Structure and Inhibition of the CO2-Sensing Carbonic Anhydrase Can2 from the Pathogenic Fungus Cryptococcus neoformans

Computational analysis of Ayurvedic metabolites for potential treatment of drug-resistant Candida auris

This study explored the effectiveness of secondary metabolites of referred traditional Ayurvedic plants in treating fungal infections, particularly targeting Candida auris. Recognized as a global health threat, this fungus is notorious for its resistance to several antifungal treatments. The inhibition of lanosterol 14α-demethylase causes the depletion of ergosterol, ultimately resulting in the inhibition of fungal cell growth. A total of 469 metabolites, including alkaloids, flavonoids, and tannins from Ayurvedic plants, were screened against CYP51 (PDB ID: 4UYL) using molecular docking. Key active site residues, namely HIS461, CYS463, and TYR122, were targeted to inhibit the ergosterol synthesis, with VNI employed to benchmark the findings. Shortlisted metabolites underwent physicochemical analysis, ADMET analyses, and the principles of medicinal chemistry, which were confirmed through pharmacokinetic simulations. Further, this study investigated the molecular dynamics (MD) of co-crystalized VNI, trans-p-coumaric acid, and MCPHB [(r)-n-(1'-methoxycarbonyl-2'-phenylethyl)-4-hydroxybenzamide] to evaluate RMSD, RMSF, Rg, SASA, cross-correlation of residue motions, PCA, and free energy decomposition. The top compounds demonstrated favorable drug-like criteria. They exhibited good absorption potential with high gastrointestinal uptake. Distribution and metabolism were manageable with low risks of drug-drug interactions. Excretion profiles indicated proper clearance, and toxicity assessments showed low potential for cardiovascular issues. The results showed stable interactions for trans-p-coumaric acid and MCPHB, suggesting that all the ligands maintain stable binding interactions with the protein, which preserves structural integrity across all systems. This comprehensive approach suggests that these natural metabolites from Ayurvedic medicine could potentially serve as primary agents against fungal diseases, pending further validation through controlled in vitro and in vivo clinical trials.

Multi- and polypharmacology of carbonic anhydrase inhibitors

Eight genetically distinct families of the enzyme carbonic anhydrase (CA, EC 4.2.1.1) have been described in organisms overall in the phylogenetic tree. They catalyze the hydration of CO2 to bicarbonate and protons and are involved in pH regulation, chemosensing, and metabolism. The 15 α-CA isoforms present in humans are pharmacological drug targets known for decades, their inhibitors being used as diuretics, antiglaucoma, antiepileptic, or antiobesity drugs, as well as for the management of acute mountain sickness, idiopathic intracranial hypertension, and recently, as antitumor theragnostic agents. Other potential applications include the use of CA inhibitors (CAIs) in inflammatory conditions, cerebral ischemia, neuropathic pain, or Alzheimer/Parkinson disease management. CAs from pathogenic bacteria, fungi, protozoans, and nematodes have started to be considered as drug targets in recent years, with notable advances being registered. CAIs have a complex multipharmacology probably unique to this enzyme, which has been exploited intensely but may lead to other relevant applications in the future due to the emergence of drug design approaches that afforded highly isoform-selective compounds for most α-CAs known to date. They belong to a multitude of chemical classes (sulfonamides and isosteres, [iso]coumarins and related compounds, mono- and dithiocarbamates, selenols, ninhydrines, boronic acids, benzoxaboroles, etc). The polypharmacology of CAIs will also be discussed because drugs originally discovered for the treatment of non-CA related conditions (topiramate, zonisamide, celecoxib, pazopanib, thiazide, and high-ceiling diuretics) show effective inhibition against many CAs, which led to their repurposing for diverse pharmacological applications. SIGNIFICANCE STATEMENT: CAIs have multiple pharmacologic applications, such as diuretics, antiglaucoma, antiepileptic, antiobesity, antiacute mountain sickness, anti-idiopathic intracranial hypertension, and antitumor drugs. Their use in inflammatory conditions, cerebral ischemia, neuropathic pain, or neurodegenerations has started to be investigated recently. Parasite carbonic anhydrases are also drug targets for anti-infectives with novel mechanisms of action that can bypass drug resistance to commonly used agents. Drugs discovered for the management of other conditions that effectively inhibit these enzymes exert interesting polypharmacologic effects.

Carbonic anhydrases: Moiety appended derivatives, medicinal and pharmacological implications

In the realm of enzymology, Carbonic anhydrase (CA) emerges as a pivotal protagonist orchestrating the rapid conversion of carbon dioxide and water into bicarbonate ions and hydrogen ions, respectively. Carbonic anhydrase inhibitors (CAIs) are the class of drugs that target various isoforms of the enzyme, and these inhibitors play a crucial role in the treatment and management of multiple diseases such as cancer, glaucoma, high altitude sickness, rheumatoid arthritis, obesity, epilepsy, and sleep apnea. Several structural classes of CAIs developed till date possess unique architects of the pharmacophoric requirements around the central core moiety for the selective targeting of various isoforms of the CA. Recent advancements in drug design and development, along with technologies that aid in structure determination, have led to the development of several isoform-selective inhibitors of CA enzymes. However, their clinical development was hampered by the lack of desired therapeutic efficacy, isoform selectivity and safety profile. This review covers the most recent approaches used by different researchers concerned with the development of isoform-selective carbonic anhydrase inhibitors belonging to distinct structural classes like sulphonamides, carbazoles, selenols, coumarin, organotelluride, topiramate, thiophene, triazole, uracil-modified benzylic amines, and thiourea etc. In addition, their structure-activity relationships, biological evaluation, and in silico studies inlcuding the forthcoming avenues of advancements have been discussed. This review serves as a valuable resource for developing potent and efficacious CAIs with remarkable therapeutic implications; offering insights into their potency, specificity, and potential clinical applications.

De Novo RNA Sequencing and Transcriptome Analysis of Sclerotium rolfsii Gene Expression during Sclerotium Development

Sclerotium rolfsii is a destructive soil-borne fungal pathogen that causes stem rot in cultivated plants. However, little is known about the genetic basis of sclerotium development. In this study, we conducted de novo sequencing of genes from three different stages of S. rolfsii (mycelia, early sclerotium formation, and late sclerotium formation) using Illumina HiSeqTM 4000. We then determined differentially expressed genes (DEGs) across the three stages and annotated gene functions. STEM and weighted gene-co-expression network analysis were used to cluster DEGs with similar expression patterns. Our analysis yielded an average of 25,957,621 clean reads per sample (22,913,500-28,988,848). We identified 8929, 8453, and 3744 DEGs between sclerotium developmental stages 1 versus 2, 1 versus 3, and 2 versus 3, respectively. Additionally, four significantly altered gene expression profiles involved 220 genes related to sclerotium formation, and two modules were positively correlated with early and late sclerotium formation. These results were supported by the outcomes of qPCR and RNA-sequencing conducted on six genes. This is the first study to provide a gene expression map during sclerotial development in S. rolfsii, which can be used to reduce the re-infection ability of this pathogen and provide new insights into the scientific prevention and control of the disease. This study also provides a useful resource for further research on the genomics of S. rolfsii.

2H-chromene and 7H-furo-chromene derivatives selectively inhibit tumour associated human carbonic anhydrase IX and XII isoforms

Tumour associated carbonic anhydrases (CAs) IX and XII have been recognised as potential targets for the treatment of hypoxic tumours. Therefore, considering the high pharmacological potential of the chromene scaffold as selective ligand of the IX and XII isoforms, two libraries of compounds, namely 2H-chromene and 7H-furo-chromene derivatives, with diverse substitution patterns were designed and synthesised. The structure of the newly synthesised compounds was characterised and their inhibitory potency and selectivity towards human CA off target isoforms I, II and cancer-associated CA isoforms IX and XII were evaluated. Most of the compounds inhibit CA isoforms IX and XII with no activity against the I and II isozymes. Thus, while the potency was influenced by the substitution pattern along the chromene scaffold, the selectivity was conserved along the series, confirming the high potential of both 2H-chromene and 7H-furo-chromene scaffolds for the design of isozyme selective inhibitors.

From Benznidazole to New Drugs: Nanotechnology Contribution in Chagas Disease

Chagas disease is a neglected tropical disease caused by the protozoan Trypanosoma cruzi. Benznidazole and nifurtimox are the two approved drugs for their treatment, but both drugs present side effects and efficacy problems, especially in the chronic phase of this disease. Therefore, new molecules have been tested with promising results aiming for strategic targeting action against T. cruzi. Several studies involve in vitro screening, but a considerable number of in vivo studies describe drug bioavailability increment, drug stability, toxicity assessment, and mainly the efficacy of new drugs and formulations. In this context, new drug delivery systems, such as nanotechnology systems, have been developed for these purposes. Some nanocarriers are able to interact with the immune system of the vertebrate host, modulating the immune response to the elimination of pathogenic microorganisms. In this overview of nanotechnology-based delivery strategies for established and new antichagasic agents, different strategies, and limitations of a wide class of nanocarriers are explored, as new perspectives in the treatment and monitoring of Chagas disease.

A simple yet multifaceted 90 years old, evergreen enzyme: Carbonic anhydrase, its inhibition and activation

Advances in the carbonic anhydrase (CA, EC 4.2.1.1) research over the last three decades are presented, with an emphasis on the deciphering of the activation mechanism, the development of isoform-selective inhibitors/ activators by the tail approach and their applications in the management of obesity, hypoxic tumors, neurological conditions, and as antiinfectives.

Cloning, purification, kinetic and anion inhibition studies of a recombinant β-carbonic anhydrase from the Atlantic salmon parasite platyhelminth Gyrodactylus salaris

A β-class carbonic anhydrase (CA, EC 4.2.1.1) was cloned from the genome of the Monogenean platyhelminth Gyrodactylus salaris, a parasite of Atlantic salmon. The new enzyme, GsaCAβ has a significant catalytic activity for the physiological reaction, CO₂ + H₂O ⇋ HCO₃⁻ + H⁺ with a k_cat of 1.1 × 10⁵ s⁻¹ and a k_cat/K_m of 7.58 × 10⁶ M⁻¹ × s⁻¹. This activity was inhibited by acetazolamide (K_I of 0.46 µM), a sulphonamide in clinical use, as well as by selected inorganic anions and small molecules. Most tested anions inhibited GsaCAβ at millimolar concentrations, but sulfamide (K_I of 81 µM), N,N-diethyldithiocarbamate (K_I of 67 µM) and sulphamic acid (K_I of 6.2 µM) showed a rather efficient inhibitory action. There are currently very few non-toxic agents effective in combating this parasite. GsaCAβ is subsequently proposed as a new drug target for which effective inhibitors can be designed.

Heterologous expression and biochemical characterisation of the recombinant β-carbonic anhydrase (MpaCA) from the warm-blooded vertebrate pathogen malassezia pachydermatis

Warm-blooded animals may have Malassezia pachydermatis on healthy skin, but changes in the skin microenvironment or host defences induce this opportunistic commensal to become pathogenic. Malassezia infections in humans and animals are commonly treated with azole antifungals. Fungistatic treatments, together with their long-term use, contribute to the selection and the establishment of drug-resistant fungi. To counteract this rising problem, researchers must find new antifungal drugs and enhance drug resistance management strategies. Cyclic adenosine monophosphate, adenylyl cyclase, and bicarbonate have been found to promote fungal virulence, adhesion, hydrolase synthesis, and host cell death. The CO₂/HCO₃^-/pH-sensing in fungi is triggered by HCO₃^- produced by metalloenzymes carbonic anhydrases (CAs, EC 4.2.1.1). It has been demonstrated that the growth of M. globosa can be inhibited in vivo by primary sulphonamides, which are the typical CA inhibitors. Here, we report the cloning, purification, and characterisation of the β-CA (MpaCA) from the pathogenic fungus M. pachydermatis, which is homologous to the enzyme encoded in the genome of M. globosa and M. restricta, that are responsible for dandruff and seborrhoeic dermatitis. Fungal CAs could be thus considered a new pharmacological target for combating fungal infections and drug resistance developed by most fungi to the already used drugs.

Effect of amino acids and amines on the activity of the recombinant ι-carbonic anhydrase from the Gram-negative bacterium Burkholderia territorii

We here report a study on the activation of the ι-class bacterial CA from Burkholderia territorii (BteCAι). This protein was recently characterised as a zinc-dependent enzyme that shows a significant catalytic activity (kcat 3.0 × 105 s-1) for the physiological reaction of CO2 hydration to bicarbonate and protons. Some amino acids and amines, among which some proteinogenic derivatives as well as histamine, dopamine and serotonin, showed efficient activating properties towards BteCAι, with activation constants in the range 3.9-13.3 µM. L-Phe, L-Asn, L-Glu, and some pyridyl-alkylamines, showed a weaker activating effect towards BteCAι, with KA values ranging between 18.4 µM and 45.6 µM. Nowadays, no information is available on active site architecture, metal ion coordination and catalytic mechanism of members of the ι-group of CAs, and this study represents another contribution towards a better understanding of this still uncharacterised class of enzymes.

Inhibitory Effects of Sulfonamide Derivatives on the β-Carbonic Anhydrase (MpaCA) from Malassezia pachydermatis, a Commensal, Pathogenic Fungus Present in Domestic Animals

Fungi are exposed to various environmental variables during their life cycle, including changes in CO₂ concentration. CO₂ has the potential to act as an activator of several cell signaling pathways. In fungi, the sensing of CO₂ triggers cell differentiation and the biosynthesis of proteins involved in the metabolism and pathogenicity of these microorganisms. The molecular machineries involved in CO₂ sensing constitute a promising target for the development of antifungals. Carbonic anhydrases (CAs, EC 4.2.1.1) are crucial enzymes in the CO₂ sensing systems of fungi, because they catalyze the reversible hydration of CO₂ to proton and HCO₃^-. Bicarbonate in turn boots a cascade of reactions triggering fungal pathogenicity and metabolism. Accordingly, CAs affect microorganism proliferation and may represent a potential therapeutic target against fungal infection. Here, the inhibition of the unique β-CA (MpaCA) encoded in the genome of Malassezia pachydermatis, a fungus with substantial relevance in veterinary and medical sciences, was investigated using a series of conventional CA inhibitors (CAIs), namely aromatic and heterocyclic sulfonamides. This study aimed to describe novel candidates that can kill this harmful fungus by inhibiting their CA, and thus lead to effective anti-dandruff and anti-seborrheic dermatitis agents. In this context, current antifungal compounds, such as the azoles and their derivatives, have been demonstrated to induce the selection of resistant fungal strains and lose therapeutic efficacy, which might be restored by the concomitant use of alternative compounds, such as the fungal CA inhibitors.

Scaffolding protein CcmM directs multiprotein phase separation in β-carboxysome biogenesis

Carboxysomes in cyanobacteria enclose the enzymes Rubisco and carbonic anhydrase to optimize photosynthetic carbon fixation. Understanding carboxysome assembly has implications in agricultural biotechnology. Here we analyzed the role of the scaffolding protein CcmM of the β-cyanobacterium Synechococcus elongatus PCC 7942 in sequestrating the hexadecameric Rubisco and the tetrameric carbonic anhydrase, CcaA. We find that the trimeric CcmM, consisting of γCAL oligomerization domains and linked small subunit-like (SSUL) modules, plays a central role in mediation of pre-carboxysome condensate formation through multivalent, cooperative interactions. The γCAL domains interact with the C-terminal tails of the CcaA subunits and additionally mediate a head-to-head association of CcmM trimers. Interestingly, SSUL modules, besides their known function in recruiting Rubisco, also participate in intermolecular interactions with the γCAL domains, providing further valency for network formation. Our findings reveal the mechanism by which CcmM functions as a central organizer of the pre-carboxysome multiprotein matrix, concentrating the core components Rubisco and CcaA before β-carboxysome shell formation.

Biochemical and structural characterization of beta-carbonic anhydrase from the parasite Trichomonas vaginalis

Abstract

Trichomonas vaginalis is a unicellular parasite and responsible for one of the most common sexually transmittable infections worldwide, trichomoniasis. Carbonic anhydrases (CAs) are enzymes found in all lifeforms and are known to play a vital role in many biochemical processes in organisms including the maintenance of acid–base homeostasis. To date, eight evolutionarily divergent but functionally convergent forms of CAs (α, β, γ, δ, ζ, η, θ, and ι) have been discovered. The human genome contains only α-CAs, whereas many clinically significant pathogens express only β-CAs and/or γ-CAs. The characterization of pathogenic β- and γ-CAs provides important knowledge for targeting these biomolecules to develop novel anti-invectives against trichomoniasis. Here, we report the recombinant production and characterization of the second β-CA of T. vaginalis (TvaCA2). Light scattering analysis revealed that TvaCA2 is a dimeric protein, which was further supported with in silico modeling, suggesting similar structures between TvaCA2 and the first β-CA of T. vaginalis (TvaCA1). TvaCA2 exhibited moderate catalytic activity with the following kinetic parameters: k_cat of 3.8 × 10⁵ s⁻¹ and k_cat/K_M of 4.4 × 10⁷ M⁻¹ s⁻¹. Enzyme activity inhibition was studied with a set of clinically used sulfonamides and sulfonamide derivates. Twenty-seven out of the 39 compounds resulted in inhibition with a nanomolar range. These initial results encourage for future work entailing the design of more potent inhibitors against TvaCA2, which may provide new assets to fight trichomoniasis.

Key messages

• Protozoan parasite Trichomonas vaginalis has two β-carbonic anhydrases (TvaCA1/2).

• TvaCA1/TvaCA2 represents promising targets for antitrichomonal drug development.

• TvaCA2 is a dimer of 20.3 kDa and possesses moderate catalytic activity.

• The most efficient inhibitor was clinical drug acetazolamide with K_I of 222.9 nM.

• The 39 tested sulfonamides form the basis for the design of more potent inhibitors.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00109-021-02148-1.

An overview on the recently discovered iota-carbonic anhydrases

Carbonic anhydrases (CAs, EC 4.2.1.1) have been studied for decades and have been classified as a superfamily of enzymes which includes, up to date, eight gene families or classes indicated with the Greek letters α, β, γ, δ, ζ, η, θ, ι. This versatile enzyme superfamily is involved in multiple physiological processes, catalysing a fundamental reaction for all living organisms, the reversible hydration of carbon dioxide to bicarbonate and a proton. Recently, the ι-CA (LCIP63) from the diatom Thalassiosira pseudonana and a bacterial ι-CA (BteCAι) identified in the genome of Burkholderia territorii were characterised. The recombinant BteCAι was observed to act as an excellent catalyst for the physiologic reaction. Very recently, the discovery of a novel ι-CAs (COG4337) in the eukaryotic microalga Bigelowiella natans and the cyanobacterium Anabaena sp. PCC7120 has brought to light an unexpected feature for this ancient superfamily: this ι-CAs was catalytically active without a metal ion cofactor, unlike the previous reported ι-CAs as well as all known CAs investigated so far. This review reports recent investigations on ι-CAs obtained in these last three years, highlighting their peculiar features, and hypothesising that possibly this new CA family shows catalytic activity without the need of metal ions.

Zeta-carbonic anhydrases show CS2 hydrolase activity: A new metabolic carbon acquisition pathway in diatoms?

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CDCA1 is a carbonic anhydrase that can utilize Zn(II) or Cd(II) as catalytic metal.

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CDCA1 has been the first enzyme to show an efficient utilization of Cd(II) ions in Nature.

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By using a multidisciplinary approach, we discovered that CS₂ is a substrate for this enzyme.

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CDCA1 is the unique enzyme, known so far, able to use both CS₂ and CO₂ as substrates.

CDCA1 is a very peculiar member of the Carbonic Anhydrase (CA) family. It has been the first enzyme to show an efficient utilization of Cd(II) ions in Nature and a unique adaptation capability to live on the surface ocean. Indeed, in this environment, which is extremely depleted in essential metal ions, CDCA1 can utilize Zn(II) or Cd(II) as catalytic metal to support the metabolic needs of fast growing diatoms. In this paper we demonstrate a further catalytic versatility of this enzyme by using a combination of X-ray crystallography, molecular dynamics simulations and enzymatic experiments. First we identified the CO₂ binding site and the way in which this substrate travels from the environment to the enzyme active site. Then, starting from the observation of a structural similarity with the substrate entry route of CS₂ hydrolase from Acidanius A1-3, we hypothesized and demonstrated that also CS₂ is a substrate for CDCA1. This finding is new and unexpected since until now only few CS₂ hydrolases have been characterized, and none of them is reported to have any CO₂ hydratase action. The physiological implications of this supplementary catalytic activity still remain to be unveiled. We suggest here that it could represent another ability of diatoms expressing CDCA1 to adapt to the external environment. Indeed, the ability of this enzyme to convert CS₂ could represent an alternative source of carbon acquisition for diatoms, in addition to CO₂.

Sulphonamide inhibition profile of Staphylococcus aureus β-carbonic anhydrase

This paper presents the production and kinetic and inhibitory characterisation of β-carbonic anhydrase from the opportunistic bacterium Staphylococcus aureus (SauBCA). From the eight different carbonic anhydrase (CA) families known to date, humans have only the α-form, whereas many clinically relevant pathogens have β- and/or γ-form(s). Based on this discovery, β- and γ-CAs have been introduced as promising new anti-infective targets. The results of this study revealed that recombinant SauBCA possesses significant CO₂ hydration activity with a k_cat of 1.46 × 10⁵ s^-1 and a k_cat/K_M of 2.56 × 10⁷ s^{- 1}M^-1. Its enzymatic function was inhibited by various sulphonamides in the nanomolar - micromolar range, and the K_i of acetazolamide was 628 nM. The best inhibitor was the clinically used sulfamide agent famotidine (K_i of 71 nM). The least efficient inhibitors were zonisamide and dorzolamide. Our work encourages further investigations of SauBCA in an attempt to discover novel drugs against staphylococcal infections.

A Highlight on the Inhibition of Fungal Carbonic Anhydrases as Drug Targets for the Antifungal Armamentarium

Carbon dioxide (CO2), a vital molecule of the carbon cycle, is a critical component in living organisms' metabolism, performing functions that lead to the building of compounds fundamental for the life cycle. In all living organisms, the CO2/bicarbonate (HCO3-) balancing is governed by a superfamily of enzymes, known as carbonic anhydrases (CAs, EC 4.2.1.1). CAs catalyze the pivotal physiological reaction, consisting of the reversible hydration of the CO2 to HCO3- and protons. Opportunistic and pathogenic fungi can sense the environmental CO2 levels, which influence their virulence or environmental subsistence traits. The fungal CO2-sensing is directly stimulated by HCO3- produced in a CA-dependent manner, which directly activates adenylyl cyclase (AC) involved in the fungal spore formation. The interference with CA activity may impair fungal growth and virulence, making this approach interesting for designing antifungal drugs with a novel mechanism of action: the inhibition of CAs linked to the CO2/HCO3-/pH chemosensing and signaling. This review reports that sulfonamides and their bioisosteres as well as inorganic anions can inhibit in vitro the β- and α-CAs from the fungi, suggesting how CAs may be considered as a novel "pathogen protein" target of many opportunistic, pathogenic fungi.

Biochemical and structural characterisation of a protozoan beta-carbonic anhydrase from Trichomonas vaginalis

We report the biochemical and structural characterisation of a beta-carbonic anhydrase (β-CA) from Trichomonas vaginalis, a unicellular parasite responsible for one of the world’s leading sexually transmitted infections, trichomoniasis. CAs are ubiquitous metalloenzymes belonging to eight evolutionarily divergent groups (α, β, γ, δ, ζ, η, θ, and ι); humans express only α-CAs, whereas many clinically significant pathogens express only β- and/or γ-CAs. For this reason, the latter two groups of CAs are promising biomedical targets for novel antiinfective agents. The β-CA from T. vaginalis (TvaCA1) was recombinantly produced and biochemically characterised. The crystal structure was determined, revealing the canonical dimeric fold of β-CAs and the main features of the enzyme active site. The comparison with the active site of human CA enzymes revealed significant differences that can be exploited for the design of inhibitors selective for the protozoan enzyme with respect to the human ones.

Structural insights into novel mechanisms of inhibition of the major β-carbonic anhydrase CafB from the pathogenic fungus Aspergillus fumigatus

In fungi the β-class of carbonic anhydrases (β-CAs) are zinc metalloenzymes that are essential for growth, survival, differentiation, and virulence. Aspergillus fumigatus is the most important pathogen responsible for invasive aspergillosis and possesses two major β-CAs, CafA and CafB. Recently we reported the biochemical characterization and 1.8 Å crystal structure of CafA. Here, we report a crystallographic analysis of CafB revealing the mechanism of enzyme catalysis and establish the relationship of this enzyme to other β-CAs. While CafA has a typical open conformation, CafB, when exposed to acidic pH and/or an oxidative environment, has a novel type of active site in which a disulfide bond is formed between two zinc-ligating cysteines, expelling the zinc ion and stabilizing the inactive form of the enzyme. Based on the structural data, we generated an oxidation-resistant mutant (Y159A) of CafB. The crystal structure of the mutant under reducing conditions retains a catalytic zinc at the expected position, tetrahedrally coordinated by three residues (C57, H113 and C116) and an aspartic acid (D59), and replacing the zinc-bound water molecule in the closed form. Furthermore, the active site of CafB crystals grown under zinc-limiting conditions has a novel conformation in which the solvent-exposed catalytic cysteine (C116) is flipped out of the metal coordination sphere, facilitating release of the zinc ion. Taken together, our results suggest that A. fumigatus use sophisticated activity-inhibiting strategies to enhance its survival during infection.

Activation studies of the β-carbonic anhydrases from Malassezia restricta with amines and amino acids

The β-carbonic anhydrase (CA, EC 4.2.1.1) from the genome of the opportunistic pathogen Malassezia restricta (MreCA), which was recently cloned and characterised, herein has been investigated for enzymatic activation by a panel of amines and amino acids. Of the 24 compounds tested in this study, the most effective MreCA activators were L-adrenaline (KA of 15 nM), 2-aminoethyl-piperazine/morpholine (KAs of 0.25-0.33 µM), histamine, L-4-amino-phenylalanine, D-Phe, L-/D-DOPA, and L-/D-Trp (KAs of 0.32 - 0.90 µM). The least effective activators were L-/D-Tyr, L-Asp, L-/D-Glu, and L-His, with activation constants ranging between 4.04 and 12.8 µM. As MreCA is involved in dandruff and seborrhoeic dermatitis, these results are of interest to identify modulators of the activity of enzymes involved in the metabolic processes of such fungi.

Activation studies of the β-carbonic anhydrases from Escherichia coli with amino acids and amines

A β-carbonic anhydrase (CA, EC 4.2.1.1) from the widespread bacterium Escherichia coli (EcoCAβ), encoded by the CynT2 gene, has been investigated for its catalytic properties and enzymatic activation by a panel of amino acids and amines. EcoCAβ showed a significant catalytic activity for the hydration of CO2 to bicarbonate and a proton, with a kinetic constant kcat of 5.3 × 105 s- and a Michaelis-Menten constant KM of 12.9 mM. The most effective EcoCAβ activators were L- and D-DOPA, L-Tyr, 4-amino-Phe, serotonin and L-adrenaline, with KAs from 2.76 to 10.7 µM. L-His, 2-pyridyl-methylamine, L-Asn and L-Gln were relatively weak activators (KAs from 36.0 to 49.5 µM). D-His, L- and D-Phe, L- and D-Trp, D-Tyr, histamine, dopamine, 2-(aminoethyl)pyridine/piperazine/morpholine, L-Asp, L- and D-Glu have KAs from 11.3 to 23.7 µM. Endogenous CA activators may play a role in bacterial virulence and colonisation of the host.

Phosphonamidates are the first phosphorus-based zinc binding motif to show inhibition of β-class carbonic anhydrases from bacteria, fungi, and protozoa

A primary strategy to combat antimicrobial resistance is the identification of novel therapeutic targets and anti-infectives with alternative mechanisms of action. The inhibition of the metalloenzymes carbonic anhydrases (CAs, EC 4.2.1.1) from pathogens (bacteria, fungi, and protozoa) was shown to produce an impairment of the microorganism growth and virulence. As phosphonamidates have been recently validated as human α-CA inhibitors (CAIs) and no phosphorus-based zinc-binding group have been assessed to date against β-class CAs, herein we report an inhibition study with this class of compounds against β-CAs from pathogenic bacteria, fungi, and protozoa. Our data suggest that phosphonamidates are among the CAIs with the best selectivity for β-class over human isozymes, making them interesting leads for the development of new anti-infectives.

Molecular dynamics simulations identify the regions of compromised thermostability in SazCA

The present study examined the structure and dynamics of the most active and thermostable carbonic anhydrase, SazCA, probed using molecular dynamics simulations. The molecular system was described by widely used biological force-fields (AMBER, CHARMM22, CHARMM36, and OPLS-AA) in conjunction with TIP3P water model. The comparison of molecular dynamics simulation results suggested AMBER to be a suitable choice to describe the structure and dynamics of SazCA. In addition to this, we also addressed the effect of temperature on the stability of SazCA. We performed molecular dynamics simulations at 313, 333, 353, 373, and 393 K to study the relationship between thermostability and flexibility in SazCA. The amino acid residues VAL98, ASN99, GLY100, LYS101, GLU145, and HIS207 were identified as the most flexible residues from root-mean-square fluctuations. The salt bridge analysis showed that ion-pairs ASP113-LYS81, ASP115-LYS81, ASP115-LYS114, GLU144-LYS143, and GLU144-LYS206, were responsible for the compromised thermal stability of SazCA.

Crystal Structure of β-Carbonic Anhydrase CafA from the Fungal Pathogen Aspergillus fumigatus

The β-class of carbonic anhydrases (β-CAs) are zinc metalloenzymes widely distributed in the fungal kingdom that play essential roles in growth, survival, differentiation, and virulence by catalyzing the reversible interconversion of carbon dioxide (CO2) and bicarbonate (HCO3-). Herein, we report the biochemical and crystallographic characterization of the β-CA CafA from the fungal pathogen Aspergillus fumigatus, the main causative agent of invasive aspergillosis. CafA exhibited apparent in vitro CO2 hydration activity in neutral to weak alkaline conditions, but little activity at acidic pH. The high-resolution crystal structure of CafA revealed a tetramer comprising a dimer of dimers, in which the catalytic zinc ion is tetrahedrally coordinated by three conserved residues (C119, H175, C178) and an acetate anion presumably acquired from the crystallization solution, indicating a freely accessible ″open″ conformation. Furthermore, knowledge of the structure of CafA in complex with the potent inhibitor acetazolamide, together with its functional intolerance of nitrate (NO3-) ions, could be exploited to develop new antifungal agents for the treatment of invasive aspergillosis.

Structural and biochemical characterization of novel carbonic anhydrases from Phaeodactylum tricornutum

Carbonic anhydrases (CAs) are a well characterized family of metalloenzymes that are highly efficient in facilitating the interconversion between carbon dioxide and bicarbonate. Recently, CA activity has been associated with the LCIB (limiting CO₂-inducible protein B) protein family, which has been an interesting target in aquatic photosynthetic microorganisms. To gain further insight into the catalytic mechanism of this new group of CAs, the X-ray structure of a highly active LCIB homolog (PtLCIB3) from the diatom Phaeodactylum tricornutum was determined. The CA activities of PtLCIB3, its paralog PtLCIB4 and a variety of their mutants were also measured. It was discovered that PtLCIB3 has a classic β-CA fold and its overall structure is highly similar to that of its homolog PtLCIB4. Subtle structural alterations between PtLCIB3 and PtLCIB4 indicate that an alternative proton-shuttle cavity could perhaps be one reason for their remarkable difference in CA activity. A potential alternative proton-shuttle route in the LCIB protein family is suggested based on these results.

Anion Inhibition Studies of the β-Class Carbonic Anhydrase CAS3 from the Filamentous Ascomycete Sordaria macrospora

CAS3 is a newly cloned cytosolic β-class carbonic anhydrase (CA, EC 4.2.1.1) from the filamentous ascomycete Sordaria macrospora. This enzyme has a high catalytic activity for the physiological CO₂ hydration reaction and herein, we report the inhibition profile of CAS3 with anions and small molecules. The most effective CAS3 anions/small molecule inhibitors were diethyl-dithiocarbamate, sulfamide, sulfamate, phenyl boronic and phenyl arsonic acids, with K_Is in the range of 0.89 mM–97 µM. Anions such as iodide, the pseudohalides, bicarbonate, carbonate, nitrate, nitrite, hydrogensulfide, stannate, selenate, tellurate, tetraborate, perrhenate, perruthenate, selenocyanide and trithiocarbonate were low millimolar CAS3 inhibitors. The light halides, sulfate, hydrogensulfite, peroxydisulfate, diphosphate, divanadate, perchlorate, tetrafluoroborate, fluorosulfonate and iminodisulfonate did not significantly inhibit this enzyme. These data may be useful for developing antifungals based on CA inhibition, considering the fact that many of the inhibitors reported here may be used as lead molecules and, by incorporating the appropriate organic scaffolds, potent nanomolar inhibitors could be developed.

Sulfonamide Inhibition Studies of the β-Class Carbonic Anhydrase CAS3 from the Filamentous Ascomycete Sordaria macrospora

A new β-class carbonic anhydrase was cloned and purified from the filamentous ascomycete Sordaria macrospora, CAS3. This enzyme has a higher catalytic activity compared to the other two such enzymes from this fungus, CAS1 and CAS2, which were reported earlier, with the following kinetic parameters: k_cat of (7.9 ± 0.2) × 10⁵ s⁻¹, and k_cat/K_m of (9.5 ± 0.12) × 10⁷ M⁻¹∙s⁻¹. An inhibition study with a panel of sulfonamides and one sulfamate was also performed. The most effective CAS3 inhibitors were benzolamide, brinzolamide, dichlorophnamide, methazolamide, acetazolamide, ethoxzolamide, sulfanilamide, methanilamide, and benzene-1,3-disulfonamide, with K_Is in the range of 54–95 nM. CAS3 generally shows a higher affinity for this class of inhibitors compared to CAS1 and CAS2. As S. macrospora is a model organism for the study of fruiting body development in fungi, these data may be useful for developing antifungal compounds based on CA inhibition.

Sulfonamide Inhibition Profile of the β-Carbonic Anhydrase from Malassezia restricta, An Opportunistic Pathogen Triggering Scalp Conditions

The critical CO₂ hydration reaction to bicarbonate and protons is catalyzed by carbonic anhydrases (CAs, EC 4.2.1.1). Their physiological role is to assist the transport of the CO₂ and HCO₃⁻ at the cellular level, which will not be ensured by the low velocity of the uncatalyzed reaction. CA inhibition may impair the growth of microorganisms. In the yeasts, Candida albicans and Malassezia globosa, the activity of the unique β-CA identified in their genomes was demonstrated to be essential for growth of the pathogen. Here, we decided to investigate the sulfonamide inhibition profile of the homologous β-CA (MreCA) identified in the genome of Malassezia restricta, an opportunistic pathogen triggering dandruff and seborrheic dermatitis. Among 40 investigated derivatives, the best MreCA sulfonamide inhibitors were dorzolamide, brinzolamide, indisulam, valdecoxib, sulthiam, and acetazolamide (K_I < 1.0 μM). The MreCA inhibition profile was different from those of the homologous enzyme from Malassezia globosa (MgCA) and the human isoenzymes (hCA I and hCA II). These results might be useful to for designing CA inhibitor scaffolds that may selectively inhibit the dandruff-producing fungi.

Crystal structure and chemical inhibition of essential schistosome host-interactive virulence factor carbonic anhydrase SmCA

The intravascular parasitic worm Schistosoma mansoni is a causative agent of schistosomiasis, a disease of great global public health significance. Here we identify an α-carbonic anhydrase (SmCA) that is expressed at the schistosome surface as determined by activity assays and immunofluorescence/immunogold localization. Suppressing SmCA expression by RNAi significantly impairs the ability of larval parasites to infect mice, validating SmCA as a rational drug target. Purified, recombinant SmCA possesses extremely rapid CO₂ hydration kinetics (k_cat: 1.2 × 10⁶ s^-1; k_cat/K_m: 1.3 × 10⁸ M^-1s^-1). The enzyme’s crystal structure was determined at 1.75 Å resolution and a collection of sulfonamides and anions were tested for their ability to impede rSmCA action. Several compounds (phenylarsonic acid, phenylbaronic acid, sulfamide) exhibited favorable K_is for SmCA versus two human isoforms. Such selective rSmCA inhibitors could form the basis of urgently needed new drugs that block essential schistosome metabolism, blunt parasite virulence and debilitate these important global pathogens.

Akram Da’dara et al. report the biochemical characterization of an α-carbonic anhydrase (SmCA) expressed at the surface of the parasitic worm Schistosoma mansoni. Along with the crystal structure of SmCA, they show the function of selective inhibitors in blocking essential schistosome metabolism.

The structural basis of the low catalytic activities of the two minor β-carbonic anhydrases of the filamentous fungus Aspergillus fumigatus

The β-carbonic anhydrases (β-CAs) are widely distributed zinc-metalloenzymes that play essential roles in growth, survival, development and virulence in fungi. The majority of filamentous ascomycetes possess multiple β-CA isoforms among which major and minor forms have been characterized. We examined the catalytic behavior of the two minor β-CAs, CafC and CafD, of Aspergillus fumigatus, and found that both enzymes exhibited low CO₂ hydration activities. To understand the structural basis of their low activities, we performed X-ray crystallographic and site-directed mutagenesis studies. Both enzymes exist as homodimers. Like other Type-I β-CAs, the CafC active site has an "open" conformation in which the zinc ion is tetrahedrally coordinated by three residues (C36, H88 and C91) and a water molecule. However, L25 and L78 on the rim of the catalytic entry site protrude into the active site cleft, partially occluding access to it. Single (L25G or L78G) and double mutants provided evidence that widening the entrance to the active site greatly accelerates catalytic activity. By contrast, CafD has a typical Type-II "closed" conformation in which the zinc-bound water molecule is replaced by aspartic acid (D36). The most likely explanation for this result is that an arginine that is largely conserved within the β-CA family is replaced by glycine (G38), so that D36 cannot undergo a conformational change by forming a D-R pair that creates the space for a zinc-bound water molecule and switches the enzyme to the active form. The CafD structure also reveals the presence of a "non-catalytic" zinc ion in the dimer interface, which may contribute to stabilizing the dimeric assembly.

Anion Inhibition Profile of the β-Carbonic Anhydrase from the Opportunist Pathogenic Fungus Malassezia Restricta Involved in Dandruff and Seborrheic Dermatitis

Carbonic anhydrases (CAs, EC 4.2.1.1) are ubiquitous metalloenzymes, which catalyze the crucial physiological CO₂ hydration/dehydration reaction (CO₂ + H₂O ⇌ HCO₃^- + H⁺) balancing the equilibrium between CO₂, H₂CO₃, HCO₃^- and CO₃^2-. It has been demonstrated that their selective inhibition alters the equilibrium of the metabolites above affecting the biosynthesis and energy metabolism of the organism. In this context, our interest has been focalized on the fungus Malassezia restricta, which may trigger dandruff and seborrheic dermatitis altering the complex bacterial and fungal equilibrium of the human scalp. We investigated a rather large number of inorganic metal-complexing anions (a well-known class of CA inhibitors) for their interaction with the β-CA (MreCA) encoded by the M. restricta genome. The results were compared with those obtained for the two human ?-CA isoforms (hCAI and hCAII) and the β-CA from Malassezia globosa. The most effective MreCA inhibitors were diethyldithiocarbamate, sulfamide, phenyl arsenic acid, stannate, tellurate, tetraborate, selenocyanate, trithiocarbonate, and bicarbonate. The different K_I values obtained for the four proteins investigated might be attributed to the architectural features of their catalytic site. The anion inhibition profile is essential for better understanding the inhibition/catalytic mechanisms of these enzymes and for designing novel types of inhibitors, which may have clinical applications for the management of dandruff and seborrheic dermatitis.

Cloning, Purification, and Characterization of a β-Carbonic Anhydrase from Malassezia restricta, an Opportunistic Pathogen Involved in Dandruff and Seborrheic Dermatitis

The cloning, purification, and initial characterization of the β-carbonic anhydrase (CA, EC 4.2.1.1) from the genome of the opportunistic pathogen Malassezia restricta (MreCA), which a fungus involved in dandruff and seborrheic dermatitis (SD), is reported. MreCA is a protein consisting of 230 amino acid residues and shows high catalytic activity for the hydration of CO₂ into bicarbonate and protons, with the following kinetic parameters: k_cat of 1.06 × 10⁶ s⁻¹ and k_cat/K_M of 1.07 × 10⁸ M⁻¹ s⁻¹. It is also sensitive to inhibition by the sulfonamide acetazolamide (K_I of 50.7 nM). Phylogenetically, MreCA and other CAs from various Malassezia species seem to be on a different branch, distinct from that of other β-CAs found in fungi, such as Candida spp., Saccharomyces cerevisiae, Aspergillus fumigatus, and Sordaria macrospora, with only Cryptococcus neoformans and Ustilago maydis enzymes clustering near MreCA. The further characterization of this enzyme and the identification of inhibitors that may interfere with its life cycle might constitute new strategies for fighting dandruff and SD.

Benzenesulfonamides incorporating nitrogenous bases show effective inhibition of β-carbonic anhydrases from the pathogenic fungi Cryptococcus neoformans, Candida glabrata and Malassezia globosa

There is an urgent need for new chemotherapic agents to treat human fungal infections due to emerging and spreading globally resistance mechanisms. Among the new targets that have been recently investigated for the development of antifungal drugs there are the metallo-enzymes Carbonic Anhydrases (CAs, EC 4.2.1.1). The inhibition of the β-CAs identified in many pathogenic fungi leads to an impairment of parasite growth and virulence, which in turn leads to a significant anti-infective effect. Based on antifungal nucleoside antibiotics, the inhibition of the β-CAs from the resistance-showing fungi Candida glabrata (CgNce103), Cryptococcus neoformans (Can2) and Malasszia globosa (MgCA) with a series of benzenesulfonamides bearing nitrogenous bases, such as uracil and adenine, is here reported. Many such compounds display low nanomolar (<100 nM) inhibitory potency against Can2 and CgNce103, whereas the activity of MgCA is considerably less affected (inhibition constants in the range 138.8-5601.5 nM). The β-CAs inhibitory data were compared with those against α-class human ubiquitous isoforms. Interesting selective inhibitory activities for the target fungal CAs over hCA I and II were reported, which make nitrogenous base benzenesulfonamides interesting tools and leads for further investigations in search of new antifungal with innovative mechanisms of action.

N-Nitrosulfonamides as Carbonic Anhydrase Inhibitors: A Promising Chemotype for Targeting Chagas Disease and Leishmaniasis

Trypanosoma cruzi and Leishmania spp. are protozoa of the Trypanosomatidae family, respectively, responsible of the neglected tropical disorders (NTDs) Chagas disease and leishmaniasis. The present pharmacotherapy is often ineffective and exhibits serious side effects. The metalloenzyme carbonic anhydrases (CAs, EC 4.2.1.1) recently identified in these protozoans (α-TcCA and β-LdcCA) are novel promising targets for chemotherapeutic interventions. Herein, we report a series of N-nitrosulfonamides, as a novel chemotype to yield the target CA isoform selective inhibition over ubiquitous human isozymes. Two derivatives selected among the most active and selective ones for TcCA/LdcCA over off-target CAs were progressed as silver salts to in vitro studies with various developmental forms and spp of Trypanosoma cruzi and leishmania. Excellent values of parasites growth inhibition (IC₅₀) were observed, with some selectivity index (over cytotoxicity for macrophages and Vero cells) being comparable or better than reference drugs. These findings make N-nitrosulfonamides and their salts promising lead compounds for a rational optimization of innovative agents for the treatment of Chagas disease and leishmaniasis based on CA inhibition.

Novel 2-indolinones containing a sulfonamide moiety as selective inhibitors of candida β-carbonic anhydrase enzyme

Inhibition of the β-carbonic anhydrase (CA, EC 4.2.1.1) from pathogenic Candida glabrata (CgNce103) by 1H-indole-2,3-dione 3-[N-(4-sulfamoylphenyl)thiosemicarbazones] 4a–m was investigated. All the compounds were found to be potent inhibitors of CgNce103, with inhibition constants in the range of 6.4-63.9 nM. The 5,7-dichloro substituted derivative 4l showed the most effective inhibition (K_I of 6.4 nM) as well as the highest selectivity for inhibiting CgNce103 over the cytosolic human (h) isoforms hCA I and II. A possible binding interaction of compound 4l within the active site of CgNce103 has been proposed based on docking studies.

Sulfonamide inhibition studies of two β-carbonic anhydrases from the ascomycete fungus Sordaria macrospora, CAS1 and CAS2

The two β-carbonic anhydrases (CAs, EC 4.2.1.1) recently cloned and purified from the ascomycete fungus Sordaria macrospora, CAS1 and CAS2, were investigated for their inhibition with a panel of 39 aromatic, heterocyclic, and aliphatic sulfonamides and one sulfamate, many of which are clinically used agents. CAS1 was efficiently inhibited by tosylamide, 3-fluorosulfanilamide, and 3-chlorosulfanilamide (KIs in the range of 43.2-79.6 nM), whereas acetazolamide, methazolamide, topiramate, ethoxzolamide, dorzolamide, and brinzolamide were medium potency inhibitors (KIs in the range of 360-445 nM). CAS2 was less sensitive to sulfonamide inhibitors. The best CAS2 inhibitors were 5-amino-1,3,4-thiadiazole-2-sulfonamide (the deacetylated acetazolamide precursor) and 4-hydroxymethyl-benzenesulfonamide, with KIs in the range of 48.1-92.5 nM. Acetazolamide, dorzolamide, ethoxzolamide, topiramate, sulpiride, indisulam, celecoxib, and sulthiame were medium potency CAS2 inhibitors (KIs of 143-857 nM). Many other sulfonamides showed affinities in the high micromolar range or were ineffective as CAS1/2 inhibitors. Small changes in the structure of the inhibitor led to important differences of the activity. As these enzymes may show applications for the removal of anthropically generated polluting gases, finding modulators of their activity may be crucial for designing environmental-friendly CO2 capture processes.

Activation of β- and γ-carbonic anhydrases from pathogenic bacteria with tripeptides

Six tripeptides incorporating acidic amino acid residues were prepared for investigation as activators of β- and γ-carbonic anhydrases (CAs, EC 4.2.1.1) from the pathogenic bacteria Vibrio cholerae, Mycobacterium tuberculosis, and Burkholderia pseudomallei. The primary amino acid residues that are involved in the catalytic mechanisms of these CA classes are poorly understood, although glutamic acid residues near the active site appear to be involved. The tripeptides that contain Glu or Asp residues can effectively activate VchCAβ and VchCAγ (enzymes from V. cholerae), Rv3273 CA (mtCA3, a β-CA from M. tuberculosis) and BpsCAγ (γ-CA from B. pseudomallei) at 0.21-18.1 µM levels. The position of the acidic residues in the peptide sequences can significantly affect bioactivity. For three of the enzymes, tripeptides were identified that are more effective activators than both l-Glu and l-Asp. The tripeptides are also relatively selective because they do not activate prototypical α-CAs (human carbonic anhydrases I and II). Because the role of CA activators in the pathogenicity and life cycles of these infectious bacteria are poorly understood, this study provides new molecular probes to explore such processes.

Discovering a new class of antifungal agents that selectively inhibits microbial carbonic anhydrases

Infections caused by pathogens resistant to the available antimicrobial treatments represent nowadays a threat to global public health. Recently, it has been demonstrated that carbonic anhydrases (CAs) are essential for the growth of many pathogens and their inhibition leads to growth defects. Principal drawbacks in using CA inhibitors (CAIs) as antimicrobial agents are the side effects due to the lack of selectivity toward human CA isoforms. Herein we report a new class of CAIs, which preferentially interacts with microbial CA active sites over the human ones. The mechanism of action of these inhibitors was investigated against an important fungal pathogen, Cryptococcus neoformans, revealing that they are also able to inhibit CA in microbial cells growing in vitro. At our best knowledge, this is the first report on newly designed synthetic compounds selectively targeting β-CAs and provides a proof of concept of microbial CAs suitability as an antimicrobial drug target.

Discovery of potent anti-convulsant carbonic anhydrase inhibitors: Design, synthesis, in vitro and in vivo appraisal

We report the design, synthesis and pharmacological assessment of novel benzenesulfonamide derivatives acting as effective carbonic anhydrase (CA, EC 4.2.1.1) inhibitors. All the synthesized compounds were screened for their CA inhibitory action against four isoforms of human origin (h), i.e. hCA I, hCA II, hCA VII and hCA IX. In-vitro carbonic anhydrase inhibition studies have shown that first series, 4-(2-(4-(4-substitutedpiperazin-1-yl)benzylidene)hydrazinyl)benzenesulfonamides (4a- 4i) bestowed low nanomolar range to medium nanomolar range inhibitors against hCA II and hCA VII, effectively involved in epileptogenesis. Furthermore, compounds belonging to the second series, 4-(2-(4-(4-substitutedpiperazin-yl)benzylidene)hydrazinecarbonyl)benzenesulfonamides (8a-8k) showed effective inhibition against hCA VII, being less effective against other hCA isoforms. Inspiring with obtained CA inhibition results, we have chosen some of the potent hCA II and hCA VII inhibitors (4g, 4i and 8d) to test their anti-convulsant efficacy in MES and sc-PTZ seizure tests in Swiss Albino male mice. In result, these compounds significantly attenuated both electrical (MES) as well as chemical (sc-PTZ) induced seizures. Next, in advance anticonvulsant tests, compound 8d displayed long duration of action in time course study and successfully attenuated MES induced seizure in mice up to 6 h after drug administration without showing neurotoxicity in rotarod test. Moreover, this compound was also found to be orally active and effectively abolished generalized tonic-clonic seizures in male Wistar rats upon oral administration, being non-toxic in sub acute toxicity studies.

Dioxygen, an unexpected carbonic anhydrase ligand

Carbonic anhydrases (CAs, EC 4.2.1.1) are ubiquitous metalloenzymes, grouped into seven different classes, which catalyze the reaction of CO₂ hydration to bicarbonate and protons. All of the fifteen human isoforms reported to date belong to the α-class and contain zinc as a cofactor. The structure of human Zn,Cu-CA II has been solved which contains a copper ion bound at its N-terminal, coordinated to His4 and His64. In the active site a dioxygen molecule is coordinated to the zinc ion. Since dioxygen is a rather unexpected CA ligand, molecular dynamics (MD) simulations were performed which suggested a superoxide character of the zinc bound O₂.

Benzoxaborole compounds for therapeutic uses: a patent review (2010- 2018)

INTRODUCTION

Benzoxaborole is a versatile boron-heterocyclic scaffold which has found in the last 10 years a broad spectrum of applications in medicinal chemistry, due to its physicochemical and drug-like properties. Use of benzoxaborole moiety in the design of compounds led to the discovery of new classes of anti-bacterial, anti-fungal, anti-protozoal, anti-viral as well as anti-inflammatory agents with interesting drug development perspectives.

AREAS COVERED

This article reviews the patent literature as well as chemistry literature during the period 2010-2018 where in several benzoxaborole derivatives with therapeutic options were reported.

EXPERT OPINION

Two benzoxaborole derivatives are already clinically used for the treatment of onychomycosis (tavaborole) and atopic dermatitis (crisaborole), with several others in various phases of clinical trials. By inhibiting enzymes essential in the life cycle of fungal, protozoan, bacterial and viral pathogens, it is probable that other compounds may soon enter the armamentarium of anti-infective agents. On the other hand, phosphodiesterase 4 seems to be the human target responsible of the anti-inflammatory action of some benzoxaboroles. The chemical versatility, peculiar mechanism of action related to the electron deficient nature of the boron atom, and ease of preparation make benzoxaboroles a highly interesting field for the pharmaceutical industry.

Discovery of Benzenesulfonamide Derivatives as Carbonic Anhydrase Inhibitors with Effective Anticonvulsant Action: Design, Synthesis, and Pharmacological Evaluation

Two series of novel benzenesulfonamide derivatives were synthesized and evaluated for their human carbonic anhydrase (CA, EC 4.2.1.1) inhibitory activity against four isoforms, hCA I, hCA II, hCA VII, and hCA IX. It was found that compounds of both series showed low to medium nanomolar inhibitory potential against all isoforms. Some of these derivatives displayed selective inhibition against the epileptogenesis related isoforms hCA II and VII, within the nanomolar range. These potent hCA II and VII inhibitors were evaluated as anticonvulsant agents against MES and sc-PTZ induced convulsions. These sulfonamides effectively abolished induced seizures in both models. Furthermore, time dependent seizure protection capability of the most potent compound was also evaluated. A long duration of action was displayed, with efficacy up to 6 h after drug administration. The compound appeared as an orally active anticonvulsant agent without showing neurotoxicity in a rotarod test, a nontoxic chemical profile being observed in subacute toxicity study.

Natural Polyphenols Selectively Inhibit β-Carbonic Anhydrase from the Dandruff-Producing Fungus Malassezia globosa: Activity and Modeling Studies

Around 50 % of the worldwide population is affected by dandruff, which is triggered by a variety of factors. The yeast Malassezia globosa has been labeled as the most probable causative agent for the onset of dandruff. The β-carbonic anhydrase (CA) of MgCA was recently validated as an anti-dandruff target, with its inhibition being responsible for in vivo growth defects in the fungus. As classical CA inhibitors of the sulfonamide type give rise to permeability problems through biological membranes, finding non-sulfonamide alternatives for MgCA inhibition is of considerable interest in the cosmetic field. We recently screened a large library of human (h) CA inhibitors for MgCA inhibition, including different chemotypes, such as monothiocarbamates, dithiocarbamates, phenols, and benzoxaboroles. Herein, we expanded the research toward new MgCA inhibitors by considering a set of natural polyphenols (including flavones, flavonols, flavanones, flavanols, isoflavones, and depsides) that exhibited MgCA inhibitory activity in the micromolar range, as well as selectivity for the fungal isozyme over off-target human isoforms. The binding mode of representative derivatives within the MgCA catalytic cleft was investigated by docking studies using a homology-built model.

A class of carbonic anhydrase I - selective activators

A series of ureido and bis-ureido derivatives were prepared by reacting histamine with alkyl/aryl-isocyanates or di-isocyanates. The obtained derivatives were assayed as activators of the enzyme carbonic anhydrase (CA, EC 4.2.1.1), due to the fact that histamine itself has this biological activity. Although inhibition of CAs has pharmacological applications in the field of antiglaucoma, anticonvulsant, anticancer, and anti-infective agents, activation of these enzymes is not yet properly exploited pharmacologically for cognitive enhancement or Alzheimer's disease treatment, conditions in which a diminished CA activity was reported. The ureido/bis-ureido histamine derivatives investigated here showed activating effects only against the cytosolic human (h) isoform hCA I, having no effect on the widespread, physiologically dominant isoform hCA II. This is the first report in which CA I-selective activators were identified. Such compounds may constitute interesting tools for better understanding the physiological/pharmacological effects connected to activation of this widespread CA isoform, whose physiological function is not fully understood.

Benzoxaboroles as Efficient Inhibitors of the β-Carbonic Anhydrases from Pathogenic Fungi: Activity and Modeling Study

A series of 6-substituted benzoxaboroles were investigated as inhibitors of the β-class carbonic anhydrase from three pathogenic fungi (Cryptococcus neoformans, Candida glabrata, and Malassezia globosa). Independently from the nature of the substituents on the phenyl of the urea/thiourea group, all reported derivatives showed nanomolar inhibitory activities against Can2 and CgNce103 vs micromolar inhibition against MgCA. Selectivity over human CA I and CA II was noticed. The observed structure-activity relationship trends have been rationalized by modeling study of selected compounds into the active site of Can2 and MgCA. The present letter demonstrates that benzoxaborole chemotype may offer interesting opportunities for the inhibition of β-CA from pathogenic fungi and for the development of antifungal agents with a new mechanism of action.

Structure and function of carbonic anhydrases

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyse the interconversion between CO2 and bicarbonate as well as other hydrolytic reactions. Among the six genetic families known to date, the α-, β-, γ-, δ-, ζ- and η-CAs, detailed kinetic and X-ray crystallographic studies have allowed a deep understanding of the structure-function relationship in this superfamily of proteins. A metal hydroxide nucleophilic species of the enzyme, and a unique active site architecture, with half of it hydrophilic and the opposing part hydrophobic, allow these enzymes to act as some of the most effective catalysts known in Nature. The CA activation and inhibition mechanisms are also known in detail, with a large number of new inhibitor classes being described in the last years. Apart from the zinc binders, some classes of inhibitors anchor to the metal ion coordinated nucleophile, others occlude the entrance of the active site cavity and more recently, compounds binding outside the active site were described. CA inhibition has therapeutic applications for drugs acting as diuretics, antiepileptics, antiglaucoma, antiobesity and antitumour agents. Targeting such enzymes from pathogens may lead to novel anti-infectives. Successful structure-based drug design campaigns allowed the discovery of highly isoform selective CA inhibitors (CAIs), which may lead to a new generation of drugs targeting these widespread enzymes. The use of CAs in CO2 capture processes for mitigating the global temperature rise has also been investigated more recently.