A new approach to antiglaucoma drugs: carbonic anhydrase inhibitors with or without NO donating moieties. Mechanism of action and preliminary pharmacology

Hydrophobic substituents of the phenylmethylsulfamide moiety can be used for the development of new selective carbonic anhydrase inhibitors

A new series of compounds containing a sulfamide moiety as zinc-binding group (ZBG) has been synthesized and tested for determining inhibitory properties against four human carbonic anhydrase (hCA) isoforms, namely, CAs I, II, IX, and XII. The X-ray structure of the cytosolic dominant isoform hCA II in complex with the best inhibitor of the series has also been determined providing further insights into sulfamide binding mechanism and confirming that such zinc-binding group, if opportunely derivatized, can be usefully exploited for obtaining new potent and selective CAIs. The analysis of the structure also suggests that for drug design purposes the but-2-yn-1-yloxy moiety tail emerges as a very interesting substituent of the phenylmethylsulfamide moiety due to its capability to establish strong van der Waals interactions with a hydrophobic cleft on the hCA II surface, delimited by residues Phe131, Val135, Pro202, and Leu204. Indeed, the complementarity of this tail with the cleft suggests that different substituents could be used to discriminate between isoforms having clefts with different sizes.

Quinazoline-sulfonamides with potent inhibitory activity against the α-carbonic anhydrase from Vibrio cholerae

Thirteen novel sulfonamide derivatives incorporating the quinazoline scaffold were synthesized by simple, eco-friendly procedures. These compounds were tested for their ability to inhibit the α-carbonic anhydrases (CA, EC 4.2.1.1) from Vibrio cholerae (VchCA) as well as the human α-CA isoforms, hCA I and hCA II. Nine compounds were highly effective, nanomolar inhibitors of the pathogenic enzyme VchCA. Three of them were also highly effective sub-nanomolar inhibitors of the cytosolic isoform II. The best VchCA inhibitor had a KI of 2.7 nM. Many of these developed compounds showed high selectivity for inhibition of the bacterial over the mammalian CA isoforms, with one compound possessing selectivity ratios as high as 97.9 against hCA I and 9.7 against hCA II. Compound 9d was another highly effective VchCA inhibitor presenting a selectivity ratio of 99.1 and 8.1 against hCA I and hCA II, respectively. These results suggest that sulfonamides with quinazoline backbone could be considered suitable tools to better understand the role of bacterial CAs in pathogenesis.

Discovery of a new family of carbonic anhydrases in the malaria pathogen Plasmodium falciparum--the η-carbonic anhydrases

The genome of the protozoan parasite Plasmodium falciparum, the causative agent of the most lethal type of human malaria, contains a single gene annotated as encoding a carbonic anhydrase (CAs, EC 4.2.1.1) thought to belong to the α-class, PfCA. Here we demonstrate the kinetic properties of PfCA for the CO2 hydration reaction, as well as an inhibition study of this enzyme with inorganic and complex anions and other molecules known to interact with zinc proteins, including sulfamide, sulfamic acid, and phenylboronic/arsonic acids, detecting several low micromolar inhibitors. A closer examination of the sequence of this and the CAs from other Plasmodium spp., as well as a phylogenetic analysis, revealed that these protozoa encode for a yet undisclosed, new genetic family of CAs termed the η-CA class. The main features of the η-CAs are described in this report.

Carbonic anhydrase inhibitors: Synthesis, molecular docking, cytotoxic and inhibition of the human carbonic anhydrase isoforms I, II, IX, XII with novel benzenesulfonamides incorporating pyrrole, pyrrolopyrimidine and fused pyrrolopyrimidine moieties

A series of novel pyrroles, pyrrolopyrimidines, pyrazolopyrrolopyrimidine, triazolopyrrolopyrimidines, tetrazolopyrrolopyrimidine, triazinopyrrolopyrimidines and pyrrolopyrimidotriazepines bearing the biologically active benzenesulfonamide moiety were synthesized by using pyrrole-o-amino-carbonitrile as key intermediate. All the synthesized compounds were evaluated for their in vitro carbonic anhydrase (CA, EC 4.2.1.1) inhibitory effects against the human (h) isoforms hCA I, II, IX and XII. Among the tested derivatives, compounds 16, 18 and 20-24 showed potent activity as inhibitors for the tumor associated transmembrane isoforms (hCA IX and XII) in the nanomolar and subnanomolar range, with high selectivity. All compounds underwent cytotoxic activity assays on human breast cancer cell line (MCF-7) showing effective activity, comparable to that of the clinically used drug doxorubicin.

Furazan and furoxan sulfonamides are strong α-carbonic anhydrase inhibitors and potential antiglaucoma agents

A series of furazan and furoxan sulfonamides were prepared and studied for their ability to inhibit human carbonic anhydrase (CA, EC 4.2.1.1) isoforms hCA I, hCA II, hCA IX, and hCA XII. The simple methyl substituted products 3-5 were potent inhibitors. Differing structural modifications of these leads had differing effects on potency and selectivity. In particular, products in which the sulfonamide group is separated from the hetero ring by a phenylene bridge retained high potency only on the hCA XII isoform. The sulfonamides 3-5 exerted intraocular pressure (IOP) lowering effects in vivo in hypertensive rabbits more efficiently than dorzolamide. Some other products (39-42), although less effective in vitro hCA II/XII inhibitors, also effectively lowered IOP in two different animal models of glaucoma.

Glaucoma and the applications of carbonic anhydrase inhibitors

Inhibition of carbonic anhydrase (CA, EC 4.2.1.1) has pharmacologic applications in the treatment of glaucoma, a disease affecting a large number of people and characterized by an elevated intraocular pressure (IOP). At least three isoforms, CA II, IV and XII are targeted by the sulfonamide inhibitors, some of which are clinically used drugs. Acetazolamide, methazolamide and dichlorophenamide are first generation CA inhibitors (CAIs) still used as systemic drugs for the management of this disease. Dorzolamide and brinzolamide represent the second generation inhibitors, being used topically, as eye drops, with less side effects compared to the first generation drugs. Third generation inhibitors have been developed by using the tail approach, but they did not reach the clinics yet. The most promising such derivatives are the sulfonamides incorporating either tails with nitric oxide releasing moieties or hybrid drugs possessing prostaglandin (PG) F agonist moieties in their molecules. Recently, the dithiocarbamates have also been described as CAIs possessing IOP lowering effects in animal models of glaucoma. CAIs are used alone or in combination with other drugs such as adrenergic agonist/antagonists, or PG analogs, being an important component of the antiglaucoma drugs armamentarium.

Systemic medication and intraocular pressure in a British population: the EPIC-Norfolk Eye Study

OBJECTIVE

To determine the association between systemic medication use and intraocular pressure (IOP) in a population of older British men and women.

DESIGN

Population-based, cross-sectional study.

PARTICIPANTS

We included 7093 participants from the European Prospective Investigation into Cancer-Norfolk Eye Study. Exclusion criteria were a history of glaucoma therapy (medical, laser, or surgical), IOP asymmetry between eyes of >5 mmHg, and missing data for any covariables. The mean age of participants was 68 years (range, 48-92) and 56% were women.

METHODS

We measured IOP using the Ocular Response Analyzer. Three readings were taken per eye and the best signal value of the Goldmann-correlated IOP value considered. Participants were asked to bring all their medications and related documentation to the health examination, and these were recorded by the research nurse using an electronic case record form. The medication classes examined were angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, α-blockers, β-blockers, calcium channel blockers, diuretics, nitrates, statins, insulin, biguanides, sulfonylureas, aspirin, and other nonsteroidal anti-inflammatory drugs. We examined associations between medication use and IOP using multivariable linear regression models adjusted for age, sex, and body mass index. Models containing diabetic medication were further adjusted for glycosylated hemoglobin levels.

MAIN OUTCOME MEASURES

Mean IOP of the right and left eyes.

RESULTS

Use of systemic β-blockers (-0.92 mmHg; 95% CI, -1.19, -0.65; P<0.001) and nitrates (-0.63 mmHg; 95% CI, -1.12, -0.14; P = 0.011) were independently associated with lower IOP. The observed associations between statin or aspirin use with IOP were no longer significant after adjustment for β-blocker use.

CONCLUSIONS

This is the first population-based study to demonstrate and quantify clinically significant differences in IOP among participants using systemic β-blockers or nitrates. Lower IOP observed in participants using statins or aspirin was explained by concurrent systemic β-blocker use. The study findings may have implications for the management of glaucoma patients with comorbidity, and may provide insight into the pathophysiologic processes underlying IOP.

Inhibition of human carbonic anhydrase isozymes I, II, IX and XII with a new series of sulfonamides incorporating aroylhydrazone-, [1,2,4]triazolo[3,4-b][1,3,4]thiadiazinyl- or 2-(cyanophenylmethylene)-1,3,4-thiadiazol-3(2H)-yl moieties

A series of benzenesulfonamides incorporating aroylhydrazone, piperidinyl, sulfone, [1,2,4]triazolo[3,4-b][1,3,4]thiadiazinyl- or 2-(cyanophenyl-methylene)-1,3,4-thiadiazol-3(2H)-yl moieties was investigated as inhibitors of four α-carbonic anhydrases (CAs, EC 4.2.1.1), the human (h) isoforms hCA I, II (cytosolic, offtarget enzymes) and hCA IX and XII (transmembrane, tumor-associated isoforms). Low nanomolar activity was observed against hCA II (KIs of 0.56-17.1 nM) with these sulfonamides, whereas the slow cytosolic isoform hCA I was less inhibited by these compounds (KIs of 86.4 nM-32.8 µM). Most of these sulfonamides significantly inhibited CA IX, with KIs in the range of 4.5-47.0 nM, although some of the derivatives incorporating bulkier bicyclic moieties, as well as 2-thienyl fragments, showed a weaker activity against this isoform (KIs in the range 50.1-553 nM). All the investigated compounds also inhibited CA XII with KIs in the range 0.85-376 nM. The best inhibitors were those incorporating bulky [1,2,4]triazolo[3,4-b][1,3,4]thiadiazinyl moieties and 1,3,4-thiadiazol-3(2H)-yl groups.

Carbonic anhydrase inhibitors drug design

Inhibition of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) has pharmacologic applications in the field of antiglaucoma, anticonvulsant, antiobesity, and anticancer agents but is also emerging for designing anti-infectives (antifungal and antibacterial agents) with a novel mechanism of action. As a consequence, the drug design of CA inhibitors (CAIs) is a very dynamic field. Sulfonamides and their isosteres (sulfamates/sulfamides) constitute the main class of CAIs which bind to the metal ion in the enzyme active site. Recently the dithiocarbamates, possessing a similar mechanism of action, were reported as a new class of inhibitors. Other families of CAIs possess a distinct mechanism of action: phenols, polyamines, some carboxylates, and sulfocoumarins anchor to the zinc-coordinated water molecule. Coumarins and five/six-membered lactones are prodrug inhibitors, binding in hydrolyzed form at the entrance of the active site cavity. Novel drug design strategies have been reported principally based on the tail approach for obtaining all these types of CAIs, which exploit more external binding regions within the enzyme active site (in addition to coordination to the metal ion), leading thus to isoform-selective compounds. Sugar-based tails as well as click chemistry were the most fruitful developments of the tail approach. Promising compounds that inhibit CAs from bacterial and fungal pathogens, of the dithiocarbamate, phenol and carboxylate types have also been reported.

Sulfonamide inhibition studies of the γ-carbonic anhydrase from the oral pathogen Porphyromonas gingivalis

A carbonic anhydrase (CA, EC 4.2.1.1) denominated PgiCA, belonging to the γ-class, from the oral pathogenic bacteria Porphyromonas gingivalis, the main causative agent of periodontitis, was investigated for its inhibition profile with sulfonamides and one sulfamate. Dichlorophenamide, topiramate and many simple aromatic/heterocyclic sulfonamides were ineffective as PgiCA inhibitors whereas the best inhibition was observed with halogenosulfanilamides incorporating heavy halogens, 4-hydroxy- and 4-hydroxyalkyl-benzenesulfonamides, acetazolamide, methazolamide, zonisamide, indisulam, celecoxib, saccharin and hydrochlorothiazide (KIs in the range of 131-380nM). The inhibition profile of PgiCA was very different from that of CAM, hCA I and II or the β-CA from a protozoan parasite (Leishmania donovani chagasii). Identification of potent and possibly selective inhibitors of PgiCA may lead to pharmacological tools useful for understanding the physiological role(s) of this enzyme.

A class of sulfonamides with strong inhibitory action against the α-carbonic anhydrase from Trypanosoma cruzi

Trypanosoma cruzi, the causative agent of Chagas disease, encodes for an α-carbonic anhydrase (CA, EC 4.2.1.1) possessing high catalytic activity (TcCA) which was recently characterized (Pan et al. J. Med. Chem. 2013, 56, 1761-1771). A new class of sulfonamides possessing low nanomolar/subnanomolar TcCA inhibitory activity is described here. Aromatic/heterocyclic sulfonamides incorporating halogeno/methoxyphenacetamido tails inhibited TcCA with KIs in the range of 0.5-12.5 nM, being less effective against the human off-target isoforms hCA I and II. A homology model of TcCA helped us to rationalize the excellent inhibition profile of these compounds against the protozoan enzyme, a putative new antitrypanosoma drug target. These compounds were ineffective antitrypanosomal agents in vivo due to penetrability problems of these highly polar molecules that possess sulfonamide moieties.

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

INTRODUCTION

The benzothiadiazines and high ceiling diuretics (hydrochlorothiazide, hydroflumethiazide, quinethazone, metolazone, chlorthalidone, indapamide, furosemide and bumetanide) contain primary sulfamoyl moieties acting as zinc-binding groups in the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). These drugs are widely used clinically and were recently shown to weakly inhibit isoforms CA I and II, but to possess stronger activity against isoforms involved in other important pathologies, for example, obesity, cancer, epilepsy and hypertension.

AREAS COVERED

The class of clinically used diuretics, with CA inhibitory properties, is the main topic of the review. A patent literature review covering the period from 2005 to 2013 is presented.

EXPERT OPINION

This section presents an overview of the patent literature in the sulfonamide diuretic field. Most of the patents deal with the combination of diuretic sulfonamide CA inhibitors with other agents useful in the management of cardiovascular diseases and obesity. Such combinations exert a better therapeutic activity compared to similar diuretics that do not inhibit CAs, raising the question of the polypharmacological and drug repositioning effects of these old drugs. These effects seem to be due to the potent inhibition of such drugs against CA isoforms present in kidneys and blood vessels, which explain both the blood pressure lowering effects as well as organ-protective activity of the drugs. An explanation of these data is provided by the fact that inhibition of the renal CAs leads to a large increase of the nitrite excretion in urine, suggesting that renal CAs are involved in nitrite reabsorption in humans. Important lessons for the drug design of sulfonamide CA inhibitors (CAIs) can be drawn from these data.

Anion inhibition studies of the α-carbonic anhydrase from the pathogenic bacterium Vibrio cholerae

An α-carbonic anhydrase (CA, EC 4.2.1.1) has been recently cloned and characterized in the human pathogenic bacterium Vibrio cholerae, denominated VchCA (Del Prete et al. J. Med. Chem.2012, 55, 10742). This enzyme shows a good catalytic activity for the CO2 hydration reaction, comparable to that of the human (h) isoform hCA I. Many inorganic anions and several small molecules were investigated as VchCA inhibitors. Inorganic anions such as cyanate, cyanide, hydrogen sulfide, hydrogen sulfite, and trithiocarbonate were effective VchCA inhibitors with inhibition constants in the range of 33-88μM. Other effective inhibitors were diethyldithiocarbamate, sulfamide, sulfamate, phenylboronic acid and phenylarsonic acid, with KIs of 7-43μM. Halides (bromide, iodide), bicarbonate and carbonate were much less effective VchCA inhibitors, with KIs in the range of 4.64-28.0mM. The resistance of VchCA to bicarbonate inhibition may represent an evolutionary adaptation of this enzyme to living in an environment rich in this ion, such as the gastrointestinal tract, as bicarbonate is a virulence enhancer of this bacterium.

QSAR studies of sulfamate and sulfamide inhibitors targeting human carbonic anhydrase isozymes I, II, IX and XII

The last version of the PRECLAV algorithm was used to investigate a series of sulfamate/sulfamide carbonic anhydrase (CA, EC 4.2.1.1) inhibitors. PRECLAV allows identification of outliers for lead hopping, significant molecular fragments and similarity computation of a calibration set vs. a prediction set of compounds, from the viewpoint of computed QSAR. In the current study the database included 65 sulfamates and sulfamides as calibration set and 51 not yet synthesized sulfamates and sulfamides as prediction set. The dependent property was inhibitory activity for human (h) CA isozymes I, II, IX and XII. There were no outliers for lead hopping in the calibration set. In some cases, replacing of the O-SO2-NH2 by the NH-SO2-NH2 moiety, led to modifications in the structure of molecular fragments in another regions of the molecule. According to the descriptors in the obtained models, the inhibition of all CA isozymes was strongly influenced by the molecular shape and size of the sulfamates/sulfamides (which incorporate a substituted aryl-ureido scaffold). The lipophilicity of the inhibitors seemed to be a minor factor influencing CA inhibitory action. The presence of specific PRECLAV molecular fragments such as a C6 (totally substituted benzene), F, O and NO2 increases the activity of inhibitors against certain isoforms. The presence of molecular fragments such as C, CH, CxHy (substituted benzene/naphthalene) and NH decreased the activity of inhibitors against certain isoforms. In the prediction set, we evidenced seven compounds estimated to be highly active inhibitors for at least three of the investigated isozymes and eight molecules estimated to possess low activity against at least three CAs. The paper suggests the structure of some possible interesting inhibitors incorporating F, O and NO2 fragments that may have affinity for certain human CAs.

Amide derivatives of benzene-sulfonanilide, pharmaceutical composition thereof and method for cancer treatment using the same (US20120095092)

A series of sulfonamide derivatives incorporating an aromatic scaffold based on 1,4-phenylene diamine was prepared by a succession of five reactions. The lead molecule of these compounds was nimesulide (4-nitro-2-phenoxymethane-sulfoanilide), a cyclooxygenase (COX) inhibitor acting on both COX-1 and 2 isoforms, with some selectivity for COX-2. The new compounds from the patent are claimed to act as efficient antitumor agents, against a multitude of tumor types, such as leukemia, non-small cell lung cancer, colon cancer, brain cancer, melanoma, ovarian cancer, etc., although no COX inhibition data or other rationale to explain their biological effects are provided. As these compounds incorporate a methanesulfonamide moiety it is not unexpected that they may also appreciably inhibit tumor-associated carbonic anhydrases (CAs), such as isoforms CA IX and XII.

Dorzolamide-induced relaxation of intraocular porcine ciliary arteries in vitro depends on nitric oxide and the vascular endothelium

PURPOSE

Carbonic anhydrase inhibitors (CAIs) are used to reduce aqueous production in glaucoma, which includes a direct effect on the ciliary body. However, CAIs also affect ciliary blood flow, but the mechanisms of action of CAIs on the tone of intraocular ciliary arteries supplying the ciliary body have not been studied in detail.

MATERIALS AND METHODS

The intraocular part of porcine ciliary arteries was isolated and mounted in a wire myograph system for isometric tension recordings. After contraction with the thromboxane analogue U46619, the vasorelaxing effect of the CAIs acetazolamide, brinzolamide and dorzolamide was studied. Subsequently, the involvement of the carbonic anhydrase reaction and nitric oxide (NO) in dorzolamide-induced vasorelaxation was characterized.

RESULTS

All CAIs induced relaxation of contracted ciliary arteries, but the effect of dorzolamide was most pronounced. Dorzolamide-induced relaxation was unaffected by changes in pH and CO(2), and by removal of substrates to the carbonic anhydrase enzyme, but was abolished after inhibition of NO synthase and guanylyl cyclase and after removal of the vascular endothelium.

CONCLUSIONS

Dorzolamide-induced vasorelaxation of ciliary arteries is independent of changes in the substances involved in the carbonic anhydrase reaction, but depends on NO and the vascular endothelium. The mechanism of action of dorzolamide in ocular disease may involve an effect on vascular tone mediated by NO.

Flavones and structurally related 4-chromenones inhibit carbonic anhydrases by a different mechanism of action compared to coumarins

An inhibition study of several carbonic anhydrase (CA, EC 4.2.1.1) isoforms with flavones and aminoflavones, compounds possessing a rather similar scaffold with the coumarins, recently discovered inhibitors of this enzyme, is reported. The natural product flavone and some of its hydroxylated derivatives did not show time-dependent inhibition of the CAs, sign that they are not hydrolyzed within the enzyme active site as the (thio)coumarins and lactones. These compounds were low micromolar inhibitors of hCA I, II, IX and XII, with K(I)s in the range of 1.88-9.07 μM. A series of substituted 2-amino-3-phenyl-4H-chromen-4-ones, incorporating chloro- and methoxy substituents in various positions of the heterocycle, were then prepared and assayed as hCA I and II inhibitors, showing activity in the micromolar range. Some of these derivatives, as well as cis+trans resveratrol, were then assayed for the inhibition of all catalytically active mammalian CA isoforms, hCA I, II, III, IV, VA, VB, VI, VII, IX, XII, XIII, XIV and mCA XV (h=human, m=murine enzyme). These derivatives inhibited these CAs in the submicromolar-low micromolar range. Flavones, although not as active as the coumarins, may be considered as interesting leads for the design of non-sulfonamide CA inhibitors.

Secondary/tertiary benzenesulfonamides with inhibitory action against the cytosolic human carbonic anhydrase isoforms I and II

Carbonic anhydrase inhibitors of primary sulfonamide type, RSO(2)NH(2), have clinical applications as diuretics, antiglaucoma, antiepileptic, antiobesity and antitumor drugs. Here we investigated inhibition of two human cytosolic isozymes, hCA I and II, with a series of secondary/tertiary sulfonamides, incorporating tosyl moieties (CH(3)C(6)H(4)SO(2)NR1R2). Most compounds inhibited both isoforms in low micromolar range, with inhibition constants between 0.181-6.01 μM against hCA I, and 0.209-0.779 μM against hCA II, respectively. These findings point out that substituted benzenesulfonamides may be used as leads for generating interesting CAIs probably possessing a distinct mechanism of action compared to primary sulfonamides. Indeed, classical RSO(2)NH(2) inhibitors bind in deprotonated form to the Zn(II) ion from the CA active site and participate in many other favorable interactions with amino acid residues lining the cavity. The secondary/tertiary sulfonamides cannot bind to the zinc due to steric hindrance and probably are accommodated at the entrance of the active site, in coumarin binding-site.

Dithiocarbamates strongly inhibit carbonic anhydrases and show antiglaucoma action in vivo

A series of dithiocarbamates were prepared by reaction of primary/secondary amines with carbon disulfide in the presence of bases. These compounds were tested for the inhibition of four human (h) isoforms of the zinc enzyme carbonic anhydrase, CA (EC 4.2.1.1), hCA I, II, IX, and XII, involved in pathologies such as glaucoma (CA II and XII) or cancer (CA IX). Several low nanomolar inhibitors targeting these CAs were detected. The X-ray crystal structure of the hCA II adduct with morpholine dithiocarbamate evidenced the inhibition mechanism of these compounds, which coordinate to the metal ion through a sulfur atom from the dithiocarbamate zinc-binding function. Some dithiocarbamates showed an effective intraocular pressure lowering activity in an animal model of glucoma.