Is cyanate a carbonic anhydrase substrate?

Reconsidering anion inhibitors in the general context of drug design studies of modulators of activity of the classical enzyme carbonic anhydrase

Inorganic anions inhibit the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) generally by coordinating to the active site metal ion. Cyanate was reported as a non-coordinating CA inhibitor but those erroneous results were subsequently corrected by another group. We review the anion CA inhibitors (CAIs) in the more general context of drug design studies and the discovery of a large number of inhibitor classes and inhibition mechanisms, including zinc binders (sulphonamides and isosteres, dithiocabamates and isosteres, thiols, selenols, benzoxaboroles, ninhydrins, etc.); inhibitors anchoring to the zinc-coordinated water molecule (phenols, polyamines, sulfocoumarins, thioxocoumarins, catechols); CAIs occluding the entrance to the active site (coumarins and derivatives, lacosamide), as well as compounds that bind outside the active site. All these new chemotypes integrated with a general procedure for obtaining isoform-selective compounds (the tail approach) has resulted, through the guidance of rigorous X-ray crystallography experiments, in the development of highly selective CAIs for all human CA isoforms with many pharmacological applications.

Investigation of pesticides on honey bee carbonic anhydrase inhibition

Carbonic anhydrase (CA, EC 4.2.1.1) plays crucial physiological roles in many different organisms, such as in pH regulation, ion transport, and metabolic processes. CA was isolated from the European bee Apis mellifera (AmCA) spermatheca and inhibitory effects of pesticides belonging to various classes, such as carbamates, thiophosphates, and pyrethroids, were investigated herein. The inhibitory effects of methomyl, oxamyl, deltamethrin, cypermethrin, dichlorodiphenyltrichloroethane (DDT) and diazinon on AmCA were analysed. These pesticides showed effective in vitro inhibition of the enzyme, at sub-micromolar levels. The IC50 values for these pesticides ranged between of 0.0023 and 0.0385 μM. The CA inhibition mechanism with these compounds is unknown at the moment, but most of them contain ester functionalities which may be hydrolysed by the enzyme with the formation of intermediates that can either react with amino acid residues or bid to the zinc ion from the active site.

Synthesis of sulfonamide, amide and amine hybrid pharmacophore, an entry of new class of carbonic anhydrase II inhibitors and evaluation of chemo-informatics and binding analysis

Selective inhibition of carbonic anhydrase (CA) enzyme is an active area of research for medicinal chemists. In the current account, a hybrid pharmacophore approach was employed to design sulfonamide, amide and amine containing new series of potent carbonic anhydrase II inhibitors. The aromatic fragment associated with pharmacophore was altered suitably in order to find effective inhibitors of CA-II. All the derivatives 4a-4m showed better inhibition compared to the standard acetazolamide. In particular, compound 4l exhibited significant inhibition with IC₅₀ value of 0.01796 ± 0.00036 µM. The chemo-informatics analysis justified that all the designed compounds possess <10 HBA and <5 HBD. The ligands-protein binding analyses showed that 4l confined in the active binding pocket with three hydrogen bonds observed with His63, Asn66 and Thr197 residues.

Structure and function of carbonic anhydrases

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyse the interconversion between CO2 and bicarbonate as well as other hydrolytic reactions. Among the six genetic families known to date, the α-, β-, γ-, δ-, ζ- and η-CAs, detailed kinetic and X-ray crystallographic studies have allowed a deep understanding of the structure-function relationship in this superfamily of proteins. A metal hydroxide nucleophilic species of the enzyme, and a unique active site architecture, with half of it hydrophilic and the opposing part hydrophobic, allow these enzymes to act as some of the most effective catalysts known in Nature. The CA activation and inhibition mechanisms are also known in detail, with a large number of new inhibitor classes being described in the last years. Apart from the zinc binders, some classes of inhibitors anchor to the metal ion coordinated nucleophile, others occlude the entrance of the active site cavity and more recently, compounds binding outside the active site were described. CA inhibition has therapeutic applications for drugs acting as diuretics, antiepileptics, antiglaucoma, antiobesity and antitumour agents. Targeting such enzymes from pathogens may lead to novel anti-infectives. Successful structure-based drug design campaigns allowed the discovery of highly isoform selective CA inhibitors (CAIs), which may lead to a new generation of drugs targeting these widespread enzymes. The use of CAs in CO2 capture processes for mitigating the global temperature rise has also been investigated more recently.

Carbonic anhydrase inhibition and the management of neuropathic pain

INTRODUCTION

Neuropathic pain affects up to 8% of the population with few therapeutic options for its management. No specific drugs are approved for its treatment.

AREAS COVERED

Recent advances in understanding the pathological mechanisms of this syndrome and the biochemical/pharmacological characterization of novel drug targets, evidenced carbonic anhydrase (CA, EC 4.2.1.1) inhibition as a new approach for designing antineuropathic pain agents. Expert commentary: Peripheral nerve injury negatively influences spinal γ-aminobutyric (GABA)-ergic networks via a reduction in the neuron-specific potassium-chloride (K(+)-Cl(-)) cotransporter (KCC2), which leads to neuropathic allodynia. CA inhibitors (CAIs) reduce the bicarbonate-dependent depolarization of GABAA receptors, showing analgesic effects. Novel classes of selective sulfonamide CA II/VII inhibitors showed highly improved efficacy in animal models of neuropathic pain, compared to acetazolamide, offering the basis for the development of specific therapies of this syndrome based on selective CA isoforms inhibition.

Synthesis and inhibitory properties of some carbamates on carbonic anhydrase and acetylcholine esterase

A series of carbamate derivatives were synthesized and their carbonic anhydrase I and II isoenzymes and acetylcholinesterase enzyme (AChE) inhibitory effects were investigated. All carbamates were synthesized from the corresponding carboxylic acids via the Curtius reactions of the acids with diphenyl phosphoryl azide followed by addition of benzyl alcohol. The carbamates were determined to be very good inhibitors against for AChE and hCA I, and II isoenzymes. AChE inhibition was determined in the range 0.209-0.291 nM. On the other hand, tacrine, which is used in the treatment of Alzheimer's disease possessed lower inhibition effect (Ki: 0.398 nM). Also, hCA I and II isoenzymes were effectively inhibited by the carbamates, with inhibition constants (Ki) in the range of 4.49-5.61 nM for hCA I, and 4.94-7.66 nM for hCA II, respectively. Acetazolamide, which was clinically used carbonic anhydrase (CA) inhibitor demonstrated Ki values of 281.33 nM for hCA I and 9.07 nM for hCA II. The results clearly showed that AChE and both CA isoenzymes were effectively inhibited by carbamates at the low nanomolar levels.

Protonography, a powerful tool for analyzing the activity and the oligomeric state of the γ-carbonic anhydrase identified in the genome of Porphyromonas gingivalis

Carbonic anhydrases (CAs, EC 4.2.1.1) are metalloenzymes, mostly containing zinc within their active site, which catalyze a simple but physiologically relevant reaction in all life kingdoms, carbon dioxide hydration to bicarbonate and protons. Six CA classes (α, β, γ, δ, ζ and η) and multiple CA isoforms evolved in organisms all over the phylogenetic tree, for facing the need to efficiently convert high amounts of CO2 to its hydration products. These enzymes are thus involved in many physiologic processes, such as photosynthesis, respiration, CO2 transport, electrolyte secretion in many tissues/organs; biosynthetic reactions (gluconeogenesis, lipogenesis, ureagenesis), etc. Recently, our group reported a new technique to assay CA activity on SDS-PAGE gels, named 'protonography' due to its similarity to zymography. By using protonography, the conversion of CO2 into protons can be visualized as a yellow band on a polyacrylamide gel. By using this technique we demonstrated the possibility to detect activity of the α-CA from Vibrio cholerae as well as the β- and γ-CAs present in Escherichia coli extracts. Furthermore, the activity of the newly discovered η-class enzyme from Plasmodium falciparum has also been evidenced with protonography, illustrating its wide use. Here we show that protonography can be also useful to reveal the oligomeric state of the γ-CA identified in the genome of the bacterial parasite colonizing the oral cavity, Porphyromonas gingivalis, possibly allowing for a simple and efficient diagnostic method.

Human carbonic anhydrase II-cyanate inhibitor complex: putting the debate to rest

The binding of anions to carbonic anhydrase II (CA II) has been attributed to high affinity for the active-site zinc. An anion of interest is cyanate, for which contrasting binding modes have been reported in the literature. Previous spectroscopic data have shown cyanate behaving as an inhibitor, directly binding to the zinc, in contrast to previous crystallographic data that implied that cyanate acts as a substrate mimic that is not directly bound to the zinc but overlaps with the binding site of the substrate CO2. Wild-type and the V207I variant of CA II have been expressed and X-ray crystal structures of their cyanate complexes have been determined to 1.7 and 1.5 Å resolution, respectively. The rationale for the V207I CA II variant was its close proximity to the CO2-binding site. Both structures clearly show that the cyanate binds directly to the zinc. In addition, inhibition constants (∼40 µM) were measured using (18)O-exchange mass spectrometry for wild-type and V207I CA II and were similar to those determined previously (Supuran et al., 1997). Hence, it is concluded that under the conditions of these experiments the binding of cyanate to CA II is directly to the zinc, displacing the zinc-bound solvent molecule, and not in a site that overlaps with the CO2 substrate-binding site.

Carbonic anhydrase VII is S-glutathionylated without loss of catalytic activity and affinity for sulfonamide inhibitors

Human carbonic anhydrase (CA, EC 4.2.1.1) VII is a cytosolic enzyme with high carbon dioxide hydration activity. Here we report an unexpected S-glutathionylation of hCA VII which has also been observed earlier in vivo for hCA III, another cytosolic isoform. Cys183 and Cys217 were found to be the residues involved in reaction with glutathione for hCA VII. The two reactive cysteines were then mutated and the corresponding variant (C183S/C217S) expressed. The native enzyme, the variant and the S-glutathionylated adduct (sgCA VII) as well as hCA III were fully characterized for their CO(2) hydration, esterase/phosphatase activities, and inhibition with sulfonamides. Our findings suggest that hCA VII could use the in vivo S-glutathionylation to function as an oxygen radical scavenger for protecting cells from oxidative damage, as the activity and affinity for inhibitors of the modified enzyme are similar to those of the wild type.

Investigations of the esterase, phosphatase, and sulfatase activities of the cytosolic mammalian carbonic anhydrase isoforms I, II, and XIII with 4-nitrophenyl esters as substrates

The esterase, phosphatase, and sulfatase activities of carbonic anhydrase (CA, EC 4.2.1.1) isozymes, CA I, II, and XIII with 4-nitrophenyl esters as substrates was investigated. These enzymes show esterase activity with 4-nitrophenyl acetate as substrate, with second order rate constants in the range of 753-7706M(-1)s(-1), being less effective as phosphatases (k(cat)/K(M) in the range of 14.89-1374.40M(-1)s(-1)) and totally ineffective sulfatases. The esterase/phosphatase activities were inhibited by sulfonamide CA inhibitors, proving that the zinc-hydroxide mechanism responsible for the CO(2) hydrase activities of CAs is also responsible for their esterase/phosphatase activity. CA XIII was the most effective esterase and phosphatase. CA XIII might catalyze other physiological reactions than CO(2) hydration, based on its relevant phosphatase activity.

Carbonic anhydrases as targets for medicinal chemistry

Carbonic anhydrases (CAs, EC 4.2.1.1) are zinc enzymes acting as efficient catalysts for the reversible hydration of carbon dioxide to bicarbonate. 16 different alpha-CA isoforms were isolated in mammals, where they play crucial physiological roles. Some of them are cytosolic (CA I, CA II, CA III, CA VII, CA XIII), others are membrane-bound (CA IV, CA IX, CA XII, CA XIV and CA XV), CA VA and CA VB are mitochondrial, and CA VI is secreted in saliva and milk. Three acatalytic forms are also known, the CA related proteins (CARP), CARP VIII, CARP X and CARP XI. Representatives of the beta-delta-CA family are highly abundant in plants, diatoms, eubacteria and archaea. The catalytic mechanism of the alpha-CAs is understood in detail: the active site consists of a Zn(II) ion co-ordinated by three histidine residues and a water molecule/hydroxide ion. The latter is the active species, acting as a potent nucleophile. For beta- and gamma-CAs, the zinc hydroxide mechanism is valid too, although at least some beta-class enzymes do not have water directly coordinated to the metal ion. CAs are inhibited primarily by two classes of compounds: the metal complexing anions and the sulfonamides/sulfamates/sulfamides possessing the general formula RXSO(2)NH(2) (R=aryl; hetaryl; perhaloalkyl; X=nothing, O or NH). Several important physiological and physio-pathological functions are played by CAs present in organisms all over the phylogenetic tree, related to respiration and transport of CO(2)/bicarbonate between metabolizing tissues and the lungs, pH and CO(2) homeostasis, electrolyte secretion in a variety of tissues/organs, biosynthetic reactions, such as the gluconeogenesis and ureagenesis among others (in animals), CO(2) fixation (in plants and algae), etc. The presence of these ubiquitous enzymes in so many tissues and in so different isoforms represents an attractive goal for the design of inhibitors with biomedical applications. Indeed, CA inhibitors are clinically used as antiglaucoma drugs, some other compounds being developed as antitumour agents/diagnostic tools for tumours, antiobesity agents, anticonvulsants and antimicrobials/antifungals (inhibitors targeting alpha- or beta-CAs from pathogenic organisms such as Helicobacter pylori, Mycobacterium tuberculosis, Plasmodium falciparum, Candida albicans, etc.).

Phosph(on)ate as a zinc-binding group in metalloenzyme inhibitors: X-ray crystal structure of the antiviral drug foscarnet complexed to human carbonic anhydrase I

Foscarnet (phosphonoformate trisodium salt), an antiviral used for the treatment of HIV and herpes virus infections, also acts as an activator or inhibitor of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). Interaction of the drug with 11 CA isozymes has been investigated kinetically, and the X-ray structure of its adduct with isoform I (hCA I-foscarnet complex) has been resolved. The first CA inhibitor possessing a phosphonate zinc-binding group is thus evidenced, together with the factors governing recognition of such small molecules by a metalloenzyme active site. Foscarnet is also a clear-cut example of modulator of an enzyme activity which can act either as an activator or inhibitor of a CA isozyme.

Carbonic anhydrase inhibitors. Interaction of isozymes I, II, IV, V, and IX with organic phosphates and phosphonates

The interaction of five human carbonic anhydrase (hCA, EC 4.2.1.1) isozymes, that is, hCA I, II, IV, V, and IX with a small library of phosphonic acids/organic phosphates, including methylphosphonic acid, MPA; phenylphosphonic acid, PPA; N-(phosphonoacetyl)-L-aspartic acid, PALA, methylene diphosphonic acid MDPA, the O-phosphates of serine (Ser-OP) and threonine (Thr-OP) as well as the antiviral phosphonate foscarnet has been studied. hCA I was activated by all these compounds, with the best activators being MPA and PPA (K(A)s of 0.10-1.20 microM). MPA and PPA were on the other hand nanomolar inhibitors of hCA II (K(I)s of 98-99 nM). PALA showed an affinity of 7.8 microM, whereas the other compounds were weak, millimolar inhibitors of this isozyme. The best hCA IV inhibitors were PALA (79 nM) and PPA (5.4 microM), whereas the other compounds showed K(I)s in the range of 0.31-5.34 mM. The mitochondrial isozyme was weakly inhibited by all these compounds (K(I)s in the range of 0.09-41.7 mM), similarly to the transmembrane, tumor-associated isozyme (K(I)s in the range of 0.86-2.25 mM). Thus, phosphonates may lead to CA inhibitors with selectivity against two physiologically relevant isozymes, the cytosolic hCA II or the membrane-bound hCA IV.

Carbonic anhydrase inhibitors. Interaction of isozymes I, II, IV, V, and IX with phosphates, carbamoyl phosphate, and the phosphonate antiviral drug foscarnet

A detailed inhibition study of five carbonic anhydrase (CA, EC 4.2.1.1) isozymes with inorganic phosphates, carbamoyl phosphate, the antiviral phosphonate foscarnet as well as formate is reported. The cytosolic isozyme hCA I was weakly inhibited by neutral phosphate, strongly inhibited by carbamoyl phosphate (K(I) of 9.4 microM), and activated by hydrogen- and dihydrogenphosphate, foscarnet and formate (best activator foscarnet, K(A)=12 microM). The cytosolic isozyme hCA II was weakly inhibited by all the investigated anions, with carbamoyl phosphate showing a K(I) of 0.31 mM. The membrane-associated isozyme hCA IV was the most sensitive to inhibition by phosphates/phosphonates, showing a K(I) of 84 nM for PO(4)(3-), of 9.8 microM for HPO(4)(2-), and of 9.9 microM for carbamoyl phosphate. Foscarnet was the best inhibitor of this isozyme (K(I) of 0.82 mM) highly abundant in the kidneys, which may explain some of the renal side effects of the drug. The mitochondrial isozyme hCA V was weakly inhibited by all phosphates/phosphonates, except carbamoyl phosphate, which showed a K(I) of 8.5 microM. Thus, CA V cannot be the isozyme involved in the carbamoyl phosphate synthetase I biosynthetic reaction, as hypothesized earlier. Furthermore, the relative resistance of CA V to inhibition by inorganic phosphates suggests an evolutionary adaptation of this mitochondrial isozyme to the presence of high concentrations of such anions in these energy-converting organelles, where high amounts of ATP are produced by ATP synthetase, from ADP and inorganic phosphates. The transmembrane, tumor-associated isozyme hCA IX was on the other hand slightly inhibited by all these anions.

Quantitative structure-activity relationships of carbonic anhydrase inhibitors

A review is presented of quantitative structure-activity relationships (QSARs) of different categories of carbonic anhydrase (CA) inhibitors, which are basically benzenesulfonamides, heterocyclic sulfonamides and aliphatic sulfonamides. The review shows that in all categories, the inhibition potency depends largely on the electronic properties of the sulfonamide group, which can be affected by the electronic characteristics of the substituents present on the nucleus (benzene or heterocyclic ring) of the sulfonamide molecules. Substituents themselves can be involved, along with the nucleus, in some dispersion interaction with the enzyme. Based on this review, a schematic model is presented to represent the interaction of sulfonamides with the CA.

Hydroxyurea is a carbonic anhydrase inhibitor

The interaction of hydroxyurea with the cytosolic isozymes of carbonic anhydrase (CA), hCA I and hCA II has been investigated by means of kinetic and spectroscopic techniques. Hydroxyurea acts as a weak, non-competitive inhibitor of both isozymes, for the 4-nitrophenyl acetate esterase activity, with inhibition constants around 0.1 mM for both isozymes. The spectrum of the adduct of hydroxyurea with Co(II)-hCA II is similar to the spectra of tetrahedral adducts (such as those with sulfamide, acetazolamide or cyanamide), proving a direct interaction of the inhibitor molecule with the metal center of the enzyme, whose geometry remains tetrahedral. Based on the X-ray crystal structure of the adducts of hCA II with ureate and hydroxamate inhibitors, the hypothetical binding of hydroxyurea is proposed to be achieved in deprotonated state, with the nitrogen atom coordinated to Zn(II), and the OH group of the inhibitor making a hydrogen bond with Thr 199. This binding may be exploited for the design of both CA as well as matrix metalloproteinase (MMP) inhibitors, since hydroxyurea is the simplest compound incorporating a hydroxamate functionality in its molecule. Indeed, such inhibitors of the sulfonylated amino acid hydroxamate type have been generated, with potencies in the low nanomolar range for both type of enzymes, CAs and MMPs.

Carbonic anhydrase inhibitors

At least 14 different carbonic anhydrase (CA, EC 4.2.1.1) isoforms were isolated in higher vertebrates, where these zinc enzymes play crucial physiological roles. Some of these isozymes are cytosolic (CA I, CA II, CA III, CA VII), others are membrane-bound (CA IV, CA IX, CA XII, and CA XIV), CA V is mitochondrial and CA VI is secreted in saliva. Three acatalytic forms are also known, which are denominated CA related proteins (CARP), CARP VIII, CARP X, and CARP XI. Several important physiological and physio-pathological functions are played by many CA isozymes, which are strongly inhibited by aromatic and heterocyclic sulfonamides as well as inorganic, metal complexing anions. The catalytic and inhibition mechanisms of these enzymes are understood in detail, and this helped the design of potent inhibitors, some of which possess important clinical applications. The use of such enzyme inhibitors as antiglaucoma drugs will be discussed in detail, together with the recent developments that led to isozyme-specific and organ-selective inhibitors. A recent discovery is connected with the involvement of CAs and their sulfonamide inhibitors in cancer: several potent sulfonamide inhibitors inhibited the growth of a multitude of tumor cells in vitro and in vivo, thus constituting interesting leads for developing novel antitumor therapies. Furthermore, some other classes of compounds that interact with CAs have recently been discovered, some of which possess modified sulfonamide or hydroxamate moieties. Some sulfonamides have also applications as diagnostic tools, in PET and MRI or as antiepileptics or for the treatment of other neurological disorders. Future prospects for drug design applications for inhibitors of these ubiquitous enzymes are also discussed.

Product inhibition study on carbonic anhydrase using spectroscopy and calorimetry

Kinetic and thermodynamic studies have been made on the effect of the p-nitrophenol product on the activity of bovine carbonic anhydrase in 50 mM Tris buffer pH 7.5, at 300K using UV spectrophotometry and isothermal titration calorimetry (ITC). A competitive inhibition was observed for p-nitrophenol as a product of the enzymatic reaction. A graphical fitting method was used for determination of the binding constant and enthalpy of inhibitor binding using ITC data. The dissociation binding constant was 0.10mM by the microcalorimetric method, which is in good agreement with the value of 0.11mM for the inhibition constant obtained from the spectrophotometric method.

The hydrolysis of an activated ester by a tris(4,5-di-n-propyl-2-imidazolyl)phosphine-Zn2+ complex in neutral micellar medium as a model for carbonic anhydrase

The properties of tris(4,5-di-n-propyl-2-imidazolyl)phosphine–M2+ complexes (3–M2+, M = Zn, Co) in neutral micellar media of Brij-35 and Triton X-100 have been studied in water with respect to their quantitative potenti metric titration, Co2+-visible absorption spectra, and ability of the 3–Zn2+ complex to promote the hydrolysis of the activated ester, p-nitrophenyl acetate (PNPA). Potentiometric titration of the 3–M2+(CIO4–)2 complexes in 20 mM Brij-35 media yields a steep titration curve indicative of the cooperative consumption of two hydroxides, with computed pK1 and pK2 values of 8.75 and 6.25, respectively, and the midpoint of the titration curve (pKapp) being 7.50. A similar titration of the Co2+ complex also indicates cooperative consumption of two HO–, and this is tied to the formation of a 4- or 5-coordinate complex, pKapp ~ 7.3–7.4. The cooperativity is explained in terms of sequential replacement of the two CIO4– ions associated with the 3–M2+ to eventually yield 3–M2+–HO–/(HO–(H2O)n) having the first hydroxide ligated to the metal ion and the second associated as an ion pair. The 3–Zn2+ complex catalyzes the hydrolysis of PNPA in 20 mM Brij-35 and 40 mM Triton X-100. Plots of the observed second order rate constant (k2) vs. pH in Brij-35 increase linearly with pH and plateau to a value of k2max = 0.86 M–1 s–1, with a kinetic pKa of 8.7. These data are analyzed by a process wherein the 3–Zn2+–HO– is kinetically active in the rate-limiting step of the reaction, while the ion-paired (HO–(H2O)n) exists as a spectator to the slow step, possibly promoting rapid breakdown of a tetrahedral intermediate. Analysis of the kinetic data in terms of a model that accounts for the partitioning of PNPA between water and hydrophobic micellar pseudophase indicates that the second-order rate constant of the micelle-bound ester is augmented by 45-fold due to loading of the PNPA substrate into the micelle. Key words: Brij-35, TritonX-100, neutral micelle, carbonic anhydrase model, kinetics, potentiometric titrations, catalysis, p-nitrophenyl acetate hydrolysis.

Carbonic anhydrase inhibitors: inhibition of isozymes I, II and IV by sulfamide and sulfamic acid derivatives

Sulfamide and sulfamic acid are the simplest compounds containing the SO2NH2 moiety, responsible for binding to the Zn(II) ion within carbonic anhydrase (CA, EC 4.2.1.1) active site, and thus acting as inhibitors of the many CA isozymes presently known. Here we describe two novel classes of CA inhibitors obtained by derivatizations of the lead molecules mentioned above. The new compounds, possessing the general formula RSO2NH-SO2X (X = OH, NH2), were obtained by reaction of sulfamide or sulfamic acid with alkyl/arylsulfonyl halides or arylsulfonyl isocyanates. A smaller series of derivatives has been obtained by reaction of aromatic aldehydes with sulfamide, leading to Schiff bases of the type ArCH = NSO2NH2. All the new compounds act as strong inhibitors of isozymes I, II and IV of carbonic anhydrase. Their mechanism of CA inhibition is also discussed based on electronic spectroscopic measurements on adducts with the Co(II)-substituted enzyme. These experiments led to the conclusion that the new inhibitors are directly coordinated (in a monodentate manner) to the metal ion within the enzyme active site, similarly to the classical inhibitors, the aromatic/heterocyclic sulfonamides.

Carbonic anhydrase and matrix metalloproteinase inhibitors: sulfonylated amino acid hydroxamates with MMP inhibitory properties act as efficient inhibitors of CA isozymes I, II, and IV, and N-hydroxysulfonamides inhibit both these zinc enzymes

The 14 different carbonic anhydrase (CA, EC 4.2.1.1) isozymes as well as the 23 different matrix metalloproteinases (MMPs) isolated up to now in higher vertebrates play important physiological functions in these organisms. Unsubstituted sulfonamides act as high-affinity inhibitors for the first type of these enzymes, whereas hydroxamates strongly inhibit the latter ones. Since the active site geometry around the zinc ion in these two types of metalloenzymes is rather similar, we tested whether sulfonylated amino acid hydroxamates of the type RSO(2)NX-AA-CONHOH (X = H, benzyl, substituted benzyl; AA = amino acid moiety, such as Gly, Ala, Val, Leu) with well-known inhibitory properties against MMPs and Clostridium histolyticum collagenase (ChC, another zinc enzyme related to the MMPs) might also act as CA inhibitors. We also investigated whether N-hydroxysulfonamides of the type RSO(2)NHOH (which are effective CA inhibitors) inhibit MMPs and ChC. Here we report several potent sulfonylated amino acid hydroxamate CA inhibitors (with inhibition constants in the range of 5-40 nM, against the human isozymes hCA I and hCA II, and 10-50 nM, against the bovine isozyme bCA IV), as well as preliminary SAR for this new class of non-sulfonamide CA inhibitors. Some N-hydroxysulfonamides also showed inhibitory properties (in the micromolar range) against MMP-1, MMP-2, MMP-8, MMP-9, and ChC. Thus, the SO(2)NHOH group is a new zinc-binding function for the design of MMP inhibitors. Both CA as well as MMPs are involved, among others, in carcinogenesis and tumor invasion processes. On the basis of these findings, we suggest that the mechanism of antitumor action with some hydroxamate inhibitors might also involve inhibition of some CA isozymes (such as CA IX, CA XII, and CA XIV) present only in tumor cell membranes, in addition to collagenases/gelatinases of the MMP type. Our data also suggest that it should be possible to develop dual enzyme inhibitors that would strongly inhibit both these metalloenzymes, CAs and MMPs, based on the nature of the R, AA, and X moieties in the above formula. Compact X (such as H) and AA (such as Gly) moieties favor CA over MMP inhibition, whereas bulkier X (benzyl, substituted benzyl, etc.) and AA (such as Val, Leu) moieties and substituted-aryl R groups are advantageous for obtaining potent MMP and ChC inhibitors, which show lower affinity for CA.

Carbonic anhydrase inhibitors; phosphoryl-sulfonamides--a new class of high affinity inhibitors of isozymes I and II

A series of phosphorylated aromatic/heterocyclic sulfonamides with the general formula ArSO2NHPO3H2 have been prepared by condensing ArSO2NH2 with phosphorus pentachloride, followed by controlled hydrolysis in the presence of formic acid. The new derivatives generally act as stronger inhibitors of two carbonic anhydrase (CA) isozymes, CA I and CA II, as compared to the parent unsubstituted sulfonamides from which they were obtained. The inhibition mechanism by this new class of CA inhibitors, as well as structure activity correlations for the series of investigated derivatives, are also discussed.

Carbonic anhydrase inhibitors: synthesis of water-soluble, topically effective intraocular pressure lowering aromatic/heterocyclic sulfonamides containing 8-quinoline-sulfonyl moieties: is the tail more important than the ring?

Reaction of 20 aromatic/heterocyclic sulfonamides containing a free amino, imino, hydrazino or hydroxyl group, with 8-quinoline-sulfonyl chloride afforded a series of water-soluble (as hydrochloride or triflate salts) compounds. The new derivatives were assayed as inhibitors of the zinc enzyme carbonic anhydrase (CA), and more precisely of three of its isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form), involved in important physiological processes. Efficient inhibition was observed against all three isozymes, but especially against CA II (in nanomolar range), which is the isozyme known to play a critical role in aqueous humor secretion within the ciliary processes of the eye. Some of the best inhibitors synthesized were topically applied as 2% water solutions onto the eye of normotensive and glaucomatous albino rabbits, when strong and long-lasting intraocular pressure (IOP) lowering was observed with many of them. This result prompted us to reanalyze the synthetic work done by other groups for the design of water soluble, topically effective antiglaucoma sulfonamides. According to these researchers, the IOP lowering effect is due to the intrinsic nature of the specific heterocyclic sulfonamide considered, among which the thienothiopyran-2-sulfonamide derivatives represent the best studied case. Indeed, the first agents developed for such applications, such as dorzolamide, are derivatives of this ring system. In order to prove that the tail (in this case the 8-quinoline-sulfonyl moiety) conferring water solubility to a sulfonamide CA inhibitor is more important than the ring to which the sulfonamido group is grafted, we also prepared a dorzolamide derivative to which the 8-quinoline-sulfonyl moiety was attached. This new compound is quite water soluble as hydrochloride salt, behaves as a strong CA II inhibitor, and fared better than the parent molecule in lowering IOP in experimental animals. Thus, the tail conferring water solubility to such an enzyme inhibitor is more important for its topical activity as antiglaucoma drug than the heterocyclic/aromatic ring to which the sulfonamido moiety is grafted.

Carbonic anhydrase inhibitors. Water-soluble, topically effective intraocular pressure lowering agents derived from isonicotinic acid and aromatic/heterocyclic sulfonamides: is the tail more important than the ring?

Reaction of twenty aromatic/heterocyclic sulfonamides containing a free amino, imino, hydrazino or hydroxyl group, with isonicotinoyl chloride afforded a series of water-soluble compounds (as hydrochloride or triflate salts). The new derivatives were examined as inhibitors of three carbonic anhydrase (CA) isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form). Efficient inhibition was observed against all three isozymes, but especially against CA II and CA IV (K(I) in the nanomolar range), the two isozymes known to play a critical role in aqueous humor secretion within the ciliary processes of the eye. Some of the most potent inhibitors synthesized were applied as 2% water solutions directly into the eye of normotensive or glaucomatous albino rabbits. Very strong intraocular pressure (IOP) lowering was observed for many of them, and the active drug was detected in eye tissues and fluids. According to others the IOP lowering effect of topically effective antiglaucoma sulfonamides is due to the intrinsic nature of the specific heterocyclic sulfonamide considered, among which the thienothiopyran-2-sulfonamide derivatives represent the best studied case e.g. dorzolamide. In order to prove that the tail (in this case the isonicotinoyl moiety) conferring water solubility to a sulfonamide CA inhibitor is more important than the ring to which the sulfonamido group is grafted a dorzolamide derivative to which the isonicotinoyl moiety was attached was also prepared. This new compound is more water soluble than dorzolamide (as hydrochloride salt), behaves as a strong CA II inhibitor and acts similarly to the parent derivative in lowering IOP in experimental animals. Thus, it seems that the tail conferring water solubility is more important for topical activity as an antiglaucoma drug than the heterocyclic/aromatic ring to which the sulfonamido moiety is attached.

Carbonic anhydrase inhibitors. Schiff bases of some aromatic sulfonamides and their metal complexes: towards more selective inhibitors of carbonic anhydrase isozyme IV

Reaction of three aromatic sulfonamides possessing a primary amino group, i.e., sulfanilamide, homosulfanilamide and p-aminoethyl-benzenesulfonamide with heterocyclic and aromatic aldehydes afforded a series of Schiff bases. Metal complexes of some of these Schiff bases with divalent transition ions such as Zn(II), Cu(II), Co(II) and Ni(II) have also been obtained. The new compounds were assayed as inhibitors of three isozymes of carbonic anhydrase (CA). Several of the new compounds showed a modest selectivity for the membrane-bound (bovine) isozyme CA IV (bCA IV) as compared to the cytosolic human isozymes hCA I and II, in contrast to classical inhibitors which generally possess a 17-33 times lower affinity for bCA IV. This greater selectivity toward bCA IV is due mainly to a slightly decreased potency against hCA II relative to classical inhibitors. However, metal complexes of these Schiff bases possessed an increased affinity for hCA II, being less inhibitory against bCA IV. The first type of compounds reported here (i.e., the Schiff bases of aromatic sulfonamides with heterocyclic aldehydes) might thus lead to the development of low molecular weight isozyme specific CA IV inhibitors. The difference in affinity for the three isozymes of the inhibitors reported by us here is tentatively explained on the basis of recent X-ray crystallographic studies of these isozymes and their adducts with substrates/inhibitors.

Carbonic anhydrase inhibitors. Arylsulfonylureido- and arylureido-substituted aromatic and heterocyclic sulfonamides: towards selective inhibitors of carbonic anhydrase isozyme I

Reaction of twenty aromatic/heterocyclic sulfonamides containing a free amino, imino, hydrazino or hydroxyl group, with tosyl isocyanate or 3,4-dichlorophenyl isocyanate afforded two series of derivatives containing arylsulfonylureido or diarylureido moieties in their molecule respectively. The new derivatives were assayed as inhibitors of three carbonic anhydrase (CA) isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form). Potent inhibition was observed against all three isozymes but especially against CA I, which is generally 10-75 times less susceptible to inhibition by the classical sulfonamides in clinical use as compared to the other major red cell isozyme, CA II, or the membrane-bound one, CA IV. The derivatives obtained from tosyl isocyanate were generally more potent than the corresponding ones obtained from 3,4-dichlorophenyl isocyanate. This is the first reported example of selective inhibition of CA I and might lead to more selective drugs/diagnostic agents from this class of pharmacologically relevant compounds.

Carbonic anhydrase inhibitors: N-cyanosulfonamides, a new class of high affinity isozyme II and IV inhibitors

A series of N-cyanosulfonamides has been prepared by reaction of alkyl-, arylalkyl- and arylsulfonyl halides or sulfonic acid anhydrides with cyanamide, or by reaction of cyanogen bromide with sulfamide/sulfamic acid. Other compounds have been obtained from sulfenyl chlorides, acyl chlorides, or tosyl isocyanate and cyanamide. Inhibition of three carbonic anhydrase (CA) isozymes, hCA I, hCA II and bCA IV (h = human; b = bovine) with the prepared compounds has been investigated. Very good inhibitors, as well as compounds with moderate activity against these isozymes were found, depending on the R group at which the metal-coordinating moiety of the inhibitor molecule was attached. Compounds of the types RSNHCN and RCONHCN were much less active in inhibiting all the investigated isozymes as compared to the strong inhibitors possessing the general formula RSO2NHCN. Susceptibility to inhibition with the N-cyanosulfonamides was generally: hCA II > bCA IV >> hCA I. Spectroscopic studies on Co(II)-substituted hCA II proved that the new inhibitors directly bind to the metal ion within the enzyme active site, similarly to the classical inhibitors of the unsubstituted sulfonamide type.

Carbonic anhydrase inhibitors: inhibition of isozymes I, II and IV with N-hydroxysulfonamides--a novel class of intraocular pressure lowering agents

A series of N-hydroxy sulfonamides has been prepared by reaction of alkyl-, arylalkyl- and arylsulfonyl halides or sulfonic acid anhydrides with hydroxylamine. Structurally related inhibitors were also obtained from acyl chlorides and hydroxylamine, as well as by reaction of tosyl isocyanate with hydroxylamine, sulfamic acid and sulfamide. Inhibition of three carbonic anhydrase (CA) isozymes, hCA I, hCA II and bCA IV (h = human; b = bovine) with the prepared compounds has been investigated. Good inhibitors, as well as compounds with moderate activity against these isozymes were detected, depending on the R group to which the SO2NHOH or CONHOH moieties were attached. Susceptibility to inhibition was generally: hCA II > bCA IV >> hCA I. Some of the new inhibitors showed very good antiglaucoma action when administered directly into the eye in experimental animals, acting as more efficient intraocular pressure lowering agents as compared to the clinical drug dorzolamide. This constitutes an encouraging result for obtaining novel antiglaucoma drugs from this class of CA inhibitors.

Carbonic anhydrase inhibitors: inhibition of isozymes I, II and IV with heterocyclic mercaptans, sulfenamides, sulfonamides and their metal complexes

A series of sulfenamides, sulfonamides and sulfonamide metal complexes have been prepared starting from 4,5-disubstituted-3-mercapto-1,2,4-triazole derivatives. The heterocyclic mercaptans were oxidized to the corresponding sulfenamides by hypochlorite in the presence of ammonia. The sulfonamides were obtained by oxidation of sulfenamides with potassium permanganate. The Zn(II) and Cu(II) complexes of the new heterocyclic sulfonamides have been prepared via the sodium salt of the ligand. Inhibition of three carbonic anhydrase (CA) isozymes, hCA I, hCA II and bCA IV (h = human, b = bovine) with the prepared compounds has been investigated. Mercaptans were generally less inhibitory than sulfenamides, which in turn behaved as weaker inhibitors than the sulfonamides. The strongest inhibitors were the Zn(II) and Cu(II) complexes of the heterocyclic sulfonamides. Susceptibility to inhibition was generally: hCA II > bCA IV > hCA I. Although none of the obtained simple inhibitors (mercaptans, sulfenamides, sulfonamides) possessed antiglaucoma action when administered directly into the eye in experimental animals, the Zn(II) and Cu(II) complexes of some sulfonamides acted as more efficient intraocular pressure lowering agents as compared to the clinical drug dorzolamide. This constitutes an encouraging result for obtaining novel antiglaucoma drugs from this class of CA inhibitors.