Steroid sulfatase inhibitors: a review covering the promising 2000-2010 decade

Targeting the formation of estrogens for treatment of hormone dependent diseases-current status

Local formation and action of estrogens have crucial roles in hormone dependent cancers and benign diseases like endometriosis. Drugs that are currently used for the treatment of these diseases act at the receptor and at the pre-receptor levels, targeting the local formation of estrogens. Since 1980s the local formation of estrogens has been targeted by inhibitors of aromatase that catalyses their formation from androgens. Steroidal and non-steroidal inhibitors have successfully been used to treat postmenopausal breast cancer and have also been evaluated in clinical studies in patients with endometrial, ovarian cancers and endometriosis. Over the past decade also inhibitors of sulfatase that catalyses the hydrolysis of inactive estrogen-sulfates entered clinical trials for treatment of breast, endometrial cancers and endometriosis, with clinical effects observed primarily in breast cancer. More recently, inhibitors of 17beta-hydroxysteroid dehydrogenase 1, an enzyme responsible for formation of the most potent estrogen, estradiol, have shown promising results in preclinical studies and have already entered clinical evaluation for endometriosis. This review aims to provide an overview of the current status of the use of hormonal drugs for the major hormone-dependent diseases. Further, it aims to explain the mechanisms behind the -sometimes- observed weak effects and low therapeutic efficacy of these drugs and the possibilities and the advantages of combined treatments targeting several enzymes in the local estrogen formation, or drugs acting with different therapeutic mechanisms.

Description of Chemical Synthesis, Nuclear Magnetic Resonance Characterization and Biological Activity of Estrane-Based Inhibitors/Activators of Steroidogenesis

Steroid hormones play a crucial role in several aspects of human life, and steroidogenesis is the process by which hormones are produced from cholesterol using several enzymes that work in concert to obtain the appropriate levels of each hormone at the right time. Unfortunately, many diseases, such as cancer, endometriosis, and osteoporosis as examples, are caused by an increase in the production of certain hormones. For these diseases, the use of an inhibitor to block the activity of an enzyme and, in doing so, the production of a key hormone is a proven therapeutic strategy whose development continues. This account-type article focuses on seven inhibitors (compounds 1-7) and an activator (compound 8) of six enzymes involved in steroidogenesis, namely steroid sulfatase, aldo-keto reductase 1C3, types 1, 2, 3, and 12 of the 17β-hydroxysteroid dehydrogenases. For these steroid derivatives, three topics will be addressed: (1) Their chemical synthesis from the same starting material, estrone, (2) their structural characterization using nuclear magnetic resonance, and (3) their in vitro or in vivo biological activities. These bioactive molecules constitute potential therapeutic or mechanistic tools that could be used to better understand the role of certain hormones in steroidogenesis.

2-Difluoromethoxy-Substituted Estratriene Sulfamates: Synthesis, Antiproliferative SAR, Antitubulin Activity, and Steroid Sulfatase Inhibition

2-Difluoromethoxyestratriene derivatives were designed to improve potency and in vivo stability of the drug candidate 2-methoxyestradiol (2ME2). Compound evaluation in vitro against the proliferation of MCF-7 and MDA MB-231 breast cancer cells, as inhibitors of tubulin polymerisation and also steroid sulfatase (STS) both in cell lysates and in whole cells, showed promising activities. In antiproliferative assays 2-difluoromethoxyestradiol was less potent than 2ME2, but its sulfamates were often more potent than their corresponding non-fluorinated analogues. The fluorinated bis-sulfamate is a promising antiproliferative agent in MCF-7 cells (GI50 0.28 μM) vs the known 2-methoxyestradiol-3,17-O,O-bissulfamate (STX140, GI50 0.52 μM), confirming the utility of our approach. Compounds were also evaluated in the NCI 60-cell line panel and the fluorinated bis-sulfamate derivative displayed very good overall activities with a sub-micromolar average GI50 . It was a very potent STS inhibitor in whole JEG-3 cells (IC50 3.7 nM) similar to STX140 (4.2 nM) and additionally interferes with tubulin assembly in vitro and colchicine binding to tubulin. An X-ray study of 2-difluoromethoxy-3-benzyloxyestra-1,3,5(10)-trien-17-one examined conformational aspects of the fluorinated substituent. The known related derivative 2-difluoromethyl-3-sulfamoyloxyestrone was evaluated for STS inhibition in whole JEG-3 cells and showed an excellent IC50 of 55 pM.

Dual Targeting of Steroid Sulfatase and 17β-Hydroxysteroid Dehydrogenase Type 1 by a Novel Drug-Prodrug Approach: A Potential Therapeutic Option for the Treatment of Endometriosis

A novel approach for the dual inhibition of steroid sulfatase (STS) and 17β-hydroxysteroid dehydrogenase type 1(17β HSD1) by a single drug was explored, starting from in-house 17β HSD1 inhibitors via masking their phenolic OH group with a sulfamate ester. The sulfamates were intentionally designed as drugs for the inhibition of STS and, at the same time, prodrugs for 17β-HSD1 inhibition ("drug-prodrug approach"). The most promising sulfamates 13, 16, 18-20, 22-24, 36, and 37 showed nanomolar IC₅₀ values for STS inhibition in a cellular assay and their corresponding phenols displayed potent 17β-HSD1 inhibition in cell-free and cellular assays, high selectivity over 17β-HSD2, reasonable metabolic stability, and low estrogen receptor α affinity. A close relationship was found between the liberation of the phenolic compound by sulfamate hydrolysis and 17β-HSD1 inactivation. These results showed that the envisaged drug-prodrug concept was successfully implemented. The novel compounds constitute a promising class of therapeutics for the treatment of endometriosis and other estrogen-dependent diseases.

Steroidal ferrocenes as potential enzyme inhibitors of the estrogen biosynthesis

The potential inhibitory effect of diverse triazolyl-ferrocene steroids on key enzymes of the estrogen biosynthesis was investigated. Test compounds were synthesized via copper-catalyzed cycloaddition of steroidal azides and ferrocenyl-alkynes using our efficient methodology published previously. Inhibition of human aromatase, steroid sulfatase (STS) and 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1) activities was investigated with in vitro radiosubstrate incubations. Some of the test compounds were found to be potent inhibitors of the STS. A compound bearing ferrocenyl side chain on the C-2 displayed a reversible inhibition, whereas C-16 and C-17 derivatives displayed competitive irreversible binding mechanism toward the enzyme. 17α-Triazolyl-ferrocene derivatives of 17β-estradiol exerted outstanding inhibitory effect and experiments demonstrated a key role of the ferrocenyl moiety in the enhanced binding affinity. Submicromolar IC₅₀ and K_i parameters enroll these compounds to the group of the most effective STS inhibitors published so far. STS inhibitory potential of the steroidal ferrocenes may lead to the development of novel compounds able to suppress in situ biosynthesis of 17β-estradiol in target tissues.

Synthesis of 16β-derivatives of 3-(2-bromoethyl)-estra-1,3,5(10)-trien-17β-ol as inhibitors of 17β-HSD1 and/or steroid sulfatase for the treatment of estrogen-dependent diseases

17β-Hydroxysteroid dehydrogenase type 1 (17β-HSD1) and steroid sulfatase (STS) are involved in the synthesis of the most potent estrogen in the human body, estradiol (E2). These enzymes are known to play a pivotal role in the progression of estrogen-dependent diseases, such as breast cancer and endometriosis. Therefore, the inhibition of 17β-HSD1 and/or STS represents a promising avenue to modulate the growth of estrogen-dependent tumors or lesions. We recently established the key role of a bromoethyl side chain added at the C3-position of a 16β-carbamoyl-benzyl-E2 nucleus to covalently inhibit 17β-HSD1. To extend the structure-activity relationship study to the C16β-position of this new selective irreversible inhibitor (PBRM), we synthesized a series of analog compounds by changing the nature of the C16β-side chain but keeping the 2-bromoethyl group at position C3. We determined their 17β-HSD1 inhibitions in T-47D cells (transformation of E1 into E2), but we did not obtain a stronger 17β-HSD1 inhibitor than PBRM. Compounds 16 and 17 were found to be more likely to bind to the catalytic site and showed a promising but moderate inhibitory activity with estimated IC₅₀ values of 0.5 and 0.7 µM, respectively (about 10 times higher than PBRM). Interestingly, adding one or two sulfamate groups in the D-ring's surroundings did not significantly decrease compounds' potential to inhibit 17β-HSD1, but clearly improved their potential to inhibit STS. These results open the door to the development of a new family of steroid derivatives with dual (17β-HSD1 and STS) inhibiting actions.

A Targeted-Covalent Inhibitor of 17β-HSD1 Blocks Two Estrogen-Biosynthesis Pathways: In Vitro (Metabolism) and In Vivo (Xenograft) Studies in T-47D Breast Cancer Models

Simple Summary

17β-Hydroxysteroid dehydrogenase type 1 (17β-HSD1) is responsible for the production of estrogens estradiol (E2) and 5-androsten-3β,17β-diol (5-diol). This enzyme is therefore a target of choice for the treatment of estrogen-dependent diseases such as breast cancer and endometriosis, by blocking estrogen biosynthesis. After we developed the first irreversible and non-estrogenic 17β-HSD1 inhibitor, a molecule named PBRM, our goal was to demonstrate its therapeutic potential. PBRM was able to block the formation of E2 and 5-diol in T-47D human breast cancer cells. When given orally to mice, PBRM was also able to block the tumor growth without any observed toxic effects. Thanks to its irreversible type of inhibition, PBRM retained its anti-tumor growth effect, even after reducing its frequency of administration to only once a week, a clear advantage over reversible inhibitors. These results strongly support the use of PBRM as a new approach in the treatment of breast cancer.

Abstract

17β-Hydroxysteroid dehydrogenase type 1 (17β-HSD1) plays an important role in estrogen-dependent breast tumor growth. In addition to being involved in the production of estradiol (E2), the most potent estrogen in women, 17β-HSD1 is also responsible for the production of 5-androsten-3β,17β-diol (5-diol), a weaker estrogen than E2, but whose importance increases after menopause. 17β-HSD1 is therefore a target of choice for the treatment of estrogen-dependent diseases such as breast cancer and endometriosis. After we developed the first targeted-covalent (irreversible) and non-estrogenic inhibitor of 17β-HSD1, a molecule named PBRM, our goal was to demonstrate its therapeutic potential. Enzymatic assays demonstrated that estrone (E1) and dehydroepiandrosterone (DHEA) were transformed into E2 and 5-diol in T-47D human breast cancer cells, and that PBRM was able to block these transformations. Thereafter, we tested PBRM in a mouse tumor model (cell-derived T-47D xenografts). After treatment of ovariectomized (OVX) mice receiving E1 or DHEA, PBRM given orally was able to reduce the tumor growth at the control (OVX) level without any observed toxic effects. Thanks to its irreversible type of inhibition, PBRM retained its anti-tumor growth effect, even after reducing its frequency of administration to only once a week, a clear advantage over reversible inhibitors.

Recent progress in the development of steroid sulphatase inhibitors - examples of the novel and most promising compounds from the last decade

The purpose of this review article is to provide an overview of recent achievements in the synthesis of novel steroid sulphatase (STS) inhibitors. STS is a crucial enzyme in the biosynthesis of active hormones (including oestrogens and androgens) and, therefore, represents an extremely attractive molecular target for the development of hormone-dependent cancer therapies. The inhibition of STS may effectively reduce the availability of active hormones for cancer cells, causing a positive therapeutic effect. Herein, we report examples of novel STS inhibitors based on steroidal and nonsteroidal cores that contain various functional groups (e.g. sulphamate and phosphorus moieties) and halogen atoms, which may potentially be used in therapies for hormone-dependent cancers. The presented work also includes examples of multitargeting agents with STS inhibitory activities. Furthermore, the fundamental discoveries in the development of the most promising drug candidates exhibiting STS inhibitory activities are highlighted.

Design and synthesis of dansyl-labeled inhibitors of steroid sulfatase for optical imaging

Steroid sulfatase (STS) is an important enzyme regulating the conversion of sulfated steroids into their active hydroxylated forms. Notably, the inhibition of STS has been shown to decrease the levels of active estrogens and was translated into clinical trials for the treatment of breast cancer. Based on quantitative structure-activity relationship (QSAR) and molecular modeling studies, we herein report the design of fluorescent inhibitors of STS by adding a dansyl group on an estrane scaffold. Synthesis of 17α-dansylaminomethyl-estradiol (7) and its sulfamoylated analog 8 were achieved from estrone in 5 and 6 steps, respectively. Inhibition assays on HEK-293 cells expressing exogenous STS revealed a high level of inhibition for compound 7 (IC₅₀ = 69 nM), a value close to the QSAR model prediction (IC₅₀ = 46 nM). As an irreversible inhibitor, sulfamate 8 led to an even more potent inhibition in the low nanomolar value (IC₅₀ = 2.1 nM). In addition, we show that the potent STS inhibitor 8 can be employed as an optical imaging tool to investigate intracellular enzyme sub-localization as well as inhibitory behavior. As a result, confocal microscopy analysis confirmed good penetration of the STS fluorescent inhibitor 8 in cells and its localization in the endoplasmic reticulum where STS is localized.

Design and synthesis of 3-benzylaminocoumarin-7-O-sulfamate derivatives as steroid sulfatase inhibitors

Steroid sulfatase (STS) is a sulfatase enzyme that catalyzes the conversion of sulfated steroid precursors to free steroid. The inhibition of STS could abate estrogenic steroids that stimulate the proliferation and development of breast cancer, and therefore STS is a potential target for adjuvant endocrine therapy. In this study, a series of 3-benzylaminocoumarin-7-O-sulfamate derivatives targeting STS were designed and synthesized. Structure-relationship activities (SAR) analysis revealed that attachment of a benzylamino group at the 3-position of coumarin improved inhibitory activity. Compound 3j was found to have the highest inhibition activity against human placenta isolated STS (IC₅₀  0.13 μM) and MCF-7 cell lines (IC₅₀ 1.35 µM). Kinetic studies found compound 3j to be an irreversible inhibitor of STS, with K_I and k_inact value of 86.9 nM and 158.7 min^-1, respectively.

Synthesis, and anti-proliferative, Pim-1 kinase inhibitors and molecular docking of thiophenes derived from estrone

Heterocyclization of steroids were reported to give biologically active products where ring D modification occured. Estrone (1) was used as a template to develop new heterocyclic compounds. Ring D modification of 1 through its reaction with cyanoacetylhydrazine and elemental sulfur gave the thiophene derivative 3. The latter compound reacted with acetophenone derivatives 4a-c to give the hydrazide-hydrazone derivatives 5a-c, respectively. In addition, compound 3 formed thiazole derivatives through its first reaction with phenylisothiocyanate to give the thiourea derivative 9 followed by the reaction of the later with α-halocarbonyl compounds. In the present work a series of novel estrone derivatives were designed, synthesized and evaluated for their in vitro biological activities against c-Met kinase, and six typical cancer cell lines (A549, H460, HT-29, MKN-45, U87MG and SMMC-7721). The most promising compounds 5b, 5c, 11a, 13c, 15b, 15c, 15d, 17a and 17b were further investigated against the five tyrosine kinases c-Kit, Flt-3, VEGFR-2, EGFR, and PDGFR. Compounds 5b, 15d, 17a and 17b were selected to examine their Pim-1 kinase inhibition activity where compounds 15d and 17b showed high activities. Molecular docking of some of the most potent compounds was demonstrated.

Steroid sulfatase inhibition success and limitation in breast cancer clinical assays: An underlying mechanism

Steroid sulfatase is detectable in most hormone-dependent breast cancers. STX64, an STS inhibitor, induced tumor reduction in animal assay. Despite success in phase І clinical trial, the results of phase II trial were not that significant. Breast Cancer epithelial cells (MCF-7 and T47D) were treated with two STS inhibitors (STX64 and EM1913). Cell proliferation, cell cycle, and the concentrations of estradiol and 5α-dihydrotestosterone were measured to determine the endocrinological mechanism of sulfatase inhibition. Comparisons were made with inhibitions of reductive 17β-hydroxysteroid dehydrogenases (17β-HSDs). Proliferation studies showed that DNA synthesis in cancer cells was modestly decreased (approximately 20%), accompanied by an up to 6.5% in cells in the G0/G1 phase and cyclin D1 expression reduction. The concentrations of estradiol and 5α-dihydrotestosterone were decreased by 26% and 3% respectively. However, supplementation of 5α-dihydrotestosterone produced a significant increase (approximately 35.6%) in the anti-proliferative effect of sulfatase inhibition. This study has clarified sex-hormone control by sulfatase in BC, suggesting that the different roles of estradiol and 5α-dihydrotestosterone can lead to a reduction in the effect of sulfatase inhibition when compared with 17β-HSD7 inhibition. This suggests that combined treatment of sulfatase inhibitors with 17β-HSD inhibitors such as the type7 inhibitor could hold promise for hormone-dependent breast cancer.

Intracrine Regulation of Estrogen and Other Sex Steroid Levels in Endometrium and Non-gynecological Tissues; Pathology, Physiology, and Drug Discovery

Our understanding of the intracrine (or local) regulation of estrogen and other steroid synthesis and degradation expanded in the last decades, also thanks to recent technological advances in chromatography mass-spectrometry. Estrogen responsive tissues and organs are not passive receivers of the pool of steroids present in the blood but they can actively modify the intra-tissue steroid concentrations. This allows fine-tuning the exposure of responsive tissues and organs to estrogens and other steroids in order to best respond to the physiological needs of each specific organ. Deviations in such intracrine control can lead to unbalanced steroid hormone exposure and disturbances. Through a systematic bibliographic search on the expression of the intracrine enzymes in various tissues, this review gives an up-to-date view of the intracrine estrogen metabolisms, and to a lesser extent that of progestogens and androgens, in the lower female genital tract, including the physiological control of endometrial functions, receptivity, menopausal status and related pathological conditions. An overview of the intracrine regulation in extra gynecological tissues such as the lungs, gastrointestinal tract, brain, colon and bone is given. Current therapeutic approaches aimed at interfering with these metabolisms and future perspectives are discussed.

In breast cancer subtypes steroid sulfatase (STS) is associated with less aggressive tumour characteristics

BACKGROUND

The majority of breast cancer cases are steroid dependent neoplasms, with hormonal manipulation of either CYP19/aromatase or oestrogen receptor alpha axis being the most common therapy. Alternate pathways of steroid actions are documented, but their interconnections and correlations to BC subtypes and clinical outcome could be further explored.

METHODS

We evaluated selected steroid receptors (Androgen Receptor, Oestrogen Receptor alpha and Beta, Glucocorticoid Receptor) and oestrogen pathways (steroid sulfatase (STS), 17β-hydroxysteroid dehydrogenase 2 (17βHSD2) and aromatase) in a cohort of 139 BC cases from Norway. Using logistic and cox regression analysis, we examined interactions between these and clinical outcomes such as distant metastasis, local relapse and survival.

RESULTS

Our principal finding is an impact of STS expression on the risk for distant metastasis (p<0.001) and local relapses (p <0.001), HER2 subtype (p<0.015), and survival (p<0.001). The suggestion of a beneficial effect of alternative oestrogen synthesis pathways was strengthened by inverted, but non-significant findings for 17βHSD2.

CONCLUSIONS

Increased intratumoural metabolism of oestrogens through STS is associated with significantly lower incidence of relapse and/or distant metastasis and correspondingly improved prognosis. The enrichment of STS in the HER2 overexpressing subtype is intriguing, especially given the possible role of HER-2 over-expression in endocrine resistance.

Fluorine and Fluorinated Motifs in the Design and Application of Bioisosteres for Drug Design

The electronic properties and relatively small size of fluorine endow it with considerable versatility as a bioisostere and it has found application as a substitute for lone pairs of electrons, the hydrogen atom, and the methyl group while also acting as a functional mimetic of the carbonyl, carbinol, and nitrile moieties. In this context, fluorine substitution can influence the potency, conformation, metabolism, membrane permeability, and P-gp recognition of a molecule and temper inhibition of the hERG channel by basic amines. However, as a consequence of the unique properties of fluorine, it features prominently in the design of higher order structural metaphors that are more esoteric in their conception and which reflect a more sophisticated molecular construction that broadens biological mimesis. In this Perspective, applications of fluorine in the construction of bioisosteric elements designed to enhance the in vitro and in vivo properties of a molecule are summarized.

First Dual Inhibitors of Steroid Sulfatase (STS) and 17β-Hydroxysteroid Dehydrogenase Type 1 (17β-HSD1): Designed Multiple Ligands as Novel Potential Therapeutics for Estrogen-Dependent Diseases

STS and 17β-HSD1 are attractive targets for the treatment of estrogen-dependent diseases like endometriosis and breast cancer. The simultaneous inhibition of both enzymes appears more promising than blockage of either protein alone. We describe a designed multiple ligand approach resulting in highly potent dual inhibitors. The most interesting compound 9 showed nanomolar IC₅₀ values for both proteins, membrane permeability, and no interference with estrogen receptors. It efficiently reversed E1S- and E1-induced T47D cell proliferation.

Steroid sulfatase inhibitor DU-14 protects spatial memory and synaptic plasticity from disruption by amyloid β protein in male rats

Alzheimer's disease (AD) is an age-related mental disorder characterized by progressive loss of memory and multiple cognitive impairments. The overproduction and aggregation of Amyloid β protein (Aβ) in the brain, especially in the hippocampus, are closely involved in the memory loss in the patients with AD. Accumulating evidence indicates that the Aβ-induced imbalance of dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) in the brain plays an important role in the AD pathogenesis and progression. The level of DHEA is elevated, while DHEAS is dramatically decreased in the AD brain. The present study tried to restore the balance between DHEA and DHEAS by using a non-steroidal sulfatase inhibitor DU-14, which increases endogenous DHEAS through preventing DHEAS converted back into DHEA. We found that: (1) DU-14 effectively attenuated the Aβ1-42-induced cognitive deficits in spatial learning and memory of rats in Morris water maze test; (2) DU-14 prevented Aβ1-42-induced decrease in the cholinergic theta rhythm of hippocampal local field potential (LFP) in the CA1 region; (3) DU-14 protected hippocampal synaptic plasticity against Aβ1-42-induced suppression of long term potentiation (LTP). These results provide evidence for the neuroprotective action of DU-14 against neurotoxic Aβ, suggesting that up-regulation of endogenous DHEAS by DU-14 could be beneficial to the alleviation of Aβ-induced impairments in spatial memory and synaptic plasticity.

Discovery of a sulfamate-based steroid sulfatase inhibitor with intrinsic selective estrogen receptor modulator properties

Steroid sulfatase (STS), the enzyme which converts inactive sulfated steroid precursors into active hormones, is a promising therapeutic target for the treatment of estrogen-sensitive breast cancer. We report herein the synthesis and in vitro study of dual-action STS inhibitors with selective estrogen-receptor modulator (SERM) effects. A library of tetrahydroisoquinoline-N-substituted derivatives (phenolic compounds) was synthesized by solid-phase chemistry and tested on estrogen-sensitive breast cancer T-47D cells. Three phenolic compounds devoid of estrogenic activity and toxicity emerged from this screening. Their sulfamate analogs were then synthesized, tested in STS-transfected HEK-293 cells, and found to be potent inhibitors of the enzyme (IC50 of 3.9, 8.9, and 16.6 nM). When tested in T-47D cells they showed no estrogenic activity and produced a moderate antiestrogenic activity. The compounds were further tested on osteoblast-like Saos-2 cells and found to significantly stimulate their proliferation as well as their alkaline phosphatase activity, thus suggesting a SERM activity. These results are supported by molecular docking experiments.

Sulfatase inhibitors for recidivist breast cancer treatment: A chemical review

Steroid sulfatase (STS) plays a momentous role in the conversion of sulfated steroids, which are biologically inactive, into biologically active un-sulfated steroid hormones, which support the development and growth of a number of hormone-dependent cancers, including breast cancer. Therefore, inhibitors of STS are supposed to be potential drugs for the treatment of breast and other steroid-dependent cancers. The present review concentrates on broad chemical classification of steroid sulfatase inhibitors. The inhibitors reviewed are classified into four main categories: Steroid sulfamate based inhibitors; Steroid non-sulfamate based inhibitors; Non-steroidal sulfamate based inhibitors; Non-steroidal non-sulfamate based inhibitors. A succinct overview of current treatment of cancer, estradiol precursors, STS enzyme and its role in breast cancer is herein described.

The Important Roles of Steroid Sulfatase and Sulfotransferases in Gynecological Diseases

Gynecological diseases such as endometriosis, adenomyosis and uterine fibroids, and gynecological cancers including endometrial cancer and ovarian cancer, affect a large proportion of women. These diseases are estrogen dependent, and their progression often depends on local estrogen formation. In peripheral tissues, estrogens can be formed from the inactive precursors dehydroepiandrosterone sulfate and estrone sulfate. Sulfatase and sulfotransferases have pivotal roles in these processes, where sulfatase hydrolyzes estrone sulfate to estrone, and dehydroepiandrosterone sulfate to dehydroepiandrosterone, and sulfotransferases catalyze the reverse reactions. Further activation of estrone to the most potent estrogen, estradiol, is catalyzed by 17-ketosteroid reductases, while estradiol can also be formed from dehydroepiandrosterone by the sequential actions of 3β-hydroxysteroid dehydrogenase-Δ⁴-isomerase, aromatase, and 17-ketosteroid reductase. This review introduces the sulfatase and sulfotransferase enzymes, in terms of their structures and reaction mechanisms, and the regulation and different transcripts of their genes, together with the importance of their currently known single nucleotide polymorphisms. Data on expression of sulfatase and sulfotransferases in gynecological diseases are also reviewed. There are often unchanged mRNA and protein levels in diseased tissue, with higher sulfatase activities in cancerous endometrium, ovarian cancer cell lines, and adenomyosis. This can be indicative of a disturbed balance between the sulfatase and sulfotransferases enzymes, defining the potential for sulfatase as a drug target for treatment of gynecological diseases. Finally, clinical trials with sulfatase inhibitors are discussed, where two inhibitors have already concluded phase II trials, although so far with no convincing clinical outcomes for patients with endometrial cancer and endometriosis.

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.

The Regulation of Steroid Action by Sulfation and Desulfation

Steroid sulfation and desulfation are fundamental pathways vital for a functional vertebrate endocrine system. After biosynthesis, hydrophobic steroids are sulfated to expedite circulatory transit. Target cells express transmembrane organic anion-transporting polypeptides that facilitate cellular uptake of sulfated steroids. Once intracellular, sulfatases hydrolyze these steroid sulfate esters to their unconjugated, and usually active, forms. Because most steroids can be sulfated, including cholesterol, pregnenolone, dehydroepiandrosterone, and estrone, understanding the function, tissue distribution, and regulation of sulfation and desulfation processes provides significant insights into normal endocrine function. Not surprisingly, dysregulation of these pathways is associated with numerous pathologies, including steroid-dependent cancers, polycystic ovary syndrome, and X-linked ichthyosis. Here we provide a comprehensive examination of our current knowledge of endocrine-related sulfation and desulfation pathways. We describe the interplay between sulfatases and sulfotransferases, showing how their expression and regulation influences steroid action. Furthermore, we address the role that organic anion-transporting polypeptides play in regulating intracellular steroid concentrations and how their expression patterns influence many pathologies, especially cancer. Finally, the recent advances in pharmacologically targeting steroidogenic pathways will be examined.

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.

Metabolomic, behavioral, and reproductive effects of the aromatase inhibitor fadrozole hydrochloride on the unionid mussel Lampsilis fasciola

Androgen-induced masculinization of female aquatic biota poses concerns for natural population stability. This research evaluated the effects of a twelve day exposure of fadrozole hydrochloride on the metabolism and reproductive status of the unionid mussel Lampsilis fasciola. Although this compound is not considered to be widespread in the aquatic environment, it was selected as a model aromatase (enzyme that converts testosterone to estradiol) inhibitor. Adult mussels were exposed to a control and 3 concentrations of fadrozole (2μg/L, 20μg/L, and 50μg/L), and samples of gill tissue were taken on days 4 and 12 for metabolomics analysis. Gills were used because of the variety of critical processes they mediate, such as feeding, ion exchange, and siphoning. Daily observed mussel behavior included female mantle display, foot protrusion, siphoning, and larval (glochidia) releases. Glochidia mortality was significantly higher in the 20μg/L treatment. Fewer conglutinate (packets of glochidia) releases were observed in the 50μg/L treatment, and mortality was highly correlated to release numbers. Foot protrusion was significantly higher in females in nearly all treatments, including the control, during the first 4days of observations. However, this sex difference was observed only in the 50μg/L treatment during the last 8days. Generally, metabolites were significantly altered in female gill tissue in the 2μg/L treatment whereas males were mostly affected only at the highest (50μg/L) treatment. Both sexes also revealed significant reductions in fadrozole-induced metabolic effects in gill tissue sampled after 12days compared to tissue sampled after 4days, indicating time-dependent mechanisms of disruptions in metabolic pathways and homeostatic processes to compensate for such disruptions.

Heterocyclic ring extension of estrone: synthesis and cytotoxicity of fused pyran, pyrimidine and thiazole derivatives

The one pot reaction of estrone with the aromatic aldehydes 2a-c and either of malononitrile or ethyl cyanoacetate afforded the fused pyran derivatives 4a-f. On the other hand, carrying the same reaction using thiourea instead of the cyanomethylene reagent gave the fused pyrimidine derivatives 6a-c. The latter compounds reacted with phenacyl bromide to give the thiazolo[3,2-a]pyrimidine derivatives 8a-c. The reaction of the title compound with bromine gave the monobromo derivative 13 which in turn reacted with either thiourea or cyanothioacetamide to give the thiazole derivatives 14 and 16, respectively. The cytotoxicity of the newly synthesized products was evaluated against six human cancer and normal cell lines where the results showed that compounds 4c, 4f, 6b, 8b, 8c, 10, 13, 16, 18c and 19c exhibited optimal cytotoxic effect against the cancer cell lines, with IC50's in the nM range.

Synergistic effects of E2MATE and norethindrone acetate on steroid sulfatase inhibition: a randomized phase I proof-of-principle clinical study in women of reproductive age

The combination of a progestin such as norethindrone acetate (NETA) reducing the ovarian estrogen production with a steroid sulfatase (STS) inhibitor (STS-I) decreasing the local estrogen production could result in a new treatment option for endometriosis. The study reported was a randomized, double-blind, and placebo-controlled study to investigate the pharmacodynamics, pharmacokinetics, and safety of the STS-I PGL2001 (E2MATE) and NETA. A total of 24 healthy women of reproductive age were treated with weekly doses of PGL2001 or daily doses of NETA or a combination of both compounds for 4 weeks. Four weeks of treatment with PGL2001 or PGL2001 + NETA reduced the STS activity in the endometrium by 91% (±3%) and 96% (±4%), respectively, and comparable values were observed 1 month after the treatment was stopped. The combined treatment of PGL2001 + NETA led to significantly higher STS inhibition at both times (P < .01 and P < .05, respectively). This study showed that administration of PGL2001 alone at 4 mg/week or combined with NETA to healthy women of reproductive age led to STS inhibition and changes in functional STS biomarkers in the endometrium, resulting in synergistic effects of PGL2001 and NETA on STS activity.

Design and synthesis of silicon-containing steroid sulfatase inhibitors possessing pro-estrogen antagonistic character

Steroid sulfatase (STS) is a potential target for treatment of postmenopausal hormone-dependent breast cancer. Several steroidal STS inhibitors have been reported, but steroidal compounds are difficult to optimize and may interact with other targets. On the other hand, we have shown that diphenylmethane (DPM) derivatives act as estrogen receptor (ER) agonists and antagonists. Here, we aimed to design and synthesize non-steroidal DPM-type STS inhibitors that would also serve as pro-estrogen antagonists, releasing a metabolite with ERα-antagonistic activity upon hydrolysis by STS. We synthesized a series of compounds and evaluated their biological activities by means of STS-inhibitory activity assay and ER reporter gene assay. Among them, silicon-containing compound 16a showed strong STS-inhibitory activity (IC50=0.17μM). Further, its putative metabolite (12a) exhibited potent ERα-antagonistic activity (IC50=29.7nM).

Hepatic overexpression of steroid sulfatase ameliorates mouse models of obesity and type 2 diabetes through sex-specific mechanisms

The steroid sulfatase (STS)-mediated desulfation is a critical metabolic mechanism that regulates the chemical and functional homeostasis of endogenous and exogenous molecules. In this report, we first showed that the liver expression of Sts was induced in both the high fat diet (HFD) and ob/ob models of obesity and type 2 diabetes and during the fed to fasting transition. In defining the functional relevance of STS induction in metabolic disease, we showed that overexpression of STS in the liver of transgenic mice alleviated HFD and ob/ob models of obesity and type 2 diabetes, including reduced body weight, improved insulin sensitivity, and decreased hepatic steatosis and inflammation. Interestingly, STS exerted its metabolic benefit through sex-specific mechanisms. In female mice, STS may have increased hepatic estrogen activity by converting biologically inactive estrogen sulfates to active estrogens and consequently improved the metabolic functions, whereas ovariectomy abolished this protective effect. In contrast, the metabolic benefit of STS in males may have been accounted for by the male-specific decrease of inflammation in white adipose tissue and skeletal muscle as well as a pattern of skeletal muscle gene expression that favors energy expenditure. The metabolic benefit in male STS transgenic mice was retained after castration. Treatment with the STS substrate estrone sulfate also improved metabolic functions in both the HFD and ob/ob models. Our results have uncovered a novel function of STS in energy metabolism and type 2 diabetes. Liver-specific STS induction or estrogen/estrogen sulfate delivery may represent a novel approach to manage metabolic syndrome.

Synthesis of pharmaceutically relevant 17-α-amino steroids using an ω-transaminase

An efficient and stereoselective biocatalytic route for the synthesis of 17α-amino steroids has been developed.

Induction of steroid sulfatase expression in PC-3 human prostate cancer cells by insulin-like growth factor II

Human steroid sulfatase (STS) plays an important role in regulating the formation of biologically active estrogens and may be a promising target for treating estrogen-mediated carcinogenesis. The molecular mechanism of STS gene expression, however, is still not clear. Growth factors are known to increase STS activity but the changes in STS expression have not been completely understood. To determine whether insulin-like growth factor (IGF)-II can induce STS gene expression, the effects of IGF-II on STS expression were studied in PC-3 human prostate cancer cells. RT-PCR and Western blot analysis showed that IGF-II treatment significantly increased the expression of STS mRNA and protein in concentration- and time-dependent manners. To understand the signaling pathway by which IGF-II induces STS gene expression, the effects of specific PI3-kinase/Akt and NF-κB inhibitors were determined. When the cells were treated with IGF-II and PI3-kinase/Akt inhibitors, such as LY294002, wortmannin, or Akt inhibitor IV, STS expression induced by IGF-II was significantly blocked. Moreover, we found that NF-κB inhibitors, such as MG-132, bortezomib, Bay 11-7082 or Nemo binding domain (NBD) binding peptide, also strongly prevented IGF-II from inducing STS gene expression. We assessed whether IGF-II activates STS promoter activity using transient transfection with a luciferase reporter. IGF-II significantly stimulated STS reporter activity. Furthermore, IGF-II induced expression of 17β-hydroxysteroid dehydrogenase (HSD) 1 and 3, whereas it reduced estrone sulfotransferase (EST) gene expression, causing enhanced estrone and β-estradiol production. Taken together, these results strongly suggest that IGF-II induces STS expression via a PI3-kinase/Akt-NF-κB signaling pathway in PC-3 cells and may induce estrogen production and estrogen-mediated carcinogenesis.

Steroid derivatives as inhibitors of steroid sulfatase

Sulfated steroids function as a storage reservoir of biologically active steroid hormones. The sulfated steroids themselves are biologically inactive and only become active in vivo when they are converted into their desulfated (unconjugated) form by the enzyme steroid sulfatase (STS). Inhibitors of STS are considered to be potential therapeutics for the treatment of steroid-dependent cancers such as breast, prostate and endometrial cancer. The present review summarizes steroid derivatives as inhibitors of STS covering the literature from the early years of STS inhibitor development to October of 2012. A brief discussion of the function, structure and mechanism of STS and its role in estrogen receptor-positive (ER+) hormone-dependent breast cancer is also presented. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

The structural biology of oestrogen metabolism

Many enzymes catalyse reactions that have an oestrogen as a substrate and/or a product. The reactions catalysed include aromatisation, oxidation, reduction, sulfonation, desulfonation, hydroxylation and methoxylation. The enzymes that catalyse these reactions must all recognise and bind oestrogen but, despite this, they have diverse structures. This review looks at each of these enzymes in turn, describing the structure and discussing the mechanism of the catalysed reaction. Since oestrogen has a role in many disease states inhibition of the enzymes of oestrogen metabolism may have an impact on the state or progression of the disease and inhibitors of these enzymes are briefly discussed. This article is part of a Special Issue entitled 'CSR 2013'.

Chemical synthesis, characterisation and biological evaluation of lactonic-estradiol derivatives as inhibitors of 17β-hydroxysteroid dehydrogenase type 1

To control estradiol (E2) formation, we are interested in synthesizing inhibitors of 17β-hydroxyteroid dehydrogenase type 1 (17β-HSD1). Since the results of docking experiments have shown that E2-lactone derivatives substituted in position 19 or 20 (E-ring) could generate interactions with the active site of the enzyme, we carried out their chemical synthesis. After having prepared the 16β,17β-γ-lactone-E2 in four steps starting from estrone (E1), we introduced the molecular diversity by adding a hydroxymethyl, a methylcarboxylate, a carboxy or an allyl group. The allyl derivative was used as a key intermediate to generate a hydroxyethyl side chain in α or β position. Two lactols were also obtained from two hydroxyalkyl lactones. Enzymatic assays revealed that lactone and lactol derivatives weakly inhibited 17β-HSD1 in homogenized HEK-293 cells overexpressing 17β-HSD1 (34-60% at 1 μM) and in intact T-47D cells expressing 17β-HSD1 (10-40% at 10 μM). This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Inhibition of dehydroepiandosterone sulfate action in androgen-sensitive tissues by EM-1913, an inhibitor of steroid sulfatase

Steroid sulfatase (STS) plays an important role in the formation of estrogens and androgens by allowing the conversion of inactive circulating sulfated steroids into active hormones. These steroids support the development and growth of a number of hormone-dependent cancers, including prostate cancer. Here, we tested a non-estrogenic and non-androgenic inhibitor of steroid STS, namely EM-1913, with special attention to its potential use in the treatment of prostate cancer. After determining the required dosage of dehydroepiandrosterone sulfate (DHEAS) needed to stimulate the ventral prostate and seminal vesicles in castrated rats, we measured that EM-1913 partially (26%) and almost entirely blocked (81%) the stimulating effect of DHEAS on ventral prostates and seminal vesicles, respectively. In addition, the homogenization of these two tissues allowed us to confirm that they were completely deprived of STS activity following a treatment with EM-1913. This effect is also reflected in blood, since the plasma level of DHEAS was increased in animals treated with EM-1913, whereas the levels of dehydroepiandrosterone (DHEA) and dihydrotestosterone (DHT), two DHEAS metabolites, meanwhile decreased. From these results, we concluded that STS inhibitor EM-1913 is a good candidate for additional preclinical studies.

Estrogen sulfotransferase (SULT1E1) regulates inflammatory response and lipid metabolism of human endothelial cells via PPARγ

Estrogen sulfotransferase (SULT1E1) is a phase II drug-metabolizing enzyme known to catalyze sulfoconjugation of estrogens. 17β-estradiol (E2) plays a pivotal role in attenuating endothelial dysfunction. E2 can be further sulfated to estradiol sulfate (E2S) using SULT1E1. To date, there are no reports of expression and function of SULT1E1 in the endothelium. We identified that SULT1E1 is highly expressed in human umbilical vein endothelial cells (HUVECs) using immunofluorescence microscopy and Western immunoblot analyses. A synthesized siRNA targeting SULT1E1 was used to successfully suppress SULT1E1 expression and inhibit estrogen sulfation in HUVECs. This led to functional depletion, as confirmed by a SULT1E1 enzyme activity assay in vitro and by an in vivo estrogen sulfation assay. Knock-down of SULT1E1 in HUVECs resulted in regulation of genes involved in inflammation and lipid metabolism. Interestingly, this regulation was attenuated by PPARγ siRNA and by exposure to the PPARγ antagonist GW9662. Compared with cell response in the absence of estrogen, the effects of SULT1E1 interference on the inflammatory response and lipid metabolism related genes in the presence of 80nM estrogen were completely opposite. When exogenous estrogen was applied, cell responses depended on the ratio of E2 to E2S, due to the activity of SULT1E1, and the different regulation of these processes. It is suggested that E2 sulfation catalyzed by SULT1E1 plays an important role in modulating endothelial cell function.

Sulfatase inhibitors: a patent review

INTRODUCTION

Steroid sulfatase (STS) converts sulfated hormones to free hormones of importance in hormone-dependent diseases such as breast cancer and endometriosis. Carbohydrate sulfatases degrade complex carbohydrates as part of normal cellular turnover; certain lysosomal storage disorders (LSDs) involve defective processing of sulfated glycosaminoglycans by mutant sulfatases.

AREAS COVERED

Aryl sulfamates have been developed as STS inhibitors, and STX64 and PGL2001 are under evaluation in Phase I and II clinical trials for treatment of endometrial and metastatic breast and prostate cancers and endometriosis. Dual-acting compounds have emerged that are aromatase inhibitors (AIs), selective estrogen receptor antagonists, or inhibitors of microtubule polymerization. Sulfamidase inhibitors as pharmacological chaperones to assist maturation of folding-defective mutants for the treatment of Sanfilippo type A disease are under investigation. Coverage: The patent literature after the mid-1990s.

EXPERT OPINION

The failure of STX64 in a Phase II monotherapy clinical trial should not dissuade further investigations in multidrug regimens, particularly in combination with AIs. The recent development of dual-acting compounds may enhance the potential for success in the clinic. Further investigations into aryl sulfamates are required to clarify the molecular mechanism of action; additionally, new reversible sulfatase inhibition concepts are needed for the development of pharmacological chaperones for sulfatase LSDs.

Naturally occurring steroids in Xenopus oocyte during meiotic maturation. Unexpected presence and role of steroid sulfates

In the ovary, oocytes are surrounded by follicle cells and arrested in prophase of meiosis I. Although steroidogenic activity of follicle cells is involved in oogenesis regulation, clear qualitative and quantitative data about the steroid content of follicles are missing. We measured steroid levels of Xenopus oocytes and follicles by gas chromatography-mass spectrometry. We show that dehydroepiandrosterone sulfate is the main steroid present in oocytes. Lower levels of free steroids are also detected, e.g., androgens, whereas progesterone is almost undetectable. We propose that sulfatation is a protective mechanism against local variations of active steroids that could be deleterious for follicle-enclosed oocytes. Steroid levels were measured after LH stimulation, responsible for the release by follicle cells of a steroid signal triggering oocyte meiosis resumption. Oocyte levels of androgens rise slowly during meiosis re-entry whereas progesterone increases abruptly to micromolar concentration, therefore representing the main physiological mediator of meiosis resumption in Xenopus oocyte.