Potent inhibition of steroid sulfatase activity by 3-O-sulfamate 17alpha-benzyl(or 4'-tert-butylbenzyl)estra-1,3,5(10)-trienes: combination of two substituents at positions C3 and c17alpha of estradiol

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.

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.

Antiestrogenic Activity and Possible Mode of Action of Certain New Nonsteroidal Coumarin-4-acetamides

The preparation of certain 2-(2-oxo-2H-chromen-4-yl)-N-substituted acetamides IIIa-h was planned as a step in the development of new modified nonsteroidal antiestrogens. The purity of target compounds IIIa-h was checked by thin-layer chromatography (TLC), and their structures were confirmed using various spectroscopic tools including IR, ¹H-NMR, ¹³C-NMR, and MS spectroscopy. Viability tests were applied using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay to evaluate the cytotoxic effect of the synthesized compounds against two breast cancer cell lines, MCF-7 and MDA-MB-231. Compound IIIb proved the most active against MCF-7 cells, with an IC₅₀ value of 0.32 μM. The results of an analysis of in vitro antiestrogenic activity indicated that only compound IIIb exhibited antiestrogenic activity; its IC₅₀ value of 29.49 μM was about twice as potent as that of the reference compound, MIBP. The aromatase activity was evaluated for the synthesized target compounds IIIa-g and the intermediates Ib and IIa. A significant aromatase inhibition was observed for the intermediate Ib and compound IIIe, with IC₅₀ values of 14.5 and 17.4 μM, respectively. Compound IIIb, namely 7-methoxy-4-(2-oxo-2-(piperidin-1-yl)ethyl)-2H-chromen-2-one, could be used as an antiestrogen and/or cytotoxic agent with selective activity against tumor cells.

Synthesis and in vitro evaluation of piperazinyl-ureido sulfamates as steroid sulfatase inhibitors

Two new piperazinyl-ureido single ring aryl sulfamate-based inhibitor series were designed against the emerging oncology drug target steroid sulfatase (STS), for which there are existing potent steroidal and non-steroidal agents in clinical trials. 4-(Piperazinocarbonyl)aminosulfamates (5-31) were obtained by reacting 4-hydroxyarylamines with phenylchloroformate, subsequent sulfamoylation of the resulting hydroxyarylcarbamates and coupling of the product with 1-substituted piperazines. Pyrimidinyl-piperazinourea sulfamates (35-42) were synthesized by pyrimidine ring closure of 4-Boc-piperazine-1-carboxamidine with 3-(dimethylamino)propenones, deprotection and coupling with the sulfamoylated building block. Target ureidosulfamates 5-31 and 35-42 were evaluated both as STS inhibitors in vitro using a lysate of JEG-3 human placenta choriocarcinoma cell line and in a whole cell assay. SAR conclusions were drawn from both series. In series 35-42 the best inhibitory activity is related to the presence of a benzofuryl on the pyrimidine ring. In series 5-31 the best inhibitory activity was shown by the ureas bearing 4-chlorophenyl, 3,4-dichlorophenyl groups or aliphatic chains at the piperazino 4-nitrogen displaying IC₅₀ in the 33-94 nM concentration range. Final optimization to the low nanomolar level was achieved through substitution of the arylsulfamate ring with halogens. Four halogenated arylsulfamates of high potency were achieved and two of these 19 and 20 had IC₅₀ values of 5.1 and 8.8 nM respectively and are attractive for potential in vivo evaluation and further development. We demonstrate the optimization of this new series to low nanomolar potency, employing fluorine substitution, providing potent membrane permeant inhibitors with further development potential indicating piperazinyl-ureido aryl sulfamate derivatives as an attractive new class of STS inhibitors.

Estrogen signaling: An emanating therapeutic target for breast cancer treatment

Breast cancer, a most common malignancy in women, was known to be associated with steroid hormone estrogen. The discovery of estrogen receptor (ER) gave us not only a powerful predictive and prognostic marker, but also an efficient target for the treatment of hormone-dependent breast cancer with various estrogen ligands. ER consists of two subtypes i.e. ERα and ERβ, that are mostly G-protein-coupled receptors and activated by estrogen, specially 17β-estradiol. The activation is followed by translocation into the nucleus and binding with DNA to modulate activities of different genes. ERs can manage synthesis of RNA through genomic actions without directly binding to DNA. Receptors are tethered by protein-protein interactions to a transcription factor complex to communicate with DNA. Estrogens also exhibit nongenomic actions, a characteristic feature of steroid hormones, which are so rapid to be considered by the activation of RNA and translation. These are habitually related to stimulation of different protein kinase cascades. Majority of post-menopausal breast cancer is estrogen dependent, mostly potent biological estrogen (E2) for continuous growth and proliferation. Estrogen helps in regulating the differentiation and proliferation of normal breast epithelial cells. In this review we have investigated the important role of ER in development and progression of breast cancer, which is complicated by receptor's interaction with co-regulatory proteins, cross-talk with other signal transduction pathways and development of treatment strategies viz. selective estrogen receptor modulators (SERMs), selective estrogen receptor down regulators (SERDs), aromatase and sulphatase inhibitors.

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.

Synthesis of novel 16-spiro steroids: 7-(Aryl)tetrahydro-1H-pyrrolo[1,2-c][1,3]thiazolo estrone hybrid heterocycles

The 1,3-dipolar cycloaddition of azomethine ylides generated in situ from the reaction of isatins or acenaphthylene-1,2-dione and 1,3-thiazolane-4-carboxylic acid to various exocyclic dipolarophiles synthesized from estrone afforded a library of novel C-16 spiro oxindole or acenaphthylene-1-one - 7-(aryl)tetrahydro-1H-pyrrolo[1,2-c][1,3]thiazole - estrone hybrid heterocycles. These reactions occur regio- and stereo-selectively affording a single isomer of the spiro estrones in excellent yields with the formation of two C-C and one C-N bonds along with the generation of four new contiguous stereo-centers in a single step.

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".

Current status on development of steroids as anticancer agents

Steroids are important biodynamic agents. Their affinities for various nuclear receptors have been an interesting feature to utilize them for drug development particularly for receptor mediated diseases. Steroid biochemistry and its crucial role in human physiology, has attained importance among the researchers. Recent years have seen an extensive focus on modification of steroids. The rational modifications of perhydrocyclopentanophenanthrene nucleus of steroids have yielded several important anticancer lead molecules. Exemestane, SR16157, fulvestrant and 2-methoxyestradiol are some of the successful leads emerged on steroidal pharmacophores. The present review is an update on some of the steroidal leads obtained during past 25 years. Various steroid based enzyme inhibitors, antiestrogens, cytotoxic conjugates and steroidal cytotoxic molecules of natural as well as synthetic origin have been highlighted. 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.

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.

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

The steroid sulfatase (STS) plays a major role in the regulation of steroid hormone concentrations in several human tissues and target organs and therefore, represents an interesting target to regulate estrogen and androgen levels implicated in different diseases. In this review article, the emphasis is put on STS inhibitors reported in the fruitful 2000-2010 decade, which consolidated the first ones that were previously developed (1990-1999). The inhibitors reviewed are divided into four categories according to the fact that they are sulfamoylated or not or that they have a steroid nucleus or not. Other topics such as function, localization, structure and mechanism as well as applications of STS inhibitors are also briefly discussed to complement the information on this crucial steroidogenic enzyme and its inhibitors.

Molecular therapy of breast cancer: progress and future directions

Breast cancer is a major cause of death in Western women, with a 10% lifetime risk of the disease. Most breast cancers are estrogen-dependent. Molecular therapies for breast cancer have developed rapidly in the past few decades and future treatment strategies are being investigated. The selective estrogen receptor (ER) modulator tamoxifen, which until now has served as a standard therapy, functions not only as an estrogen antagonist but also as an estrogen agonist in terms of bone maintenance. Aromatase inhibitors have performed well in international trials and have become a new standard therapy for estrogen-dependent breast cancer. The systematic study of estrogen activation pathways suggests that the enzymes steroid sulfatase and 17beta-hydroxysteroid dehydrogenase type 1, which both have pivotal roles in estrogen biosynthesis, are promising targets; the results of a phase I trial of steroid sulfatase inhibitors are encouraging. The activity of the human epidermal growth factor receptor (HER) pathway correlates negatively with that of the ER. HER2 is overexpressed in 22% of all breast cancers. In the decade since HER2 began being targeted, the monoclonal antibody trastuzumab has been used as well as pertuzumab and HER2 vaccines. Among the estrogen-independent breast cancers, the basal-like subtype has low survival, and therapeutic improvement is a priority. Crosstalk between ER and HER2 signaling pathways means that combinatory therapies may hold the key to enhancement of treatment responses. Other molecular therapies involving functional genomics and RNA interference studies also hold promise.

Synthesis of Libraries of 16β-Aminopropyl Estradiol Derivatives for Targeting Two Key Steroidogenic Enzymes

Two libraries, each consisting of 48 16beta-aminopropyl estradiol derivatives, phenols and sulfamates, respectively, were synthesized by solid-phase parallel chemistry through a seven-step reaction sequence. Following the attachment of a C18-steroid sulfamate precursor on a trityl chloride resin, diversity elements were first introduced on the 16beta-aminopropyl chain of the steroid by acylation reactions with eight Fmoc-amino acids. After deprotection, the free amine function of the resulting compounds was reacted with six carboxylic acids for the introduction of a second diversity level. The two variants employed for the cleavage of compounds from the solid support, acidic and nucleophilic, allowed the corresponding libraries of sulfamate and phenol derivatives in yields of 8-50 % and 13-58 % to be obtained with an average HPLC purity of 94 % and 91 %, respectively. Potent steroid sulfatase inhibitors and interesting SAR results were generated from the screening of the sulfamate library. Furthermore, moderate inhibitors of type 1 17beta-HSD resulted from the partial screening of phenol library. Thus, these two categories of compounds were synthesized to rapidly identify potential inhibitors of steroid biosynthesis for the hormonal therapy of estrogen-dependent diseases, and also to demonstrate the versatility and efficiency of the recently developed sulfamate linker.

Inhibition of estrone sulfatase by aromatase inhibitor-based estrogen 3-sulfamates

Our rationale is based on the finding that estrone 3-sulfamate (EMATE, 2d), a typical estrone sulfatase (ES) inhibitor, can be hydrolyzed and the pharmacological effect of the free estrogen contributes to the bioactivity of the sulfamate. A number of 3-sulfamoylated derivatives of the good aromatase inhibitors, 2- and 4-halogeno (F, Cl, and Br) estrones and their estradiol analogs as well as 6beta-methyl and phenyl estrones, were synthesized and evaluated as inhibitors of ES in human placental microsomes in comparison with the lead compound EMATE. Among them, 2-chloro- and 2-bromoestrone 3-sulfamates (2b and 2c), along with their estradiol analogs 3b and 3c, were powerful competitive inhibitors with K(i)'s ranging between 4.0 and 11.3 nM (K(i) for EMATE, 73 nM). These four sulfamates as well as the 2-fluoro analogs 2a and 3a inactivated ES in a time-dependent manner more efficiently than EMATE, and 2-halogeno estrone sulfamates 2 also caused a concentration-dependent loss of ES activity. The results may be useful for developing a new class of drugs having a dual function, ES inhibition and aromatase inhibition, for the treatment of breast cancer.

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.

Recent insight on the control of enzymes involved in estrogen formation and transformation in human breast cancer

The great majority of breast cancers are in their early stage hormone-dependent and it is well accepted that estradiol (E2) plays an important role in the genesis and evolution of this tumor. Human breast cancer tissues contain all the enzymes: estrone sulfatase, 17beta-hydroxysteroid dehydrogenase, aromatase involved in the last steps of E2 bioformation. Sulfotransferases which convert estrogens into the biologically inactive estrogen sulfates are also present in this tissue. Quantitative data show that the 'sulfatase pathway', which transforms estrogen sulfates into the bioactive unconjugated E2, is 100-500 times higher than the 'aromatase pathway', which converts androgens into estrogens. The treatment of breast cancer patients with anti-aromatases is largely developed with very positive results. However, the formation of E2 via the 'sulfatase pathway' is very important in the breast cancer tissue. In recent years it was found that antiestrogens (e.g. tamoxifen, 4-hydroxytamoxifen), various progestins (e.g. promegestone, nomegestrol acetate, medrogestone, dydrogesterone, norelgestromin), tibolone and its metabolites, as well as other steroidal (e.g. sulfamates) and non-steroidal compounds, are potent sulfatase inhibitors. In another series of studies, it was found that E2 itself has a strong anti-sulfatase action. This paradoxical effect of E2 adds a new biological response of this hormone and could be related to estrogen replacement therapy in which it was observed to have either no effect or to decrease breast cancer mortality in postmenopausal women. Interesting information is that high expression of steroid sulfatase mRNA predicts a poor prognosis in patients with +ER. These progestins, as well as tibolone, can also block the conversion of estrone to estradiol by the inhibition of the 17beta-hydroxysteroid dehydrogenase type I (17beta-HSD-1). High expressison of 17beta-HSD-1 can be an indicator of adverse prognosis in ER-positive patients. It was shown that nomegestrol acetate, medrogestone, promegestone or tibolone, could stimulate the sulfotransferase activity for the local production of estrogen sulfates. This is an important point in the physiopathology of this disease, as it is well known that estrogen sulfates are biologically inactive. A possible correlation between this stimulatory effect on sulfotransferase activity and breast cancer cell proliferation is presented. In agreement with all this information, we have proposed the concept of selective estrogen enzyme modulators (SEEM). In conclusion, the blockage in the formation of estradiol via sulfatase, or the stimulatory effect on sulfotransferase activity in combination with anti-aromatases can open interesting and new possibilities in clinical applications in breast cancer.

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.

Stilbene-Based Inhibitors of Estrone Sulfatase with a Dual Mode of Action in Human Breast Cancer Cells

Estrone sulfate (E1S) is an endogenous prodrug that delivers estrone and, subsequently, estradiol to target cells, after hydrolysis by the enzyme estrone sulfatase, which is active in various tissues including hormone-dependent breast cancer. Blockade of this enzyme should reduce the estrogen level in breast cancer cells and prevent hormonal growth stimulation. In this study, a number of sulfamoyloxy-substituted stilbenes with side chains that guarantee antiestrogenic activity were synthesized and evaluated as inhibitors of estrone sulfatase. They inhibited this enzyme in human MDA-MB 231 breast cancer cells, with IC(50) values in the submicromolar range. The effects of both the free hydroxy derivatives and the sulfamates on gene activation were determined in transfected MCF-7/2a breast cancer cells stimulated either with estradiol or with estrone sulfate. The analysis of data revealed a dual mode of action of the majority of compounds. They blocked gene expression by inhibition of estrone sulfatase and by antiestrogenic action. This pharmacological profile was also observed in assays on antiproliferative activity. The most potent derivative 8 g inhibited the growth of wild-type human MCF-7 cells with an IC(50) value of 13 nM.

Sulfatases: Structure, Mechanism, Biological Activity, Inhibition, and Synthetic Utility

Sulfatases, which cleave sulfate esters in biological systems, play a key role in regulating the sulfation states that determine the function of many physiological molecules. Sulfatase substrates range from small cytosolic steroids, such as estrogen sulfate, to complex cell-surface carbohydrates, such as the glycosaminoglycans. The transformation of these molecules has been linked with important cellular functions, including hormone regulation, cellular degradation, and modulation of signaling pathways. Sulfatases have also been implicated in the onset of various pathophysiological conditions, including hormone-dependent cancers, lysosomal storage disorders, developmental abnormalities, and bacterial pathogenesis. These findings have increased interest in sulfatases and in targeting them for therapeutic endeavors. Although numerous sulfatases have been identified, the wide scope of their biological activity is only beginning to emerge. Herein, accounts of the diversity and growing biological relevance of sulfatases are provided along with an overview of the current understanding of sulfatase structure, mechanism, and inhibition.

Differential effects of progestins on breast tissue enzymes

There is substantial evidence that mammary cancer tissue contains all the enzymes responsible for the local biosynthesis of estradiol (E2) from circulating precursors. Two principal pathways are implicated in the final steps of E2 formation in breast cancer tissue: the 'aromatase pathway' that transforms androgens into estrogens and the 'sulfatase pathway' that converts estrone sulfate (E1S) into estrone (E1) via estrone sulfatase. The final step is the conversion of weak E1 to potent biologically active E2 via reductive 17beta-hydroxysteroid dehydrogenase type 1 activity. It is also well established that steroid sulfotransferases, which convert estrogens into their sulfates, are present in breast cancer tissues. One of the possible means of blocking E2 effects in breast cancer is to use anti-estrogens, which act by binding to the estrogen receptor (ER). Another option is to block E2 using anti-enzymes (anti-sulfatase, anti-aromatase, or anti-17beta-hydroxysteroid dehydrogenase (17beta-HSD). Various progestins (e.g. promegestone, nomegestrol acetate, medrogestone, 17-deacetyl norgestimate, dydrogesterone and its 20-dihydro derivative), as well as tibolone and its metabolites, have been shown to inhibit estrone sulfatase and 17beta-hydroxysteroid dehydrogenase. Some progestins and tibolone can also stimulate sulfotransferase activity. These various progestins may therefore provide a new option for the treatment of breast cancer.

The selective estrogen enzyme modulators in breast cancer: a review

It is well established that increased exposure to estradiol (E(2)) is an important risk factor for the genesis and evolution of breast tumors, most of which (approximately 95-97%) in their early stage are estrogen-sensitive. However, two thirds of breast cancers occur during the postmenopausal period when the ovaries have ceased to be functional. Despite the low levels of circulating estrogens, the tissular concentrations of these hormones are significantly higher than those found in the plasma or in the area of the breast considered as normal tissue, suggesting a specific tumoral biosynthesis and accumulation of these hormones. Several factors could be implicated in this process, including higher uptake of steroids from plasma and local formation of the potent E(2) by the breast cancer tissue itself. This information extends the concept of 'intracrinology' where a hormone can have its biological response in the same organ where it is produced. There is substantial information that mammary cancer tissue contains all the enzymes responsible for the local biosynthesis of E(2) from circulating precursors. Two principal pathways are implicated in the last steps of E(2) formation in breast cancer tissues: the 'aromatase pathway' which transforms androgens into estrogens, and the 'sulfatase pathway' which converts estrone sulfate (E(1)S) into E(1) by the estrone-sulfatase. The final step of steroidogenesis is the conversion of the weak E(1) to the potent biologically active E(2) by the action of a reductive 17beta-hydroxysteroid dehydrogenase type 1 activity (17beta-HSD-1). Quantitative evaluation indicates that in human breast tumor E(1)S 'via sulfatase' is a much more likely precursor for E(2) than is androgens 'via aromatase'. Human breast cancer tissue contains all the enzymes (estrone sulfatase, 17beta-hydroxysteroid dehydrogenase, aromatase) involved in the last steps of E(2) biosynthesis. This tissue also contains sulfotransferase for the formation of the biologically inactive estrogen sulfates. In recent years, it was demonstrated that various progestins (promegestone, nomegestrol acetate, medrogestone, dydrogesterone, norelgestromin), tibolone and its metabolites, as well as other steroidal (e.g. sulfamates) and non-steroidal compounds, are potent sulfatase inhibitors. Various progestins can also block 17beta-hydroxysteroid dehydrogenase activities. In other studies, it was shown that medrogestone, nomegestrol acetate, promegestone or tibolone can stimulate the sulfotransferase activity for the local production of estrogen sulfates. All these data, in addition to numerous agents which can block the aromatase action, lead to the new concept of 'Selective Estrogen Enzyme Modulators' (SEEM) which can largely apply to breast cancer tissue. The exploration of various progestins and other active agents in trials with breast cancer patients, showing an inhibitory effect on sulfatase and 17beta-hydroxysteroid dehydrogenase, or a stimulatory effect on sulfotransferase and consequently on the levels of tissular levels of E(2), will provide a new possibility in the treatment of this disease.

Synthesis, in vitro and in vivo activity of benzophenone-based inhibitors of steroid sulfatase

Steroid sulfatase (STS) is an important new therapeutic target in oncology. Attempts to design nonsteroidal STS inhibitors, because of the oestrogenicity of the original lead oestrone 3-O-sulfamate in rodents, have led to the discovery of benzophenone-4,4'-O,O-bis-sulfamate (BENZOMATE, 3). The nonfused bicyclic BENZOMATE is a highly potent STS inhibitor in vitro, inhibiting STS activity in intact MCF-7 breast cancer cells by > 70% at 0.1 microM and in placental microsomes by > 98% at 10 microM. When MCF-7 cells were pre-treated with 3 at 1 microM and then washed to remove unbound inhibitor, the initial 94% inhibition was reduced to 89% suggesting that 3, like other sulfamate-based STS inhibitors, inhibits the enzyme irreversibly. This agent also inhibits rat liver STS activity by 84% and 93% respectively 24 h after a single dose of 1 or 10 mg/kg, demonstrating that BENZOMATE possesses similar in vivo potency to the established potent nonsteroidal inhibitor 667COUMATE. Several modifications were made to BENZOMATE structurally and effects on in vitro activity were examined. These structure-activity relationship studies show that its carbonyl and bis-sulfamate groups are pivotal for activity, although conformational flexibility is not required. Two rigid anthraquinone-based sulfamate derivatives however showed inhibitory activity significantly better than BENZOMATE in the MCF-7 cell assay. BENZOMATE and related analogues therefore represent an important class of non-steroidal STS inhibitor and lead compounds for future drug design.

2-phenylindole sulfamates: inhibitors of steroid sulfatase with antiproliferative activity in MCF-7 breast cancer cells

A number of 2-phenylindole sulfamates with lipophilic side chains in 1- or 5-position of the indole were synthesized and evaluated as steroid sulfatase (estrone sulfatase) inhibitors. Most of the new sulfamates inhibited the enzymatic hydrolysis of estrone sulfate in MDA-MB 231 breast cancer cells with IC(50) values between 2 nM and 1 microM. A favorable position for a long side chain is the nitrogen of a carbamoyl group at C-5 of the indole when the phenyl ring carries the sulfamate function. These derivatives inhibit gene activation in estrogen receptor (ER)-positive MCF-7 breast cancer cells in submicromolar concentrations and reduce cell proliferation with IC(50) values of ca. 1 microM. All of the potent inhibitors were devoid of estrogenic activity and have the potential for in vivo application as steroid sulfatase inhibitors.

Sulfamates and their therapeutic potential

Starting from the very simple molecule sulfamic acid, O-substituted-, N-substituted-, or di-/tri-substituted sulfamates may be obtained, which show specific biological activities which were or started to be exploited for the design of many types of therapeutic agents. Among them, sulfamate inhibitors of aminoacyl-tRNA synthetases (aaRSs) were recently reported, constituting completely new classes of antibiotics, useful in the fight of drug-resistant infections. Anti-viral agents incorporating sulfamate moieties have also been obtained, with at least two types of such derivatives investigated: the nucleoside/nucleotide human immunodeficiency virus (HIV) reverse transcriptase inhibitors, and the HIV protease inhibitors (PIs). In the increasing armamentarium of anti-cancer drugs, the sulfamates occupy a special position, with at least two important targets evidenced so far: the steroid sulfatases (STSs) and the carbonic anhydrases (CAs). An impressing number of inhibitors of STSs of the sulfamate type have been reported in the last years, with several compounds, such as 667COUMATE among others, progressing to clinical trials for the treatment of hormone-dependent tumors (breast and prostate cancers). This field is rapidly evolving, with many types of new inhibitors being constantly reported and designed in such a way as to increase their anti-tumor properties, and decrease undesired features (for example, estrogenicity, a problem encountered with the first generation such inhibitors, such as EMATE). Among the many isozymes of CAs, at least two, CA IX and CA XII, are highly overexpressed in tumors, being generally absent in the normal tissues. Inhibition of tumor-associated CAs was hypothesized to lead to novel therapeutic approaches for the treatment of cancer. Many sulfamates act as very potent (low nanomolar) CA inhibitors. The X-ray crystal structure of the best-studied isozyme, CA II, with three sulfamates (sulfamic acid, topiramate, and EMATE) has recently been reported, which allowed for a rationale drug design of new inhibitors. Indeed, low nanomolar CA IX inhibitors of the sulfamate type have been reported, although such compounds also act as efficient inhibitors of isozymes CA I and II, which are not associated with tumors. A large number of anti-convulsant sulfamates have been described, with one such compound, topiramate, being widely used clinically as anti-epileptic drug. By taking into consideration a side effect of topiramate, an anti-epileptic drug leading to weight loss in some patients, it has recently been proposed to use this drug and related sulfamates for the treatment of obesity. The rationale of this use is based on the inhibition of the mitochondrial CA isozyme, CA V, involved in lipogenesis. Some sulfamates were also shown to possess potent inhibitory activity against acyl coenzyme A:cholesterol acyltransferase, an enzyme involved in cholesterol metabolism. One such agent, avasimibe, is in advanced clinical trials for the treatment of hyperlipidemia and atherosclerosis. Thus, the sulfamate moiety offers very attractive possibilities for the drug design of various pharmacological agents, which are on one hand due to the relative ease with which such compounds are synthesized, and on the other one, due to the fact that biological activity of most of them is impressive.

Development of novel steroid sulfatase inhibitors. I. Synthesis and biological evaluation of biphenyl-4-O-sulfamates

Compounds which interfere with steroid sulfatase (STS) are expected as important novel therapeutic drugs for postmenopausal breast tumor. Therefore, a number of strategies have been adopted to design and synthesize potent, nonestrogenic STS inhibitors. We chose biphenyl as a scaffold for STS inhibitors and synthesized some biphenyl-4-O-sulfamate derivatives (29-43). Their inhibitory activity on STS and estrogenicity were evaluated. Substitution of electron-withdrawing groups (e.g., cyano, nitro) at the 2'- or 4'-position of biphenyl-4-O-sulfamate remarkably increased STS-inhibitory activity. Especially, 2',4'-dicyanobiphenyl-4-O-sulfamate (35, TZS-8478) showed very potent STS-inhibitory activity in vitro. The administration of TZS-8478 (0.5 mg/kg per day, p.o., for 5 days) completely inhibited rat liver and uterine STS similarly to EMATE (1). Furthermore, TZS-8478 (10 mg/kg per day, p.o., for 5 days) had no stimulative effect on uterine growth in ovariectomized rats, and its desulfamoylated compound (20) was little bound to the human estrogen receptor alpha. The identification of a potent steroid sulfatase inhibitor without estrogenicity, such as TZS-8478, should be of considerable value in evaluating the potential of steroid sulfatase inhibition for breast tumor therapy.

Nortropinyl-Arylsulfonylureas as novel, reversible inhibitors of human steroid sulfatase

Steroid sulfatase (STS) has emerged as an attractive target for a range of estrogen- and androgen-dependent diseases. Searching for novel chemotypes as STS inhibitors, we identified nortropinyl-arylsulfonylurea 3 as a hit from high-throughput screening. A series of analogues was prepared in order to explore the essential structural elements for STS inhibition, and first structure-activity relationships were established. Mechanistic investigations revealed that the compounds are reversible, competitive inhibitors of STS.

Solid-phase parallel synthesis of 17alpha-substituted estradiol sulfamate and phenol libraries using the multidetachable sulfamate linker

We report an application of the multidetachable sulfamate linker in the synthesis of two model libraries of N-derivatized 17alpha-piperazinomethyl estradiols (phenols and sulfamates) by solid-phase parallel chemistry. The solid-phase precursor, a 3-sulfamoyl-17alpha-(N-trifluoroacetyl-piperazinomethyl) estradiol, was synthesized in solution from estrone and loaded efficiently onto trityl chloride resin as polymeric support. After cleavage of the trifluoroacetyl protecting group, sequential acylation reactions with five Fmoc-protected amino acids and five carboxylic acids were performed to introduce two levels of molecular diversity. Finally, the resins were split into two parts, and acidic (5% trifluoroacetic acid in dichloromethane) and nucleophilic (piperazine in tetrahydrofuran) cleavages were used to generate libraries A (5 x 5 sulfamates) and B (5 x 5 phenols) members in overall yields of 18-66% and high HPLC purities (87-96%) without purification steps. A preliminary screening test for inhibition of steroid sulfatase showed that the phenols were clearly weaker inhibitors, as compared to their sulfamate analogues. The most potent inhibitors were those with suitable hydrophobic amino acid and carboxylic acid substituents. Thus, compounds with a phenylalanine residue as the first element of diversity inhibited over 90% of steroid sulfatase activity at a concentration of 1 nM in homogenates of HEK-293 transfected cells, being as potent as the leading inhibitor 17alpha-tert-butylbenzyl estradiol 3-O-sulfamate previously reported. These results suggest that the steroid sulfatase inhibitory potency of estradiol derivatives, sulfamoylated or not, can be increased by the hydrophobic effect of a suitable substituent introduced in the proximity of the D ring of the steroid. The present work also demonstrated the efficiency and the cleavage versatility of the sulfamate linker to generate libraries of compounds with relevant biological importance, phenols and sulfamates.

D-ring modified estrone derivatives as novel potent inhibitors of steroid sulfatase

A series of novel D-ring modified derivatives of estrone was synthesized and tested as inhibitors of steroid sulfatase (STS). The steroidal D-ring was cleaved via an iodoform reaction and thermal condensation of the resulting marrianolic acid derivative gave 16,17-seco-estra-1,3,5(10)-triene-16,17-imide derivatives, where a piperidinedione moiety is in place of the D-ring. This synthetic approach was found to give a higher overall yield than the literature method of Beckmann rearrangement. A range of alkyl side chains have been introduced on the nitrogen atom of the imido-ring and the corresponding 3-O-sulfamates synthesized. The new D-ring modified estrone derivatives bearing a propyl (39) and a 1-pyridin-3-ylmethyl (46) moiety had IC(50) values of 1 nM when tested in placental microsomes for the inhibition of STS. These compounds are therefore up to 18-fold more potent than EMATE, the very first highly potent irreversible steroidal STS inhibitor.

Sulfamoyloxy-substituted 2-phenylindoles: antiestrogen-based inhibitors of the steroid sulfatase in human breast cancer cells

Estrone sulfate (E1S) is an endogenous prodrug that delivers estrone and, subsequently, estradiol to the target cells following the hydrolysis by the enzyme estrone sulfatase which is active in various tissues including hormone dependent breast cancer cells. Blockade of this enzyme should reduce the estrogen level in breast cancer cells and prevent hormonal growth stimulation. Sulfamates of a variety of phenolic compounds have been shown to be inhibitors of estrone sulfatase. Our rational is based on findings that these inhibitors can undergo hydrolysis and the pharmacological effects of the free hydroxy compounds contribute to the bioactivity of the sulfamates. A desirable action of the metabolites would be an estrogen antagonism to block stimulatory effects of residual amounts of estrogens. Thus, we synthesized a number of sulfamoyloxy-substituted 2-phenylindoles with side chains at the indole nitrogen that guarantee antiestrogenic activity. All of the new sulfamates were studied for their inhibitory effects on the enzyme estrone sulfatase from human breast cancer cells and their (anti)hormonal activities in stably transfected human MCF-7/2a mammary carcinoma cells. The hormonal profile of the sulfamates was partly reflected by the properties of the corresponding hydroxy precursors. Some of the sulfamoylated antiestrogens strongly inhibited estrone sulfatase activity with IC(50) values in the submicromolar range. They were devoid of agonist activity and suppressed estrone sulfate-stimulated gene expression mainly by blocking the enzyme. Examples are the disulfamates of the indoles ZK 119, 010 and ZK 164, 015. Their IC(50)s for sulfatase inhibition were 0.3 and 0.2 microM, respectively, and 50 and 80 nM, respectively, for the inhibition of E1S-stimulated luciferase expression in transfected MCF-7 cells. With some of the new sulfamates an additional direct antiestrogenic effect was noticed which might be due to a partial hydrolysis during incubation and would improve the growth inhibitory effect on estrogen-sensitive breast cancer cells.

Cutaneous androgen metabolism: basic research and clinical perspectives

The skin, especially the pilosebaceous unit composed of sebaceous glands and hair follicles, can synthesize androgens de novo from cholesterol or by locally converting circulating weaker androgens to more potent ones. As in other classical steroidogenic organs, the same six major enzyme systems are involved in cutaneous androgen metabolism, namely steroid sulfatase, 3beta-hydroxy-steroid dehydrogenase, 17beta-hydroxysteroid dehydrogenase, steroid 5alpha-reductase, 3alpha-hydroxysteroid dehydrogenase, and aromatase. Steroid sulfatase, together with P450 side chain cleavage enzyme and P450 17-hydroxylase, was found to reside in the cytoplasm of sebocytes and keratinocytes. Strong steroid sulfatase immunoreactivity was observed in the lesional skin but not in unaffected skin of acne patients. 3beta-hydroxysteroid dehydrogenase has been mainly immunolocalized to sebaceous glands, with the type 1 being the key cutaneous isoenzyme. The type 2 17beta-hydroxysteroid dehydrogenase isoenzyme predominates in sebaceous glands and exhibits greater reductive activity in glands from facial areas compared with acne nonprone areas. In hair follicles, 17beta-hydroxysteroid dehydrogenase was identified mainly in outer root sheath cells. The type 1 5alpha-reductase mainly occurs in the sebaceous glands, whereby the type II isoenzyme seems to be localized in the hair follicles. 3alpha-hydroxysteroid dehydrogenase converts dihydrotestosterone to 3alpha-androstanediol, and the use of 3alpha-androstanediol glucuronide serum level to reflect the hyperandrogenic state in hirsute women may be a reliable parameter, especially for idiopathic hirsutism. In acne patients it is still controversial if 3alpha-androstanediol glucuronide or androsterone glucuronide could serve as suitable serum markers for measuring androgenicity. Aromatase, localized to sebaceous glands and to both outer as well as inner root sheath cells of anagen terminal hair follicles, may play a "detoxifying" role by removing excess androgens. Pharmacologic development of more potent specific isoenzyme antagonists may lead to better clinical treatment or even prevention of androgen-dependent dermatoses.

A multidetachable sulfamate linker successfully used in a solid-Phase strategy to generate libraries of sulfamate and phenol derivatives

The sulfamates and phenols constitute two families of compounds with numerous interesting biological properties. Using the ability of a new multidetachable sulfamate linker to generate these two families of compounds from the same resin, we designed and synthesized libraries of estradiol derivatives, sulfamoylated or not. A C-16beta side chain was then judiciously diversified to target two key steroidogenic enzymes, the steroid sulfates and the type 1 17beta-HSD. Four libraries of sulfamate and phenol derivatives were easily obtained by solid-phase parallel synthesis in good crude overall yields (13-62%) and HPLC purities (85-96%). Such strategy using the new two-in-line sulfamate linker could be also extended to other therapeutic targets than steroidogenic enzymes, thus adding to its potential.