Localization of Estrone Sulfatase in Human Breast Carcinomas

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.

Steroid sulfatase and estrogen sulfotransferase in human carcinomas

Estrogens are closely involved in the development of hormone-dependent carcinomas. Estrone is locally produced from circulating inactive estrone sulfate by steroid sulfatase (STS), while estrone is inversely inactivated into estrone sulfate by estrogen sulfotransferase (EST). Recent studies suggested importance of this STS pathway in various human carcinomas. Therefore, in this review, we summarized recent results of STS and EST in several estrogen-dependent carcinomas. STS and EST expressions were detected in the breast and endometrial carcinomas, and activation of STS pathway due to increment in STS and/or decrement in EST expressions plays important role in their estrogen-dependent growth. STS expression was also reported in the ovarian and prostate carcinomas. STS/EST status was associated with intratumoral estrogen level in the colon carcinoma, and STS-negative/EST-positive colon carcinoma patients had longer survival. Therefore, STS pathway and estrogen actions may play an important role in the development of these carcinomas, and further investigations are required.

Steroid sulfatase inhibitors: promising new tools for breast cancer therapy?

Inhibition of aromatase is currently well-established as the major treatment option of hormone-dependent breast cancer in postmenopausal women. However, despite the effects of aromatase inhibitors in both early and metastatic breast cancer, endocrine resistance may cause relapses of the disease and progression of metastasis. Thus, driven by the success of manipulating the steroidogenic enzyme aromatase, several alternative enzymes involved in steroid synthesis and metabolism have recently been investigated as possible drug targets. One of the most promising targets is the steroid sulfatase (STS) which converts steroid sulfates like estrone sulfate (E1S) and dehydroepiandrosterone sulfate (DHEAS) to estrone (E1) and dehydroepiandrosterone (DHEA), respectively. Estrone and DHEA may thereafter be used for the synthesis of more potent estrogens and androgens that may eventually fuel hormone-sensitive breast cancer cells. The present review summarizes the biology behind steroid sulfatase and its inhibition, the currently available information derived from basic and early clinical trials in breast cancer patients, as well as ongoing research. Article from the Special Issue on Targeted Inhibitors.

Expression of Estrogen Sulfotransferase 1E1 and Steroid Sulfatase in Breast Cancer: A Immunohistochemical Study

It is known that the steroid sulfatase (STS) and the estrogen sulfotransferase (EST1E1) are commonly expressed in human breast carcinomas. STS and EST1E1 combined action could maintain the equilibrium between sulfated (inactive) and unconjugated (active) estrogens, which might have effects on development of hormone dependent breast cancer.

We studied the expression of the STS and EST1E1 in 88 breast carcinomas and 57 adjacent non-malignant tissues by immunohistochemistry. The results were correlated with the tumor expression of estrogen receptor α (ER-α) and β (ER-β), progesterone receptor A (PR-A) and B (PR-B) and the proliferation marker CDC47, the tumoral type and stage and the age at surgery.

STS expression was higher in carcinoma specimens than in adjacent normal tissues, although not to a significant level (p = 0.064) and it was positively associated with CDC47 expression (p < 0.05). These observations support the hypothesis that STS is overexpressed in breast cancer and associated with a worse prognosis.

EST1E1 was observed for the first time in the nuclei of epithelial and tumoral cells. Tumor expression of EST1E1 was positively correlated with ER-β (p < 0.01) and PR-B (p < 0.05), two steroid receptors already associated with an improve prognosis for breast cancer.

Controlling the STS overexpression in carcinomas could be a way to inhibit cancer growth. The significance of the association between EST1E1 and ER-β or PR-B should be further studied since these two receptors are transcription activators and may regulate the expression of protective enzymes like EST1E1.

Intracrinology of sex steroids in ductal carcinoma in situ (DCIS) of human breast: comparison to invasive ductal carcinoma (IDC) and non-neoplastic breast

Sex steroids, including those through intratumoral production in an intracrine manner, play important roles in the development of invasive ductal carcinoma (IDC) of human breast, but biological and/or clinical significance of intratumoral production and metabolism of sex steroids, have remained largely unknown in the ductal carcinoma in situ (DCIS), an important precursor lesion of IDC. We recently examined tissue concentration of estradiol and 5-dihydrotestosterone using liquid chromatography/electrospray tandem mass spectrometry in non-neoplastic breast, DCIS, and IDC tissues. Results of our study suggest that intratumoral concentrations of both estradiol and 5-dihydrotestosterone are increased in DCIS, which is considered due to intratumoral production of these sex steroids. Therefore, both estradiol and 5-dehydrotestosterone are considered to play important roles in the development of DCIS as well as IDC through an intracrine manner. Intratumoral metabolism and synthesis of estrogens and androgens as a result of the interactions of various enzymes are therefore also considered to play important roles in hormone dependent DCIS. Aromatase, which is one of the estrogen synthesis enzymes, plays an important role in intratumoral production of estrogen but other enzymes also play pivotal roles in intratumoral estrogen and androgen productions in human breast carcinoma. Therefore, in this review, we also focused on the importance of key intracrine enzymes such as 17beta-hydroxysteroid dehydrogenases, steroid sulfatase,estrogen sulfotransferase, 5alpha-reductases in both IDC and DCIS.

Aromatase in human breast carcinoma as a key regulator of intratumoral sex steroid concentrations

It is well-known that estrogens are closely involved in the growth of human breast carcinomas, and that the great majority of breast carcinoma express estrogen receptors. Recent studies have demonstrated that estrogens are locally produced and act on the breast carcinoma tissue. Among these pathways, aromatase is a key enzyme for intratumoral production of estrogens in breast carcinomas, and aromatase inhibitors are currently used in the breast carcinoma in postmenopausal women as an estrogen deprivation therapy. This review summarizes the results of recent studies on the expression and regulation of aromatase in breast carcinoma tissues, and discusses the potential biological and/or clinical significance of aromatase. Aromatase is abundantly expressed in various cell types, such as carcinoma cells, intratumoral stromal cells, and adipocytes adjacent to the carcinoma, in breast carcinoma tissues. Further, a key regulator for aromatase expression differed according to cell type. In addition, aromatase suppressed in situ production of bioactive androgen, 5alpha-dihydrotestosterone (DHT), in breast carcinoma. Aromatase inhibitors may thus have additional antiproliferative effects through increasing local DHT concentration with estrogen deprivation.

Human liver-specific organic anion transporter-2 is a potent prognostic factor for human breast carcinoma

Human liver-specific organic anion transporter-2 (LST-2/OATP8/SLCO1B3) has been demonstrated to be expressed in various gastrointestinal carcinomas and also to play pivotal roles in the uptake of a wide variety of both endogenous and exogenous anionic compounds, including bile acids, conjugated steroids and hormones, into hepatocytes in the human liver. However, the biological significance of LST-2 in human carcinomas remains unknown. In the present study, we examined the expression of LST-2 in 102 cases of breast carcinoma using immunohistochemistry and correlated the findings with various clinicopathological parameters in order to examine the possible biological and clinical significance of LST-2. LST-2 immunoreactivity was detected in 51 cases (50.0%); of these 51 positive cases, LST-2 immunoreactivity was inversely correlated with tumor size (P = 0.0289). In addition, LST-2 immunoreactivity was significantly associated with a decreased risk of recurrence and improved prognosis by both univariate (P = 0.02 and P = 0.01) and multivariate (P = 0.03 and P = 0.01) analyses. In the estrogen receptor-positive groups, the LST-2-positive patients showed good prognoses. Considering that LST-2 transports estrone-3-sulfate, these results suggest that LST-2 overexpression is associated with a hormone-dependent growth mechanism of the breast cancer. The results of our present study demonstrate that LST-2 immunoreactivity is a potent prognostic factor in human breast cancer.

In situ production of sex steroids in human breast carcinoma

It is well known that sex steroids are closely involved in the growth of human breast carcinomas, and the great majority of breast carcinomas express sex steroid receptors. In particular, recent studies have demonstrated that estrogens and androgens are locally produced and act in breast carcinoma tissues without release into plasma. Blockade of intratumoral estrogen production potentially leads to an improvement in the prognosis of invasive breast carcinoma patients, and, therefore, it is important to obtain a better understanding of sex steroid-producing enzymes in breast carcinoma. In this review, we summarize recent studies on tissue concentration of sex steroids and expression of enzymes related to intratumoral production of estrogens [aromatase, steroid sulfatase (STS), and 17beta-hydroxysteroid dehydrogenase type 1 (17betaHSD1)], and androgens (17betaHSD5 and 5alpha-reductase) in invasive and in situ (noninvasive) breast carcinomas, and discuss the significance of intratumoral production of sex steroids in breast carcinoma.

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.

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.

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

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

Estrogen Inhibits Cell Proliferation throughIn situProduction in Human Thymoma

PURPOSE

We showed previously estrogen receptor (ER) alpha as an independent prognostic marker in human thymoma. Estrogen sulfotransferase (EST), steroid sulfatase (STS), 17beta-hydroxysteroid dehydrogenase (17beta-HSD), and aromatase are considered to play important roles in hormone metabolism of estrogen-dependent tumors.

EXPERIMENTAL DESIGN

We examined estrogen production using primary cultures of human thymoma epithelial cells (TEC), intratumoral estradiol (E(2)) concentrations, and status of these enzymes above using immunohistochemistry or semiquantitative reverse transcription-PCR. We then correlated these findings with clinicopathologic variables and/or clinical outcome in 132 patients.

RESULTS

E(2) inhibited cell proliferation via ERalpha in TEC, which synthesized estrone and E(2). Intratumoral E(2) concentrations were inversely correlated with EST, positively correlated with STS or 17beta-HSD type 1, and significantly higher in lower-grade or early-stage thymoma. EST status was positively correlated with tumor size, clinical stage, histologic differentiation, and Ki-67 labeling index and significantly associated with adverse clinical outcome and turned out to be a potent independent prognostic factor. STS and/or 17beta-HSD type 1 status was inversely correlated with Ki-67 labeling index and associated with lower histologic grade or early clinical stages.

CONCLUSIONS

E(2) inhibits proliferation of TEC through ERalpha, which suggests that E(2) may be effective in treatment of thymoma, especially inoperable tumor, possibly through suppressing its cell proliferation activity. EST status is a potent prognostic factor in thymoma through inactivating estrogens. In situ estrogen synthesis through intracrine mechanism therefore may play important roles in tumorigenesis and/or development of thymoma through regulation of cell proliferation in an intracrine manner.

Steroid sulfatase and estrogen sulfotransferase in human endometrial carcinoma

PURPOSE

Intratumoral metabolism and synthesis of estrogens are considered to play important roles in the pathogenesis and/or development of human endometrial carcinoma. Steroid sulfatase hydrolyzes biologically inactive estrogen sulfates to active estrogens, whereas estrogen sulfotransferase sulfonates estrogens to estrogen sulfates. However, the status of steroid sulfatase and/or estrogen sulfotransferase in human endometrial carcinoma has not been examined.

EXPERIMENTAL DESIGN

We first examined the expression of steroid sulfatase and estrogen sulfotransferase in 6 normal endometrium and 76 endometrial carcinoma using immunohistochemistry to elucidate the possible involvement of steroid sulfatase and estrogen sulfotransferase. We then evaluated the enzymatic activity and the semiquantitative analysis of mRNA using reverse transcription-PCR in 21 endometrial carcinomas. We correlated these findings with various clinicopathological parameters including the expression of aromatase, 17beta-hydroxysteroid dehydrogenase type 1 and type 2.

RESULTS

Steroid sulfatase and estrogen sulfotransferase immunoreactivity was detected in 65 of 76 (86%) and 22 of 76 (29%) cases, respectively. Results of immunoreactivity for steroid sulfatase and estrogen sulfotransferase were significantly correlated with those of enzymatic activity and semiquantitative analysis of mRNA. No significant correlations were detected among the expression of the enzymes involved in intratumoral estrogen metabolism. There was a significant correlation between steroid sulfatase/estrogen sulfotransferase ratio and clinical outcomes of the patients. However, there were no significant differences between steroid sulfatase or estrogen sulfotransferase and estrogen receptor, progesterone receptor, Ki67, histologic grade, or clinical outcomes of the patients.

CONCLUSIONS

Results of our study demonstrated that increased steroid sulfatase and decreased estrogen sulfotransferase expression in human endometrial carcinomas may result in increased availability of biologically active estrogens and may be related to estrogen-dependent biological features of carcinoma.

Analysis for Localization of Steroid Sulfatase in Human Tissues

Human steroid sulfatase (STS) is an enzyme that hydrolyzes several sulfated steroids, such as estrone sulfate, dehydroepiandrosterone sulfate, and cholesterol sulfate, and results in the production of active substances. STS has been demonstrated in human breast cancer tissues and is considered to be involved in intratumoral estrogen production. It is very important to analyze the cellular distribution of STS with accuracy in human tissues in order to obtain a better understanding of the biological significance of STS. Therefore, this chapter describes several morphological approaches used to study the localization of STS, including immunohistochemistry, mRNA in situ hybridization, and laser capture microdissection/reverse transcription-polymerase chain reaction, in human tissues.

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

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

Intracrine mechanism of estrogen synthesis in breast cancer

It has been demonstrated that biologically active estrogens are locally produced from circulating inactive steroids in an intracrine mechanism in the breast carcinoma. The in situ production of estrogens is considered to play an important role in the proliferation of breast cancer cells, especially in the postmenopausal women. Therefore, the total blockade of this pathway may lead to an improvement in the prognosis in breast cancer patients due to the inhibition of estrogenic actions. In this review, we describe the recent studies of enzymes related to intracrine mechanism of estrogen synthesis, including aromatase, steroid sulfatase (STS), and 17beta-hydroxysteroid dehydrogenase, in human breast carcinoma tissues, and discuss the biological significance of local production of estrogens in human breast cancer.

Steroid sulfatase and estrogen sulfotransferase in the atherosclerotic human aorta

Various epidemiological studies have demonstrated a relatively low incidence of cardiovascular events in premenopausal women and its marked increment after menopause. In addition, estrogens have been postulated to exert direct anti-atherogenic effects via binding to estrogen receptors in vascular smooth muscle cells (VSMCs). However, not all postmenopausal women develop atherosclerosis despite decreased levels of serum estrogen. Therefore, we believe it is important to examine the status of estrogen metabolism in situ in the human cardiovascular system. Estrone sulfate (E1S) is a major circulating plasma estrogen that is converted into the biologically active estrogen, estrone (E1) by steroid sulfatase (STS). E1 is also sulfated and reverted into E1S by estrogen sulfotransferase (EST). These two enzymes have recently been shown to play important roles in the in situ estrogen actions of estrogen-dependent human tissues and various sex steroid-dependent tumors. STS and EST, however, have not been studied in detail in the human vascular system associated with atherosclerotic changes. In the present study, we evaluated the relative abundance of STS- and EST-immunoreactive protein and mRNA expression in human aorta using immunohistochemistry and reverse transcription followed by quantitative polymerase chain reaction in addition to enzyme activity. STS expression levels were found to be significantly higher in the VSMCs obtained from female aortas with mild atherosclerotic changes than in those with severe atherosclerotic changes and in male aortas regardless of atherosclerotic changes. EST expression levels in the VSMCs of these aortas, however, were significantly higher in female aortas with severe atherosclerotic changes and in male aortas than in female aortas with mild atherosclerotic changes. We believe it is important to examine factors regulating the expression and activity of these estrogen-metabolizing enzymes in the human aorta. Various cytokines have been proposed to function as regulators of these enzymes in other tissues. In the present study, we studied the effects of interleukin (IL)-1beta, known to be produced in human atherosclerotic lesions, on the expression of these enzymes using cultured human VSMCs originally obtained from a female patient. IL-1beta markedly inhibited the expression of STS mRNA and enzyme activity, but stimulated the expression of EST mRNA and enzyme activity. In addition, IL-1beta also reduced E2 production from E1S and E1 in VSMCs. Results from the present study seem to suggest that the expression levels of both STS and EST mRNA and activity may be significantly associated with the degree of atherosclerotic changes in the female aorta, which may be related to cytokines produced in situ, such as IL-1beta, in human atherosclerotic lesions.

Steroid sulfatase and estrogen sulfotransferase in normal human tissue and breast carcinoma

Steroid sulfatase (STS) hydrolyzes inactive estrone sulfate (E1-S) to estrone (E1), while estrogen sulfotransferase (EST; SULT 1E1 or STE gene) sulfonates estrogens to estrogen sulfates. They are considered to play important roles in the regulation of local estrogenic actions in various human tissues, however, their biological significance remains largely unknown. Therefore, we examined the expression of STS and EST in non-pathologic human tissues and breast carcinomas. STS expression was very weak except for the placenta, while EST expression was markedly detected in various tissues examined. In breast carcinoma tissues, STS and EST immunoreactivity was detected in carcinoma cells in 74 and 44% of cases, respectively, and was significantly associated with their mRNA levels and enzymatic activities. STS immunoreactivity was significantly correlated with the tumor size, and an increased risk of recurrence. EST immunoreactivity was inversely correlated with the tumor size or lymph node status. Moreover, EST immunoreactivity was significantly associated with a decreased risk of recurrence or improved prognosis. Our results suggest that EST is involved in protecting various peripheral tissues from excessive estrogenic effects. In the breast carcinoma, STS and EST are suggested to play important roles in the regulation of in situ estrogen production in the breast carcinomas.

Role of steroid sulfatase in local formation of estrogen in post-menopausal breast cancer patients

More than two-thirds of breast cancers occur in post-menopausal women, and depend on the estrogens for their proliferation and survival. For the treatment of estrogen-dependent breast cancers, two major treatment options are now available. One is selective estrogen receptor modulator (SERM) such as Tamoxifen and another is aromatase inhibitor such as Anastrozole, Letrozole and Exemestane, which reduce local in situ formation of estrogens. Although these therapies are clinically active for advanced and early breast cancers, de novo and/or acquired resistance to SERM and/or aromatase inhibitors are also clinical problem. Recent studies suggest that local formation of estrogens in the breast tumors is more important than circulating estrogen in plasma for the growth and survival of estrogen-dependent breast cancer in post-menopausal women. The rationale for the importance of local formation of estrogens is based on the following evidences. Estradiol (E2) levels in breast tumors are equivalent to those of pre-menopausal patients, although plasma E2 levels are 50-fold lower after menopause. E2 concentrations in breast tumors of post-menopausal women are 10-40 times higher than serum level. Biosynthesis of estrogens in breast tumors tissues occurs via two major different routes, one is aromatase pathway and another is steroid-sulfatase (STS) pathway. Whereas many studies has been reported about aromatase inhibitor and its clinical trial results in breast cancer patients, limited information are available regarding to other estrogen regulating enzymes including STS, its role in breast tumors and STS inhibitors. STS is the enzyme that hydrolyses estrone 3-sulfate (E1S) and dehydroepiandrosterone-sulfate (DHEA-S) to their active un-sulfoconjugated forms, thereby stimulating the growth and survival of estrogen-dependent breast tumors. It has been well known that E1S level are much higher than E2 level both in plasma and tumor of post-menopausal patients. Recent reports show that more than 80% of breast tumors are stained with anti-STS antibody and the expression of STS is an independent prognostic factor in breast cancer. Taking these findings into consideration, local formation of estrogens could be partially synthesized from large amount of E1S by STS, which exist in breast cancer. On the other hand, aromatase localizes in stroma and adipocyte surrounding breast cancer. Furthermore, since estrogen formation from E1S and DHEA-S (STS pathway) cannot be blocked by aromatase inhibitors, STS is thought to be a new molecular target for the treatment of estrogen-dependent tumor post-SERM and/or aromatase inhibitors. In this symposium, these recent rationale for the importance of STS in post-menopausal breast cancer patients is reviewed as well as STS inhibitor.

In situ production of estrogens in human breast carcinoma

Recent studies have demonstrated that biologically active estrogens are locally produced from circulating inactive steroids in the estrogen-dependent breast carcinoma. The in situ production of estrogens in the breast carcinoma is considered to play an important role in the proliferation of breast cancer cells, especially in the postmenopausal women. Therefore, the total blockade of this pathway may inhibit estrogenic actions in breast cancer tissues and lead to an improvement in the prognosis in these patients. In this review, we describe the recent studies concerning the expression of enzymes related to intratumoral estrogen production, including aromatase, 17beta-hydroxysteroid dehydrogenase, steroid sulfatase, and estrogen sulfotransferase in human breast carcinoma tissues, and discuss the biological significance of local production of estrogens in human breast cancer.

Systemic distribution of steroid sulfatase and estrogen sulfotransferase in human adult and fetal tissues

Estrogens play a key role in various target tissues. Enzymes involved in the biosynthesis and metabolism of these sex steroids also regulate estrogenic actions in these tissues. Estrone sulfate (E1S) is a major circulating plasma estrogen that is converted into the biologically active estrogen, estrone (E1), by steroid sulfatase (STS). E1 is also sulfated and reverted into E1S by estrogen sulfotransferase (EST). These two enzymes have recently been shown to play important roles in the in situ estrogen actions of various sex steroid-dependent human tumors. However, the distribution of STS and EST in normal adult and fetal human tissues remains largely unknown. Therefore, in this study, in addition to examining the tissue distribution of both STS and EST mRNA in human adult and fetal tissues using RT followed by quantitative PCR, we studied the activity of these enzymes using (3)H-labeled E1/E1S as substrates in the homogenates of various human adult tissues. We also examined the localization of STS and EST protein in human adult and fetal tissues using immunohistochemistry, and that of EST mRNA in the adult kidney using laser dissection microscopy and PCR. STS mRNA, enzyme activity, and immunoreactivity were either absent or detected at very low levels in all adult and fetal tissues examined in this study. EST mRNA expression, however, was detected in all of the tissues examined, except for adult spleen and pancreas. EST enzyme activities were consistent with those of mRNA expression in the great majority of the tissues examined. Marked EST immunoreactivity was detected in hepatocytes, adrenal gland (adult, zona fasciculate to the reticularis; fetus, fetal zone), and epithelial cells of the gastrointestinal tract, smooth muscle cells of the tunica media in aorta, Leydig cells of the testis, and syncytiotrophoblast of the placenta. Patterns of EST immunolocalization were similar between adult and fetal human tissues, but EST immunoreactivity was detected in the urinary tubules of adult kidney, whereas in the fetal kidney, it was localized in the interstitial cells surrounding the urinary tubules. In the adult kidney, the presence of EST mRNA was also confirmed in the cells of urinary tubules using laser dissection microscopy and RT-PCR. Although the number of human tissues available for examination in this study was limited, our results suggest that between the enzymes involved in estrogen activation or inactivation, EST and not STS is the more widely expressed enzyme in various peripheral tissues in humans. We speculate that EST may play an important role in protecting peripheral tissues from possible excessive estrogenic effects.

Involvement of up-regulation of 17beta-hydroxysteroid dehydrogenase type 1 in maintenance of intratumoral high estradiol levels in postmenopausal breast cancers

Estradiol (E2) and estrone (E1) levels as well as mRNA expression levels of aromatase, sulfatase and 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) in breast cancer tissues were studied to elucidate the mechanism involved in the maintenance of the intratumoral high E2 levels in postmenopausal patients with very low serum E2 levels. Intratumoral E2 levels of postmenopausal patients (127.2 +/- 17.5 pg/g) (mean +/- SE) were not significantly different from those of premenopausal patients (110.1 +/- 10.1 pg/g) (p = 0.36). The mRNA expression levels of aromatase and sulfatase, determined by a quantitative real-time PCR, were not significantly different between premenopausal and postmenopausal breast cancers, but 17beta-HSD1 mRNA expression levels were significantly higher in postmenopausal than premenopausal breast cancers (p < 0.05). Intratumoral E2/E1 ratios were significantly higher in postmenopausal than premenopausal breast cancers (p < 0.01). These results demonstrate that the increased conversion from E1 to E2 catalyzed by 17beta-HSD1 may play an important role in the maintenance of the intratumoral high E2 levels in postmenopausal patients.