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

Sulfamates in drug design and discovery: Pre-clinical and clinical investigations

In the present article, we reviewed the sulfamate-containing compounds reported as bioactive molecules. The possible molecular targets of sulfamate derivatives include steroid sulfatase enzyme, carbonic anhydrases, acyl transferase, and others. Sulfamate derivatives can help treat hormone-dependent tumors including breast, prostate, and endometrial cancers, Binge eating disorder, migraine, glaucoma, weight loss, and epilepsy. Sulfamate derivatives can act also as calcium sensing receptor agonists and can aid in osteoporosis. Furthermore, acyl sulfamate derivatives can act as antibacterial agents against Gram-positive bacteria. A recent study revealed a new side effect of topiramate, a sulfamate-containing compound, which is sialolithiasis. The structural and biological characteristics of the reviewed compounds are presented in detail.

SULFATION PATHWAYS: A role for steroid sulphatase in intracrine regulation of endometrial decidualisation

In women, establishment of pregnancy is dependent upon 'fine-tuning' of the endometrial microenvironment, which is mediated by terminal differentiation (decidualisation) of endometrial stromal fibroblasts (ESFs). We have demonstrated that intracrine steroid metabolism plays a key role in regulating decidualisation and is essential for time-dependent expression of key factors required for endometrial receptivity. The primary aim of the current study was to determine whether sulphated steroids can act as precursors to bioactive sex steroids during decidualisation. We used primary human ESF and a robust in vitro model of decidualisation to assess the expression of genes associated with sulphation, desulphation and transport of sulphated steroids in human ESF as well as the impact of the steroid sulphatase (STS) inhibitor STX64 (Irosustat). We found evidence for an increase in both expression and activity of STS in response to a decidualisation stimulus with abrogation of oestrone biosynthesis and decreased secretion of the decidualisation marker IGFBP1 in the presence of STX64. These results provide novel insight into the contribution of STS to the intracrine regulation of decidualisation.

Estrogen Activation by Steroid Sulfatase Increases Colorectal Cancer Proliferation via GPER

CONTEXT

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

OBJECTIVE

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

DESIGN, SETTING, PATIENTS, AND INTERVENTIONS

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

PRIMARY OUTCOME MEASURE

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

RESULTS

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

CONCLUSION

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

Estrone Sulfate Transport and Steroid Sulfatase Activity in Colorectal Cancer: Implications for Hormone Replacement Therapy

Hormone replacement therapy (HRT) affects the incidence and potential progression of colorectal cancer (CRC). As HRT primarily consists of estrone sulfate (E₁S), understanding whether this conjugated estrogen is transported and metabolized in CRC will define its potential effect in this malignancy. Here, we show that a panel of CRC cell lines (Colo205, Caco2, HCT116, HT-29) have steroid sulfatase (STS) activity, and thus can hydrolyze E₁S. STS activity is significantly higher in CRC cell lysate, suggesting the importance of E₁S transport in intracellular STS substrate availability. As E₁S transport is regulated by the expression pattern of certain solute carrier organic anion transporter polypeptides, we show that in CRC OATP4A1 is the most abundantly expressed transporter. All four CRC cell lines rapidly transported E₁S into cells, with this effect significantly inhibited by the competitive OATP inhibitor BSP. Transient knockdown of OATP4A1 significantly disrupted E₁S uptake. Examination of estrogen receptor status showed ERα was present in Colo205 and Caco2 cells. None of the cells expressed ERβ. Intriguingly, HCT116 and HT29 cells strongly expressed the G protein coupled estrogen receptor (GPER), and that stimulation of this receptor with estradiol (E₂) and G1, a GPER agonist, significantly (p < 0.01) increased STS activity. Furthermore, tamoxifen and fulvestrant, known GPER agonist, also increased CRC STS activity, with this effect inhibited by the GPER antagonist G15. These results suggest that CRC can take up and hydrolyze E₁S, and that subsequent GPER stimulation increases STS activity in a potentially novel positive feedback loop. As elevated STS expression is associated with poor prognosis in CRC, these results suggest HRT, tamoxifen and fulvestrant may negatively impact CRC patient outcomes.

Discovery and Development of the Aryl O-Sulfamate Pharmacophore for Oncology and Women's Health

In 1994, following work from this laboratory, it was reported that estrone-3-O-sulfamate irreversibly inhibits a new potential hormone-dependent cancer target steroid sulfatase (STS). Subsequent drug discovery projects were initiated to develop the core aryl O-sulfamate pharmacophore that, over some 20 years, have led to steroidal and nonsteroidal drugs in numerous preclinical and clinical trials, with promising results in oncology and women's health, including endometriosis. Drugs have been designed to inhibit STS, e.g., Irosustat, as innovative dual-targeting aromatase-steroid sulfatase inhibitors (DASIs) and as multitargeting agents for hormone-independent tumors, such as the steroidal STX140 and nonsteroidal counterparts, acting inter alia through microtubule disruption. The aryl sulfamate pharmacophore is highly versatile, operating via three distinct mechanisms of action, and imbues attractive pharmaceutical properties. This Perspective gives a personal view of the work leading both to the therapeutic concepts and these drugs, their current status, and how they might develop in the future.

Estrogen O-sulfamates and their analogues: Clinical steroid sulfatase inhibitors with broad potential

Estrogen sulfamate derivatives were the first irreversible active-site-directed inhibitors of steroid sulfatase (STS), an emerging drug target for endocrine therapy of hormone dependent diseases that catalyzes inter alia the hydrolysis of estrone sulfate to estrone. In recent years this has stimulated clinical investigation of the estradiol derivative both as an oral prodrug and its currently ongoing exploration in endometriosis. 2-Substituted steroid sulfamate derivatives show considerable potential as multi-targeting agents for hormone-independent disease, but are also potent STS inhibitors. The steroidal template has spawned nonsteroidal STS inhibitors one of which, Irosustat, has been evaluated clinically in breast cancer, endometrial cancer and prostate cancer and there is potential for innovative dual-targeting approaches. This review surveys the role of estrogen sulfamates, their analogues and current status.

Metabolism of Dehydroepiandrosterone Sulfate and Estrone-Sulfate by Human Platelets

The aim of the present research was to study the uptake of DHEAS, and to establish the intracrine capacity of human platelets to produce sex steroid hormones. The DHEAS transport was evaluated through the uptake of [3H]-DHEAS in the presence or absence of different substrates through the organic anion transporting polypeptide (OATP) family. The activity of sulfatase enzyme was evaluated, and the metabolism of DHEAS was measured by the conversion of [3H]-DHEAS to [3H]-androstenedione, [3H]-testosterone, [3H]-estrone and [3H]-17β-estradiol. Results indicated the existence in the plasma membrane of an OATP with high affinity for DHEAS and estrone sulphate (E1S). The platelets showed the capacity to convert DHEAS to active DHEA by the steroid-sulfatase activity. The cells resulted to be a potential site for androgens production, since they have the capacity to produce androstenedione and testosterone; in addition, they reduced [3H]-estrone to [3H]-17β-estradiol. This is the first demonstration that human platelets are able to import DHEAS and E1S using the OATP family and to convert DHEAS to active DHEA, and to transform E1S to 17β-estradiol.

Phase I study of STX 64 (667 Coumate) in breast cancer patients: the first study of a steroid sulfatase inhibitor

PURPOSE

Inhibition of steroid sulfatase (STS), the enzyme responsible for the hydrolysis of steroid sulfates, represents a potential novel treatment for postmenopausal women with hormone-dependent breast cancer. Estrone and DHEA are formed by this sulfatase pathway and can be converted to steroids (estradiol and androstenediol, respectively), which have potent estrogenic properties.

EXPERIMENTAL DESIGN

STX64 (667 Coumate), a tricylic coumarin-based sulfamate that irreversibly inhibits STS activity, was selected for entry into the first phase I trial of a STS inhibitor in postmenopausal women with breast cancer. STX64 was administered orally (nine patients at 5 mg and five patients at 20 mg) as an initial dose followed 1 week later by 3 x 2 weekly cycles, with each cycle comprising daily dosing for 5 days followed by 9 days off treatment. Blood and tumor tissue samples were collected for the assessment of STS activity and serum was obtained for steroid hormone measurements before and after treatment.

RESULTS

The median inhibition of STS activity by STX64 was 98% in peripheral blood lymphocytes (PBL) and 99% in breast tumor tissue at the end of the 5-day dosing period. As expected, serum concentrations of estrone, estradiol, androstenediol, and DHEA all decreased significantly from pretreatment levels. Unexpectedly, androstenedione and testosterone concentrations also decreased. Four patients, all of whom had previously progressed on aromatase inhibitors, showed evidence of stable disease for 2.75 to 7 months. The drug was well tolerated with only minor drug-related adverse events recorded.

CONCLUSION

STX64 is a potent, well-tolerated STS inhibitor. It inhibits STS activity in PBLs and tumor tissues and causes significant decreases in serum concentrations of steroids with estrogenic properties.

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.

Anti-cancer activities of novel D-ring modified 2-substituted estrogen-3-O-sulfamates

Sulfamoylated derivatives of the endogenous estrogen metabolite 2-methoxyestradiol (2-MeOE2 (7)), such as 2-methoxy-3-O-sulfamoyl estrone (2-MeOEMATE (1)), display greatly enhanced activity against the proliferation of human cancer cells and inhibit steroid sulphatase (STS), another current oncology target. We explore here the effects of steroidal D-ring modification on the activity of such 2-substituted estrogen-3-O-sulfamates in respect of inhibition of tumour cell proliferation and steroid sulphatase. The novel 17-deoxy analogues of 2-MeOEMATE and the related 2-ethyl and 2-methylsulfanyl compounds showed greatly reduced inhibition of MCF-7 proliferation. Introduction of a 17alpha-benzyl substituent to such 2-substituted estrogen sulfamates also proved deleterious to anti-proliferative activity but could, in one case, enhance STS inhibition with respect to the parent substituted estrone sulfamate. In contrast, selected 17-oxime derivatives of 2-MeOEMATE displayed an enhanced anti-proliferative activity. These results illustrate that enhanced in vitro anti-cancer activity can be achieved in the 2-substituted estrogen sulfamate series and highlight, in particular, the importance of potential hydrogen bonding effects around the steroidal D-ring in the activity of these molecules. The SAR parameters established herein will assist the future design of anti-proliferative and anti-endocrine agents as potential therapeutics for both hormone dependent and independent cancers.

The role of steroid sulphatase in regulating the oestrogenicity of oestrogen sulphamates

Oestrogen sulphamates have increased systemic, but reduced hepatic oestrogenicity which results from their sequestration and transport through the liver by red blood cells. Oestrogen sulphamates act as prodrugs for the release of natural oestrogens but, as yet, there is little information as to how the sulphamoyl moiety is cleaved from the steroid nucleus. In the present investigation we have used the potent steroid sulphatase (STS) inhibitor, 667 COUMATE, to explore the possibility that STS might be responsible for the hydrolysis of oestrogen sulphamates. Administration of oestrone sulphamate (10 microg/day, s.c., for 5 days) to ovariectomised rats resulted in a 3.5-fold increase in the uterine weights of treated animals. Co-administration of oestrone sulphamate and 667 COUMATE (2 mg/kg) completely blocked STS activity in treated animals and completely abrogated the ability of oestrone sulphamate to stimulate uterine growth. In vitro studies, using [(3)H]oestrone sulphamate or [(3)H]oestrone, revealed that the uptake of the sulphamate derivative (95.9+/-2.4%) by red blood cells was considerably higher than that for the non-sulphamoylated oestrogen (25.1+/-1.9%). Results from these studies demonstrate convincingly that STS is the enzyme responsible for the removal of the sulphamoyl group from oestrogen sulphamates. This enzyme therefore has a crucial role in regulating the oestrogenicity associated with this class of drug.

Steroid sulphatase inhibitors for breast cancer therapy

In contrast to aromatase inhibitors, which are now in clinical use, the development of steroid sulphatase (STS) inhibitors for breast cancer therapy is still at an early stage. STS regulates the formation of oestrone from oestrone sulphate (E1S) but also controls the hydrolysis of dehydroepiandrosterone sulphate (DHEA-S). DHEA can be reduced to 5-androstenediol (Adiol), a steroid with potent oestrogenic properties. The active pharmacophore for potent STS inhibitors has now been identified, i.e. a sulphamate ester group linked to an aryl ring. This has led to the development of a number of STS inhibitors, some of which are due to enter Phase I trials in the near future. Such first generation inhibitors include the tricyclic coumarin-based 667 COUMATE. Aryl sulphamates, such as 667 COUMATE, are taken up by red blood cells (rbc), binding to carbonic anhydrase II (CA II), and transit the liver without undergoing first-pass inactivation. 667 COUMATE is also a potent inhibitor of CA II activity with an IC50 of 17 nM. Second generation STS inhibitors, such as 2-methoxyoestradiol bis-sulphamate (2-MeOE2bisMATE), in addition to inhibiting STS activity, also inhibit the growth of oestrogen receptor negative (ER-) tumours in mice and are anti-angiogenic. As the active pharmacaphores for the inhibition of aromatase and STS are now known it may be possible to develop third generation inhibitors that are capable of inhibiting the activities of both enzymes. Whilst exploring the potential of such a strategy it was discovered that 667 COUMATE possessed weak aromatase inhibitory properties with an IC50 of 300 nM in JEG-3 cells. The identification of potent STS inhibitors will allow the therapeutic potential of this new class of drug to be explored in post-menopausal women with hormone-dependent breast cancer. Second generation inhibitors, such as 2-MeOE2bisMATE, which also inhibit the growth of ER- tumours should be active against a wide range of cancers.

Microtiter plate cellular assay for human steroid sulfatase with fluorescence readout

Steroid sulfatase (STS; E.C. 3.1.6.2) is an enzyme involved in the local production of estrogens and androgens in target organs. Inhibitors of steroid sulfatase activity are considered novel therapeutic agents for the treatment of different pathologic conditions, including cancers of breast, endometrium, and prostate and disorders of the pilosebaceous unit. Evaluation of steroid sulfatase inhibition in cells up to now has been a cumbersome process, involving the extraction of a radioactive cleavage product into organic solvents. Here, we describe a rapid, nonradioactive cellular assay in microtiter plate format, using 4-methylumbelliferyl sulfate as a substrate. The reaction product, 4-methylumbelliferone, is read in a fluorescence microtiter plate reader. Several cell lines were assayed for sulfatase activity. To increase the sensitivity of the assay, we developed a Chinese hamster ovary (CHO) cell line stably transfected with a cDNA encoding the human steroid sulfatase. The steroid sulfatase activity in transfected cells correlated with the presence of the enzyme in these cells, as determined by immunofluorescence. For most STS inhibitors tested, including estrone-3-O-sulfamate, the results from the CHO cellular assay were in good agreement with those from a standard cell-free assay.

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

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

Inhibition of steroid sulphatase activity by tricyclic coumarin sulphamates

The identification of the active pharmacophore required for potent inhibition of steroid sulphatase activity, i.e. an aryl-O-sulphamate structure, has led to the synthesis and testing of a large number of 1-4 ring-based inhibitors. 4-Methylcoumarin-7-O-sulphamate (COUMATE) was one of the first non-steroid based inhibitors identified. In an attempt to increase the potency of this class of inhibitor a series of tricyclic COUMATEs (665-6615 COUMATEs) have been synthesised and evaluated. Using placental microsomes as a source of oestrone sulphatase (E1-STS) the size of the third ring of the tricyclic COUMATEs was found to have a marked effect on inhibitor potency. Whereas 665- and 6615-COUMATEs had IC(50)s of 200 and 370 nM, respectively, the most potent inhibitor in vitro in this series was 6610 COUMATE with an IC(50) of 1 nM. Selected inhibitors were tested for their in vivo potency by administration of a single dose (0.1 or 1 mg/kg, p.o.) to female rats. Surprisingly, in vivo 6615 COUMATE proved to be the most active drug, inhibiting rat liver E1-STS activity by 23 and 94% when assayed 24 h after administration of the 0.1 and 1 mg/kg doses. E1-STS activity in brain tissue and white blood cells was also found to be inhibited when selected drugs were tested. These studies have identified a number of tricyclic COUMATEs with therapeutic potential.

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.