QSAR studies on structurally similar 2-(4-methanesulfonylphenyl)pyran-4-ones as selective COX-2 inhibitors: a Hansch approach

QSAR analysis based on classical Hansch approach was adopted on two recently reported novel series of 2-phenylpyran-4-ones as selective cyclooxygenase-2 (COX-2) inhibitors. The 6-methyl derivatives of title compounds bifurcate as 3-phenoxypyran-4-ones (subset A) and 3-phenylpyran-4-ones (subset B) among series 1. Series 2 consists of 5-chloro derivatives of title compounds. Various regression equations were derived to study the influence of phenoxy and phenyl ring substituents of series 1 compounds on COX-2, COX-1 and selective COX-2 over COX-1 inhibitory activity. The best triparametric equation derived for 36 compounds of series 1 explains the hydrophobic, electronic and steric requirements for improved COX-2 inhibitory activity. QSAR model derived to explore the selective COX-2 over COX-1 inhibition showed that selectivity could be influenced by size and lipophilicity of substituents. The size of the first atom of 2 substituents appears to have negative effect on selectivity, whereas highly polar 3 substituents at R are favorable for improved selectivity. QSAR investigations on series 2 compounds revealed some interesting correlation of COX-2 inhibitory activity with calculated physicochemical properties of whole molecules. The positive logP confirms the hydrophobic interaction of series 2 compounds with COX-2 enzyme. The positive MR term indicates that an overall increase in size and polarizabilty of the molecules increases COX-2 inhibitory activity. The positive contribution of structural variable suggests biphenyl analogs are extremely potent COX-2 inhibitors.     

Resveratrol analogues as selective cyclooxygenase-2 inhibitors: synthesis and structure-activity relationship

Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is found in grapes and various medical plants. Among cytotoxic, antifungal, antibacterial cardioprotective activity resveratrol also demonstrates non-selective cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) inhibition. In order to find more selective COX-2 inhibitors a series of methoxylated and hydroxylated resveratrol derivatives were synthesized and evaluated for their ability to inhibit both enzymes using in vitro inhibition assays for COX-1 and COX-2 by measuring PGE(2) production. Hydroxylated but not methoxylated resveratrol derivatives showed a high rate of inhibition. The most potent resveratrol compounds were 3,3',4',5-tetra-trans-hydroxystilbene (COX-1: IC(50)=4.713, COX-2: IC(50)=0.0113 microM, selectivity index=417.08) and 3,3',4,4',5,5'-hexa-hydroxy-trans-stilbene (COX-1: IC(50)=0.748, COX-2: IC(50)=0.00104 microM, selectivity index=719.23). Their selectivity index was in part higher than celecoxib, a selective COX-2 inhibitor already established on the market (COX-1: IC(50)=19.026, COX-2: IC(50)=0.03482 microM, selectivity index=546.41). Effect of structural parameters on COX-2 inhibition was evaluated by quantitative structure-activity relationship (QSAR) analysis and a high correlation was found with the topological surface area TPSA (r=0.93). Docking studies on both COX-1 and COX-2 protein structures also revealed that hydroxylated but not methoxylated resveratrol analogues are able to bind to the previously identified binding sites of the enzymes. Hydroxylated resveratrol analogues therefore represent a novel class of highly selective COX-2 inhibitors and promising candidates for in vivo studies.     

Ligand based design and synthesis of pyrazole based derivatives as selective COX-2 inhibitors

The design and synthesis of novel pyrazole based derivatives has been carried out using the ligand based approach like pharmacophore and QSAR modelling of reported pyrazoles from the available literature to investigate the chemical features that are essential for the design of selective and potent COX-2 inhibitors. Both pharmacophore and QSAR models with good statistical parameters were selected for the design of the lead molecule. Also by exploiting the chemical structures of selective and marketed COX-2 inhibitors, celecoxib and SC-558 were used in designing the molecules which are used in the treatment of inflammation and related disorders. The therapeutic action of the Non-Steroidal Anti-inflammatory Agents (NSAIDs) is based primarily on the COX-2 inhibition. With this background we have synthesized some azomethine derivatives of 3-methyl-1-substituted-4-phenyl-6-[{(1E)-phenylmethylene}amino]-1,4-dihydro pyrano[2,3-c]pyrazole-5-carbonitrile 6(a-o) and were characterized by ¹HNMR, ¹³CNMR and Mass spectral techniques. All the synthesized pyrazole derivatives were tested for in vitro membrane stability property in both COX-1 & COX-2 inhibition studies and in vivo anti-inflammatory activity by carrageenan induced rat paw edema model. Among them, compound 6k showed very good activity by in vivo anti-inflammatory activity with 0.8575 mmol/kg as ED₅₀. Similarly compounds 6m, 6o, 6i and 6h exhibited comparable anti-inflammatory activity to standard drugs. Also the active compounds were further screened for ulcerogenic activity and were found be safer with less ulcer index compared to the marketed drugs like aspirin, ibuprofen and celecoxib.     

A novel genetic model of selective COX-2 inhibition: comparison with COX-2 null mice

Prostaglandin H Synthase (PGHS) is a bi-functional enzyme with a cyclooxygenase (COX) activity and a functionally linked peroxidase (POX) activity that exists in two isoforms (COX-1, COX-2). Non-steroidal anti-inflammatory drugs (NSAIDs), including the selective COX-2 inhibitors, block COX activity while leaving POX activity unscathed. Recently, some selective COX-2 inhibitors were withdrawn from the market due to elevated cardiovascular risk in placebo-controlled trials. Mice deficient for PGHS2 were developed in 1995 and through numerous subsequent studies have revealed significant roles in renal development, ductus arteriosus patency/closure, skin carcinogenesis and cardiovascular function. In this short review, we compare a novel genetic COX-2 selective inhibition mouse model with the originally described COX-2 null mice in these different physiological functions.     

Inhibitory mode of 2-acetoxyphenyl alkyl sulfides against COX-1 and COX-2: QSAR analyses

Selective inhibition of cyclooxygenase-2 (COX-2) inhibitors is an important strategy in design of potent anti-inflammatory compounds with significantly reduced side effects. Therefore, QSAR studies of 2-acetoxyphenyl alkyl sulfides were performed using Bioloom, CAChe 6.1, and Dragon 3.0 for the COX-2 and COX-1 inhibition. The analyses have produced good predictive and statistically significant QSAR models. These studies suggest that lipophilicity affects both COX-1 and COX-2 inhibition in different manner and indicator variables like presence of aromatic ring and triple bond play an important role in COX-2 selectivity. Branching in the molecule, higher path length 6 rich in polarizability, and lesser number of carbonyl groups would be favorable for COX-2 inhibition. Fourth highest eigenvalue of burden matrix corresponding to atomic mass would be favorable for COX-2 inhibition and sixth lowest eigenvalue of burden matrix corresponding to Sanderson electronegativities is conducive for COX-1 inhibition. Lower path length 3 rich in atomic mass and lesser degree of unsaturation in the molecule would be favorable for COX-1 inhibition.     

Synthesis and biological evaluation of 1,3,4-triaryl-3-pyrrolin-2-ones, a new class of selective cyclooxygenase-2 inhibitors

The synthesis and structure activity relationships (SAR) of a series of novel selective COX-2 inhibitors are reported. The results show that some of the 1,3,4-triaryl-3-pyrrolin-2-ones 1 are more potent as COX-2 inhibitors than celecoxib, and that lactam Id has the same selectivity.     

Cardiovascular and gastrointestinal effects of COX-2 inhibitors and NSAIDs: achieving a balance

Conventional 'nonselective' nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used for the treatment of pain and inflammation; however, the potential gastrointestinal risks associated with their use can be a cause for concern. In response to the adverse effects that can accompany nonselective NSAID use, selective cyclo-oxygenase (COX)-2 inhibitors were developed to target the COX-2 isoenzyme, thus providing anti-inflammatory and analgesic benefits while theoretically sparing the gastroprotective activity of the COX-1 isoenzyme. Data from large-scale clinical trials have confirmed that the COX-2 inhibitors are associated with substantial reductions in gastrointestinal risk in the majority of patients who do not receive aspirin. However, some or all of the gastrointestinal benefit of COX-2 inhibitors may be lost in patients who receive low, cardioprotective doses of aspirin, and recent evidence suggests that some of these agents, at some doses, may be associated with an increased risk for cardiovascular adverse events compared with no therapy. The risks and benefits of conventional NSAIDs and of COX-2 inhibitors must be weighed carefully; in clinical practice many patients who might benefit from NSAID or COX-2 therapy are likely to be elderly and at relatively high risk for gastrointestinal and cardiovascular adverse events. These patients are also more likely to be taking low-dose aspirin for cardiovascular prophylaxis and over-the-counter NSAIDs for pain. Identifying therapies that provide relief from arthritis related symptoms, confer optimum cardioprotection, and preserve the gastrointestinal mucosa is complex. Factors to consider include the interference of certain NSAIDs with the antiplatelet effects of aspirin, differences in the adverse gastrointestinal event rates among nonselective NSAIDs and selective COX-2 inhibitors, emerging data regarding the relative risks for cardiovascular events associated with these drugs, and the feasibility and cost of co-therapy with proton pump inhibitors.     

Design,Synthesis and Biological Evaluation of New N-Acyl Hydrazones with a Methyl Sulfonyl Moiety as Selective COX-2 Inhibitors

The mechanism of action of nonsteroidal anti-inflammatory drugs (NSAIDs) is inhibition of specific prostaglandin (PG) synthesis by inhibition of cyclooxygenase (COX) enzymes. The two COX isoenzymes show 60 % similarity. It is known that the nonspecific side effects of conventional NSAIDs are physiologically caused by inhibition of the COX-1 enzyme. Therefore, the use of COX-2 selective inhibitors is seen to be a more beneficial approach in reducing these negative effects. However, some of the existing COX-2 selective inhibitors show cardiovascular side effects. Therefore, studies on the development of new selective COX-2 inhibitors remain necessary. It is important to develop new COX-2 inhibitors in the field of medicinal chemistry. Accordingly, novel N-acyl hydrazone derivatives were synthesized as new COX-2 inhibitors in this study. The hydrazone structure, also known for its COX activity, is important in terms of many biological activities and was preferred as the main structure in the design of these compounds. A methyl sulfonyl pharmacophore was added to the structure in order to increase the affinity for the polar side pocket present in the COX-2 enzyme. It is known that methyl sulfonyl groups are suitable for polar side pockets. The synthesis of the compounds ( 3a – 3j ) was characterized by spectroscopic methods. Evaluation of in vitro COX-1/COX-2 enzyme inhibition was performed by fluorometric method. According to the enzyme inhibition results, the obtained compounds displayed the predicted selectivity for COX-2 enzyme inhibition. Compound 3j showed important COX-2 inhibition with a value of IC₅₀=0.143 uM. Interaction modes between the COX-2 enzyme and compound 3j were investigated by docking studies.     

Chemistry and pharmacokinetics of diarylthiophenes and terphenyls as selective COX-2 inhibitors

DuP697, 2-bromo-4-(4′-sulfonylmethyl)phenyl-5-(4′-fluoro)phenylthiophene, is a selective type 2 cyclooxygenase (COX-2) inhibitor. Its relatively weak COX-2 selectivity coupled with a poor human pharmacokinetic profile led us to seek improvements on the in vitro selectivity while at the same time, addressing some of its pharmacokinetic liabilities. In this paper we discuss some strategies at solving the PK issue within a class of COX-2 inhibitors. The result of these efforts led to the discovery of a new class of COX-2 inhibitors the terphenyls, which prove to be superior alternatives to the diarylthiophenes.     

Yin-yang: balancing act of prostaglandins with opposing functions to regulate inflammation

For many years, cyclooxygenase-2 (COX-2), a critical enzyme for PG production, has been the favorite target for anti-inflammatory drug development. However, recent revelations regarding the adverse effects of selective COX-2 inhibitors have stimulated intense debate. Interestingly, in the early phase of inflammation, COX-2 facilitates inflammatory PG production while in the late phase it has anti-inflammatory effects. Moreover, although some PGs are proinflammatory, others have anti-inflammatory effects. Thus, it is likely that PGs with opposing effects maintain homeostasis, although the molecular mechanism(s) remains unclear. We report here that an inflammatory PG, PGD2, via its receptor, mediates the activation of NF-kappaB stimulating COX-2 gene expression. Most interestingly, an anti-inflammatory PG (PGA1) suppresses NF-kappaB activation and inhibits COX-2 gene expression. We propose that while pro- and anti-inflammatory PGs counteract each other to maintain homeostasis, selective COX-2 inhibitors may disrupt this balance, thereby resulting in reported adverse effects.     

Fluorescence quenching analysis of the association and dissociation of a diarylheterocycle to cyclooxygenase-1 and cyclooxygenase-2: dynamic basis of cyclooxygenase-2 selectivity

Cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) are the enzymes responsible for the biosynthesis of the precursor to the biologically active prostaglandins, prostacyclin, and thromboxane and are the molecular targets for nonsteroidal antiinflammatory drugs (NSAIDs). Selective COX-2 inhibitors are antiinflammatory and analgesic but lack gastrointestinal toxicity, an undesirable side effect attributed to COX-1 inhibition. Crystallographic analysis of selective COX inhibitors complexed with either isoform provides some information about the molecular determinants of selectivity but does not provide information about the dynamics of inhibitor association/dissociation. We employed rapid-mixing techniques and fluorescence quenching to monitor the association and dissociation of a selective COX-2 inhibitor to COX-1 or COX-2. The association of the fluorescent diaryloxazole, SC299, with both enzymes occurs in a time-dependent fashion. Its binding to COX-2 occurs in three kinetically distinct steps whereas its binding to COX-1 occurs in two steps. In contrast to the relatively rapid association of SC299 with both enzymes, its dissociation from COX-2 is quite slow and occurs over several hours whereas the dissociation from COX-1 is complete in less than 1 min. The selectivity of SC299 as a COX-2 inhibitor correlates to its relative rates of dissociation from the two COX isoforms. A model is proposed for diarylheterocycle binding to COX's that integrates these kinetic data with available structural information.     

Selective COX-2 inhibitors. Part 2: synthesis and biological evaluation of 4-benzylideneamino- and 4-phenyliminomethyl-benzenesulfonamides

Two series of 4-benzylideneamino- and 4-phenyliminomethyl-benzenesulfonamide derivatives were designed and synthesized for the evaluation as selective cyclooxygenase-2 (COX-2) inhibitors in a cellular assay using human whole blood (HWB). Extensive structure-activity relationships (SAR) were studied within these series. Several compounds were found to be novel and selective COX-2 inhibitors. Among them, the most potent and selective was 4-(3-carboxy-4-hydroxy-benzylideneamino)benzenesulfonamide (20, LA2135), (IC(50)'s for COX-1: 85.13 microM; COX-2: 0.74 microM; SI: 114.5), being more active COX-2 selective than celecoxib.     

Indolyl esters and amides related to indomethacin are selective COX-2 inhibitors

Previous studies from our laboratory have revealed that esterification/amidation of the carboxylic acid moiety in the nonsteroidal anti-inflammatory drug, indomethacin, generates potent and selective COX-2 inhibitors. In the present study, a series of reverse ester/amide derivatives were synthesized and evaluated as selective COX-2 inhibitors. Most of the reverse esters/amides displayed time-dependent COX-2 inhibition with IC₅₀ values in the low nanomolar range. Replacement of the 4-chlorobenzoyl group on the indole nitrogen with a 4-bromobenzyl moiety resulted in compounds that retained selective COX-2 inhibitory potency. In addition to inhibiting COX-2 activity in vitro, the reverse esters/amides also inhibited COX-2 activity in the mouse macrophage-like cell line, RAW264.7. Overall, this strategy broadens the scope of our previous methodology of neutralizing the carboxylic acid group in NSAIDs as a means of generating COX-2-selective inhibitors and is potentially applicable to other NSAIDs.     

Synthesis and activity of sulfonamide-substituted 4,5-diaryl thiazoles as selective cyclooxygenase-2 inhibitors.

A series of sulfonamide-substituted 4,5-diarylthiazoles was prepared via three synthetic routes as selective COX-2 inhibitors. Recently in the synthesis of selective COX-2 inhibitors we have discovered that the sulfonamide moiety is a suitable replacement for the methylsulfonyl moiety yielding compounds with activity both in vitro and in vivo.     

Selective COX-2 inhibitors. Part 1: synthesis and biological evaluation of phenylazobenzenesulfonamides

A series of phenylazobenzenesulfonamide derivatives were designed and synthesized for the evaluation as selective cyclooxygenase-2 (COX-2) inhibitors in a cellular assay using human whole blood (HWB) and an enzymatic assay using purified ovine enzymes. Extensive structure-activity relationships (SAR) were studied within this series, and several of selective COX-2 inhibitors have been identified. Among them, compound 8, 4-(4-amino-2-methylsulfanyl-phenylazo)benzenesulfonamide, showed a potent inhibitory activity to the cyclooxygenase enzymes (IC(50)'s for COX-1: 23.28 microM; COX-2: 2.04 microM), being active but less COX-2 selective than celecoxib.     

Selective inhibition of cyclooxygenase-2 by C-phycocyanin, a biliprotein from Spirulina platensis

We report data from two related assay systems (isolated enzyme assays and whole blood assays) that C-phycocyanin a biliprotein from Spirulina platensis is a selective inhibitor of cyclooxygenase-2 (COX-2) with a very low IC(50) COX-2/IC(50) COX-1 ratio (0.04). The extent of inhibition depends on the period of preincubation of phycocyanin with COX-2, but without any effect on the period of preincubation with COX-1. The IC(50) value obtained for the inhibition of COX-2 by phycocyanin is much lower (180 nM) as compared to those of celecoxib (255 nM) and rofecoxib (401 nM), the well-known selective COX-2 inhibitors. In the human whole blood assay, phycocyanin very efficiently inhibited COX-2 with an IC(50) value of 80 nM. Reduced phycocyanin and phycocyanobilin, the chromophore of phycocyanin are poor inhibitors of COX-2 without COX-2 selectivity. This suggests that apoprotein in phycocyanin plays a key role in the selective inhibition of COX-2. The present study points out that the hepatoprotective, anti-inflammatory, and anti-arthritic properties of phycocyanin reported in the literature may be due, in part, to its selective COX-2 inhibitory property, although its ability to efficiently scavenge free radicals and effectively inhibit lipid peroxidation may also be involved.     

Evaluation of classical NSAIDs and COX-2 selective inhibitors on purified ovine enzymes and human whole blood.

Cyclooxygenase is the key enzyme in the biosynthesis of prostanoids, biologically active substances involved in several physiological processes and also in pathological conditions such as inflammation. It has been well known for 10 years that this enzyme exists under two forms: a constitutive (COX-1) and an inducible form (COX-2). Both enzymes are sensitive to inhibition by conventional non-steroidal anti-inflammatory drugs (NSAIDs). Observations were made that COX-1 was mainly involved in homeostatic processes, while the COX-2 expression was associated with pathological conditions leading to the development of COX-2 selective inhibitors. Several methods have been reported for the evaluation of the COX-1 and COX-2 inhibitory potency and selectivity of conventional or COX-2 selective NSAIDs. In this study, we evaluated the COXs inhibitory profile of both conventional NSAIDs and COX-2 selective inhibitors using two different in vitro methods: the first test was performed using purified enzymes while the second method consisted of a whole blood assay. The results obtained with reference drugs in these two assays will be discussed and compared in this article.     

Rational design of 6-methylsulfonylindoles as selective cyclooxygenase-2 inhibitors

The introduction of 3-arylmethyl, 3-aryloxy and 3-arylthio moieties into a 6-methylsulfonylindole framework using rational drug design led to potent, selective COX-2 inhibitors having efficacy in a rat carrageenan air pouch model. Incorporation of a conformationally more rigid 3-aroyloxy substituent onto the 6-methylsulfonylindole scaffold led to selective, but considerably less potent COX-2 inhibitors. Variation of the hydrophilicity and size of the indole 2-substituent of 3-arylthio-6-methylsulfonylindole inhibitors led to modulation of the COX-2 human whole blood (HWB) potency and selectivity.     

Pyridazinones as selective cyclooxygenase-2 inhibitors

Pyridazinone was found to be an excellent core template for selective COX-2 inhibitors. Two potent, selective and orally active COX-2 inhibitors, which were highly efficacious in rat paw edema and rat pyresis models, have been obtained.