Carbonic anhydrase inhibitors. Inhibition of the transmembrane isozyme XII with sulfonamides—a new target for the design of antitumor and antiglaucoma drugs?

The inhibition of a newly cloned human carbonic anhydrase (CA, EC 4.2.1.1), isozyme XII (hCA XII), has been investigated with a series of sulfonamides, including some clinically used derivatives (acetazolamide, methazolamide, ethoxzolamide, dichlorophenamide, dorzolamide, brinzolamide, benzolamide, and sulpiride, or indisulam, a compound in clinical development as antitumor drug), as well as the sulfamate antiepileptic drug topiramate. Some simple amino-/hydrazine-/hydroxy-substituted aromatic/heterocyclic sulfonamides have also been included in the study. All types of activity have been detected, with several medium potency inhibitors (K(I)s in the range of 34-220 nM), whereas ethoxzolamide and several halogenated sulfanilamides showed stronger potency, with K(I)s in the range of 11-22 nM. The antiglaucoma sulfonamides used clinically, except dichlorophenamide, which is a moderate inhibitor (K(I) of 50 nM), as well as topiramate, indisulam, and sulpiride behave as very potent hCA XII inhibitors, with K(I)s in the range of 3.0-5.7 nM. Several subnanomolar inhibitors (K(I)s in the range of 0.30-0.85 nM) have also been detected. Compounds with excellent selectivity against hCA XII over hCA II have been found, showing selectivity ratios in the range of 177.7-566.7. Apparently, hCA XII is a target of the antiglaucoma sulfonamides, and potent hCA XII inhibitors may be developed/used for the management of hypoxic tumors, together with inhibitors of the other tumor-associated isozyme, CA IX.     

Carbonic anhydrase inhibitors. Inhibition of the human cytosolic isozyme VII with aromatic and heterocyclic sulfonamides

The inhibition of a newly cloned human carbonic anhydrase (CA, EC 4.2.1.1), isozyme VII (hCA VII), has been investigated with a series of aromatic and heterocyclic sulfonamides, including some of the clinically used derivatives (acetazolamide, methazolamide, ethoxzolamide, dichlorophenamide, dorzolamide, brinzolamide and benzolamide), as well as the sulfamate antiepileptic drug topiramate. Inhibition data for the the other physiologically relevant cytosolic isoforms hCA I, hCA II and mCA XIII are also provided for comparison. hCA VII shows a high catalytic activity for the CO(2) hydration reaction, with a k(cat) of 9.5 x 10(5)s(-1) and k(cat)/K(m) of 8.3 x 10(7)M(-1)s(-1) at pH7.5 and 20 degrees C. A very interesting inhibition profile against hCA VII with this series of 32 sulfonamides/sulfamates was observed. hCA VII shows high affinity for all the investigated compounds, with inhibition constants in the range of 0.45-210 nM. Topiramate, ethoxzolamide and benzolamide showed subnanomolar hCA VII inhibitory activity, whereas acetazolamide, methazolamide, dorzolamide and brinzolamide showed K(I)-s in the range of 2.1-3.5 nM. Dichlorophenamide was slightly less active (K(I) of 26.5 nM). A number of heterocyclic or bicyclic aromatic sulfonamides also showed excellent hCA VII inhibitory properties (K(I)-s in the range of 4.3-7.0 nM) whereas many monosubstituted or disubstituted benzenesulfonamides were less active (K(I)-s in the range of 45-89 nM). The least active hCA VII inhibitors were some substituted benzene-1,3-disulfonamides as well as some halogenated sulfanilamides (K(I)-s in the range of 100-210 nM). The inhibition profile of hCA VII is rather different of that of the other cytosolic isozymes, providing thus a possibility for the design of more selective, hCA VII-specific inhibitors. In addition, these data furnish further evidence that hCA VII is the isozyme responsible for the anticonvulsant/antiepileptic activity of sulfonamides and sulfamates.     

Carbonic anhydrase inhibitors: inhibition of the human transmembrane isozyme XIV with a library of aromatic/heterocyclic sulfonamides

The first inhibition study of the transmembrane carbonic anhydrase (CA, EC 4.2.1.1) isozymes hCA XIV with a library of aromatic and heteroaromatic sulfonamides synthesized earlier is reported. Most of the inhibitors were sulfanilamide, homosulfanilamide and 4-aminoethyl-benzenesulfonamide derivatives, to which tails that would induce diverse physicochemical properties have been attached at the amino moiety. Several of these compounds were metanilamide, benzene-1,3-disulfonamide or the 1,3,4-thiadiazole/thiadiazoline-2-sulfonamide derivatives. The tails incorporated in these molecules were of the alkyl/aryl-carboxamido/ sulfonamido-, ureido- or thioureido-types. The sulfanilamides acylated at the 4-amino group with short aliphatic/aromatic moieties incorporating 2-6 carbon atoms showed modest hCA XIV inhibitory activity (K(I)-s in the range of 1.25-4.2 microM) which were anyhow better than that of sulfanilamide (K(I) of 5.4 microM). Better activity showed the homosulfanilamide and 4-aminoethyl-benzenesulfonamide derivatives bearing arylsulfonamido/ureido and thioureido moieties, with K(I)'s in the range of 203-935 nM. The best activity was observed for the heteroaromatic compounds incorporating 1,3,4-thiadiazole/thiadiazoline-2-sulfonamide and 5-arylcarboxamido/sulfonamido moieties, with K(I)'s in the range of 10-85 nM. All these compounds were generally also much better inhibitors of the other two transmembrane CA isozyme, hCA IX and XII. Thus, highly potent hCA XIV inhibitors were detected, but isozyme-specific inhibitors were not discovered for the moment.     

Carbonic anhydrase inhibitors: cloning and sulfonamide inhibition studies of a carboxyterminal truncated alpha-carbonic anhydrase from Helicobacter pylori

A library of sulfonamides/sulfamates has been investigated for the inhibition of the carboxyterminal truncated form of the alpha-carbonic anhydrase (CA, EC 4.2.1.1) isolated from the gastric pathogen Helicobacter pylori (hpCA). This enzyme, incorporating 202 amino acid residues, showed a catalytic activity similar to that of the full length hpCA, with k(cat) of 2.35 x 10(5)s(-1) and k(cat)/K(M) of 1.56 x 10(7)M(-1)s(-1) at 25 degrees C and pH of 8.9, for the CO(2) hydration reaction. All types of activity for inhibition of the bacterial enzyme have been detected. Dorzolamide and simple 4-substituted benzenesulfonamides were weak hpCA inhibitors (inhibition constants, K(I)s, in the range of 830-4310 nM). Sulfanilamide, orthanilamide, some of their derivatives, and indisulam showed better activity (K(I)s in the range of 310-562 nM), whereas most of the clinically used CA inhibitors, such as methazolamide, ethoxzolamide, dichlorophenamide, brinzolamide, topiramate, zonisamide, etc., acted as medium potency hpCA inhibitors (K(I)s in the range of 124-287 nM). Some potent hpCA inhibitors were detected too (K(I)s in the range of 20-96 nM) such as acetazolamide, 4-amino-6-chloro-1,3-benzenedisulfonamide, 4-sulfanilyl-aminoethyl-benzenesulfonamide, and 4-(2-amino-pyrimidin-4-yl)-benzenesulfonamide. Most of the investigated derivatives acted as better inhibitors of the human isoform hCA II than as hpCA inhibitors. Since hpCA is essential for the survival of the pathogen in acid, its inhibition by compounds such as those investigated here might be used as a new pharmacologic tool in the management of drug resistant H. pylori.     

Carbonic anhydrase inhibitors. Inhibition of transmembrane isozymes XII (cancer-associated) and XIV with anions

Metal complexing anions represent an important class of inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). The first inhibition study of the transmembrane isozymes CA XII (tumor-associated) and XIV with anions is reported. These isozymes showed inhibition profiles with physiologic/non-physiologic anions quite distinct from any other cytosolic (CA I and II) or transmembrane isoforms (e.g., CA IX) investigated earlier. hCA XII has a good affinity for fluoride and bicarbonate but is not inhibited by heavier halides, perchlorate, nitrate, and nitrite. The best hCA XII inhibitors were cyanide (K(I) of 1 microM) and azide (K(I) of 80 microM). hCA XIV was on the other hand weakly inhibited by fluoride and not at all inhibited by perchlorate, but showed good affinity for most other anions investigated here. Chloride and bicarbonate showed K(I)s in the range of 0.75-0.77 mM for this isoform. The best hCA XIV anion inhibitors were sulfate, phenylarsonic, and phenylboronic acid (K(I) in the range of 10-92 microM).     

Carbonic anhydrase inhibitors. Inhibition of isoforms I, II, IV, VA, VII, IX, and XIV with sulfonamides incorporating fructopyranose-thioureido tails

A series of aromatic/heterocyclic sulfonamides incorporating 2,3:4,5-bis-O-(isopropylidene)-beta-d-fructopyranosyl-thioureido moieties has been synthesized and assayed for the inhibition of seven human isoforms of the zinc enzyme carbonic anhydrase (hCA, EC 4.2.1.1). The new derivatives behaved as weak hCA I inhibitors (K(I)s of 9.4 -13.3microM), were efficient hCA II inhibitors (K(I)s of 6-750nM), and slightly inhibited isoforms hCA IV and hCA VA. Only the sulfanilamide derivative showed efficient and selective inhibition of hCA IV (K(I) of 10nM). These derivatives also showed excellent hCA VII inhibitory activity (K(I)s of 10-79nM), being less efficient as inhibitors of the transmembrane isoforms hCA IX (K(I)s of 10-4500nM) and hCA XIV (K(I)s of 21-3500nM). Two of the new compounds showed anticonvulsant action in a maximal electroshock seizure test in mice, with the fluorosulfanilamide derivative being a more efficient anticonvulsant than the antiepileptic drug topiramate.     

Inhibition of membrane-associated carbonic anhydrase isozymes IX, XII and XIV with a library of glycoconjugate benzenesulfonamides

A library of glycoconjugate benzenesulfonamides that contain diverse carbohydrate-triazole tails were investigated for their ability to inhibit the enzymatic activity of the three human transmembrane carbonic anhydrase (CA) isozymes hCA IX, hCA XII and hCA XIV. These isozymes have their CA domains located extracellularly, unlike the physiologically dominant hCA II, and are of immense current interest as druggable targets. Elevated expression of isozymes IX and XII is a marker for a broad spectrum of hypoxic tumors-this physiology may facilitate a novel approach to discriminate between healthy cells and cancerous cells. Many of these glycoconjugates were potent inhibitors (low nM), but importantly exhibited different isozyme selectivity profiles. The most potent hCA IX inhibitor was the glucuronic acid derivative 20 (K(i)=23nM). This compound was uniquely hCA IX selective cf. all other isozymes (16.4-, 16.8- and 4.6-fold selective against hCA II, XII, and XIV, respectively). At hCA XII there were many inhibitors with K(i)s<10nM that also demonstrated excellent selectivity (up to 344-fold) against other isozymes. Potent hCA XIV inhibitors were also identified, several with K(i)s approximately 10nM, however no hCA XIV-selective derivatives were evidenced from this library. The sugar tails of this study have shown promise as a valuable approach to both solubilize the aromatic sulfonamide CA recognition pharmacophore and to deliver potent inhibition and isozyme differentiation of the transmembrane CAs.     

Carbonic anhydrase inhibitors: inhibition of human cytosolic isozymes I and II and tumor-associated isozymes IX and XII with S-substituted 4-chloro-2-mercapto-5-methyl-benzenesulfonamides

A series of S-substituted 4-chloro-2-mercapto-5-methyl-benzenesulfonamides has been investigated as inhibitors of four isoforms of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1), that is, the cytosolic, ubiquitous isozymes CA I and II, as well as the transmembrane, tumor-associated isozymes CA IX and XII. The new derivatives were inefficient inhibitors of isoform I (K(I)s in the range of 2.7-18.7 microM) but generally had low nanomolar affinity for the inhibition of the other three isoforms (K(I)s in the range of 2.4-214 nM against hCA II; 1.4-47.5 nM against hCA IX, and 1.7-569 nM against hCA XII, respectively). Some selectivity for the inhibition of the tumor-associated versus the cyctosolic isoform II with some of these compounds has also been evidenced. As CA IX is an important marker of tumor hypoxia and its predictive, prognostic, and druggability potentials for designing antitumor therapies were recently validated, detection of selective, potent CA IX inhibitors may be relevant in the fight against cancers overexpressing CA isozymes.     

Carbonic anhydrase inhibitors. Selective inhibition of human tumor-associated isozymes IX and XII and cytosolic isozymes I and II with some substituted-2-mercapto-benzenesulfonamides

A series of 2-mercapto-substituted-benzenesulfonamides has been prepared by a unique two-step procedure starting from the corresponding 2-chloro-substituted benzenesulfonamides. Compounds bearing an unsubstituted mercapto group and the corresponding S-benzoyl derivatives were investigated as inhibitors of four isoforms of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1), i.e., the cytosolic, ubiquitous isozymes CA I and II, as well as the transmembrane, tumor associated isozymes CA IX and XII. These derivatives were medium potency hCA I inhibitors (K(I)s in the range of 1.5-5.7 microM), two derivatives were strong hCA II inhibitors (K(I)s in the range of 15-16 nM), whereas the others showed weak activity. These compounds inhibited hCA IX with inhibition constants in the range 160-1950 nM and hCA XII with inhibition constants in the range 1.2-413 nM. Some of these derivatives showed a certain degree of selectivity for inhibition of the tumor-associated over the cytosolic isoforms, being thus interesting leads for the development of potentially novel applications in the management of hypoxic tumors which overexpress CA IX and XII.     

Carbonic anhydrase inhibitors: Synthesis and inhibition of the human carbonic anhydrase isoforms I,II, VII,IX and XII with benzene sulfonamides incorporating 4,5,6,7-tetrabromophthalimide moiety

A series of 4,5,6,7-tetrabromo-1,3-dioxoisoindolin-2-yl benzenesulfonamide derivatives (compounds 1–8) was synthesized by reaction of benzene sulfonamide derivatives with 4,5,6,7-tetrabromophthalic anhydride moiety. These new sulfonamides were investigated as inhibitors of the zinc metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) and more specifically against the human (h) cytosolic isoforms hCA I, II and VII and the transmembrane tumor-associated isoform hCA IX and XII. The new compounds were good hCA I inhibitors (Kis in the range of 143 to >10,000 nM), but were moderately effective, as hCA II inhibitors (Kis of 47–190 nM) and poor hCA VII inhibitors (Kis in the range of 54–175 nM) compared to acetazolamide. The tumor-associated hCA IX was effectively inhibited with Kis ranging between 8.5 and 234 nM and hCA XII with inhibition constants in the range of 6.1–197 nM with high selectivity ratio. The structure–activity relationship (SAR) with this series of sulfonamides is straightforward, with the main features leading to good activity for each isoforms being established. The high sequence hCA alignment homology and molecular docking study of compounds was performed to rationalize the SAR reported over here.     

Carbonic anhydrase inhibitors: synthesis and inhibition of cytosolic/tumor-associated carbonic anhydrase isozymes I, II, IX, and XII with N-hydroxysulfamides--a new zinc-binding function in the design of inhibitors

A small library of N-hydroxysulfamides was synthesized by an original approach in order to investigate whether this zinc-binding function is efficient for the design of inhibitors targeting the cytosolic (hCA I and II) and transmembrane, tumor-associated (hCA IX and XII) isozymes of carbonic anhydrase (CA, EC 4.2.1.1). The parent derivative, N-hydroxysulfamide was a more potent inhibitor as compared to sulfamide or sulfamic acid against all isozymes, with inhibition constants in the range of 473 nM-4.05 microM. Its substituted n-decyl-, n-dodecyl-, benzyl-, and biphenylmethyl-derivatives were less inhibitory against hCA I (K(I)s in the range of 5.8-8.2 microM) but more inhibitory against hCA II (K(I)s in the range of 50.5-473 nM). The same situation was true for the tumor-associated isozymes, with K(I)s in the range of 353-790 nM against hCA IX and 372-874 nM against hCA XII. Some sulfamides/sulfamates possessing similar substitution patterns have also been investigated for the inhibition of these isozymes, being shown that in some particular cases sulfamides are more efficient inhibitors as compared to the corresponding sulfamates. Potent CA inhibitors targeting the cytosolic or tumor-associated CA isozymes can thus be designed from various classes of sulfonamides, sulfamides, or sulfamates and their derivatives, considering the extensive interactions in which the inhibitor and the enzyme active site are engaged, based on recent X-ray crystallographic data.     

Carbonic anhydrase inhibitors. Zonisamide is an effective inhibitor of the cytosolic isozyme II and mitochondrial isozyme V: solution and X-ray crystallographic studies

The antiepileptic drug zonisamide was considered to act as a weak inhibitor of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1) (with a K(I) of 4.3 microM against the cytosolic isozyme II). Here we prove that this is not true. Indeed, testing zonisamide in the classical assay conditions of the CO2 hydrase activity of hCA II, with incubation times of enzyme and inhibitor solution of 15 min, a K(I) of 10.3 microM has been obtained. However, when the incubation between enzyme and inhibitor was prolonged to 1 h, the obtained K(I) was of 35.2 nM, of the same order of magnitude as that of the clinically used sulfonamides/sulfamates acetazolamide, methazolamide, ethoxzolamide and topiramate (K(I)s in the range of 5.4-15.4 nM). The inhibition of the human mitochondrial isozyme hCA V with these compounds has been also tested by means of a dansylamide competition binding assay, which showed zonisamide and topiramate to be effective inhibitors, with K(I)s in the range of 20.6-25.4 nM. The X-ray crystal structure of the adduct of hCA II with zonisamide has also been solved at a resolution of 1.70 A, showing that the sulfonamide moiety participates in the classical interactions with the Zn(II) ion and the residues Thr199 and Glu106, whereas the benzisoxazole ring is oriented toward the hydrophobic half of the active site, establishing a large number of strong van der Waals interactions (<4.5 A) with residues Gln92, Val121, Phe131, Leu198, Thr200, Pro202.     

Carbonic anhydrase inhibitors: synthesis and inhibition of cytosolic/tumor-associated carbonic anhydrase isozymes I, II, and IX with sulfonamides incorporating 1,2,4-triazine moieties

A series of benzenesulfonamide derivatives incorporating triazine moieties in their molecules was obtained by reaction of cyanuric chloride with sulfanilamide, homosulfanilamide, or 4-aminoethylbenzenesulfonamide. The dichlorotriazinyl-benzenesulfonamides intermediates were subsequently derivatized by reaction with various nucleophiles, such as water, methylamine, or aliphatic alcohols (methanol and ethanol). The library of sulfonamides incorporating triazinyl moieties was tested for the inhibition of three physiologically relevant carbonic anhydrase (CA, EC 4.2.1.1) isozymes, the cytosolic hCA I and II, and the transmembrane, tumor-associated hCA IX. The new compounds reported here inhibited hCA I with K(I)s in the range of 75-136nM, hCA II with K(I)s in the range of 13-278nM, and hCA IX with K(I)s in the range of 0.12-549nM. The first hCA IX-selective inhibitors were thus detected, as the chlorotriazinyl-sulfanilamide and the bis-ethoxytriazinyl derivatives of sulfanilamide/homosulfanilamide showed selectivity ratios for CA IX over CA II inhibition in the range of 166-706. Furthermore, some of these compounds have subnanomolar affinity for hCA IX, with K(I)s in the range 0.12-0.34nM. These derivatives are interesting candidates for the development of novel unconventional anticancer strategies targeting the hypoxic areas of tumors. Clear renal cell carcinoma, which is the most lethal urologic malignancy and is both characterized by very high CA IX expression and chemotherapy unresponsiveness, could be the leading candidate of such novel therapies.     

Purification and inhibition studies with anions and sulfonamides of an α-carbonic anhydrase from the Antarctic seal Leptonychotes weddellii

A high activity α-carbonic anhydrase (CA, EC 4.2.1.1) has been purified from various tissues of the Antarctic seal Leptonychotes weddellii. The new enzyme, denominated lwCA, has a catalytic activity for the physiologic CO(2) hydration to bicarbonate reaction, similar to that of the high activity human isoform hCA II, with a k(cat) of 1.1×10(6) s(-1), and a k(cat)/K(m) of 1.4×10(8) M(-1) s(-1). The enzyme was highly inhibited by cyanate, thiocyanate, cyanide, bicarbonate, carbonate, as well as sulfamide, sulfamate, phenylboronic/phenylarsonic acids (K(I)s in the range of 46-100 μM). Many clinically used sulfonamides, such as acetazolamide, methazolamide, dorzolamide, brinzolamide and benzolamide were low nanomolar inhibitors, with K(I)s in the range of 5.7-67 nM. Dichlorophenamide, zonisamide, saccharin and hydrochlorothiazide were weaker inhibitors, with K(I)s in the range of 513-5390 nM. The inhibition profile with anions and sulfonamides of the seal enzyme was rather different from those of the human isoforms hCA I and II. The high sensitivity to bicarbonate inhibition of lwCA, unlike that of the human enzymes, may reflect an evolutionary adaptation to the deep water, high CO(2) partial pressure and hypoxic conditions in which Weddell seals spend much of their life.     

Carbonic anhydrase inhibitors. Inhibition of the membrane-bound human and bovine isozymes IV with sulfonamides

An inhibition study of the human and bovine membrane-associated isozymes of carbonic anhydrase (CA, EC 4.2.1.1), hCA IV and bCA IV, with a series of sulfonamides and sulfamates, some of which are widely clinically used, such as acetazolamide, methazolamide, ethoxzolamide, topiramate, dorzolamide, dichlorophenamide, celecoxib, and valdecoxib among others, is reported. In contrast to bCA IV, which is generally strongly inhibited by most of these derivatives, hCA IV has a rather different inhibition profile. Several of these compounds such as acetazolamide, ethoxzolamide, and bromosulfanilamide are potent hCA IV inhibitors (K(i)'s of 74-93 nM), others, such as celecoxib and some halogenated sulfanilamides are medium potency inhibitors (K(i)'s of 450-880 nM) whereas most of them are weak hCA IV inhibitors (methazolamide: 6.2 microM; dorzolamide 8.5 microM; topiramate 4.9 microM; dichlorophenamide: 15.3 microM). The hCA IV/bCA IV inhibition ratios for all the investigated compounds ranged between 1.05 (for acetazolamide) and 198.37 (for dorzolamide). Based on these results, we doubt that hCA IV is indeed one of the main contributors to the intraocular pressure (IOP) lowering effects of sulfonamide CA inhibitors, in addition to hCA II, as hypothesized earlier by Maren et al. (Mol. Pharmacol.1993, 44, 901-906). Indeed, both the very good hCA IV inhibitors (acetazolamide and ethoxzolamide) as well as the quite weak hCA IV inhibitors (methazolamide, dorzolamide, or dichlorophanamide) are effective in lowering IOP when administered either systemically or topically. The membrane-associated isozyme which probably is critical for aqueous humor secretion is hCA XII and not hCA IV.     

Carbonic anhydrase inhibitors. Synthesis and inhibition of cytosolic/tumor-associated carbonic anhydrase isozymes I, II, and IX with boron-containing sulfonamides, sulfamides, and sulfamates: toward agents for boron neutron capture therapy of hypoxic tumors

A library of boron-containing carbonic anhydrase (CA, EC 4.2.1.1) inhibitors, including sulfonamides, sulfamides, and sulfamates is reported. The new compounds have been synthesized by derivatization reactions of 4-carboxy-/amino-/hydroxy-phenylboronic acid pinacol esters with amino/isothiocyanato-substituted aromatic/heteroaromatic sulfonamides or by sulfamoylation reactions with sulfamoyl chloride. The new derivatives have been assayed for the inhibition of three physiologically relevant CA isozymes, the cytosolic CA I and II, and the transmembrane, tumor-associated isozyme CA IX. Effective inhibitors were detected both among sulfonamides, sulfamates, and sulfamides. Against the human isozyme hCA I the new compounds showed inhibition constants in the range of 34-94nM, against hCA II in the range of 3.1-48nM, and against hCA IX in the range of 7.3-89nM, respectively. As hypoxic tumors highly overexpress CA IX, the design of boron-containing inhibitors with high affinity for the tumor-associated CA isozymes may lead to important advances in boron neutron capture therapy (BNCT) applications targeting such tumors, which are non-responsive to both classical chemo- and radiotherapy.     

Carbonic anhydrase inhibitors. Inhibition of the prokariotic beta and gamma-class enzymes from Archaea with sulfonamides

A detailed inhibition study of carbonic anhydrases (CAs, EC 4.2.1.1) belonging to the beta- and gamma-families from Archaea with sulfonamides has been performed. Compounds included in this study were the clinically used sulfonamide CA inhibitors, such as acetazolamide, methazolamide, ethoxzolamide, topiramate, valdecoxib, celecoxib, dorzolamide, sulfanilamide, dichlorophanamide, as well as sulfanilamide analogs, halogenated sulfanilamides, and some 1,3-benzenedisulfonamide derivatives. The two gamma-CAs from Methanosarcina thermophila (Zn-Cam and Co-Cam) showed very different inhibitory properties with these compounds, as compared to the alpha-CA isozymes hCA I, II, and IX, and the beta-CA from Methanobacterium thermoautotrophicum (Cab). The best Zn-Cam inhibitors were sulfamic acid and acetazolamide, with inhibition constants in the range of 63-96 nM, whereas other investigated aromatic/heterocylic sulfonamides showed a rather levelled behavior, with KIs in the range of 0.12-1.70 microM. The best Co-Cam inhibitors were topiramate and p-aminoethyl-benzenesulfonamide, with KIs in the range of 0.12-0.13 microM, whereas the worst one was homosulfanilamide (KI of 8.50 microM). In the case of Cab, the inhibitory power of these compounds varied to a much larger extent, with sulfamic acid and sulfamide showing millimolar affinities (KIs in the range of 44-103 mM), whereas the best inhibitor was ethoxzolamide, with a KI of 5.35 microM. Most of these sulfonamides showed inhibition constants in the range of 12-100 microM against Cab. Thus, the three CA families investigated up to now possess a very diverse affinity for sulfonamides, the inhibitors with important medicinal, and environmental applications.     

Carbonic anhydrase inhibitors: inhibition of the human isozymes I, II, VA, and IX with a library of substituted difluoromethanesulfonamides

An inhibition study of the human cytosolic isozymes I, and II, the mitochondrial isoform VA, and the tumor-associated, transmembrane isozyme IX of carbonic anhydrase (CA, EC 4.2.1.1) with a library of aromatic/heteroaromatic/polycyclic difluoromethanesulfonamides is reported. Most of the inhibitors were derivatives of benzenedifluoromethanesulfonamide incorporating substituted-phenyl moieties, or were methylsulfonamide and difluoromethyl-sulfonamide derivatives of the sulfamates COUMATE and EMATE, respectively. Except for the methylsulfonamide-COUMATE derivative which behaved as a potent CA II inhibitor (K(I) of 32nM), these sulfonamides were moderate inhibitors of all isozymes, with inhibition constants in the range of 96-5200nM against hCA I, of 80-670nM against hCA II, and of 195-9280nM against hCA IX, respectively. Remarkably, some derivatives, such as 3-bromophenyl-difluoromethanesulfonamide, showed a trend to selectively inhibit the mitochondrial isoform CA VA, showing selectivity ratios for inhibiting CA VA over CA II of 3.53; over CA I of 6.84 and over CA IX of 9.34, respectively, although it is a moderate inhibitor (K(I) of 160nM). Some of these derivatives may be considered as leads for the design of isozyme selective CA inhibitors targeting the mitochondrial isozyme CA VA, with potential use as anti-obesity agents.     

Phenylethynylbenzenesulfonamide regioisomers strongly and selectively inhibit the transmembrane, tumor-associated carbonic anhydrase isoforms IX and XII over the cytosolic isoforms I and II

A series of compounds incorporating regioisomeric phenylethynylbenzenesulfonamide moieties has been investigated for the inhibition of four human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, hCA I, II, IX and XII. Inhibition between the low nanomolar to the milliomolar range has been observed against them, with several low nanomolar and tumor-CA selective inhibitors detected. The position of the sulfamoyl group with respect to the alkyne functionality, and the nature of the moieties substituting the second aromatic ring were the principal structural features influencing CA inhibition. The para-sulfamoyl-substituted derivatives were effective inhibitors of CA IX and XII, the meta-substituted regioisomers of CA I, IX and XII, whereas the ortho-substituted sulfonamides were weak inhibitors of CA I, II and IX, but inhibited significantly CA XII.     

Carbonic anhydrase inhibitors: inhibition of the tumor-associated isozyme IX with aromatic and heterocyclic sulfonamides

The inhibition of the tumor-associated transmembrane carbonic anhydrase IX (CA IX) isozyme has been investigated with a series of aromatic and heterocyclic sulfonamides, including the six clinically used derivatives acetazolamide, methazolamide, ethoxzolamide, dichlorophenamide, dorzolamide and brinzolamide. Inhibition data for the physiologically relevant isozymes I and II (cytosolic forms) and IV (membrane-bound) were also provided for comparison. A very interesting and unusual inhibition profile against CA IX with these sulfonamides has been observed. Several nanomolar (K(I)-s in the range of 14-50 nM) CA IX inhibitors have been detected, both among the aromatic (such as orthanilamide, homosulfonilamide, 4-carboxy-benzenesulfonamide, 1-naphthalenesulfonamide and 1,3-benzenedisulfonamide derivatives) as well as the heterocylic (such as 1,3,4-thiadizole-2-sulfonamide, etc.) sulfonamides examined. Because CA IX is a highly active isozyme predominantly expressed in tumor tissues with poor prognosis of disease progression, this finding is very promising for the potential design of CA IX-specific inhibitors with applications as anti-tumor agents.