The conversion of androstenedione to estrone, estradiol, and testosterone in breast tissue

Association of the urinary polycyclic aromatic hydrocarbons with sex hormones stratified by menopausal status older than 20 years: a mixture analysis

We examined the relationships between exposure to polycyclic aromatic hydrocarbons (PAH) metabolites and sex hormones in pre- and postmenopausal women from the 2013-2016 National Health and Nutrition Examination Survey. The study comprised 648 premenopausal and 370 postmenopausal women (aged 20 years or older) with comprehensive data on PAH metabolites and sex steroid hormones. To evaluate the correlations between individual or mixture of the PAH metabolites and sex hormones stratified by menopausal status, we used linear regression and Bayesian kernel machine regression (BKMR). After controlling for confounders, 1-Hydroxynaphthalene (1-NAP) was inversely associated with total testosterone (TT), and 1-NAP, 3-Hydroxyfluorene (3-FLU), and 2-Hydroxyfluorene (2-FLU) were inversely associated with estradiol (E2). 3-FLU was positively associated with sex hormone-binding globulin (SHBG) and TT/E2, whereas 1-NAP and 2-FLU were inversely associated with free androgen index (FAI). In the BKMR analyses, chemical combination concentrations at or above the 55th percentile were inversely connected to E2, TT, and FAI values but positively correlated with SHBG when compared with the matching 50th percentile. In addition, we only found that mixed exposure to PAHs was positively associated with TT and SHBG in premenopausal women. Exposure to PAH metabolites, either alone or as a mixture, was negatively associated with E2, TT, FAI, and TT/E2 but positively associated with SHBG. These associations were stronger among postmenopausal women.

The association between sex hormones and periodontitis among American adults: A cross-sectional study

INTRODUCTION

After adulthood, as a person grows older, the secretion of sex hormones in the body gradually decreases, and the risk of periodontitis increases. But the relationship between sex hormones and periodontitis is still controversial.

METHODS

We investigated the association between sex hormones and periodontitis among Americans over 30 years old. 4,877 participants containing 3,222 males and 1,655 postmenopausal females who had had periodontal examination and detailed available sex hormone levels, were included in our analysis from the 2009-2014 National Health and Nutrition Examination Surveys cycles. We applied multivariate linear regression models to estimate the connection between sex hormones and periodontitis after converting sex hormones into categorical variables through tertile. Additionally, to ensure the stability of the analysis results, we carried out a trend test, subgroup analysis, and interaction test.

RESULTS

After fully adjusting the covariates, estradiol levels were not associated with periodontitis in both males and females with a P for trend = 0.064 and 0.064, respectively. For males, we found that sex hormone-binding globulin was positively associated with periodontitis (tertile3 vs tertile1: OR=1.63, 95% CI=1.17-2.28, p = 0.004, P for trend = 0.005). Congruously, free testosterone (tertile3 vs tertile1: OR=0.60, 95% CI=0.43-0.84, p = 0.003), bioavailable testosterone (tertile3 vs tertile1: OR=0.51, 95% CI=0.36-0.71, p < 0.001), and free androgen index (tertile3 vs tertile1: OR=0.53, 95% CI=0.37-0.75, p < 0.001) was found to be negatively associated with periodontitis. Moreover, subgroup analysis of age found a closer relationship between sex hormones and periodontitis in those younger than 50 years.

CONCLUSION

Our research suggested that males with lower bioavailable testosterone levels affected by sex hormone-binding globulin were at a higher risk of periodontitis. Meanwhile, estradiol levels were not associated with periodontitis in postmenopausal women.

Association of urinary organophosphate esters level with sex steroid hormones levels in adult males: A nationwide study, NHANES 2013-2014

BACKGROUND

Exposure to environmental pollution via different mechanisms is associated with multiple endocrine dysfunctions. Organophosphate esters (OPEs) are endocrine-disrupting chemicals that affect sex steroid hormones.

PURPOSE

We aimed to study the effect of OPEs and their metabolites, such as dibutyl phosphate [DPHP], bis(1,3-dichloro-2-propyl) phosphate [BDCPP], bis(2-chloroethyl) phosphate [BCEP], and dibutyl phosphate [DBUP], on sex steroid hormones in males.

DESIGN, SETTING, PARTICIPANTS, AND INTERVENTION

This cross-sectional analytical study analyzed data from the 2013-2014 National Health and Nutrition Examination Survey among 763 male participants aged ≥20 years.

MAIN OUTCOME MEASURES

The relationships between the metabolites of OPEs and total testosterone, estradiol, sex hormone-binding globulin, and the ratio of total testosterone to estradiol (a parameter derived from total testosterone and estradiol) were evaluated using multivariate linear regression models that were adjusted for potential confounders.

RESULTS

A total of 763 participants, with a mean age of 44.59 (±15.59) years, were enrolled. Of these, 65.7% participants had non-Hispanic white ancestry, 9.83% had non-Hispanic black ancestry, and 15.97% had Hispanic ancestry. Participants with higher urinary level of DPHP had a lower level of total testosterone and estradiol. Moreover, higher urinary levels of BDCPP were associated with higher estradiol.

CONCLUSION

According to our study, which is based on a representative population of US adults, exposure to OPEs was significantly associated with altered sex hormone levels (total testosterone and estradiol). Further studies focused on the underlying mechanisms regarding the association between each metabolite and sex steroid hormones are required. This article is protected by copyright. All rights reserved.

Associations between organophosphate esters and sex hormones among 6-19-year old children and adolescents in NHANES 2013-2014

BACKGROUND

Organophosphate esters (OPEs) are a class of alternative replacements for polybrominated diphenyl ethers. In vitro and in vivo studies suggested that OPEs may disrupt the homeostasis of sex steroid hormones. However, human evidence in children and adolescents is limited.

OBJECTIVES

We conducted a cross-sectional analysis of the associations between OPE biomarkers and sex steroid hormones among children (6-11 years) and adolescents (12-19 years) in the U.S. National Health and Nutrition Examination Survey, 2013-2014.

METHODS

Participants aged 6-19 years who had available data on urinary OPE metabolites, serum sex hormones [total testosterone (TT), estradiol (E₂)] and sex hormone binding globulin (SHBG) were included (n = 544). Free androgen index (FAI) calculated as TT divided by SHBG and a ratio of TT to E₂ (TT/E₂) were generated. Five urinary OPE metabolites were examined. A constructed puberty status was defined as either high steroid hormone levels (TT ≥ 50 ng/dL in males and E₂ ≥ 20 pg/ml in females) or onset of menarche. Multiple linear regression and weighted quantile sum (WQS) regression analyses stratified by sex-age and sex-puberty-status groups were conducted to examine the associations of OPE metabolites and its mixture with sex hormone levels.

RESULTS

After adjusting for covariates, dibutyl phosphate (DBUP) and dibutyl phosphate (DPHP) were significantly inversely associated with TT (or FAI) and E₂; DBUP was negatively associated with SHBG; and DPHP was positively associated with SHBG and TT/E₂ in female adolescents. In male adolescents, we observed monotonic negative associations of bis(1,3-dichloro-2-propyl) phosphate (BDCPP), DBUP or DPHP with TT (or FAI) and E₂, and positive associations of BDCPP and DPHP with SHBG. Among adolescents, the OPEs index was negatively associated with TT [WQS beta = -0.29 (95% confidence interval: -0.51, -0.07) in males and -0.15 (-0.28, -0.01) in females ], FAI [-0.46 (-0.71, -0.2) in males and -0.23 (-0.41, -0.05) in females] and E₂ [-0.25 (-0.41, -0.1) in males and -0.33 (-0.59, -0.08) in females], with stronger associations with TT and FAI in males and a slightly stronger association with E₂ in females. In addition, the OPEs index presented a comparable positive association with SHBG in both sexes of adolescents. In contrast, significant associations of individual OPE metabolites or OPEs index with sex hormones were sparse in children. Results by sex-puberty status in single pollutant and WQS regression analyses presented a similar pattern, where most of the significant associations were limited to the pubertal individuals. Of note, stronger inverse associations of the OPEs index with TT and FAI remained in pubertal boys. But the association between the OPEs index and E₂ was non-significant in pubertal girls, and only in pubertal boys did the OPEs index show a significant and stronger inverse association with E₂.

CONCLUSIONS

Exposure to OPEs, either individually or as a mixture, was associated with decreased levels of certain sex steroid hormones (TT, FAI, and E₂) and increased levels of SHBG in adolescents or pubertal individuals, with the associations presenting somewhat sex-dependent pattern. However, there is little evidence of the significant associations in children or prepubescent ones. Given the cross-sectional nature of the analysis, our findings need further confirmation.

Quantification of Dehydroepiandrosterone, 17β-Estradiol, Testosterone, and Their Sulfates in Mouse Tissues by LC-MS/MS

We report a high-performance, liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) assay to quantify without derivatizaton dehyroepiandrosterone (DHEA), 17β-estradiol (E2), testosterone (T), and their sulfates in serum and tissues. This assay functions well with multiple adipose depots, a previously unattained analysis. To delipidate and facilitate recovery, tissues were homogenized in acetonitrile, and the homogenate was frozen. The supernatant was evaporated, resuspended in an aqueous acetate buffer, and extracted with hexane to separate free (unconjugated) from sulfated steroids. Sulfated steroids in the aqueous medium were then hydrolyzed with sulfatase and extracted with hexane. Each extract was analyzed separately. HPLC resolution combined with the sensitivity and specificity of MS/MS allowed quantification of DHEA, E2, and T with 10, 10, and 5 fmol lower limits of quantification and linear ranges to 1 pmol. Application of the method to mouse serum and tissues reveals ranges of DHEA, E2, and T and their sulfates, and tissue-specific differences in steroid profile, especially white versus brown adipose. In addition, marginal decreases of T in all tissues and considerable increases in DHEA in male iWAT and eWAT in response to a high-fat diet further strengthen the inference regarding the role of steroid metabolism in adipogenesis. This assay permits detailed studies of interactions between adiposity and sex steroids in serum and tissues, including adipose.

Biological responses of progestogen metabolites in normal and cancerous human breast

At present, more than 200 progestogen molecules are available, but their biological response is a function of various factors: affinity to progesterone or other receptors, their structure, the target tissues considered, biological response, experimental conditions, dose, method of administration and metabolic transformations. Metabolic transformation is of huge importance because in various biological processes the metabolic product(s) not only control the activity of the maternal hormone but also have an important activity of its own. In this regard, it was observed that the 20-dihydro derivative of the progestogen dydrogesterone (Duphaston®) is significantly more active than the parent compound in inhibiting sulfatase and 17β-hydroxysteroid dehydrogenase in human breast cancer cells. Estrone sulfatase activity is also inhibited by norelgestromin, a norgestimate metabolite. Interesting information was obtained with a similar progestogen, tibolone, which is rapidly metabolized into the active 3α/3β-hydroxy and 4-ene metabolites. All these metabolites can inhibit sulfatase and 17β-hydroxysteroid dehydrogenase and stimulate sulfotransferase in human breast cancer cells. Another attractive aspect is the metabolic transformation of progesterone itself in human breast tissues. In the normal breast progesterone is mainly converted to 4-ene derivatives, whereas in the tumor tissue it is converted mostly to 5α-pregnane derivatives. 20α-Dihydroprogesterone is found mainly in normal breast tissue and possesses antiproliferative properties as well as the ability to act as an anti-aromatase agent. Consequently, this progesterone metabolite could be involved in the control of estradiol production in the normal breast and therefore implicated in one of the multifactorial mechanisms of the breast carcinogenesis process. In conclusion, a better understanding of both natural and synthetic hormone metabolic transformations and their control could potentially provide attractive new therapies for the treatment of hormone-dependent pathologies.

Investigation of aromatase inhibitory activity of metal complexes of 8-hydroxyquinoline and uracil derivatives

PURPOSE

Estrogens play important roles in the pathogenesis and progression of breast cancer as well as estrogen-related diseases. Aromatase is a key enzyme in the rate-limiting step of estrogen production, in which its inhibition is one strategy for controlling estrogen levels to improve prognosis of estrogen-related cancers and diseases. Herein, a series of metal (Mn, Cu, and Ni) complexes of 8-hydroxyquinoline (8HQ) and uracil derivatives (4-9) were investigated for their aromatase inhibitory and cytotoxic activities.

METHODS

The aromatase inhibition assay was performed according to a Gentest™ kit using CYP19 enzyme, wherein ketoconazole and letrozole were used as reference drugs. The cytotoxicity was tested on normal embryonic lung cells (MRC-5) using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

RESULTS

Only Cu complexes (6 and 9) exhibited aromatase inhibitory effect with IC50 0.30 and 1.7 μM, respectively. Cytotoxicity test against MRC-5 cells showed that Mn and Cu complexes (5 and 6), as well as free ligand 8HQ, exhibited activity with IC50 range 0.74-6.27 μM.

CONCLUSION

Cu complexes (6 and 9) were found to act as a novel class of aromatase inhibitor. Our findings suggest that these 8HQ-Cu-uracil complexes are promising agents that could be potentially developed as a selective anticancer agent for breast cancer and other estrogen-related diseases.

Association between body mass index and breast cancer intrinsic subtypes in Japanese women

The purpose of this study was to examine the association between body mass index (BMI) and breast cancer intrinsic subtypes in Japanese women. A more complete understanding of the subtypes of breast cancer may elucidate the mechanisms affecting the etiology and mortality associated with each subtype. Tumor data on 531 invasive breast cancer cases subtyped by estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2 (Her2) status were obtained [luminal A, luminal B, triple-negative (TN) and Her2-type]. Demographics (age at diagnosis, menopausal status and BMI) were collected from medical records. Case-only odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using logistic regression, adjusting for age at diagnosis. Of the 531 cases, 333 (62.7%) were luminal A, 85 (16.0%) were luminal B, 43 (8.1%) were Her2-type and 70 (13.2%) were TN. Compared with luminal A cases, premenopausal TN cases were more likely to be obese (OR, 4.11; 95% CI, 1.10–14.40), while postmenopausal TN cases were more likely to be underweight (OR, 3.14; 95% CI, 1.19–8.01). Premenopausal luminal B cases were likely to be underweight or obese, while luminal B and Her2-type cases were likely to be underweight. In the present study, significant heterogeneity of associations between BMI and tumor subtypes was observed. Breast cancer subtypes may have various etiologies associated with each subtype.

Effect of tibolone and its principal metabolites (3α- and 3β-hydroxy, 3α-sulfate, and 4-ene derivatives) on estrone sulfatase activity in normal and cancerous human breast tissue

BACKGROUND

Tibolone (Org-OD14) is the active substance of Livial®, a synthetic steroid with the structure 7α,17α-17-hydroxy-7-methyl-19-norpregn-5(10)-en-20-yn-3-one, possessing weak tissue-specific estrogenic, progestogenic, and androgenic properties, used to treat menopausal complaints. After oral administration, tibolone is extensively metabolized into the 3α-(Org-4904) and 3β-(Org-30126) hydroxy derivatives with estrogenic properties, its 4-ene (Org-OM38) isomer with progestogenic/androgenic activities, and the 3α-sulfate (Org-34322) derivative, a major biologically inactive circulating form. We compared the dose response of tibolone and its metabolites on estrone sulfatase activity [conversion of estrone sulfate (E1S) to estrone (E1)] in normal and cancerous human breast tissues.

MATERIALS AND METHODS

Tissue minces were incubated with physiological concentrations of [3H]-E1S (5×10-9M) alone or in the presence of tibolone and its metabolites (concentration range: 5×10-7to 5×10-5M) for 4 h. Tritiated E1, estradiol (E2), and E1S were separated and evaluated quantitatively by thin-layer chromatography.

RESULTS

The sulfatase activity was significantly higher in cancerous breast but strongly inhibited by tibolone and the different metabolites, whereas 3α- and 3β-hydroxy derivatives were the most potent inhibitors.

CONCLUSION

This very significant inhibitory effect of tibolone and its principal metabolites on the enzyme involved in E2biosynthesis in the human breast provides interesting perspectives to study the biological responses of these compounds in trials with breast cancer patients.

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.

Design and synthesis of substrate mimetics based on an indole scaffold: potential inhibitors of 17β-HSD type 1

BACKGROUND

Human 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1) acts at a pre-receptor level. It catalyzes NADPH-dependent reduction of the weak estrogen estrone into the most potent estrogen estradiol, which exerts its proliferative effects via estrogen receptors. Overexpression of 17β-HSD1 in estrogen-responsive tissues is related to the development of hormone-dependent diseases, such as breast cancer and endometriosis. 17β-HSD1 thus represents an attractive target for development of new drugs.

METHODS

We designed and synthesized a series of 3-, 5- and 6-phenyl indole derivatives as mimetics of the steroid substrate estrone. All of these compounds were evaluated for inhibition of recombinant human 17β-HSD1 from Escherichia coli, at concentrations of 0.6 μM and 6.0 μM.

RESULTS

Among 14 indole derivatives, compound 9 was an initial hit inhibitor of 17β-HSD1, with moderate inhibition (64% at 6 μM). Molecular docking into the crystal structure of 17β-HSD1 (1A27) revealed that this 5-phenyl indole derivative binds to 17β-HSD1 similarly to co-crystalized E2. Compound 9 forms two H-bonds with 17β-HSD1: one between the indole nitrogen and His222, and the second between the phenolic OH group and catalytic Tyr155.

CONCLUSIONS

The indole scaffold is one of the possible starting points for the design of substrate mimetics of the steroid substrate estrone. Our study shows that these 6- and, especially, 5-phenol indole derivatives can act as moderate inhibitors of 17β-HSD1. Based on inhibition assays and docking simulations, we can infer further improvements of the 5-phenol indole derivatives that might result in better inhibition profiles.

Steroid-converting enzymes in human ovarian carcinomas

Anti-estrogen therapies for treating ovarian carcinoma have had mixed outcomes suggesting some tumors may be estrogen-dependent. We assayed the activity levels of 17beta-hydroxysteroid dehydrogenase (17beta-HSD), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD/3-KSR) and estrone sulfatase in a series of ovarian epithelial carcinomas. 17beta-HSD activity ratios with estradiol (E(2)) and testosterone (T), and inhibition by isoform-specific inhibitors were used to estimate the contributions of 17beta-HSD isoforms. Activity levels were highest for estrone sulfatase, followed, respectively by 17beta-HSD, 3alpha-HSD/3-KSR, and 3beta-HSD. E(2)/T activity ratios varied widely between samples. A 17beta-HSD type 1 inhibition pattern was observed in 23% of the samples and a type 2 pattern in 25%. E(2) formation from estrone sulfate (E(1)S) was detected in 98% (47/48) of the samples. 17beta-HSD type 1, type 2 and type 5 mRNA was detected in matched primary tumor and metastases. Evaluation of 17beta-HSD and sulfatase activity levels, activity ratios and inhibition patterns may help predict tumor response to endocrine therapy.

17Beta-hydroxysteroid dehydrogenase enzymes and breast cancer

Sex steroids play an important role in the development and differentiation in several tissues. Biologically active hormones that are locally converted in endocrine organs in the tissue where they exert their effects without release into extracellular space is a field of endocrinology that has been called intracrinology. In pre-menopausal women the ovary is the main source of estrogens, but in post-menopausal women the estrogen production as main site of synthesis moves to peripheral tissues and almost all of the sex steroids are synthesised from precursors of adrenal origin. In breast cancer 60-80% of the tumors express high levels of oestrogen receptor (ER) alpha which gives estrogen a proliferative effect. Breast tumors tend to have a higher intratumoral estrogen concentration than normal breast tissue and plasma, and in situ synthesis and the metabolism of estrogens is believed to be of great importance for the development and progression of the disease. The activity of estrogen metabolizing enzymes in breast are mainly aromatase, estrone sulfatases and 17HSD enzymes. 17HSD1 and 17HSD2 are the family members known to be of main importance in breast cancer. High expression of 17HSD1 has been associated to poor prognosis in breast cancer and late relapse among patients with ER-positive tumors. One of the mechanisms behind high 17HSD1 expression is gene amplification. Low or absent expression of 17HSD2 is associated to decreased survival in ER-positive breast cancer. 17HSD14 is one of the latest discovered 17HSD enzymes, transfection of 17HSD14 in human breast cancer cells significantly decreased the levels of estradiol in the culture medium. Low expression of 17HSD14 mRNA expression in breast cancer was correlated to decreased survival. The understanding of intratumoral synthesis of sex steroids in breast cancer is crucial to understand the disease both in pre- and post-menopausal women. Further studies are desirable to state the direct role of these enzymes in breast cancer and which patients that may benefit from new therapeutic strategies targeting 17HSD enzymes. The new inhibitors targeting 17HSD1 have shown promising results in pre-clinical studies to have clinical potential in the future.

Trichostatin A down-regulates CYP19 transcript and protein levels in MCF-7 breast cancer cells

Epidemiological and experimental evidence implicates estrogens in the etiology and progression of breast cancer. The biosynthesis of estrogens from androgens is catalyzed by an enzymatic complex designated as aromatase (CYP19). Using quantitative real-time PCR and Western blot analysis, we demonstrated that trichostatin A (TSA) histone deacetylase inhibitor significantly reduced CYP19 transcript and protein contents in MCF-7 breast cancer cells. We also found that TSA lowered CYP19 transcript stability and significantly decreased the transcript's half-life from approximately 6h to 3.5h. Our results from experiments with a protein biosynthesis inhibitor suggest the involvement of an RNase and/or mRNA stabilization protein in CYP19 transcript stabilization. Since malignant tissue aromatase is a significant estrogen producer involved in breast tumor progression, our findings may have clinical implication.

Intracrinology of estrogens and androgens in breast carcinoma

Intratumoral metabolism and synthesis of biologically active steroids such as estradiol and 5alpha-dihydrotestosterone as a result of interactions of various enzymes are considered to play very important roles in the pathogenesis and development of hormone-dependent breast carcinoma. Among these enzymes involved in estrogen metabolism, intratumoral aromatase play an important role in converting androgens to estrogens in situ from serum and serving as the source of estrogens, especially in postmenopausal patients with breast carcinoma. However, other enzymes such as 17beta-hydroxysteroid dehydrogenase (17beta-HSD) isozymes, estrogen sulfatase (STS), and estrogen sulfotransferase, which contribute to in situ availability of biologically active estrogens, also play pivotal roles in this intratumoral estrogen production above. Androgen action on human breast carcinoma has not been well-studied but are considered important not only in hormonal regulation but also other biological features of carcinoma cells. Intracrine mechanisms also play important roles in androgen actions on human breast carcinoma cells. Among the enzymes involved in biologically active androgen metabolism and/or synthesis, both 17beta-hydroxysteroid dehydrogenase type 5 (17betaHSD5; conversion from circulating androstenedione to testosterone) and 5alpha-reductase (5alphaRed; reduction of testosterone to DHT (5alpha-dihydrotestosterone) were expressed in breast carcinoma tissues, and in situ production of DHT has been proposed in human breast cancer tissues. However, intracrine mechanisms of androgens as well as their biological or clinical significance in the patients with breast cancer have not been fully elucidated in contrast to those in estrogens.

Androgens act synergistically to enhance estrogen-induced upregulation of human tissue kallikreins 10, 11, and 14 in breast cancer cells via a membrane bound androgen receptor

The regulation of gene expression by steroid hormones plays an important role in the normal development and function of many organs, as well as in the pathogenesis of endocrine-related cancers, especially breast cancer. However, clinical data suggest that combined testosterone and estrogen treatments on post-menopausal women increase the risk of breast cancer. Experiments have shown that many, if not all kallikreins are under steroid hormone regulation in breast cancer cell lines. Their implication as prognostic and diagnostic markers has also been well-documented. Thus, we investigated the effect of combined hormone stimulation with androgens and 17beta-estradiol on the ductal caricinoma cell line BT474. This cell line has been shown to be sensitive to both, androgens (secreting PSA) and estrogens (secreting a number of kallikreins including KLK10, 11, and KLK14). We found that PSA expression was downregulated upon combined hormone stimulation, confirming reports that estrogen can antagonize and block the activity of the androgen receptor. Upon analysis of estrogen-sensitive kallikreins 10, 11, and 14, all showed to be synergistically enhanced in their expression three- to fourfold, upon joint hormone treatment versus individual hormone stimulation. The enhancement is dependent upon the action of androgens as treatment with the androgen receptor antagonist cyproterone actetate normalized the expression of KLK10, 11, and KLK14 to estrogen-stimulation levels. The synergistic effects between estrogens and androgens on estrogen-sensitive genes may have implications on the role of the kallikreins in associated risk of breast cancer and progression.

The discovery and mechanism of action of letrozole

Because estrogen contributes to the promotion and progression of breast cancer, a greater understanding of the role of estrogen in breast cancer has led to therapeutic strategies targeting estrogen synthesis, the estrogen receptor, and intracellular signaling pathways. The enzyme aromatase catalyses the final step in estrogen biosynthesis and was identified as an attractive target for selective inhibition. Modern third-generation aromatase inhibitors (AIs) effectively block the production of estrogen without exerting effects on other steroidogenic pathways. The discovery of letrozole (Femara^®) achieved the goal of discovering a highly potent and totally selective AI. Letrozole has greater potency than other AIs, including anastrozole, exemestane, formestane, and aminoglutethimide. Moreover, letrozole produces near complete inhibition of aromatase in peripheral tissues and is associated with greater suppression of estrogen than is achieved with other AIs. The potent anti-tumor effects of letrozole were demonstrated in several animal models. Studies with MCF-7Ca xenografts successfully predicted that letrozole would be clinically superior to the previous gold standard tamoxifen and also indicated that it may be more effective than other AIs. An extensive program of randomized clinical trials has demonstrated the clinical benefits of letrozole across the spectrum of hormone-responsive breast cancer in postmenopausal women.

New development in intracrinology of breast carcinoma: therapeutic horizons after aromatase inhibitors

Aromatase inhibitors have become the gold standard of endocrine therapy in postmenopausal patients with estrogen receptor-positive or estrogen-dependent breast carcinoma, replacing tamoxifen. However, it is true that there are some potential problems to be overcome or improved on regarding aromatase inhibitor treatment of breast cancer. This especially includes the presence of the estrogen receptor-positive patients who do not necessarily respond to aromatase inhibitors, may require other modes of endocrine therapy and develop resistance to aromatase inhibitor in their clinical course, and who may also need alternative modes of suppressing intratumoral estrogen signals or other intracellular signal pathways related to tumor progression or development. Intratumoral estrogen production from precursors present in circulation in an 'intracrine' manner is considered to play very important roles in the development and progression of estrogen receptor-positive breast cancer. The great majority of estrone in circulation is present as a sulfated form or estrone sulfate, and steroid sulfatase hydrolyzes circulating estrone sulfate to estrone in various human tissues in situ, which confers potent estrogenic actions. Estrone is subsequently reduced to 17β-estradiol by 17β-hydroxysteroid dehydrogenase type 1. Therefore, these two enzymes also play very important roles in intracrinology of estrogen in breast cancer in addition to intratumoral aromatase, and the potential inhibition of these two enzymes could lead to the development of a new mode of endocrine therapy based on intracrinology, which may overcome some of the problems above in aromatase inhibitor therapy. In this review, the potential advantages and pitfalls or problems associated with the inhibition of these two intratumoral enzymes in breast cancer patients will be discussed.

The aged breast

There is a clear association between the development of breast cancer and increasing age, with 80% of cancers occurring in women more than 50 years of age and one-third in women over 70 years. Following the menopause the breast undergoes involution, with the main changes affecting the terminal ductal lobular unit. There is an increase in oestrogen receptor alpha (ERalpha)-positive cells, a decrease in proliferation but, in comparison to premenopausal breasts, a greater number of ERalpha-proliferating cells. The breast cancers that occur in women >/= 75 years are more likely to be ER-positive, with a low growth rate and limited expression of HER-2 and p53. It is proposed that uneven involution of the breast, the persistence of at-risk lesions, the presence of ERalpha-proliferating cells and local oestrogen metabolism in breast adipose tissue are factors in the development of breast cancers with a well-differentiated phenotype.

New development in intracrinology of breast carcinoma

Intratumoral metabolism and synthesis of estrogens as a result of the interactions of various enzymes are considered to play very important roles in the pathogenesis and development of hormone dependent breast carcinoma. Among these enzymes, intratumoral aromatase plays as important role converting serum androgens to estrogens in situ, and serves as a source of estrogen, especially in postmenopausal patients with breast carcinoma. However, other enzymes such as the 17beta-hydroxysteroid dehydrogenase (17beta-HSD) isozymes, estrogen sulfatase (STS) and estrogen sulfotransferase, also play pivotal roles in intratumoral estrogen production. The 17beta-hydroxysteroid dehydrogenase (17beta-HSD) isozymes catalyze the interconversion of estradiol (E2) and estrone (E1), and thereby serve to modulate the tissue levels of bioactive E2 in human breast carcinoma. 17Beta-HSD type 1 catalyzes primarily the reduction of estrone (E1) to estradiol (E2), whereas 17beta-HSD type 2 catalyzes primarily the oxidation of E2 to E1. In human breast disease, 17beta-HSD type 1 is expressed in proliferative disease without atypia, atypical ductal hyperplasia, ductal carcinoma in situ and invasive ductal carcinoma. 17Beta-HSD type 2 has not been detected in any of these breast lesions. In addition, 17beta-HSD type 1 coexpression is significantly correlated with estrogen receptor status in invasive ductal carcinoma cases. These results indicate that breast carcinoma can effectively convert E1, produced as a result of in situ aromatization, to E2, a biologically potent estrogen, which exerts estrogenic actions on tumor cells through estrogen receptor, especially the alpha subtype in carcinoma cells. Therefore, inhibiting intratumoral 17beta-HSD type 1 is also considered to contribute to inhibition of cell proliferation by decreasing intratumoral estradiol. Estrogen sulfotransferase (EST; SULT 1E1 or STE gene) sulfonates estrogens to inactive estrogen sulfates, while steroid sulfatase (STS) hydrolyzes estrone sulfate (E1-S) to estrone. EST immunoreactivity was recently demonstrated to be significantly associated with a decreased risk of recurrence or improved prognosis by both uni- and multivariate analyses. STS immunoreactivity was significantly associated with an increased risk of recurrence by univariate analysis. These findings also suggest that EST and STS plays important roles in regulation of in situ estrogen production, and EST especially is a potent prognostic factor in human breast carcinoma. Therefore, the inhibition of intratumoral STS might also serve as an endocrine therapy in postmenopausal patients. It is also important to note that the status of intratumoral aromatase, 17beta-HSD type 1, EST and STS in human breast cancer tissues is variable and not necessarily correlated with each other, which suggests different potential sources of intratumoral estrogens among individual patients with breast cancer. These findings indicate that there are patients who could benefit more from inhibition of these intratumoral enzymes rather than aromatase inhibition as an endocrine therapy. Therefore, it will become very important to examine the intratumoral levels of 17beta-HSD type 1 and STS in the resected specimens of human breast carcinoma as potential targets of novel endocrine therapy in the near future.

Mammalian lignans and genistein decrease the activities of aromatase and 17beta-hydroxysteroid dehydrogenase in MCF-7 cells

Estrogen plays a major role in breast cancer development and progression. Breast tissue and cell lines contain the necessary enzymes for estrogen synthesis, including aromatase and 17beta-hydroxysteroid dehydrogenase (17beta-HSD). These enzymes can influence tissue exposure to estrogen and therefore have become targets for breast cancer treatment and prevention. This study determined whether the isoflavone genistein (GEN) and the mammalian lignans enterolactone (EL) and enterodiol (ED) would inhibit the activity of aromatase and 17beta-HSD type 1 in MCF-7 cancer cells, thereby decreasing the amount of estradiol (E2) produced and consequently cell proliferation. Results showed that 10 microM EL, ED and GEN significantly decreased the amount of estrone (E1) produced via the aromatase pathway by 37%, 81% and 70%, respectively. Regarding 17beta-HSD type 1, 50 microM EL and GEN maximally inhibited E2 production by 84% and 59%, respectively. The reduction in E1 and E2 production by EL and the reduction in E2 production by GEN were significantly related to a reduction in MCF-7 cell proliferation. 4-Hydroxyandrostene-3,17-dione (50 microM) did not inhibit aromatase but inhibited the conversion of E1 to E2 by 78%, suggesting that it is a 17beta-HSD type 1 inhibitor. In conclusion, modulation of local E2 synthesis is one potential mechanism through which ED, EL and GEN may protect against breast cancer.

Mammary steroid metabolizing enzymes in relation to hyperplasia and tumorigenesis in the dog

Progesterone and estradiol play a crucial role in the control of mammary gland proliferation and tumour formation in the dog. However, little is known whether steroid metabolizing enzymes are present within the canine mammary gland that may play a modulating role in the bioavailability of progesterone and estrogen. In this study we investigated the expression of the steroid metabolizing enzymes 5alpha-reductase (type I and type II) and aromatase in relation to hyperplasia or tumorigenesis in the canine mammary tissue. The relative mRNA concentrations were examined by a semi-quantitative reverse-transcriptase PCR analysis (RT-PCR). In addition the affinity of dihydroprogesterone (5alpha-reduced metabolite of progesterone) for canine progesterone receptors was investigated. Quantification of the RT-PCR products revealed that in mammary tumours a significantly higher expression of aromatase is present in comparison to normal mammary tissue. Furthermore, significant decrease in expression of both aromatase and 5alpha-reductase type II enzymes was found in hyperplasic mammary tissue compared to tumours. The changes in expression of type II 5alpha-reductase and aromatase were highly correlated. 5alpha-Reduction of progesterone to dihydroprogesterone resulted in a six-fold less affinity for the canine progesterone receptor. It is concluded that hyperplasia is associated with a decreased expression of type II 5alpha-reductase and aromatase enzymes, whereas in tumours the opposite situation is found.

Skeletal changes in transgenic male mice expressing human cytochrome p450 aromatase

In this study, we showed that overexpressing P450 aromatase in male mice can increase bone mass and strengthen the tibia. Probably as a result of the action of products of local estrogen biosynthesis at different stages of life, the increased bone mass in young mice was induced by decreased bone turnover, but in aged animals, it was induced by increased bone formation.

INTRODUCTION

To understand the skeletal responses to the testosterone/estrogen balance, especially to excess estrogen produced by extragonadal biosynthesis, we investigated the bone changes in transgenic mice overexpressing human aromatase.

MATERIALS AND METHODS

Sixty-one young (40 days) and 25 aged (9 months) transgenic and wildtype (WT) mice were used. Bone samples were analyzed using pQCT, histomorphometry, and mechanical testing. Concentrations of testosterone (T) and estradiol (E2) were measured in serum and testicular interstitial fluid.

RESULTS AND CONCLUSIONS

Young P450 aromatase-positive (AROM+) mice had much higher trabecular BMD in the proximal tibia than WT mice, and the tissue area was significantly smaller in the former. Histomorphometric data further showed that the longitudinal growth rate of the tibia was decreased in AROM+ mice, and the bone formation rate (BFR) was decreased in trabecular bone and periosteum. All the changes were more striking in males than in females. Aged male AROM+ mice showed similar changes in trabecular bone as young animals, but their BFR was obviously increased. Another dramatic change was in the tibias of aged AROM+ mice: length was shorter (-23.2%), whereas ash weight was much heavier (+24.0%), and bending strength was markedly higher (+21.2%) compared with WT mice. The concentration of T was decreased in both serum and testicular interstitial fluid in young AROM+ mice versus WT animals; E2 levels were increased only in the testes of young AROM+ mice. However, in aged AROM+ mice, the levels of T and E2 were highly increased in both serum and testis versus WT animals. These results are in agreement with the suggestion that enhanced production of estrogen from testosterone in the peripheral tissues as a result of aromatase action can affect skeletal growth and strengthen bone in males. The results also suggest a marked difference in response between femur and tibia.

Use of letrozole as a chemopreventive agent in aromatase overexpressing transgenic mice

Our recent studies have shown that overexpression of aromatase results in increased tissue estrogenic activity and induction of hyperplastic and dysplastic lesions in mammary glands, and gynecomastia and testicular cancer in male aromatase transgenic mice. Our studies also have shown that aromatase overexpression-induced changes in mammary glands can be abrogated with very low concentrations of letrozole, an aromatase inhibitor without any effect on normal physiology. In the present study, we have examined the effect of prior low dose letrozole treatment on pregnancy and lactation. We have also investigated the effect of low dose letrozole treatment on subsequent mammary growth and biochemical changes in these animals. There was no change in the litter size, birth weight and no visible birth defects in letrozole-treated animals. Although, there was an insignificant increase in mammary growth in aged animals after 6 weeks of letrozole treatment, the levels of expression of estrogen receptor, progesterone receptor and genes involved in cell cycle and cell proliferation remained low compared to control untreated animals. These observations indicate that aromatase inhibitors such as letrozole can be used as chemopreventive agents without effecting normal physiology in aromatase transgenic mice.

Norelgestromin as selective estrogen enzyme modulator in human breast cancer cell lines. Effect on sulfatase activity in comparison to medroxyprogesterone acetate

Human breast cancer tissue contains enzymes (estrone sulfatase, 17beta-hydroxysteroid dehydrogenase, aromatase) involved in the last steps of estradiol (E(2)) formation. In this tissue, E(2) can be synthesized by two main pathways: (1) sulfatase-transforms estrogen sulfates into bioactive E(2), and the (2) aromatase-converts androgens into estrogens. 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. In the present study, we demonstrated in T-47D and MCF-7 human breast cancer cells that norelgestromin (NGMN) (a metabolite of norgestimate) is a potent inhibitory agent of the estrone sulfatase activity. After 24h incubation of physiological concentrations of E(1)S (5 x 10(-9)mol/l) the inhibitory effect of NGMN at concentrations of 5 x 10(-9), 5 x 10(-7) and 5 x 10(-5)mol/l was 43+/-7, 74+/-4 and 97+/-2%, respectively, in T-47D cells; 25+/-4, 57+/-5 and 96+/-2% respectively, in MCF-7 cells. Comparative studies using medroxyprogesterone acetate (MPA) showed that this progestin also has an inhibitory effect on sulfatase activity, but significantly less intense than that of NGMN. The inhibition for MPA at concentrations of 5 x 10(-9), 5 x 10(-7) and 5 x 10(-5)mol/l was 31+/-5, 47+/-3 and 61+/-3%, respectively, for T-47D cells; 6+/-3, 20+/-3 and 63+/-4%, respectively, for MCF-7 cells. In conclusion, the present data show that NGMN is a very potent inhibitory agent for sulfatase activity in the hormone-dependent breast cancer cells, resulting in decreased tissue concentration of E(2). The clinical significance of this finding remains to be elucidated.

Aromatase overexpression transgenic mice model: cell type specific expression and use of letrozole to abrogate mammary hyperplasia without affecting normal physiology

Our recent studies have shown that overexpression of aromatase results in increased tissue estrogenic activity and induction of hyperplastic and dysplastic lesions in female mammary glands and gynecomastia and testicular cancer in male aromatase transgenic mice. Both aromatase mRNA and protein are overexpressed in transgenic mammary glands and its expression is not limited to epithelial cells. However, it is more in epithelial than in stromal cells. Our results also indicate aromatase overexpression-induced changes in mammary glands can be abrogated with very low concentrations of the aromatase inhibitor, letrozole. Low concentration of letrozole had no effect on normal physiology as indicated by no significant change in the circulating levels of estradiol and follicle stimulating hormone as well as no change in estrogen responsive genes such as the progesterone receptor and lactoferrin in the uterine tissue. These observations indicate that the expression of aromatase in both epithelial and stromal cells can influence the complex interactions of biochemical pathways leading to mammary carcinogenesis and that the aromatase inhibitor, letrozole can be used as chemopreventive agents without affecting normal physiology.

Paradoxical effect of estradiol: it can block its own bioformation in human breast cancer cells

The great majority of breast cancers are in their early stage hormone-dependent and it is well accepted that estradiol (E(2)) plays an important role in the genesis and evolution of this tumor. Human breast cancer tissues contain all the enzymes: estrone sulfatase, 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD), aromatase, involved in the last steps of E(2) bioformation in this tissue. Quantitative data show that the 'sulfatase pathway', which transforms estrogen sulfates into the bioactive unconjugated E(2), is 100-500 times higher than the 'aromatase pathway' which converts androgens into estrogens. In this paper we explore the effect of E(2) on the sulfatase activity using two hormone-dependent human breast cancer cells: MCF-7 and T-47D. The action of E(2) on the sulfatase activity was evaluated by the conversion of estrone sulfate (E(1)S) into E(2). The cells were incubated in Minimal Essential Medium (MEM) containing 5% steroid-depleted fetal calf serum and incubated with physiological concentrations of [(3)H]E(1)S (5 x 10(-9) M) alone (control) or in the presence of E(2) (5 x 10(-10) to 5 x 10(-5) M) for 24 h at 37 degrees C. It was found that E(2) is a potent inhibitory agent of the estrone sulfatase activity in both cell lines. A low concentration of E(2): 5 x 10(-9) M decreases the sulfatase activity by 67% in MCF-7 cells and 57% in T-47D cells. More than 80% of the decrease in the formation of E(2) was obtained with the dose of 5 x 10(-7) M in both cell lines. It is concluded that this paradoxical effect of E(2) 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. Preliminary results are indicated in the Proceedings of the 14th International Symposium of the Journal of Steroid Biochemistry & Molecular Biology (Quebec, Canada, 24-27 June 2000) [J. Steroid Biochem. Molec. Biol. 76 (2001) 95-104](1) and presented at the 83rd Annual Meeting of the Endocrine Society (Denver, USA, 20-23 June 2001 (abstract no. P2-615).

17-beta-hydroxysteroid dehydrogenase in human breast and endometrial carcinoma. A new development in intracrinology

Intratumoral metabolism and synthesis of estrogens are considered to play very important roles in the pathogenesis and development of various sex steroid-dependent neoplasms including breast and endometrial carcinoma. 17 beta-Hydroxysteroid dehydrogenase (17 beta-HSD) isozymes catalyze the interconversion of estradiol (E(2)) and estrone (E(1)), and thereby serve to modulate the tissue levels of bioactive E(2). 17 beta-HSD type 1 primarily catalyzes the reduction of E(1) to E(2), whereas 17 beta-HSD type 2 primarily catalyzes the oxidation of E(2) to E(1). In the human breast and its disorders, 17 beta-HSD type 1 is expressed in proliferative diseases without atypia, atypical ductal hyperplasia, ductal carcinoma in situ and invasive ductal carcinoma. 17 beta-HSD type 2 is not detected in any of the lesions. In addition, 17 beta-HSD type 1 coexpression is significantly correlated with estrogen receptor status in invasive ductal carcinoma cases. These results indicate that breast carcinoma can effectively convert E(1), produced as a result of in situ aromatization, to E(2), a biologically potent estrogen, and exerts estrogenic actions on tumor cells through the estrogen receptor. On the other hand, in the human endometrium, 17 beta-HSD type 2 is expressed, but not 17 beta-HSD type 1. 17 beta-HSD type 2 is expressed in the secretory phase but not in any proliferative phase in the endometrial mucosa. The enzyme is expressed in 75% of endometrial hyperplasias and 37% of carcinoma cases. In endometrial carcinoma cases, a significant inverse correlation has been detected between 17 beta-HSD type 2 immunoreactivity and age (p < 0.02). These results indicate that oxidation of E(2) to E(1) is dominant in endometrial carcinoma, 17 beta-HSD types 1 and 2 play an important role in the regulation of in situ estrogen production in breast and endometrial carcinoma.

The selective estrogen enzyme modulator (SEEM) in breast cancer

Human breast cancer tissue contains all the enzymes (estrone sulfatase, 17beta-hydroxysteroid dehydrogenase, aromatase) involved in the last steps of estradiol biosynthesis. This tissue also contains sulfotransferase for the formation of the biologically inactive estrogen sulfates. In the last years, it was demonstrated that various progestins (promegestone, nomegestrol acetate, medrogestone), as well as tibolone and its metabolites are potent inhibitors of sulfatase and 17beta-hydroxysteroid dehydrogenase activities. It was also 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, will provide a new possibility in the treatment of this disease.

Estrone sulfatase versus estrone sulfotransferase in human breast cancer: potential clinical applications

Estrone sulfate (E1S) is concentrated in high levels in human breast cancer tissue. The values are particularly high in postmenopausal women and many times those circulating in the plasma. Also, the tissular concentration of this conjugate are significantly higher in tumoural tissue than in the area of the breast considered as normal. The enzyme which hydrolyzes E1S: sulfatase, as well as the enzyme which biosynthesises this conjugate: sulfotransferase, are present in significant concentrations in breast cancer tissue. Consequently, E1S is a balance between the activities of the two enzymes. As breast cancer tissue has all the enzymes necessary for the synthesis of estradiol (E2), and the formation of E2 from E1S 'via sulfatase' is the main pathway, it was very attractive to explore inhibitory agents of this enzyme. It was observed that different substances including antiestrogens (4-hydroxytamoxifen, ICI 164,384) and various progestins (promegestone, nomegestrol acetate, medrogestone) as well as Org OD14 (tibolone) can block the sulfatase activity. In addition, it was demonstrated that different progestins (medrogestone, nomegestrol acetate, TX-525) and org OD14 can stimulate the sulfotransferase activity for the formation of the biologically inactive E1S. It is concluded that the inhibition of sulfatase and the stimulation of sulfotransferase activity can open interesting possibilities to explore these effects in patients with breast cancer.

Intratumoral aromatase in human breast, endometrial, and ovarian malignancies

In human estrogen-dependent neoplasms such as breast, endometrioid endometrial, and surface epithelial-stromal ovarian carcinomas, intratumoral aromatase is considered to play important roles in converting circulating androgens derived from adrenal cortex and/or ovary to estrogens, possibly in association with 17 beta-HSD type 1 and estrogen sulfatase. Analysis of intratumoral aromatase in these estrogen-dependent neoplasms is important not only in understanding the development and biological behavior of these tumors, but also in the clinical management of these patients, because suppression of intratumoral aromatase by newly developed aromatase inhibitors may provide new potentials in endocrine therapy of these patients.

From Endocrinology to Intracrinology

Recently, in situ formation of active sex steroids at the sites of their actions from biologically inactive precursors in the circulation have been demonstrated to play very important roles in sex steroid-dependent neoplasms. These tissues in which the conversion occurs are designated as intracrine tissues and their mechanisms of actions can be designated as intracrinology in contrast to endocrinology. Aromatase, which converts serum androgens to estrone, and 17B-hydroxysteroid dehydrogenase I, which is involved primarily in the conversion of estrone to estradiol, are two major enzymes which function in the in situ formation of biologically active estrogens from circulatory androgens. In human estrogen-dependent neoplasms, including breast, endometrioid endometrial, and common epithelial ovarian carcinoma, we recently demonstrated overexpression of aromatase, especially in stromal cells at sites of frank invasion possibly under a new promoter usage and that of 17B-hydroxysteroid dehydrogenase I in these carcinoma cells. These estrogen-dependent carcinomas are considered to have a common characteristic in estrogen metabolism (i.e., the expression of aromatase in the stromal cells and of 17B-hydroxysteroid dehydrogenase I in the epithelial cells). With these in situ mechanisms of generating biologically active estrogens from circulating androgens, that is, "intracrine manner," these estrogen-dependent neoplasms can exert estrogenic actions on carcinoma cells despite low circulating serum estrogen levels, as observed in postmenopausal women. Evaluation of intracrine mechanisms can provide new insights into various estrogen-related biological phenomena in humans.

Aromatase in human bone tissue

Peripheral aromatization of androgens exert estrogenic actions in many tissues. Recently in situ production of estrogens by aromatase was detected in human bone and cultured osteoblasts and has been proposed to participate in the maintenance of bone mass. We examined aromatase expression by immunohistochemistry and mRNA in situ hybridization in 16 cases of tibia (female 2 male, 14 female, 62 +/- 5.2 years old) and quantified the level of aromatase mRNA in 28 cases of rib, femur, and lumbar vertebrae (16 male, 12 female, 58.0 +/- 11.3 years old) by reverse transcriptase-polymerase chain reaction (RT-PCR) in order to study whether or not and in which cell types aromatase was expressed in human bone tissues. We also studied alternative use of multiple exons 1 of its gene and immunolocalization of type I 17 beta-hydroxysteroid dehydrogenase (HSD), which converts estrone produced by aromatase to estradiol. Strong aromatase immunoreactivity and mRNA hybridization as well as type I 17 beta-HSD immunoreactivity were detected in lining cells, osteoblasts, chondrocytes of articular cartilage, and adipocytes adjacent to bone trabeculae in all the cases examined. Amounts of aromatase mRNA varied greatly among the subjects (11.25 +/- 9.77, 0.61-42.84 attomol/ng of total RNA). The amount of aromatase expression was not correlated with age or gender of the subjects but positively correlated with the degree of osteroporotic changes evaluated by radiological findings of lumbar vertebrae. Analysis of multiple exons 1 revealed that 1b or fibroblast type was predominantly (23/26) utilized as a promoter of aromatase gene expression. These results demonstrated that aromatase is expressed widely in human bone tissue and may play important roles in maintenance of human bone tissue.

Effect of nomegestrol acetate on estrone-sulfatase and 17beta-hydroxysteroid dehydrogenase activities in human breast cancer cells

It is well recognized that estradiol (E2) is one of the most important hormones supporting the growth and evolution of breast cancer. Consequently, to block this hormone before it enters the cancer cell or in the cell itself, has been one of the main targets in recent years. In the present study we explored the effect of the progestin, nomegestrol acetate, on the estrone sulfatase and 17beta-hydroxysteroid dehydrogenase (17beta-HSD) activities of MCF-7 and T-47D human breast cancer cells. Using physiological doses of estrone sulfate (E1S: 5 x 10(-9)M), nomegestrol acetate blocked very significantly the conversion of E1S to E2. In the MCF-7 cells, using concentrations of 5 x 10(-6)M and 5 x 10(-5) M of nomegestrol acetate, the decrease of E1S to E2 was, respectively, -43% and -77%. The values were, respectively, -60% and -71% for the T-47D cells. Using E1S at 2 x 10(-6) M and nomegestrol acetate at 10(-5) M, a direct inhibitory effect on the enzyme of -36% and -18% was obtained with the cell homogenate of the MCF-7 and T-47D cells, respectively. In another series of studies, it was observed that after 24 h incubation of a physiological concentration of estrone (E1: 5 x 10(-9)M) this estrogen is converted in a great proportion to E2. Nomegestrol acetate inhibits this transformation by -35% and -85% at 5 x 10(-7)M and 5 x 10(-5)M, respectively in T-47D cells; whereas in the MCF-7 cells the inhibitory effect is only significant, -48%, at 5 x 10(-5)M concentration of nomegestrol acetate. It is concluded that nomegestrol acetate in the hormone-dependent MCF-7 and T-47D breast cancer cells significantly inhibits the estrone sulfatase and 17beta-HSD activities which converts E1S to the biologically active estrogen estradiol. This inhibition provoked by this progestin on the enzymes involved in the biosynthesis of E2 can open new clinical possibilities in breast cancer therapy.

Anti-tumour effect of aromatase inhibitor, CGS16949A, on human breast cancer cells

The growth inhibitory effect of a new non-steroidal aromatase inhibitor, CGS16949A (Fadrozole hydrochloride: [4-(5,6,7,8-tetrahydro-imidazo-[1,5a]-pyridin-5-yl) benzonitrile monohydro chloride]) was studied in human breast cancer cells MCF-7 and T47D. The aromatase activity of MCF-7 was inhibited by CGS16949A in a dose-dependent manner (IC50: 2.8 x 10(-9) M). The cells were incubated for 120 h in phenol red free RPMI 1640 containing 5% stripped foetal calf serum, 10(-8) M testosterone and various concentrations of CGS16949A. Testosterone-induced MCF-7 growth was inhibited by CGS16949A almost completely at the concentrations as low as 10(-9) M, but was not inhibited by antiandrogenic cyproterone acetate (6-chloro-1 beta,2 beta-dihydro-17-hydroxy-3'-H- cyclopropa[1,2]-pregna-1,4,6-triene-3,20-dione acetate: CPA). On the other hand, the growth of T47D stimulated by testosterone was not inhibited by CGS16949A, but was inhibited by CPA. These data suggested that the aromatization of androgens should participate in the growth of MCF-7 and that one of the growth inhibitory mechanisms of CGS16949A should be the inhibition of the intracellular aromatase activity.

Aromatase gene expression in adipose tissue: relationship to breast cancer

Recent studies have established that concentration gradients of aromatase expression occur within the breast, with the highest levels of expression occurring in sites proximal to a tumor. These variations in aromatase expression correlate with regional differences in the relative proportions of the histologic components of breast adipose tissue, in particular adipocytes and stromal cells, since regions containing the highest numbers of stromal cells are the sites of elevated aromatase transcript levels. Although the initiating events are unknown, it is proposed that, once neoplastic cells start to replicate, tumor growth will be promoted by locally increased estrogen levels. In turn, growth factors produced by the tumor in response to locally increased estrogen levels may further increase aromatase expression in the surrounding adipose tissue. Thus a positive feed-back loop is established in which locally-produced estrogens and tumor-derived growth factors act by paracrine and autocrine mechanisms to sustain the growth and development of the tumor. Further support for this concept is obtained from the observation that aromatase expression in breast adipose is regulated by enhancer elements that appear to respond positively to growth factors, in contrast to expression in granulosa cells, which is inhibited by growth factors.

Immunolocalization of aromatase and other steroidogenic enzymes in human breast disorders

Numerous studies have shown that human breast cancer tissue has the potential to synthesize estrogen through aromatization, which may act as a local growth factor of hormone-dependent cancer cells. This study was performed to localize the site of aromatization in human breast disorders by immunohistochemistry and correlate the findings with steroid receptors, clinicopathological findings, and other steroidogenic enzymes. Specimens from 60 cases of breast disorders, including 33 cases of breast cancer and 27 cases of benign proliferative disorders, were studied immunohistochemically for aromatase. In the carcinoma cases estrogen receptor (ER) and progesterone receptor (PgR) status was determined by enzyme immunoassay and immunohistochemistry, and other steroidogenic enzymes, including P450scc (side-chain cleavage), 3 beta HSD (hydroxysteroid dehydrogenase), and P450c17, were immunolocalized. Aromatase was immunolocalized in interstitial cells and adipocytes as well as other cells in both benign and malignant breast tissues. However, strong immunoreactivity was observed in adipocytes adjacent to carcinoma in all carcinoma cases and in interstitial or stromal cells around carcinomatous glands in 20 carcinoma cases. Intratumoral staining for aromatase did not correlate significantly with age, clinical stage, histopathological type, lymph nodes metastasis, or ER and PgR status. P450scc and 3 beta HSD were focally observed in 18 and 12 cases of carcinoma, respectively, but P450c17 was never observed. Aromatase expression in stromal or interstitial cells, including adipocytes, in breast cancer may be induced by carcinoma cells and locally synthesized estrogens could function as paracrine hormones. Intratumoral aromatase in human breast neoplasms correlated with malignant phenotypes but not with ER status or prognostic parameters, suggesting that other synthetic systems probably generate any biologically significant locally synthesized estrogens in hormone-dependent breast malignancy.

Breast cancer and expression of aromatase in breast adipose tissue

Extraglandular conversion of C19 steroids to estrogens takes place primarily in the stromal cell component of adipose tissue and is catalyzed by an enzyme complex comprising aromatase cytochrome P450 (P450arom; the product of the CYP19 gene) together with the flavoprotein NADPH-cytochrome P450 reductase. It has been proposed that increased local aromatase activity in breast adipose tissue may influence the growth o f breast carcinomas. Using competitive polymerase chain reaction following reverse transcription (RT-PCR), we quantified P450arom transcripts in breast adipose tissue from mastectomy specimens. In 10 of 15 patients, the highest transcript levels were found in the quadrant where the tumor was located. We also found the highest proportions of adipose stromal cells versus adipocytes in these quadrants. These findings suggest that regional differences in the relative proportions o f these histologic components give rise to local elevated concentrations of estrogens. Although the initiating events are not known, once a neoplastic change has occurred, tumor growth may be promoted by these locally increased estrogen levels. Our data regarding hormonally regulated use of tissue-specific promoters for CYP19 gene transcription suggest preferential utilization of certain upstream regulatory regions of the gene in breast adipose tissue, resulting in increased expression of aromatase.

Lack of evidence for aromatase expression in human ovarian epithelial carcinoma

It is controversial whether ovarian epithelial carcinoma possesses steroidogenic enzymes. We investigated aromatase expression in ovarian epithelial carcinoma, and compared it with the normal ovary and placenta. Samples were obtained from an ovarian carcinoma cell line SK-OV-3, ovarian tumour tissues from four patients with epithelial carcinoma and one patient with dysgerminoma. Aromatase enzymatic activity was measured in microsome fractions by quantitating 3H2O released from [1-3H] androstenedione and [3H]oestrone converted from [1,2,6,7-3H] androstenedione. Aromatase messenger ribonucleic acid (mRNA) was determined by reverse transcription-polymerase chain reaction (RT-PCR) using oligonucleotide primers synthesized according to the published human aromatase gene sequence. No aromatase activity was detected in either of two mucinous cystadenocarcinoma specimens or in SK-OV-3 cells, while aromatization proceeded with apparent Michaelis-Menten kinetics in the normal ovaries and placentas. The apparent Km value was 200 nmol/L for the ovary. Aromatase mRNA was detected in dysgerminoma, and the normal ovary and placenta, but not in any of three mucinous cystadenocarcinoma specimens, one serous cystadenocarcinoma specimen and SK-OV-3 cells. These results for both enzyme activity and gene expression suggest that the human ovarian epithelial carcinoma lacks aromatase. The demonstration of absence of aromatase gene expression raises the possibility that aromatase activity in ovaries bearing epithelial carcinoma may be associated with hyperplastic stromal rather than tumour cells.

Regulation of aromatase expression in human tissues

Extraglandular conversion of C19 steroids to estrogens takes place primarily in the stromal cell compartments of adipose tissue and is catalyzed by aromatase cytochrome P450 (P450arom, the product of the CYP19 gene). CYP19 gene expression and aromatase activity in breast adipose stromal cells in culture are subject to complex hormonal regulation, which was recently found to be mediated in part by alternative use of tissue-specific promoters of the CYP19 gene. It has been proposed that increased local aromatase activity in breast adipose tissue may influence the growth of breast carcinomas. Using competitive RT-PCR, we quantified P450arom transcripts in breast adipose tissue from mastectomy specimens. In 10 out of 15 patients, the highest transcript levels were found in the quadrant where the tumor was located. We also found the highest proportions of adipose stromal cells vs. adipocytes in these quadrants. These findings suggest that regional differences in the relative proportions of the histologic components give rise to local elevated concentrations of estrogens. Although the initiating events are not known, once a neoplastic change has occurred, tumor growth may be promoted by these locally increased estrogen levels. We are currently investigating alternative promoter use for CYP19 gene transcription to explain this association. Our results underscore the importance of aromatase inhibitors as effective agents in treatment of hormone-responsive breast cancer, since aromatase inhibitors reduce local aromatase activity as well as blood estradiol levels.