Estrone sulfate stimulates growth of nitrosomethylurea-induced breast carcinoma in vivo in the rat

Increases in serum estrone sulfate level are associated with increased mammographic density during menopausal hormone therapy

BACKGROUND

Menopausal hormone therapy increases mammographic density. We determined whether increases in serum estrone sulfate (E(1)S) levels during menopausal hormone therapy predict increased mammographic density.

METHODS

We measured percent mammographic density and serum E(1)S levels in 428 participants of the Postmenopausal Estrogen/Progestin Interventions study who were randomly assigned to daily conjugated equine estrogen (CEE) 0.625 mg alone, CEE + daily medroxyprogesterone acetate (MPA) 2.5 mg, CEE + cyclical MPA (10 mg days 1-12 per 28-day cycle), or CEE + cyclical micronized progesterone (10 mg days 1-12). Serum E(1)S levels were determined by RIA. Information about covariates was determined by annual questionnaire. Using linear regression, we determined the association between change in E(1)S level from baseline to 12 months and change in percent mammographic density (by semiquantitative interactive threshold method).

RESULTS

After controlling for baseline mammographic density, age, body mass index, alcohol intake, parity, smoking, ethnicity, physical activity, and age at first pregnancy, mammographic density increased by 1.3% for every 1 ng/mL increase in E(1)S level (P < 0.0001). The association between change in E(1)S level and change in mammographic density differed by treatment group (greater effect in CEE + cyclical MPA group versus CEE group; P = 0.05). After controlling for treatment group, change in the ratio of E(1)S to E(1) was also positively associated with change in mammographic density.

CONCLUSIONS

Increases in serum E(1)S levels during menopausal hormone therapy are associated with increases in mammographic density. The relative contribution of E(1)S and E(1) to stimulation of breast tissue awaits further elucidation.

Estrone sulfate (E1S), a prognosis marker for tumor aggressiveness in prostate cancer (PCa)

Seeking insight into the possible role of estrogens in prostate cancer (PCa) evolution, we assayed serum E2, estrone (E1), and estrone sulfate (E1S) in 349 PCa and 100 benign prostatic hyperplasia (BPH) patients, and in 208 control subjects in the same age range (50-74 years). E1 (pmol/L+/-S.D.) and E1S (nmol/L+/-S.D.) in the PCa and BPH patients (respectively 126.1+/-66.1 and 2.82+/-1.78, and 127.8+/-56.4 and 2.78+/-2.12) were significantly higher than in the controls (113.8+/-47.6 and 2.11+/-0.96). E2 was not significantly different among the PCa, BPH, and control groups. These assays were also carried out in PCa patients after partition by prognosis (PSA, Gleason score (GS), histological stage, and surgical margins (SM)). Significantly higher E1S levels were found in PCa with: PSA>10 ng/L (3.05+/-1.92) versus PSA<or=10 ng/mL (2.60+/-1.55), stage pT3-T4 (2.99+/-1.80) versus pT2 (2.58+/-1.58), and positive (3.26+/-1.95) versus negative margins (2.52+/-1.48). E1 was higher in poor- than in better-prognosis PCa. E2 was significantly higher in PCa with GS>or=4+3 (109.5+/-43.8) versus GS<or=3+4 (100.6+/-36.5) and increased significantly when GS increased from 3+3 to 4+4. Estrogens, especially E1S appeared to be possible markers of PCa progression. Attempting to identify potential sources of E2 in PCa according to prognosis, as well as in BPH, we found a significant correlation coefficient between E1S and E2 (0.266-0.347) in poor-prognosis PCa and no correlation in BPH (0.026) and better-prognosis PCa (0.013-0.104). It is as though during progression of PCa from good to poor prognosis there were a shift in the E1 to E2 metabolic pathway from predominantly oxidative to predominantly reductive.

Commercial cows' milk has uterotrophic activity on the uteri of young ovariectomized rats and immature rats

Cows' milk contains considerable quantities of estrogens, mainly in the form of estrone sulfate (ES). To determine whether the commercial milk has any biologically significant hormonal effects, 2 series of uterotrophic tests were performed, 1 with young ovariectomized rats and the other with sexually immature rats. Thirty-six rats were used for each test. They were divided into 3 groups of 12 animals each, and were kept for 7 days on powdered chow with 1 of 3 drinking solutions: low-fat milk (LFM), artificial milk (AM, negative control), or AM containing ES at 100 ng/ml (positive control). At autopsy, both the wet and blotted uterine weights were measured. The cell heights of uterine epithelia in ovariectomized rats were also determined. The significance of differences among groups was tested by Dunnett's multiple comparisons test. In each test, the weights of the uteri in the LFM group were significantly greater than those of the respective weights in the AM group (p < 0.01). Furthermore, in ovariectomized rats, the uterine epithelial-cell height in the LFM group was significantly greater than that observed in the AM group (p < 0.01). The uterotrophic effect of 100 ng/ml ES solution was greater than that of LFM in immature rats (p < 0.01), whereas the effect of the solution was almost comparable to that of LFM in young ovariectomized rats (p > 0.05). In conclusion, commercially available milk has uterotrophic effects in both young ovariectomized rats and sexually immature rats.

Steroid sulfatase: molecular biology, regulation, and inhibition

Steroid sulfatase (STS) is responsible for the hydrolysis of aryl and alkyl steroid sulfates and therefore has a pivotal role in regulating the formation of biologically active steroids. The enzyme is widely distributed throughout the body, and its action is implicated in physiological processes and pathological conditions. The crystal structure of the enzyme has been resolved, but relatively little is known about what regulates its expression or activity. Research into the control and inhibition of this enzyme has been stimulated by its important role in supporting the growth of hormone-dependent tumors of the breast and prostate. STS is responsible for the hydrolysis of estrone sulfate and dehydroepiandrosterone sulfate to estrone and dehydroepiandrosterone, respectively, both of which can be converted to steroids with estrogenic properties (i.e., estradiol and androstenediol) that can stimulate tumor growth. STS expression is increased in breast tumors and has prognostic significance. The role of STS in supporting tumor growth prompted the development of potent STS inhibitors. Several steroidal and nonsteroidal STS inhibitors are now available, with the irreversible type of inhibitor having a phenol sulfamate ester as its active pharmacophore. One such inhibitor, 667 COUMATE, has now entered a phase I trial in postmenopausal women with breast cancer. The skin is also an important site of STS activity, and deficiency of this enzyme is associated with X-linked ichthyosis. STS may also be involved in regulating part of the immune response and some aspects of cognitive function. The development of potent STS inhibitors will allow investigation of the role of this enzyme in physiological and pathological processes.

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.

Constitutive expression of the steroid sulfatase gene supports the growth of MCF-7 human breast cancer cells in vitro and in vivo

Many human breast tumors are driven by high intratumor concentrations of 17beta-estradiol that appear to be locally synthesized. The role of aromatase is well established, but the possible contribution of the steroid sulfatase (STS), which liberates estrogens from their biologically inactive sulfates, has been inadequately assessed and remains unclear. To evaluate the role of STS further, we transduced estrogen-dependent MCF-7 human breast cancer cells with a retroviral vector directing the constitutive expression of the human STS gene. Gene integration was confirmed by Southern hybridization, production of the appropriately sized messenger RNA by Northern hybridization, and expression of functional protein by metabolism of [(3)H]estrone sulfate to [(3)H]estrone. Maximum velocity estimates of estrone formation are 64.2 pmol estrone/mg protein.h in STS-transduced cells (STS Clone 20), levels comparable to those seen in some human breast tumors. Lower levels of endogenous activity are seen in MCF-7 cells (13.0 pmol estrone/mg protein.h) and in cells transduced with vector lacking the STS gene (Vector 3 cells; 12.0 pmol estrone/mg protein.h). 17beta-Estradiol sulfate induces expression of the progesterone receptor messenger RNA only in STS Clone 20 cells, whereas estrone sulfate produces the greatest stimulation of anchorage-independent growth in these cells. STS Clone 20 cells retain responsiveness to antiestrogens, which block the ability of estrogen sulfate to increase the proportion of cells in both the S and G(2)/M phases of the cell cycle. Consistent with these in vitro observations, only STS Clone 20 cells exhibit a significant increase in the proportion of proliferating tumors in nude ovariectomized mice supplemented with 17beta-estradiol sulfate. The primary activity in vivo appears to be from intratumor STS, rather than hepatic STS. Surprisingly, 17beta-estradiol sulfate appears more effective than 17beta-estradiol when both are administered at comparable concentrations. This effect, which is seen only in STS Clone 20 cells, may reflect differences in the cellular pharmacology of exogenous estrogens compared with those released by the activity of intracellular STS. These studies directly demonstrate that intratumor STS activity can support estrogen-dependent tumorigenicity in an experimental model and may contribute to the promotion of human breast tumors.

Determinants of tissue estradiol levels and biologic responsiveness in breast tumors

Estradiol stimulates the growth of breast tumor cells in both pre- and post menopausal women. Following the menopause, the levels of estradiol in breast tumor tissues are similar to those from tumors obtained prior to cessation of ovarian function, even though plasma estrogen levels are 10-50 fold lower in post- than in premenopausal women. These observations suggested the possibility of enhanced estradiol uptake from plasma or in situ synthesis in post-menopausal women. We systematically studied these possibilities in a series of model systems. Initially we demonstrated a very high affinity estradiol binding site in tissues from castrated rats. Enhanced uptake occurred under conditions of low plasma estrogen levels when compared to animals with higher estradiol levels. In situ synthesis also occurred both through the sulfatase and aromatase pathways. In further studies, we compared uptake from plasma with in situ synthesis via aromatase in a nude mouse model. Under the conditions utilized, in situ synthesis resulted in much higher tissue estradiol levels and tumor growth rates than did uptake from plasma. During these studies we demonstrated that tumors deprived of estradiol developed mechanisms rendering them more sensitive to estrogen. This involved the ability of cells to adapt to estradiol deprivation to allow them to be responsive to four log lower amounts of estrogen than when studied under wild type conditions. In addition, cells adapted by increasing their level of aromatase and thus developing the capability to become more sensitive to estrogen precursors. Taken together, these studies demonstrate that breast cancer tissue is highly plastic and can adapt to conditions of estrogen deprivation via a variety of mechanisms.

The development of A-ring modified analogues of oestrone-3-O-sulphamate as potent steroid sulphatase inhibitors with reduced oestrogenicity

Steroid sulphatases regulate the formation of oestrogenic steroids which can support the growth of endocrine-dependent breast tumours. The development of potent steroid sulphatase inhibitors could therefore have considerable therapeutic potential. Several such inhibitors have now been developed of which the most potent to date is oestrone-3-O-sulphamate (EMATE). Unexpectedly, this inhibitor proved to be a potent oestrogen. In an attempt to reduce the oestrogenicity, whilst retaining the potent sulphatase inhibitory properties associated with this type of molecule, a number of A-ring modified derivatives were designed and synthesized. A-ring modified compounds included the 2-methoxy, 2/4-nitro, 2/4-n-propyl and 2/4-allyl EMATE analogues. The ability of these derivatives to inhibit oestrone sulphatase activity was examined using placental microsomes. The allyl-substituted EMATE derivatives were more potent inhibitors than the propyl analogues but were all considerably less potent than EMATE. In contrast, the 2-methoxy and 2/4-nitro analogues were potent sulphatase inhibitors with 4-nitro EMATE being 5 times more active than EMATE. The 4-nitro, 2-methoxy, 4-n-propyl and 4-allyl derivatives were also tested in vivo for their oestrogenicity and ability to inhibit sulphatase activity. While both 4-nitro and 2-methoxy EMATE were potent inhibitors in vivo, 2-methoxy EMATE had no stimulatory effect on uterine growth in ovariectomized rats. The identification of a potent steroid sulphatase inhibitor lacking any oestrogenicity, such as 2-methoxy EMATE, should be of considerable value in evaluating the potential of steroid sulphatase inhibition for breast cancer therapy.

Measurement of oestrone sulphatase activity in white blood cells to monitor in vivo inhibition of steroid sulphatase activity by oestrone-3-O-sulphamate

Formation of oestrone via the sulphatase pathway is considered to be a major source of the oestrogen present in breast tumours. Several inhibitors of steroid sulphatase have now been developed for use in the treatment of postmenopausal women with breast cancer. In order to be able to monitor the extent and duration of the inhibition of oestrone sulphatase (E1-STS) readily, we have developed a method to measure the activity of this enzyme in white blood cells (WBCs). Hydrolysis of oestrone sulphate by E1-STS in WBCs was linear with respect to time and the volume of WBCs used. To examine whether the extent of inhibition of E1-STS activity in WBCs, by the inhibitor oestrone-3-O-sulphamate (EMATE), reflected inhibition in other body tissues, activity in WBCs was compared with that in liver and spleen tissue samples from rats. Two hours after an oral dose of EMATE the extent of inhibition of E1-STS detected in WBCs was the same as in the liver. The duration of the inhibition of E1-STS by EMATE, examined over a 1-28 day period in rats, was similar whether monitored in WBCs, liver or spleen. Measurements of E1-STS activity in WBCs were also used to examine the effectiveness of EMATE (0.5 mg/kg) in two male volunteers. E1-STS activity was rapidly inhibited and had only recovered by 27% after 1 month. A marked decrease in the ratio of plasma dehydroepiandrosterone:dehydroepiandrosterone-sulphate (DHA:DHA-S) concentrations was also detected, confirming that EMATE also inhibits DHA-STS activity. The ability to monitor the extent and duration of steroid sulphatase inhibition in WBCs will facilitate the evaluation of this new form of endocrine therapy in women with breast cancer.

Evidence of in situ estrogen synthesis in nitrosomethylurea-induced rat mammary tumors via the enzyme estrone sulfatase

A variety of indirect evidence suggests that mammary tumors can synthesize free estrogens in situ via the sulfatase enzyme. The present study utilized an isotopic kinetic technique to provide direct confirmation of local tumor synthesis. Animals bearing nitrosomethylurea (NMU)-induced rat mammary tumors were infused with 14C-estrone as well as 3H-estrone sulfate and plasma:tissue gradients for each steroid measured. Liver, serving as a control tissue, uniformly synthesized free estrone from estrone sulfate with local synthesis in this organ providing an average of 78 +/- 1.0% of the estrone in this tissue. In rat mammary tumors, five out of seven synthesized estrone locally with individual values ranging from 19 to 50% synthesized in tissue. These data indicate that liver uniformly converts estrone sulfate to free estrone, whereas the majority, but not all, breast tumors synthesize estrogen locally via this pathway.

In vivo inhibition of oestrone sulphatase and dehydroepiandrosterone sulphatase by oestrone-3-O-sulphamate

Many tumours in endocrine-sensitive tissues, such as the breast and endometrium, are hormone-dependent and the hydrolysis of oestrone sulphate (EIS) to oestrone by oestrone sulphatase (EI-STS) is a major source of oestrogen in such tumours. Oestrone-3-O-sulphamate (EMATE) has been shown to be a potent EI-STS inhibitor in vitro, and in this study its ability to inhibit enzyme activity in vivo was examined. EMATE was initially administered to female rats for 7 days, after which liver EI-STS activity was measured. As EMATE also inhibits a related sulphatase in vitro, dehydroepiandrosterone sulphatase (DHA-STS), its effect on the activity of this enzyme in vivo was also investigated. DHA-STS has a pivotal role in regulating the synthesis of another steroid with potent oestrogenic properties, androstenediol. Administration of EMATE almost completely inhibited liver EI-STS (99%) and DHA-STS (99%) activities and was active when given by the oral or subcutaneous routes. After a single dose of EMATE or following the cessation of multiple doses for 10 days, liver EI-STS activity remained inhibited ( > 95%) for up to 7 and 10 days, respectively. Other compounds, such as 4-hydroxytamoxifen and the "pure" antioestrogen ICI 182,780, which are reported to inhibit EI-STS activity in vitro, did not inhibit activity in vivo. In a preliminary study, EMATE, when injected over a 12-day period, effectively reduced the growth of EIS-stimulated nitrosomethyl-urea-induced mammary tumours in ovariectomised rats and inhibited tumour sulphatase activity in treated animals.

Estrogenicity, antiestrogenicity and estrone sulfatase inhibition of estrone-3-amine and estrone-3-thiol

Estrogen levels in breast tumors of post-menopausal women are at least 10 times higher than estrogen levels in plasma. The high level of estrogen in these tumors is postulated to be due to in situ formation of estrogen, possibly through conversion of estrone sulfate to estrone by the enzyme estrone sulfatase. Thus, inhibitors of estrone sulfatase are potential agents for the treatment of hormone-dependent breast cancers. We designed and synthesized a series of estra-1,3,5(10)triene-17-one, 3-amino and estra-1,3,5(10)triene-17-one, 3-thio derivatives. We have shown previously that several of these compounds substantially inhibit estrone sulfatase, exceeding Danazol in their inhibitory activity. However, little is known about the metabolism of these compounds and the possible effects of their metabolites in vivo. Two probable metabolites of the synthetic estrone analogs are estra-1,3,5(10)triene-17-one, 3-amine (E1-NH2), and estra-1,3,5(10)triene-17-one, 3-thiol (E1-SH). We tested these two compounds for estrogenicity, antiestrogenicity and inhibition of estrone sulfatase activity using a combination of in vivo and in vitro assays. The ovariectomized rat uterine weight gain assay was used to test for estrogenicity. Neither E1-NH2 nor E1-SH were estrogenic, as indicated by a lack of uterine weight gain when given at 25 micrograms/day for 7 days. The test compounds also were not antiestrogenic, in that they did not block estrone-induced uterine weight gain when given (100 micrograms/day) simultaneously with estrone (2 micrograms/day). Both compounds showed low affinity for the estrogen receptor. Using rat uterine cytosol as a source of estrogen receptor, the compounds displaced only a small percentage of [3H]estradiol binding, even when present at 1000-fold excess. Inhibition of estrone sulfatase activity was tested using human placental microsomes as a source of estrone sulfatase. E1-NH2 and E1SH showed very low levels of estrone sulfatase inhibition (15.1 and 9.8%, respectively) under conditions where Danazol showed more than 60% inhibition. Our results indicate that neither of these two compounds would present significant problems if they were the primary metabolite in a treatment involving estrone sulfatase inhibition of estrogen-dependent breast cancer.

Inhibition of steroid sulphatase activity by steroidal methylthiophosphonates: potential therapeutic agents in breast cancer

The hydrolysis of steroid sulphates, by steroid sulphatase, is an important source of oestrogenic steroids (oestrone, oestradiol and 5-androstene-3 beta,17 beta-diol) which are found in tumours. In the present study, we have examined the effect of dehydroepiandrosterone-3-O-methylthiophosphonate (DHA-3-MTP), pregnenolone-3-O-methylthiophosphonate (pregnenolone-3-MTP) and cholesterol-3-O-methylthiophosphonate (cholesterol-3-MTP) on the inhibition of oestrone sulphatase as well as DHA sulphatase activities in intact MCF-7 breast cancer cells and in placental microsomes. All three methylthiophosphonates significantly (P < 0.01) inhibited the hydrolysis of oestrone sulphate (E1 S) in intact MCF-7 cells (31-85% inhibition at 1 microM and 53-97% inhibition at 10 microM). Significant inhibition of DHA sulphatase was also achieved. At a concentration of 50 microM, all three compounds inhibited the hydrolysis of dehydroepiandrosterone sulphate (DHAS) by > 95%. Using human placental microsomes, the Km and Vmax of E1S were determined to be 8.1 microM and 43 nmol/h/mg protein. The corresponding Ki values for DHA-3-MTP, pregnenolone-3-MTP and cholesterol-3-MTP were found to be 4.5, 1.4 and 6.2 microM, respectively. Such inhibitors which are resistant to metabolism may have considerable potential as therapeutic agents and may have additional advantage over aromatase inhibitors in also reducing tumour concentrations of the oestrogenic steroid, 5-androstene-3 beta,17 beta-diol, by inhibiting the hydrolysis of DHAS.

Detection of breast cancer-associated estrone sulfatase in breast cancer biopsies and cell lines using polymerase chain reaction

Steroid sulfatase (STS) is a single enzyme with a range of substrate specificities, including estrone sulfate. Using a 2.4 kb cDNA clone, expression of human STS was undetectable by Northern hybridization, but STS RNA was detected in human placenta, human breast cancer samples, and in breast carcinoma cell lines following reverse transcriptase-PCR amplification, using specific primers to yield a product of 472 bp. In preliminary studies, stimulation of MCF-7 cell lines with estradiol (10(-8) M) resulted in an increased level of amplifiable STS RNA, and this upregulation of STS RNA could be abolished by tamoxifen. The estrone sulfatase activity in mammary tumors derived from N-nitrosomethylurea (NMU) treated rats was significantly decreased in animals treated with tamoxifen compared to control animals, regardless of the response of the tumors to the antiestrogen (P < 0.05). Although tamoxifen does not inhibit the estrone sulfatase enzyme in vitro, it may modulate the expression of STS RNA and the enzyme activity in vivo.

Estrone sulfate promotes human breast cancer cell replication and nuclear uptake of estradiol in MCF-7 cell cultures

Estradiol levels in breast tumors from post-menopausal women are similar to those in pre-menopausal women even though plasma estrogens are much lower after the menopause. In situ estrogen production by the tumor provides a potential means of maintaining high estradiol levels in post-menopausal breast cancer tissue. The estrone sulfatase pathway has been proposed as the mediator of in situ estrogen production. A number of studies suggest that estrone sulfate may be converted into estradiol in breast tumors via the catalytic activity of estrone sulfatase and 17 beta-hydroxysteroid dehydrogenase. However, these studies used pharmacologic levels of estrogen sulfates and have not shown that physiologic levels can support biologic effects. Accordingly, the present study examined the dose relationship of estrone sulfate to a variety of biologic endpoints in MCF-7 breast cancer cells in culture. These cells converted physiologic concentrations of estrone sulfate to quantities of free estradiol capable of stimulating cell growth. Under these conditions, the nuclear steroids observed were free estrone and estradiol. Increase in cell number after 6 days of exposure to steroid required 100 nM estrone sulfate. However, S-phase, a more sensitive measure of cell proliferation, was stimulated by 0.1 nM estrone sulfate, a clearly physiologic concentration. Stimulation of estrogen-dependent protein markers such as pS2 and progesterone receptor required much higher concentrations of estrone sulfate. These effects were mediated through the estrogen receptor since the pure anti-estrogen, ICI 164384, blocked all effects produced by estrone sulfate. While it has been suggested that anti-estrogens may partly exert their effects by inhibition of sulfatase and 17 beta-hydroxysteroid dehydrogenase, this did not occur under our experimental conditions. These data provide evidence of the relevance of the estrone sulfatase pathway since biologic effects can be demonstrated in response to physiologic concentrations of estrone sulfate.

Inhibition of oestrogen synthesis in postmenopausal women with breast cancer

The effectiveness in reducing oestrogen exposure, of an aromatase inhibitor, and a sulphatase inhibitor, as measured by in vivo studies in breast cancer patients, has been investigated. 4-Hydroxyandrostenedione (4HA) was shown to diminish plasma oestrogen levels, to inhibit peripheral and local aromatization and to cause a concomitant decrease in the activity of DNA-polymerase-alpha, measured as an indicator of cellular proliferation. The source of oestrone sulphate in breast tissues was examined, and it was shown that the tissue content of this conjugate derived from circulating oestrone, but no evidence could be found for the direct accumulation of conjugate from the plasma. Administration of Danazol was found to cause a fall in plasma oestrone levels, and to diminish the conversion ratio of oestrone sulphate to oestrone in some patients. It also inhibited tissue sulphatase activity. Although it is concluded that this drug is only a weak sulphatase inhibitor, these observations indicate the potential value of developing more efficient sulphatase inhibitors. Enzyme inhibition is now a proven effective treatment for breast cancer and the development of more efficient inhibitors is an important objective.

Aromatase inhibitors: clinical pharmacology and therapeutic implications in breast cancer

Aminoglutethimide was the first aromatase inhibitor to be used in breast cancer therapy but, since it interacts with the synthetic glucocorticoids, hydrocortisone must also be given as a replacement. The most important side-effects of aminoglutethimide are at the level of the central nervous system. Other aromatase inhibitors with greater potency and selectivity are being developed. Pyridoglutethimide, a compound resulting from modifications to the structure of aminoglutethimide, seems to be devoid of sedative properties according to preliminary tests on the central nervous system. 4-Hydroxyandrostenedione is significantly more potent and better tolerated than aminoglutethimide. Fadrozole (CGS 16,949 A) is 200-400 times more potent than aminoglutethimide and is now in phase II of its clinical development. CGS 20,267 has no effect on adrenal steroidogenesis and is currently in phase I of its clinical development. Availability of newer aromatase inhibitors could make a worthwhile contribution to endocrine therapy in breast cancer.

Oestrone sulphatase activity in mammary tumours and the liver of N-nitrosomethylurea treated rats

Oestrone sulphatase may be an important means of production of intra-tumoural oestrogens in breast cancer cells. The N-nitrosomethylurea induced rat mammary tumours, which is a good model of human breast carcinoma, was utilised to examine the significance of intra-tumoural oestrone sulphatase levels. The particular fraction (100,000 g pellet) was prepared from both the liver and the tumour of NMU treated rats and assayed for sulphatase activity. The tumour enzyme had an optimum pH of 7.2, Km value of 14.8 microM and Vmax of 0.90 nmoles min-1 mg-1, while the hepatic enzyme was optimal at pH 7.4, Km of 10.8 microM and Vmax of 3.71 nmoles min-1 mg-1. The relationship of intra-tumoural sulphatase levels with tumour regression and progression in endocrine responsive tumours was investigated. Tumour regression as a result of oophorectomy was associated with a significantly decreased intra-tumoural sulphatase level (mean level = 0.165 nmoles min-1 mg-1) in comparison to a control group (mean level = 0.319 nmoles min-1 mg-1, P less than 0.05) in which the tumours remained stable. This significant difference was not observed in the corresponding hepatic samples suggesting that it is the intra-tumoural rather than the peripheral production of oestrogens by oestrone sulphatase that is important in supporting growth of endocrine responsive tumours.

In vitro effect of synthetic progestogens on estrone sulfatase activity in human breast carcinoma

The effect of progesterone and nine synthetic progestogens on the activity rate of microsome estrone sulfatase obtained from human breast carcinoma tissues was studied. The progestogens were classified into three groups: group I with a strict inhibitor effect: demegestone and chlormadinone acetate; group II with a strict activator effect: medroxyprogesterone acetate, quingestanol acetate, lynestrenol and progesterone and group III with a nonsignificant effect: dydrogesterone, promegestone, norgestrel and danazol. Demegestone was the most potent inhibitor and medroxyprogesterone acetate and quingestanol acetate had the highest activator effect. The effect of Triton X-100, a nonionic detergent, was also tested. This detergent consistently increased the microsome estrone sulfatase activity. A comparison was made between the effects of demegestone, medroxyprogesterone acetate and danazol on estrone sulfatase activity measured with or without Triton X-100 in the incubation medium. The presence of the detergent modified the progestogen action. Our results suggest that synthetic progestogens can influence the estrone sulfatase activity measured in human breast carcinoma tissues. However, the effect of progestogens was dependent on experimental conditions. Progestogens such as demegestone and chlormadinone acetate which inhibited estrone sulfatase activity in intact preparations, can reduce the intracellular production of biological active estrogen via the sulfatase pathway.

Regulation of oestradiol 17 beta hydroxysteroid dehydrogenase in breast tissues: the role of growth factors

Oestradiol 17 beta-hydroxysteroid dehydrogenase (E2DH) is present in normal and malignant breast tissues and regulates the interconversion of oestrone and the biologically active oestrogen, oestradiol. Studies we have previously carried out have indicated that concentrations of oestradiol and the conversion of oestrone to oestradiol are higher in breast tumours than in normal breast tissues. We are currently isolating and characterizing factors produced by breast tumours which are capable of stimulating E2DH (reductive) activity. The production of such factors by breast tumours, which stimulate the conversion of oestrone to oestradiol, would provide a favourable oestrogenic environment to promote tumour growth and may account for the increased concentrations of oestradiol in breast tumours.