Thiol-ene click chemistry for the synthesis of highly effective glycosyl sulfonamide carbonic anhydrase inhibitors.

Thiol-ene click chemistry has been applied for obtaining sulfonamide carbonic anhydrase (CA, EC 4.2.1.1) inhibitors incorporating sugar moieties. Most of these new compounds were moderate CA I inhibitors, effective CA II inhibitors, and low nanomolar/subnanomolar inhibitors of the tumor-associated isoforms CA IX and XII.

Synthesis of rhodamine B-benzenesulfonamide conjugates and their inhibitory activity against human α- and bacterial/fungal ß-carbonic anhydrases.

A series of fluorescent sulfonamide carbonic anhydrase (CA, EC 4.2.1.1) inhibitors were obtained by attaching rhodamine B moieties to the scaffold of benzenesulfonamides. The new compounds have been investigated for the inhibition of 12 human α-CA isoforms (hCA I-hCA XIV), three bacterial and one fungal ß-class enzymes from the pathogens Mycobacterium tuberculosis and Candida albicans. All types of inhibitory activities have been detected, with several compounds showing low nanomolar inhibition against the transmembrane isoforms hCA IX, XII (cancer-associated) and XIV. The ß-CAs were inhibited in the micromolar range by these compounds which may have applications for the imaging of hypoxic tumors or bacteria due to their fluorescent moieties.

Water-dispersible sugar-coated iron oxide nanoparticles. An evaluation of their relaxometric and magnetic hyperthermia properties.

Synthesis of functionalized magnetic nanoparticles (NPs) for biomedical applications represents a current challenge. In this paper we present the synthesis and characterization of water-dispersible sugar-coated iron oxide NPs specifically designed as magnetic fluid hyperthermia heat mediators and negative contrast agents for magnetic resonance imaging. In particular, the influence of the inorganic core size was investigated. To this end, iron oxide NPs with average size in the range of 4-35 nm were prepared by thermal decomposition of molecular precursors and then coated with organic ligands bearing a phosphonate group on one side and rhamnose, mannose, or ribose moieties on the other side. In this way a strong anchorage of the organic ligand on the inorganic surface was simply realized by ligand exchange, due to covalent bonding between the Fe(3+) atom and the phosphonate group. These synthesized nanoobjects can be fully dispersed in water forming colloids that are stable over very long periods. Mannose, ribose, and rhamnose were chosen to test the versatility of the method and also because these carbohydrates, in particular rhamnose, which is a substrate of skin lectin, confer targeting properties to the nanosystems. The magnetic, hyperthermal, and relaxometric properties of all the synthesized samples were investigated. Iron oxide NPs of ca. 16-18 nm were found to represent an efficient bifunctional targeting system for theranostic applications, as they have very good transverse relaxivity (three times larger than the best currently available commercial products) and large heat release upon application of radio frequency (RF) electromagnetic radiation with amplitude and frequency close to the human tolerance limit. The results have been rationalized on the basis of the magnetic properties of the investigated samples.

Anti-virulence strategy against Brucella suis: synthesis, biological evaluation and molecular modeling of selective histidinol dehydrogenase inhibitors.

In the facultative intracellular pathogen Brucella suis, histidinol dehydrogenase (HDH) activity, catalyzing the last step in histidine biosynthesis, is essential for intramacrophagic replication. The inhibition of this virulence factor by substituted benzylic ketones was a proof of concept that disarming bacteria leads to inhibition of intracellular bacterial growth in macrophage infection. This work describes the design, synthesis and evaluation of 19 new potential HDH inhibitors, using a combination of classical approaches and docking studies. The IC(50)-values of these inhibitors on HDH activity were in the nanomolar range, and several of them showed a 70-100% inhibition of Brucella growth in minimal medium. One selected compound yielded a strong inhibitory effect on intracellular replication of B. suis in human macrophages at concentrations as low as 5 µM, with an overall survival of intramacrophagic bacteria reduced by a factor 10(3). Docking studies with two inhibitors showed a good fitting in the catalytic pocket and also interaction with the second lipophilic pocket binding the cofactor NAD(+). Experimental data confirmed competition between inhibitors and NAD(+) at this site. Hence, these inhibitors can be considered as promising tools in the development of novel anti-virulence drugs.

Sulfonamides incorporating boroxazolidone moieties are potent inhibitors of the transmembrane, tumor-associated carbonic anhydrase isoforms IX and XII.

A new series of sulfonamides was synthesized by the reaction of the boroxazolidone complex of l-lysine with isothiocyanates incorporating sulfamoyl moieties and diverse organic scaffolds. The obtained thioureas have been investigated as inhibitors of four physiologically relevant human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, hCA I, II, IX and XII. Inhibition between the low nanomolar to the micromolar range has been observed against them, with several low nanomolar and tumor-CA selective inhibitors detected. These boron-containing compounds might be useful for the management of hypoxic tumors overexpressing hCA IX/XII by means of boron neutron capture therapy, a technique not investigated so far with inhibitors of this enzyme.

Inhibition of carbonic anhydrase IX: a new strategy against cancer.

Of the thirteen active carbonic anhydrase (CA) isozymes, the transmembrane isoform CA IX has been shown to be linked with carcinogenesis. CA IX presents an ectopic expression in a multitude of carcinomas derived from cervix, uteri, kidney, lung, oesophagus, breast, colon, etc., contrasting with its restricted expression in normal tissues, namely in the epithelia of the gastrointestinal tract. It has been demonstrated that this membrane-bound CA is strongly overexpressed in hypoxic tumors, participating in tumor cell environment acidosis and contributing to malignant progression and poor treatment outcome. Targeting CA IX could thus be an important means of controlling cancer disease. Modulation of extracellular tumor pH via inhibition of CA IX activity represents a promising approach to novel anticancer therapies. Much attention has recently been paid to the CA IX inhibitors drug design, and efforts have been made to obtain isozyme IX inhibitors, with putative applications as antitumor drugs/diagnostic agents. This review will focus on the different CA IX inhibitors described in the literature which could represent excellent potential as candidate therapeutic agents in cancer chemotherapy.

Carbonic anhydrase inhibitors; fluorinated phenyl sulfamates show strong inhibitory activity and selectivity for the inhibition of the tumor-associated isozymes IX and XII over the cytosolic ones I and II.

A series of fluorinated-phenylsulfamates have been prepared by sulfamoylation of the corresponding phenols and the inhibition of four physiologically relevant carbonic anhydrase (CA, EC 4.2.1.1) isozymes, the cytosolic CA I and II (off-targets), and the transmembrane, tumor-associated CA IX and XII is investigated. Unlike the lead molecule (phenylsulfamate), a very potent CA I and II inhibitor and a modest CA IX/XII inhibitor, the fluorinated sulfamates were stronger inhibitors of CA IX (K(I)s of 2.8-47 nM) and CA XII (K(I)s of 1.9-35 nM) than of CA I (K(I)s of 53-415 nM) and CA II (K(I)s of 20-113 nM). Some of these compounds were selective CA IX over CA II inhibitors, with selectivity ratios in the range of 11.4-12.1, making them interesting candidates for targeting hypoxic tumors overexpressing CA IX and/or XII.

Carbonic anhydrase activators: activation of human isozymes I, II and IX with phenylsulfonylhydrazido l-histidine derivatives.

Activation of the human carbonic anhydrase (CA, EC 4.2.1.1) isozymes I, II (cytosolic) and IX (transmembrane, tumor-associated isoform) with a series of arylsulfonylhydrazido-l-histidines incorporating 4-substituted-phenyl, pentafluorophenyl- and beta-naphthyl moieties was investigated. The compounds showed a weak hCA I activation profile, but were more efficient as hCA II and IX activators. The 4-iodophenyl-substituted derivative behaved as a strong and isozyme selective hCA II activator, with an activation constant of 0.21muM. This is the first isoform-selective, potent CA activator reported to date.

Carbonic anhydrase inhibitors. Inhibition of the human cytosolic isoforms I and II and transmembrane, tumor-associated isoforms IX and XII with boronic acids.

A series of aromatic, arylalkenyl- and arylalkyl boronic acids were assayed as inhibitors of four physiologically relevant carbonic anhydrase (CA, EC 4.2.1.1) isoforms, the cytosolic human (h) hCA I and II, and the transmembrane, tumor-associated hCA IX and XII. The best hCA I and II inhibitor was biphenyl boronic acid with, a K(I) of 3.7-4.5 microM, whereas the remaining derivatives showed inhibition constants in the range of 6.0-1560 microM for hCA I and of 6.0-1050 microM for hCA II, respectively. hCA IX and XII were effectively inhibited by most of the aromatic boronic acids (K(I)s of 7.6-12.3 microM) whereas the arylalkenyl and aryl-alkyl derivatives generally showed weaker inhibitory properties (K(I)s of 34-531 microM). The nature of the moiety substituting the boronic acid group strongly influenced the CA inhibitory activity, with inhibitors possessing low micromolar to millimolar activity being detected in this small series of investigated compounds. This study proves that the B(OH)(2) moiety represents a new zinc-binding group for the generation of effective CA inhibitors targeting isoforms with medicinal chemistry applications. The boronic acids probably bind to the Zn(II) ion within the CA active site leading to a tetrahedral geometry of the metal ion and of the B(III) derivative.

Carbonic anhydrase inhibitors: design of membrane-impermeant copper(II) complexes of DTPA-, DOTA-, and TETA-tailed sulfonamides targeting the tumor-associated transmembrane isoform IX.

The synthesis and carbonic anhydrase (CA, EC 4.2.1.1) inhibitory activity of two series of aromatic sulfonamides and their Cu(II) derivatives, incorporating metal-complexing moieties of the DTPA, DOTA, and TETA type are reported. The new compounds were designed in such a way as to possess high affinity for Cu(II) ions, exploiting four pendant carboxylate moieties in the DTPA derivatives, as well as the cyclen/cyclam macrocyles, and three pendant acetate moieties in the DOTA and TETA derivatives. The new derivatives showed modest inhibition of the cytosolic isoform CA I (K(I) values in the range of 66-2130 nM), were better CA II inhibitors (K(I) values in the range of 21-360 nM), and excellent inhibitors of the tumor-associated isoform CA IX (K(I) values in the range of 4.1-110 nM), with selectivity ratios for the inhibition of the tumor (CA IX) over the cytosolic (CA II) isozyme in the range of 10.74-20.88 for the best derivatives. Copper complexes were more inhibitory than the corresponding ligand sulfonamides, and showed membrane impermeability, thus, having the possibility to specifically target the transmembrane CA IX that has an extracellular active site. Incorporation of radioactive copper isotopes in this type of CA inhibitor may lead to interesting diagnostic/therapeutic applications for such compounds.

Carbonic anhydrase inhibitors: design of spin-labeled sulfonamides incorporating TEMPO moieties as probes for cytosolic or transmembrane isozymes.

A series of spin-labeled sulfonamides incorporating TEMPO moieties were synthesized by a procedure involving the formation of a thiourea functionality between the benzenesulfonamide and free radical fragment of the molecules. The new compounds were tested as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) and showed efficient inhibition of the physiologically relevant isozymes hCA II and hCA IX (hCA IX being predominantly found in tumors) and moderate to weak inhibitory activity against hCA I. Some derivatives were also selective for inhibiting the tumor-associated isoform over the cytosolic one CA II, and presented significant changes in their ESR signals when complexed to the enzyme active site, being interesting candidates for the investigation of hypoxic tumors overexpressing CA IX by ESR techniques, as well as for imaging/treatment purposes.

Design of zinc binding functions for carbonic anhydrase inhibitors.

Zinc ion plays a crucial role in the protein's functions and is linked to a variety of physiological processes. It constitutes an essential component of numerous enzymes especially carbonic anhydrase (CAs, EC 4.2.1.1), a pharmaceutically-important metalloprotein which catalyses efficiently the reversible hydration of carbon dioxide to bicarbonate with discharge of a proton. The potential therapeutic applications of selective carbonic anhydrase inhibitors has become an important challenge over the last few years, as some isoforms of this enzyme on the 16 described in higher vertebrates have been found to be involved in important pathologies such as cancer, obesity and ophthalmologic diseases. Coordination of the inhibitor with the zinc ion present in the active site is an important determinant which has to be taken into consideration for the design of isozyme-specific and organ-selective inhibitors. Besides the well known sulfonamide function, others zinc binding groups have been described constituting a new platform for the development of novel pharmacological agents. In this review, recent studies on the discovery of new zinc binding function will be discussed.

Carbonic anhydrase inhibitors: copper(II) complexes of polyamino-polycarboxylamido aromatic/heterocyclic sulfonamides are very potent inhibitors of the tumor-associated isoforms IX and XII.

Reaction of EDTA/DTPA dianhydride with aromatic/heterocyclic sulfonamides afforded a series of derivatives incorporating polyaminopolycarboxylate tails and benzenesulfonamide or 1,3,4-thiadiazole-2-sulfonamide heads. These compounds have been used as ligands to prepare Cu(II) complexes. Both parent sulfonamides as well as their copper complexes behaved as potent inhibitors of four carbonic anhydrase (CA, EC 4.2.1.1) isoforms, the cytosolic CA I and II, and transmembrane CA IX and XII. Some Cu(II) complexes showed subnanomolar affinities and some selectivity for the inhibition of the tumor-associated isoforms IX and XII and might be used as PET hypoxia markers of tumors.

Carbonic anhydrase IX: a new druggable target for the design of antitumor agents.

Carbonic anhydrases (CAs, EC 4.2.1.1) are a family of enzymes widespread in all life kingdoms. In mammals, isozyme CA IX is highly overexpressed in many cancer types being present in few normal tissues. Its expression is strongly induced by hypoxia present in many tumors, being regulated by the HIF transcription factor and correlated with a poor response to classical chemo- and radiotherapies. CA IX was recently shown to contribute to acidification of the tumor environment, by efficiently catalyzing the hydration of carbon dioxide to bicarbonate and protons with its extracellularly situated active site, leading both to the acquisition of metastasic phenotypes and to chemoresistance with weakly basic anticancer drugs. Inhibition of this enzymatic activity by specific and potent inhibitors was shown to revert these acidification processes, establishing a clear-cut role of CA IX in tumorigenesis. The development of a wide range of potent and selective CA IX inhibitors belonging to diverse chemical classes, such as membrane-impermeant, fluorescent or metal-containing such agents, could thus provide useful tools for highlighting the exact role of CA IX in hypoxic cancers, to control the pH (im)balance of tumor cells, and to develop novel diagnostic or therapeutic applications for the management of tumors. Indeed, both fluorescent inhibitors or positively charged, membrane impermeant sulfonamides have been recently developed as potent CA IX inhibitors and used as proof-of-concept tools for demonstrating that CA IX constitutes a novel and interesting target for the anticancer drug development.

Targeting of the Brucella suis virulence factor histidinol dehydrogenase by histidinol analogues results in inhibition of intramacrophagic multiplication of the pathogen.

Brucella suis histidinol dehydrogenase (HDH) can be efficiently targeted by substrate analogues. The growth of this pathogen in minimal medium was inhibited and the multiplication in human macrophages was totally abolished in the presence of the drugs. These effects have been shown to be correlated with the previously described inhibition of Brucella HDH activity.

Carbonic anhydrase inhibitors: Selective inhibition of the extracellular, tumor-associated isoforms IX and XII over isozymes I and II with glycosyl-thioureido-sulfonamides.

A series of glycosyl-thioureido sulfonamides incorporating glucosamine, galactosamine, and mannosamine tails, and sulfanilamide, halogenosulfanilamide, and metanilamide heads was synthesized. Many of the new compounds showed micromolar-submicromolar affinity for the inhibition of the cytosolic isoforms I and II of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1), but low nanomolar binding to the tumor-associated isozymes, CA IX and XII. The selectivity ratios for the inhibition of the tumor-associated over the cytosolic isozymes were in the range of 107-955 for the most selective such inhibitors.

Metal binding functions in the design of carbonic anhydrase inhibitors.

The carbonic anhydrases (CAs, EC 4.2.1.1) are zinc containing metalloenzymes which catalyse efficiently the reversible hydration of carbon dioxide to bicarbonate with discharge of a proton, playing important physiological and physiopathological functions. To date, 16 different carbonic anhydrase isoforms have been described in higher vertebrates, including humans, and some of them have been considered as important targets for inhibitors with therapeutic applications. The catalytic and structural role of zinc in these enzyme are understood in great detail, and this provided molecular basis for the design of potent inhibitors, some of which possessing important clinical applications mainly as topically acting anti-glaucoma drugs, anticancer or antiobesity agents. The metal binding function is a critically important factor in the development of isozyme-specific and organ-selective inhibitors. Discovery of compounds that possess zinc binding function different from that of the classical one (sulfonamide type) is in constant progress and can offer opportunities for developing novel pharmacological agents. In the present review we will discuss the different zinc binding function reported in the literature up to now in the design of carbonic anhydrase inhibitors.

Carbonic anhydrase inhibitors: the X-ray crystal structure of the adduct of N-hydroxysulfamide with isozyme II explains why this new zinc binding function is effective in the design of potent inhibitors.

N-Hydroxysulfamide is a 2000-fold more potent inhibitor of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1) as compared to sulfamide. It also inhibits other physiologically relevant isoforms, such as the tumor-associated CA IX and XII (K(I)s in the range of 0.865-1.34microM). In order to understand the binding of this inhibitor to the enzyme active site, the X-ray crystal structure of the human hCA II-N-hydroxysulfamide adduct was resolved. The inhibitor coordinates to the active site zinc ion by the ionized primary amino group, participating in an extended network of hydrogen bonds with amino acid residues Thr199, Thr200 and two water molecules. The additional two hydrogen bonds in which N-hydroxysulfamide bound to hCA II is involved as compared to the corresponding adduct of sulfamide may explain its higher affinity for the enzyme, also providing hints for the design of tight-binding CA inhibitors possessing an organic moiety substituting the NH group in the N-hydroxysulfamide structure.

Carbonic anhydrase inhibitors: Hypoxia-activatable sulfonamides incorporating disulfide bonds that target the tumor-associated isoform IX.

An approach for designing bioreductive, hypoxia-activatable carbonic anhydrase (CA, EC 4.2.1.1) inhibitors targeting the tumor-associated isoforms is reported. Sulfonamides incorporating 3,3'-dithiodipropionamide/2,2'-dithiodibenzamido moieties were prepared and reduced enzymatically/chemically in conditions present in hypoxic tumors, leading to thiols. The X-ray crystal structure of the most promising compound, 4-(2-mercaptophenylcarboxamido)benzenesulfonamide, which as disulfide showed a K(I) against hCA IX of 653 nM (in reduced form of 9.1 nM), in adduct with hCA II showed the inhibitor making favorable interactions with Gln92, Val121, Phe131, Leu198, Thr199, Thr200, Pro201, and Pro202, whereas the sulfamoyl moiety was coordinated to the Zn2+ ion. The same interactions were preserved in the adduct with hCA IX, but in addition, a hydrogen bond between the SH moiety of the inhibitor and the amide nitrogen of Gln67 was evidenced, which may explain the almost 2 times more effective inhibition of the tumor-associated isozyme over the cytosolic isoform.