Carbonic anhydrase inhibitors. Inhibition of the beta-class enzyme from the yeast Saccharomyces cerevisiae with anions

The protein encoded by the Nce103 gene of Saccharomyces cerevisiae, a beta-carbonic anhydrase (CA, EC 4.2.1.1) designated as scCA, has been cloned, purified, characterized kinetically, and investigated for its inhibition with a series simple, inorganic anions such as halogenides, pseudohalogenides, bicarbonate, carbonate, nitrate, nitrite, hydrogen sulfide, bisulfite, perchlorate, sulfate, and some of its isosteric species. The enzyme showed high CO(2) hydrase activity, with a k(cat) of 9.4x10(5) s(-1) and k(cat)/K(m) of 9.8x10(7) M(-1) s(-1). scCA was weakly inhibited by metal poisons (cyanide, azide, cyanate, thiocyanate, K(I)s of 16.8-55.6 mM) and strongly inhibited by bromide, iodide, and sulfamide (K(I)s of 8.7-10.8 microM). The other investigated anions showed inhibition constants in the low millimolar range.     

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: synthesis and inhibition studies against mammalian isoforms I-XV with a series of 2-(hydrazinocarbonyl)-3-substituted-phenyl-1H-indole-5-sulfonamides

A series of 2-(hydrazinocarbonyl)-3-substitutedphenyl-1H-indole-5-sulfonamides possessing various 2-, 3- or 4- substituted phenyl groups with methyl-, halogeno- and methoxy- functionalities, as well as the perfluorophenyl moiety have been synthesized and evaluated as inhibitors of 13 catalytically active, mammalian carbonic anhydrase (CA, EC 4.2.1.1) isoforms, that is, CA I-CA XV (of human (h) or murine (m) origin). The new compounds were ineffective inhibitors of isozymes hCA III, hCA IV, hCA VA, hCA VB, hCA VI and mCA XIII, moderate inhibitors of hCA I, hCA VII, hCA IX and mCA XV, and excellent, low-nanomolar inhibitors of hCA II and hCA XIV. The substitution pattern of the aromatic group in the 3-position of the indole ring influenced biological activity and isozyme inhibition profiles in this series of sulfonamides. Some of the best and most selective hCA XIV and mCA XV inhibitors ever reported have been identified in this study.     

Mink Growth Hormone Structural–Functional Relationships: Effects of Renaturing and Storage Conditions

Fourier-transform infrared spectroscopy, in vitro bioassay and enzyme-linked immunoassay were used to study the structural-functional relationships of recombinant mink growth hormone (mGH), refolded and stored under different conditions. Porcine GH (pGH) was synthesized and used as an example. These two hormones, when refolded and stored the same way, had the same secondary structures, biological and immunological efficacy, and biological potency. Only the immunological potency differed, mGH being significantly less potent than pGH. Renaturation pH and storing frozen or at 4 °C in 5% glycerol did not affect either the secondary structure or the activity. However, freeze-drying raised the content of buried α-helices and lowered that of solvated α-helices and of unordered structures. These conformational changes were associated with a reduction of immunological and biological potency of mGH and of immunological potency of pGH. These findings provide original information on the secondary structure of mGH, and show that conformational changes induced by lyophilization adversely affect its activity.     

Binding of glutamine to glutamine-binding protein from Escherichia coli induces changes in protein structure and increases protein stability

Glutamine-binding protein (GlnBP) from Escherichia coli is a monomeric protein localized in the periplasmic space of the bacterium. It is responsible for the first step in the active transport of L-glutamine across the cytoplasmic membrane. The protein consists of two similar globular domains linked by two peptide hinges, and X-ray crystallographic data indicate that the two domains undergo large movements upon ligand binding. Fourier transform infrared spectroscopy (FTIR) was used to analyze the structure and thermal stability of the protein in detail. The data indicate that glutamine binding induces small changes in the secondary structure of the protein and that it renders the structure more thermostable and less flexible. Detailed analyses of IR spectra show a lower thermal sensitivity of alpha-helices than beta-sheets in the protein both in the absence and in the presence of glutamine. Generalized two-dimensional (2D) analyses of IR spectra reveal the same sequence of unfolding events in the protein in the absence and in the presence of glutamine, indicating that the amino acid does not affect the unfolding pathway of the protein. The data give new insight into the structural characteristics of GlnBP that are useful for both basic knowledge and biotechnological applications.     

Carbonic anhydrase inhibitors. Novel sulfanilamide/acetazolamide derivatives obtained by the tail approach and their interaction with the cytosolic isozymes I and II, and the tumor-associated isozyme IX

A series of sulfonamides has been obtained by reacting sulfanilamide or 5-amino-1,3,4-thiadiazole-2-sulfonamide with omega-chloroalkanoyl chlorides, followed by replacement of the omega-chlorine atom with secondary amines. Tails incorporating heterocyclic amines belonging to the morpholine, piperidine and piperazine ring systems have been attached to these sulfonamides, by means of an alkanoyl-carboxamido linker containing from two to five carbon atoms. The new derivatives prepared in this way were tested as inhibitors of three carbonic anhydrase (CA, EC 4.2.1.1) isozymes, the cytosolic isozymes CA I and II, and the catalytic domain of the transmembrane, tumor-associated isozyme CA IX. Several low nanomolar CA I and CA II inhibitors were detected both in the aromatic and heterocyclic sulfonamide series, whereas the best hCA IX inhibitors (inhibition constants in the range of 22-35 nM) all belonged to the acetazolamide-like derivatives.     

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 cytosolic and tumor-associated carbonic anhydrase isozymes I, II, and IX with a series of 1,3,4-thiadiazole- and 1,2,4-triazole-thiols

A series of heterocyclic mercaptans incorporating 1,3,4-thiadiazole- and 1,2,4-triazole rings have been prepared and assayed for the inhibition of three physiologically relevant carbonic anhydrase (CA, EC 4.2.1.1) isozymes, the cytosolic human isozymes I and II, and the transmembrane, tumor-associated hCA IX. Against hCA I the investigated thiols showed inhibition constants in the range of 97 nM to 548 microM, against hCA II in the range of 7.9-618 microM, and against hCA IX in the range of 9.3-772 microM. Thiadiazoles were generally more active than triazoles against all investigated isozymes. Generally, the best inhibitors were the simple derivative 5-amino-1,3,4-thiadiazole-2-thiol and its N-acetylated derivative, which were anyhow at least two orders of magnitude less effective inhibitors when compared to the corresponding sulfonamides, acetazolamide, and its deacetylated derivative. An exception was constituted by 5-(2-pyridylcarboxamido)-1,3,4-thiadiazole-2-thiol, which is the first hCA I-selective inhibitor ever reported, possessing an inhibition constant of 97 nM against isozyme I, and being a 105 times less effective hCA II inhibitor, and 3154 times less effective hCA IX inhibitor. Thus, the thiol moiety may lead to effective CA inhibitors targeting isozyme I, whereas it is a less effective zinc-binding function for the design of CA II and CA IX inhibitors over the sulfonamide group.     

A mutational analysis of the 8-17 deoxyribozyme core

The 8-17 deoxyribozyme is a small RNA-cleaving DNA enzyme of significant applicative interest. We measured the kinetics of over 60 variants of 8-17, mutated within the "core" region. The data were analyzed according to a conceptual framework in which deleterious substitutions can either decrease the stability of the reaction's transition state, or favor unreactive ground-state conformations. In agreement with earlier in vitro evolution studies, the most severe functional effects were observed upon mutating four conserved residues, whose role was further explored by replacing them with non-standard nucleotides. Removal or modification of individual functional groups on the A6 and G7 bases suggested that these residues are involved in a close-contact interaction and form a network of functionally important hydrogen bonds. Mutagenesis of residues C13 and G14 was less revealing, but argued strongly against a role of C13 as a general acid/base catalyst. The use of non-standard nucleotides also led to the identification of one deoxyribozyme variant that, under some ionic conditions, is substantially more active than the wild-type construct. Finally, the effects of mutations in the intramolecular "core stem" correlated only in part with changes in helical stability, suggesting that a stable stem is required but not sufficient for optimal activity.     

Astrocyte-derived ATP induces vesicle shedding and IL-1 beta release from microglia

ATP has been indicated as a primary factor in microglial response to brain injury and inflammation. By acting on different purinergic receptors 2, ATP is known to induce chemotaxis and stimulate the release of several cytokines from these cells. The activation of purinergic receptors 2 in microglia can be triggered either by ATP deriving from dying cells, at sites of brain injury or by ATP released from astrocytes, in the absence of cell damage. By the use of a biochemical approach integrated with video microscopy experiments, we investigated the functional consequences triggered in microglia by ATP released from mechanically stimulated astrocytes, in mixed glial cocultures. Astrocyte-derived ATP induced in nearby microglia the formation and the shedding of membrane vesicles. Vesicle formation was inhibited by the ATP-degrading enzyme apyrase or by P2X(7)R antagonists. Isolation of shed vesicles, followed by IL-1beta evaluation by a specific ELISA revealed the presence of the cytokine inside the vesicular organelles and its subsequent efflux into the extracellular medium. IL-1beta efflux from shed vesicles was enhanced by ATP stimulation and inhibited by pretreatment with the P2X(7) antagonist oxidized ATP, thus indicating a crucial involvement of the pore-forming P2X(7)R in the release of the cytokine. Our data identify astrocyte-derived ATP as the endogenous factor responsible for microvesicle shedding in microglia and reveal the mechanisms by which astrocyte-derived ATP triggers IL-1beta release from these cells.