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

Potent Dual Inhibitors of Steroid Sulfatase and 17β-Hydroxysteroid Dehydrogenase Type 1 with a Suitable Pharmacokinetic Profile for In Vivo Proof-of-Principle Studies in an Endometriosis Mouse Model

Treating estrogen-dependent diseases like endometriosis with drugs suppressing local estrogen activation may be superior to existing endocrine therapies. Steroid sulfatase (STS) and 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1) are key enzymes of local estrogen activation. We describe the rational design, synthesis, and biological profilation of furan-based compounds as a novel class of dual STS/17β-HSD1 inhibitors (DSHIs). In T47D cells, compound 5 showed irreversible inhibition of STS and potent, reversible inhibition of 17β-HSD1. It was selective over 17β-HSD2 and displayed high metabolic stabilities in human and mouse liver S9 fractions. No effect on cell viability was detected up to 31 μM (HEK293) and 23 μM (HepG2), respectively, and there was no activation of the aryl hydrocarbon receptor (AhR) up to 3.16 μM. Single daily application to mice revealed steady-state plasma levels high enough to make this compound eligible for an in vivo proof-of-principle study in a mouse endometriosis model.

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.

Steroid Sulphatase and Its Inhibitors: Past, Present, and Future

Steroid sulphatase (STS), involved in the hydrolysis of steroid sulphates, plays an important role in the formation of both active oestrogens and androgens. Since these steroids significantly impact the proliferation of both oestrogen- and androgen-dependent cancers, many research groups over the past 30 years have designed and developed STS inhibitors. One of the main contributors to this field has been Prof. Barry Potter, previously at the University of Bath and now at the University of Oxford. Upon Prof. Potter’s imminent retirement, this review takes a look back at the work on STS inhibitors and their contribution to our understanding of sulphate biology and as potential therapeutic agents in hormone-dependent disease. A number of potent STS inhibitors have now been developed, one of which, Irosustat (STX64, 667Coumate, BN83495), remains the only one to have completed phase I/II clinical trials against numerous indications (breast, prostate, endometrial). These studies have provided new insights into the origins of androgens and oestrogens in women and men. In addition to the therapeutic role of STS inhibition in breast and prostate cancer, there is now good evidence to suggest they may also provide benefits in patients with colorectal and ovarian cancer, and in treating endometriosis. To explore the potential of STS inhibitors further, a number of second- and third-generation inhibitors have been developed, together with single molecules that possess aromatase–STS inhibitory properties. The further development of potent STS inhibitors will allow their potential therapeutic value to be explored in a variety of hormone-dependent cancers and possibly other non-oncological conditions.

Direct quantification of anorethidrani disuccinate and determination of sterol metabolites by chemical derivatization combined with LC-MS/MS: Application to a Phase I pharmacokinetic study in humans

Anorethidrani disuccinate (ACP) is a domestically designed A-decarbonized steroid that is currently being investigated in Phase I clinical trials for the treatment of solid tumors. Only the parent drug exhibited antitumor activity; its sterol metabolite M2 showed obvious antiestrogenic effects. We have developed a rapid, sensitive, and robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the direct quantification of ACP and a chemical derivatization method that can be used to quantify M2 derivatized with glycidyl trimethyl ammonium chloride (GTMA). A simple protein precipitation procedure was performed to quantify ACP. Injections were obtained within 3.5 min on an Eclipse Plus Phenyl-Hexyl column (50 mm × 2.1 mm i.d., 1.8 μm) with gradient elution; the calibration curve was linear over the range of 2.00-8000 ng/mL. For quantification of M2 in plasma, analytes were extracted by protein precipitation and converted to their GTMA derivatives at 60 °C for 2 h at pH 12; the analytes and coelutants were separated on a Luna C8(2) column (50 mm × 2.0 mm i.d., 5.0 μm). The precision (RSD) and accuracy (RE) of the intra- and interday determinations were within 10%. The derivatization procedure is a novel method for sterol determination by LC-MS/MS. The results confirmed the usefulness of this method for characterizing the pharmacokinetic profiles of ACP and its major metabolite M2 in a Phase I pharmacokinetic study.

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.

Targeted NF1 cancer therapeutics with multiple modes of action: small molecule hormone-like agents resembling the natural anticancer metabolite, 2-methoxyoestradiol

Background:

Both the number and size of tumours in NF1 patients increase in response to the rise in steroid hormones seen at puberty and during pregnancy. The size of tumours decreases after delivery, suggesting that hormone-targeting therapy might provide a viable new NF1 treatment approach. Our earlier studies demonstrated that human NF1 tumour cell lines either went through apoptosis or ceased growth in the presence of 2-methoxyoestradiol (2ME2), a naturally occurring anticancer metabolite of 17-β estradiol. Previous reports of treatment with sulfamoylated steroidal and non-steroidal derivatives of 2ME2 showed promising reductions in tumour burden in hormone-responsive cancers other than NF1. Here we present the first studies indicating that 2ME2 derivatives could also provide an avenue for treating NF1, for which few treatment options are available.

Methods:

STX3451, (2-(3-Bromo-4,5-dimethoxybenzyl)-7-methoxy-6-sulfamoyloxy-1,2,3,4-tetrahydroisoquinoline), a non-steroidal sulphamate analogue of 2ME2, was tested in dose-dependent studies of malignant and benign NF1 human tumour cell lines and cell lines with variable controlled neurofibromin expression. The mechanisms of action of STX3451 were also analysed.

Results:

We found that STX3451-induced apoptosis in human malignant peripheral nerve sheath tumour (MPNST) cell lines, even in the presence of elevated oestrogen and progesterone. It inhibits both PI3 kinase and mTOR signalling pathways. It disrupts actin- and microtubule-based cytoskeletal structures in cell lines derived from human MPNSTs and in cells derived from benign plexiform neurofibromas. STX3451 selectively kills MPNST-derived cells, but also halts growth of other tumour-derived NF1 cell lines.

Conclusion:

STX3451 provides a new approach for inducing cell death and lowering tumour burden in NF1 and other hormone-responsive cancers with limited treatment options.

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

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

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

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

(125)I-Labelled 2-Iodoestrone-3-sulfate: synthesis, characterization and OATP mediated transport studies in hormone dependent and independent breast cancer cells

INTRODUCTION

Organic Anion Transporting Polypeptides (OATP) are a family of membrane associated transporters that facilitate estrone-3-sulphate (E3S) uptake by hormone dependent, post-menopausal breast cancers. We have established E3S as a potential ligand for targeting hormone dependent breast cancer cells, and in this study sought to prepare and investigate radioiodinated E3S as a tool to study the OATP system.

METHODS

2- and 4-Iodoestrone-3-sulfates were prepared from estrone via aromatic iodination followed by a rapid and high yielding sulfation procedure. The resulting isomers were separated by preparative HPLC and verified by (1)H NMR and analytical HPLC. Transport studies of 2- and 4-[(125)I]-E3S were conducted in hormone dependent (i.e. MCF-7) and hormone independent (i.e. MDA-MB-231) breast cancer cells in the presence or absence of the specific transport inhibitor, bromosulfophthalein (BSP). Cellular localization of OATP1A2, OATP2B1, OATP3A1 and OATP4A1 were determined by immunofluorescence analysis using anti-Na(+)/K(+) ATPase-α (1:100 dilution) and DAPI as plasma membrane and nuclear markers, respectively.

RESULTS

Significantly (p<0.01) higher total accumulation of 2-[(125)I]-E3S was observed in hormone dependent MCF-7 as compared to hormone independent MDA-MB-231 breast cancer cells. In contrast 4-[(125)I]-E3S did not show cellular accumulation in either case. The efficiency of 2-[(125)I]-E3S transport (expressed as a ratio of Vmax/Km) was 2.4 times greater in the MCF-7 as compared to the MDA-MB-231 breast cancer cells. OATP1A2, OATP3A1 and OATP4A1 expression was localized in plasma membranes of MCF-7 and MDA-MB-231 cells confirming the functional role of these transporters in radioiodinated E3S cellular uptake.

CONCLUSION

An efficient method for the preparation of 2- and 4-[(125)I]-E3S was developed and where the former demonstrated potential as an in vitro probe for the OATP system. The new E3S probe can be used to study the OATP system and as a platform to create radiopharmaceuticals for imaging breast cancer.

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".

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.

Anticancer steroids: linking natural and semi-synthetic compounds

Steroids, a widespread class of natural organic compounds occurring in animals, plants and fungi, have shown great therapeutic value for a broad array of pathologies. The present overview is focused on the anticancer activity of steroids, which is very representative of a rich structural molecular diversity and ability to interact with various biological targets and pathways. This review encompasses the most relevant discoveries on steroid anticancer drugs and leads through the last decade and comprises 668 references.

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.

Synthesis and evaluation of analogues of estrone-3-O-sulfamate as potent steroid sulfatase inhibitors

Estrone sulfamate (EMATE) is a potent irreversible inhibitor of steroid sulfatase (STS). In order to further expand SAR, the compound was substituted at the 2- and/or 4-positions and its 17-carbonyl group was also removed. The following general order of potency against STS in two in vitro systems is observed for the derivatives: The 4-NO(2) > 2-halogens, 2-cyano > EMATE (unsubstituted)>17-deoxyEMATE > 2-NO(2) > 4-bromo>2-(2-propenyl), 2-n-propyl > 4-(2-propenyl), 4-n-propyl > 2,4-(2-propenyl)= 2,4-di-n-propyl. There is a clear advantage in potency to place an electron-withdrawing substituent on the A-ring with halogens preferred at the 2-position, but nitro at the 4-position. Substitution with 2-propenyl or n-propyl at the 2- and/or 4-position of EMATE, and also removal of the 17-carbonyl group are detrimental to potency. Three cyclic sulfamates designed are not STS inhibitors. This further confirms that a free or N-unsubstituted sulfamate group (H(2)NSO(2)O-) is a prerequisite for potent and irreversible inhibition of STS as shown by inhibitors like EMATE and Irosustat. The most potent derivative synthesized is 4-nitroEMATE (2), whose IC(50)s in placental microsomes and MCF-7 cells are respectively 0.8 nM and 0.01 nM.

Steroid sulfatase inhibitors for estrogen- and androgen-dependent cancers

Estrogens and androgens are instrumental in the maturation of many hormone-dependent cancers. Consequently, the enzymes involved in their synthesis are cancer therapy targets. One such enzyme, steroid sulfatase (STS), hydrolyses estrone sulfate, and dehydroepiandrosterone sulfate to estrone and dehydroepiandrosterone respectively. These are the precursors to the formation of biologically active estradiol and androstenediol. This review focuses on three aspects of STS inhibitors: 1) chemical development, 2) biological activity, and 3) clinical trials. The aim is to discuss the importance of estrogens and androgens in many cancers, the developmental history of STS inhibitor synthesis, the potency of these compounds in vitro and in vivo and where we currently stand in regards to clinical trials for these drugs. STS inhibitors are likely to play an important future role in the treatment of hormone-dependent cancers. Novel in vivo models have been developed that allow pre-clinical testing of inhibitors and the identification of lead clinical candidates. Phase I/II clinical trials in postmenopausal women with breast cancer have been completed and other trials in patients with hormone-dependent prostate and endometrial cancer are currently active. Potent STS inhibitors should become therapeutically valuable in hormone-dependent cancers and other non-oncological conditions.

Structure-activity relationship for the first-in-class clinical steroid sulfatase inhibitor Irosustat (STX64, BN83495)

Structure-activity relationship studies were conducted on Irosustat (STX64, BN83495), the first steroid sulfatase (STS) inhibitor to enter diverse clinical trials for patients with advanced hormone-dependent cancer. The size of its aliphatic ring was expanded; its sulfamate group was N,N-dimethylated, relocated to another position and flanked by an adjacent methoxy group; and series of quinolin-2(1H)-one and quinoline derivatives of Irosustat were explored. The STS inhibitory activities of the synthesised compounds were assessed in a preparation of JEG-3 cells. Stepwise enlargement of the aliphatic ring from 7 to 11 members increases potency, although a further increase in ring size is detrimental. The best STS inhibitors in vitro had IC50 values between 0.015 and 0.025 nM. Other modifications made to Irosustat were found to either abolish or significantly weaken its activity. An azomethine adduct of Irosustat with N,N-dimethylformamide (DMF) was isolated, and crystal structures of Irosustat and this adduct were determined. Docking studies were conducted to explore the potential interactions between compounds and the active site of STS, and suggest a sulfamoyl group transfer to formylglycine 75 during the inactivation mechanism.

Development of steroid sulfatase inhibitors

Hydrolysis of biologically inactive steroid sulfates to unconjugated steroids by steroid sulfatase (STS) is strongly implicated in rendering estrogenic stimulation to hormone-dependent cancers such as those of the breast. Considerable progress has been made in the past two decades with regard to the discovery, design and development of STS inhibitors. We outline historical aspects of their development, cumulating in the discovery of the first clinical trial candidate STX64 (BN83495, Irosustat) and other sulfamate-based inhibitors. The development of reversible STS inhibitors and the design of dual inhibitors of both aromatase and STS is also discussed.

Structure-activity relationships of C-17-substituted estratriene-3-O-sulfamates as anticancer agents

The synthesis and antiproliferative activities of analogues of 2-substituted estradiol-3,17-O,O-bis-sulfamates (E2bisMATEs) are discussed. Modifications of the C-17 substituent confirm that an H-bond acceptor is essential for high activity; its optimal linkage to C-17 and the local environment in which it resides are defined. In the non-sulfamoylated series 17β-acyl substitution delivers 48b, the most potent compound identified to date. In the sulfamate series a number of permutations of linker and H-bond acceptor deliver excellent activity, with 55, 61, 65, 49a, and 49b proving especially promising. The in vivo potential of these compounds was explored in the NCI hollow fiber assay and also in a mouse Matrigel model of antiangiogenesis in which 49 and 55 show significant inhibitory activity.

Hybrid dual aromatase-steroid sulfatase inhibitors with exquisite picomolar inhibitory activity

Single agents against multiple drug targets are highly topical. Hormone-dependent breast cancer (HDBC) may be more effectively treated by dual inhibition of aromatase and steroid sulfatase (STS), and several dual aromatase-sulfatase inhibitors (DASIs) have been recently reported. The best compounds from two leading classes of DASI, 3 and 9, are low nanomolar inhibitors. In search of a novel class of DASI, core motifs of two leading classes were combined to give a series of hybrid structures, with several compounds showing markedly improved dual inhibitory activities in the picomolar range in JEG-3 cells. Thus, DASIs 14 (IC50: aromatase, 15 pM; STS, 830 pM) and 15 (IC50: aromatase, 18 pM; STS, 130 pM) are the first examples of an exceptional new class of highly potent dual inhibitor that should encourage further development toward multitargeted therapeutic intervention in HDBC.

Docking, synthesis, and in vitro evaluation of antimitotic estrone analogs

In the present study, Autodock 4.0 was employed to discover potential carbonic anhydrase IX inhibitors that are able to interfere with microtubule dynamics by binding to the Colchicine binding site of tubulin. Modifications at position 2' of estrone were made to include moieties that are known to improve the antimitotic activity of estradiol analogs. 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10),15-tetraen-3-ol-17-one estronem (C9) and 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (C12) were synthesized and tested in vitro. Growth studies were conducted utilizing spectrophotometrical analysis with crystal violet as DNA stain. Compounds C9 and C12 were cytotoxic in MCF-7 and MDA-MB-231 tumorigenic and metastatic breast cancer cells, SNO non-keratinizing squamous epithelium cancer cells and HeLa cells after 48 h exposure. Compounds C9 inhibited cell proliferation to 50% of the vehicle-treated controls from 110 to 160 nm and C12 at concentrations ranging from 180 to 220 nm. Confocal microscopy revealed abnormal spindle morphology in mitotic cells. Cell cycle analysis showed an increase in the number of cells in the G(2) /M fraction after 24 h and an increase in the number of cell in the sub-G(1) fraction after 48 h, indicating that the compounds are antimitotic and able to induce apoptosis.

In vitro effects of 2-methoxyestradiol-bis-sulphamate on the non-tumorigenic MCF-12A cell line

A priority in recent anti-cancer drug development has been attaining better side-effect profiles for potential compounds. To produce highly specific cancer therapies it is necessary to understand both the effects of the proposed compound on cancer and on normal cells comprising the rest of the human body. Thus in vitro evaluation of these compounds against non-carcinogenic cell lines is of critical importance. One of the most recent developments in experimental anti-cancer agents is 2-methoxyestradiol-bis-sulphamate (2ME-BM), a sulphamoylated derivative of 2-methoxyestradiol. The aim of this study was to evaluate the in vitro effects of 2ME-BM on cell proliferation, morphology and mechanisms of cell death in the non-carcinogenic MCF-12A breast epithelial cell line. The study revealed changes in proliferative capacity, morphology and cell death induction in response to 2ME-BM exposure (24 h at 0.4 microM). Microscopy showed decreased cell density and cell death-associated morphology (increased apoptotic characteristics), a slight increase in acidic intracellular vesicles and insignificant ultra-structural aberrations. Mitotic indices revealed a G(2)M-phase cell cycle block. This was confirmed by flow cytometry, where an increased fraction of abnormal cells and a decrease in cyclin B1 levels were observed. These results evidently demonstrate that the non-carcinogenic MCF-12A cell line is less susceptible when compared to 2ME-BM-exposed cancer cell lines previously tested. Further in vitro research into the mechanism of this potentially useful compound is warranted.

Chiral aromatase and dual aromatase-steroid sulfatase inhibitors from the letrozole template: synthesis, absolute configuration, and in vitro activity

To explore aromatase inhibition and to broaden the structural diversity of dual aromatase-sulfatase inhibitors (DASIs), we introduced the steroid sulfatase (STS) inhibitory pharmacophore to letrozole. Letrozole derivatives were prepared bearing bis-sulfamates or mono-sulfamates with or without adjacent substituents. The most potent of the achiral and racemic aromatase inhibitor was 40 (IC 50 = 3.0 nM). Its phenolic precursor 39 was separated by chiral HPLC, and the absolute configuration of each enantiomer was determined using vibrational and electronic circular dichroism in tandem with calculations of the predicted spectra. Of the two enantiomers, ( R)-phenol ( 39a) was the most potent aromatase inhibitor (IC 50 = 0.6 nM, comparable to letrozole), whereas the ( S)-sulfamate, ( 40b) inhibited STS most potently (IC 50 = 553 nM). These results suggest that a new structural class of DASI for potential treatment of hormone-dependent breast cancer has been identified, and this is the first report of STS inhibition by an enantiopure nonsteroidal compound.

A review of coumarin derivatives in pharmacotherapy of breast cancer

The coumarin (benzopyran-2-one, or chromen-2-one) ring system, present in natural products (such as the anticoagulant warfarin) that display interesting pharmacological properties, has intrigued chemists and medicinal chemists for decades to explore the natural coumarins or synthetic analogs for their applicability as drugs. Many molecules based on the coumarin ring system have been synthesized utilizing innovative synthetic techniques. The diversity oriented synthetic routes have led to interesting derivatives including the furanocoumarins, pyranocoumarins, and coumarin sulfamates (COUMATES), which have been found to be useful in photochemotherapy, antitumor and anti-HIV therapy, and as stimulants for central nervous system, antibacterials, anti-inflammatory, anti-coagulants, and dyes. Of particular interest in breast cancer chemotherapy, some coumarins and their active metabolite 7-hydroxycoumarin analogs have shown sulfatase and aromatase inhibitory activities. Coumarin based selective estrogen receptor modulators (SERMs) and coumarin-estrogen conjugates have also been described as potential antibreast cancer agents. Since breast cancer is the second leading cause of death in American women behind lung cancer, there is a strong impetus to identify potential new drug treatments for breast cancer. Therefore, the objective of this review is to focus on important coumarin analogs with antibreast cancer activities, highlight their mechanisms of action and structure-activity relationships on selected receptors in breast tissues, and the different methods that have been applied in the construction of these pharmacologically important coumarin analogs.

Inactivation of recombinant human steroid sulfatase by KW-2581

Steroid sulfatase (STS) catalyses the hydrolysis of the sulfate esters of 3-hydroxy steroids, which are inactive transport or precursor forms of the active 3-hydroxy steroids. STS inhibitors are expected to block the local production and, consequently to reduce the active steroid levels; therefore, they are considered as potential new therapeutic agents for the treatment of estrogen- and androgen-dependent disorders such as breast and prostate cancers. KW-2581 is a novel steroidal STS inhibitor. In the present study, we found KW-2581 inhibited recombinant human STS (rhSTS) activity with an IC(50) of 2.9 nM when estrone sulfate was used as a substrate. The potency of KW-2581 was approximately 5-fold higher than that of a non-steroidal STS inhibitor, 667 COUMATE. KW-2581 was able to equally inhibit rhSTS activity when dehydroepiandrosterone sulfate was used as another substrate. KW-2581 inhibited rhSTS activity in a time- and concentration-dependent manner (k(inact), 0.439 min(-1); K(i, app), 15 nM), suggesting that it is an active site-directed irreversible inhibitor. Both decrease of KW-2581 concentration and increase of the des-sulfamoylated form's concentration were simultaneously observed during the reaction in a time-dependent manner with corresponding to the decrease of STS activity. Our findings for the first time demonstrated the production of des-sulfamoylated form of the compound as a consequence of STS inactivation.

Dual aromatase-steroid sulfatase inhibitors

By introducting the steroid sulfatase inhibitory pharmacophore into aromatase inhibitor 1 (YM511), two series of single agent dual aromatase-sulfatase inhibitors (DASIs) were generated. The best DASIs in vitro (JEG-3 cells) are 5, (IC50(aromatase) = 0.82 nM; IC50(sulfatase) = 39 nM), and 14, (IC50(aromatase) = 0.77 nM; IC50(sulfatase) = 590 nM). X-ray crystallography of 5, and docking studies of selected compounds into an aromatase homology model and the steroid sulfatase crystal structure are presented. Both 5 and 14 inhibit aromatase and sulfatase in PMSG pretreated adult female Wistar rats potently 3 h after a single oral 10 mg/kg dose. Almost complete dual inhibition is observed for 5 but the levels were reduced to 85% (aromatase) and 72% (sulfatase) after 24 h. DASI 5 did not inhibit aldosterone synthesis. The development of a potent and selective DASI should allow the therapeutic potential of dual aromatase-sulfatase inhibition in hormone-dependent breast cancer to be assessed.

2-substituted estradiol bis-sulfamates, multitargeted antitumor agents: synthesis, in vitro SAR, protein crystallography, and in vivo activity

The anticancer activities and SARs of estradiol-17-O-sulfamates and estradiol 3,17-O,O-bis-sulfamates (E2bisMATEs) as steroid sulfatase (STS) inhibitors and antiproliferative agents are discussed. Estradiol 3,17-O,O-bis-sulfamates 20 and 21, in contrast to the 17-O-monosulfamate 11, proved to be excellent STS inhibitors. 2-Substituted E2bisMATEs 21 and 23 additionally exhibited potent antiproliferative activity with mean graph midpoint values of 18-87 nM in the NCI 60-cell-line panel. 21 Exhibited antiangiogenic in vitro and in vivo activity in an early-stage Lewis lung model, and 23 dosed p.o. caused marked growth inhibition in a nude mouse xenograft tumor model. Modeling studies suggest that the E2bisMATEs and 2-MeOE2 share a common mode of binding to tubulin, though COMPARE analysis of activity profiles was negative. 21 was cocrystallized with carbonic anhydrase II, and X-ray crystallography revealed unexpected coordination of the 17-O-sulfamate of 21 to the active site zinc and a probable additional lower affinity binding site. 2-Substituted E2bisMATEs are attractive candidates for further development as multitargeted anticancer agents.

A novel steroidal selective steroid sulfatase inhibitor KW-2581 inhibits sulfated-estrogen dependent growth of breast cancer cells in vitro and in animal models

We screened a series of 17beta-(N-alkylcarbamoyl)-estra-1,3,5(10)trine-3-O-sulfamate derivatives, and describe here a potent and selective steroid sulfatase (STS) inhibitor with antitumor effects in breast cancer models in vitro and in vivo. In biochemical assays using crude enzymes isolated from recombinant Chinese hamster ovary cells expressing human arylsulfatses (ARSs), one of the best compounds, KW-2581, inhibited STS activity with an IC(50) of 4.0 nM, while > 1000-fold higher concentrations were required to inhibit the other ARSs. The failure to stimulate the growth of MCF-7 human breast cancer cells as well as in uteri in ovariectomized rats indicated the lack of estrogenicity of this compound. In MCF-7 cells transfected with the STS gene, termed MCS-2 cells, KW-2581 inhibited the growth of cells stimulated by estrone sulfate (E1S) but also 5-androstene-3beta, 17beta-diol 3-sulfate (ADIOLS) and dehydroepiandrostenedione 3-sulfate. We found that oral administration of KW-2581 inhibited both E1S- and ADIOLS-stimulated growth of MCS-2 cells in a mouse hollow fiber model. In a nitrosomethylurea-induced rat mammary tumor model, KW-2581 induced regression of E1S-stimulated tumor growth as effectively as tamoxifen or another STS inhibitor, 667 Coumate. Dose-response studies in the same rat model demonstrated that more than 90% inhibition of STS activity in tumors was necessary to induce tumor shrinkage. STS activity in tumors has well correlated with that in leukocytes, suggesting that STS activity in leukocytes could be used as an easily detectable pharmacodynamic marker. These findings demonstrate that KW-2581 is a candidate for development as a therapeutic agent for the treatment of hormone receptors-positive breast cancer.

Effects of stable transfection of human fetal osteoblast cells with estrogen receptor-alpha on regulation of gene expression by tibolone

Tibolone is a synthetic steroid which undergoes tissue selective metabolism into several metabolites having estrogenic, progestogenic or androgenic activities. The effects of 3 alpha-hydroxy tibolone (Org 4094), 3 beta-hydroxy tibolone (Org 30126) and their sulfated metabolites were investigated on human fetal osteoblasts (hFOB). Tibolone had no effect on selected osteoblast marker proteins in estrogen-receptor negative hFOB cells. In contrast, 3 alpha-hydroxy and 3beta-hydroxy tibolone resulted in dose-dependent increases in alkaline phosphatase activity in estrogen receptor (ER) alpha-positive hFOB cells. The maximum increase for both metabolites was comparable to the effects of an optimal dose of 17beta-estradiol, and occurred at 10 muM. At 20 muM, both metabolites increased mRNA levels for alkaline phosphatase and type 1 collagen and protein levels for osteocalcin. Sulfated metabolites of tibolone also increased alkaline phosphatase activity. The estrogen receptor antagonist ICI 182, 780 inhibited stimulation of alkaline phosphatase activity by sulfated and non-sulfated tibolone metabolites, but was more potent on the former. Taken together, these results suggest that stable transfection of ER alpha into hFOB cells confers regulation by 3 alpha-hydroxy and 3beta-hydroxy tibolone metabolites of osteoblast metabolism.

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.

The regulation and inhibition of 17beta-hydroxysteroid dehydrogenase in breast cancer

17Beta-hydroxysteroid dehydrogenase Type 1 (17beta-HSD1) has a pivotal role in regulating the synthesis of oestradiol (E2) within breast tumours. In whole body studies in postmenopausal women with breast cancer the conversion of oestrone (E1) to E2 (4.4+/-1.1%) was much lower than the inactivation of E2 to E1 (17.3+/-5.0%). In contrast, an examination of in vivo oestrogen metabolism within breast tumours revealed that whereas little metabolism of E2 occurred, E1 was converted to E2 to a much greater extent in malignant (48+/-14%) than in normal (19+/-6%) breast tissue. Findings from these studies originally suggested that oestrogen metabolism within breast tumours may differ from the mainly oxidative direction found in most other body tissues and that the activity of 17beta-HSD1 might be regulated by tumour-derived factors. Several growth factors (e.g. IGF-I, IGF-II) and cytokines (e.g. IL-6, TNFalpha) have now been identified which can markedly stimulate the activity of 17beta-HSD1 and such a mechanism may account for the high concentrations of E2 found in most breast tumours. Cells of the immune system, which can infiltrate breast tumours, are thought to be a major source of the growth factors and cytokines which can modulate 17beta-HSD1 activity. Given the central role that 17beta-HSD1 has in regulating breast tumour E2 concentrations the development of potent inhibitors of this enzyme has recently attracted considerable attention. Our initial studies in this area explored the use of derivatives of E1 as inhibitors, with 2-ethyl- and 2-methoxy E1 being found to inhibit 17beta-HSD1 activity in T-47D breast cancer cells by 96+/-2 and 91+/-1% respectively at 10 microM, but with a lack of specificity. Using the E1 scaffold a number of potent, selective 17beta-HSD1 inhibitors have now been identified including E1- and 2-ethyl-E1 containing a side chain with a m-pyridylmethylamidomethyl functionality extending from the 16beta position of the steroid nucleus. At 10 microM these compounds both inhibited 17beta-HSD1 activity by >90%, however some inhibition of 17beta-HSD2 activity was exhibited by the E1 derivative (25%) but not the 2-ethyl analogue. It is now apparent that 17beta-HSD1 activity contributes to the high E2 concentrations found in most breast tumours. The identification of potent, selective novel 17beta-HSD1 inhibitors will allow their efficacy to be tested in in vitro and in vivo studies.

Inhibition of MDA-MB-231 cell cycle progression and cell proliferation by C-2-substituted oestradiol mono- and bis-3-O-sulphamates

A natural metabolite of oestradiol (E2), 2-methoxyoestradiol (2-MeOE2), exerts both antitumour and antiangiogenic effects. 2-MeOE2 is currently in clinical trials for the treatment of a variety of cancers. We have previously shown that a number of sulphamoylated analogues of 2-MeOE2 possess enhanced potency and bioavailability with respect to 2-MeOE2. In our study, the effects of C-2-substituted E2 derivatives, with sulphamoylation at the C-3 and/or C-17 position, on ERalpha -ve MDA-MB-231 breast cancer cells were evaluated. Sulphamoylated derivatives were potent inhibitors of cell proliferation, and these effects were irreversible when compared to growth inhibitory effects induced by 2-MeOE2. Cell cycle analysis suggested that these derivatives caused cells to arrest at the G2-M phase of the cell cycle. Sulphamoylated analogues suppressed the clonogenic potential of MDA-MB-231 cells and also their growth on Matrigel culture substratum. Immunofluorescence studies showed fragmented nuclear bodies and an abnormal microtubule cytoskeleton in cells exposed to one of the potent compounds, 2-MeOE2-bis-sulphamate. In addition, these analogues induced phosphorylation of BCL-2, a protein considered to be the guardian of microtubule integrity. In each of the assays, the sulphamoylated derivatives were at least 10-fold more potent than the parent compound 2-MeOE2. In view of the enhanced potencies associated with sulphamoylated E2 derivatives in ERalpha -ve cells, these analogues should hold considerable therapeutic potential for the treatment of hormone-independent breast cancers.

A-ring-substituted estrogen-3-O-sulfamates: potent multitargeted anticancer agents

Efficient and flexible syntheses of 2-substituted estrone, estradiol and their 3-O-sulfamate (EMATE) derivatives have been developed using directed ortho-lithiation methodology. 2-Substituted EMATEs display a similar antiproliferative activity profile to the corresponding estradiols against a range of human cancer cell lines. 2-Methoxy (3, 4), 2-methylsulfanyl (20, 21) and 2-ethyl EMATEs (32, 33) proved the most active compounds with 2-ethylestradiol-3-O-sulfamate (33), displaying a mean activity over the NCI 55 cell line panel 80-fold greater than the established anticancer agent 2-methoxyestradiol (2). 2-Ethylestradiol-3-O-sulfamate (33) was also an effective inhibitor of angiogenesis using three in vitro markers, and various 2-substituted EMATEs also proved to be inhibitors of steroid sulfatase (STS), a therapeutic target for the treatment of hormone-dependent breast cancer. The potential of this novel class of multimechanism anticancer agents was confirmed in vivo with good activity observed in the NCI hollow fiber assay and in a MDA-MB-435 xenograft mouse model.

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.

The effects of 2-methoxyoestrogen sulphamates on the in vitro and in vivo proliferation of breast cancer cells

2-Methoxyoestrogen sulphamates are a new class of compounds, which inhibit breast cancer cell proliferation and are also potent inhibitors of steroid sulphatase (STS) activity. In the present study, we have used two cell proliferation assays (MTS and AB) to identify potent new compounds in this class. Similar IC(50) values were obtained using these assays with two of the most potent compounds identified being 2-methoxyoestradiol-bis-sulphamate (2-MeOE2bisMATE) and 2-methoxyoestradiol-17beta-cyanomethyl-3-O-sulphamate (2-MeOE2CyMATE). Both compounds inhibited the proliferation of MCF-7 (ER+) and MDA-MB-231 (ER-) breast cancer cells. Using the AB assay, which allows repeat measurements of cell proliferation without killing cells, both compounds were shown to inhibit cell proliferation in an irreversible manner. As STS may be involved in the removal of the sulphamoyl moiety of these compounds, which could reduce their potency, their ability to inhibit the proliferation of MCF-7 cells transfected with the cDNA for STS was also examined. Although the STS activity was 20-fold higher in these cells than in non-transfected MCF-7 cells, no decrease in the ability of these compounds to inhibit cell proliferation was detected. To test the efficacy of these compounds in vivo, nude mice were inoculated with MCF-7 cells in Matrigel and stimulated to grow with oestradiol. Three weeks after the oral administration of 2-MeOE2bisMATE or 2-MeOE2CyMATE (20mg/kg/day, 5 days/week) tumour volumes had regressed by 52% and 22%, respectively. Both compounds also inhibited liver and tumour STS activity by >90%. The potent anti-proliferative effects of these compounds, and their ability to inhibit tumour growth and STS activity in vivo, indicates that they are suitable for development as novel therapeutic agents, which should be active against a wide range of cancers.

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.

2-(1-Adamantyl)-4-(thio)chromenone-6-carboxylic Acids: Potent Reversible Inhibitors of Human Steroid Sulfatase

Steroid sulfatase (STS) is an attractive target for the potential therapy of a number of estrogen- and androgen-dependent disorders. Most potent STS inhibitors known so far act as irreversible enzyme blockers and feature an aryl sulfamate moiety; even minor modifications at the sulfamate group result in drastically decreased activity. On the basis of a recently reported subclass of highly potent STS inhibitors, i.e., chromenone sulfamates, we now extended the investigation of structure-activity relationships to hitherto unstudied sulfamate replacements. Thereby, we discovered 2-(1-adamantyl)-4-(thio)chromenone-6-carboxylic acids (5d and 5j) as potent, reversible inhibitors of STS. In a cell-free system using purified human STS, both new inhibitors show similar Ki values (0.50 microM and 0.53 microM, respectively). However, the thio analogue 5j is superior to 5d (IC50 = 0.18 microM versus 9.4 microM) in a cellular assay system using CHO cells overexpressing STS. Compound 5j is an example of a reversible STS inhibitor with potent activity toward the target enzyme in a cellular test system. Moreover, 5d,j are stable and have no estrogenic potential.

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.

2-Alkylsulfanyl estrogen derivatives: synthesis of a novel class of multi-targeted anti-tumour agents

A flexible, direct, high yielding synthesis of 2-alkylsulfanyl estrogens from estrone has been developed. 2-Methylsulfanyl estradiol (2-MeSE2) 7 displays a similar anti-proliferative activity to the established 2-methoxyestradiol (2-MeOE2) 1, whilst its 3-O-sulfamate derivative (2-MeSE2MATE) 9 exhibits greatly enhanced anti-proliferative activity, combined with significant inhibition of steroid sulfatase, an enzyme target for the treatment of hormone-dependent tumours.

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.

2-Difluoromethyloestrone 3-O-sulphamate, a highly potent steroid sulphatase inhibitor

Steroid sulphatase is a target enzyme of growing therapeutic importance. The synthesis and in vitro biological evaluation of three novel 2-substituted analogues of oestrone 3-O-sulphamate (EMATE), an established steroid sulphatase inhibitor, are described. One inhibitor, 2-difluoromethyloestrone 3-O-sulphamate (6), was found to have an IC50 of 100 pM and be some 90-fold more potent than EMATE in inhibiting steroid sulphatase activity in a placental microsomal preparation, rendering this agent the most potent steroidal STS inhibitor in vitro reported to date. Lowering of the pKa value of the leaving parent steroid phenol by the 2-difluoromethyl group during irreversible enzyme sulphamoylation most likely facilitates the potent inactivation of steroid sulphatase by (6). However, our preliminary molecular docking studies using the X-ray crystal structure of steroid sulphatase suggest that F.......H interactions between the 2-difluoromethyl group of (6) and hydrogen bond donor residues lining the catalytic site of STS might also contribute to the high potency observed for (6).

Pharmacokinetics and efficacy of 2-methoxyoestradiol and 2-methoxyoestradiol-bis-sulphamate in vivo in rodents

2-Methoxyoestradiol (2-MeOE2) is an endogenous oestrogen metabolite that inhibits the proliferation of cancer cells in vitro, and it is also antiangiogenic. In vivo 2-MeOE2, when administered at relatively high doses, inhibits the growth of tumours derived from breast cancer cells, sarcomas and melanomas. Sulphamoylated derivatives of 2-MeOE2 are more potent inhibitors of in vitro breast cancer cell growth than 2-MeOE2. In the present study, we have compared the pharmacokinetic profiles and metabolism of 2-MeOE2 and its sulphamoylated derivative, 2-methoxyoestradiol-bis-sulphamate (2-MeOE2bisMATE), in adult female rats. Their ability to inhibit tumour growth was compared in nude mice bearing xenografts derived from MDA-MB-435 (oestrogen receptor negative) melanoma cancer cells. After a single oral 10 mg kg⁻¹ dose of 2-MeOE2bisMATE, significant concentrations of this compound were still detectable at 24 h. In contrast, no 2-MeOE2 or metabolites were detected in plasma at any time after a 10 mg kg⁻¹ oral dose. Thus, the bioavailability of 2-MeOE2 is very low, whereas for 2-MeOE2bisMATE it was 85%. No significant metabolites of 2-MeOE2bisMATE were detected in plasma after oral or intravenous dosing, showing that this drug is resistant to metabolism. In the tumour efficacy model, oral administration of 2-MeOE2bisMATE, at 20 mg kg⁻¹ day⁻¹ daily for 28 days, almost completely inhibited tumour growth. Inhibition of tumour growth was maintained for a further 28 days after the cessation of dosing. At this dose level, 2-MeOE2 did not inhibit tumour growth. The resistance to metabolism shown by 2-MeOE2bisMATE and its ability to inhibit tumour growth in vivo suggest that this compound should have considerable potential for development as a novel anticancer drug.