively. Using this developed and validated method, the comprehensive metabolic profiling of 16 EMs in urine samples of 86 postmenopausal female breast cancer patients and 36 healthy controls was investigated by systematic statistical analysis. As a result, the circulating levels of 6 EMs were found to be different by a comparison of patients and healthy controls. The parent estrogens, estrone (E1) and 17β-estradiol (E2), as well as 2-hydroxyestradiol (2-OHE2) and 4-hydroxyestradiol (4-OHE2) were produced in higher abundance, whereas 16α-hydroxyestrone (16α-OHE1) and 2-methoxyestradiol (2-MeOE2) were decreased in the breast cancer group. 2-OHE2 and 4-OHE2 in particular showed significant elevation in patients, which are consistent with the carcinogenic mechanism hypothesis that catechol estrogens can react with DNA via quinones, resulting in mutations to induce breast cancer. Thus, 2,4-hydroxylation may be the dominant metabolic pathway for parent estrogens rather than 16α-hydroxylation. The lower level of 2-MeOE2 in the breast cancer group was believed to correlate with its protective effect against tumor formation. This study could provide valuable information on the association of the EM metabolic pathway with carcinogenesis as well as identify potential biomarkers for estrogen-induced breast cancer risk.

Steroid sulfatase: a pivotal player in estrogen synthesis and metabolism

Steroid sulfatase plays a pivotal role in regulating the formation of biologically active steroids from inactive steroid sulfates. It is responsible for the hydrolysis of estrone sulfate and dehydroepiandrosterone sulfate to estrone and dehydroepiandrosterone, respectively, both of which can be subsequently reduced to steroids with estrogenic properties (i.e. estradiol and androstenediol) that can stimulate the growth of tumors in hormone-responsive tissues of the breast, endometrium and prostate. Hence, the action of steroid sulfatase is implicated in physiological processes and pathological conditions. It has been five years since our group last reviewed the important role of this enzyme in steroid synthesis and the progress made in the development of potent inhibitors of this important enzyme target. This timely review therefore concentrates on recent advances in steroid sulfatase research, and summarises the findings of clinical trials with Irosustat (BN83495), the only steroid sulfatase inhibitor that is being trialed in postmenopausal women with breast or endometrial cancer.

Uptake transporter organic anion transporting polypeptide 1B3 contributes to the growth of estrogen-dependent breast cancer

Estrone-3-sulfate is one of the most abundant estrogen precursors in postmenopausal women. We previously showed that estrone-3-sulfate transporters are present in human breast cancer-derived MCF-7 cells (J. Pharmacol. Exp. Ther. 311 (2004) 1032-1037) and that inhibition of estrone-3-sulfate uptake resulted in the suppression of cell growth (Pharm. Res. 22 (2005) 1634-1641); therefore, estrone-3-sulfate transporter should be a novel target for therapy of hormone-dependent breast cancers. The purpose of the present study is to identify the transporter(s) responsible for the uptake of estrone-3-sulfate in breast cancer cells. We obtained two subclones of MCF-7 cells with different estrone-3-sulfate uptake activities and searched for differentially expressed transporter genes by means of DNA microarray analysis. Among several candidate transporters identified, OATP1B3 was further evaluated, since the uptake characteristics of estrone-3-sulfate by MCF-7 cells seemed consistent with the transport properties of OATP1B3. The contribution of OATP1B3 to estrone-3-sulfate uptake by MCF-7 cells was examined by the relative activity factor (RAF) method, and was calculated to amount to 6%. This result suggests that OATP1B3 is one of the transporters contributing to the supply of the estrogen precursor estrone-3-sulfate to estrogen-dependent breast cancer cells.

Effect of testosterone on E1S-sulfatase activity in non-malignant and cancerous breast cells in vitro

INTRODUCTION

Testosterone (T) is a therapeutic option for women with hypoactive sexual desire disorder. T may have an impact on the mammary gland by altering local estrogen synthesis. The aim of the present study was to measure the effect of T on estrone-sulfate (E1S)-sulfatase (STS) expression, and activity using hormone-dependent BC cells with high and low aggressive potential (BT-474, MCF-7), and HBL-100 as a breast cell line of non-malignant origin.

METHODS

Cells were incubated in RPMI 1640 medium containing 5% steroid-depleted fetal calf serum for 3d, and subsequently incubated in absence or presence of T alone, and combined with anastrozole (A) at 10(-8)M, and 10(-6)M at 37 degrees C for either 24h or directly in cell extracts ("direct"). STS protein expression was measured by dot-blot (immunoblotting), and STS, HSD17B1 and HSD17B2 mRNA levels by quantitative RT-PCR. STS activity was evaluated by incubating homogenized breast cells with [(3)H]-E1S and separating the products E1, and E2 by thin layer chromatography.

RESULTS

Basal STS mRNA expression did not reveal group differences. However, STS mRNA was decreased by T+A in MCF-7 cells. 17HSDB1 expression was decreased by T+A in BT-474 cells, and 17HSDB2 expression was decreased by A and T+A treatment in MCF-7 cells. Basal and T treated STS protein expression was significantly higher in malignant compared to non-malignant breast cells. However, T did not induce significant intra-cell line differences. Similarly, basal and T treated STS activity was significantly higher in highly malignant compared to non-malignant breast cells. Regardless of cell lines, T slightly decreased STS activity after "direct" incubation, but led to an increase of local estrogen formation after 24h which was attenuated, and partly reversed by A, respectively.

CONCLUSIONS

The more aggressive the breast cell line, the higher the local estrogen formation. The transition from normal to malignant seems to be accompanied by an altered autoregulation. The given local endocrine milieu seems to be essential for response to T.

Effects of tibolone on estrogen biosynthesis in the mammary tissue of postmenopausal monkeys

OBJECTIVE

To evaluate the long-term effects of tibolone on estrone sulfate (E1S)-sulfatase activity in breast tissue in a primate model (Macaca fascicularis) in comparison with conventional hormone therapies.

DESIGN

Ovariectomized female animals (n = 112) were randomized into five groups and treated for 2 years. Treatment included tibolone at 0.05 mg/kg (LoTib, n = 23) or 0.2 mg/kg (HiTib, n = 23), conjugated equine estrogens at 0.042 mg/kg (CEE, n = 24), CEE + medroxyprogesterone acetate at 0.167 mg/kg (CEE+MPA, n = 21), or placebo (controls, n = 21). E1S-sulfatase activity was evaluated by incubating homogenized breast tissue with [H]-E1S. Thin-layer chromatography was performed to separate the products estrone (E1) and estradiol (E2). Histomorphometry was performed to measure the amount of epithelial and fat tissue in the mammary gland.

RESULTS

Significantly more E2 than E1 was produced in all groups. E1S-sulfatase activity did not differ among the groups. E1S-sulfatase activity was highest in HiTib animals with less fatty breasts (5.9 fmol total estrogen/mg of protein/min; P < or =0.05) and lowest in HiTib animals with more fatty breasts (2.8 fmol total estrogen/mg of protein/min; P = 0.004 relative to less fatty breasts).

CONCLUSIONS

We conclude that tibolone had a differential effect on local estrogen biosynthesis in animals with high and low breast fat content. Therefore, breast tissue composition affects the steroidogenic response to hormonal treatment.

Chromatographic analysis and decomposition product characterization of compound SR16157 (NSC 732011)

SR16157 (21-(2-N,N-diethylaminoethyl)oxy-7alpha-methyl-19-norpregna-1,3,5(10)-triene-3-O-sulfamate) is a novel, dual-acting estrone sulfatase inhibitor currently in preclinical development for use in breast cancer therapy. The compound has a dual mechanism of action: the sulfamate-containing parent compound SR16157 inhibits estrogen biosynthesis by irreversibly inhibiting the enzyme estrone sulfatase. The phenolic metabolite, SR16137, generated by the sulfatase enzyme is a potent antiestrogen in breast tissues and has beneficial effects in bone and the cardiovascular system. As part of the ongoing preclinical studies, an HPLC assay method has been developed and validated for SR16157. The assay method is specific, accurate (recovery=99.4-101.1), linear (r(2)> or =0.9999), precise (intraday R.S.D.< or =1.1%, intermediate R.S.D.< or =0.8%), and sensitive (limit of detection=1.0 microg/ml). It separates SR16157 from its impurities and forced decomposition products, which have been characterized by LC coupled with mass and UV spectral data. Major decomposition pathways are hydrolysis, hydroxylation, and oxidation.

Effects of black cohosh on estrogen biosynthesis in normal breast tissue in vitro

OBJECTIVES

To investigate the effect of black cohosh on the estrogen biosynthesis in the breast in vitro.

METHODS

Steroid sulfatase (STS) activity was studied in normal breast tissue obtained from pre- and postmenopausal women undergoing reduction mammoplasty. STS protein expression was studied by immunohistochemistry and western blotting. Breast tissue was incubated in vitro without or with black cohosh (iCR) at concentrations ranging from 0.1mg/ml to 1 ng/ml. STS activity was evaluated by incubating homogenized breast tissue with [3H]-estrone sulfate, separating the formed products, estrone (E1) and estradiol (E2), by thin layer chromatography and measuring the amounts of E1 and E2 by scintillation counting.

RESULTS

STS protein expression and enzymatic activity were detected in all specimens investigated. In all groups, significantly more E1 than E2 was produced. Local estrogen formation was decreased in premenopausal breast tissue by treatment with iCR at 0.1mg/ml (p<or=0.05).

CONCLUSIONS

iCR decreases local estrogen formation in normal human breast tissue in vitro. This may contribute to the lack of hormonal effects of black cohosh in breast tissue observed in previous studies.

Differential effect of hormone therapy on E1S-sulfatase activity in non-malignant and cancerous breast cells in vitro

Breast tissue possesses the enzymes for local estrogen biosynthesis. We measured the effect of Estradiol (E2), Tibolone (OrgOD14) and its metabolite Org4094 on estrone sulfate (E1S)-sulfatase (STS) using breast cancer (MCF-7) and non-malignant breast cells (HBL-100). Cells were cultured in 5% steroid depleted fetal calf serum for 3 days and subsequently incubated with each steroid for either 24 h or directly in cell extracts. STS mRNA and protein expression, and its subcellular localization were determined by semi-quantitative RT-PCR, immunoblotting, and confocal immunofluorescence microscopy. STS activity was evaluated by incubating homogenized breast cells with [(3)H]-E1S. The products E1 and E2 were separated by thin layer chromatography. STS was co-localized with the Golgi marker protein GM130 and the endoplasmic reticulum marker protein calnexin. Treatment did not significantly alter STS mRNA expression. STS protein expression was increased by each steroid in HBL-100 cells but by E2 only in MCF-7 cells. 24 h incubation with OrgOD14 and Org4094 did not alter STS activity in both cell lines. However, STS activity was significantly diminished in HBL-100 but slightly increased in MCF-7 cells by 24 h treatment with E2. "Direct" incubation of cell extracts, eliminating cellular regulation of metabolism, reduced estrogen biosynthesis regardless of cell line and treatment. In conclusion, the immediate reduction of estrogen biosynthesis by OrgOD14 is counteracted by an increased STS protein expression. On the contrary, E2 exerts a differential effect on STS in HBL-100 and MCF-7 cells. The transition from normal to malignant breast cells may be accompanied by an abolished autoregulation of local estrogen formation.

Conversion of circulating estrone sulfate to 17beta-estradiol by ovarian tumor tissue: a possible mechanism behind elevated circulating concentrations of 17beta-estradiol in postmenopausal women with ovarian tumors

AIM

Elevated serum levels of 17beta-estradiol (E2) are frequently found in postmenopausal women with ovarian tumors not classified as estrogen-producing. Conversion of circulating estrone sulfate (E1S) to E2 is one alternative way of E2 formation in target tissues in postmenopausal women. Our aim was to find out if conversion of circulating E1S to E2 by the tumor tissue could be a reason for elevated serum E2 levels in postmenopausal women with 'non-estrogen-producing' ovarian tumors.

METHOD

Serum E2 was measured in 12 postmenopausal women with 'non-estrogen-producing' ovarian tumors (nine benign, three malignant). Total hydrolysis of and [3H]E2 formation from [3H]E1S by the tumor tissue homogenates was studied in vitro.

RESULTS

Serum E2 showed significant positive correlations with total hydrolysis of and [3H]E2 formation from [3H]E1S in the total material as well as in the benign tumor subgroup. [3H]E2 formation was the most important independent variable.

CONCLUSION

Conversion of circulating E1S to E2 by the tumor tissue could be one important reason for elevated S-E2 levels in postmenopausal women with 'non-estrogen-producing' ovarian tumors.

Organic Anion Transporting Polypeptide 2B1 and Breast Cancer Resistance Protein Interact in the Transepithelial Transport of Steroid Sulfates in Human Placenta

The human placenta has both protective and nurturing functions for the fetal organism. Uptake and elimination of xenobiotics and endogenous substances are facilitated by various transport proteins from the solute carrier (SLC) and ABC families, respectively. A functional interaction of uptake and elimination, which is a prerequisite for vectorial transport across cellular barriers, has not been described for placenta. In this study, we examined expression of organic anion transporter (OAT) 4 (SLC22A11), organic anion transporting polypeptide (OATP) 2B1 (SLCO2B1, OATP-B), and breast cancer resistance protein (BCRP) (ABCG2) in human placenta (n = 71) because all three proteins are involved in transmembranal transfer of estrone 3 sulfate (E3S; metabolic product) and dehydroepiandrosterone sulfate (DHEAS; precursor molecule). On the mRNA level, we found a significant correlation of OATP2B1 and BCRP (R(2) = 0.534; p < 0.01) but not between OAT4 and BCRP (R(2) = -0.104; p > 0.05). Localization studies confirmed basal expression of OATP2B1 and apical expression of BCRP. To study functional interactions between OATP2B1 and BCRP, we developed a Madin-Darby canine kidney cell model expressing both transport proteins simultaneously (OATP2B1 and BCRP in the basal and apical membrane, respectively). Using this cell model in a transwell system resulted in a significantly increased basal to apical transport of both E3S and DHEAS, when both transporters were expressed with no change of transfer in the apical to basal direction. Taken together, these data show the potential for a functional interaction of OATP2B1 and BCRP in transepithelial transport of steroid sulfates in human placenta.

A Role for Sulfation-Desulfation in the Uptake of Bisphenol A into Breast Tumor Cells

Bisphenol A (BPA) is a widely used plasticizer whose estrogenic properties may impact hormone-responsive disorders and fetal development. In vivo, BPA appears to have greater activity than is suggested by its estrogen receptor (ER) binding affinity. This may be a result of BPA sulfation/desulfation providing a pathway for selective uptake into hormone-responsive cells. BPA is a substrate for estrogen sulfotransferase, and bisphenol A sulfate (BPAS) and disulfate are substrates for estrone sulfatase. Although the sulfated xenobiotics bind poorly to the ER, both stimulated the growth of receptor-positive breast tumor cells. Treatment of MCF-7 cells with BPAS leads to desulfation and uptake of BPA. No BPAS is found inside the cells. These findings suggest a mechanism for the selective uptake of BPA into cells expressing estrone sulfatase. Therefore, sulfation may increase the estrogenic potential of xenobiotics.

Steroids and receptors in canine mammary cancer

The aims of this study were to investigate the serum and tissue content of androgens and estrogens in canine inflammatory mammary carcinomas (IMC) as well as in non-inflammatory malignant mammary tumors (MMT), and assessed the immunoexpression of estrogen and androgen receptors using immunohistochemistry. Profiles for the androgens dehydroepiandrosterone (DHEA), androstenedione (A4), and testosterone (T), and for the estrogens 17beta estradiol (E2) and estrone-sulphate (SO4E1) were measured both in tissue homogenates and in serum of MMT and IMC by EIA techniques in 42 non-inflammatory malignant mammary tumors (MMT) and in 14 inflammatory mammary carcinomas (IMC), prospectively collected from 56 female dogs. Androgen receptor (AR) and estrogen receptor alpha (ERalpha) and beta (ERbeta) expression was studied using immunohistochemistry (strepavidin-biotin-peroxidase method) in samples of 32 MMT and 14 IMC, and counted by a computer image analyzer. IMC serum and tissue levels of androgens were significantly higher than MMT levels. Tissue content of estrogens was also significantly higher in IMC than in MMT. Serum values of SO4E1 were significantly higher in IMC, but serum levels of E2 were significantly lower in IMC compared to MMT cases. Medium-high androgen receptor intensity was observed in 64.28% of IMC and 40.62% of MMT. No important differences were found between ERalpha expression in IMC (100% negative) and MMT (90% negative). ERbeta and AR were intensely expressed in highly malignant inflammatory mammary carcinoma cells. To our knowledge, this is the first report relative to AR immunohistochemistry in canine mammary cancer and to estrogens or androgens in serum of dogs with benign or malignant mammary tumors.

Hormonal environment in the induction of breast cancer in castrated rats using dimethylbenzanthracene: influence of the presence or absence of ovarian activity and of treatment with estradiol, tibolone, and raloxifene

OBJECTIVE

The influence of hormone therapy on the induction or the promotion of breast cancer has yet to be determined. Recent studies establish a cause-effect relation between hormones and cancer, although epidemiological data and studies of tumor behavior give rise to doubts. The aim of the study was to observe and evaluate the influence of different hormonal environments on the induction of breast cancer in a well-established experimental model.

DESIGN

In this experimental animal study, breast cancer was induced by using a single intragastric dose of 20 mg of dimethylbenzanthracene in prepubertal Sprague-Dawley rats randomized into five groups: group 1 (control); group 2 (castrated prepubertal animals); and groups 3, 4, and 5 (castration of prepubertal animals followed by hormonal treatment starting at puberty [11 weeks] with tibolone, raloxifene, and estradiol, respectively). Follicle-stimulating hormone and estradiol levels were measured at 6, 11, 16, and 31 weeks.

RESULTS

Absence of ovarian activity was observed in groups 2, 3, 4, and 5, as well as the expected variations in hormone levels in all groups. Breast cancers were obtained in 100% of the animals in the control group, with an average of four (two to seven) tumors per animal in this group. Only one cancer appeared in groups 2, 3, and 4, and none appeared in group 5.

CONCLUSIONS

In this experimental model and using the hormone treatments chosen, neither the treatments nor the absence of ovarian activity induced breast cancer.

Ageing, hormonal behaviour and cyclin D1 in ductal breast carcinomas

Owing to the gradual modification of breast tissue in postmenopausal women, there can be differential effects on local oestrogen receptor (ER) expression, with potential impingement on the biological behaviour of cancer cells in the ageing. A series of 45 ductal carcinoma (DC) cases were selected in postmenopausal women who were not being treated with HRT. Immunohistochemical analyses were performed for hormone receptors and Ki67 expression. Fluorescence in situ hybridisation (FISH) analysis was carried out to study CCND1 amplification. The selected population was subdivided into three groups by age and was subjected to statistical studies: linear model analysis, estimation of relative incidence (RI), multivariate analysis, and nonparametric tests were performed to investigate whether there were any links between age and molecular variables in DCs. The results show a low rate of proliferation and high ER expression in the oldest age group. In the same group a close correlation was found between high ER expression and CCN in the older age group D1 amplification (P=0.000), as was a more advanced phenotype in terms of tumour size and presence of positive lymph nodes than in the other age groups considered. The results suggest that ductal breast cancer has a favourable molecular prognosis, especially in extreme old age. In particular, there is an inverse correlation between ageing and proliferation rate despite the presence of an accentuated proliferation stimulus (high ER with CCD1 amplifications) in the oldest group relative to the other groups considered.

Effect of nomegestrol acetate on estrogen biosynthesis and transformation in MCF-7 and T47-D breast cancer cells

Although ovaries serve as the primary source of estrogen for pre-menopausal women, after menopause estrogen biosynthesis from circulating precursors occurs in peripheral tissues by the action of several enzymes, 17beta-hydroxysteroid dehydrogenase 1 (17beta-HSD1), aromatase and estrogen sulfatase. In the breast, both normal and tumoral tissues have been shown to be capable of synthesizing estrogens, and this local estrogen production can be implicated in the development of breast tumors. In these tissues, estradiol (E(2)) can be synthesized by three pathways: (1) estrone sulfatase transforms estrogen sulfates into bioactive estrogens, (2) 17beta-HSD1 converts estrone (E(1)) into E(2), (3) aromatase which converts androgens into estrogens is also present and contributes to the in situ synthesis of active estrogens but to a far lesser extent than estrone sulfatase. Quantitative assessment of E(2) formation in human breast tumors indicates that metabolism of estrone sulfate (E(1)S) via the sulfatase pathway produces 100-500 times more E(2) than androgen aromatization. Breast tissue also possesses the estrogen sulfotransferase involved in the conversion of estrogens into their sulfates that are biologically inactive. In the present review, we summarized the action of the 19-nor-progestin nomegestrol acetate (NOMAC) on the sulfatase, 17beta-HSD1 and sulfotransferase activities in the hormone-dependent MCF-7 and T47-D human breast cancer cell lines. Using physiological doses of substrates NOMAC blocks very significantly the conversion of E(1)S to E(2). It inhibits the transformation of E(1) to E(2). NOMAC has a stimulatory effect on sulfotransferase activity in both cell lines, with a strong stimulating effect at low doses but only a weak effect at high concentrations. The effects on the three enzymes are always stronger in the progesterone-receptor rich T47-D cell line as compared with the MCF-7 cell line. Besides, no effect is found for NOMAC on the transformation of androstenedione to E(1) in the aromatase-rich choriocarcinoma cell line JEG-3. In conclusion, the inhibitory effect provoked by NOMAC on the enzymes involved in the biosynthesis of E(2) (sulfatase and 17HSD pathways) in estrogen-dependent breast cancer, as well as the stimulatory effect on the formation of the inactive E(1)S, can open attractive perspectives for future clinical trials.

Involvement of Estrone-3-Sulfate Transporters in Proliferation of Hormone-Dependent Breast Cancer Cells

Although circulating estrone-3-sulfate is a major precursor of biologically active estrogen, permeation across the plasma membrane is unlikely to occur by diffusion because of the high hydrophilicity of the molecule. The object of this study was to clarify the involvement of specific transporter(s) in the supply of estrone-3-sulfate to human breast cancer-derived T-47D cells, which grow in an estrogen-dependent manner. The proliferation of T-47D cells was increased by the addition of estrone-3-sulfate, or estradiol, to the cultivation medium. The initial uptake rate of estrone-3-sulfate kinetically exhibited a single saturable component, with Km and Vmax values of 7.6 microM and 172 pmol/mg of protein/min, respectively. The replacement of extracellular Na+ with Li+, K+, or N-methylglucamine+ had no effect on the uptake of [3H]estrone-3-sulfate. The uptake was strongly inhibited by sulfate conjugates of steroid hormones, but not by estradiol-17beta-glucuronide. Taurocholate and sulfobromophthalein inhibited the uptake, whereas other tested anionic and cationic compounds did not. The expression of organic anion transporting polypeptides, OATP-D and OATP-E, which are candidate transporters of estrone-3-sulfate, was detected by reverse transcription-polymerase chain reaction analysis, although their actual involvement in the uptake of estrogen remains to be clarified. In conclusion, the uptake of estrone-3-sulfate by T-47D cells was mediated by a carrier-mediated transport mechanism, suggesting that the estrogen precursor is actively imported by estrogen-dependent breast cancer cells.

Gonadotropin-releasing hormone agonist inhibits estrone sulfatase expression of cystic endometriosis in the ovary

OBJECTIVE

To clarify the inhibitory effect of GnRH agonist on estrone (E(1)) sulfatase expression.

DESIGN

Retrospective immunohistochemical study.

SETTING

The Jikei University Hospital, Tokyo, Japan.

PATIENT(S)

Thirty-three women who had undergone cystectomy of the ovary or oophorectomy and were proved histopathologically to have cystic endometriosis in the ovary.

INTERVENTION(S)

Fifteen of the 33 patients were treated with GnRH agonists monthly for 2-6 months before surgery. The other 18 patients did not receive any hormonal therapy. Tissue sections were immunostained with an anti-E(1) sulfatase monoclonal antibody (KM1049) originating from human placenta.

MAIN OUTCOME MEASURE(S)

Microscopic evaluation to assess the presence and localization of E(1) sulfatase and to describe any variations in its expression with or without treatment with GnRH agonist.

RESULT(S)

Immunostaining showed that E(1) sulfatase was localized only on the glandular epithelial cells of cystic endometriosis in the ovary. The immunostaining with anti-E(1) sulfatase proved that GnRH agonist inhibited E(1) sulfatase expression in the cystic endometriosis in the ovary.

CONCLUSION(S)

Gonadotropin-releasing hormone agonist inhibits E(1) sulfatase expression in cystic endometriosis in the ovary.

Differential effects of progestins on breast tissue enzymes

There is substantial evidence that mammary cancer tissue contains all the enzymes responsible for the local biosynthesis of estradiol (E2) from circulating precursors. Two principal pathways are implicated in the final steps of E2 formation in breast cancer tissue: the 'aromatase pathway' that transforms androgens into estrogens and the 'sulfatase pathway' that converts estrone sulfate (E1S) into estrone (E1) via estrone sulfatase. The final step is the conversion of weak E1 to potent biologically active E2 via reductive 17beta-hydroxysteroid dehydrogenase type 1 activity. It is also well established that steroid sulfotransferases, which convert estrogens into their sulfates, are present in breast cancer tissues. One of the possible means of blocking E2 effects in breast cancer is to use anti-estrogens, which act by binding to the estrogen receptor (ER). Another option is to block E2 using anti-enzymes (anti-sulfatase, anti-aromatase, or anti-17beta-hydroxysteroid dehydrogenase (17beta-HSD). Various progestins (e.g. promegestone, nomegestrol acetate, medrogestone, 17-deacetyl norgestimate, dydrogesterone and its 20-dihydro derivative), as well as tibolone and its metabolites, have been shown to inhibit estrone sulfatase and 17beta-hydroxysteroid dehydrogenase. Some progestins and tibolone can also stimulate sulfotransferase activity. These various progestins may therefore provide a new option for the treatment of breast cancer.

Breast cancer tissue estrogens and their manipulation with aromatase inhibitors and inactivators

Despite the dramatic fall in plasma estrogen levels at menopause, only minor differences in breast tissue estrogen levels have been reported comparing pre- and postmenopausal women. Thus, postmenopausal breast tissue has the ability to maintain concentrations of estrone (E1) and estradiol (E2) that are 2-10- and 10-20-fold higher than the corresponding plasma estrogen levels. This finding may be explained by uptake of estrogens from the circulation and/or local estrogen production. Local aromatase activity in breast tissue seems to be of crucial importance for the local estrogen production in some patients while uptake from the circulation may be more important in other patients. Beside aromatase, breast tissue expresses estrogen sulfotransferase and sulfatase as well as dehydrogenase activity, allowing estrogen storage and release in the cells as well as conversions between estrone and estradiol. The activity of the enzyme network in breast cancer tissue is modified by a variety of factors like growth factors and cytokines. Aromatase inhibitors have been used for more than two decades in the treatment of postmenopausal metastatic breast cancer and are currently investigated in the adjuvant treatment and even prevention of breast cancer. Novel aromatase inhibitors and inactivators have been shown to suppress plasma estrogen levels effectively in postmenopausal breast cancer patients. However, knowledge about the influence of these drugs on estrogen levels in breast cancer tissue is limited. Using a novel HPLC-RIA method developed for the determination of breast tissue estrogen concentrations, we measured tissue E1, E2 and estrone sulfate (E1S) levels in postmenopausal breast cancer patients before and during treatment with anastrozole. Our findings revealed high breast tumor tissue estrogen concentrations that were effectively decreased by anastrozole. While E1S was the dominating estrogen fraction in the plasma, estradiol was the estrogen fraction with the highest concentration in tumor tissue. Moreover, plasma estrogen levels did not correlate with tissue estrogen concentrations. The overall experience with aromatase inhibitors and inactivators concerning their influences on breast tissue estrogen concentrations is summarized.

Mortality from site-specific malignancies in type 2 diabetic patients from Verona

OBJECTIVE

The aim of the present work was to compare mortality from site-specific malignancies in type 2 diabetic patients with those in the general population.

RESEARCH DESIGN AND METHODS

Mortality from site-specific cancers was assessed in a population-based cohort of 7,148 type 2 diabetic patients from Verona (Northern Italy) during a 10-year follow-up (1987-1996) by reviewing death certificates. Standardized mortality ratio (SMR) data were computed using as reference mortality rates in the general population of Verona.

RESULTS

During follow-up, 641 patients (378 men and 263 women) died of malignancies. The most common causes of death among site-specific malignancies were digestive tumors both in men (140 of 378, 37.0%) and women (105 of 263, 39.9%), respiratory tumors in men (103 of 378, 27.2%), and tumors of the reproductive system in women (79 of 263, 30.0%). A slight increase in the overall mortality from malignancies was observed in diabetic patients and achieved statistical significance in women (observed/expected = 1.16, 95% CI 1.02-1.30; P = 0.019) but not in men (observed/expected = 1.07, 0.97-1.19; P = 0.163). Excess mortality from hepatic cancer (SMR = 1.86, 1.44-2.38) was observed in both men and women. In addition, women with diabetes experienced a higher mortality from pancreatic tumors (observed/expected = 1.78, 1.13-2.67) and breast tumors (observed/expected = 1.40, 1.06-1.81). Excess mortality from breast cancer was confined to obese women with diabetes.

CONCLUSIONS

Mortality from site-specific malignancies is different in type 2 diabetic patients than in the general population. Better control of body weight seems necessary to prevent the excess mortality from breast cancer in women.

Steroid hormone profile of canine inflammatory mammary carcinoma: a preliminary study

Inflammatory mammary carcinoma (IMC) is the most aggressive spontaneous type of mammary malignant tumor both in women and dogs. Latest studies in dogs indicate that different endocrine mechanisms seem to be involved in inflammatory carcinomas (IMCs). The aim of the present study was to characterize the steroid hormone profile of inflammatory carcinoma, and to compare it with mammary dysplasias, benign tumors and other malignant tumors. Eighty-six mammary samples (10 normal mammary tissue, 21 dysplasias, 26 benign, 22 malignant, and 7 IMC) from 30 female dogs were used. Hormone levels of progesterone (P4), 17beta-estradiol (E2), androstenedione (A4), dehydroepiandrosterone (DHEA), and estrone sulphate (E1SO4) in tissue homogenates were measured by enzyme immunoassays (EIAs) techniques, previously validated for this species. IMC displayed the following steroid profile: P4: 13.80+/-0.56 microg/g; E2: 675.19+/-33.00 ng/g; A4: 631.73+/-70.73 microg/g; DHEA: 702.22+/-89.93 microg/g, and E1SO4: 2.84+/-0.32 mg/g. All of these hormones were significantly higher (P<0.001) compared with the hormone steroid profile determined for malignant, benign, dysplasias, and normal mammary tissue. The most relevant finding was the increased levels, two or three times, of both DHEA and E1SO4 in IMC respect to other groups (P<0.001). These results, together with the highest immunohistochemical expression of P450scc found in IMC, suggest the hypothesis that an autocrine mechanism could be especially involved in the development of canine inflammatory carcinoma.

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.

Distribution of 16alpha-[18F]fluoro-estradiol-3,17beta-disulfamate in rats, tumour-bearing mice and piglets

Based on a high affinity to the enzyme estrone sulfatase (ES), 16alpha-[18F]fluoroestradiol-3,17beta-disulfamate ([18F]FESDS) has been suggested as a potential PET radiotracer for imaging steroid-dependent breast tumours. The distribution of [18F]FESDS was studied in rats, tumour-bearing nude mice and piglets. In all species evidence for binding to a second target, the enzyme carbonic anhydrase (CA), was obtained. ES and CA inhibitors significantly reduced the radiotracer uptake in various organs but not in tumours. It is concluded that [18F]FESDS binds to ES and CA in vivo but this binding is not strong enough to allow tumour imaging with positron emission tomography (PET).

Hormone receptors and proliferation in breast carcinomas of equivalent histologic grades in pre- and postmenopausal women

Breast cancers in younger, premenopausal women are more likely to exhibit an adverse prognostic profile (including negative steroid hormone receptors and a high rate of cellular proliferation) and poor outcome than breast cancers in postmenopausal women. It has been hypothesized that this adverse prognostic profile is a result of the higher histologic grade of breast cancers in pre- compared with post-menopausal women. To assess the association of expression of steroid hormone receptors and indicators of proliferation while controlling for histologic grade, we identified 100 infiltrating ductal carcinomas from premenopausal women 45 years of age or younger and 100 from postmenopausal women 65 years of age or older. The carcinomas were selected so that the histologic grades (low versus high) were distributed equally between the 2 groups. Estrogen receptors (ER), progesterone receptors (PR), p27(Kip1) and Ki-67 (to measure rate of proliferation) were assessed by immunohistochemistry and compared between groups. Clinical information and survival data were also analyzed. ER content was lower and proliferation was higher in carcinomas in premenopausal women (p = 0.048 and p = 0.005, respectively). By univariate analysis, p27(Kip1) and PR were not different between the groups; however, in multivariate analysis, p27(Kip1) was higher in postmenopausal women, but only in a subgroup with highly proliferative carcinomas. Overall survival was similar in the pre- and postmenopausal women. Furthermore, low p27(Kip1) and African-American ethnicity predicted a poorer overall survival in the premenopausal, but not in the postmenopausal, women in our study. After controlling for histologic grade, a lower expression of ER and a higher proliferative index were detected in breast carcinomas in premenopausal women. Therefore, some prognostic indicators, such as ER and proliferative rate, may be more closely associated with menopausal status than histologic grade. Our data also suggest that some prognostic factors are not equally effective as predictors of survival in pre- and postmenopausal women.

Nonsteroidal compounds designed to mimic potent steroid sulfatase inhibitors

Chemical synthesis and enzyme inhibition results are reported for a series of nonsteroidal sulfatase inhibitors, 1-(p-sulfamoyloxyphenyl)-5-(p-t-butylbenzyl)-5-alkanols and the lower active phenolic analogues. These compounds conserve some structural elements from the previously reported potent steroidal inhibitor 3-O-sulfamate-17alpha-(p-t-butylbenzyl)-17beta-hydroxy-estra-1,3,5(10)-triene, while the C18-methyl group and the hydrocarbon backbone represented by the steroid rings B, C, and D were replaced with a free conformational chain. Using estrone sulfate (100 microM) as substrate and homogenate of transfected HEK-293 cells as source of steroid sulfatase activity, the IC(50) values of the best inhibitors, the undecanol derivatives, were 0.4+/-0.1 and >300 nM, respectively, in the sulfamate and phenolic series. Although these sulfamoylated nonsteroidal inhibitors appear a bit less active than their steroidal analogues, they are however more potent than known inhibitors estrone-3-O-sulfamate and p-(O-sulfamoyl)-N-tetradecanoyl tyramine. The optimal side-chain length for the inhibition of steroid sulfatase activity was found to be six carbons, which corresponds to the number of carbons that mimic the B, C and D steroid rings, between C6 and C17. Furthermore, compounds with only the t-butylbenzyl group or the alkyl chain of six carbons are less potent inhibitors compared to the one that include both of these hydrophobic substituents. Such results suggest that compound from this later category better mimic the steroidal inhibitor.

Natural modulators of estrogen biosynthesis and function as chemopreventive agents

There is clearly a need for novel breast cancer chemopreventive agents with enhanced potency and specificity with little or no side effects. To this end, several new chemical moieties have been synthesized or isolated from natural sources. In this review, we have described some agents currently in use or under development for treatment or prevention of breast cancer, as well as our own strategies for the discovery of natural product modulators of estrogen biosynthesis and function. In particular, bioassay-guided fractionation of active plant extracts is a unique method for identifying agents with novel mechanisms of action, some of which should be useful for prevention of human cancer. Further, with the advent of combinatorial chemistry and high throughput screening, even greater progress may now be expected with natural product leads.

Tibolone: a compound with tissue specific inhibitory effects on sulfatase

The aim was to test whether sulfatase activity is differently regulated by tibolone in human bone, endometrium and breast cells since selective inhibition of sulfatases in various tissues may contribute to the tissue-specificity of tibolone. Tibolone, its 3 alpha- and 3 beta-hydroxy metabolites and their 3-sulfated forms, and its Delta(4)-isomer strongly (70-90%) inhibited the sulfatase activity in human breast cell lines (two T-47D clones) and intermediately (8-43%) in human endometrial cells (HEC-1A). In contrast, they did not inhibit sulfatase in two human osteoblast-like cell lines (MG 63, HOS TE-85). The specific sulfatase inhibitor, EMATE, showed inhibition in all cell lines. Just as estrone sulfate, 3 alpha-sulfated tibolone was also converted by sulfatase to the unconjugated 3 alpha-hydroxy-tibolone intracellularly in all cell lines. The tissue specific inhibition pattern of sulfatase activity by tibolone and its metabolites suggest that tibolone could be protective against development of mammary carcinomas, whereas it retains favorable estrogenic effects on bone.

Aromatase inhibitors for breast cancer: pharmacoeconomic considerations

Although the anti-oestrogen tamoxifen is recognised as the treatment of choice for both premenopausal and postmenopausal women with advanced hormone-dependent breast cancer, oestrogen deprivation can also be achieved, with apparently less adverse-effects, through selective inhibition of aromatase. Recent clinical trials have demonstrated the efficacy and tolerability of the new generation of aromatase inhibitors as second-line and first-line therapy in postmenopausal women with breast cancers who were eligible for endocrine treatment. Speculating that administration of aromatase inhibitors will not be limited to postmenopausal breast cancer, a pharmacoeconomic perspective is considered based on available data and putative therapeutic application during various phases of the disease.

Steroid sulfatase activity in the rat ovary, cultured granulosa cells, and a granulosa cell line

Direct production of gonadal steroids from sulfated adrenal androgens may be an important alternative or complementary pathway for ovarian steroidogenesis. The conversion of sulfated adrenal androgens, present in serum at micromolar concentrations in adult women, into unconjugated androgens or estrogens requires steroid sulfatase (STS) activity. STS activity has not been characterized in the rat ovary. Substantial STS activity was present in homogenates of rat ovaries, primary cultures of rat granulosa cells, and a granulosa cell line, as determined by conversion of radiolabeled estrone sulfate (E1S) to unconjugated estrone. The potent inhibitor estrone sulfamate eliminated the STS activity. Using E1S as a substrate with microsomes prepared from a granulosa cell line, the K(m) of STS activity was approximately 72 microM, a value in agreement with previously published data for rat STS. Therefore, ovarian cells possess STS and can remove the sulfate from adrenal androgens such as dehydroepiandrosterone sulfate (DHEA-S). Using DHEA-S as a steroidogenic substrate represents an alternative model for the production of ovarian steroids versus the "two cell, two gonadotropin" model of ovarian estrogen synthesis, whereby thecal cells produce androgens from substrate cholesterol and granulosa cells convert the androgens into estrogens. The relative contribution of STS activity to ovarian steroidogenesis remains unclear but may have important physiological and pathophysiological implications.

Estrogens and women's health: interrelation of coronary heart disease, breast cancer and osteoporosis

The determinants of blood levels of estrogen, estrogen metabolites, and relation to receptors and post-transitional effects are the likely primary cause of breast cancer. Very high risk women for breast cancer can now be identified by measuring bone mineral density and hormone levels. These high risk women have rates of breast cancer similar to risk of myocardial infarction. They are candidates for SERM therapies to reduce risk of breast cancer. The completion of the Women's Health Initiative and other such trials will likely provide a definite association of risk and benefit of both estrogen alone and estrogen-progesterone therapy, coronary heart disease, osteoporotic fracture, and breast cancer. The potential intervention of hormone replacement therapy, obesity, or weight gain and increased atherogenic lipoproteinemia may be of concern and confound the results of clinical trials. Estrogens, clearly, are important in the risk of bone loss and osteoporotic fracture. Obesity is the primary determinant of postmenopausal estrogen levels and reduced risk of fracture. Weight reduction may increase rates of bone loss and fracture. Clinical trials that evaluate weight loss should monitor effects on bone. The beneficial addition of increased physical activity, higher dose of calcium or vitamin D, or use of bone reabsorption drugs in coordination with weight loss should be evaluated. Any therapy that raises blood estrogen or metabolite activity and decreases bone loss may increase risk of breast cancer. Future clinical trials must evaluate multiple endpoints such as CHD, osteoporosis, and breast cancer within the study. The use of surrogate markers such as bone mineral density, coronary calcium, carotid intimal medial thickness and plaque, endothelial function, breast density, hormone levels and metabolites could enhance the evaluation of risk factors, genetic-environmental intervention, and new therapies.

Structure-activity relationships of 17alpha-derivatives of estradiol as inhibitors of steroid sulfatase

The steroid sulfatase or steryl sulfatase is a microsomal enzyme widely distributed in human tissues that catalyzes the hydrolysis of sulfated 3-hydroxy steroids to the corresponding free active 3-hydroxy steroids. Since androgens and estrogens may be synthesized inside the cancerous cells starting from dehydroepiandrosterone sulfate (DHEAS) and estrone sulfate (E(1)S) available in blood circulation, the use of therapeutic agents that inhibit steroid sulfatase activity may be a rewarding approach to the treatment of androgeno-sensitive and estrogeno-sensitive diseases. In the present study, we report the chemical synthesis and biological evaluation of a new family of steroid sulfatase inhibitors. The inhibitors were designed by adding an alkyl, a phenyl, a benzyl, or a benzyl substituted at position 17alpha of estradiol (E(2)), a C18-steroid, and enzymatic assays were performed using the steroid sulfatase of homogenized JEG-3 cells or transfected in HEK-293 cells. We observed that a hydrophobic substituent induces powerful inhibition of steroid sulfatase while a hydrophilic one was weak. Although a hydrophobic group at the 17alpha-position increased the inhibitory activity, the steric factors contribute to the opposite effect. As exemplified by 17alpha-decyl-E(2) and 17alpha-dodecyl-E(2), a long flexible side chain prevents adequate fitting into the enzyme catalytic site, thus decreasing capacity to inhibit the steroid sulfatase activity. In the alkyl series, the best compromise between hydrophobicity and steric hindrance was obtained with the octyl group (IC(50) = 440 nM), but judicious branching of side chain could improve this further. Benzyl substituted derivatives of estradiol were better inhibitors than alkyl analogues. Among the series of 17alpha-(benzyl substituted)-E(2) derivatives studied, the 3'-bromobenzyl, 4'-tert-butylbenzyl, 4'-butylbenzyl, and 4'-benzyloxybenzyl groups provided the most potent inhibition of steroid sulfatase transformation of E(1)S into E(1) (IC(50) = 24, 28, 25, and 22 nM, respectively). As an example, the tert-butylbenzyl group increases the ability of the E(2) nucleus to inhibit the steroid sulfatase by 3000-fold, and it also inhibits similarly the steroid sulfatase transformations of both natural substrates, E(1)S and DHEAS. Interestingly, the newly reported family of steroid sulfatase inhibitors acts by a reversible mechanism of action that is different from the irreversible mechanism of the known inhibitor estrone sulfamate (EMATE).