Carbonic anhydrase inhibitors: N-(p-sulfamoylphenyl)-α-d-glycopyranosylamines as topically acting antiglaucoma agents in hypertensive rabbits

PEG Linker Length Strongly Affects Tumor Cell Killing by PEGylated Carbonic Anhydrase Inhibitors in Hypoxic Carcinomas Expressing Carbonic Anhydrase IX

Hypoxic tumors overexpress membrane-bound isozymes of carbonic anhydrase (CA) CA IX and CA XII, which play key roles in tumor pH homeostasis under hypoxia. Selective inhibition of these CA isozymes has the potential to generate pH imbalances that can lead to tumor cell death. Since these isozymes are dimeric, we designed a series of bifunctional PEGylated CA inhibitors (CAIs) through the attachment of our preoptimized CAI warhead 1,3,4-thiadiazole-2-sulfonamide to polyethylene glycol (PEG) backbones with lengths ranging from 1 KDa to 20 KDa via a succinyl linker. A detailed structure−thermal properties and structure–biological activity relationship study was conducted via differential scanning calorimetry (DSC) and via viability testing in 2D and 3D (tumor spheroids) cancer cell models, either CA IX positive (HT-29 colon cancer, MDA-MB 231 breast cancer, and SKOV-3 ovarian cancer) or CA IX negative (NCI-H23 lung cancer). We identified PEGylated CAIs DTP1K 28, DTP2K 23, and DTP3.4K 29, bearing short and medium PEG backbones, as the most efficient conjugates under both normoxic and hypoxic conditions, and in the tumor spheroid models. PEGylated CAIs did not affect the cell viability of CA IX-negative NCI-H23 tumor spheroids, thus confirming a CA IX-mediated cell killing for these potential anticancer agents.

Structural Basis of Nanomolar Inhibition of Tumor-Associated Carbonic Anhydrase IX: X-Ray Crystallographic and Inhibition Study of Lipophilic Inhibitors with Acetazolamide Backbone

This study provides a structure-activity relationship study of a series of lipophilic carbonic anhydrase (CA) inhibitors with an acetazolamide backbone. The inhibitors were tested against the tumor-expressed CA isozyme IX (CA IX), and the cytosolic CA I, CA II, and membrane-bound CA IV. The study identified several low nanomolar potent inhibitors against CA IX, with lipophilicities spanning two log units. Very potent pan-inhibitors with nanomolar potency against CA IX and sub-nanomolar potency against CA II and CA IV, and with potency against CA I one order of magnitude better than the parent acetazolamide 1 were also identified in this study, together with compounds that displayed selectivity against membrane-bound CA IV. A comprehensive X-ray crystallographic study (12 crystal structures), involving both CA II and a soluble CA IX mimetic (CA IX-mimic), revealed the structural basis of this particular inhibition profile and laid the foundation for further developments toward more potent and selective inhibitors for the tumor-expressed CA IX.

Pyridinium derivatives of 3-aminobenzenesulfonamide are nanomolar-potent inhibitors of tumor-expressed carbonic anhydrase isozymes CA IX and CA XII

Building on the conclusions of previous inhibition studies with pyridinium-benzenesulfonamides from our team and on the X-ray crystal structure of the lead compound identified, a series of 24 pyridinium derivatives of 3-aminobenzenesulfonamide was synthesized and investigated for carbonic anhydrase inhibition. The new pyridinium-sulfonamides were evaluated as inhibitors of four human carbonic anhydrase (CA, EC 4.2.1.1) isoforms, namely CA I, CA II (cytosolic), CA IX and XII (transmembrane, tumor-associated forms). Excellent inhibitory activity in the nanomolar range was observed against CA IX with most of these sulfonamides, and against CA XII (nanomolar/sub-nanomolar) with some of the new compounds. These sulfonamides were generally potent inhibitors of CA II and CA I too. Docking studies revealed a preference of these compounds to bind the P1 hydrophobic site of CAs, supporting the observed inhibition profile. The salt-like nature of these positively charged sulfonamides can further focus the inhibitory ability on membrane-bound CA IX and CA XII and could efficiently decrease the viability of three human carcinomas under hypoxic conditions where these isozymes are over-expressed, thus recommending the new compounds as potential diagnostic tools or therapeutic agents.

Design, synthesis and biological evaluation of carbohydrate-based sulphonamide derivatives as topical antiglaucoma agents through selective inhibition of carbonic anhydrase II

A series of new carbohydrate-based sulphonamide derivatives were designed, synthesised by employing the so-call ‘sugar-tail’ approach. The compounds were evaluated in vitro against a panel of CAs. Compared to their parent compound p-sulfamoylbenzoic acid, these compounds showed nearly 100-fold improvement in their binding affinities against hCA II in vitro. All of compounds showed great water solubility and the pH value of their water solutions of compounds is 7.0. Such properties are advantageous to make them much less irritating to the eye when applied topical glaucomatous drugs, compared to the relatively highly acidic dorzolamide preparations (pH 5.5). Notably, compounds 7d, 7 g, 7 h demonstrated to topically lower intraocular pressure (IOP) in glaucomatous animals better than brinzolamide when applied as a 1% solution directly into the eye. Low cytotoxicity on human cornea epithelial cell was observed in the tested concentrations by the MTT assay.

Study of glycation process of human carbonic anhydrase II as well as investigation concerning inhibitory influence of 3-beta-hydroxybutyrate on it

Glycation is a non-enzymatic reaction between carbonyl groups in sugar and free amino groups in proteins. This reaction leads to changes in structure and functions of proteins in which the advanced glycation end products (AGEs) are the final outcome and cause many complications in diabetic patients. We herein examined the effect of fasting on the glycation process of human Carbonic anhydrase II under physiological conditions (37 °C and pH 7.4) employing various techniques, including Ultraviolet-visible spectroscopy, fluorescence spectroscopy and CD Spectroscopy. We found an increased 3-beta-hydroxybutyrate upon fasting. We studied various samples of control carbonic anhydrase (without glucose and 3-beta-hydroxybutyrate), carbonic anhydrase with glucose, carbonic anhydrase treated with 3-beta-hydroxybutyrate (BHB) and carbonic anhydrase along with glucose and 3-beta-hydroxybutyrate. The samples were incubated for 35 days under physiological conditions. Our results indicated that 3-beta-hydroxybutyrate inhibited the glycation process, decreased glucose binding to the protein, prevented the formation of AGEs, and modified the enzyme activity. Our findings would open new windows toward the enzymatic procedure which would have profound implication in understanding the diabetes mechanisms.

Nanotechnology for Medical and Surgical Glaucoma Therapy-A Review

Glaucoma is the second leading cause of blindness worldwide. Even though significant advances have been made in its management, currently available antiglaucoma therapies suffer from considerable drawbacks. Typically, the success and efficacy of glaucoma medications are undermined by their limited bioavailability to target tissues and the inadequate adherence demonstrated by patients with glaucoma. The latter is due to a gradual decrease in tolerability of lifelong topical therapies and the significant burden to patients of prescribed stepwise antiglaucoma regimens with frequent dosing which impact quality of life. On the other hand, glaucoma surgery is restricted by the inability of antifibrotic agents to efficiently control the wound healing process without causing severe collateral damage and long-term complications. Evolution of the treatment paradigm for patients with glaucoma will ideally include prevention of retinal ganglion cell degeneration by the successful delivery of neurotrophic factors, anti-inflammatory drugs, and gene therapies. Nanotechnology-based treatments may surpass the limitations of currently available glaucoma therapies through optimized targeted drug delivery, increased bioavailability, and controlled release. This review addresses the recent advances in glaucoma treatment strategies employing nanotechnology, including medical and surgical management, neuroregeneration, and neuroprotection.

RES-loaded pegylated CS NPs: for efficient ocular delivery

The objective of this study is to develop resveratrol (RES) loaded polyethylene glycols (PEGs) modified chitosan (CS) nanoparticles (NPs) by ionic gelation method for the treatment of glaucoma. While increasing the concentration of PEG, the particle size and polydispersity index of the formulations increased. Entrapment efficiency and RES loading (RL) of NPs decreased while increasing PEG concentration. The in vitro release of NPs showed an initial burst release of RES (45%) followed by controlled release. Osmolality of formulations revealed that the prepared NPs were iso-osmolar with the tear. Ocular tolerance of the NPs was evaluated using hen's egg test on the chorioallantoic membrane and it showed that the NPs were non-irritant. RES-loaded PEG-modified CS NPs shows an improved corneal permeation compared with RES dispersion. Fluorescein isothiocyanate loaded CS NPs accumulated on the surface of the cornea but the PEG-modified CS NPs crossed the cornea and reached retinal choroid. RES-loaded PEG-modified CS NPs reduced the intra-ocular pressure (IOP) by 4.3 ± 0.5 mmHg up to 8 h in normotensive rabbits. These results indicate that the developed NPs have efficient delivery of RES to the ocular tissues and reduce the IOP for the treatment of glaucoma.

Rational design of reversible inhibitors for trehalose 6-phosphate phosphatases

In some organisms, environmental stress triggers trehalose biosynthesis that is catalyzed collectively by trehalose 6-phosphate synthase, and trehalose 6-phosphate phosphatase (T6PP). T6PP catalyzes the hydrolysis of trehalose 6-phosphate (T6P) to trehalose and inorganic phosphate and is a promising target for the development of antibacterial, antifungal and antihelminthic therapeutics. Herein, we report the design, synthesis and evaluation of a library of aryl d-glucopyranoside 6-sulfates to serve as prototypes for small molecule T6PP inhibitors. Steady-state kinetic techniques were used to measure inhibition constants (K_i) of a panel of structurally diverse T6PP orthologs derived from the pathogens Brugia malayi, Ascaris suum, Mycobacterium tuberculosis, Shigella boydii and Salmonella typhimurium. The binding affinities of the most active inhibitor of these T6PP orthologs, 4-n-octylphenyl α-d-glucopyranoside 6-sulfate (9a), were found to be in the low micromolar range. The K_i of 9a with the B. malayi T6PP ortholog is 5.3 ± 0.6 μM, 70-fold smaller than the substrate Michaelis constant. The binding specificity of 9a was demonstrated using several representative sugar phosphate phosphatases from the HAD enzyme superfamily, the T6PP protein fold family of origin. Lastly, correlations drawn between T6PP active site structure, inhibitor structure and inhibitor binding affinity suggest that the aryl d-glucopyranoside 6-sulfate prototypes will find future applications as a platform for development of tailored second-generation T6PP inhibitors.

PEGylated Bis-Sulfonamide Carbonic Anhydrase Inhibitors Can Efficiently Control the Growth of Several Carbonic Anhydrase IX-Expressing Carcinomas

A series of aromatic/heterocyclic bis-sulfonamides were synthesized from three established aminosulfonamide carbonic anhydrase (CA, EC 4.2.1.1) inhibitor pharmacophores, coupled with either ethylene glycol oligomeric or polymeric diamines to yield bis-sulfonamides with short or long (polymeric) linkers. Testing of novel inhibitors and their precursors against a panel of membrane-bound CA isoforms, including tumor-overexpressed CA IX and XII and cytosolic isozymes, identified nanomolar-potent inhibitors against both classes and several compounds with medium isoform selectivity in a detailed structure-activity relationship study. The ability of CA inhibitors to kill tumor cells overexpressing CA IX and XII was tested under normoxic and hypoxic conditions, using 2D and 3D in vitro cellular models. The study identified a nanomolar potent PEGylated bis-sulfonamide CA inhibitor (25) able to significantly reduce the viability of colon HT-29, breast MDA-MB231, and ovarian SKOV-3 cancer cell lines, thus revealing the potential of polymer conjugates in CA inhibition and cancer treatment.

Development of dorzolamide loaded 6-o-carboxymethyl chitosan nanoparticles for open angle glaucoma

Chitosan (CS) is a biodegradable, biocompatible, and mucoadhesive natural polymer soluble in acidic pH only and can be irritating to the eye. Objective of the study was to synthesize water soluble 6-O-carboxymethyl (OCM-CS) derivative of CS, and to develop CS and OCM-CS nanoparticles (NPs) loaded with dorzolamide hydrochloride (DRZ). CS was reacted with monochloroacetic acid (MCA) for OCM-CS synthesis and was characterized by FT-IR, DSC, and ¹³C NMR. CS and OCM-CS NPs were prepared by ionic gelation method. Ocular irritation potential were evaluated and therapeutic efficacy was measured by reduction in intraocular pressure (IOP) in normotensive rabbits. Maximum yield was obtained when the ratio of water/isopropyl alcohol was 1/4 at 55°C. The FT-IR, DSC and ¹³C NMR confirmed the formation of an ether linkage between hydroxyl groups of CS and MCA. The particle size and zeta potential of optimised CSNPs was 250.3 ± 2.62 nm and +33.47 ± 0.723 mV, whereas those for OCM-CSNPs were 187.1 ± 2.72 nm and 30.87 ± 0.86 mV. The entrapment efficiency was significantly improved for OCM-CSNPs, compared to CSNPs. OCM-CSNPs had tailored drug release and improved bioavailability with reduction in pulse entry as compared to CSNPs. Hence, it can be concluded that DRZ loaded OCM-CSNPs would be better alternative option to available eye drops for glaucoma treatment.

Design of cationic nanostructured heterolipid matrices for ocular delivery of methazolamide

Solid lipid nanoparticles (SLNs) formulated from one type of lipid (homolipid) suffer from low drug encapsulation and drug bursting due to crystallization of the lipid into the more ordered β modification, which leads to decreased drug entrapment and faster drug release. This study assessed the feasibility of using nanostructured lipid matrices (NLMs) for ocular delivery of methazolamide-(MZA) adopting heterolipids composed of novel mixtures of Compritol (®) and cetostearyl alcohol (CSA), and stabilized by Tween 80(®). The systems were prepared using the modified high shear homogenization followed by ultrasonication method, which avoids the use of organic solvents. A 3(2) full factorial design was constructed to study the influence of two independent variables, namely the ratio of CSA:Compritol and the concentration of Tween 80, each in three levels. The dependent variables were the entrapment efficiency percentages (EE%), mean particle size (PS), polydispersity index (PDI), and zeta potential (ZP). In vivo intraocular pressure (IOP) lowering activity for the selected formulae was compared to that of MZA solution. The results showed that increasing the ratio of CSA to Compritol increased the EE% and PS, while increasing the concentration of Tween 80, decreased PS with no significant effect on EE%. The ZP values of all formulae were positive, and greater than 30 mV. The best formula, composed of 4% CSA, 2% Compritol, 0.15% stearylamine, and 2% Tween 80, with EE% of 25.62%, PS of 207.1 nm, PDI of 0.243, and ZP of 41.50 mV, showed in vitro sustained release properties for 8 hours and lowered the intraocular pressure by 8.3 mmHg within 3 hours, with this drop in pressure lasting for 12 hours.

Carbonic anhydrase inhibitors and activators for novel therapeutic applications

Carbonic anhydrases (CAs, Enzyme Commission number 4.2.1.1) catalyze a simple but fundamental reaction, CO2 hydration to yield bicarbonate and protons. CAs belonging to the α-, β-, γ-, δ- and ζ-families are found in many organisms all over the phylogenetic tree and their inhibition/activation have been studied in detail, leading to various therapeutic applications. Inhibition of mammalian α-CAs is exploited by some diuretics, whereas antiglaucoma, anticonvulsant, anti-obesity, altitude sickness and anti-tumor drugs/diagnostic agents target various of the 15 isoforms described so far in these organisms. Activation of some CAs may also have applications in therapy. Bacterial and fungal β-CA inhibitors or nematode α-CA inhibitors have been described that may lead to novel classes of anti-infectives.

Nanovesicular formulation of brimonidine tartrate for the management of glaucoma: in vitro and in vivo evaluation

In this study, nanovesicles were developed for brimonidine tartrate by film hydration technique and dispersed in viscous carbopol solution for ocular delivery. Scanning electron microscopy revealed spherical shape of the vesicles. As high as 32.27% drug entrapment efficiency was achieved depending upon the surfactant/cholesterol molar ratio (7:4 to 7:8). The vesicles were in the size range of 298.0-587.9 nm. Release study showed a biphasic drug-release pattern for the lyophilized vesicular formulation in buffered saline solution, i.e., initial burst release followed by gradual release over the period of 8 h. On contrary, the isolated vesicles reduced the burst effect in 3 h by two to three times and the drug release was comparatively slower at the intermediate ratio in both cases. With variation in cholesterol content, the drug release followed either first order or Higuchi's kinetics. Physically the lyophilized vesicular formulations were more stable at refrigerated temperature. DSC and X-RD analyses indicated loss of drug crystallinity in the vesicles. FTIR spectroscopy did not reveal any interaction between drug and excipients. The lyophilized formulation showed better ocular hypotensive activity than marketed drops on albino rabbits and in vivo efficacy was sustained up to 7.5 h. Furthermore, the formulation was found to be non-irritant to the rabbit eye. Hence, the lyophilized vesicles, when dispersed in viscous carbopol solution, had the potential in reducing dosing frequency and could improve patient compliance.

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.

Pharmacological significance of triazole scaffold

The triazole nucleus is one of the most important and well known heterocycles which is a common and integral feature of a variety of natural products and medicinal agents. Triazole nucleus is present as a core structural component in an array of drug categories such as antimicrobial, anti-inflammatory, analgesic, antiepileptic, antiviral, antineoplastic, antihypertensive, antimalarial, local anaesthetic, antianxiety, antidepressant, antihistaminic, antioxidant, antitubercular, anti-Parkinson's, antidiabetic, antiobesity and immunomodulatory agents, etc. The broad and potent activity of triazole and their derivatives has established them as pharmacologically significant scaffolds. The basic heterocyclic rings present in the various medicinal agents are 1,2,3-triazole and 1,2,4-triazole. A large volume of research has been carried out on triazole and their derivatives, which has proved the pharmacological importance of this heterocyclic nucleus. The present paper is an attempt to review the pharmacological activities reported for triazole derivatives in the current literature with an update of recent research findings on this nuclei.

Therapeutic applications of glycosidic carbonic anhydrase inhibitors

The zinc enzymes carbonic anhydrases (CAs, EC 4.2.1.1) are very efficient catalysts for the reversible hydration of carbon dioxide to bicarbonate and hence play an important physiological role. In humans, 16 different isozymes have been described, some of them being involved in various pathological disorders. Several of these isozymes are considered as drug targets, and the design of selective inhibitors is a long-standing goal that has captured the attention of researchers for 40 years and has lead to clinical applications against different pathologies such as glaucoma, epilepsy, and cancer. Among the different strategies developed for designing selective CA inhibitors (CAIs), the "sugar approach" has recently emerged as a new attractive and versatile tool. Incorporation of glycosyl moieties in different aromatic/heterocyclic sulfonamide/sulfamides/sulfamates scaffolds has led to the development of numerous and very effective inhibitors of potential clinical value. The clinical use of a highly active carbohydrate-based CA inhibitor, i.e., topiramate, constitutes an interesting demonstration of the validity of this approach. Other carbohydrate-based compounds also demonstrate promising potential for the treatment of ophthalmologic diseases. This review will focus on the development of this emerging sugar-based approach for the development of CAIs.

Antibacterial, antifungal and cytotoxic properties of novel N-substituted sulfonamides from 4-hydroxycoumarin

A new series of 4-({[2, 4-dioxo-2H-chromen-3 (4H)-ylidene] methyl} amino) sulfonamides have been obtained by the condensation reaction of 4-hydroxycoumarin with various sulfonamides (sulfanilamide, sulfaguanidine, p-aminomethyl-sufanilamide, p-aminoethylsufanilamide, sulfathiazole, sulfamethoxazole, sulfamethazine and 4-[(2-amino-4-pyrimidinyl) amino] benzenesulfonamide) in the presence of an excess of ethylorthoformate. These compounds were screened for their in-vitro antibacterial activity against four Gram-negative (E. coli, S. flexneri, P. aeruginosa and S. typhi) and two Gram-positive (B. subtilis and S. aureus) bacterial strains and for in-vitro antifungal activity against T. longifusus, C. albicans, A. flavus, M. canis, F. solani and C. glaberata. Results revealed that a significant antibacterial activity was observed by compounds (4) and (5), (6) and (8) against two Gram-negative, (P. aeruginosa and S. typhi) and two Gram-positive (B. subtilis and S. aureus) species, respectively. Of these (4) was found to be the most active. Similarly, for antifungal activity compounds (3) and (8) showed significant activity against M. canis and, (6) and (8) against F. solani. The brine shrimp bioassay was also carried out to study their in-vitro cytotoxic properties and only two compounds, (4) and (8) possessing LD50 = 2.9072 x 10(-4) and 3.2844 x 10(-4) M, respectively, displayed potent cytotoxic activity against Artemia salina

Antibacterial, antifungal and cytotoxic properties of some sulfonamide-derived chromones

A series of antibacterial and antifungal sulfonamide (sulfanilamide, sulfaguanidine, sulfamethaxozole, 4-aminoethylbenzene-sulfonamide and 4-amino-6-trifluoromethyl-benzene-1,3-disulfonamide) derived chromones, previously reported as inhibitors of carbonic anhydrase, have been screened for in-vitro antibacterial activity against four Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi and Shigella flexener) and two Gram-positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains, and for in-vitro antifungal activity against Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani, Candida glaberata. All compounds (1)-(5) showed significant antibacterial activity against all four Gram-negative species and both Gram-positive species. However, three of them, (1), (4) and (5), were found to be comparatively much more active compared to (2) and (3). Of these, (5) was found to be the most active one. For antifungal activity, generally compounds (1) and (2) showed significant activity against more than three strains whereas (3)-(5) also showed significant activity against varied fungal strains. In the brine shrimp bioassay for in-vitro cytotoxic properties, only two compounds, (4) and (5) displayed potent cytotoxic activity, LD50 = 2.732 x 10(-4)M) and LD50 = 2.290 x 10(-4)M) respectively, against Artemia salina.

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.

Carbonic anhydrase inhibitors. Inhibition of cytosolic isoforms I and II, and extracellular isoforms IV, IX, and XII with sulfamides incorporating sugar moieties

A series of glycosylated sulfamides possessing a diverse substitution pattern, with benzylated, peracetylated, and unsaturated six- and five-membered ring sugar moieties attached to the NHSO(2)NH(2) zinc binding group is reported. These derivatives were tested for the inhibition of five human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, hCA I, II, IV, IX, and XII. Against hCA I the sulfamides behaved as weak inhibitors, whereas they showed low nanomolar activity against hCA II, IX, and XII, being slightly less effective as hCA IV inhibitors. One compound showed selectivity for inhibiting the tumor-associated isoforms hCA IX and XII over the ubiquitous cytosolic hCA II. The sulfamide zinc binding group may thus indeed lead to very effective glycosylated inhibitors targeting several physiologically relevant isozymes.

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

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

Carbonic anhydrase inhibitors: Binding of an antiglaucoma glycosyl-sulfanilamide derivative to human isoform II and its consequences for the drug design of enzyme inhibitors incorporating sugar moieties

N-(4-Sulfamoylphenyl)-alpha-d-glucopyranosylamine, a promising topical antiglaucoma agent, is a potent inhibitor of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1). The high resolution X-ray crystal structure of its adduct with the target isoform involved in glaucoma, CA II, is reported here. The sugar sulfanilamide derivative binds to the enzyme in a totally new manner as compared to other CA-inhibitor adducts investigated earlier. The sulfonamide anchor was coordinated to the active site metal ion, and the phenylene ring of the inhibitor filled the channel leading to the active site cavity. The glycosyl moiety responsible for the high water solubility of the compound was oriented towards a hydrophilic region of the active site, where no other inhibitors were observed to be bound up to now. A network of seven hydrogen bonds with four water molecules and the amino acid residues Pro201, Pro202 and Gln92 further stabilize the enzyme-inhibitor adduct. Topiramate, another sugar-based CA inhibitor, binds in a completely different manner to CA II as compared to the sulfonamide investigated here. These findings are useful for the design of potent, sugar-derived enzyme inhibitors.

Liposomes as an ocular delivery system for acetazolamide: in vitro and in vivo studies

The purpose of this study was to formulate topically effective controlled release ophthalmic acetazolamide liposomal formulations. Reverse-phase evaporation and lipid film hydration methods were used for the preparation of reverse-phase evaporation (REVs) and multilamellar (MLVs) acetazolamide liposomes consisting of egg phosphatidylcholine (PC) and cholesterol (CH) in the molar ratios of (7:2), (7:4), (7:6), and (7:7) with or without stearylamine (SA) or dicetyl phosphate (DP) as positive and negative charge inducers, respectively. The prepared liposomes were evaluated for their entrapment efficiency and in vitro release. Multilamellar liposomes entrapped greater amounts of drug than REVs liposomes. Drug loading was increased by increasing CH content as well as by inclusion of SA. Drug release rate showed an order of negatively charged > neutral > positively charged liposomes, which is the reverse of the data of drug loading efficiency. Physical stability study indicated that approximately 89%, 77%, and 69% of acetazolamide was retained in positive, negative, and neutral MLVs liposomal formulations up to a period of 3 months at 4 degrees C. The intraocular pressure (IOP)-lowering activity of selected acetazolamide liposomal formulations was determined and compared with that of plain liposomes and acetazolamide solution. Multilamellar acetazolamide liposomes revealed more prolonged effect than REVs liposomes. The positively charged and neutral liposomes exhibited greater lowering in IOP and a more prolonged effect than the negatively charged ones. The positive multilamellar liposomes composed of PC:CH:SA (7:4:1) molar ratio showed the maximal response, which reached a value of -7.8 +/- 1.04 mmHg after 3 hours of topical administration.

3-demethoxy-3-glycosylaminothiocolchicines: Synthesis of a new class of putative muscle relaxant compounds

A novel class of 3-demethoxy-3-glycosylaminothiocolchicines (7) was prepared and tested for muscle relaxant activity. The syntheses were performed starting from the new 3-amino-3-demethoxythiocolchicine (5) prepared in good yield from 3-O-demethylthiocolchicine (1c) using the Buchwald-Hartwig reaction. The condensation of 5 with a series of pentose and hexose sugars (6) gave a series of 3-demethoxy-3-glycosylaminothiocolchicines (7). Their preparation was accomplished by adapting and improving a previous procedure for the preparation of N-arylglycosylamines. In particular, replacing traditional heating with microwave irradiation represents the key improvement of the process. The biological activity of the 3-demethoxy-3-glycosylaminothiocolchicines (7) was evaluated on GABA and strychnine-sensitive glycine receptors present in rat brain and spinal cord.

Preparation and evaluation of reverse-phase evaporation and multilamellar niosomes as ophthalmic carriers of acetazolamide

Niosomes have been reported as a possible approach to improve the low corneal penetration and bioavailability characteristics shown by conventional ophthalmic vehicles. Niosomes formed from Span 40 or Span 60 and cholesterol in the molar ratios of 7:4, 7:6 and 7:7 were prepared using reverse-phase evaporation and thin film hydration methods. The prepared systems were characterized for entrapment efficiency, size, shape and in vitro drug release. Stability studies were carried out to investigate the leaching of drug from niosomes during storage. The intraocular pressure (IOP) lowering activity of acetazolamide niosomal formulations in rabbits was measured using ShiØtz tonometer. Histological examination for the corneal tissues of rabbits receiving niosomal formulations was carried out for assessment of the ocular irritancy of niosomes. The results showed that the type of surfactant, cholesterol content and the method of preparation altered the entrapment efficiency and drug release rate from niosomes. Higher entrapment efficiency was obtained with multilamellar niosomes prepared from Span 60 and cholesterol in a 7:6 molar ratio. Niosomal formulations have shown a fairly high retention of acetazolamide inside the vesicles (approximately 75%) at a refrigerated temperature up to a period of 3 months. Each of the tested acetazolamide niosomes prepared by either method produced a significant decrease in IOP compared to the solution of free drug and plain niosomes. Multilamellar acetazolamide niosomes formulated with Span 60 and cholesterol in a 7:4 molar ratio were found to be the most effective and showed prolonged decrease in IOP. Histological examination of corneal tissues after instillation of niosomal formulation for 40 days showed slight irritation in the substantia propria of the eye which is reversible and no major changes in tissues were observed.

Carbonic anhydrase inhibitors. Inhibition of cytosolic/tumor-associated carbonic anhydrase isozymes I, II, IX, and XII with Schiff’s bases incorporating chromone and aromatic sulfonamide moieties, and their zinc complexes

A series of Schiff's bases was prepared by reaction of 3-formyl-chromone or 6-methyl-3-formyl-chromone with aromatic sulfonamides, such as sulfanilamide, homosulfanilamide, 4-aminoethyl-benzenesulfonamide, a pyrimidinyl-substituted sulfanilamide derivative, sulfaguanidine and 4-amino-6-trifluoromethyl-benzene-1,3-disulfonamide. The zinc complexes of these sulfonamides have also been obtained. The new derivatives and their Zn(II) complexes were investigated for the inhibition of four physiologically relevant isozymes of carbonic anhydrase (CA, EC 4.2.1.1): the cytosolic isoforms I and II, as well as the tumor-associated, transmembrane isozymes CA IX and XII. Except for the sulfaguanidine-derived compounds which were devoid of activity against all isozymes, the other sulfonamides and their metal complexes showed interesting inhibitory activity. Against isozyme CA I, the inhibition constants were in the range of 13-100 nM, against isozyme CA II in the range of 1.9-102 nM, against isozyme CA IX in the range of 6.3-48nM, and against CA XII in the range of 5.9-50nM. Generally, the formyl-chromone derived compounds were better CA inhibitors as compared to the corresponding 6-methyl-chromone derivatives, and for the simple, benzenesulfonamide derivatives activity increased with an increase of the spacer from sulfanilamide to homosulfanilamide and 4-aminoethylbenzenesulfonamide derivatives, respectively. Some of these compounds may show applications for the development of therapies targeting hypoxic tumors in which CA IX and XII are often highly overexpressed.