Inhibitors of steroidogenesis as agents for the treatment of hormone-dependent cancers

Recent advances in the development of 17beta-hydroxysteroid dehydrogenase inhibitors

The family of 17β-hydroxysteroid dehydrogenases (17β-HSDs) occupies a prominent place due to its number of isoforms, which carry out a bidirectional transformation (reduction of a steroid carbonyl to alcohol and oxidation of a steroid alcohol to ketone) depending on the nature of the cofactor present. Involved in the activation or inactivation of key estrogens and androgens, 17β-HSDs are therefore therapeutic targets whose selective inhibition would make it possible to be considered for the treatment of several diseases, such as breast cancer, prostate cancer, endometriosis, Alzheimer's disease and osteoporosis. This review article is a continuation of those having reported the great diversity of inhibitors developed over the last years but focusses on inhibitors recently developed. Work to obtain more effective inhibitors that target the first known isoforms (types 1, 2, 3, 5 and 7) has continued, among others, but new inhibitors that target the isoforms more recently reported in the literature (types 10, 12, 13 and 14) are now being reported. Dual inhibitors of two enzymes (17β-HSD1 and steroid sulfatase) were also reported. These inhibitors were grouped according to the 17β-HSD type inhibited and their backbone (steroidal or non-steroidal) when necessary. They were also reported in chronological order and according to the research group.

Studies on the binding of nitrogenous bases to protoporphyrin IX iron(II) in aqueous solution at high pH values

Studies are reported on the formation of low-spin six-coordinate [Fe(PPIX)L₂] complexes from iron(II) protoporphyrin where L is one of a series of nitrogenous ligands (aliphatic, aromatic or heterocyclic). The bonding constants have been determined by titration of the metal complex with these ligands and are compared in relation to previous studies. The adduct formation was monitored utilising optical spectroscopy. In addition, Mӧssbauer spectroscopic experiments were conducted to monitor the electronic environment around the central iron atom in these complexes. The two complementary spectroscopic methods indicated that all nitrogen ligands formed low-spin octahedral complexes. The magnitude of the overall binding constants (β₂ values) are discussed and related to (a) the pK_a values of the free ligands and (b) the Mössbauer parameter ΔE_Q, which represents the quadrupole splitting of the haem iron. The β₂ and ΔE_Q values are also discussed in terms of the structure of the ligand. Cooperative binding was observed for nearly all the ligands with Hill coefficients close to 2 for iron(II) protoporphyrin; one of these ligands displayed a much greater affinity than any we previously studied, and this was a direct consequence of the structure of the ligand. Overall conclusions on these and previous studies are drawn in terms of aliphatic ligands versus aromatic ring structures and the absence or presence of sterically hindered nitrogen atoms. The implications of the work for the greater understanding of haem proteins in general and in particular how the nitrogenous ligand binding results are relevant to and aid the understanding of the binding of inhibitor molecules to the cytochrome P₄₅₀ mono-oxygenases (for therapeutic purposes) are also discussed. Changes in the electronic absorption spectra of five-coordinate [Fe(II)(PPIX)(2-MeIm)] that occurred as the temperature was lowered from room temperature to 78° K.

Antimicrobial Activity and DFT Studies of a Novel Set of Spiropyrrolidines Tethered with Thiochroman-4-one/Chroman-4-one Scaffolds

A novel series of 14 spiropyrrolidines bearing thiochroman-4-one/chroman-4-one, and oxindole/acenaphthylene-1,2-dione moieties were synthesized and characterized by spectroscopic techniques, as well as by three X-ray diffraction studies, corroborating the stereochemistry. Quantum chemical calculations studies, using the DFT approach, were performed to rationalize the stereochemical outcome. These N-heterocycles were evaluated for their antibacterial and antifungal activities against some pathogenic organisms. Several compounds displayed moderate to excellent activity towards the screened microbe strains in the study compared to Amoxicillin (AMX), Ampicillin (AMP), and Amphotericin B. Furthermore, a structural activity relationship (SAR) was established considering the synthesized compounds. Pharmacokinetic studies reveal that these derivatives exhibit an acceptable predictive ADMET profile (Absorption, Distribution, Metabolism, Excretion and Toxicity) and good drug-likeness.

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

Simple Summary

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

Abstract

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

Steroidomics for the Prevention, Assessment, and Management of Cancers: A Systematic Review and Functional Analysis

Steroidomics, an analytical technique for steroid biomarker mining, has received much attention in recent years. This systematic review and functional analysis, following the PRISMA statement, aims to provide a comprehensive review and an appraisal of the developments and fundamental issues in steroid high-throughput analysis, with a focus on cancer research. We also discuss potential pitfalls and proposed recommendations for steroidomics-based clinical research. Forty-five studies met our inclusion criteria, with a focus on 12 types of cancer. Most studies focused on cancer risk prediction, followed by diagnosis, prognosis, and therapy monitoring. Prostate cancer was the most frequently studied cancer. Estradiol, dehydroepiandrosterone, and cortisol were mostly reported and altered in at least four types of cancer. Estrogen and estrogen metabolites were highly reported to associate with women-related cancers. Pathway enrichment analysis revealed that steroidogenesis; androgen and estrogen metabolism; and androstenedione metabolism were significantly altered in cancers. Our findings indicated that estradiol, dehydroepiandrosterone, cortisol, and estrogen metabolites, among others, could be considered oncosteroids. Despite noble achievements, significant shortcomings among the investigated studies were small sample sizes, cross-sectional designs, potential confounding factors, and problematic statistical approaches. More efforts are required to establish standardized procedures regarding study design, analytical procedures, and statistical inference.

Two New Diketomorpholine Derivatives and a New Highly Conjugated Ergostane-Type Steroid from the Marine Algal-Derived Endophytic Fungus Aspergillus alabamensis EN-547

Chemical investigation of the marine algal-derived endophytic fungus Aspergillus alabamensis EN-547 resulted in the isolation of 4-epi-seco-shornephine A methyl ester (1) and 4-epi-seco-shornephine A carboxylic acid (2), two new secondary metabolites having a rare diketomorpholine motif, and 28-acetoxy-12β,15α,25-trihydroxyergosta-4,6,8(14),22-tetraen-3-one (3), a new highly conjugated ergostane-type steroid, together with four known metabolites (4-7). Their chemical structures were elucidated by detailed analysis of their NMR spectra, ECDs, HRESIMS, optical rotation, and X-ray crystallographic data, and by comparison with literature data as well. The antimicrobial activities of compounds 1-7 were evaluated.

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".

Hydrometallation-asymmetric conjugate addition: application to complex molecule synthesis

Copper catalysis allows alkyl zirconium species, generated in situ from alkenes, to undergo conjugate addition reactions. A hydrometallation-catalytic asymmetric 1,4-addition was used to synthesize either enantiomer of a natural product in one step from commercially available materials. Hydrometallation-addition sequences applied to steroids containing a cross-conjugated dienone or 1,6-acceptor give highly functionalized products.

Coumarin-based drugs: a patent review (2008 -- present)

INTRODUCTION

Coumarins are a group of plant-derived polyphenolic compounds. They belong to the benzopyrones family and possess a wide variety of cytoprotective and modulatory functions, which may be translated to therapeutic potentials for multiple diseases. Their physicochemical properties seem to define the extent of the biological activity.

AREAS COVERED

In this review recent patent publications (2008 – 2011), describing coumarins and their derivatives, are analyzed. Synthesis, combinatorial techniques, biological evaluation in vitro/in vivo/ex vivo, e.g. antimitotic, immunomodulating, antiviral, anticancer and cytotoxic agents, as well as some new biological assays, are included. In addition to selected biological data, a wide range of pharmaceutical applications and pharmaceutical compositions are also summarized.

EXPERT OPINION

Several natural and synthetic coumarins and derivatives with potent in vivo/in vitro biological responses appear to be promising anticancer activities. Their clinical evaluation will be critical to assess therapeutic utility. The compounds for which the mechanism of action is well defined can serve as lead compounds for the design of new more promising molecules.

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

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

Contribution to the development of inhibitors of 17β-hydroxysteroid dehydrogenase types 1 and 7: key tools for studying and treating estrogen-dependent diseases

17β-Hydroxysteroid dehydrogenases (17β-HSDs) belong to a group of key enzymes involved in the biosynthesis of steroidal hormones by catalyzing the reduction of 17-ketosteroids or the oxidation of 17β-hydroxysteroids. From three members known in the early nineties, the 17β-HSD functional family has grown to 15 members over the last 20 years. This growing number of 17β-HSD isoforms questioned the importance of each member, especially in their implication in estrogen- and androgen-dependent diseases, such as breast and prostate cancers. One of the strategies used to address the physiological importance of 17β-HSDs is to use potent and selective inhibitors. Furthermore, enzyme inhibitors could also be of therapeutic interest by reducing the level of estradiol (E2). Focusing on estrogens, we targeted 17β-HSD types 1 and 7, two enzymes able to transform the weak estrogen estrone (E1) into the potent estrogen E2. The present review article gives a description of different classes of inhibitors of 17β-HSD1 (C6-derivatives of E2, C16-derivatives of E2 as alkylating and dual action compounds, E2-adenosine hybrids, E2-simplified adenosine hybrids, and C16-derivatives of E1 or E2) and of inhibitors of 17β-HSD7, all these inhibitors developed in our laboratory. The chemical structures and inhibitory activity of these steroidal inhibitors, their potential as therapeutic agents, and their use as tools to elucidate the role of these enzymes in particular biological systems will be discussed. Article from the Special issue on Targeted Inhibitors.

Small molecule inhibitors of retinoic acid 4-hydroxylase (CYP26): synthesis and biological evaluation of imidazole methyl 3-(4-(aryl-2-ylamino)phenyl)propanoates

The synthesis and potent inhibitory activity of novel imidazole methyl 3-(4-(aryl-2-ylamino)phenyl)propanoates in a MCF-7 CYP26A1 microsomal assay is described. The induction of CYP26A1 mRNA was used to evaluate the ability of the compounds to enhance the biological effects of all-trans retinoic acid (ATRA) in a retinoid-responsive neuroblastoma cell line. The most promising inhibitor, 3-imidazol-1-yl-2-methyl-3-[4-(naphthalen-2-ylamino)-phenyl]-propionic acid methyl ester (20), with an IC(50) of 3 nM (compared with liarozole IC(50) of 540 nM and R116010 IC(50) of 10 nM) was further evaluated for CYP selectivity using a panel of CYP enzymes, mutagenicity (Ames screen), and hepatic stability.

Preparation of 6beta-estradiol derivative libraries as bisubstrate inhibitors of 7beta-hydroxysteroid dehydrogenase type using the multidetachable sulfamate linker

Combinatorial chemistry is a powerful tool used to rapidly generate a large number of potentially biologically active compounds. In our goal to develop bisubstrate inhibitors of 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) that interact with both the substrate (estrone or estradiol) and the cofactor (NAD(P)H) binding sites, we used parallel solid-phase synthesis to prepare three libraries of 16beta-estradiol derivatives with two or three levels of molecular diversity. From estrone, we first synthesized a sulfamate precursor that we loaded on trityl chloride resin using the efficient multidetachable sulfamate linker strategy recently developed in our laboratory. We then introduced molecular diversity [one or two amino acid(s) followed by a carboxylic acid] on steroid nucleus by Fmoc peptide chemistry. Finally, after a nucleophilic cleavage, libraries of 30, 63 and 25 estradiol derivatives were provided. A library of 30 sulfamoylated estradiol derivatives was also generated by acidic cleavage and its members were screened for inhibition of steroid sulfatase. Biological evaluation on homogenated HEK-293 cells overexpressing 17beta-HSD1 of the estradiol derivatives carrying different oligoamide-type chains at C-16 first revealed that three levels of molecular diversity (a spacer of two amino acids) were necessary to interact with the adenosine part of the cofactor binding site. Second, the best inhibition was obtained when hydrophobic residues (phenylalanine) were used as building blocks.

Estrogen formation in endometrial and cervix cancer cell lines: involvement of aromatase, steroid sulfatase and 17beta-hydroxysteroid dehydrogenases (types 1, 5, 7 and 12)

The involvement of aromatase, steroid sulfatase (STS) and reductive 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) in the production of estrogens was determined in four cell lines of endometrial cancer (Ishikawa, HEC-1A, HEC-1B and RL-95) and one cell line of cervix cancer (Hela) in culture. After incubation with 4-androstene-3,17-dione (4-dione), there are no estrogens, estrone (E1) and estradiol (E2), detected suggesting that the pathway of aromatase is not important in these cell lines. In whole cells, the results show low percentages of transformation of estrone sulfate (E1S) into E1 suggesting that the entrance of E1S is difficult. However, in homogenized cells the STS activity was much higher and fully blocked by an inhibitor. Using selective inhibitors for each reductive 17beta-HSD (types 1, 5, 7 and 12), alone or in combination, we did not succeed in completely blocking the conversion of E1 into E2, suggesting that another 17beta-HSD (known or unknown) is involved in the formation of E2 from E1.

Effect of 2-(4-aminophenylmethyl)-6-hydroxy-3,4-dihydronaphthalen-1(2H)-one on all-transand 13-cis-retinoic acid levels in plasma quantified by high perfomance liquid chromatography coupled to tandem mass spectrometry

The effect of the titled tetralone as a retinoic acid metabolism blocking agent (RAMBA) in vivo in comparison with ketoconazole, a well known cytochrome P450 inhibitor, was studied. Development of a HPLC/MS/MS method for the quantification of retinoic acid levels extracted from rat plasma was used to demonstrate that ketoconazole and the tetralone (100 mg/kg) enhanced the endogenous plasma concentration of retinoic acid. Levels of retinoid were raised from a control value of 0.11 to 0.15 and 0.17 ng/mL after treatment with tetralone and ketoconazole respectively showing that the tetralone and ketoconazole lead to comparable effects, indicating an inhibitory activity of the tetralone on retinoic acid metabolism.

Some 1,2-Diphenylethane Derivatives as Inhibitors of Retinoic Acid—Metabolising Enzymes

In a search for novel inhibitors of RA-metabolising enzyme inhibitors as potential anti-cancer agents some 1,2-ethandiones, 2-hydroxyethanones and 1-ethylenedioxyethanones based on aryl-substituted 1,2-diphenylethane have been examined. Several of the compounds were weak inhibitors of the non-specific rat liver microsomal P450 enzymes and moderate inhibitors of the RA-induced enzymes in cultured human genital fibroblasts, where the RA-specific enzyme CYP26 is probably expressed. The 2-hydroxyethanone (13) with a 1-(4-dimethylaminophenyl) substituent was overall the most potent compound for rat liver microsomal enzyme (IC50 = 52.1 microM; ketoconazole, 2.8 microM) and the RA-induced enzyme (100 microM, 65.9% inhibition; ketoconazole, 20 microM, 75.0%). Modification of the dimethylamino group in (13) with more hydrophobic dialkylamino functions or separate modification of the 2-(2,4-dichlorophenyl) function did not improve potency.

Inhibitors of type 1 17β-hydroxysteroid dehydrogenase with reduced estrogenic activity: Modifications of the positions 3 and 6 of estradiol

Breast cancer is the second most frequent cancer affecting women. Among all endocrine therapies for the treatment of breast cancer, inhibition of estrogen biosynthesis is becoming an interesting complementary approach to the use of antiestrogens. The enzyme type 1 17beta-hydroxysteroid dehydrogenase (17beta-HSD) plays a critical role in the biosynthesis of estradiol catalyzing preferentially the reduction of estrone into estradiol, the most active estrogen. Consequently, this enzyme is an interesting biological target for designing drugs for the treatment of estrogen-sensitive diseases such as breast cancer. Our group has reported the synthesis and the biological evaluation of N-methyl, N-butyl 6beta-(thiaheptamamide)estradiol as a potent reversible inhibitor of type 1 17beta-HSD. Unfortunately, this inhibitor has shown an estrogen effect, thus reducing its possible therapeutic interest. Herein three strategies to modify the biological profile (estrogenicity and inhibitory potency) of the initial lead compound were reported. In a first approach, the thioether bond was replaced with a more stable ether bond. Secondly, the hydroxyl group at position 3, which is responsible for a tight binding with the estrogen receptor, was removed. Finally, the amide group of the side-chain was changed to a methyl group. Moreover, the relationship between the inhibitory potency and the configuration of the side-chain at position 6 was investigated. The present study confirmed that the 6beta-configuration of the side chain led to a much better inhibition than the 6alpha-configuration. The replacement of the 3-OH by a hydrogen atom as well as that of the amide group by a methyl was clearly unfavorable for the inhibition of type 1 17beta-HSD. Changing the thioether for an ether bond decreased by 10-fold the estrogenic profile of the lead compound while the inhibitory potency on type 1 17beta-HSD was only decreased by 5-fold. This study contributes to the knowledge required for the development of compounds with the desired profile, that is, a potent inhibitor of type 1 17beta-HSD without estrogen-like effects.

Benzofuran- and furan-2-yl-(phenyl)-3-pyridylmethanols: Synthesis and inhibition of P450 aromatase

A series of benzofuran-2-yl-(phenyl)-3-pyridylmethanol derivatives were prepared using an efficient 1-step procedure in good yields. In addition furan-2-yl-(phenyl)-3-pyridylmethanol derivatives were also prepared to determine the effect of the benzene ring in benzofuran with respect to inhibitory activity. The pyridylmethanol derivatives were all evaluated in vitro for inhibitory activity against aromatase (P450(AROM), CYP19), using human placental microsomes. The benzofuran-2-yl-(phenyl)-3-pyridylmethanol derivatives showed good to moderate activity (IC50 = 1.3-25.1 microM), which was either better than or comparable with aminoglutethimide (IC50 = 18.5 microM) but lower than arimidex (IC50 = 0.6 microM), with the 4-methoxyphenyl substituted derivative displaying optimum activity. Molecular modelling of the benzofuran-2-yl-(4-fluorophenyl)-3-pyridylmethanol derivative suggested activity to reside with the (S)-enantiomer. The furan-2-yl-(phenyl)-3-pyridylmethanol derivatives were devoid of activity indicating the essential role of the benzene ring of the benzofuran component for enzyme binding.

A 3D QSAR model of 17beta-HSD1 inhibitors based on a thieno[2,3-d]pyrimidin-4(3H)-one core applying molecular dynamics simulations and ligand-protein docking

The 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) enzyme plays a crucial role in female hormonal regulation by catalysing the NADPH-dependent reduction of the less potent estrone E1 into the biologically active estradiol E2. Because 17beta-HSD1 is a key enzyme in E2 biosynthesis, it has emerged as an attractive drug target for inhibitor development. Herein we report the plausible binding modes and a 3D QSAR model of 17beta-HSD1 inhibitors based on a (di)cycloalkenothieno[2,3-d]pyrimidin-4(3H)-one core. Two generated enzyme complexes with potent inhibitors were subjected to molecular dynamics simulation to mimic the dynamic process of inhibitor binding. A set of 17beta-HSD1 inhibitors based on the thieno[2,3-d]pyrimidin-4(3H)-one core were docked into the resulting active site, and a CoMFA model employing the most extensive training set to date was generated. The model was validated with an external test set. Active site residues involved in inhibitor binding and CoMFA fields for steric and electrostatic interactions were identified. The model will be used to guide structural modifications of 17beta-HSD1 inhibitors based on a thieno[2,3-d]pyrimidin-4(3H)-one core in order to improve the biological activity as well as in the design of novel 17beta-HSD1 inhibitors.

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.

Proliferative effect of androst-4-ene-3,17-dione and its metabolites in the androgen-sensitive LNCaP cell line

As a therapeutic approach for the treatment of androgen-sensitive diseases, it would be tempting to lower the level of the potent androgens testosterone (T) and dihydrotestosterone (DHT) by using inhibitors of type 3 and type 5 17beta-hydroxysteroid dehydrogenases (17beta-HSDs). However, the efficiency of such a strategy will be optimal only if androst-4-ene-3,17-dione (Delta4-dione), the precursor of T, does not possess per se agonist activity on the androgen receptor (AR). To determine if the proliferative effect previously observed on AR(+) cells for Delta4-dione originates from its direct (per se) action on AR or from its transformation into a metabolite, we started a series of experimentations using the human prostate cancer LNCaP cell line, which expresses a highly sensitive AR. By real-time RT-PCR analysis, we detected type 1 5alpha-reductase (5alpha-R), a small amount of type 5 17beta-HSD, but not type 2 5alpha-R nor type 3 17beta-HSD. We then studied the transformation of labeled Delta4-dione in LNCaP cells after 1-7 days and the most important metabolite detected was 5alpha-androstane-3,17-dione (A-dione), which is the product of 5alpha-R activity. We measured only low levels of androsterone (ADT) and epi-ADT. This result was next confirmed by using an inhibitor of 5alpha-R that completely inhibited the transformation of Delta4-dione into A-dione, and consequently into ADT and epi-ADT. The proliferative effect of Delta4-dione (carefully purified) on LNCaP (AR(+)) cells was next determined in presence or absence of the 5alpha-R inhibitor. Although the cells proliferate in the presence of Delta4-dione only, no cell proliferation was observed with a combination of Delta4-dione and 5alpha-R inhibitor, suggesting that Delta4-dione is not androgenic per se. We next determined that A-dione and epi-ADT stimulated cell growth with the same pattern and potency as Delta4-dione, whereas ADT had a 3.5-fold lower proliferative activity. In conclusion, Delta4-dione is not in itself an agonist steroid on LNCaP (AR(+)) cells, and its proliferative activity appears to be mediated by its transformation into A-dione and/or into epi-ADT.

Design and synthesis of bisubstrate inhibitors of type 1 17beta-hydroxysteroid dehydrogenase: overview and perspectives

Type 1 17beta-hydroxysteroid dehydrogenase (17beta-HSD1) is a key steroidogenic enzyme that catalyses the reduction of steroid estrone into the most potent endogenous estrogen estradiol using the cofactor NAD(P)H. Bisubstrate inhibition is a good way to enhance the potency of inhibitors of cofactor-assisted enzymes. The design of a bisubstrate inhibitor of 17beta-HSD1, the estradiol/adenosine hybrid EM-1745, is reviewed and strategies for future designs of inhibitors are proposed.

Chemical synthesis and in vitro biological evaluation of a phosphorylated bisubstrate inhibitor of type 3 17beta-hydroxysteroid dehydrogenase

Type 3 17beta-hydroxysteroid dehydrogenase (17beta-HSD) catalyzes the last step in the biosynthesis of the potent androgen testosterone (T) by selectively reducing the C17 ketone of 4-androstene-3,17-dione (delta4-dione), with NADPH as cofactor. This enzyme is thus an interesting therapeutic target for androgen-sensitive diseases. Using an efficient convergent chemical approach we synthesized a phosphorylated version of the best delta4-dione/adenosine hybrid inhibitor of type 3 17beta-HSD previously reported. An appropriately protected C2' phosphorylated adenosine was first prepared and linked by esterification to the steroid delta4-dione bearing an alkyl spacer. After three deprotection steps, the phosphorylated bisubstrate inhibitor was obtained. The inhibitory potency of this compound was evaluated on homogenated HEK-293 cells overexpressing type 3 17beta-HSD and compared to the best non-phosphorylated bisubstrate inhibitor. Unexpectedly, the phosphorylated derivative was slightly less potent than the non-phosphorylated bisubstrate inhibitor of type 3 17beta-HSD. Two hypotheses are discussed to explain this result: 1) the phosphorylated adenosine moiety does not interact optimally with the cofactor-binding site and 2) the bisubstrate inhibitors, phosphorylated or not, interact only with the substrate-binding site of type 3 17beta-HSD.

Novel azolyl-(phenylmethyl)]aryl/heteroarylamines: potent CYP26 inhibitors and enhancers of all-trans retinoic acid activity in neuroblastoma cells

The synthesis and potent inhibitory activity of novel 4-[(imidazol-1-yl and triazol-1-yl)(phenyl)methyl]aryl-and heteroaryl amines versus a MCF-7 CYP26A1 cell assay is described. Biaryl imidazole ([4-(imidazol-1-yl-phenyl-methyl)-phenyl]-naphthalen-2-yl-amine (8), IC(50)=0.5 microM; [4-(imidazol-1-yl-phenyl-methyl)-phenyl]-indan-5-yl-amine (9), IC(50)=1.0 microM) and heteroaryl imidazole derivatives ((1H-benzoimidazol-2-yl)-{4-[(5H-imidazol-1-yl)-phenyl-methyl]-phenyl}-amine (15), IC(50)=2.5 microM; benzooxazol-2-yl-{4-[(5H-imidazol-1-yl)-phenyl-methyl]-phenyl}-amine (16), IC(50)=0.9 microM; benzothiazol-2-yl-{4-[(5H-imidazol-1-yl)-phenyl-methyl]-phenyl}-amine (17), IC(50)=1.5 microM) were the most potent CYP26 inhibitors. Using a CYP26A1 homology model differences in activity were investigated. Incubation of SH-SY5Y human neuroblastoma cells with the imidazole aryl derivative 8, and the imidazole heteroaryl derivatives 16 and 17 potentiated the atRA-induced expression of CYP26B1. These data suggest that further structure-function studies leading to clinical development are warranted.

Homology model of human retinoic acid metabolising enzyme cytochrome P450 26A1 (CYP26A1): active site architecture and ligand binding

Homology models of cytochrome P450 RA1 (CYP26A1) were constructed using three human P450 structures, CYP2C8, CYP2C9 and CYP3A4 as templates for the model building. Using MOE software the lowest energy CYP26A1 model was then assessed for stereochemical quality and side chain environment. Further active site optimisation of the CYP26A1 model built using the CYP3A4 template was performed by molecular dynamics to generate a final CYP26A1 model. The natural substrate, all-trans-retinoic acid (atRA), and inhibitor R 15866, were docked into the model allowing further validation of the active site architecture. Using the docking studies structurally and functionally important residues were identified with subsequent characterisation of secondary structure. Multiple hydrophobic interactions, including the side chains of TRP112, PHE299, PHE222, PHE84, PHE374 and PRO371, are important for binding of atRA and R115866. Additional hydrogen bonding interactions were noted as follows: atRA-- C==O of the atRA carboxylate group and ARG86; R115866--benzothiazole nitrogen and the backbone NH of SER115.

Therapeutic potential of sulfamides as enzyme inhibitors

Sulfamide, a quite simple molecule incorporating the sulfonamide functionality, widely used by medicinal chemists for the design of a host of biologically active derivatives with pharmacological applications, may give rise to at least five types of derivatives, by substituting one to four hydrogen atoms present in it, which show specific biological activities. Recently, some of these compounds started to be exploited for the design of many types of therapeutic agents. Among the enzymes for which sulfamide-based inhibitors were designed, are the carbonic anhydrases (CAs), a large number of proteases belonging to the aspartic protease (HIV-1 protease, gamma-secretase), serine protease (elastase, chymase, tryptase, and thrombin among others), and metalloprotease (carboxypeptidase A (CPA) and matrix metalloproteinases (MMP)) families. Some steroid sulfatase (STS) and protein tyrosine phosphatase inhibitors belonging to the sulfamide class of derivatives have also been reported. In all these compounds, many of which show low nanomolar affinity for the target enzymes for which they have been designed, the free or substituted sulfamide moiety plays important roles for the binding of the inhibitor to the active site cavity, either by directly coordinating to a metal ion found in some metalloenzymes (CAs, CPA, STS), usually by means of one of the nitrogen atoms present in the sulfamide motif, or as in the case of the cyclic sulfamides acting as HIV protease inhibitors, interacting with the catalytically critical aspartic acid residues of the active site by means of an oxygen atom belonging to the HN-SO2-NH motif, which substitutes a catalytically essential water molecule. In other cases, the sulfamide moiety is important for inducing desired physico-chemical properties to the drug-like compounds incorporating it, such as enhanced water solubility, better bioavailability, etc., because of the intrinsic properties of this highly polarized moiety when attached to an organic scaffold. This interesting motif is thus of great value for the design of pharmacological agents with a lot of applications.

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

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

Synthesis and CYP26A1 inhibitory activity of 1-[benzofuran-2-yl-(4-alkyl/aryl-phenyl)-methyl]-1H-triazoles

Methodology previously described by our group was applied to the preparation of a series of 4-alkyl/aryl-substituted 1-[benzofuran-2-yl-phenylmethyl]-1H-triazoles. The [1,2,4]-triazole derivatives were prepared for a range of alkyl and aryl substituents, and for the 4-methyl, 4-ethyl, 4-(i)propyl, 4-(t)butyl, 4-phenyl and 4-chlorophenyl derivatives, the minor [1,3,4]-triazole isomer also isolated. All the triazole derivatives were evaluated for CYP26A1 inhibitory activity using a MCF-7 cell-based assay. The 4-ethyl and 4-phenyl-1,2,4-triazole derivatives displayed inhibitory activity (IC(50) 4.5 and 7 microM, respectively) comparable with that of the CYP26 inhibitor liarozole (IC(50) 7 microM). Using a CYP26A1 homology model (based on CYP3A4) template, docking experiments were performed with MOE with multiple hydrophobic interactions observed in addition to coordination between the triazole nitrogen and the haem transition metal.

Focused Libraries of 16-Substituted Estrone Derivatives and Modified E-Ring Steroids: Inhibitors of 17ß-Hydroxysteroid Dehydrogenase Type 1

17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1), an oxidoreductase which has a preferential reductive activity using NADPH as cofactor, converts estrone to estradiol and is expressed in many steroidogenic tissues including breast and in malignant breast cells. As estradiol stimulates the growth and development of hormone-dependent breast cancer, inhibition of the final step of its synthesis is an attractive target for the treatment of this disease. The parallel synthesis of novel focused libraries of 16-substituted estrone derivatives and modified E-ring pyrazole steroids as new potent 17beta-HSD1 inhibitors is described. Substituted 3-O-sulfamoylated estrone derivatives were used as templates and were immobilised on 2-chlorotrityl chloride resin to give resin-bound scaffolds with a multi-detachable linker. Novel focused libraries of 16-substituted estrone derivatives and new modified E-ring steroids were assembled from these immobilised templates using solid-phase organic synthesis and solution-phase methodologies. Among the derivatives synthesised, the most potent 17beta-HSD1 inhibitors were 25 and 26 with IC50 values in T-47D human breast cancer cells of 27 and 165 nm, respectively. Parallel synthesis resulting in a library of C5'-linked amides from the pyrazole E-ring led to the identification of 62 with an IC50 value of 700 nM. These potent inhibitors of 17beta-HSD1 have a 2-ethyl substituent which will decrease their estrogenic potential. Several novel 17beta-HSD1 inhibitors emerged from these libraries and these provide direction for further template exploration in this area. A new efficient diastereoselective synthesis of 25 has also been developed to facilitate supply for in vivo evaluation, and an X-ray crystal structure of this inhibitor is presented.

3Beta-alkyl-androsterones as inhibitors of type 3 17beta-hydroxysteroid dehydrogenase: inhibitory potency in intact cells, selectivity towards isoforms 1, 2, 5 and 7, binding affinity for steroid receptors, and proliferative/antiproliferative activities on AR+ and ER+ cell lines

Type 3 17beta-hydroxysteroid dehydrogenase (17beta-HSD) is involved in the biosynthesis of the potent androgen testosterone (T), which plays an important role in androgen-sensitive diseases. In an attempt to design compounds to lower the level of T, we designed androsterone (ADT) derivatives substituted at the position 3beta as inhibitors of type 3 17beta-HSD, and then selected the eight most potent ones (compounds 1-8) for additional studies. In an intact cell assay, they inhibited efficiently the conversion of natural substrate 4-androstene-3,17-dione into T, although they were less active in intact cells (IC50 approximately 1 microM) than in homogenated cells (IC50=57-100 nM). A study of the inhibitory potency with four other 17beta-HSDs revealed they were selective, since they do not inhibit reductive types 1, 5 and 7, nor oxidative type 2. Interestingly, they did not show any binding affinity for steroid receptors (androgen, estrogen, glucocorticoid and progestin). Only two inhibitors, 3beta-phenyl-ADT (5) and 3beta-phenylmethyl-ADT (6) showed some proliferative activities on an AR+ cell line and on an ER+ cell line, but their effects were not mediated through the androgen or estrogen receptors. This study identified selective inhibitors of type 3 17beta-HSD acting through a mixed-type inhibition, and devoid of non-suitable androgenic and estrogenic proliferative activities. The more potent inhibitors were 3beta-hexyl-ADT (2), 3beta-cyclohexylethyl-ADT (4) and 3beta-phenylethyl-ADT (7).

Estrone and estradiol C-16 derivatives as inhibitors of type 1 17beta-hydroxysteroid dehydrogenase

Three series of steroid derivatives, enones 1, enols 2 and saturated alcohols 3, were easily synthesized from estrone according to a sequence of three reactions: an aldol condensation with an aromatic aldehyde (R(a-g)CHO) to afford 1, the carbonyl reduction of 1 to obtain the enol 2, and the double bond reduction of 2 to give 3 with the R(a-g) group 16beta-oriented. All compounds were tested as inhibitors of type 1 17beta-HSD. The inhibitory potency increases in the following order 1<2<3, suggesting that the presence of a flexible 16beta-methylene group allows a better positioning of the aryl moiety. With an IC50 of 0.8 microM, the 16beta-benzyl-E2 (3a) is the best inhibitor in this series.

Inhibition of Vitamin D3 metabolism enhances VDR signalling in androgen-independent prostate cancer cells

Induction of growth arrest and differentiation by 1alpha,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) occurs in non-malignant cell types but is often reduced in cancer cells. For example, androgen-independent prostate cancer cells, DU-145 and PC-3, are relatively insensitive to the anti-proliferative action of 1,25-(OH)(2)D(3). This appears to be due to increased 1,25-(OH)(2)D(3)-metabolism, as a result of CYP24 enzyme-induction, which in turn leads to decreased anti-proliferative efficacy. In the in vitro rat kidney mitochondria assay, the 2-(4-hydroxybenzyl)-6-methoxy-3,4-dihydro-2H-naphthalen-1-one (4) was found to be a potent inhibitor of Vitamin D(3) metabolising enzymes (IC(50) 3.5 microM), and was shown to be a more potent inhibitor than the broad spectrum P450 inhibitor ketoconazole (IC(50) 20 microM). The combination of the inhibitor and 1,25-(OH)(2)D(3) caused a greater inhibition of proliferation in DU-145 cells than when treated with both agents alone. Examination of the regulation of VDR target gene mRNA in DU-145 cells revealed that co-treatment of 1,25-(OH)(2)D(3) plus inhibitor of Vitamin D(3) metabolising enzymes co-ordinately upregulated CYP24, p21(waf1/cip1) and GADD45alpha.

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.

Synthesis and CYP24 inhibitory activity of 2-substituted-3,4-dihydro-2H-naphthalen-1-one (tetralone) derivatives

The synthesis of novel 2-benzyl- and 2-benzylidene-3,4-dihydro-2H-naphthalen-1-one (tetralone) derivatives and their inhibitory activity versus kidney mitochondrial 25-hydroxyvitamin D(3) 24-hydroxylase (CYP24) is described. The 2-benzylidenetetralone derivatives were found to be very weak inhibitors (IC(50) 20 >100 microM), whereas the 2-benzyltetralone derivatives showed promising inhibitory activity (IC(50) 0.9 microM for the most active derivative) compared with ketoconazole (IC(50) 20 microM).

A letrozole-based dual aromatase-sulphatase inhibitor with in vivo activity

The role of aromatase inhibitors in the treatment of hormone-dependent breast cancer is well established. However, it is now recognised that steroid sulphatase (STS) inhibitors represent a new form of endocrine therapy. To explore the potential advantage of dual inhibition by a single agent, we recently developed a series of dual aromatase-sulphatase inhibitors (DASIs) based on the aromatase inhibitor YM511. We report here a new structural class of DASI obtained by obtained introducing the pharmacophore for STS inhibition, i.e. a phenol sulphamate ester into another established aromatase inhibitor letrozole. Hence, the bis-sulphamate 9 was synthesised which exhibited IC(50) values of 3044 nM for aromatase and >10 microM for STS in JEG-3 cells. However, at a single oral dose of 10mg/kg, 9 inhibited aromatase and rat liver STS by 60% and 88%, respectively, 24h after administration. A proposed metabolite of 9, carbinol 10, was synthesised. Despite also showing weak STS inhibition in JEG-3 cells, 10 inhibited rat liver STS activity to the same extent as 9 at a single oral dose of 10mg/kg. Thus, the concept of a letrozole-based DASI has been validated and could be further developed and modified for therapeutic exploitation.

Effect of nomegestrol acetate on estrogen biosynthesis and transformation in MCF-7 and T47-D breast cancer cells

Although ovaries serve as the primary source of estrogen for pre-menopausal women, after menopause estrogen biosynthesis from circulating precursors occurs in peripheral tissues by the action of several enzymes, 17beta-hydroxysteroid dehydrogenase 1 (17beta-HSD1), aromatase and estrogen sulfatase. In the breast, both normal and tumoral tissues have been shown to be capable of synthesizing estrogens, and this local estrogen production can be implicated in the development of breast tumors. In these tissues, estradiol (E(2)) can be synthesized by three pathways: (1) estrone sulfatase transforms estrogen sulfates into bioactive estrogens, (2) 17beta-HSD1 converts estrone (E(1)) into E(2), (3) aromatase which converts androgens into estrogens is also present and contributes to the in situ synthesis of active estrogens but to a far lesser extent than estrone sulfatase. Quantitative assessment of E(2) formation in human breast tumors indicates that metabolism of estrone sulfate (E(1)S) via the sulfatase pathway produces 100-500 times more E(2) than androgen aromatization. Breast tissue also possesses the estrogen sulfotransferase involved in the conversion of estrogens into their sulfates that are biologically inactive. In the present review, we summarized the action of the 19-nor-progestin nomegestrol acetate (NOMAC) on the sulfatase, 17beta-HSD1 and sulfotransferase activities in the hormone-dependent MCF-7 and T47-D human breast cancer cell lines. Using physiological doses of substrates NOMAC blocks very significantly the conversion of E(1)S to E(2). It inhibits the transformation of E(1) to E(2). NOMAC has a stimulatory effect on sulfotransferase activity in both cell lines, with a strong stimulating effect at low doses but only a weak effect at high concentrations. The effects on the three enzymes are always stronger in the progesterone-receptor rich T47-D cell line as compared with the MCF-7 cell line. Besides, no effect is found for NOMAC on the transformation of androstenedione to E(1) in the aromatase-rich choriocarcinoma cell line JEG-3. In conclusion, the inhibitory effect provoked by NOMAC on the enzymes involved in the biosynthesis of E(2) (sulfatase and 17HSD pathways) in estrogen-dependent breast cancer, as well as the stimulatory effect on the formation of the inactive E(1)S, can open attractive perspectives for future clinical trials.

Synthesis and evaluation of 4-triazolylflavans as new aromatase inhibitors

Aromatase is a target of pharmacological interest for the treatment of estrogen-dependent cancers. Azole derivatives such as letrozole or anastrozole have been developed for aromatase inhibition and are used for the treatment of breast tumors. In this paper, four 4-triazolylflavans were synthesized and were found to exhibit moderate to high inhibitory activity against aromatase.