Dual aromatase-sulfatase inhibitors based on the anastrozole template: synthesis, in vitro SAR, molecular modelling and in vivo activity

Development of benzofuran-derived sulfamates as dual aromatase-steroid sulfatase inhibitors (DASIs): design, synthesis and biological evaluation

Resistance of oestrogen receptor-positive (ER+) breast cancer, the most prevalent type of breast cancer accounting for ∼70% of all cases, to current therapies necessitates the study of alternative strategies. One promising strategy is the multi-targeting approach using dual aromatase-steroid sulfatase inhibitors (DASIs). Herein, we describe the development of DASIs using a common benzofuran pharmacophore. Triazole benzofuran sulfamates were found to have low nM aromatase (Arom) inhibitory activity but no steroid sulfatase (STS) inhibitory activity (IC50 > 10 μM); by contrast, benzofuran ketone sulfamates demonstrated low nM STS inhibitory activity but no Arom inhibitory activity (IC50 > 1 μM). The addition of a methyl group at the 3rd position of the benzofuran ring in the benzofuran ketone sulfamate 19 (R1 = CH3) had a notable effect, resulting in dual aromatase and STS inhibitory activities with the 4-chloro derivative 19b (Arom IC50 = 137 nM, STS IC50 = 48 nM) and 4-methoxy derivative 19e (Arom IC50 = 35 nM, STS IC50 = 164 nM) optimal for dual inhibition. Arom/STS inhibition results combined with molecular dynamics studies provided a clear rationale for the activity observed.

Secosteroid thiosemicarbazides and secosteroid-1,2,4-triazoles as antiproliferative agents targeting breast cancer cells: Synthesis and biological evaluation

A convenient and selective approach to 13,17-secoestra-1,3,5(10)-trien-17-oic acid [N'-arylcarbothioamido]hydrazides and hybrid molecules containing secosteroid and 1,2,4-triazole fragments was disclosed and these novel types of secosteroids were screened for cytotoxicity against hormone-dependent human breast cancer cell line MCF-7. Most of secosteroid-1,2,4-triazole hybrids showed significant cytotoxic effect comparable or superior to that of the reference drug cisplatin. Hit secosteroid-1,2,4-triazole hybrids 4b and 4h were characterized by high cytotoxicity and good selectivity towards MCF-7 breast cancer cells. PARP cleavage (marker of apoptosis) and ERα and cyclin D1 downregulation were discovered in MCF-7 cells treated with lead secosteroid-1,2,4-triazole hybrid 4b. The synthesized secosteroids may be considered as new promising anticancer agents.

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.

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

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

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.

Designing multi-targeted agents: An emerging anticancer drug discovery paradigm

The dominant paradigm in drug discovery is to design ligands with maximum selectivity to act on individual drug targets. With the target-based approach, many new chemical entities have been discovered, developed, and further approved as drugs. However, there are a large number of complex diseases such as cancer that cannot be effectively treated or cured only with one medicine to modulate the biological function of a single target. As simultaneous intervention of two (or multiple) cancer progression relevant targets has shown improved therapeutic efficacy, the innovation of multi-targeted drugs has become a promising and prevailing research topic and numerous multi-targeted anticancer agents are currently at various developmental stages. However, most multi-pharmacophore scaffolds are usually discovered by serendipity or screening, while rational design by combining existing pharmacophore scaffolds remains an enormous challenge. In this review, four types of multi-pharmacophore modes are discussed, and the examples from literature will be used to introduce attractive lead compounds with the capability of simultaneously interfering with different enzyme or signaling pathway of cancer progression, which will reveal the trends and insights to help the design of the next generation multi-targeted anticancer agents.

n-Bu4NI/TBHP-catalyzed C–N bond formation via cross-dehydrogenative coupling of 1H-1,2,4-triazoles (N–H) and methylarenes (Csp3–H)

An efficient n-Bu₄NI/TBHP-catalyzed protocol for C–N bond formation via cross-dehydrogenative coupling of 1H-1,2,4-triazoles (N–H) and methylarenes (C_sp3–H) has been developed under metal free conditions.

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.

Synthetic methodologies of achiral diarylmethanols, diaryl and triarylmethanes (TRAMs) and medicinal properties of diaryl and triarylmethanes-an overview

This review covers the synthesis of achiral diarylmethanols, diaryl and triarylmethanes and the bioactivities of diaryl and triarylmethanes during 1995 to 2013.

Synthesis and structure-activity relationship studies of derivatives of the dual aromatase-sulfatase inhibitor 4-{[(4-cyanophenyl)(4H-1,2,4-triazol-4-yl)amino]methyl}phenyl sulfamate

4-{[(4-Cyanophenyl)(4H-1,2,4-triazol-4-yl)amino]methyl}phenyl sulfamate and its ortho-halogenated (F, Cl, Br) derivatives are first-generation dual aromatase and sulfatase inhibitors (DASIs). Structure-activity relationship studies were performed on these compounds, and various modifications were made to their structures involving relocation of the halogen atom, introduction of more halogen atoms, replacement of the halogen with another group, replacement of the methylene linker with a difluoromethylene linker, replacement of the para-cyanophenyl ring with other ring structures, and replacement of the triazolyl group with an imidazolyl group. The most potent in vitro DASI discovered is an imidazole derivative with IC50 values against aromatase and steroid sulfatase in a JEG-3 cell preparation of 0.2 and 2.5 nM, respectively. The parent phenol of this compound inhibits aromatase with an IC50 value of 0.028 nM in the same assay.

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.

17α-ethynyl-5α-androstane-3α, 17β-diol treatment of MNU-induced mammary cancer in rats

N-methyl-N-nitrosourea (MNU) induces estrogen-dependent mammary tumors in female Lewis rats. We explored the antineoplastic activity of a synthetic androstane derivative, 17α-ethynyl-5α-androstane-3α, 17β-diol (HE3235), as a single agent or in combination with docetaxel compared to tamoxifen, anastrazole, and docetaxel monotherapies against MNU-induced mammary tumors in female Lewis rats. Treatment with HE3235 alone rapidly reduced tumor burden, similar in effect to tamoxifen and anastrozole. The combination of HE3235 with docetaxel was more effective than any single agent, although without apparent toxicity. Only HE3235 or HE3235 plus docetaxel continued to suppress tumor growth after cessation of treatment. HE3235 treatment increased immunohistochemical markers of apoptosis and expression of proapoptotic genes and estrogen receptor beta and decreased expression of antiapoptotic genes, androgen receptor, and estrogen receptor alpha. These data warrant clinical investigation of HE3235 for breast cancer treatment.

Aromatase and dual aromatase-steroid sulfatase inhibitors from the letrozole and vorozole templates

Concurrent inhibition of aromatase and steroid sulfatase (STS) may provide a more effective treatment for hormone-dependent breast cancer than monotherapy against individual enzymes, and several dual aromatase-sulfatase inhibitors (DASIs) have been reported. Three aromatase inhibitors with sub-nanomolar potency, better than the benchmark agent letrozole, were designed. To further explore the DASI concept, a new series of letrozole-derived sulfamates and a vorozole-based sulfamate were designed and biologically evaluated in JEG-3 cells to reveal structure-activity relationships. Amongst achiral and racemic compounds, 2-bromo-4-(2-(4-cyanophenyl)-2-(1H-1,2,4-triazol-1-yl)ethyl)phenyl sulfamate is the most potent DASI (aromatase: IC₅₀ =0.87 nM; STS: IC₅₀ =593 nM). The enantiomers of the phenolic precursor to this compound were separated by chiral HPLC and their absolute configuration determined by X-ray crystallography. Following conversion to their corresponding sulfamates, the S-(+)-enantiomer was found to inhibit aromatase and sulfatase most potently (aromatase: IC₅₀ =0.52 nM; STS: IC₅₀ =280 nM). The docking of each enantiomer and other ligands into the aromatase and sulfatase active sites was also investigated.

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.

Steroid sulfatase inhibitors: promising new tools for breast cancer therapy?

Inhibition of aromatase is currently well-established as the major treatment option of hormone-dependent breast cancer in postmenopausal women. However, despite the effects of aromatase inhibitors in both early and metastatic breast cancer, endocrine resistance may cause relapses of the disease and progression of metastasis. Thus, driven by the success of manipulating the steroidogenic enzyme aromatase, several alternative enzymes involved in steroid synthesis and metabolism have recently been investigated as possible drug targets. One of the most promising targets is the steroid sulfatase (STS) which converts steroid sulfates like estrone sulfate (E1S) and dehydroepiandrosterone sulfate (DHEAS) to estrone (E1) and dehydroepiandrosterone (DHEA), respectively. Estrone and DHEA may thereafter be used for the synthesis of more potent estrogens and androgens that may eventually fuel hormone-sensitive breast cancer cells. The present review summarizes the biology behind steroid sulfatase and its inhibition, the currently available information derived from basic and early clinical trials in breast cancer patients, as well as ongoing research. Article from the Special Issue on Targeted Inhibitors.

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.

Bicyclic derivatives of the potent dual aromatase-steroid sulfatase inhibitor 2-bromo-4-{[(4-cyanophenyl)(4h-1,2,4-triazol-4-yl)amino]methyl}phenylsulfamate: synthesis, SAR, crystal structure, and in vitro and in vivo activities

The design and synthesis of a series of bicyclic ring containing dual aromatase-sulfatase inhibitors (DASIs) based on the aromatase inhibitor (AI) 4-[(4-bromobenzyl)(4H-1,2,4-triazol-4-yl)amino]benzonitrile are reported. Biological evaluation with JEG-3 cells revealed structure-activity relationships. The X-ray crystal structure of sulfamate 23 was determined, and selected compounds were docked into the aromatase and steroid sulfatase (STS) crystal structures. In the sulfamate-containing series, compounds containing a naphthalene ring are both the most potent AI (39, IC(50 AROM)=0.25 nM) and the best STS inhibitor (31, IC(50 STS)=26 nM). The most promising DASI is 39 (IC(50 AROM)=0.25 nM, IC(50 STS)=205 nM), and this was evaluated orally in vivo at 10 mg kg(-1), showing potent inhibition of aromatase (93 %) and STS (93 %) after 3 h. Potent aromatase and STS inhibition can thus be achieved with a DASI containing a bicyclic ring system; development of such a DASI could provide an attractive new option for the treatment of hormone-dependent breast cancer.

A new therapeutic strategy against hormone-dependent breast cancer: the preclinical development of a dual aromatase and sulfatase inhibitor

PURPOSE

The production of E2 is paramount for the growth of estrogen receptor-positive breast cancer. Various strategies have been used, including the use of enzyme inhibitors against either aromatase (AROM) or steroid sulfatase (STS), in an attempt to ablate E2 levels. Both these enzymes play a critical role in the formation of estrogenic steroids and their inhibitors are now showing success in the clinic.

EXPERIMENTAL DESIGN

We show here, in a xenograft nude mouse model, that the inhibition of both enzymes using STX681, a dual AROM and STS inhibitor (DASI), is a potential new therapeutic strategy against HDBC. MCF-7 cells stably expressing either AROM cDNA (MCF-7(AROM)) or STS cDNA (MCF-7(STS)) were generated. Ovariectomized MF-1 female nude mice receiving s.c. injections of either androstenedione (A(4)) or E2 sulfate and bearing either MCF-7(AROM) or MCF-7(STS) tumors were orally treated with STX64, letrozole, or STX681. Treatment was administered for 28 days. Mice were weighed and tumor measurements were taken weekly.

RESULTS

STX64, a potent STS inhibitor, completely blocked MCF-7(STS) tumor growth but failed to attenuate MCF-7(AROM) tumor growth. In contrast, letrozole inhibited MCF-7(AROM) tumors but had no effect on MCF-7(STS) tumors. STX681 completely inhibited the growth of both tumors. AROM and STS activity was also completely inhibited by STX681, which was accompanied by a significant reduction in plasma E2 levels.

CONCLUSIONS

This study indicates that targeting both the AROM and the STS enzyme with a DASI inhibits HDBC growth and is therefore a potentially novel treatment for this malignancy.

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.