Carbonic anhydrase inhibitors: synthesis and inhibition of cytosolic/tumor-associated carbonic anhydrase isozymes I, II, and IX with bis-sulfamates

pH regulators and their inhibitors in tumor microenvironment

As an important characteristic of tumor, acidic tumor microenvironment (TME) is closely related to immune escape, invasion, migration and drug resistance of tumor. The acidity of the TME mainly comes from the acidic products produced by the high level of tumor metabolism, such as lactic acid and carbon dioxide. pH regulators such as monocarboxylate transporters (MCTs), carbonic anhydrase IX (CA IX), and Na+/H+ exchange 1 (NHE1) expel protons directly or indirectly from the tumor to maintain the pH balance of tumor cells and create an acidic TME. We review the functions of several pH regulators involved in the construction of acidic TME, the structure and structure-activity relationship of pH regulator inhibitors, and provide strategies for the development of small-molecule antitumor inhibitors based on these targets.

Evaluation of Betulinic Acid Derivatives as PET Tracers for Hypoxia-Induced Carbonic Anhydrase IX (CA IX) Expression

Non-invasive visualisation of the expression of hypoxia-related proteins, such as carbonic anhydrase IX (CA IX), by positron emission tomography (PET) could provide important information on the oxygenation status of tumours. Since betulinic acid derivatives bind specifically to CA IX the aim of the study was the development betulinic acid-based 68Ga-labelled PET tracers and to evaluate the hypoxia detecting properties in vitro and in vivo. The binding of betulinic acid (B-DOTA) and betulinyl-3-sulfamate (BS-DOTA) was assessed in two rat tumour cell lines (AT1 prostate and Walker-256 mammary carcinomas). AT1 cells express CA IX in a hypoxia-dependent manner whereas Walker-256 cells, expressing almost no CA IX in wildtype, were transfected with the rat Car9 gene. In vivo measurements were carried out in a small animal PET/CT in AT1 tumours in rats breathing room air, 8% or 100% O2. In AT1 cells hypoxia-induced overexpression of CA IX led to a stronger binding of BS-DOTA but not of B-DOTA. The BS-DOTA binding correlated linearly with the CA IX protein expression and could be blocked by an excess of unlabelled tracer. In the transfected Walker-256 cells no specific binding of either of the tracers was seen. In vivo the intratumoral accumulation of BS-DOTA was increased in animals kept under inspiratory hypoxia and reduced by hyperoxia. Therefore, betulinyl-3-sulfamate could be used as a PET tracer of CA IX expression in tumours and to provide information about the oxygenation status. However, accumulation data indicated that binding not only depends on hypoxia-induce CA IX expression but also on the tumour-line-specific basal expression and on the initial oxygenation status of the tumour.

Carbonic Anhydrase IX Inhibitors as Candidates for Combination Therapy of Solid Tumors

Combination therapy is becoming imperative for the treatment of many cancers, as it provides a higher chance of avoiding drug resistance and tumor recurrence. Among the resistance-conferring factors, the tumor microenvironment plays a major role, and therefore, represents a viable target for adjuvant therapeutic agents. Thus, hypoxia and extracellular acidosis are known to select for the most aggressive and resilient phenotypes and build poorly responsive regions of the tumor mass. Carbonic anhydrase (CA, EC 4.2.1.1) IX isoform is a surficial zinc metalloenzyme that is proven to play a central role in regulating intra and extracellular pH, as well as modulating invasion and metastasis processes. With its strong association and distribution in various tumor tissues and well-known druggability, this protein holds great promise as a target to pharmacologically interfere with the tumor microenvironment by using drug combination regimens. In the present review, we summarized recent publications revealing the potential of CA IX inhibitors to intensify cancer chemotherapy and overcome drug resistance in preclinical settings.

Betulin Sulfonamides as Carbonic Anhydrase Inhibitors and Anticancer Agents in Breast Cancer Cells

Hypoxia-regulated protein carbonic anhydrase IX (CA IX) is up-regulated in different tumor entities and correlated with poor prognosis in breast cancer patients. Due to the radio- and chemotherapy resistance of solid hypoxic tumors, derivatives of betulinic acid (BA), a natural compound with anticancer properties, seem to be promising to benefit these cancer patients. We synthesized new betulin sulfonamides and determined their cytotoxicity in different breast cancer cell lines. Additionally, we investigated their effects on clonogenic survival, cell death, extracellular pH, HIF-1α, CA IX and CA XII protein levels and radiosensitivity. Our study revealed that cytotoxicity increased after treatment with the betulin sulfonamides compared to BA or their precursors, especially in triple-negative breast cancer (TNBC) cells. CA IX activity as well as CA IX and CA XII protein levels were reduced by the betulin sulfonamides. We observed elevated inhibitory efficiency against protumorigenic processes such as proliferation and clonogenic survival and the promotion of cell death and radiosensitivity compared to the precursor derivatives. In particular, TNBC cells showed benefit from the addition of sulfonamides onto BA and revealed that betulin sulfonamides are promising compounds to treat more aggressive breast cancers, or are at the same level against less aggressive breast cancer cells.

MSBA-S - A pentacyclic sulfamate as a new option for radiotherapy of human breast cancer cells

Many pentacyclic triterpenoids show anti-cancer and anti-inflammatory properties. Recently, we detected a pronounced cytotoxicity and radiosensitivity of two betulinyl sulfamates in human breast cancer cells. Besides betulinic acid scaffold (BSBA-S), we synthesized several new sulfamate-coupled scaffolds from oleanolic acid (OSBA-S), ursolic acid (USBA-S), platanic acid (PSBA-S) and maslinic acid (MSBA-S). Highest cytotoxicity was monitored in breast cancer cell lines after MSBA-S treatment showing in SRB assays IC₅₀ values between 3.7 μM and 5.8 μM. Other sulfamate/triterpene conjugates, however, were less cytotoxic holding IC₅₀ values between 6.6 μM and >50 µM, respectively. MSBA-S-treated breast cancer cells displayed significantly reduced clonogenic survival and an increased rate of apoptosis as compared to the other conjugates. In addition, MSBA-S in combination with irradiation resulted in effects on radiosensitivity in MDA-MB-231 cells (DMF₁₀ = 1.14). In particular, ROS formation was strongly assessed in MSBA-S-treated breast cancer cells. Our findings suggest that the sulfamate derivative of maslinic acid MSBA-S might be a new option for the radiation therapy in breast cancer cells.

Combined 3-O-acetylbetulin treatment and carbonic anhydrase IX inhibition results in additive effects on human breast cancer cells

Hypoxia plays a key role in tumor progression and resistance to radiotherapy. Expression of the transmembrane-tethered enzyme carbonic anhydrase IX (CA IX) is strongly induced by hypoxia. High CA IX expression levels correlate with poor prognosis in cancer patients. Previously, we showed that the downregulation of CA IX expression by siRNA interference and the inhibition of CA IX activity results in increased cytotoxicity, inhibition of migration and radiosensitization of hypoxic cancer cells. Betulinic acid (BA) is a natural compound derived from birch bark. It has shown promising anti-tumor effects due to its cancer cell specific cytotoxic properties. We have shown that BA inhibits the HIF-1α pathway, resulting in apoptosis, inhibition of migration and enhanced cytotoxicity of breast cancer cells. In this study, we investigate the effects of the novel betulin derivative 3-O-acetylbetulin (3-AC) and carbonic anhydrase inhibitors (CAI) octyl disulfamate (OCT) or 4-(3-[4-fluorophenyl]ureido)benzenesulfonamide (SLC-0111), on cellular and radiobiological parameters in MDA-MB-231 and MCF-7 cells. Treatment with 3-AC or OCT alone only caused moderate cytotoxicity, reduction in cell migration, ROS production and DNA damage. However, the combined treatment with 3-AC and CAI strongly enhanced radiosensitivity, increased cytotoxicity, inhibited cell motility and enhanced DNA damage. Our findings suggest that the combination of two bioactive drugs 3-AC and a CAI, such as OCT or SLC-0111, could be a promising therapeutic approach for targeting hypoxic tumor cells.

Carbonic anhydrase IX as a novel candidate in liquid biopsy

Among the diagnostic techniques for the identification of tumour biomarkers, the liquid biopsy is considered one that offers future research on precision diagnosis and treatment of tumours in a non-invasive manner. The approach consists of isolating tumor-derived components, such as circulating tumour cells (CTC), tumour cell-free DNA (ctDNA), and extracellular vesicles (EVs), from the patient peripheral blood fluids. These elements constitute a source of genomic and proteomic information for cancer treatment. Within the tumour-derived components of the body fluids, the enzyme indicated with the acronym CA IX and belonging to the superfamily of carbonic anhydrases (CA, EC 4.2.1.1) is a promising aspirant for checking tumours. CA IX is a transmembrane-CA isoform that is strongly overexpressed in many cancers being not much diffused in healthy tissues except the gastrointestinal tract. Here, it is summarised the role of CA IX as tumour-associated protein and its putative relationship in liquid biopsyfor diagnosing and monitoring cancer progression.

In vitro assessment of triterpenoids NVX-207 and betulinyl-bis-sulfamate as a topical treatment for equine skin cancer

Equine sarcoid (ES) is the most prevalent skin tumor in equids worldwide. Additionally, aging grey horses frequently suffer from equine malignant melanoma (EMM). Current local therapies targeting these skin tumors remain challenging. Therefore, more feasible topical treatment options should be considered. In order to develop a topical therapy against ES and EMM, betulinyl-bis-sulfamate and NVX-207, derivatives of the naturally occurring betulin and betulinic acid, respectively, were evaluated for their antiproliferative (crystal violet staining assay), cytotoxic (MTS assay) and apoptotic (AnnexinV staining, cell cycle investigations) effects on primary ES cells, EMM cells and equine dermal fibroblasts in vitro. The more potent derivative was assessed for its in vitro penetration and permeation on isolated equine skin within 30 min and 24 h using Franz-type diffusion cells and HPLC analysis. Betulinyl-bis-sulfamate and NVX-207 inhibited the proliferation and metabolism in ES cells, EMM cells and fibroblasts significantly (p < 0.001) in a time- and dose-dependent manner. NVX-207 had superior anticancer effects compared to betulinyl-bis-sulfamate. Both compounds led to the externalization of phosphatidylserines on the cell membrane and DNA fragmentation, demonstrating that the effective mode of action was apoptosis. After 48 h of treatment with NVX-207, the number of necrotic cells was less than 2% in all cell types. Detected amounts of NVX-207 in the different skin layers exceeded the half-maximal inhibitory concentrations calculated by far. Even though data obtained in vitro are auspicious, the results are not unconditionally applicable to the clinical situation. Consequently, in vivo studies are required to address the antitumoral effects of topically applied NVX-207 in ES and EMM patients.

Multivalent Carbonic Anhydrases Inhibitors

Biomolecular recognition using a multivalent strategy has been successfully applied, this last decade on several biological targets, especially carbohydrate-processing enzymes, proteases, and phosphorylases. This strategy is based on the fact that multivalent interactions of several inhibitory binding units grafted on a presentation platform may enhance the binding affinity and selectivity. The zinc metalloenzymes carbonic anhydrases (CAs, EC 4.2.1.1) are considered as drug targets for several pathologies, and different inhibitors found clinical applications as diuretics, antiglaucoma agents, anticonvulsants, and anticancer agents/diagnostic tools. Their main drawback is related to the lack of isoform selectivity leading to serious side effects for all pathologies in which they are employed. Thus, the multivalent approach may open new opportunities in the drug design of innovative isoform-selective carbonic anhydrase inhibitors with biomedical applications.

Sulfamates in drug design and discovery: Pre-clinical and clinical investigations

In the present article, we reviewed the sulfamate-containing compounds reported as bioactive molecules. The possible molecular targets of sulfamate derivatives include steroid sulfatase enzyme, carbonic anhydrases, acyl transferase, and others. Sulfamate derivatives can help treat hormone-dependent tumors including breast, prostate, and endometrial cancers, Binge eating disorder, migraine, glaucoma, weight loss, and epilepsy. Sulfamate derivatives can act also as calcium sensing receptor agonists and can aid in osteoporosis. Furthermore, acyl sulfamate derivatives can act as antibacterial agents against Gram-positive bacteria. A recent study revealed a new side effect of topiramate, a sulfamate-containing compound, which is sialolithiasis. The structural and biological characteristics of the reviewed compounds are presented in detail.

Inhibition of carbonic anhydrase IX targets primary tumors, metastases, and cancer stem cells: Three for the price of one

Human carbonic anhydrase (CA) IX is a tumor-associated protein, since it is scarcely present in normal tissues, but highly overexpressed in a large number of solid tumors, where it actively contributes to survival and metastatic spread of tumor cells. Due to these features, the characterization of its biochemical, structural, and functional features for drug design purposes has been extensively carried out, with consequent development of several highly selective small molecule inhibitors and monoclonal antibodies to be used for different purposes. Aim of this review is to provide a comprehensive state-of-the-art of studies performed on this enzyme, regarding structural, functional, and biomedical aspects, as well as the development of molecules with diagnostic and therapeutic applications for cancer treatment. A brief description of additional pharmacologic applications for CA IX inhibition in other diseases, such as arthritis and ischemia, is also provided.

Synthesis and carbonic anhydrase inhibitory properties of novel chalcone substituted benzenesulfonamides

Carbonic anhydrases (CAs, EC 4.2.1.1) are crucial metalloenzymes involved in many bioprocesses, through catalysis of the reversible hydration/dehydration process of CO2/HCO3-. The inhibition of human CA isoforms I and II with a new series of sulfonamide derivatives incorporating substituted chalcone moieties were studied in this study. All these newly synthesized sulfonamides demonstrated important inhibitory profiles to these CA isoforms with KIs in the range of 9.88 to 55.43nM, making these compounds interesting leads, with potential applications in medicinal chemistry.

A substituted sulfonamide and its Co (II), Cu (II), and Zn (II) complexes as potential antifungal agents

A sulfonamide 1-tosyl-1-H-benzo(d)imidazol-2-amine (TBZA) and three new complexes of Co(II), Cu(II), and Zn(II) have been synthesized. The compounds have been characterized by elemental analyses, FTIR, ¹H, and ¹³C-NMR spectroscopy. The structure of the TBZA, and its Co(II) and Cu(II) complexes, was determined by X-ray diffraction methods. TBZA and its Co(II) complex crystallize in the triclinic P-1 space group, while the Cu(II) complex crystallizes in the monoclinic P2₁/c space group. Antifungal activity was screened against eight pathogenic yeasts: Candida albicans (DMic 972576), Candida krusei (DMic 951705), Candida glabrata (DMic 982882), Candida tropicalis (DMic 982884), Candida dubliniensis (DMic 93695), Candida guilliermondii (DMic 021150), Cryptococcus neoformans (ATCC 24067), and Cryptococcus gattii (ATCC MYA-4561). Results on the inhibition of various human (h) CAs, hCA I, II, IV, VII, IX, and XII, and pathogenic beta and gamma CAs are also reported.

Betulinyl Sulfamates as Anticancer Agents and Radiosensitizers in Human Breast Cancer Cells

Betulinic acid (BA), a natural compound of birch bark, is cytotoxic for many tumors. Recently, a betulinyl sulfamate was described that inhibits carbonic anhydrases (CA), such as CAIX, an attractive target for tumor-selective therapy strategies in hypoxic cancer cells. Data on combined CAIX inhibition with radiotherapy are rare. In the human breast cancer cell lines MDA-MB231 and MCF7, the effects of BA and betulinyl sulfamates on cellular and radiobiological behavior under normoxia and hypoxia were evaluated. The two most effective betulinyl sulfamates CAI 1 and CAI 3 demonstrated a 1.8–2.8-fold higher cytotoxicity than BA under normoxia in breast cancer cells, with IC₅₀ values between 11.1 and 18.1 µM. BA exhibits its strongest cytotoxicity with IC₅₀ values of 8.2 and 16.4 µM under hypoxia. All three substances show a dose-dependent increase in apoptosis, inhibition of migration, and inhibition of hypoxia-induced gene expression. In combination with irradiation, betulinyl sulfamates act as radiosensitizers, with DMF10 values of 1.47 (CAI 1) and 1.75 (CAI 3) under hypoxia in MDA-MB231 cells. BA showed additive effects in combination with irradiation. Taken together; our results suggest that BA and betulinyl sulfamates seem to be attractive substances to combine with radiotherapy; particularly for hypoxic breast cancer.

Discovering novel carbonic anhydrase type IX (CA IX) inhibitors from seven million compounds using virtual screening and in vitro analysis

Carbonic anhydrase type IX (CA IX) enzyme is mostly over expressed in different cancer cell lines and tumor tissues. Potent CA IX inhibitors can be effective for adjusting the pH imbalance in tumor cells. In the present work, we represented the successful application of high throughput virtual screening (HTVS) of large dataset from ZINC database included of ∼7 million compounds to discover novel inhibitors of CA IX. HTVS and molecular docking were performed using consequence Glide/standard precision (SP), extra precision (XP) and induced fit docking (IFD) molecular docking protocols. For each compound, docking code calculates a set of low-energy poses and then exhaustively scans the binding pocket of the target with small compounds. Novel CA IX inhibitor candidates were suggested based on molecular modeling studies and a few of them were tested using in vitro analysis. These compounds were determined as good inhibitors against human CA IX target with Ki in the range of 0.85-1.58 μM. In order to predict the pharmaceutical properties of the selected compounds, ADME (absorption, distribution, metabolism and excretion) analysis was also carried out.

Carbonic anhydrase IX as an imaging and therapeutic target for tumors and metastases

Carbonic anhydrase IX (CAIX) which is a zinc containing metalloprotein, efficiently catalyzes the reversible hydration of carbon dioxide. It is constitutively up-regulated in several cancer types and has an important role in tumor progression, acidification and metastasis. High expression of CAIX generally correlates with poor prognosis and is related to a decrease in the disease-free interval following successful therapy. Therefore, it is considered as a prognostic indicator in oncology.In this review, we describe CAIX regulation and its role in tumor hypoxia, acidification and metastasis. In addition, the molecular imaging of CAIX and its potential for use in cancer detection, diagnosis, staging, and for use in following therapy response is discussed. Both antibodies and small molecular weight compounds have been used for targeted imaging of CAIX expression. The use of CAIX expression as an attractive and promising candidate marker for systemic anticancer therapy is also discussed.

A new β-carbonic anhydrase from Brucella suis, its cloning, characterization, and inhibition with sulfonamides and sulfamates, leading to impaired pathogen growth

A β-carbonic anhydrase (CA, EC 4.2.1.1) from the bacterial pathogen Brucella suis, bsCA II, has been cloned, purified, and characterized kinetically. bsCA II showed high catalytic activity for the hydration of CO(2) to bicarbonate, with a k(cat) of 1.1×10(6), and k(cat)/K(m) of 8.9×10(7)M(-1)s(-1). A panel of sulfonamides and sulfamates have been investigated for inhibition of this enzyme. All types of activities, from the low nanomolar to the micromolar, have been detected for these derivatives, which showed inhibition constants in the range of 7.3nM-8.56μM. The best bsCA II inhibitors were some glycosylated sulfanilamides, aliphatic sulfamates, and halogenated sulfanilamides, with inhibition constants of 7.3-87nM. Some of these dual inhibitors of bsCA I and II, also inhibited bacterial growth in vitro, in liquid cultures. These promising data on live bacteria allow us to propose bacterial β-CA inhibition as an approach for obtaining anti-infective agents with a new mechanism of action compared to classical antibiotics.

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

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

Carbonic anhydrases: novel therapeutic applications for inhibitors and activators

Carbonic anhydrases (CAs), a group of ubiquitously expressed metalloenzymes, are involved in numerous physiological and pathological processes, including gluconeogenesis, lipogenesis, ureagenesis, tumorigenicity and the growth and virulence of various pathogens. In addition to the established role of CA inhibitors (CAIs) as diuretics and antiglaucoma drugs, it has recently emerged that CAIs could have potential as novel anti-obesity, anticancer and anti-infective drugs. Furthermore, recent studies suggest that CA activation may provide a novel therapy for Alzheimer's disease. This article discusses the biological rationale for the novel uses of inhibitors or activators of CA activity in multiple diseases, and highlights progress in the development of specific modulators of the relevant CA isoforms, some of which are now being evaluated in clinical trials.

Synthesis and biological activity of new 2-amino-8-chloro-5,5-dioxo[1,2,4]triazolo[2,3-b][1,4,2]benzodithiazines

Two series of 1-(6-chloro-1,1-dioxo-1,4,2-benzodithiazin-3-yl)-4-arylsemicarbazides 6-17 and 2-arylamino-8-chloro-5,5-dioxo[1,2,4]triazolo[2,3-b][1,4,2]benzodithiazines 18-26 were prepared in order to evaluate their biological activity. Compounds 6 and 18-26 were tested for their in vitro cytotoxic potency against 12 human cancer cell lines. The compounds 6 and 19 were inactive, whereas triazolobenzodithiazines 18, 20-26 possess tumor growth inhibitory properties. The prominent methyl 8-chloro-2-(4-chlorophenylamino)-5,5-dioxo[1,2,4]triazolo[2,3-b][1,4,2]benzodithiazine-7-carboxylate (21) exhibited potency higher or comparable to cisplatin. Moreover, compounds 6, 9, 19 and 23-25 with structure similar to other chemotherapeutic agents were tested for their antibacterial activity and exhibited MIC and MBC against Staphylococcus aureus (3.9-31.5 microg ml).

Carbonic Anhydrase Inhibitors. The Mitochondrial Isozyme VB as a New Target for Sulfonamide and Sulfamate Inhibitors

A lately discovered carbonic anhydrase (hCA, EC 4.2.1.1), the mitochondrial hCA VB, was cloned, expressed, and purified. Kinetic parameters proved it to be 3.37 times more effective than hCA VA as a catalyst for the physiological reaction, with kcat = 9.5 x 10(5) s(-1) and kcat/K(M) = 9.8 x 10(7) M(-1) s(-1), being second only to hCA II among the 16 isoforms presently known in humans. We investigated the inhibition of hCA VB with a library of sulfonamides/sulfamates, some of which are clinically used compounds. Benzenesulfonamides were ineffective inhibitors, whereas derivatives bearing 4-amino, 4-hydrazino, 4-methyl, 4-carboxy moieties or halogenated sulfanilamides were more effective (Ki's of 1.56-4.3 microM). Among the 10 clinically used compounds, acetazolamide, benzolamide, topiramate, and indisulam showed effective inhibitory activity (Ki's of 18-62 nM). Three compounds showed better activity against hCA VB over hCA II, among which were sulpiride and ethoxzolamide, which were 2 times more effective inhibitors of the mitochondrial over the cytosolic isozyme. hCA VB is a druggable target and some of its inhibitors may lead to the development of novel antiobesity therapies.

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

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

Carbonic anhydrase inhibitors: Inhibition of the transmembrane isozyme XIV with sulfonamides

The inhibition of the last human carbonic anhydrase (CA, EC 4.2.1.1) isozyme (hCA XIV) discovered has been investigated with a series of sulfonamides, including some clinically used derivatives (acetazolamide, methazolamide, ethoxzolamide, dichlorophenamide, dorzolamide, brinzolamide, benzolamide, and zonisamide), as well as the sulfamate antiepileptic drug topiramate. The full-length hCA XIV is an enzyme showing a medium-low catalytic activity, quite similar to that of hCA XII, with the following kinetic parameters at 20 degrees C and pH 7.5, for the CO2 hydration reaction: k(cat) = 3.12 x 10(5) s(-1) and k(cat)/K(M) = 3.9 x 10(7) M(-1) s(-1). All types of activities have been detected for the investigated compounds, with several micromolar inhibitors, including zonisamide, topiramate, and simple sulfanilamide derivatives (K(I)-s in the range of 1.46-6.50 microM). In addition, topiramate and zonisamide were observed to behave as weak hCA XII inhibitors, while zonisamide was an effective hCA IX inhibitor (K(I) of 5.1 nM). Some benzene-1,3-disulfonamide derivatives or simple five-membered heteroaromatic sulfonamides showed K(I)-s in the range of 180-680 nM against hCA XIV, whereas the most effective of such inhibitors, including 3-chloro-/bromo-sulfanilamide, benzolamide-like, ethoxzolamide-like, and acetazolamide/methazolamide-like derivatives, showed inhibition constant in the range of 13-48 nM. The best hCA XIV inhibitor was aminobenzolamide (K(I) of 13 nM), but no CA XIV-selective derivatives were evidenced. There are important differences of affinity of these sulfonamides/sulfamates for the three transmembrane CA isozymes, with CA XII showing the highest affinity, followed by CA IX, whereas CA XIV usually showed the lowest affinity for these inhibitors.

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

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