Sulfamates and their therapeutic potential

Extension of the CHARMM General Force Field to sulfonyl-containing compounds and its utility in biomolecular simulations

Presented is an extension of the CHARMM General Force Field (CGenFF) to enable the modeling of sulfonyl-containing compounds. Model compounds containing chemical moieties such as sulfone, sulfonamide, sulfonate, and sulfamate were used as the basis for the parameter optimization. Targeting high-level quantum mechanical and experimental crystal data, the new parameters were optimized in a hierarchical fashion designed to maintain compatibility with the remainder of the CHARMM additive force field. The optimized parameters satisfactorily reproduced equilibrium geometries, vibrational frequencies, interactions with water, gas phase dipole moments, and dihedral potential energy scans. Validation involved both crystalline and liquid phase calculations showing the newly developed parameters to satisfactorily reproduce experimental unit cell geometries, crystal intramolecular geometries, and pure solvent densities. The force field was subsequently applied to study conformational preference of a sulfonamide based peptide system. Good agreement with experimental IR/NMR data further validated the newly developed CGenFF parameters as a tool to investigate the dynamic behavior of sulfonyl groups in a biological environment. CGenFF now covers sulfonyl group containing moieties allowing for modeling and simulation of sulfonyl-containing compounds in the context of biomolecular systems including compounds of medicinal interest.

(In)organic anions as carbonic anhydrase inhibitors

Carbonic anhydrases (CAs, EC 4.2.1.1) are widespread enzymes in all life kingdoms with five distinct genetic families known to date, the α-, β-, γ-, δ- and ζ-CAs. With the exception of the δ-class, which is less investigated to date, enzymes from the remaining classes found in vertebrates, corals, fungi, bacteria and archaea have been studied for their inhibition with simple inorganic anions as well as more complex inorganic and organic ones. In this paper we review the available data for the inhibition of these enzymes with all anions except sulfonamides and their bioisosteres (sulfamates, sulfamides) which have been reviewed earlier. Anion inhibitors are important both for understanding the inhibition/catalytic mechanisms of these enzymes and for designing novel types of inhibitors which may have clinical applications for the management of a variety of disorders in which CAs are involved. Environmental aspects of CO(2) fixation by CAs present in plants, corals, algae or diatoms and how this may be affected by inhibitors are also discussed.

Aminoacyl-tRNA synthetase inhibitors as potential antibiotics

Increasing resistance to antibiotics is a major problem worldwide and provides the stimulus for development of new bacterial inhibitors with preferably different modes of action. In search for new leads, several new bacterial targets are being exploited beside the use of traditional screening methods. Hereto, inhibition of bacterial protein synthesis is a long-standing validated target. Aminoacyl-tRNA synthetases (aaRSs) play an indispensable role in protein synthesis and their structures proved quite conserved in prokaryotes and eukaryotes. However, some divergence has occurred allowing the development of selective aaRS inhibitors. Following an outline on the action mechanism of aaRSs, an overview will be given of already existing aaRS inhibitors, which are largely based on mimics of the aminoacyl-adenylates, the natural reaction intermediates. This is followed by a discussion on more recent developments in the field and the bioavailability problem.

The effect of topiramate on tumor-related angiogenesis and on the serum proteome of mice bearing Lewis lung carcinoma

Topiramate has been used in patients with brain tumors who develop epilepsy. In our previous research we found topiramate could inhibit tumor metastases of Lewis lung carcinoma in C57BL/6 mice. In this study we aimed to assess the antimetastatic activity of topiramate and determine its mechanism of action. After confirming the effects of topiramate on Lewis lung carcinoma in C57BL/6 mice, we assessed the mRNA expression of carbonic anhydrases II and IX, and the vascular endothelial growth factor (VEGF) distribution in tumor tissue. We studied the role of topiramate on primary angiogenesis using a chicken embryo chorioallantoic membrane angiogenesis model, and analyzed the protein profile of serum from mice treated with or without topiramate by two-dimensional electrophoresis. We found that topiramate significantly reduced the primary tumor growth (P<0.05) and the degree of damage to the lung alveoli caused by metastatic tumor deposits. The two-dimensional electrophoresis revealed changes that occurred with topiramate treatment and four down-regulated protein spots were clearly identified as tropomyosin, osteopontin, transthyretin, and serum amyloid A-1. The mRNA and protein expression of serum amyloid A-1, osteopontin and its receptor, integrin α(v)β(3) in tumor tissue were reconfirmed. The results suggest that topiramate has antitumor and antimetastatic effects on Lewis lung carcinoma. Its mechanism of action may be related to its inhibition of angiogenesis by down-regulation of osteopontin, VEGF and carbonic anhydrase II.

Bidentate Zinc chelators for alpha-carbonic anhydrases that produce a trigonal bipyramidal coordination geometry

A series of new zinc binding groups (ZBGs) has been evaluated kinetically on 13 carbonic anhydrase (CA) isoforms. The fragments show affinity for all isoforms with IC(50) values in the range of 2-11 microM. The crystal structure of hCA II in complex with one such fragment reveals a bidentate binding mode with a trigonal-bipyramidal coordination geometry at the Zn(2+) center. The fragment also interacts with Thr199 and Thr200 through hydrogen bonding and participates in a water network. Further development of this ZBG should increase the binding affinity leading to a structurally distinct and promising class of CA inhibitors.

Carbonic anhydrase inhibition as a cancer therapy: a review of patent literature, 2007 - 2009

IMPORTANCE OF THE FIELD

The functional contribution of membrane-bound extracellular carbonic anhydrases (CAs) to hypoxic tumor growth and progression has long been hypothesized; however, recent convergent evidence from a number of groups strongly implicates these CAs as key prosurvival enzymes during tumor hypoxia. From this perspective targeting the inhibition of cancer-associated CA enzymes, most notably CA IX and XII, has recently been identified as a mechanistically novel scientific opportunity with great potential as a new cancer drug target.

AREAS COVERED IN THIS REVIEW

This review covers world patent applications filed during the 2007 - 2009 period for small molecule approaches; non-small molecule approaches are not within the scope of this review.

WHAT THE READER WILL GAIN

The reader will be provided with a background of the biology of CAs as well as the recent research findings that have validated the crucial prosurvival role of CAs in hypoxic tumors. The review will highlight small molecule molecular methods that modulate CAs as an anti-cancer therapeutic strategy.

TAKE HOME MESSAGE

Much of what has been reported in the patent literature during the period 2007 - 2009 is based on alleged therapeutic benefits of CA inhibitors in cancer. Recently appropriate CA-relevant cell and animal models of tumor hypoxia for the evaluation of compounds have become available and the verification of the ability of small molecules to modulate CA activity as a cancer therapy or as a diagnostic and/or prognostic tool is now possible and probable. The CA field will thus provide for a scientifically exciting and possibly rewarding next few years, accelerated by the growing interest in the potential clinical applications of this enzyme class in oncology.

Therapeutic applications of glycosidic carbonic anhydrase inhibitors

The zinc enzymes carbonic anhydrases (CAs, EC 4.2.1.1) are very efficient catalysts for the reversible hydration of carbon dioxide to bicarbonate and hence play an important physiological role. In humans, 16 different isozymes have been described, some of them being involved in various pathological disorders. Several of these isozymes are considered as drug targets, and the design of selective inhibitors is a long-standing goal that has captured the attention of researchers for 40 years and has lead to clinical applications against different pathologies such as glaucoma, epilepsy, and cancer. Among the different strategies developed for designing selective CA inhibitors (CAIs), the "sugar approach" has recently emerged as a new attractive and versatile tool. Incorporation of glycosyl moieties in different aromatic/heterocyclic sulfonamide/sulfamides/sulfamates scaffolds has led to the development of numerous and very effective inhibitors of potential clinical value. The clinical use of a highly active carbohydrate-based CA inhibitor, i.e., topiramate, constitutes an interesting demonstration of the validity of this approach. Other carbohydrate-based compounds also demonstrate promising potential for the treatment of ophthalmologic diseases. This review will focus on the development of this emerging sugar-based approach for the development of CAIs.

Novel indoline-based acyl-CoA: cholesterol acyltransferase inhibitor: Effects of introducing a methanesulfonamide group on physicochemical properties and biological activities

A novel series of indoline-based acyl-CoA: cholesterol acyltransferase (ACAT) inhibitors with a methanesulfonamide group at the 5-position were synthesized and their lipophilicity and biological activities were evaluated. Hepatic ACAT inhibitory and anti-foam cell formation activity increased dependent on lipophilicity of derivatives with various alkyl chains at the 1-position. The logD(7.0)-biological activity curve of the derivatives with a methanesulfonamide group shifted leftward compared to that of Pactimibe derivatives with a carboxymethyl group, and derivatives with no substituent, suggesting that a methanesulfonamide group plays an important role in the interaction with ACAT protein. Among derivatives, N-(1-ethyl-5-methanesulfonylamino-4,6-dimethylindolin-7-yl)-2,2-dimethylpropanamide (1b) had about twofold lower logD(7.0) than Pactimibe, while it showed twofold higher hepatic ACAT inhibition than and the same anti-foam cell formation as Pactimibe, respectively. The C(max) of 1b (10mg/kg, po) was higher than that of Pactimibe in rats. The plasma protein binding ratio of 1b was lower than that of Pactimibe: 64.8% and 97.9%, respectively. Compound 1b showed greater inhibitory effects on hepatic cholesterol secretion in mice than Pactimibe. In conclusion, the introduction of a methanesulfonamide group is effective to design less lipophilic, more efficacious and more bioavailable indoline-based ACAT inhibitors than previous indoline-based inhibitors.

Novel acyl phosphate mimics that target PlsY, an essential acyltransferase in gram-positive bacteria

PlsY is a recently discovered acyltransferase that executes an essential step in membrane phospholipid biosynthesis in Gram- positive bacteria. By using a bioisosteric replacement approach to generate substrate-based inhibitors of PlsY as potential novel antibacterial agents, a series of stabilized acyl phosphate mimetics, including acyl phosphonates, acyl alpha,alpha-difluoromethyl phosphonates, acyl phosphoramides, reverse amide phosphonates, acyl sulfamates, and acyl sulfamides were designed and synthesized. Several acyl phosphonates, phosphoramides, and sulfamates were identified as inhibitors of PlsY from Streptococcus pneumoniae and Bacillus anthracis. As anticipated, these inhibitors were competitive inhibitors with respect to the acyl phosphate substrate. Antimicrobial testing showed the inhibitors to have generally weak activity against Gram-positive bacteria with the exception of some acyl phosphonates, reverse amide phosphonates, and acyl sulfamates, which had potent activity against multiple strains of B. anthracis.

Structure-activity relationship studies of curcumin analogues

Two series of curcumin analogues, a total of twenty-four compounds, were synthesized and evaluated. The most potent compound, compound 23, showed potent growth inhibitory activities on both prostate and breast cancer lines with IC(50) values in sub-micromolar range, fifty times more potent than curcumin. Curcumin analogues might be potential anti-tumor agents for breast and prostate cancers.

Topiramate induced agranulocytosis

A man in his 40s with a past history of neutropenia during zonisamide administration developed agranulocytosis 1 month after adding on topiramate to treat intractable partial epilepsy. His concurrent medication included phenytoin and acetazolamide. His white blood cell count recovered 5 days after discontinuation of topiramate. Topiramate is a sulfamate whose mechanism of antiepileptic activity is considered to include inhibition of carbonic anhydrase. Topiramate has a potential risk for haematopoietic adverse events; such events are rare and are related to immuno-allergic reaction or toxic effect of sulfonamides and sulfamates, including carbonic anhydrase inhibitors. Because this class of drugs is commonly used as an anti-glaucoma or diuretic agent, particular attention should be paid when initiating topiramate to a patient with a history of sulfonamide or sulfamate induced agranulocytosis, or when co-administrating topiramate with sulfonamides and sulfamates including carbonic anhydrase inhibitors.

Novel acyl phosphate mimics that target PlsY, an essential acyltransferase in gram-positive bacteria

PlsY is a recently discovered acyltransferase that executes an essential step in membrane phospholipid biosynthesis in Gram- positive bacteria. By using a bioisosteric replacement approach to generate substrate-based inhibitors of PlsY as potential novel antibacterial agents, a series of stabilized acyl phosphate mimetics, including acyl phosphonates, acyl alpha,alpha-difluoromethyl phosphonates, acyl phosphoramides, reverse amide phosphonates, acyl sulfamates, and acyl sulfamides were designed and synthesized. Several acyl phosphonates, phosphoramides, and sulfamates were identified as inhibitors of PlsY from Streptococcus pneumoniae and Bacillus anthracis. As anticipated, these inhibitors were competitive inhibitors with respect to the acyl phosphate substrate. Antimicrobial testing showed the inhibitors to have generally weak activity against Gram-positive bacteria with the exception of some acyl phosphonates, reverse amide phosphonates, and acyl sulfamates, which had potent activity against multiple strains of B. anthracis.

Carbonic anhydrase IX: a new druggable target for the design of antitumor agents

Carbonic anhydrases (CAs, EC 4.2.1.1) are a family of enzymes widespread in all life kingdoms. In mammals, isozyme CA IX is highly overexpressed in many cancer types being present in few normal tissues. Its expression is strongly induced by hypoxia present in many tumors, being regulated by the HIF transcription factor and correlated with a poor response to classical chemo- and radiotherapies. CA IX was recently shown to contribute to acidification of the tumor environment, by efficiently catalyzing the hydration of carbon dioxide to bicarbonate and protons with its extracellularly situated active site, leading both to the acquisition of metastasic phenotypes and to chemoresistance with weakly basic anticancer drugs. Inhibition of this enzymatic activity by specific and potent inhibitors was shown to revert these acidification processes, establishing a clear-cut role of CA IX in tumorigenesis. The development of a wide range of potent and selective CA IX inhibitors belonging to diverse chemical classes, such as membrane-impermeant, fluorescent or metal-containing such agents, could thus provide useful tools for highlighting the exact role of CA IX in hypoxic cancers, to control the pH (im)balance of tumor cells, and to develop novel diagnostic or therapeutic applications for the management of tumors. Indeed, both fluorescent inhibitors or positively charged, membrane impermeant sulfonamides have been recently developed as potent CA IX inhibitors and used as proof-of-concept tools for demonstrating that CA IX constitutes a novel and interesting target for the anticancer drug development.

Molecular pharmacodynamics, clinical therapeutics, and pharmacokinetics of topiramate

Topiramate (TPM; TOPAMAX) is a broad-spectrum antiepileptic drug (AED) that is approved in many world markets for preventing or reducing the frequency of epileptic seizures (as monotherapy or adjunctive therapy), and for the prophylaxis of migraine. TPM, a sulfamate derivative of the naturally occurring sugar D-fructose, possesses several pharmacodynamic properties that may contribute to its clinically useful attributes, and to its observed adverse effects. The sulfamate moiety is essential, but not sufficient, for its pharmacodynamic properties. In this review, we discuss the known pharmacodynamic and pharmacokinetic properties of TPM, as well as its various clinically beneficial and adverse effects.

Homology modeling and receptor-based 3D-QSAR study of carbonic anhydrase IX

Carbonic anhydrase (CA) IX is a very interesting subject for study due to its overexpression in cancer and its expression in very few normal tissues. There are not yet experimental 3D structures of the catalytic domain of this isozyme, and only a few computational studies have been reported. A homology model of CA IX was developed, and using Gold software 124 CA IX inhibitors were docked. The best poses of the ligands were then used as an alignment tool for the development of the first reported CA IX 3D-QSAR model. The obtained results confirm the reliability of the constructed CA IX model and the proposed computational strategy for investigating CAs.

IA, database of known ligands of aminoacyl-tRNA synthetases

The IA database contains 240 structures of known inhibitors of aminoacyl-tRNA synthetases. Structures can be downloaded in different file formats (mol, sdf, smile, png). The search engine offers possibility of searching for the ligands with a given functional group. Additionally, one can search for ligands that act on selected synthetases and from particular references. The data include information which synthetase a given ligand inhibits together with the inhibition constant (IC50) if known.

Carbonic anhydrase inhibitors: X-ray and molecular modeling study for the interaction of a fluorescent antitumor sulfonamide with isozyme II and IX

The X-ray crystal structure of the fluorescent antitumor sulfonamide carbonic anhydrase (CA, EC, 4.2.1.1) inhibitor (4-sulfamoylphenylethyl)thioureido fluorescein (1) in complex with the cytosolic isoform hCA II is reported, together with a modeling study of the adduct of 1 with the tumor-associated isoform hCA IX. Its binding to hCA II is similar to that of other benzesulfonamides, with the ionized sulfonamide coordinated to the Zn2+ ion within the enzyme active site, and also participating in a network of hydrogen bonds with residues Thr199 and Glu106. The scaffold of 1 did not establish polar interactions within the enzyme active site but made hydrophobic contacts (<4.5 A) with Gln92, Val121, Phe131, Val135, Leu198, Thr199, Thr200, and Pro202. The substituted 3-carboxy-amino-phenyl functionality was at van der Waals distance from Phe131, Gly132, and Val135. The bulky tricyclic fluorescein moiety was located at the rim of the active site, on the protein surface, and strongly interacted with the alpha-helix formed by residues Asp130-Val135. All these interactions were preserved in the hCA IX-1 adduct, but the carbonyl moiety of the fluorescein tail of 1 participates in a strong hydrogen bond with the guanidine moiety of Arg130, an amino acid characteristic of the hCA IX active site. This may account for the roughly 2 times higher affinity of 1 for hCA IX over hCA II and may explain why in vivo the compound specifically accumulates only in hypoxic tumors overexpressing CA IX and not in the normal tissues. The compound is in clinical studies as an imaging tool for acute hypoxic tumors.

Molecular modeling study for the binding of zonisamide and topiramate to the human mitochondrial carbonic anhydrase isoform VA

Zonisamide and topiramate are two antiepileptic drugs known to induce weight loss in epilepsy patients. These molecules were recently shown to act as carbonic anhydrase (CA) inhibitors, being presumed that the weight loss may be due to the inhibition of the mitochondrial isozymes CA VA and CA VB involved in metabolic processes, among which lipid biosynthesis. To better understand the interaction of these compounds with CAs, here, we report a homology modeling and molecular dynamics simulations study on their adducts with human carbonic anhydrase VA (hCA VA). According to our results, in both cases the inhibitor sulfamate/sulfonamide moiety participates in the canonical interactions with the catalytic zinc ion, whereas the organic scaffold establishes a large number of van der Waals and polar interactions with the active site cleft. A structural comparison of these complexes with the corresponding homologues with human carbonic anhydrase II (hCA II) provides a rationale to the different affinities measured for these drugs toward hCA VA and hCA II. In particular, our data suggest that a narrower active site cleft, together with a different hydrogen bond network arrangement of hCA VA compared to hCA II, may account for the different Kd values of zonisamide and topiramate toward these physiologically relevant hCA isoforms. These results provide useful insights for future design of more isozyme-selective hCA inhibitors with potential use as anti-obesity drugs possessing a novel mechanism of action.

Carbonic anhydrase activators: activation of the human isoforms VII (cytosolic) and XIV (transmembrane) with amino acids and amines

An activation study of the human carbonic anhydrase (hCA, EC 4.2.1.1) isozymes VII and XIV using a small library of natural/non-natural amino acids and aromatic/heterocyclic amines is reported. hCA VII was efficiently activated by L-/D-His, dopamine and serotonin (K(A)s of 0.71-0.93 microM). The best hCA XIV activators were histamine (K(A) of 10 nM), L-Phe, L-/D-His and 4-amino-L-Phe (K(A)s of 0.24-2.90 microM). In view of the significant expression levels of CA VII and CA XIV in the brain, selective activation of these isoforms may be useful when developing pharmacologic agents for the management of major disorders such as epilepsy and Alzheimer's disease.

Topiramate for the treatment of binge eating disorder associated with obesity: a placebo-controlled study

BACKGROUND

In a single-center, placebo-controlled study, topiramate reduced binge eating and weight in patients with binge eating disorder (BED) and obesity. The current investigation evaluated the safety and efficacy of topiramate in a multicenter, placebo-controlled trial.

METHODS

Eligible patients between 18 and 65 years with >or= 3 binge eating days/week and a body mass index (BMI) between 30 and 50 kg/m2 were randomized.

RESULTS

A total of 407 patients enrolled; 13 failed to meet inclusion criteria, resulting in 195 topiramate and 199 placebo patients. Topiramate reduced binge eating days/week (-3.5 +/- 1.9 vs. -2.5 +/- 2.1), binge episodes/week (-5.0 +/- 4.3 vs. -3.4 +/- 3.8), weight (-4.5 +/- 5.1 kg vs. .2 +/- 3.2 kg), and BMI (-1.6 +/- 1.8 kg/m2 vs. .1 +/- 1.2 kg/m2) compared with placebo (p < .001). Topiramate induced binge eating remission in 58% of patients (placebo, 29%; p < .001). Discontinuation rates were 30% in each group; adverse events (AEs) were the most common reason for topiramate discontinuation (16%; placebo, 8%). Paresthesia, upper respiratory tract infection, somnolence, and nausea were the most common AEs with topiramate.

CONCLUSIONS

This multicenter study in patients with BED associated with obesity demonstrated that topiramate was well tolerated and efficacious in improving the features of BED and in reducing obesity.

Carbonic anhydrase inhibitors: Binding of an antiglaucoma glycosyl-sulfanilamide derivative to human isoform II and its consequences for the drug design of enzyme inhibitors incorporating sugar moieties

N-(4-Sulfamoylphenyl)-alpha-d-glucopyranosylamine, a promising topical antiglaucoma agent, is a potent inhibitor of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1). The high resolution X-ray crystal structure of its adduct with the target isoform involved in glaucoma, CA II, is reported here. The sugar sulfanilamide derivative binds to the enzyme in a totally new manner as compared to other CA-inhibitor adducts investigated earlier. The sulfonamide anchor was coordinated to the active site metal ion, and the phenylene ring of the inhibitor filled the channel leading to the active site cavity. The glycosyl moiety responsible for the high water solubility of the compound was oriented towards a hydrophilic region of the active site, where no other inhibitors were observed to be bound up to now. A network of seven hydrogen bonds with four water molecules and the amino acid residues Pro201, Pro202 and Gln92 further stabilize the enzyme-inhibitor adduct. Topiramate, another sugar-based CA inhibitor, binds in a completely different manner to CA II as compared to the sulfonamide investigated here. These findings are useful for the design of potent, sugar-derived enzyme inhibitors.

Carbonic anhydrase inhibitors: Inhibition of cytosolic/tumor-associated isoforms I, II, and IX with iminodiacetic carboxylates/hydroxamates also incorporating benzenesulfonamide moieties

The synthesis of a new class of sulfonamide carbonic anhydrase (CA, EC 4.2.1.1) inhibitors (CAIs), also possessing carboxylate/hydroxamate moieties in their molecule, is reported. These compounds may act on dual antitumor targets, the tumor-associated CA isozymes (CA IX) and some matrix metalloproteinases (MMPs). The compounds were prepared by an original method starting from iminodiacetic acid, and assayed as inhibitors of three isozymes, hCA I, II (cytosolic), and IX (transmembrane). The new derivatives showed weak inhibitory activity against isozyme I (K(I)s in the range of 95-8300 nM), were excellent to moderate CA II inhibitors (K(I)s in the range of 8.4-65 nM), and very good and selective CA IX inhibitors (K(I)s in the range of 3.8-26 nM). The primary sulfonamide moiety is a better zinc-binding group in the design of CAIs as compared to the carboxylate/hydroxamate one, but the presence of hydroxamate functionalities in the molecule of CAIs leads to selectivity for the tumor-associated isozyme IX over the ubiquitous, cytosolic isoform II.

A novel dual-target steroid sulfatase inhibitor and antiestrogen: SR 16157, a promising agent for the therapy of breast cancer

Endocrine therapy is the ideal treatment choice for estrogen receptor alpha (ERalpha)-positive breast cancer patients. Principal used therapies target either the ERalpha e.g. by selective ERalpha modulators (SERMs) such as tamoxifen or target estrogen biosynthesis with aromatase inhibitors. Steroid sulfatase (STS) plays a crucial role in formation of compounds with estrogenic properties, converting inactive sulfate-conjugated steroids to active non-conjugated forms. Steroid sulfates are considered as a reservoir for active steroids due to their prolonged half-life and increased concentration in plasma. STS is present in several tissues including the breast, and the STS the mRNA level and enzyme activity is significantly increased in ERalpha-positive breast tumors. Inhibition of STS is therefore a new approach for decreasing estrogenic steroids that stimulate breast cancer. The novel dual-acting compound SR 16157 is designed as a sulfamate-containing STS inhibitor that releases a tissue-selective SERM SR 16137. Use of a dual-target STS inhibitor and SERM represents a new strategy in the treatment of hormone-dependent breast cancer. In this study, we tested the potential of SR 16157 and SR 16137 on STS activity, cell growth and ERalpha function in MCF-7 breast cancer cells. We confirmed that the dual-target compound SR 16157 exerts STS inhibition and antiestrogenic effects. SR 16157 was a highly effective growth inhibitor, being 10 times more potent than the antiestrogens SR 16137 and tamoxifen. Relative to tamoxifen, SR 16137 displays profoundly improved ERalpha binding affinity and antiestrogenic effects on expression of estrogen-regulated genes. Thus, the dual-target SR 16157 is possibly a promising new treatment alternative, superior to tamoxifen.

Carbonic anhydrase inhibitors. N-cyanomethylsulfonamides--a new zinc binding group in the design of inhibitors targeting cytosolic and membrane-anchored isoforms

A series of N-cyanomethyl aromatic sulfonamides and bis-sulfonamides was prepared by reaction of arylsulfonyl halides with aminoacetonitrile. The obtained derivatives incorporated various aryl moieties, such as 4-halogeno/alkyl/aryl/nitro-substituted-phenyl, pentafluorophenyl or 2-naphthyl. Moderate inhibitory activity was detected for some compounds against the cytosolic human isoform II of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1), hCA II, with inhibition constants of 90, 180 and 560n M for the 4-nitrophenyl-, 4-iodophenyl- and pentafluorophenyl-N-cyanomethylsulfonamides, respectively. Other derivatives acted as weak inhibitors of isoforms hCA I (KIs of 720 nM-45 microM), hCA II (KIs of 1000-9800 nM) and hCA IX (KIs of 900-10200 nM). Thus, the N-cyanomethylsulfonamide zinc binding group is less effective than the sulfonamide, sulfamate or sulfamide ones for the design of effective CA inhibitors.

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.

Boronic acids as inhibitors of steroid sulfatase

Steroid sulfatase (STS) catalyzes the hydrolysis of steroidal sulfates such as estrone sulfate (ES1) to the corresponding steroids and inorganic sulfate. STS is considered to be a potential target for the development of therapeutics for the treatment of steroid-dependent cancers. Two steroidal and two coumarin- and chromenone-based boronic acids were synthesized and examined as inhibitors of purified STS. The boronic acid analog of estrone sulfate bearing a boronic acid moiety at the 3-position in place of the sulfate group was a good competitive STS inhibitor with a K(i) of 2.8microM at pH 7.0 and 6.8microM at pH 8.8. The inhibition was reversible and kinetic properties corresponding to the mechanism for slow-binding inhibitors were not observed. An estradiol derivative bearing a boronic acid group at the 3-position and a benzyl group at the 17-position was a potent reversible, non-competitive STS inhibitor with a K(i) of 250nM. However, its 3-OH analog, a known STS inhibitor, exhibited an almost identical affinity for STS and also bound in a non-competitive manner. It is suggested that these compounds prefer to bind in a hydrophobic tunnel close to the entrance to the active site. The coumarin and chromenone boronic acids were modest inhibitors of STS with IC(50)s of 86 and 171microM, respectively. Surprisingly, replacing the boronic acid group of the chromenone derivative with an OH group yielded a good reversible, mixed type inhibitor with a K(i) of 4.6microM. Overall, these results suggest that the boronic acid moiety must be attached to a platform very closely resembling a natural substrate in order for it to impart a beneficial effect on binding affinity compared to its phenolic analog.

Carbonic anhydrase inhibitors: X-ray crystallographic studies for the binding of 5-amino-1,3,4-thiadiazole-2-sulfonamide and 5-(4-amino-3-chloro-5-fluorophenylsulfonamido)-1,3,4-thiadiazole-2-sulfonamide to human isoform II

The X-ray crystal structures of 5-amino-1,3,4-thiadiazole-2-sulfonamide (the acetazolamide precursor) and 5-(4-amino-3-chloro-5-fluorophenylsulfonamido)-1,3,4-thiadiazole-2-sulfonamide in complex with the human isozyme II of carbonic anhydrase (CA, EC 4.2.1.1) are reported. The thiadiazole-sulfonamide moiety of the two compounds binds in the canonic manner to the zinc ion and interacts with Thr199, Glu106, and Thr200. The substituted phenyl tail of the second inhibitor was positioned in the hydrophobic part of the binding pocket, at van der Waals distance from Phe131, Val 135, Val141, Leu198, Pro202, and Leu204. These structures may help in the design of better inhibitors of these widespread zinc-containing enzymes.

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.

Carbonic Anhydrase Inhibitors: Clash with Ala65 as a Means for Designing Inhibitors with Low Affinity for the Ubiquitous Isozyme II, Exemplified by the Crystal Structure of the Topiramate Sulfamide Analogue

The sulfamide analogue of the antiepileptic drug topiramate is a 210 times less potent inhibitor of isozyme II of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1) compared to topiramate but effectively inhibits isozymes CA VA, VB, VII, XIII, and XIV (KI in the range of 21-35 nM). Its weak binding to CA II is due to a clash between one methyl group of the inhibitor and Ala65 and may be exploited for the drug design of compounds with lower affinity for this ubiquitous isozyme, as Ala65 is unique to CA II. As shown by X-ray crystallography, the sulfamide analogue binds to CA II with the deprotonated sulfamide moiety coordinated to Zn(II) and with the organic scaffold making an extended network of hydrogen bonds with Thr199, Gln92, His94, Asn62, and Thr200. Its binding to this isozyme is more similar to that of topiramate and quite different from that of the topiramate cyclic sulfate analogue RWJ-37947.

Synthesis and evaluation of general mechanism-based inhibitors of sulfatases based on (difluoro)methyl phenyl sulfate and cyclic phenyl sulfamate motifs

Several model mechanism-based inhibitors (MbIs) were designed and evaluated for their ability to inhibit sulfatases. The MbI motifs were based on simple aromatic sulfates, which are known to be commonly accepted substrates across this highly conserved enzyme class, so that they might be generally useful for sulfatase labeling studies. (Difluoro)methyl phenol sulfate analogs, constructed to release a reactive quinone methide trap, were not capable of irreversibly inactivating the sulfatase active site. On the other hand, the cyclic sulfamates (CySAs) demonstrated inhibition profiles consistent with an active site-directed mode of action. These molecules represent a novel scaffold for labeling sulfatases and for probing their catalytic mechanism.