Diuretics with carbonic anhydrase inhibitory action: a patent and literature review (2005 - 2013)

Advances in structure-based drug discovery of carbonic anhydrase inhibitors

INTRODUCTION

The enzyme carbonic anhydrase (CA, EC 4.2.1.1) is found in numerous organisms across the tree of life, with seven distinct classes known to date. CA inhibition can be exploited for the treatment of edema, glaucoma, seizures, obesity, cancer and infectious diseases. A myriad of CA inhibitor (CAI) classes and inhibition mechanisms have been identified over the past decade, mainly through structure-based drug design approaches. Five different CA inhibition mechanisms are presently known. Areas covered: Recent advances in structure-based CAI design are reviewed, with periodic table-based organization of inhibitor classes. Expert opinion: Various structure-based drug design studies have led to deep understanding of factors governing tight binding and selectivity for the various isoforms. Carboxylic acids, phenols, polyamines, diols, borols, boronic acids, coumarins and sulfonamides represent successful stories which led to an anti-tumor sulfonamide in Phase I clinical trials (SLC-0111). For many inhibitor classes, no detailed crystallographic data are available. Detailed structural characterization of all CAI classes may lead to further advances in the field with potential therapeutic implications in the management of indications including neuropathic pain, cerebral ischemia, arthritis and tumor imaging.

Synthesis 4-[2-(2-mercapto-4-oxo-4H-quinazolin-3-yl)-ethyl]-benzenesulfonamides with subnanomolar carbonic anhydrase II and XII inhibitory properties

Condensation of substituted anthranilic acids with 4-isothiocyanatoethyl-benzenesulfonamide led to series of heterocyclic benzenesulfonamides incorporating 2-mercapto-quinazolin-4-one tails. These sulfonamides were investigated as inhibitors of the human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms hCA I and II (cytosolic isozymes), as well as hCA XII (a transmembrane, tumor-associated enzyme also involved in glaucoma-genesis). The new sulfonamides acted as medium potency inhibitors of hCA I (KIs of 28.5-2954nM), being highly effective as hCA II (KIs in the range of 0.62-12.4nM) and XII (KIs of 0.54-7.11nM) inhibitors. All substitution patterns present in these compounds (e.g., halogens, methyl and methoxy moieties, in positions 6, 7 and/or 8 of the 2-mercapto-quinazolin-4-one ring) led to highly effective hCA II/XII inhibitors. These compounds should thus be of interest as preclinical candidates in pathologies in which the activity of these enzymes should be inhibited, such as glaucoma (CA II and XII as targets) or some tumors in which the activity of isoforms CA II and XII is dysregulated.

Legionella pneumophila Carbonic Anhydrases: Underexplored Antibacterial Drug Targets

Carbonic anhydrases (CAs, EC 4.2.1.1) are metalloenzymes which catalyze the hydration of carbon dioxide to bicarbonate and protons. Many pathogenic bacteria encode such enzymes belonging to the α-, β-, and/or γ-CA families. In the last decade, enzymes from some of these pathogens, including Legionella pneumophila, have been cloned and characterized in detail. These enzymes were shown to be efficient catalysts for CO₂ hydration, with k_cat values in the range of (3.4–8.3) × 10⁵ s⁻¹ and k_cat/K_M values of (4.7–8.5) × 10⁷ M⁻¹·s⁻¹. In vitro inhibition studies with various classes of inhibitors, such as anions, sulfonamides and sulfamates, were also reported for the two β-CAs from this pathogen, LpCA1 and LpCA2. Inorganic anions were millimolar inhibitors, whereas diethyldithiocarbamate, sulfamate, sulfamide, phenylboronic acid, and phenylarsonic acid were micromolar ones. The best LpCA1 inhibitors were aminobenzolamide and structurally similar sulfonylated aromatic sulfonamides, as well as acetazolamide and ethoxzolamide (K_Is in the range of 40.3–90.5 nM). The best LpCA2 inhibitors belonged to the same class of sulfonylated sulfonamides, together with acetazolamide, methazolamide, and dichlorophenamide (K_Is in the range of 25.2–88.5 nM). Considering such preliminary results, the two bacterial CAs from this pathogen represent promising yet underexplored targets for obtaining antibacterials devoid of the resistance problems common to most of the clinically used antibiotics, but further studies are needed to validate them in vivo as drug targets.

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.

Microwave assisted synthesis of novel acridine-acetazolamide conjugates and investigation of their inhibition effects on human carbonic anhydrase isoforms hCA I, II, IV and VII

4-Amino-N-(5-sulfamoyl-1,3,4-thiadiazol-2-yl)benzamide was condensed with cyclic-1,3-diketones (dimedone and cyclohexane-1,3-dione) and aromatic aldehydes under microwave irradiation, leading to a series of acridine-acetazolamide conjugates. The new compounds were investigated as inhibitors of carbonic anhydrases (CA, EC 4.2.1.1), and more precisely cytosolic isoforms hCA I, II, VII and membrane-bound one hCA IV. All investigated isoforms were inhibited in low micromolar and nanomolar range by the new compounds. hCA IV and VII were inhibited with KIs in the range of 29.7-708.8nM (hCA IV), and of 1.3-90.7nM (hCA VII). For hCA I and II the KIs were in the range of 6.7-335.2nM (hCA I) and of 0.5-55.4nM (hCA II). The structure-activity relationships (SAR) for the inhibition of these isoforms with the acridine-acetazolamide conjugates reported here were delineated.

Drug interaction considerations in the therapeutic use of carbonic anhydrase inhibitors

INTRODUCTION

Carbonic anhydrase inhibitors (CAIs) of the sulfonamide and sulfamate type are clinically used drugs as diuretics, antiglaucoma, antiepileptic, antiobesity and anti-high altitude disease agents. Anticancer agents based on CAIs are also in clinical development for the management of hypoxic, metastatic tumors. Acetazolamide, methazolamide, dichlorophenamide, dorzolamide and brinzolamide are mainly used as antiglaucoma drugs, sulthiame, topiramate and zonisamide as antiepileptic/antiobesity agents, celecoxib and polmacoxib are dual carbonic anhydrase/cycloxygenase inhibitors. Girentuximab, a monoclonal antibody and SLC-0111, a sulfonamide inhibitor, are in clinical trials as anticancer agents.

AREAS COVERED

The drug interactions with many classes of pharmacological agents are reviewed. Some of these drugs, such as acetazolamide, topiramate and celecoxib show a large number of interactions with non-steroidal anti-inflammatory drugs (NSAIDs), diuretics, antiepileptics, immunosupressants, anticholinesterase drugs, β-blockers, anesthetics, oral contraceptives, anticancer agents, antifungals, anti-mycobacterials, lithium, metformin and clopidogrel.

EXPERT OPINION

The multiple drug interactions in which CAIs are involved should be carefully considered when such drugs are used in combination with the drug classes mentioned above, as the risks of developing toxicity and serious side effects if the dosages are not adjusted are high. There are also synergistic effects between CAIs and some NSAIDs, anticancer agents and benzodiazepines for the management of cystoid macular edema, some tumor types and neuropathic pain, respectively.

Kinetic target-guided synthesis in drug discovery and chemical biology: a comprehensive facts and figures survey

For the last 15 years, kinetic target-guided syntheses, including in situ click chemistry, have been used as alternative methods to find ligands to therapeutically relevant proteins. In this review, a comprehensive survey of biological targets used in kinetic target-guided synthesis covers historical and recent examples. The chemical reactions employed and practical aspects, including controls, library sizes and product detection, are presented. A particular focus is on the reagents and warhead selection and design with a critical overview of the challenges encountered. As protein supply remains a key success factor, it appears that increased efforts should be taken toward miniaturization in order to expand the scope of this strategy and qualify it as a fully fledged drug discovery tool.

Isatin analogs as novel inhibitors of Candida spp. β-carbonic anhydrase enzymes

Enzyme inhibition data of structurally novel isatin-containing sulfonamides were determined for two carbonic anhydrases (CAs, EC 4.2.1.1) from pathogenic Candida species (CaNce103 from C. albicans and CgNce103 from C. glabrata). The compounds show KI values in the low nanomolar range for the fungal CAs, while they have significantly higher KI values for the human CAs. Homology models were constructed for the CaNce103 and CgNce103 and subsequently the ligands were docked into these models to rationalize their enzyme inhibitory properties.

Everything we always wanted to know about furosemide but were afraid to ask

Furosemide is a widely used, potent natriuretic drug, which inhibits the Na(+)-K(+)-2Cl(-) cotransporter (NKCC)-2 in the ascending limb of the loop of Henle applied to reduce extracellular fluid volume expansion in heart and kidney disease. Undesirable consequences of furosemide, such as worsening of kidney function and unpredictable effects on sodium balance, led to this critical evaluation of how inhibition of NKCC affects renal and cardiovascular physiology. This evaluation reveals important knowledge gaps, involving furosemide as a drug, the function of NKCC2 (and NKCC1), and renal and systemic indirect effects of NKCC inhibition. Regarding renal effects, renal blood flow and glomerular filtration rate could become compromised by activation of tubuloglomerular feedback or by renin release, particularly if renal function is already compromised. Modulation of the intrarenal renin angiotensin system, however, is ill-defined. Regarding systemic effects, vasodilation followed by nonspecific NKCC inhibition and changes in venous compliance are not well understood. Repetitive administration of furosemide induces short-term (braking phenomenon, acute diuretic resistance) and long-term (chronic diuretic resistance) adaptations, of which the mechanisms are not well known. Modulation of NKCC2 expression and activity in kidney and heart failure is ill-defined. Lastly, furosemide's effects on cutaneous sodium stores and on uric acid levels could be beneficial or detrimental. Concluding, a considerable knowledge gap is identified regarding a potent drug with a relatively specific renal target, NKCC2, and renal and systemic actions. Resolving these questions would increase the understanding of NKCCs and their actions and improve rational use of furosemide in pathophysiology of fluid volume expansion.

Synthesis of novel sulfonamides under mild conditions with effective inhibitory activity against the carbonic anhydrase isoforms I and II

Novel sulfonamide derivatives 6a-i, as new carbonic anhydrase inhibitors which candidate for glaucoma treatment, were synthesized from the reactions of 4-amino-N-(4-sulfamoylphenyl) benzamide 4 and sulfonyl chloride derivatives 5a-i with high yield (71-90%). The structures of these compounds were confirmed by using spectral analysis (FT-IR, (1)H NMR, (13)C NMR, LC/MS and HRMS). The inhibition effects of 6a-i on the hydratase and esterase activities of human carbonic anhydrase isoenzymes, hCA I and II, which were purified from human erythrocytes with Sepharose®4B-l-tyrosine-p-aminobenzene sulfonamide affinity chromatography, were studied as in vitro, and IC50 and Ki values were determined. The results show that newly synthesized compounds have quite powerful inhibitory properties.

Synthesis and in vivo diuretic activity of some new benzothiazole sulfonamides containing quinoxaline ring system

A series of new 6-substituted-N-[3-{2-(substituted phenyl)-ethenyl} quinoxaline-2(1H)-ylidene]-1,3-benzothiazole-2-amine (4a-f) were designed and synthesized by condensing 2-amino-benzothiazole-6-sulfonic acid amide (1) with chalcones of quinoxaline-2-one (3a-f) in a hope to obtain promising and a new class of diuretic agents. Structures of all the newly synthesized compounds were characterized by spectral data and elemental analysis. The pharmacological studies in experimental rats indicates that compound 4c possesses excellent in vivo diuretic activity of 1.13 and appears to be a better diuretic agent than the reference drugs, acetazolamide (1.0) and urea (0.88). Insight of the binding mode of the synthesized compounds (ligand) into the binding sites of carbonic anhydrase enzyme (PDF code: 4KUV) was provided by docking studies, performed with the help of Maestro 9.0 docking software. Further pharmacokinetic and toxicological studies are needed to confirm the safety of compound 4c which emerged as a lead diuretic compound.

How many carbonic anhydrase inhibition mechanisms exist?

Six genetic families of the enzyme carbonic anhydrase (CA, EC 4.2.1.1) were described to date. Inhibition of CAs has pharmacologic applications in the field of antiglaucoma, anticonvulsant, anticancer, and anti-infective agents. New classes of CA inhibitors (CAIs) were described in the last decade with enzyme inhibition mechanisms differing considerably from the classical inhibitors of the sulfonamide or anion type. Five different CA inhibition mechanisms are known: (i) the zinc binders coordinate to the catalytically crucial Zn(II) ion from the enzyme active site, with the metal in tetrahedral or trigonal bipyramidal geometries. Sulfonamides and their isosters, most anions, dithiocarbamates and their isosters, carboxylates, and hydroxamates bind in this way; (ii) inhibitors that anchor to the zinc-coordinated water molecule/hydroxide ion (phenols, carboxylates, polyamines, 2-thioxocoumarins, sulfocoumarins); (iii) inhibitors which occlude the entrance to the active site cavity (coumarins and their isosters), this binding site coinciding with that where CA activators bind; (iv) compounds which bind out of the active site cavity (a carboxylic acid derivative was seen to inhibit CA in this manner), and (v) compounds for which the inhibition mechanism is not known, among which the secondary/tertiary sulfonamides as well as imatinib/nilotinib are the most investigated examples. As CAIs are used clinically in many pathologies, with a sulfonamide inhibitor (SLC-0111) in Phase I clinical trials for the management of metastatic solid tumors, this review updates the recent findings in the field which may be useful for a structure-based drug design approach of more selective/potent modulators of the activity of these enzymes.

New natural product carbonic anhydrase inhibitors incorporating phenol moieties

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyze the fundamental reaction of CO2 hydration in all living organisms, being actively involved in the regulation of a plethora of patho/physiological conditions. They represent a typical example of enzyme convergent evolution, as six genetically unrelated families of such enzymes were described so far. The need to find selective CA inhibitors (CAIs) triggered the investigation of natural product libraries, which proved to be a valid source of agents with such an activity, as demonstrated for the phenols, polyamines and coumarins. Herein we report an in vitro inhibition study of human (h) CA isoforms hCAs I, II, IV, VII and XII with a panel of natural polyphenols including flavones, flavonols, flavanones, flavanols, isoflavones and depsides, some of which extracted from Quercus ilex and Salvia miltiorrhiza. Several of the investigated derivatives showed interesting inhibition activity and selectivities for inhibiting some important isoforms over the off-target ones hCA I and II.

Inhibition of mammalian carbonic anhydrase isoforms I-XIV with a series of phenolic acid esters

A series of phenolic acid esters incorporating caffeic, ferulic, and p-coumaric acid, and benzyl, m/p-hydroxyphenethyl- as well as p-hydroxy-phenethoxy-phenethyl moieties were investigated for their inhibitory effects against the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). Many of the mammalian isozymes of human (h) or murine (m) origin, hCA I-hCA XII, mCA XIII and hCA XIV, were inhibited in the submicromolar range by these derivatives (with KIs of 0.31-1.03 μM against hCA VA, VB, VI, VII, IX and XIV). The off-target, highly abundant isoforms hCA I and II, as well as hCA III, IV and XII were poorly inhibited by many of these esters, although the original phenolic acids were micromolar inhibitors. These phenols, like others investigated earlier, possess a CA inhibition mechanism distinct of the sulfonamides/sulfamates, clinically used drugs for the treatment of a multitude of pathologies, but with severe side effects due to hCA I/II inhibition. Unlike the sulfonamides, which bind to the catalytic zinc ion, phenols are anchored at the Zn(II)-coordinated water molecule, binding more externally within the active site cavity, and making contacts with amino acid residues at the entrance of the active site. As this is the region with the highest variability between the many CA isozymes found in mammals, this class of compounds shows isoform-selective inhibitory profiles, which may be exploited for obtaining pharmacological agents with less side effects compared to other classes of inhibitors.

Poly(amidoamine) dendrimers show carbonic anhydrase inhibitory activity against α-, β-, γ- and η-class enzymes

Four generations of poly(amidoamine) (PAMAM) dendrimers incorporating benzenesulfonamide moieties were investigated as inhibitors of carbonic anhydrases (CAs, EC 4.2.1.1) belonging to the α-, β-, γ- and η-classes which are present in pathogenic bacteria, fungi or protozoa. The following bacterial, fungal and protozoan organisms were included in the study: Vibrio cholerae, Trypanosoma cruzi, Leishmania donovani chagasi, Porphyromonas gingivalis, Cryptococcus neoformans, Candida glabrata, and Plasmodium falciparum. The eight pathozymes present in these organisms were efficiently inhibited by the four generations PAMAM-sulfonamide dendrimers, but multivalency effects were highly variable among the different enzyme classes. The Vibrio enzyme VchCA was best inhibited by the G3 dendrimer incorporating 32 sulfamoyl moieties. The Trypanosoma enzyme TcCA on the other hand was best inhibited by the first generation dendrimer G0 (with 4 sulfamoyl groups), whereas for other enzymes the optimal inhibitory power was observed for the G1 or G2 dendrimers, with 8 and 16 sulfonamide functionalities. This study thus proves that the multivalency may be highly relevant for enzyme inhibition for some but not all CAs from pathogenic organisms. On the other hand, some dendrimers investigated here showed a better inhibitory power compared to acetazolamide for enzymes from widespread pathogens, such as the η-CA from Plasmodium falciparum. Overall, the main conclusion is that this class of molecules may lead to important developments in the field of anti-infective CA inhibitors.

Inhibition studies of new ureido-substituted sulfonamides incorporating a GABA moiety against human carbonic anhydrase isoforms I-XIV

Reaction of γ-Boc-GABA, prepared by protecting the γ-amino moiety of the amino butyric acid with the tert-butyloxycarbonyl (Boc) protecting group, with 4-methyl/ethyl benzenesulfonamide, followed by removal of the Boc protecting group in 3 M HCl afforded the corresponding hydrochlorides, which were further derivatized by reaction with a varying of aryl isocyanates to give a new classes of ureido substituted benzenesulfonamide containing a GABA moiety. Inhibition studies of the human carbonic anhydrase(CA, EC 4.2.1.1) isoforms, CA I–XIV with these new compounds revealed that they possess moderate-weak inhibition potency against hCA III, IV, VA, VI and XIII, rather efficient inhibitory power against hCA I, VI, and IX, and excellent inhibition of the physiologically relevant hCA II and VII, as well as of the two tumor-associated isoforms CA IX and XII. The inhibition profile of the new ureido-substituted benzenesulfonamides reported here is thus very different from the corresponding ureido-substituted analogs incorporating sulfanilamide, which were previously investigated as inhibitors of some of these enzymes.

Synthesis of sulfonamides incorporating piperazinyl-ureido moieties and their carbonic anhydrase I, II, IX and XII inhibitory activity

By using SLC-0111 (4-fluorophenylureido-benzenesulfonamide), a sulfonamide carbonic anhydrase (CA, EC 4.2.1.1) inhibitor in Phase I clinical trials as an antitumor agent as lead molecule, a series of benzenesulfonamide derivatives incorporating ureido moieties was synthesized. The new compounds contain a 4-N-substituted piperazine fragment in which the ureido linker has been included, and were tested as inhibitors of the cytosolic human (h) hCA I and II isoforms, as well as the transmembrane, tumor-associated enzymes hCA IX and XII. Depending on the substitution pattern at the piperazine ring, low nanomolar inhibitors were detected against all four isoforms, making the new class of sulfonamides of interest for various pharmacologic applications.

Acetazolamide for the treatment of idiopathic intracranial hypertension

Idiopathic intracranial hypertension (IIH) is characterized by an increase of intracranial pressure in the absence of neurologic tumors. The sulfonamide carbonic anhydrase (CA, EC 4.2.1.1) inhibitor (CAI) acetazolamide (AAZ), a compound developed in the 1950s as a diuretic drug and presently used as an antiglaucoma, antiepileptic and diuretic agent, is effective in the treatment of IIH. AAZ is a low nanomolar inhibitor of CA isoforms involved in cerebrospinal fluid (CSF) secretion. Inhibition of brain/choroid plexus CA II, IV, VA and XII leads to a decreased CSF fluid secretion and control of the intracranial pressure. Although many sulfonamide/sulfamate CAIs are in clinical use for decades, apparently only AAZ is being currently used clinically for IIH. We speculate that more lipophilic CAIs such as methazolamide, zonisamide or topiramate should lead to a more effective control of increased intracranial pressure, thus having the opportunity to become useful in the management of IIH.

A magnificent enzyme superfamily: carbonic anhydrases, their purification and characterization

In this paper, we reviewed the purification and characterization methods of the α-carbonic anhydrase (CA, EC 4.2.1.1) class. Six genetic families (α-, β-, γ-, δ-, ζ- and η-CAs) all know to date, all encoding such enzymes in organisms widely distributed over the phylogenetic tree. Starting from the manuscripts published in the 1930s on the isolation and purification of α-CAs from blood and other tissues, and ending with the recent discovery of the last genetic family in protozoa, the η-CAs, considered for long time an α-CA, we present historically the numerous and different procedures which were employed for obtaining these catalysts in pure form. α-CAs possess important application in medicine (as many human α-CA isoforms are drug targets) as well as biotechnological processes, in which the enzymes are ultimately used for CO2 capture in order to mitigate the global warming effects due to greenhouse gases. Recently, it was discovered an involvement of CAs in cancerogenesis as well as infection caused by pathogenic agents such as bacteria, fungi and protozoa. Inhibition studies of CAs identified in the genome of the aforementioned organisms might lead to the discovery of innovative drugs with a novel mechanism of action.

Discovery of novel isatin-based sulfonamides with potent and selective inhibition of the tumor-associated carbonic anhydrase isoforms IX and XII

A series of 2/3/4-[(2-oxo-1,2-dihydro-3H-indol-3-ylidene)amino]benzenesulfonamides, obtained from substituted isatins and 2-, 3- or 4-aminobenzenesulfonamide, showed low nanomolar inhibitory activity against the tumor associated carbonic anhydrase (CA, EC 4.2.1.1) isoforms IX and XII - recently validated antitumor drug targets, being much less effective as inhibitors of the off-target cytosolic isoforms CA I and II.

Dendrimers incorporating benzenesulfonamide moieties strongly inhibit carbonic anhydrase isoforms I-XIV

As extension of our previous study herein we report a comprehensive investigation of poly(amidoamine) (PAMAM) dendrimers as modulators of the human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms I-XIV. Interestingly inhibitory activity was observed for the non-functionalized dendrimers against the hCA I, VII, IX, XII and XIV isoforms, whereas activation properties were reported only for the cytosolic abundant hCA II. Highly efficient inhibitory action against many isoforms having medicinal chemistry applications, such as hCA II, V, VII, IX, XII and XIV, was observed for the PAMAM functionalized counterparts bearing 4, 8, 16 and 32 benzenesulfonamide moieties. Possible applications of dendrimer-CA inhibitors as therapeutic/diagnostic agents are envisaged.

Sulfonamide bearing pyrazolylpyrazolines as potent inhibitors of carbonic anhydrase isoforms I, II, IX and XII

A series of pyrazolylpyrazolines was designed, synthesized and evaluated for carbonic anhydrase (CA, EC 4.2.1.1) inhibitory activity against cytosolic human (h) isozymes hCA I and hCA II as well as transmembrane tumor associated isozymes, hCA IX and hCA XII. All the tested compounds exhibited an excellent CA activity profile against hCA I, hCA II and hCA XII when compared to the reference drug acetazolamide (AZA). Compounds 6d, 6f and 7a-7f have exhibited better inhibition profile against hCA XII (Ki = 0.47-5.1 nM) as compared with AZA (Ki = 5.7 nM) especially, compounds 6a, 7a, 7c and 7d which were nearly 10-fold better than reference drug. Against hCA II, all of the tested compounds were better than the standard drug especially compounds 6c, 6d, 7c and 7d (Ki = 1.1-1.7 nM) were many fold better inhibitors than AZA (Ki = 12.1 nM). In addition, they acted as selective CA inhibitors of isoform hCA XII over the physiological isoform hCA I.

Design and synthesis of benzothiazole-6-sulfonamides acting as highly potent inhibitors of carbonic anhydrase isoforms I, II, IX and XII

A series of novel 2-aminobenzothiazole derivatives bearing sulfonamide at position 6 was designed, synthesized and investigated as inhibitors of four isoforms of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1), the cytosolic CA I and II, and the tumor-associated isozymes CA IX and XII. Docking and binding energy studies were carried out to reveal details regarding the favorable interactions between the scaffolds of these new inhibitors and the active sites of the investigated CA isoforms. Most of the novel compounds were acting as highly potent inhibitors of the tumor-associated hCA IX and hCA XII with KIs in the nanomolar range. The ubiquitous and dominant rapid cytosolic isozyme hCA II was also inhibited with KIs ranging from 3.5 to 45.4 nM. The favorable interactions between some of the new compounds and the active site of different CA isoforms were delineated by using molecular docking which may be useful for designing compounds with high affinity and selectivity for some CAs with biomedical applications.

Poly(amidoamine) Dendrimers with Carbonic Anhydrase Inhibitory Activity and Antiglaucoma Action

Four generations of poly(amidoamine) (PAMAM) dendrimers decorated with benzenesulfonamide moieties were prepared by derivatizing the amino groups of the dendrimer with 4-carboxy-benzenesulfonamide functionalities. Compounds incorporating 4, 8, 16, and 32 sulfonamide moieties were thus obtained, which showed an increasing carbonic anhydrase (CA, EC 4.2.1.1) inhibitory action with the increase of the number of sulfamoyl groups in the dendrimer. Best inhibitory activity (in the low nanomolar-subnanomolar range) was observed for isoforms CA II and XII, involved among others in glaucoma. In an animal model of this disease, the chronic administration of such dendrimers for 5 days led to a much more efficient drop of intraocular pressure compared to the standard drug dorzolamide.

New insights into carbonic anhydrase inhibition, vasodilation, and treatment of hypertensive-related diseases

Carbonic anhydrase (CA) and its inhibitors are relevant to many physiological processes and diseases. The enzyme is differentially expressed throughout the body, in concentration and subcellular location, and as 13 catalytically active isoforms. Blood vessels contain small amounts of CA, but the enzyme's role in vascular physiology and blood pressure regulation is uncertain. However, considerable recent evidence points to vasodilation by CA inhibitors. CA inhibition in vascular smooth muscle, endothelium, heart, blood cells, and nervous system could all contribute. It is equally plausible that other targets besides CA for all known CA inhibitors may account for their vascular effects. I will review this knowledge and important remaining gaps relating to treatment of hypertensive-related diseases with potent sulfonamide inhibitors, such as acetazolamide; but also the possibility that CA inhibition by thiazides and loop diuretics, although generally weaker, may have antihypertensive effects beyond their inhibition of renal sodium transporters.

Inhibitory effects of nitrite on the reactions of bovine carbonic anhydrase II with CO2 and bicarbonate consistent with zinc-bound nitrite

Carbonic anhydrase (CA) is a zinc enzyme that catalyzes hydration of carbon dioxide (CO2) and dehydration of bicarbonate in red blood cells, thus facilitating CO2 transport and excretion. Bovine CA II may also react with nitrite to generate nitric oxide, although nitrite is a known inhibitor of the CO2 hydration reaction. To address the potential in vivo interference of these reactions and the nature of nitrite binding to the enzyme, we here investigate the inhibitory effect of 10-30 mM nitrite on Michaelis-Menten kinetics of CO2 hydration and bicarbonate dehydration by stopped-flow spectroscopy. Our data show that nitrite significantly affects the apparent dissociation constant KM for CO2 (11 mM) and bicarbonate (221 mM), and the turnover number kcat for the CO2 hydration (1.467 × 10(6) s(-1)) but not for the bicarbonate dehydration (7.927 × 10(5) s(-1)). These effects demonstrate mixed and competitive inhibition for the reaction with CO2 and bicarbonate, respectively, and are consistent with nitrite binding to the active site zinc. The high apparent dissociation constant found here for CO2, bicarbonate and nitrite (16-120 mM) are all overall consistent with published data and reveal a large capacity of free enzyme available for binding each of the three substrates at their in vivo levels, with little or no significant interference among reactions. The low affinity of the enzyme for nitrite suggests that the in vivo interaction between red blood cell CA II and nitrite requires compartmentalization at the anion exchanger protein of the red cell membrane to be physiologically relevant.

Synthesis of Schiff base derivatives of 4-(2-aminoethyl)-benzenesulfonamide with inhibitory activity against carbonic anhydrase isoforms I, II, IX and XII

Schiff base derivatives were obtained by reaction of 4-(2-aminoethyl)benzenesulfonamide with aromatic aldehydes. The corresponding secondary amine derivatives were also prepared by reduction of the imine compounds with NaBH4. These derivatives were investigated as inhibitors of four human carbonic anhydrase (CA, EC 4.2.1.1) isoforms, the cytosolic isozymes hCA I and II, as well as, the transmembrane, tumor-associated hCA IX and XII. Some of the newly synthesised compounds showed effective inhibitory activities against these CA isozymes. Many low nanomolar inhibitors were detected against all isoforms among the secondary amines whereas the Schiff bases were by far less active compared to the corresponding reduced derivatives among all investigated isoforms.

Sulfonamides and their isosters as carbonic anhydrase inhibitors

Molecules containing the sulfonamide group (R-SO2NH2) as well as its structurally related isosters, sulfamido (R-NH-SO2NH2) and sulfamato (R-O-SO2NH2), constitute the most important class of inhibitors acting on the metalloenzyme carbonic anhydrase (EC 4.2.1.1). Despite their presence in the literature, in general the reports lack of a clear and organic overview linking the main structural features of the clinically used inhibitors with the therapeutic aspects. The current review is intended to highlight the structural basis of the interactions of sulfonamide-like groups within the active site of the carbonic anhydrases and will summarize the clinical use of the most interesting molecules for the treatment of relevant pathologies, such as glaucoma, obesity, cancer and CNS-affecting diseases.

Sulfonamide inhibition studies of the γ-carbonic anhydrase from the Antarctic cyanobacterium Nostoc commune

A carbonic anhydrase (CA, EC 4.2.1.1) belonging to the γ-class has been cloned, purified and characterized from the Antarctic cyanobacterium Nostoc commune. The enzyme showed a good catalytic activity for the physiologic reaction (hydration of carbon dioxide to bicarbonate and a proton) with the following kinetic parameters, kcat of 9.5×10(5)s(-1) and kcat/KM of 8.3×10(7)M(-1)s(-1), being the γ-CA with the highest catalytic activity described so far. A range of aromatic/heterocyclic sulfonamides and one sulfamate were investigated as inhibitors of the new enzyme, denominated here NcoCA. The best NcoCA inhibitors were some sulfonylated sulfanilamide derivatives possessing elongated molecules, aminobenzolamide, acetazolamide, benzolamide, dorzolamide, brinzolamide and topiramate, which showed inhibition constants in the range of 40.3-92.3nM. As 1,5-bisphosphate carboxylase/oxygenase (RubisCO) and γ-CAs are closely associated in carboxysomes of cyanobacteria for enhancing the affinity of RubisCO for CO2 and the efficiency of photosynthesis, investigation of this new enzyme and its affinity for modulators of its activity may bring new insights in these crucial processes.

A class of sulfonamide carbonic anhydrase inhibitors with neuropathic pain modulating effects

A series of benzene sulfonamide carbonic anhydrase (CA, EC 4.2.1.1) inhibitors which incorporate lipophilic 4-alkoxy- and 4-aryloxy moieties, together with several derivatives of ethoxzolamide and sulfanilamide are reported. These derivatives were investigated as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) of which multiple isoforms are known, and some appear to be involved in pain. These sulfonamides showed modest inhibition against the cytosolic isoform CA I, but were generally effective, low nanomolar CA II, VII, IX and XII inhibitors. X-ray crystallographic data for the adduct of several such sulfonamides with CA II allowed us to rationalize the good inhibition data. In a mice model of neuropathic pain induced by oxaliplatin, one of the strong CA II/VII inhibitors reported here induced a long lasting pain relieving effect, a fact never observed earlier. This is the first report of rationally designed sulfonamide CA inhibitors with pain effective modulating effects.

7-Amino-3,4-dihydro-1H-quinolin-2-one, a compound similar to the substituted coumarins, inhibits α-carbonic anhydrases without hydrolysis of the lactam ring

7-Amino-3,4-dihydro-1H-quinolin-2-one, a compound structurally similar to coumarins, recently discovered class of inhibitors of the α-carbonic anhydrases (CAs, EC 4.2.1.1) was investigated for its interaction with all human (h) CA isoforms, hCA I-XIV. The compound was not an inhibitor of the cytosolic, widespread isoform hCA II (K(I) > 10 µM), was a weak inhibitor of hCA I, III, IV, VA, VI and XIII (K(I)s in the range of 0.90-9.5 µM) but effectively inhibited the cytosolic isoform hCA VII (K(I) of 480 nM) as well as the transmembrane isoforms hCA IX, XII and XIV (K(I)s in the range of 16.1-510 nM). Against many CA isoforms this lactam was a better inhibitor compared to the structurally similar 4-methyl-7-aminocoumarin, but unlike this compound, the lactam ring was not hydrolyzed and the inhibition was due to the intact bicyclic amino-quinolinone scaffold. Bicyclic lactams strucurally related to coumarins are thus a new class of CA inhibitors possessing however a distinct inhibition mechanism compared to the coumarins which undergo a hydrolysis of their lactone ring for generating the enzyme inhibitory species.

Dithiocarbamates with potent inhibitory activity against the Saccharomyces cerevisiae β-carbonic anhydrase

Dithiocarbamates (DTCs) prepared from primary or secondary amines, which incorporated amino/hydroxyl-alkyl, mono-/bicyclic aliphatic/heterocyclic rings based on the quinuclidine, piperidine, hydroxy-/carboxy-/amino-substituted piperidine, morpholine and piperazine scaffolds, were investigated for the inhibition of α- and β-carbonic anhydrases (CAs, EC 4.2.1.1) of pharmacologic relevance, such as the human (h) isoform hCA I and II, as well as the Saccharomyces cerevisiae β-CA, scCA. The yeast and its β-CA were shown earlier to be useful models of pathogenic fungal infections. The DTCs investigated here were medium potency hCA I inhibitors (K(I)s of 66.5-910 nM), were more effective as hCA II inhibitors (K(I)s of 8.9-107 nM) and some of them showed excellent, low nanomolar activity against the yeast enzyme, with inhibition constants ranging between 6.4 and 259 nM. The detailed structure activity relationship for inhibition of the yeast and human enzymes is discussed. Several of the investigated DTCs showed excellent selectivity ratios for inhibiting the yeast over the human cytosolic CA isoforms.

X-ray crystallographic and kinetic investigations of 6-sulfamoyl-saccharin as a carbonic anhydrase inhibitor

Sulfamoylated saccharin binds to human carbonic anhydrase II through the SO₂NH₂and not CONHSO₂moiety.