Quantitative structure-activity relationship study on some 5-lipoxygenase inhibitors

A quantitative structure-activity relationship (QSAR) study has been made on some lipoxygenase inhibitors belonging to the series of omega-phenylalkyl hydroxamic acids, omega-naphthylalkyl hydroxamic acids, eicosatetraenoic acids, and 1H.benzimidazole-4-ols. It was found that the hydrophobic character of the molecules and the size of their substituents selectively govern their lipoxygenase inhibitory activity. The enzyme active site possesses a non-heme ferric ion, a hydrophobic domain, and a carboxylic acid binding site. It was found that while the functional group of inhibitors must interact with the ferric ion, the substituent on one side of it would be involved in hydrophobic interaction and that on the other side in van der Waals interaction with the enzyme so leading to an enhancement in the inhibitory activity of the inhibitors.     

Quantitative structure-activity relationship study on some dihydropteridine reductase inhibitors

The dihydropteridine reductase (DHPR) inhibitory potencies of some 4-phenyltetrahydropyridines, 4-phenylpiperidines, and 4-phenylpyridines, are analyzed in relation to their physico-chemical and molecular properties. They are found to have significant correlation with Hammett constant sigma and the van der Waals volume Vw. The correlation is linear with sigma and parabolic with Vw. Hence, it is argued that DHPR inhibition involves dispersion interaction and is enhanced by electron donation from the substituents but hindered by steric effects produced by large substituents. It is also found that these electronic and steric effects are significant only when they are produced by substituents being at specific position in the molecules.     

A quantitative structure-activity relationship study on some aromatic/heterocyclic sulfonamides and their charged derivatives acting as carbonic anhydrase inhibitors

A quantitative structure-activity relationship (QSAR) study is made on a series of aromatic/heterocyclic sulfonamides and their charged derivatives acting as carbonic anhydrase (CA) inhibitors. These compounds were studied by Scozzafava et al. (J. Med. Chem. 2000; 43: 292) for the selective inhibition of CAs--sulfonamides generally do not discriminate between different CA isozymes and hence exhibit many undesirable side effects when used as drugs against a particular disease. In this communication, an attempt has been made to investigate the physicochemical and structural properties that can make them selective for a given CA isozyme. Based on in vitro data reported by Scozzafava et al. against two cytosolic isozymes and one membrane-bound isozyme, the QSAR study has shown that uncharged compounds cannot be made selective for cytosolic or membrane-bound isozyme since in both the cases the compounds appear to follow the same mechanism of inhibition. However, for the charged compounds the polarizability of the molecule seems to greatly favor the inhibition of the membrane-bound enzyme, and hence they can be made selective for this enzyme by enhancing their polarizability, which is found to play no role in the inhibition of cytosolic enzymes.     

Exploring structure-activity relationship of S-substituted 2-mercaptoquinazolin-4(3H)-one including 4-ethylbenzenesulfonamides as human carbonic anhydrase inhibitors

Abstract

Inhibitory action of newly synthesised 4-(2-(2-substituted-thio-4-oxoquinazolin-3(4H)-yl)ethyl)benzenesulfonamides compounds 2–13 against human carbonic anhydrase (CA, EC 4.2.1.1) (hCA) isoforms I, II, IX, and XII, was evaluated. hCA I was efficiently inhibited by compounds 2–13 with inhibition constants (K_Is) ranging from 57.8–740.2?nM. Compounds 2, 3, 4, and 12 showed inhibitory action against hCA II with K_Is between 6.4 and 14.2?nM. CA IX exhibited significant sensitivity to inhibition by derivatives 2–13 with K_I values ranging from 7.1 to 93.6?nM. Compounds 2, 3, 4, 8, 9, and 12 also exerted potent inhibitory action against hCA XII (K_Is ranging from 3.1 to 20.2?nM). Molecular docking studies for the most potent compounds 2 and 3 were conducted to exhibit the binding mode towards hCA isoforms as a promising step for SAR analyses which showed similar interaction with co-crystallized ligands. As such, a subset of these mercaptoquinazolin-4(3H)-one compounds represented interesting leads for developing new efficient and selective carbonic anhydrase inhibitors (CAIs) for the management of a variety of diseases including glaucoma, epilepsy, arthritis and cancer.     

Quantitative structure-activity relationship study of benzylsulfanyl imidazoles as cytokine release inhibitors

Benzylsulfanyl imidazole derivatives (Figure 1) have shown their ability to inhibit the release of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) from peripheral blood mononuclear cells or human whole blood. Such anticytokine actions of these congeners are quantitatively studied using Fujita-Ban and Hansch type analyses. The Fujita-Ban study resulted in the contributions of different substituents and the parent moiety for the inhibitions of cytokines TNF-alpha and IL-1beta. The substituents that have a higher positive contribution to the given activity, relative to substituents of the parent moiety at different positions were then used to obtain a trend for the active analogues. None of the substituents present at X, Y, 2-R and 3-R, appears to be advantageous over the substituents of the parent moiety for inhibition of both the cytokines. However, the substituents at 4-R, 5-R and 6-R help to improve the inhibitory actions of the compounds for both cytokines. The optimal activities seem to be manifested by compounds in which 4-R, 5-R and 6-R are substituted respectively by OH (or SOCH3 and SO2CH3), Cl and OH for inhibition of TNF-alpha, whereas by SOCH3 (or SO2CH3 and OH), H and OH for inhibition of IL-1beta. The Hansch type analysis, on the other hand, revealed that the F-substituents of the X-position and a less bulky structural moiety such as--S(CH2)2--at the Y-incision are advantageous in improving the inhibitory action towards TNF-alpha. Similarly, a less bulky/polar substituent present at 2-R and not having a hydrogen-bond donor property, while a more hydrophobic substituent at 3-R and hydrogen-bond acceptor substituent at 4-R are helpful in augmenting inhibitory activity of a compound. However, for inhibition of cytokine IL-1beta, it emerged that the X-substituents that transmits a higher negative resonance effect, the Y-substituent that offers less molecular bulk are beneficial. The R-substituents, being more electron donors at the meta-position, less hydrophobic at the para-position and offering smaller refractivity (less bulky and or polar) at the ortho-position are likewise helpful in improving the activity of a compound.     

Branchial carbonic anhydrase (CA) of gills of Chasmagnathus granulata (Crustacea Decapoda)

The occurrence, localization and response to environmental salinity of carbonic anhydrase (CA) activity were studied in all of the gills of the euryhaline crab Chasmagnathus granulata from Mar Chiquita coastal lagoon (Buenos Aires Province, Argentina). CA activity in all gills appeared to be dependent on salinity. The pattern of distribution of CA activity among gills was different upon transition of C. granulata from osmoionoconformity (more uniform distribution) to hyperregulation (highest activity in posterior gills 6-8). Upon abrupt salinity change a differential response of CA activity occurred among gills which could suggest a differential role of CA in ion transport process in different gills of this crab. Furthermore, CA activity in anterior and posterior gills was found in cytosolic and microsomal fractions, although highest activity appeared to be membrane-associated. Both pools of CA were also strongly influenced by salinity and very sensitive to sulfonamide acetazolamide. The results suggest a differential participation of branchial CA in ionoregulatory mechanisms of C. granulata.     

QSAR study on benzenesulphonamide carbonic anhydrase inhibitors: topological approach using Balaban index

QSAR study on benzenesulphonamide carbonic anhydrase inhibitors has been made using the most discriminatory Balaban index (J). The regression analysis has shown that even in monoparametric regression this index gave excellent results. Furthermore, using the combination of the Balaban Index (J) with the first-order Randic connectivity index ((1)chi) and indicator parameters, tremendous improvement in the statistics has been observed. The results are critically discussed on the basis of regression data and cross-validation parameters.     

Quantitative structure-activity relationship (QSAR) of indoloacetamides as inhibitors of human isoprenylcysteine carboxyl methyltransferase

A QSAR is developed for the isoprenylcysteine carboxyl methyltransferase (ICMT) inhibitory activities of a series of indoloacetamides (n=72) that are structurally related to cysmethynil, a selective ICMT inhibitor. Multivariate analytical tools (principal component analysis (PCA) and projection to latent structures (PLS)), multi-linear regression (MLR) and comparative molecular field analysis (CoMFA) are used to develop a suitably predictive model for the purpose of optimizing and identifying members with more potent inhibitory activity. The resulting model shows that good activity is determined largely by the characteristics of the substituent attached to the indole nitrogen, which should be a lipophilic residue with fairly wide dimensions. In contrast, the substituted phenyl ring attached to the indole ring must be of limited dimensions and lipophilicity.     

Quantitative assessment of specific carbonic anhydrase inhibitors effect on hypoxic cells using electrical impedance assays

Carbonic anhydrase IX (CA IX) is an important orchestrator of hypoxic tumour environment, associated with tumour progression, high incidence of metastasis and poor response to therapy. Due to its tumour specificity and involvement in associated pathological processes: tumourigenesis, angiogenesis, inhibiting CA IX enzymatic activity has become a valid therapeutic option. Dynamic cell-based biosensing platforms can complement cell-free and end-point analyses and supports the process of design and selection of potent and selective inhibitors. In this context, we assess the effectiveness of recently emerged CA IX inhibitors (sulphonamides and sulphocoumarins) and their antitumour potential using an electrical impedance spectroscopy biosensing platform. The analysis allows discriminating between the inhibitory capacities of the compounds and their inhibition mechanisms. Microscopy and biochemical assays complemented the analysis and validated impedance findings establishing a powerful biosensing tool for the evaluation of carbonic anhydrase inhibitors potency, effective for the screening and design of anticancer pharmacological agents.     

Quantitative structure-activity relationship study of 5-iodo- and diaryl-analogues of tubercidin: inhibitors of adenosine kinase

The adenosine kinase inhibitory (AKI) activity of 5-iodo and diaryl analogues of tubercidin is quantitatively analyzed using Fujita-Ban and Hansch type analyses. The Fujita-Ban analysis being a non-parametric approach assigned the highest contribution to Cl at the X-position, C6H4-4-Cl, C6H5, 2-furanyl and I at the Y-position and CH2NH2 and CH3 at the Z-position. In addition, a OH substituent at the C-position also emerged as a better choice possibly due to its engagement in hydrogen bonding with some active site function. Thus a compound having Cl, C6H4-4-Cl, CH2NH2 and OH respectively at X-, Y-, Z- and C-positions is predicted to have a potency nearly 1.5 orders of magnitude higher than the most potent compound of the parent data set. The Hansch type analysis, on the other hand, is a parametric approach and is carried out on two sub-sets of original compounds. This sub-division is based on size and nature of the substituents present at the X- and Y-positions. For the compounds in the first sub-set the derived significant correlation equation suggested that the substituent at the Y-position exhibiting a higher field effect and a substituent such as Cl and CH2NH2 at X- and Z-positions, respectively, are important for a compound to show increased AKI activity. Thio/alkylthio at X and CH2OCH3 at Z, on the other hand, lead to a detrimental effect. Similarly for the compounds in the second subset, the derived significant correlation equation showed that a substituent at the X-position having a higher negative field effect, a substituent at the Y-position having bulky groups and the C-position occupied by a OH group are essential for enhancement of the activity of a compound.     

A nuclear-magnetic-resonance study of the binding of novel N-hydroxybenzenesulphonamide carbonic anhydrase inhibitors to native and cadmium-111-substituted carbonic anhydrase

Various ring- and nitrogen-substituted benzenesulphonamides have been prepared and tested as potential inhibitors of carbonic anhydrase. N-Methoxysulphonamides showed no inhibitory activity, as predicted by the classic work of Krebs on N-substituted inhibitors. By contrast, N-hydroxysulphonamides proved to be very effective inhibitors of carbonic anhydrase. Using 111Cd-NMR it has been possible to analyse the molecular interaction of 4-fluoro-N-hydroxybenzenesulphon[15N]amide, with 111Cd-substituted bovine carbonic anhydrase. A large cadmium-111:nitrogen-15 spin-coupling shows that this inhibitor is directly bound to the metal via its nitrogen rather than through an oxygen atom. The mode of this binding is similar to that for the unsubstituted sulphonamide inhibitor, 4-fluorobenzenesulphon[15N]amide. The 111Cd-chemical shift of the signal for the inhibited enzyme shows that the N-hydroxysulphonamide is bound as its anion. From the relative intensities of free and complexed enzyme signals it can be deduced that the cadmium enzyme complex with the N-hydroxysulphonamide has a longer life-time than that formed with the unsubstituted sulphonamide. By contrast, native zinc-containing bovine carbonic anhydrase shows similar I50 values with both of these sulphonamides. Attempts to monitor the binding using 15N-NMR were unsuccessful, possibly due to a very long relaxation time for the nitrogen nucleus in the N-hydroxysulphonamide when bound to the enzyme leading to loss of the 15N signal.     

A high activity carbonic anhydrase isoenzyme (CA II) is present in mammalian spermatozoa

Summary Human and rat spermatozoa were stained for different carbonic anhydrase (CA) isoenzymes using specific antisera to human CA I, II and VI in conjunction with the immunofluorescence technique. The spermatozoa of both species were found to contain only CA II, which was located principally in the postacrosomal region of the human spermatozoa and in the acrosomal cap region of the rat spermatozoa. The presence of CA II could be confirmed by immunoblotting, which revealed a 29 K polypeptide in both the human and rat spermatozoa. No CA I or VI-specific fluorescence could be detected in the spermatozoa of either species. The immunoblottings were also negative. The results show mammalian spermatozoa to contain the high activity carbonic anhydrase isoenzyme II. Its presence is probably linked to hydration of CO₂ produced by active energy metabolism and thereby to the maintaining of an adequate intraspermatozoal bicarbonate concentration as required for the maintenance of sperm motility.     

A high activity carbonic anhydrase isoenzyme (CA II) is present in mammalian spermatozoa

Human and rat spermatozoa were stained for different carbonic anhydrase (CA) isoenzymes using specific antisera to human CA I, II and VI in conjunction with the immunofluorescence technique. The spermatozoa of both species were found to contain only CA II, which was located principally in the postacrosomal region of the human spermatozoa and in the acrosomal cap region of the rat spermatozoa. The presence of CA II could be confirmed by immunoblotting, which revealed a 29 K polypeptide in both the human and rat spermatozoa. No CA I or VI-specific fluorescence could be detected in the spermatozoa of either species. The immunoblottings were also negative. The results show mammalian spermatozoa to contain the high activity carbonic anhydrase isoenzyme II. Its presence is probably linked to hydration of CO2 produced by active energy metabolism and thereby to the maintaining of an adequate intraspermatozoal bicarbonate concentration as required for the maintenance of sperm motility.     

Effects of human carbonic anhydrase III (CA III) on synovial and muscle fibroblast glycosaminoglycan metabolism

We investigated the ability of CA III, isolated from adult human skeletal muscle, to regulate cell growth and glycosaminoglycan (GAG) formation in connective tissue cells derived from various human tissues. Unlike muscle, dermal, and cartilage fibroblasts, synovial connective tissue cells were substantially activated by CA III and showed enhanced hyaluronic acid (HA) synthesis. Cell culture experiments showed that CA III induced a 2- to 11-fold increase in [14C]HA synthesis by human synovial fibroblasts (SF) in a dose-dependent manner (P less than 0.001); erythrocyte CA I and CA II were inactive. Exposure of SF and muscle fibroblasts to CA III also resulted in a 20-45% and 16-70% increased 35S incorporation into proteoglycans, respectively. When adult human skin and cartilage fibroblasts were studied in the presence of CA III, no differences in the level of DNA and GAG formation were noted. These latter cell types were clearly activated by a platelet (CTAP-III) growth factor. The potential physiological implications of these observations are discussed.     

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 K_i 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.     

Quantitative structure-activity relationship study of orally active cyclooxygenase-2 (COX-2) inhibitors of derivatives of 3-phenoxypyran-4-one

The cyclooxygenase (COX) inhibition activities of the derivatives of 3-phenoxypyran-4-one were analyzed through multiple-regression analysis (MRA). Appropriate physicochemical parameters, identified for the substitutents of phenyl ring, attached to 3-phenoxypyran-4-one moiety were quantitatively correlated with COX-2 and COX-1 inhibition activities of these compounds. The derived significant correlation equation for COX-2 inhibition suggested that the ortho-substituent with negative resonance parameter, the para-substituent with lower dipole moment and the meta-substituent having higher resonance parameter were advantageous for the activity. The derived correlation equation for COX-1 inhibition suggested the significance of resonance effect for ortho-substituents and electron-donating effect for para-substituent. A few potential congeners were also suggested for further synthesis.     

Potent isothiocyanate inhibitors of carbonic anhydrase: synthesis and evaluation

The reversible hydration of carbon dioxide by carbonic anhydrase (CA) regulates pH and carbon dioxide concentrations in diverse biological systems. Potent irreversible inhibition of CA would facilitate study of the dynamics of CA turnover as well as therapeutic effects due to long-term inhibition of the enzyme. We have synthesized isothiocyanate-containing sulfonamide inhibitors of CA from the corresponding aminosulfonamides. Significant increases in apparent binding of some of the isothiocyanate inhibitors over the amine analogues were consistent with covalent inhibition of the enzyme.     

Quantitative structure-activity relationship study on some nonpeptidal cholecystokinin antagonists.

A quantitative structure-activity relationship (QSAR) analysis has been performed on a series of 1,4-benzodiazepine derivatives, which were found to act as antagonists of cholecystokinin (CCK), a gastrointestinal peptide hormone. The CCK acts with three different receptor subtypes termed as CCK-A, CCK-B, and gastrin receptor, which can be found in peripheral system, brain, and stomach, respectively. With all the three subtypes, the binding of the compounds is found to significantly depend on the lipophilicity of the compounds and their ability to form the hydrogen bonds with the receptor. However, the binding sites in CCK-A receptor seem to be slightly rigid as compared to those in CCK-B or gastrin receptor. The latter two appear to have similar binding features.     

Quantitative structure-activity relationship of hydroxyl-substituent Schiff bases in radical-induced hemolysis of human erythrocytes

The major objective of this work was to explore the quantitative structure-activity relationship (QSAR) of hydroxyl-substituent Schiff bases in protecting human erythrocytes against 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH)- induced hemolysis, in which 10 Schiff bases including 4-phenyliminomethylphenol (PIH); 4-((4-hydroxybenzylidene) amino)phenol (PAH); 2-methoxy-4-((4-hydroxyphenylimino)methyl)phenol (PMH); 4-((furan-2-ylmethylene)amino) phenol (FAH); 4-((4-N,N-dimethylaminobenzylidene)amino)phenol (PDH); 2-((4-N,N-dimethylaminobenzylidene)amino) phenol (ODH); 2-(naphthalene-1-yliminomethyl)phenol (NAH); 2-(benzyliminomethyl)phenol (BPH); 1,4-di((2-hydroxyphenylimino) methyl)benzene (DOH); 1,4-di((4-hydroxyphenylimino)methyl)benzene DPH, were available for this in vitro experimental system. The results revealed that the radical-scavenging activity of the --OH attached to the para position of methylene in Schiff base was much lower than that attached to the ortho position of the N atom. The large conjugate system and low steric hindrance in the framework of Schiff base benefit the Schiff base to trap radicals. Meanwhile, since a Schiff base, even without any substituent, can also play an antioxidative role in this experimental system, the QSAR results suggest that hydroxyl-substituent Schiff bases are potential drugs in the treatment of radical-related diseases, and provide more information for designing novel drugs.