Dipotassium-trioxohydroxytetrafluorotriborate, K₂[B₃O₃F₄OH], is a potent inhibitor of human carbonic anhydrases

Halogenated Boroxine K2[B3O3F4OH] Modulates Metabolic Phenotype and Autophagy in Human Bladder Carcinoma 5637 Cell Line

Halogenated boroxine K2[B3O3F4OH] (HB), an inorganic derivative of cyclic anhydride of boronic acid, is patented as a boron-containing compound with potential for the treatment of both benign and malignant skin changes. HB has effectively inhibited the growth of several carcinoma cell lines. Because of the growing interest in autophagy induction as a therapeutic approach in bladder carcinoma (BC), we aimed to assess the effects of HB on metabolic phenotype and autophagy levels in 5637 human bladder carcinoma cells (BC). Cytotoxicity was evaluated using the alamar blue assay, and the degree of autophagy was determined microscopically. Mitochondrial respiration and glycolysis were measured simultaneously. The relative expression of autophagy-related genes BECN1, P62, BCL-2, and DRAM1 was determined by real-time PCR. HB affected cell growth, while starvation significantly increased the level of autophagy in the positive control compared to the basal level of autophagy in the untreated negative control. In HB-treated cultures, the degree of autophagy was higher compared to the basal level, and metabolic phenotypes were altered; both glycolysis and oxidative phosphorylation (OXPHOS) were decreased by HB at 0.2 and 0.4 mg/mL. Gene expression was deregulated towards autophagy induction and expansion. In conclusion, HB disrupted the bioenergetic metabolism and reduced the intracellular survival potential of BC cells. Further molecular studies are needed to confirm these findings and investigate their applicative potential.

Boron-containing carbonic anhydrases inhibitors

Over the last decades, the medicinal chemistry of boron-based compounds has been extensively explored, designing valuable small molecule drugs to tackle diseases and conditions, such as cancer, infections, inflammatory and neurological disorders. Notably, boron has proven to also be a valuable element for the development of inhibitors of the metalloenzymes carbonic anhydrases (CAs), a class of drug targets with significant potential in medicinal chemistry. Incorporating boron into carbonic anhydrase inhibitors (CAIs) can modulate the ligand ability to recognize the target and/or influence selectivity towards different CA isoforms, using the tail approach and boron-based tails. The electron-deficient nature of boron and its associated properties have also led to the discovery of novel zinc-binding CAIs, such as boronic acids and the benzoxaboroles, capable of inhibiting the CAs upon a Lewis acid-base mechanism of action. The present manuscript reviews the state-of-the-art of boron-based CAIs. As research in the applications of boron compounds in medicinal chemistry continues, it is anticipated that new boron-based CAIs will soon expand the current array of such compounds. However, further research is imperative to fully unlock the potential of boron-based CAIs and to advance them towards clinical applications.

Redox Mechanisms Underlying the Cytostatic Effects of Boric Acid on Cancer Cells-An Issue Still Open

Boric acid (BA) is the dominant form of boron in plasma, playing a role in different physiological mechanisms such as cell replication. Toxic effects have been reported, both for high doses of boron and its deficiency. Contrasting results were, however, reported about the cytotoxicity of pharmacological BA concentrations on cancer cells. The aim of this review is to briefly summarize the main findings in the field ranging from the proposed mechanisms of BA uptake and actions to its effects on cancer cells.

New in vitro findings about halogenated boroxine cytotoxicity and deregulation of cell death-related genes in GR-M melanoma cells

Anti-proliferative effects of halogenated boroxine - K₂(B₃O₃F₄OH) (HB) - have been confirmed in multiple cancer cell lines, including melanoma, but the exact mechanism of action is still unknown. This study aimed to determine its cytotoxic effects on human Caucasian melanoma (GR-M) cell growth in vitro as well as on the expression of cell death-related genes BCL-2, BECN1, DRAM1, and SQSTM1. GR-M and peripheral blood mononuclear (PBM) cells were treated with different HB concentrations and their growth inhibition and relative gene expression profiles were determined using the Alamar blue assay and real-time PCR. HB significantly inhibited cell growth of both GR-M and PBM cells but was even more effective in GR-M melanoma cells, as significant inhibition occurred at a lower HB concentration of 0.2 mg/mL. GR-M BCL-2 expression was significantly downregulated (P=0.001) at HB concentration of 0.4 mg/mL, which suggests that HB is a potent tumour growth inhibitor. At the same time, it upregulated BCL-2 expression in normal (PBM) cells, probably by activating protective mechanisms against induced cytotoxicity. In addition, all but the lowest HB concentrations significantly upregulated SQSTM1 (P=0.001) in GR-M cells. Upregulated BECN1 expression suggests early activation of autophagy at the lowest HB concentration in SQSTM1 cells and at all HB concentrations in PBM cells. Our findings clearly show HB-associated cell death and, along with previous cytotoxicity studies, reveal its promising anti-tumour potential.

Halogenated boroxine increases propensity to apoptosis in leukemia (UT-7) but not non-tumor cells in vitro

A hallmark of the development of solid and hematological malignancies is the dysregulation of apoptosis, which leads to an imbalance between cell proliferation, cell survival and death. Halogenated boroxine [K₂ (B₃ O₃ F₄ OH)] (HB) is a derivative of cyclic anhydride of boronic acid, with reproducible anti-tumor and anti-proliferative effects in different cell models. Notably, these changes are observed to be more profound in tumor cells than in normal cells. Here, we investigated the underlying mechanisms through an extensive evaluation of (a) deregulated target genes and (b) their interactions and links with main apoptotic pathway genes upon treatment with an optimized concentration of HB. To provide deeper insights into the mechanism of action of HB, we performed identification, visualization, and pathway association of differentially expressed genes (DEGs) involved in regulation of apoptosis among tumor and non-tumor cells upon HB treatment. We report that HB at a concentration of 0.2 mg·mL^-1 drives tumor cells to apoptosis, whereas non-tumor cells are not affected. Comparison of DEG profiles, gene interactions and pathway associations suggests that the HB effect and tumor-'selectivity' can be explained by Bax/Bak-independent mitochondrial depolarization by ROS generation and TRAIL-like activation, followed by permanent inhibition of NFκB signaling pathway specifically in tumor cells.

In silico prediction suggests inhibitory effect of halogenated boroxine on human catalase and carbonic anhydrase

Background

This research work included bioinformatics modeling of the dipotassium-trioxohydroxytetrafluorotriborate-halogenated boroxine molecule, as well as simulation and prediction of structural interactions between the halogenated boroxine molecule, human carbonic anhydrase, and human catalase structures. Using computational methods, we tried to confirm the inhibitory effect of halogenated boroxine on the active sites of these previously mentioned enzymes. The three-dimensional crystal structures of human catalase (PDB ID: 1DGB) and human carbonic anhydrase (PDB ID: 6FE2) were retrieved from RCSB Protein Data Bank and the protein preparation was performed using AutoDock Tools. ACD/ChemSketch and ChemDoodle were used for creating the three-dimensional structure of halogenated boroxine. Molecular docking was performed using AutoDock Vina, while the results were visualized using PyMOL.

Results

Results obtained in this research are showing evidence that there are interactions between the halogenated boroxine molecule and both previously mentioned proteins (human carbonic anhydrase and human catalase) in their active sites, which led us to the conclusion that the inhibitory function of halogenated boroxine has been confirmed.

Conclusion

These findings could be an important step in determining the exact mechanisms of inhibitory activity and will hopefully serve in further research purposes of complex pharmacogenomics studies.

Novel boron-containing compound, halogenated boroxine, induces selective cytotoxicity through apoptosis triggering in UT-7 leukemia

Apoptosis induction is a promising approach in targeting tumor cells. As halogenated boroxine (HB) shows antitumor activity, but its mechanism of action in hematological tumors remains unclear, in this study, we aimed to analyze apoptosis triggering in normal and UT-7 leukemia cells by HB. Methods for assessing cell viability and cytotoxicity, apoptosis detection, relative expression of 84 apoptosis-associated genes and BCL-2, and functional analysis were applied. Pronounced HB activities in inhibition of cell viability, cytotoxicity, and apoptosis induction with measurable differences between tumor and normal cells were found. HB modulated the expression of 21 genes, predominantly downregulated the antiapoptotic genes in leukemia. The functional association revealed HB's impact on inhibition of NF-κB signaling pathway. BCL-2 expression decreasing was found only in UT-7 leukemia. This study identified HB as an apoptosis inducer affecting leukemia but not normal cells considering mechanisms of selective activity that may be a great advantage of HB applications.

Biochemical and histomorphological findings in Swiss Wistar rats treated with potential boron-containing therapeutic - K2[B3O3F4OH]

BACKGROUND

Boron and boron containing compounds are known for their biological and protective roles being non-toxic and non-mutagenic in low concentrations. Male rats were exposed to halogenated boroxine (HB), dipotassium-trioxohydroxytetrafluorotriborate K₂[B₃O₃F₄OH], a potential new boron-containing therapeutic, aiming to determine concentrations with no adverse effects on selected serum biochemical parameters and histomorphological features.

METHODS

HB was prepared by reacting potassium hydrofluoride (KHF₂) with boric acid in molar ratios 2:3 at room temperature and its primary structure contains 4 fluorine atoms substituted in 6-membered ring. In concentrations of 10, 25, 35 and 45 mg/kg, HB was administered intraperitoneally as a single dose. Biochemical parameters were observed 24 and 96 h following the treatment. Effects of HB on biochemical blood parameters were also observed 24 h following continuous nine days application in concentrations of 10 mg/kg intraperitoneally and 50 mg/kg per os. Histomorphological observation of kidneys, liver, spleen, lungs and heart was performed for all treated animals.

RESULTS

Administration of single high dose of HB (35 mg/kg-45 mg/kg) effected high levels of urea and creatinine, which indicated renal injury that appeared to be temporary. Possible cause of concern is pancreatic injury indicated by elevated levels of serum amylase in the groups of animals that received the highest dosages of the substance. Histopathological examination of selected tissues revealed mild to moderate lesions in the kidneys and livers associated with administration of HB.

CONCLUSION

Observation of biochemical serum parameters or histopathology of examined tissues revealed no adverse effects of HB either after the administration of single dose lower than 35 mg/kg or following repeated administration at 10 mg/kg. These dosages should be further considered for potential therapeutic applications.

Halogenated boroxine dipotassium trioxohydroxytetrafluorotriborate K2[B3O3F4OH] inhibits emerging multidrug-resistant and β-lactamase-producing opportunistic pathogens

Halogenated boroxine dipotassium trioxohydroxytetrafluorotriborate, K₂[B₃O₃F₄OH] (boroxine) was previously shown to be very effective in inhibition of several carcinoma cell lines, including the skin cancer. Here, we investigated its antimicrobial potential by targeting the multidrug-resistant opportunistic pathogens associated with skin and wound infections. The antimicrobial testing against eleven bacterial and four fungal species revealed good activity of boroxine against pathogenic filamentous fungi Penicillium funiculosum and Aspergillus niger (MIC₅₀ 64 and 128 µg/ml), and a moderate bioactivity against the yeast Candida albicans (MIC₅₀ 512 µg/ml). Among the tested multidrug-resistant bacteria, the best antibacterial effect, stable over a 24-h period, was observed against the methicillin-resistant Staphylococcus aureus strain (MRSA) at MIC of 1024 µg/ml. The atomic force microscopy (AFM) used to investigate the morphology of S. aureus cells revealed indentations on its cell envelope after the boroxine exposure. These results show that in addition to the antitumor effect, boroxine exerts wide spectrum antimicrobial activity, thus may help preventing the development of skin and wound-related opportunistic infections.

Bioflavonoids protect cells against halogenated boroxine-induced genotoxic damage by upregulation of hTERT expression

Plant bioflavonoids are widely present in the human diet and have various protective properties. In this study, we have demonstrated the capacity of delphinidin and luteolin to increase human telomerase reverse transcriptase (hTERT) expression level and act as protective agents against halogenated boroxine-induced genotoxic damage. Halogenated boroxine K2(B3O3F4OH) (HB), is a novel compound with potential for the treatment of both benign and malignant skin changes. In vivo and in vitro studies have confirmed the inhibitory effects of HB on carcinoma cell proliferation and cell cycle progression as well as enzyme inhibition. However, minor genotoxic effects of HB are registered in higher applied concentrations, but those can be suppressed by in vitro addition of delphinidin and luteolin in appropriate concentrations. Fresh peripheral blood samples were cultivated for 72 h followed by independent and concomitant treatments of HB with luteolin or delphinidin. We analyzed the differences in relative hTERT expression between series of treatments compared with controls, which were based on normalized ratios with housekeeping genes. The obtained results have shown that selected bioflavonoids induce upregulation of hTERT that may contribute to the repair of genotoxic damage in vitro.

In vitro and in vivo antitumour effects of phenylboronic acid against mouse mammary adenocarcinoma 4T1 and squamous carcinoma SCCVII cells

The cytotoxic activity of phenylboroxine acid was evaluated in vitro on mouse mammary adenocarcinoma 4T1, mouse squamous cell carcinoma SCCVII, hamster lung fibroblast V79 and mouse dermal fibroblasts L929 cell lines. The cytotoxic effects were dose dependent for all tested tumour and non-tumour cell lines. Under in vivo conditions, three application routes of phenylboronic acid were studied: intra-peritoneal (i.p.), intra-tumour (i.t.) and per-oral. After tumour transplantation in syngeneic mice, phenylboronic acid was shown to slow the growth of both tumour cell lines (4T1 and SCCVII) compared with the control. The inhibitory effects were pronounced during the application of phenylboronic acid. For both tested tumour cell lines, the most prominent antitumour effect was obtained by intraperitoneal administration, followed significantly by oral administration.

Synthesis and carbonic anhydrase inhibition of polycyclic imides incorporating N-benzenesulfonamide moieties

A series of polycyclic imides was prepared by reaction of the benzenesulfonamide with an appropriate polycyclic acid anhydride in refluxing glacial acetic acid. The synthesized mono- and bis-sulfonamides were evaluated as a carbonic anhydrase inhibitors (CA, EC 4.2.1.1), more precisely against the human (h) isoforms hCA I, II, IX and XII, some of which are involved in various pathologies, such as glaucoma, epilepsy and cancer. Several low nanomolar and isoform-selective hCA II, IX and XII inhibitors were detected, and the structure-activity relationship for CA inhibition with this class of compounds is discussed in details. Computational studies allowed us to explain the efficacy and isoform-selective behaviour for some of these enzyme inhiibtors.

Advantages of an Electrochemical Method Compared to the Spectrophotometric Kinetic Study of Peroxidase Inhibition by Boroxine Derivative

In this study, boroxine derivative (K₂[B₃O₃F₄OH]) was tested as an inhibitor of horseradish peroxidase (HRP) by spectrophotometric and electrochemical methods. The activity of horseradish peroxidase was first studied under steady-state kinetic conditions by a spectrophotometric method which required the use of guaiacol as a second substrate to measure guaiacol peroxidation. The results of this method have shown that, by changing the concentration of guaiacol as the literature suggests, a different type of inhibition is observed than when changing the concentration of hydrogen peroxide as the substrate. This suggests that guaiacol interferes with the reaction in some way. The electrochemical method involves direct electron transfer of HRP immobilized in Nafion nanocomposite films on a glassy carbon (GC) electrode, creating a sensor with an electro-catalytic response to the reduction of hydrogen peroxide. The electrochemical method simplifies kinetic assays by removing the requirement of reducing substrates.

N-Substituted and ring opened saccharin derivatives selectively inhibit transmembrane, tumor-associated carbonic anhydrases IX and XII

A series of N-substituted saccharins incorporating aryl, alkyl and alkynyl moieties, as well as some ring opened derivatives were prepared and investigated as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). The widespread cytosolic isoforms CA I and II were not inhibited by these sulfonamides whereas transmembrane, tumor-associated ones were effectively inhibited, with K_Is in the range of 22.1-481nM for CA IX and of 3.9-245nM for hCA XII. Although the inhibition mechanism of these tertiary/secondary sulfonamides is unknown for the moment, the good efficacy and especially selectivity for the inhibition of the tumor-associated over the cytosolic, widespread isoforms, make these derivatives of considerable interest as enzyme inhibitors with various pharmacologic applications.

Synthesis and biological evaluation of cyclic imides incorporating benzenesulfonamide moieties as carbonic anhydrase I, II, IV and IX inhibitors

A group of cyclic imides was synthesized by reaction of amino-substituted benzenesulfonamides with a series of acid anhydrides such as succinic, maleic, tetrahydrophthalic, pyrazine-2,3-dicarboxylic acid anhydride, and substituted phthalic anhydrides. The synthesized sulfonamides were evaluated as carbonic anhydrase (CA, EC 4.2.1.1) inhibitors against the human (h) isoforms hCA I, II, IV and IX, involved in a variety of diseases among which glaucoma, retinitis pigmentosa, etc. Some of these sulfonamides showed effective inhibitory action (in the nanomolar range) against the cytosolic isoform hCA II and the transmembrane, tumor-associated one hCA IX, making them interesting candidates for preclinical evaluation in glaucoma or various tumors in which the two enzymes are involved. hCA I and IV were on the other hand less inhibited by these sulfonamides, with inhibition constants in the micromolar range.

Inhibition of Horseradish Peroxidase Activity by Boroxine Derivative, Dipotassium-trioxohydroxytetrafluorotriborate K2[B3O3F4OH]

Recently research shows that horseradish peroxidase, HRP, when combined with other compounds, is highly reactive toward different human tumour cells and that better understanding of catalytic mechanism and inhibition HPR could lead to a new targeted cancer therapy. Thus, the inhibition of HRP activity by dipotassium-trioxohydroxytetrafluorotriborate K2[B3O3F4OH] was investigated for possible explanation of previously observed antitumour activities of this promising drug. HRP activity was studied under steady-state kinetic conditions by a spectrophotometric method. In the absence of the inhibitor values of Km = 0.47 mM and Vmax = 0.34 mM min−1, respectively, were determined. The hydrogen peroxide H2O2 kinetic measurements show a competitive inhibition with the inhibition constant KI = 2.56 mM. The activation energy Ea values were found to be very similar for both reactions; in the absence of inhibitor activation energy was 17.7 kJ mol−1 and in the presence of inhibitor activation energy was 16.3 kJ mol−1. The values of Arrhenius constants were found to be different; A = 4.635 s−1 was measured in the absence of inhibitor while in the presence of inhibitor Arrhenius constant was 1.745 s−1 showing that K2[B3O3F4OH] initiates conformational change in the structure of the HRP and subsequently reduces its activity.

Dithiocarbamates effectively inhibit the β-carbonic anhydrase from the dandruff-producing fungus Malassezia globosa

A series of dithiocarbamates (DTCs) was investigated for the inhibition of the β-class carbonic anhydrase (CAs, EC 4.2.1.1) from the fungal parasite Malassezia globosa, MgCA, a validated anti-dandruff drug target. These DTCs incorporate various scaffold, among which those of N,N-dimethylaminoethylenediamine, the aminoalcohols with 3-5 carbon atoms in their molecule, 3-amino-quinuclidine, piperidine, morpholine and piperazine derivatives, as well as phenethylamine and its 4-sulfamoylated derivative. Several DTCs resulted more effective in inhibiting MgCA compared to the standard sulfonamide drug acetazolamide (K_I of 74μM), with K_Is ranging between 383 and 6235nM. A computational approach, involving a homology modeling of the enzyme and docking inhibitors within its active site, helped us rationalize the results. This study may contribute to better understand the inhibition profile of MgCA, and offer new ideas for the design of modulators of activity which belong to less investigated chemical classes, thus potentially useful to combat dandruff and other fungal infections.

Discovery of 4-sulfamoyl-phenyl-β-lactams as a new class of potent carbonic anhydrase isoforms I, II, IV and VII inhibitors: The first example of subnanomolar CA IV inhibitors

A series of benzenesulfonamides incorporating 1,3,4-trisubstituted-β-lactam moieties was prepared from sulfanilamide Schiff bases and in situ obtained ketenes, by using the Staudinger cycloaddition reaction. The new compounds were assayed as inhibitors of four human isoforms of the metalloenzyme carbonic anhydrase (hCA, EC 4.2.1.1) involved in various physiological/pathological conditions, hCA I, II, IV and VII. Excellent inhibitory activity was observed against all these isoforms, as follows: hCA I, involved in some eye diseases was inhibited with K_Is in the range of 7.3-917nM; hCA II, an antiglaucoma drug target, with K_Is in the range of 0.76-163nM. hCA IV, an isoform involved in several pathological conditions such as glaucoma, retinitis pigmentosa and edema was potently inhibited by the lactam-sulfonamides, with K_Is in the range of 0.53-51.0nM, whereas hCA VII, a recently validated anti-neuropathic pain target was the most inhibited isoform by these derivatives, with K_Is in the range of 0.68-9.1nM. The structure-activity relationship for inhibiting these CAs with the new lactam-sulfonamides is discussed in detail.

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.

Bortezomib inhibits mammalian carbonic anhydrases

We investigated the carbonic anhydrase (CA, EC 4.2.1.1) inhibitory activity of the clinically used antitumor agent bortezomib, a marketed proteasome inhibitor, against all the catalytically active mammalian isoforms CA I-VII, IX, XII-XV. Bortezomib effectively inhibited all these CAs in the micromolar range. hCA II, the physiologically dominant cytosolic isoform showed the highest affinity for the drug, with a K_I of 1.16μM. The cytosolic slow isoform hCA I was also effectively inhibited, with a K_I of 1.29μM, whereas the next best affinity was observed for the membrane-anchored form mCA XV, with a K_I of 2.68μM, followed by two transmembrane isoforms, hCA IX and XIV (K_Is of 3.28-3.38μM). The remaining cytosolic (CA III, VII and XIII), membrane-anchored (CA IV), mitochondrial (CA VA, VB), transmembrane (CA XII) and secreted (CA VI) isoforms were slightly less inhibited by bortezomib compared to isoforms discussed above, with K_Is ranging between 4.38 and 8.45μM. These data may shed some light on possible side effects and novel antitumor mechanisms of action of this drug.

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.

Cloning, expression, purification and sulfonamide inhibition profile of the complete domain of the η-carbonic anhydrase from Plasmodium falciparum

We report the cloning, purification and characterization of the full domain of carbonic anhydrase (CA, EC 4.2.1.1) from Plasmodium falciparum, which incorporates 358 amino acid residues (from 181 to 538, in the sequence of this 600 amino acid long protein), called PfCAdom. The enzyme, which belongs to the η-CA class showed the following kinetic parameters: kcat of 3.8×10(5)s(-1) and kcat/Km of 7.2×10(7)M(-1)×s(-1), being 13.3 times more effective as a catalyst compared to the truncated form PfCA. PfCAdom is more effective than the human (h) isoform hCA I, being around 50% less effective compared to hCA II, one of the most catalytically efficient enzymes known so far. Intriguingly, the sulfonamides CA inhibitors generally showed much weaker inhibitory activity against PfCAdom compared to PfCA, prompting us to hypothesize that the 69 amino acid residues insertion present in the active site of this η-CA is crucial for the active site architecture. The best sulfonamide inhibitors for PfCAdom were acetazolamide, methazolamide, metanilamide and sulfanilamide, with KIs in the range of 366-808nM.

Bortezomib inhibits bacterial and fungal β-carbonic anhydrases

Inhibition of the β-carbonic anhydrases (CAs, EC 4.2.1.1) from pathogenic fungi (Cryptococcus neoformans, Candida albicans, Candida glabrata, Malassezia globosa) and bacteria (three isoforms from Mycobacterium tuberculosis, Rv3273, Rv1284 and Rv3588), as well from the insect Drosophila melanogaster (DmeCA) and the plant Flaveria bidentis (FbiCA1) with the boronic acid peptidomimetic proteosome inhibitor bortezomib was investigated. Bortezomib was a micromolar inhibitor of all these enzymes, with KIs ranging between 1.12 and 11.30μM. Based on recent crystallographic data it is hypothesized that the B(OH)2 moiety of the inhibitor is directly coordinated to the zinc ion from the enzyme active site. The class of boronic acids, an under-investigated type of CA inhibitors, may lead to the development of anti-infectives with a novel mechanism of action, based on the pathogenic organisms CA inhibition.