Characterization of estrogen-dependent growth of cultured MCF-7 human breast-cancer cells expressing 17beta-hydroxysteroid dehydrogenase type 1

Intracrinology-revisited and prostate cancer

The formation of steroid hormones in peripheral target tissues is referred to as their intracrine formation. This process occurs in hormone dependent malignancies such as prostate and breast cancer in which the disease can be either castrate resistant or occur post-menopausally, respectively. In these instances, the major precursor steroid of androgens and estrogens is dehydroepiandrosterone (DHEA) and DHEA-SO4. This article reviews the major pathways by which adrenal steroids are converted to the potent male sex hormones, testosterone (T) and 5α-dihydrotestosterone (5α-DHT) and the discrete enzyme isoforms involved in castration resistant prostate cancer. Previous studies have mainly utilized radiotracers to investigate these pathways but have not used prevailing concentrations of precursors found in castrate male human serum. In addition, the full power of stable-isotope dilution liquid chromatography tandem mass spectrometry has not been applied routinely. Furthermore, it is clear that adaptive responses occur in the transporters and enzyme isoforms involved in response to androgen deprivation therapy that need to be considered.

Estrogen Activation by Steroid Sulfatase Increases Colorectal Cancer Proliferation via GPER

CONTEXT

Estrogens affect the incidence and progression of colorectal cancer (CRC), although the precise molecular mechanisms remain ill-defined.

OBJECTIVE

The present study investigated prereceptor estrogen metabolism through steroid sulphatase (STS) and 17β-hydroxysteroid dehydrogenase activity and subsequent nongenomic estrogen signaling in human CRC tissue, in The Cancer Genome Atlas colon adenocarcinoma data set, and in in vitro and in vivo CRC models. We aimed to define and therapeutically target pathways through which estrogens alter CRC proliferation and progression.

DESIGN, SETTING, PATIENTS, AND INTERVENTIONS

Human CRC samples with normal tissue-matched controls were collected from postmenopausal female and age-matched male patients. Estrogen metabolism enzymes and nongenomic downstream signaling pathways were determined. CRC cell lines were transfected with STS and cultured for in vitro and in vivo analysis. Estrogen metabolism was determined using an ultra-performance liquid chromatography-tandem mass spectrometry method.

PRIMARY OUTCOME MEASURE

The proliferative effects of estrogen metabolism were evaluated using 5-bromo-2'-deoxyuridine assays and CRC mouse xenograft studies.

RESULTS

Human CRC exhibits dysregulated estrogen metabolism, favoring estradiol synthesis. The activity of STS, the fundamental enzyme that activates conjugated estrogens, is significantly (P < 0.001) elevated in human CRC compared with matched controls. STS overexpression accelerates CRC proliferation in in vitro and in vivo models, with STS inhibition an effective treatment. We defined a G-protein-coupled estrogen receptor (GPER) proproliferative pathway potentially through increased expression of connective tissue growth factor in CRC.

CONCLUSION

Human CRC favors estradiol synthesis to augment proliferation via GPER stimulation. Further research is required regarding whether estrogen replacement therapy should be used with caution in patients at high risk of developing CRC.

Enzyme Inhibitor Screening Using a Homogeneous Proximity-Based Immunoassay for Estradiol

The authors have previously reported a homogeneous time-resolved fluorescence proximity immunoassay for estradiol. The assay was based on luminescence resonance energy transfer between a long lifetime fluorescent europium(III) chelate-dyed nanoparticle donor and a short lifetime, near-infrared fluorescent acceptor. The energy transfer prolonged the lifetime of the sensitized acceptor emission, and the fluorescence of the acceptor was measured using a time-resolved detection. The developed immunoassay was employed to screen inhibitors for enzyme 17β-hydroxysteroid dehydrogenase type 1. The enzyme overexpressed in MCF-7 cells catalyzed a reversible conversion of estroneto17β-estradiol. The inhibition efficiency of the tested molecule was obtained by comparing the final concentration of converted estradiol after 60 min of conversion reaction in a sample and in a conversion control not containing an inhibitor. The Zβ factor calculated using the E2 concentrations of the homogeneous assay was 0.64, demonstrating a relatively good performance of the assay. The results from the homogeneous assay were comparable with the results obtained using radioactively labeled estrone as a substrate and high-performance liquid chromatography (HPLC) separation of estrone and converted estradiol after the enzyme reaction. Thus, this homogeneous assay can simplify the primary screening of potential new drug molecules by replacing a tedious radiometric HPLC method.

Interaction of Androst-5-ene-3β,17β-diol and 5α-androstane-3β,17β-diol with estrogen and androgen receptors: a combined binding and cell study

Androst-5-ene-3β,17β-diol (ADIOL) and 5α-androstane-3β,17β-diol (3β-DIOL), metabolites of dehydroepiandrosterone (DHEA) and dihydrotestosterone (DHT), respectively, are known to possess estrogenic properties. To better understand their hormonal action and roles in the proliferation of breast cancer (BC) cells, we studied their binding to sex-hormone receptors in estrogen receptor (ER)-positive (ZR-75-1 and T-47D) and ER-negative (MDA-MB-231) human BC cells. The results demonstrated that estradiol (E2), ADIOL and 3β-DIOL stimulated the proliferation of ZR-75-1 and T-47D cells, but had no effect on ER-negative cells. In the presence of estradiol, ADIOL and 3β-DIOL inhibited the estrogen-stimulated BC cell growth. This inhibition was counteracted by anti-androgens, which were unable to affect the ADIOL and 3β-DIOL stimulatory effects in E2-free medium. On the other hand, in the presence of tamoxifen, ADIOL and 3β-DIOL showed an additional anti-proliferative activity on hormone-sensitive BC cells compared with tamoxifen treatment alone. These results are similar to previous reports obtained using MCF-7 cells, which confirmed that ADIOL and 3β-DIOL stimulated estrogen-dependent BC cell growth via ERs, but inhibited growth via androgen receptors (ARs). Several steroids bind to both ER and AR in a different preference and degree, i.e. E2>estrone (E1)>ADIOL>3β-DIOL>testosterone (T)>DHT for ER and DHT>T>3β-DIOL>ADIOL>E1>E2 for AR. The relative binding affinities of ADIOL, 3β-DIOL, and E2 corresponded well to their respective potential in stimulating cell proliferation of ZR-75-1 and T-47D cells in our results. The intrinsic relationship between cell proliferation effects and binding affinities for receptors of several steroids was revealed here by a combined binding and cell study. This article is part of a Special Issue entitled 'Synthesis and biological testing of steroid derivatives as inhibitors'.

The diversity of sex steroid action: novel functions of hydroxysteroid (17β) dehydrogenases as revealed by genetically modified mouse models

Disturbed action of sex steroid hormones, i.e. androgens and estrogens, is involved in the pathogenesis of various severe diseases in humans. Interestingly, recent studies have provided data further supporting the hypothesis that the circulating hormone concentrations do not explain all physiological and pathological processes observed in hormone-dependent tissues, while the intratissue sex steroid concentrations are determined by the expression of steroid metabolising enzymes in the neighbouring cells (paracrine action) and/or by target cells themselves (intracrine action). This local sex steroid production is also a valuable treatment option for developing novel therapies against hormonal diseases. Hydroxysteroid (17β) dehydrogenases (HSD17Bs) compose a family of 14 enzymes that catalyse the conversion between the low-active 17-keto steroids and the highly active 17β-hydroxy steroids. The enzymes frequently expressed in sex steroid target tissues are, thus, potential drug targets in order to lower the local sex steroid concentrations. The present review summarises the recent data obtained for the role of HSD17B1, HSD17B2, HSD17B7 and HSD17B12 enzymes in various metabolic pathways and their physiological and pathophysiological roles as revealed by the recently generated genetically modified mouse models. Our data, together with that provided by others, show that, in addition to having a role in sex steroid metabolism, several of these HSD17B enzymes possess key roles in other metabolic processes: for example, HD17B7 is essential for cholesterol biosynthesis and HSD17B12 is involved in elongation of fatty acids. Additional studies in vitro and in vivo are to be carried out in order to fully define the metabolic role of the HSD17B enzymes and to evaluate their value as drug targets.

A validated and rapid high-performance liquid chromatography method for the quantification of conversion of radio-labelled sex steroids

The 17β-hydroxysteroid dehydrogenase enzymes modify the availability of potent sex steroids and have thus attracted interest in the study of several steroid-dependent pathologies including breast, endometrial and prostate cancers. An increased awareness of the importance of steroidogenic enzymes has brought forth a demand for efficient assays to study the effects of individual enzymes on steroid levels. Methods used for assessing steroid conversion are often laborious and frequently involve hazardous sample preparation steps. We developed and validated an optimised simple method for sample preparation of sex steroids using protein precipitation by the addition of zinc sulphate/sodium hydroxide. The interconversion of radio-labelled oestrogens and androgens was quantified using high-performance liquid chromatography separation of oestrone, oestradiol, androstenedione and testosterone followed by online radiometric flow scintillation analysis. The method, which can be applied for assessing, e.g., the efficacy of inhibitors of steroidogenic enzymes, was successfully used for evaluating oestrogenic interconversion in breast cancer cell lines MCF7 and T-47D.

Berries and ellagic acid prevent estrogen-induced mammary tumorigenesis by modulating enzymes of estrogen metabolism

To determine whether dietary berries and ellagic acid prevent 17beta-estradiol (E(2))-induced mammary tumors by altering estrogen metabolism, we randomized August-Copenhagen Irish rats (n = 6 per group) into five groups: sham implant + control diet, E(2) implant + control diet (E(2)-CD), E(2) + 2.5% black raspberry (E(2)-BRB), E(2) + 2.5% blueberry (E(2)-BB), and E(2) + 400 ppm ellagic acid (E(2)-EA). Animals were euthanized at early (6 wk), intermediate (18 wk), and late (24 wk) phases of E(2) carcinogenesis, and the mammary tissue was analyzed for gene expression changes using quantitative real-time PCR. At 6 weeks, E(2) treatment caused a 48-fold increase in cytochrome P450 1A1 (CYP1A1; P < 0.0001), which was attenuated by both BRB and BB diets to 12- and 21-fold, respectively (P < 0.001). E(2) did not alter CYP1B1 levels, but both berry and EA diets significantly suppressed it by 11- and 3.5-fold, respectively, from baseline (P < 0.05). There was a 5-fold increase in 17beta-hydroxysteroid dehydrogenase 7 (17betaHSD7), and this was moderately abrogated to approximately 2-fold by all supplementation (P < 0.05). At 18 weeks, CYP1A1 was elevated by 15-fold in E(2)-CD and only E(2)-BB reduced this increase to 7-fold (P < 0.05). Catechol-O-methyltransferase expression was elevated 2-fold by E(2) treatment (P < 0.05), and all supplementation reversed this. At 24 weeks, CYP1A1 expression was less pronounced but still high (8-fold) in E(2)-treated rats. This increase was reduced to 3.2- and 4.6-fold by E(2)-BRB and E(2)-EA, respectively (P < 0.05), but not by E(2)-BB. Supplementation did not alter the effect of E(2) on steroid receptors. The diets also significantly suppressed mammary tumor incidence (10-30%), volume (41-67%), and multiplicity (38-51%; P < 0.05). Berries may prevent mammary tumors by suppressing the levels of E(2)-metabolizing enzymes during the early phase of E(2) carcinogenesis.

17beta-hydroxysteroid dehydrogenase type 1 stimulates breast cancer by dihydrotestosterone inactivation in addition to estradiol production

The active estrogen estradiol (E2) stimulates breast cancer cell (BCC) growth, whereas the androgen dihydrotestosterone (DHT) has shown an antiproliferative effect. The principal product synthesized by the 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) is E2, although we have demonstrated that the purified enzyme also inactivates DHT. However, the direct roles of 17beta-HSD1 in sex-hormone regulation and BCC proliferation have not been completely established. Here, we show that 17beta-HSD1 inhibition suppresses DHT catabolism by 19%, whereas knockdown of the gene expression increases the concentration of DHT by 41% in the T47D BCC line. The 17beta-HSD1/DHT complex crystal structure reveals that DHT binds in both normal and reverse modes, but the latter mode leading to O3 reduction is preferred with stronger interactions. Using RNA interference and an inhibitor of 17beta-HSD1, we demonstrate that 17beta-HSD1 expression is negatively correlated to DHT levels in BCC but positively correlated to estrone reduction, E2 levels, and cell proliferation. 17beta-HSD1 inhibition reduces DHT inactivation, increasing the antiproliferative effect by DHT in T47D cells after 8 d treatment. Thus, 17beta-HSD1 up-regulates BCC growth by a dual action on estradiol synthesis and DHT inactivation. We have further demonstrated that 17beta-HSD1 can enhance the E2-induced expression of the endogenous estrogen-responsive gene pS2, providing an important information regarding the modulation of the estrogen responsiveness by 17beta-HSD1 that may also contribute to BCC growth. These results strongly support the rationale for inhibiting 17beta-HSD1 in breast cancer therapy to eliminate estrogen activation via the sulfatase pathway while avoiding the deprivation of DHT.

17beta-hydroxysteroid dehydrogenases in human breast cancer

Estrogen plays a pivotal role in development and progression of human breast carcinoma. Before menopause the main source of estrogen in women is circulating estrogen secreted from the ovary, but following menopause the source changes to the hormone that is converted from circulating adrenal androgens in peripheral tissues. Therefore, adrenal androgens have to be converted to estrogen to stimulate breast carcinoma cells. In these steps, several enzymes such as aromatase, steroid sulfatase, and 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) are involved in the production of estrogens. The reaction related to 17beta-HSDs activity is one of the last steps of estradiol biosynthesis, and 14 isozymes of 17beta-HSD have been identified at this juncture. The balance of the relative expression levels of 17beta-HSD isozymes in human breast carcinomas is thought to play a pivotal role in supply of estradiol to estrogen receptor positive carcinoma cells. Understanding the character of 17beta-HSD isozymes in human breast carcinoma thus provides important information on the mechanisms of biosynthesis of estradiol in breast carcinoma and for development of a therapeutic agent targeted for inhibition of local estradiol synthesis in breast carcinoma cells. In the present review we summarize the roles played by 17beta-HSDs in human breast carcinoma to obtain a better understanding of the properties of 17beta-HSDs in human breast carcinoma.

A 3D QSAR model of 17beta-HSD1 inhibitors based on a thieno[2,3-d]pyrimidin-4(3H)-one core applying molecular dynamics simulations and ligand-protein docking

The 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) enzyme plays a crucial role in female hormonal regulation by catalysing the NADPH-dependent reduction of the less potent estrone E1 into the biologically active estradiol E2. Because 17beta-HSD1 is a key enzyme in E2 biosynthesis, it has emerged as an attractive drug target for inhibitor development. Herein we report the plausible binding modes and a 3D QSAR model of 17beta-HSD1 inhibitors based on a (di)cycloalkenothieno[2,3-d]pyrimidin-4(3H)-one core. Two generated enzyme complexes with potent inhibitors were subjected to molecular dynamics simulation to mimic the dynamic process of inhibitor binding. A set of 17beta-HSD1 inhibitors based on the thieno[2,3-d]pyrimidin-4(3H)-one core were docked into the resulting active site, and a CoMFA model employing the most extensive training set to date was generated. The model was validated with an external test set. Active site residues involved in inhibitor binding and CoMFA fields for steric and electrostatic interactions were identified. The model will be used to guide structural modifications of 17beta-HSD1 inhibitors based on a thieno[2,3-d]pyrimidin-4(3H)-one core in order to improve the biological activity as well as in the design of novel 17beta-HSD1 inhibitors.

Improved Homogeneous Proximity-Based Screening Assay of Potential Inhibitors of 17β-Hydroxysteroid Dehydrogenases

17beta-Hydroxysteroid dehydrogenases (17beta-HSDs) are substrate- and tissue-specific isoenzymes that regulate activation and inactivation of steroid hormones. Up-regulation and downregulation in expression of 17beta-HSDs are linked to onset of many steroid-dependent diseases, such as colon, prostate, and breast cancer; thus 17beta-HSDs are potential drug screening targets. Currently their enzymatic activities are usually measured using laborious chromatographic separations followed by radioactive detection of substrate and product. We have previously reported the use of a homogeneous luminescence resonance energy transfer-based immunoassay for 17beta-estradiol in screening of potential inhibitors of 17beta-HSD type 1 (17beta-HSD-1). By replacing the previously used cell-based enzyme reactions with recombinant enzyme reactions the sensitivity of the screening assay improved considerably. In addition, the single assay was able to detect the influence of a tested compound not only on 17beta-HSD-1 but also on 17beta-HSD type 2 (17beta-HSD-2), catalyzing the opposite reaction. The screening results of the tested molecules obtained from the optimized immunoassay were very similar when compared with the results of high performance liquid chromatography separation analysis. The Z factors were 0.79 and 0.83 for 17beta-HSD-1 and 17beta-HSD-2 assays, respectively. Thus the immunoassay measuring samples converted with the recombinant enzymes was a very suitable method for primary high throughput screening, and it could be used also in further characterization of potential drugs.

Human hydroxysteroid (17-beta) dehydrogenase 1 expression enhances estrogen sensitivity of MCF-7 breast cancer cell xenografts

Hydroxysteroid (17-beta) dehydrogenase 1 (HSD17B1) catalyzes the conversion between estrone (E1) and estradiol (E2). The reaction is reversible in vitro, but the data in cultured cells suggest that E2 production is the predominant reaction in physiological conditions. However, the hypothesis has not been verified in vivo. In the present study, estrogen-dependent MCF-7 human breast cancer cells were stably transfected with an expression plasmid for human HSD17B1. The enzyme efficiently converted E1 to E2 and enhanced the estrogen-dependent growth of cultured MCF-7 cells in the presence of hormonally less active E1. The HSD17B1-expressing cells also formed estrogen-dependent tumors in immunodeficient nude mice. After treating the mice with an appropriate dose of the substrate (E1, 0.1 micromol/kg x d), a marked difference in tumor growth was observed between nontransfected and HSD17B1-transfected MCF-7 cells, mean tumor weights at the end of E1 treatment being 23.2 and 130.4 mg, respectively. Furthermore, estrogen-dependent growth of the HSD17B1-expressing xenografts in the presence of E1 was markedly inhibited by administering 5 micromol/kg x d of a specific HSD17B1 inhibitor. After a 4-wk treatment, the tumor size was reduced by 59.8% as compared with the nontreated tumors, whereas the uterine growth of the mice was not affected by the HSD17B1 inhibitor used. This was in line with the induction of apoptosis of the tumors. The results evidently show that estrogenic response for E1 is enhanced by the local action of HSD17B1 in vivo, and thus, the enzyme is a potential target for pharmacological inhibition of estrogen action.

Expression of aromatase and 17beta-hydroxysteroid dehydrogenase types 1, 7 and 12 in breast cancer. An immunocytochemical study

It is known that there is a local biosynthesis of estradiol (E2) in breast carcinoma. The steroidogenic enzymes involved in E2 formation are aromatase which transforms testosterone into E2 and androstenedione into estrone (E1) and reductive 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) which convert E1 into E2. Using immunocytochemistry, we have studied the expression of aromatase and the three reductive 17beta-HSDs 17beta-HSD types 1, 7 and 12 in 41 specimens of female human breast carcinoma and adjacent non-malignant tissues. These results were correlated with the estrogen receptor alpha (ERalpha) and beta (ERbeta), progesterone receptor, androgen receptor, CDC47 and c-erb B-2 expressions and with the tumor stages. Aromatase was found in 58%, 17beta-HSD type 7 in 47% and 17beta-HSD type 12 in 83% of the breast cancer specimens. The 17beta-HSD type 1 could be detected in only one tumor. A significant correlation was observed between the aromatase, 17beta-HSD type 7 and 17beta-HSD type 12 expression, as well as between each of the two enzymes 17beta-types 7 and 12 and the ERbeta expression. The expression of 17beta-HSD type 12 was significantly higher in breast carcinoma specimens than in normal tissue. There was also a significant association of CDC 47 expression with ERbeta, AR and 17beta-HSD type 12. The results indicate that aromatase, 17beta-HSD type 7 and 17beta-HSD type 12, but not 17beta-HSD type 1, are commonly expressed in human breast cancer. Moreover, the high expression of both 17beta-HSD type 12 and ERbeta in breast carcinoma cells may play a role in the development and/or progression of breast cancer.

Control of cell proliferation by steroids: the role of 17HSDs

Sex steroid hormone signaling regulates the development, growth, and functioning of the breast and the prostate and plays a role in the development and progression of cancer in these organs. The intracellular concentration of active sex steroid hormones in target tissues is regulated by several enzymes, including 17beta-hydroxysteroid dehydrogenases (17HSDs). Changes in the expression patterns of these enzymes may play a pathophysiological role in malignant transformation. We recently analyzed the mRNA expressions of the 17HSD type 1, 2, and 5 enzymes in about 800 breast carcinoma specimens. Both 17HSD type 1 and 2 mRNAs were detected in normal breast tissue from premenopausal women but not in specimens from postmenopausal women. The patients with tumors expressing 17HSD type 1 mRNA or protein had significantly shorter overall and disease-free survival than the other patients. The expression of 17HSD type 5 was significantly higher in breast tumor specimens than in normal tissue. Cox multivariate analyses showed that 17HSD type 1, tumor size, and estrogen receptor alpha (ERalpha) had independent prognostic significance. We developed, using a LNCaP prostate cancer cell line, a model to study the malignant transformation of prostate cancer and showed that androgen-sensitive LNCaP cells are transformed into neuroendocrine-like cells when cultured without androgens and, eventually into highly proliferating androgen-independent cells. We conducted Northern hybridizations and microarrays to analyze the gene expression during these processes. Substantial changes in the expressions of steroid metabolizing enzymes occurred during the transformation process. The variations in steroid-metabolizing enzymes during cancer progression may be crucial in the regulation of the growth and function of organs.

Evaluation of inhibitors for 17beta-hydroxysteroid dehydrogenase type 1 in vivo in immunodeficient mice inoculated with MCF-7 cells stably expressing the recombinant human enzyme

17Beta-hydroxysteroid dehydrogenase (17HSD1) is an enzyme activating estrone (E1) to estradiol (E2). In the present study, a mechanistic animal model was set up for evaluating putative inhibitors for the human enzyme in vivo. Estrogen-dependent MCF-7 human breast carcinoma cells were stably transfected with a plasmid expressing human 17HSD1. These cells formed estrogen-dependent tumors in immunodeficient mice. In the optimized model, tumor sizes were decreased in both ovariectomized and intact vehicle-treated mice, whereas they were maintained or slightly increased in mice supplemented 2 weeks with an appropriate dose of the 17HSD1-substrate E1. Tumor sizes in mice treated with 0.1 micromol/kg/d of E1 were reduced by administering 5 micromol/kg/d of different 17HSD1-inhibitors and a 86% reduction in size was detected with the most potent inhibitor. A dose-response relationship in the inhibitory effect of this compound further confirmed the validity of the model for testing the drug candidates in vivo.

The role of 17beta-hydroxysteroid dehydrogenases in modulating the activity of 2-methoxyestradiol in breast cancer cells

The bis-sulfamoylated derivative of 2-methoxyestradiol (2-MeOE2), 2-methoxyestradiol-3,17-O,O-bis-sulfamate (2-MeOE2bisMATE), has shown potent antiproliferative and antiangiogenic activity in vitro and inhibits tumor growth in vivo. 2-MeOE2bisMATE is bioavailable, in contrast to 2-MeOE2 that has poor bioavailability. In this study, we have examined the role of 17beta-hydroxysteroid dehydrogenase (17beta-HSD) type 2 in the metabolism of 2-MeOE2. In MDA-MB-231 cells, which express high levels of 17beta-HSD type 2, and in MCF-7 cells transfected with 17beta-HSD type 2, high-performance liquid chromatography analysis showed that a significant proportion of 2-MeOE2 was metabolized to inactive 2-methoxyestrone. Furthermore, MCF-7 cells transfected with 17beta-HSD type 2 were protected from the cytotoxic effects of 2-MeOE2. In contrast, no significant metabolism of 2-MeOE2bisMATE was detected in transfected cells and 17beta-HSD type 2 transfection did not offer protection against 2-MeOE2bisMATE cytotoxicity. This study may go some way to explaining the poor bioavailability of 2-MeOE2, as the gastrointestinal mucosa expresses high levels of 17beta-HSD type 2. In addition, this study shows the value of synthesizing sulfamoylated derivatives of 2-MeOE2 with C17-position modifications as these compounds have improved bioavailability and potency both in vitro and in vivo.

Enzymes as modulators in malignant transformation

Experimental data suggest that sex steroids have a role in the development of breast and prostate cancers. The biological activity of sex steroid hormones in target tissues is regulated by several enzymes, including 17beta-hydroxysteroid dehydrogenases (17HSD). Changes in the expression patterns of these enzymes may significantly modulate the intracellular steroid content and play a pathophysiological role in malignant transformation. To further clarify the role of 17HSDs in breast cancer, we analyzed the mRNA expressions of the 17HSD type 1, 2, and 5 enzymes in 794 breast carcinoma specimens. Both 17HSD type 1 and 2 mRNAs were detected in normal breast tissue from premenopausal women but not in specimens from postmenopausal women. Of the breast cancer specimens, 16% showed signals for 17HSD type 1 mRNA, 25% for type 2, and 65% for type 5. No association between the 17HSD type 1, 2, and 5 expressions was detected. The patients with tumors expressing 17HSD type 1 mRNA or protein had significantly shorter overall and disease-free survival than the other patients. The expression of 17HSD type 5 was significantly higher in breast tumor specimens than in normal tissue. The group with 17HSD type 5 overexpression had a worse prognosis than the other patients. Cox multivariate analyses showed that 17HSD type 1 mRNA, tumor size, and ERalpha had independent prognostic significance. Using an LNCaP prostate cancer cell line, we developed a cell model to study the progression of prostate cancer. In this model, androgen-sensitive LNCaP cells are transformed in culture conditions into more aggressive, androgen-independent cells. The model was used to study androgen and estrogen metabolism during the transformation process. Our results indicate that substantial changes in androgen and estrogen metabolism occur in the cells during the process. A remarkable decrease in oxidative 17HSD activity was seen, whereas reductive activity seemed to increase. Since local steroid metabolism controls the bioavailability of active steroid hormones of target tissues, the variations in steroid-metabolizing enzymes during cancer progression may be crucial in the regulation of the growth and function of organs.

Recent insight on the control of enzymes involved in estrogen formation and transformation in human breast cancer

The great majority of breast cancers are in their early stage hormone-dependent and it is well accepted that estradiol (E2) plays an important role in the genesis and evolution of this tumor. Human breast cancer tissues contain all the enzymes: estrone sulfatase, 17beta-hydroxysteroid dehydrogenase, aromatase involved in the last steps of E2 bioformation. Sulfotransferases which convert estrogens into the biologically inactive estrogen sulfates are also present in this tissue. Quantitative data show that the 'sulfatase pathway', which transforms estrogen sulfates into the bioactive unconjugated E2, is 100-500 times higher than the 'aromatase pathway', which converts androgens into estrogens. The treatment of breast cancer patients with anti-aromatases is largely developed with very positive results. However, the formation of E2 via the 'sulfatase pathway' is very important in the breast cancer tissue. In recent years it was found that antiestrogens (e.g. tamoxifen, 4-hydroxytamoxifen), various progestins (e.g. promegestone, nomegestrol acetate, medrogestone, dydrogesterone, norelgestromin), tibolone and its metabolites, as well as other steroidal (e.g. sulfamates) and non-steroidal compounds, are potent sulfatase inhibitors. In another series of studies, it was found that E2 itself has a strong anti-sulfatase action. This paradoxical effect of E2 adds a new biological response of this hormone and could be related to estrogen replacement therapy in which it was observed to have either no effect or to decrease breast cancer mortality in postmenopausal women. Interesting information is that high expression of steroid sulfatase mRNA predicts a poor prognosis in patients with +ER. These progestins, as well as tibolone, can also block the conversion of estrone to estradiol by the inhibition of the 17beta-hydroxysteroid dehydrogenase type I (17beta-HSD-1). High expressison of 17beta-HSD-1 can be an indicator of adverse prognosis in ER-positive patients. It was shown that nomegestrol acetate, medrogestone, promegestone or tibolone, could stimulate the sulfotransferase activity for the local production of estrogen sulfates. This is an important point in the physiopathology of this disease, as it is well known that estrogen sulfates are biologically inactive. A possible correlation between this stimulatory effect on sulfotransferase activity and breast cancer cell proliferation is presented. In agreement with all this information, we have proposed the concept of selective estrogen enzyme modulators (SEEM). In conclusion, the blockage in the formation of estradiol via sulfatase, or the stimulatory effect on sulfotransferase activity in combination with anti-aromatases can open interesting and new possibilities in clinical applications in breast cancer.

The selective estrogen enzyme modulators in breast cancer: a review

It is well established that increased exposure to estradiol (E(2)) is an important risk factor for the genesis and evolution of breast tumors, most of which (approximately 95-97%) in their early stage are estrogen-sensitive. However, two thirds of breast cancers occur during the postmenopausal period when the ovaries have ceased to be functional. Despite the low levels of circulating estrogens, the tissular concentrations of these hormones are significantly higher than those found in the plasma or in the area of the breast considered as normal tissue, suggesting a specific tumoral biosynthesis and accumulation of these hormones. Several factors could be implicated in this process, including higher uptake of steroids from plasma and local formation of the potent E(2) by the breast cancer tissue itself. This information extends the concept of 'intracrinology' where a hormone can have its biological response in the same organ where it is produced. There is substantial information that mammary cancer tissue contains all the enzymes responsible for the local biosynthesis of E(2) from circulating precursors. Two principal pathways are implicated in the last steps of E(2) formation in breast cancer tissues: the 'aromatase pathway' which transforms androgens into estrogens, and the 'sulfatase pathway' which converts estrone sulfate (E(1)S) into E(1) by the estrone-sulfatase. The final step of steroidogenesis is the conversion of the weak E(1) to the potent biologically active E(2) by the action of a reductive 17beta-hydroxysteroid dehydrogenase type 1 activity (17beta-HSD-1). Quantitative evaluation indicates that in human breast tumor E(1)S 'via sulfatase' is a much more likely precursor for E(2) than is androgens 'via aromatase'. Human breast cancer tissue contains all the enzymes (estrone sulfatase, 17beta-hydroxysteroid dehydrogenase, aromatase) involved in the last steps of E(2) biosynthesis. This tissue also contains sulfotransferase for the formation of the biologically inactive estrogen sulfates. In recent years, it was demonstrated that various progestins (promegestone, nomegestrol acetate, medrogestone, dydrogesterone, norelgestromin), tibolone and its metabolites, as well as other steroidal (e.g. sulfamates) and non-steroidal compounds, are potent sulfatase inhibitors. Various progestins can also block 17beta-hydroxysteroid dehydrogenase activities. In other studies, it was shown that medrogestone, nomegestrol acetate, promegestone or tibolone can stimulate the sulfotransferase activity for the local production of estrogen sulfates. All these data, in addition to numerous agents which can block the aromatase action, lead to the new concept of 'Selective Estrogen Enzyme Modulators' (SEEM) which can largely apply to breast cancer tissue. The exploration of various progestins and other active agents in trials with breast cancer patients, showing an inhibitory effect on sulfatase and 17beta-hydroxysteroid dehydrogenase, or a stimulatory effect on sulfotransferase and consequently on the levels of tissular levels of E(2), will provide a new possibility in the treatment of this disease.

17 beta-hydroxysteroid dehydrogenases--their role in pathophysiology

17 beta-Hydroxysteroid dehydrogenases (17HSDs) regulate the biological activity of sex steroid hormones in a variety of tissues by catalyzing the interconversions between highly active steroid hormones, e.g. estradiol and testosterone, and corresponding less active hormones, estrone and androstenedione. Epidemiological and endocrine evidence indicates that estrogens play a role in the etiology of breast cancer, while androgens are involved in mechanisms controlling the growth of normal and malignant prostatic cells. Using LNCaP prostate cancer cell lines, we have developed a cell model to study the progression of prostate cancer. In the model LNCaP cells are transformed in culture condition into more aggressive cells. Our data suggest that substantial changes in androgen and estrogen metabolism occur in the cells, leading to increased production of active estrogens during the process. In breast cancer, the reductive 17HSD type 1 activity is predominant in malignant cells, while the oxidative 17HSD type 2 mainly seems to be present in non-malignant breast epithelial cells. Deprivation of an estrogen response by using specific 17HSD type 1 inhibitors is a tempting approach in treating estrogen-dependent breast cancer. Our recent studies demonstrate that in addition to sex hormone target tissues, estrogens may be important in the development of cancer in some other tissues previously not considered to be estrogen target tissues, such as the gastrointestinal tract.

17 beta-hydroxysteroid dehydrogenases and cancers

17 beta-Hydroxysteroid dehydrogenases (17HSDs) catalyze the interconversions between active 17 beta-hydroxysteroids and less-active 17-ketosteroids thereby affecting the availability of biologically active estrogens and androgens in a variety of tissues. The enzymes have different enzymatic properties and characteristic cell-specific expression patterns, suggesting differential physiological functions for the enzymes. Epidemiological and endocrine evidence indicate that estrogens play a key role in the etiology of breast cancer while androgens are involved in mechanisms controlling the growth of prostatic cells, both normal and malignant. Recently, we have developed, using LNCaP prostate cancer cell lines, a cell model to study the progression of prostate cancer. In the model LNCaP cells are transformed in culture condition to more aggressive cells, able to grow in suspension cultures. Our results suggest that substantial changes in androgen and estrogen metabolism occur in the cells during the process. These changes lead to increased production of active estrogens during transformation of the cells. Data from studies of breast cell lines and tissues suggest that the oxidative 17HSD type 2 may predominate in human non-malignant breast epithelial cells, while the reductive 17HSD type 1 activity prevails in malignant cells. Deprivation of an estrogen response by using specific 17HSD type 1 inhibitors is a tempting approach to treat estrogen-dependent breast cancer. Our recent studies demonstrate that in addition to sex hormone target tissues, estrogens may be important in the development of cancer in some other tissues previously not considered as estrogen target tissues such as colon. Our data show that the abundant expression of 17HSD type 2 present in normal colonic mucosa is significantly decreased during colon cancer development.

Acute and chronic effects of genistein, tyrphostin and lavendustin A on steroid synthesis in luteinized human granulosa cells

BACKGROUND

Phytoestrogens, including genistein and other inhibitors of tyrosine kinases (TKs), inhibit specific steroidogenic enzymes. This study was designed to compare the effects of genistein, with two other TK inhibitors, on steroid synthesis in human granulosa luteal (GL) cells and to identify which steroidogenic enzymes they may affect.

METHODS

GL cells, obtained from women undergoing IVF procedures, were cultured for various periods of time with and without substrates for progesterone and estradiol synthesis, in the presence or absence of the TK inhibitors.

RESULTS

The TK inhibitors significantly suppressed progesterone and estradiol synthesis in a dose-dependent manner over a 48 h culture period. Progesterone production in the presence of 10(-7) mol/l pregnenolone during a 4 h period was inhibited by both acute (4 h) and chronic (24 h) exposure of GL cells to 50 micromol/l genistein (P < 0.05) whilst no significant effects of 50 micromol/l tyrphostin A23 were observed. Genistein (4 and 24 h exposure) inhibited the production of estradiol using 10(-7) mol/l estrone as a substrate, but inhibition of estradiol synthesis using androstenedione or testosterone as substrates was only observed after a 24 h exposure. In contrast, tyrphostin acutely stimulated estradiol synthesis when androstenedione and testosterone were used as substrates (P < 0.05) but not estrone.

CONCLUSIONS

Genistein directly inhibits 3 and 17beta-hydroxysteroid dehydrogenase activity, whilst tyrphostin has an acute stimulatory effect on aromatase activity. Over a longer time (24 and/or 48 h period), both TK inhibitors suppress steroid synthesis.

Dehydroepiandrosterone stimulates proliferation and gene expression in MCF-7 cells after conversion to estradiol

Dehydroepiandrosterone (DHEA) is a mitogen for estrogen-dependent MCF-7 breast cancer cells. Our aims were to determine whether DHEA required conversion to estrogens in order to stimulate cell proliferation and estrogen-dependent gene expression. After incubation of cells with 100 nM DHEA for 4 days, estradiol was present in the medium at a concentration of approximately 200 pM. Other compounds identified were testosterone ( approximately 300 pM) and estrone. Significant stimulation of cell proliferation by 1 nM estradiol and 100 nM DHEA was observed after 38 h and 4 days of incubation, respectively, indicating the necessity of DHEA conversion. DHEA doses > or = 10 nM induced estrogen-dependent reporter gene expression in MCF-7 cells transfected with a luciferase reporter gene under the control of the estrogen response element. DHEA-dependent stimulation of proliferation and luciferase induction could be inhibited by the anti-estrogens ICI182,780 and tamoxifen, respectively, and by the aromatase inhibitor 4-hydroxyandrostenedione. An androgenic effect of DHEA on proliferation and gene expression of MCF-7 cells was not observed. We conclude that conversion of DHEA to estrogens, particularly estradiol, is required to exert a mitogenic response.

Structure and function of 17beta-hydroxysteroid dehydrogenase type 1 and type 2

17beta-Hydroxysteroid dehydrogenases (17HSDs) catalyze the interconversions between high-activity 17beta-hydroxysteroids and low-activity 17-ketosteroids. Several distinct 17HSD isoenzymes have been characterized. They have unique tissue distribution patterns suggesting a specific function for each of the isoenzymes in modifying sex steroid hormone activity. The activities of 17HSDs are essential for gonadal sex steroid biosynthesis and they are also involved in the modulation of steroid hormone action in peripheral tissues. 17HSD type 1 (17HSD1) is needed for estradiol biosynthesis in ovarian granulosa cells and it is also expressed in breast tissue, thus increasing locally estradiol concentration. 17HSD type 2 (17HSD2) is another 17HSD enzyme involved in estrogen metabolism. The type 2 enzyme has an opposite activity catalyzing estradiol to estrone, thereby reducing the exposure of tissues to estrogen action. Preliminary data suggest that 17HSD2 may predominate in human non-malignant breast epithelial cells, while 17HSD type 1 activity prevails in malignant cells. Determination of the three-dimensional structure of human 17HSD1 has led to an atomic level description of the estradiol binding pocket of the enzyme and an understanding of its mechanism of action, and the molecular basis for the estrogen-specificity of the enzyme. Deprivation of an estrogen response by using specific 17HSD1 inhibitors is a tempting approach to treat estrogen-dependent breast cancer.

Estrogen metabolism as a regulator of estrogen action in the mammary gland

Estrogen action in the target cells is dependent on estrogen receptor activity and intracellular estrogen concentration, which, in turn, is affected by the serum concentration and local metabolism in these cells. During the reproductive years the main source of estrogens is the ovarian follicles, but in postmenopausal women most of the estrogens are formed in peripheral tissues. 17Beta-hydroxysteroid dehydrogenases (17HSDs) catalyze the reaction between 17beta-hydroxysteroids and 17-ketosteroids, and several distinct 17HSD isoenzymes have been characterized. 17HSD type 1 catalyzes the reaction from low-activity estrone to high-activity estradiol. The type 2 enzyme has an opposite activity, thereby reducing the exposure of tissues to estrogen action. 17HSD type 1 is expressed both in steroidogenic tissues and in the target tissues of steroid action, such as normal and malignant breast tissue, where it may be responsible for maintaining the high intracellular estradiol concentration seen in breast cancer specimens. Therefore, 17HSD type 1 inhibitors may be useful in the treatment and/or prevention of estrogen-dependent malignancies, such as breast cancer. This article deals mainly with 17HSD types 1 and 2 and their role in estrogen action in breast tissue.

17Beta-hydroxysteroid dehydrogenases in normal human mammary epithelial cells and breast tissue

17Beta-hydroxysteroid dehydrogenase activity represents a group of several isoenzymes (17HSDs) that catalyze the interconversion between highly active 17beta-hydroxy- and low activity 17-ketosteroids and thereby regulate the biological activity of sex steroids. The present study was carried out to characterize the expression of 17HSD isoenzymes in human mammary epithelial cells and breast tissue. In normal breast tissues 17HSD types 1 and 2 mRNAs were both evenly expressed in glandular epithelium. In two human mammary epithelial cell lines, mRNAs for 17HSD types 1, 2 and 4 were detected. In enzyme activity measurements only oxidative 17HSD activity, corresponding to either type 2 or type 4 enzyme, was present. The role of 17HSD type 4 in estrogen metabolism was further investigated, using several cell lines originating from various tissues. No correlation between the presence of 17HSD type 4 mRNA and 17HSD activity in different cultured cell lines was detected. Instead, oxidative 17HSD activity appeared in cell lines where 17HSD type 2 was expressed and reductive 17HSD activity was present in cells expressing 17HSD type 1. These data strongly suggest that in mammary epithelial cell lines the oxidative activity is due to type 2 17HSD and that oxidation of 17beta-hydroxysteroids is not the primary activity of the 17HSD type 4 enzyme.

Two 17beta-hydroxysteroid dehydrogenases (17HSDs) of estradiol biosynthesis: 17HSD type 1 and type 7

Two 17beta-hydroxysteroid dehydrogenases (17HSDs), type 1 and type 7, are enzymes of estradiol biosynthesis, in addition to which rodent type 1 enzymes are also able to catalyze androgens. Both of the 17HSDs are abundantly expressed in ovaries, the type 1 enzyme in granulosa cells and type 7 in luteinized cells. The expression of 17HSD7, which has also been described as a prolactin receptor-associated protein (PRAP), is particularly up-regulated in corpus luteum during the second half of rodent pregnancy. A moderate or slight signal for mouse 17HSD7/PRAP mRNA has also been demonstrated in samples of placenta and mammary gland, for example. Human, but not rodent, 17HSD1 is expressed in placenta, breast epithelium and endometrium in addition to ovaries. A cell-specific enhancer, silencer and promoter in the hHSD17B1 gene participate in the regulation of type 1 enzyme expression. The enhancer consists of several subunits, including a retinoic acid response element, the silencer has a binding motif for GATA factors, and the proximal promoter contains adjacent and competing AP-2 and Sp binding sites.

Expression cloning of a novel estrogenic mouse 17 beta-hydroxysteroid dehydrogenase/17-ketosteroid reductase (m17HSD7), previously described as a prolactin receptor-associated protein (PRAP) in rat

17 beta-Hydroxysteroid dehydrogenases/17-ketosteroid reductases (17HSDs) modulate the biological activity of certain estrogens and androgens by catalyzing reductase or dehydrogenase reactions between 17-keto- and 17 beta-hydroxysteroids. In the present study, we demonstrate expression cloning of a novel type of 17HSD, chronologically named 17HSD type 7, from the HC11 cell line derived from mouse mammary gland. The cloned cDNA, 1.7 kb in size, encodes a protein of 334 amino acids with a calculated molecular mass of 37,317 Da. The primary structure contains segments characteristic of enzymes belonging to the short-chain dehydrogenase/reductase superfamily. Strikingly, mouse 17HSD type 7 (m17HSD7) shows 89% identity with a recently cloned rat protein called PRL receptor-associated protein (PRAP). The function of PRAP has not yet been demonstrated. The enzymatic characteristics of m17HSD7 and RT-PCR-cloned rat PRAP (rPRAP) were analyzed in cultured HEK-293 cells, where both of the enzymes efficiently catalyzed conversion of estrone (E1) to estradiol (E2). With other substrates tested no detectable 17HSD or 20 alpha-hydroxysteroid dehydrogenase activities were found. Kinetic parameters for m17HSD7 further indicate that E1 is a preferred substrate for this enzyme. Relative catalytic efficiencies (Vmax/K(m) values) for E1 and E2 are 244 and 48, respectively. As it is the case with rPRAP, m17HSD7 is most abundantly expressed in the ovaries of pregnant animals. Further studies show that the rat enzyme is primarily expressed in the middle and second half of pregnancy, in parallel with E2 secretion from the corpus luteum. The mRNA for m17HSD7 is also apparent in the placenta, and a slight signal for m17HSD7 is found in the ovaries of adult nonpregnant mice, in the mammary gland, liver, kidney, and testis. Altogether, because of their similar primary structures, enzymatic characteristics, and the tissue distribution of m17HSD7 and rPRAP, we suggest that rPRAP is rat 17HSD type 7. Furthermore, the results indicate that 17HSD7 is an enzyme of E2 biosynthesis, which is predominantly expressed in the corpus luteum of the pregnant animal.

The proximal promoter region of the gene encoding human 17beta-hydroxysteroid dehydrogenase type 1 contains GATA, AP-2, and Sp1 response elements: analysis of promoter function in choriocarcinoma cells

The 5'-flanking region from -78 to +9 in the HSD17B1 gene serves as a promoter, and an HSD17B1 silencer element is located in position -113 to -78. In the present studies, we have characterized three regulatory elements in the proximal 5'-flanking regions of the gene, using electrophoretic mobility shift assays and reporter gene analysis. First, nuclear factors recognized by antibodies against Sp1 and Sp3 were found to bind the Sp1 motif in the region from -52 to -43. Mutation of the Sp1-binding site decreased the promoter activity to 30% in JEG-3 cells and to 60% in JAR cells, suggesting that binding to the Sp1 motif has a substantial role in the complete functioning of the HSD17B1 promoter. Second, the binding of AP-2 to its motif in the region from -62 to -53 led to reduced binding of Sp1 and Sp3, and furthermore, mutation of the AP-2 element increased promoter activity to 260% in JEG-3 cells. The data thus implied that AP-2 can repress the function of the HSD17B1 promoter by preventing binding to the Sp1 motif. Finally, GATA factors, GATA-3 in particular, were demonstrated to bind their cognate sequence in the HSD17B1 silencer region, and mutations introduced into the GATA-binding site increased transcriptional activity to the level seen in constructs not containing the silencer element. Thus, GATA-3 seems to prevent transcription in the constructs, and hence, the GATA motif also may operate as a negative control element for HSD17B1 transcription.

Retinoic acids increase 17 beta-hydroxysteroid dehydrogenase type 1 expression in JEG-3 and T47D cells, but the stimulation is potentiated by epidermal growth factor, 12-O-tetradecanoylphorbol-13-acetate, and cyclic adenosine 3',5'-monophosphate only in JEG-3 cells

Human 17 beta-hydroxysteroid dehydrogenase type 1 (17HSD type 1) primarily catalyzes the reduction of low activity estrone to high activity estradiol in ovarian granulosa cells and placental trophoblasts 17HSD type 1 is also present in certain peripheral tissues, such as breast tissue. In the present study we investigated the effects of retinoic acids (RAs) together with other stimuli known to modulate estradiol production and/or cell growth on expression of 17HSD type 1 in JEG-3 choriocarcinoma cells and estrogen-responsive T47D breast cancer cells. Treatment of cultured JEG-3 and T47D cells with all-trans-RA and 9-cis-RA increased reductive 17HSD activity and 17HSD type 1 messenger RNA expression severalfold in both cell lines. On the other hand, epidermal growth factor (EGF), Ca ionophore, the protein kinase C activator 12-O-tetradecanoylphorbol-13-acetate (TPA), and cAMP elevated 17HSD type 1 expression only in JEG-3 cells. Correspondingly, the effects of RAs were potentiated by EGF, TPA, and cAMP in JEG-3 cells, whereas no such phenomenon was observed in T47D cells. In JEG-3 cells, simultaneous administration of RAs with TPA and EGF maximally resulted in approximately 40- and 20-fold increases in 17HSD type 1 messenger RNA expression, respectively. The present data indicate that RAs may stimulate estradiol biosynthesis by regulating 17HSD type 1 expression in certain breast cancer and choriocarcinoma cells. The results suggest that interaction of multiple regulatory pathways is involved in maintaining high 17HSD type 1 expression in the placenta. In addition, regulation of 17HSD type 1 expression may be different in trophoblast cells from that in breast epithelial cells.