Rofecoxib: an update on physicochemical, pharmaceutical, pharmacodynamic and pharmacokinetic aspects

Discovery of andrographolide hit analog as a potent cyclooxygenase-2 inhibitor through consensus MD-simulation, electrostatic potential energy simulation and ligand efficiency metrics

Cyclooxygenase-2 (COX-2) is the key enzyme responsible for the conversion of arachidonic acid to prostaglandins that display pro-inflammatory properties and thus, it is a potential target protein to develop anti-inflammatory drugs. In this study, chemical and bio-informatics approaches have been employed to find a novel potent andrographolide (AGP) analog as a COX-2 inhibitor having better pharmacological properties than aspirin and rofecoxib (controls). The full amino acid sequenced human Alpha fold (AF) COX-2 protein (604AA) was selected and validated for its accuracy against the reported COX-2 protein structures (PDB ID: 5F19, 5KIR, 5F1A, 5IKQ and 1V0X) followed by multiple sequence alignment analysis to establish the sequence conservation. The systematic virtual screening of 237 AGP analogs against AF-COX-2 protein yielded 22 lead compounds based on the binding energy score (< - 8.0 kcal/mol). These were further screened out to 7 analogs by molecular docking analysis and investigated further for ADMET prediction, ligand efficiency metrics calculations, quantum mechanical analysis, MD simulation, electrostatic potential energy (EPE) docking simulation, and MM/GBSA. In-depth analysis revealed that AGP analog A3 (3-[2-[(1R,4aR,5R,6R,8aR)-6-hydroxy-5,6,8a-trimethyl-2-methylidene-3,4,4a,5,7,8-hexahydro-1H-naphthalen-1-yl]ethylidene]-4-hydroxyoxolan-2-one) forms the most stable complex with the AF-COX-2 showing the least RMSD value (0.37 ± 0.03 nm), a good number of hydrogen bonds (protein-ligand H-bond = 11, and protein H-bond = 525), minimum EPE score (- 53.81 kcal/mol), and lowest MM-GBSA before and after simulation (- 55.37 and - 56.25 kcal/mol, respectively) value compared to other analogs and controls. Thus, we suggest that the identified A3 AGP analog could be developed as a promising plant-based anti-inflammatory drug by inhibiting COX-2.

Differential effects of cyclooxygenase-2 (COX-2) inhibitors on endoplasmic reticulum (ER) stress in human coronary artery endothelial cells

Selective cyclooxygenase-2 (COX-2) inhibitor rofecoxib was pulled off the market because of its association with increased risk of adverse cardiovascular effects. The precise underlying mechanism for the differential effects of COX-2 inhibitors on cardiovascular risk is not known. Since endoplasmic reticulum (ER) stress is implicated in atherogenesis, we examined the effects of COX-2 inhibitors on ER stress in primary human coronary artery endothelial cells (HCAEC), human umbilical vein endothelial cells (HUVEC), and human pulmonary artery endothelial cells (HPAEC). ER stress was measured in HCAEC treated with either tunicamycin (TM) or high-concentrations (27.5 mM) of dextrose (HD) using the secreted alkaline phosphatase (ES-TRAP) assay. Markers of the unfolded protein response (UPR) such as activating transcription factor 6 (ATF6), glucose-regulated protein 78 (GRP78), inositol-requiring enzyme 1α (IRE1α), phospho-IRE1α, protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), and phospho-PERK were measured by Western blot. Treatment of HCAEC with TM and HD decreased secreted alkaline phosphatase activity indicating increased ER stress. Treatment of cells exposed to TM or HD with celecoxib, meloxicam, ibuprofen, and acetylsalicylic acid, but not rofecoxib, resulted in a dose-dependent decrease in ER stress. High-dextrose and TM increased IRE1α and PERK phosphorylation and ATF6 and GRP78 expression. Treatment with celecoxib, but not rofecoxib, inhibited these markers of the UPR. Treatment with selective COX-2 inhibitors, with the exception of rofecoxib, suppressed ER stress as measured with both alkaline phosphatase activity assays and markers for the UPR. The inability of rofecoxib to inhibit ER stress, unlike the other cyclooxygenase inhibitors tested, may have contributed to its unfavorable effects on cardiovascular outcomes.

Molecular docking study and molecular dynamic simulation of human cyclooxygenase-2 (COX-2) with selected eutypoids

Inflammation is a key factor linked to almost all chronic and degenerative diseases implicit with certain levels of pain. In studies, over the past few years, it has been discovered that prostaglandins are the main cause of this inflammation and therefore could be blocked. Although no steroidal medications can be effective, natural compounds may offer a safer and often an effective alternative treatment for pain relief, especially for long-term use. Hence to find out natural anti-inflammatory compounds, we have highlighted five important butenolides that are eutypoid A, B, C, D and E with structure similar to that of rofecoxib, by ADMET and druglikeness analysis, followed by molecular docking with human COX-2 enzyme. Molecular docking studies revealed the importance of hydrophobic and hydrophilic amino acid residues for the stability of the ligands and that eutypoids C and E are the best candidates for the synthetic drugs with binding energy of -10.39 kcal/mol and -9.87 kcal/mol, respectively. The resulting complexes were then subject to 50 ns molecular dynamics (MD) simulation studies with the GROMACS package to analyze the stability of docked protein-ligand complexes and to assess the fluctuation and conformational changes during protein-ligand interaction. From the RMSD, RMSF, number of hydrogen bonds, SASA, PCA and MM/PBSA binding free energy analysis, we have found that out of five selected compounds eutypoid E showed good binding free energy of -174.45 kJ/mol, which is also good in other structural analyses. This compound displayed excellent pharmacological and structural properties to be drug candidates.Communicated by Ramaswamy H. Sarma.

Physicochemical characterization and solubility enhancement studies of allopurinol solid dispersions

Allopurinol is a commonly used drug in the treatment of chronic gout or hyperuricaemia associated with treatment of diuretic conditions. One of the major problems with the drug is that it is practically insoluble in water, which results in poor bioavailability after oral administration. In the present study, solid dispersions of allopurinol were prepared by solvent evaporation, kneading method, co-precipitation method, co-grinding method and closed melting methods to increase its water solubility. Hydrophilic carriers such as polyvinylpyrrolidone, polyethylene glycol 6000 were used in the ratio of 1:1, 1:2 and 1:4 (drug to carrier ratio). The aqueous solubility of allopurinol was favored by the presence of both polymers. These new formulations were characterized in the liquid state by phase solubility studies and in the solid state by differential scanning calorimetry, powder X-ray diffraction, UV and Fourier Transform Infrared spectroscopy. Solid state characterizations indicated that allopurinol was present as an amorphous material and entrapped in polymer matrix. In contrast to the very slow dissolution rate of pure allopurinol, the dispersion of the drug in the polymers considerably enhanced the dissolution rate. Solid dispersion prepared with polyvinylpyrrolidone showed highest improvement in wettability and dissolution rate of allopurinol. Mathematical modeling of in vitro dissolution data indicated the best fitting with Korsemeyer-Peppas model and the drug release kinetics primarily as Non-Fickian diffusion. Therefore, the present study showed that polyvinylpyrrolidone and polyethylene glycol 6000 have a significant solubilizing effect on allopurinol.

COX-2 Inhibition by Use of Rofecoxib or High Dose Aspirin Enhances ADP-Induced Platelet Aggregation in Fresh Blood

Aim:

Increased cardiovascular risk after use of selective or nonselective cyclooxygenase-2 (COX-2)-inhibitors might partly be caused by enhanced platelet aggregability. However, an effect of COX-2 inhibition on platelets has so far not been observed in humans.

Methods:

We tested in healthy volunteers the effect of COX-2-inhibition nearly in-vivo, i.e. immediately after and even during blood sampling.

Results:

Measurement within 2 minutes after venipuncture, but not 60 minutes later, showed that 50 mg of rofecoxib (n=12) or 500 (n=8) or 1000 (n=8) mg of aspirin increased ADP-induced platelet aggregation in a whole-blood aggregometer to, respectively, 152, 176 and 204 % of basal level (p<0.01). No significant differences in aggregability were observed after ingestion of 80 mg of aspirin (n=16), or placebo (n=8). Plasma 6-keto-PGF1α was decreased to 74 % after rofecoxib and to 76 and 70 % after 500 and 1000 mg of aspirin but did not change after low dose aspirin. Continuous photometrical measurement of aggregation in blood flowing from a cannulated vein revealed that high dose aspirin did not elicit aggregation by itself, but increased ADP-induced aggregation in proportion to the decrease in prostacyclin formation (r=0.68, p = 0.004). Since in these experiments thromboxane production was virtually absent, the enhanced aggregation after partial COX-2 inhibition was not caused by unopposed thromboxane formation.

Conclusions:

We conclude that both selective and nonselective COX-2 inhibition enhances ADP-induced platelet aggregation in humans. This effect can only be detected during or immediately after venipuncture, possibly because of the short half-life of prostacyclin.

Pharmacokinetic-pharmacodynamic modelling of the analgesic effects of lumiracoxib, a selective inhibitor of cyclooxygenase-2, in rats

BACKGROUND AND PURPOSE

This study establishes a pharmacokinetic/pharmacodynamic (PK/PD) model to describe the time course and in vivo mechanisms of action of the antinociceptive effects of lumiracoxib, evaluated by the thermal hyperalgesia test in rats.

EXPERIMENTAL APPROACH

Female Wistar fasted rats were injected s.c. with saline or carrageenan in the right hind paw, followed by either 0, 1, 3, 10 or 30 mg*kg(-1) of oral lumiracoxib at the time of carrageenan injection (experiment I), or 0, 10 or 30 mg*kg(-1) oral lumiracoxib at 4 h after carrageenan injection (experiment II). Antihyperalgesic responses were measured as latency time (LT) to a thermal stimulus. PK/PD modelling of the antinociceptive response was performed using the population approach with NONMEM VI.

RESULTS

A two-compartment model described the plasma disposition. A first-order model, including lag time and decreased relative bioavailability as a function of the dose, described the absorption process. The response model was: LT=LT(0)/(1 +MED). LT(0) is the baseline response, and MED represents the level of inflammatory mediators. The time course of MED was assumed to be equivalent to the predicted profile of COX-2 activity and was modelled according to an indirect response model with a time variant synthesis rate. Drug effects were described as a reversible inhibition of the COX-2 activity. The in vivo estimate of the dissociation equilibrium constant of the COX-2-lumiracoxib complex was 0.24 microg*mL(-1).

CONCLUSIONS

The model developed appropriately described the time course of pharmacological responses to lumiracoxib, in terms of its mechanism of action and pharmacokinetics.

Evaluation of [(11)C]rofecoxib as PET tracer for cyclooxygenase 2 overexpression in rat models of inflammation

BACKGROUND

Overexpression of cyclooxygenase type 2 (COX-2) is triggered by inflammatory stimuli, but it also plays a prominent role in the initiation and progression of various diseases. This study aims to investigate [(11)C]rofecoxib as a positron emission tomography (PET) tracer for COX-2 expression.

METHODS

[(11)C]Rofecoxib was prepared by methylation of its sulphinate precursor. Regional brain distribution and specific binding of [(11)C]rofecoxib in healthy rats was studied by ex vivo biodistribution and autoradiography. Regional brain distribution and PET imaging studies were also performed on rats with severe encephalitis, caused by nasal infection with herpes simplex virus (HSV). Finally, ex vivo biodistribution and blocking studies were carried in rats with a sterile inflammation, induced by intramuscular turpentine injection.

RESULTS

[(11)C]rofecoxib brain uptake in control animals corresponded with the known distribution of COX-2. Pretreatment with NS398 significantly reduced tracer uptake in the cingulate/frontopolar cortex, whereas the reduction in hippocampus approached significance. Ex vivo autoradiography also revealed preferential tracer uptake in hippocampus and cortical areas that could be blocked by NS398. In HSV-infected animals, [(11)C]rofecoxib uptake was moderately increased in all brain regions, but it could not be blocked with indomethacin. Yet, some PET images revealed increased tracer uptake in brain areas with microglia activation. In turpentine-injected animals, [(11)C]rofecoxib uptake in inflamed muscle was not higher than in control muscle and could not be blocked with NS398. Indomethacin caused a slight reduction in muscle uptake.

CONCLUSIONS

Despite the apparent correlation between [(11)C]rofecoxib uptake and COX-2 distribution in healthy rats, [(11)C]rofecoxib could not unambiguously detect COX-2 overexpression in two rat models of inflammation.

Predicting effect of food on extent of drug absorption based on physicochemical properties

PURPOSE

To develop a statistical model for predicting effect of food on the extent of absorption (area under the curve of time-plasma concentration profile, AUC) of drugs based on physicochemical properties.

MATERIALS AND METHODS

Logistic regression was applied to establish the relationship between the effect of food (positive, negative or no effect) on AUC of 92 entries and physicochemical parameters, including clinical doses used in the food effect study, solubility (pH 7), dose number (dose/solubility at pH 7), calculated Log D (pH 7), polar surface area, total surface area, percent polar surface area, number of hydrogen bond donor, number of hydrogen bond acceptors, and maximum absorbable dose (MAD).

RESULTS

For compounds with MAD >or= clinical dose, the food effect can be predicted from the dose number category and Log D category, while for compounds with MAD < clinical dose, the food effect can be predicted from the dose number category alone. With cross validation, 74 out of 92 entries (80%) were predicted into the correct category. The correct predictions were 97, 79 and 68% for compounds with positive, negative and no food effect, respectively.

CONCLUSIONS

A logistic regression model based on dose, solubility, and permeability of compounds is developed to predict the food effect on AUC. Statistically, solubilization effect of food primarily accounted for the positive food effect on absorption while interference of food with absorption caused negative effect on absorption of compounds that are highly hydrophilic and probably with narrow window of absorption.

Effect of cyclooxygenase inhibitors on pentylenetetrazol (PTZ)-induced convulsions: Possible mechanism of action

Cyclooxygenase (COX) is reported to play a significant role in neurodegenerative and neuropsychiatric disorders, and may play a significant role in the pathogenesis of epilepsy. Various neurotransmitter abnormalities, especially of GABA and glutamate, have been reported to play a key role in the pathophysiology of epilepsy. The objective of the present study was to elucidate the effect of cyclooxygenase inhibitors on pentylenetetrazol (PTZ)-induced (80 mg/kg) convulsions in mice with possible mechanism of action. Various COX-inhibitors were administered 45 min prior to the PTZ administration. Onset, duration of clonic convulsions and percentage mortality/recovery were recorded. Pretreatment with COX-inhibitors aspirin (10 and 20 mg/kg, p.o.), naproxen (7 and 14 mg/kg, p.o.), nimesulide (1-5 mg/kg, p.o.) or rofecoxib (1-4 mg/kg, p.o.) dose-dependently showed protection against PTZ-induced convulsions. COX-2 inhibitors were more effective as compared to non-selective COX-inhibitors. Rofecoxib (1 mg/kg) or nimesulide (1 mg/kg) also enhanced the sub-protective effect of diazepam or muscimol showing GABAergic modulation of COX-2 inhibitors. COX-2 inhibitors also antagonized the effect of flumazenil (4 mg/kg)- against PTZ-induced convulsions further confirming the GABAergic mechanism. In conclusion, the results of the present study strongly suggest the possible role of cyclooxygenase isoenzymes in the pathophysiology of epilepsy and the use of COX-inhibitors as an adjuvant therapy in the treatment of epilepsy.

Studies on dissolution enhancement and mathematical modeling of drug release of a poorly water-soluble drug using water-soluble carriers

Role of various water-soluble carriers was studied for dissolution enhancement of a poorly soluble model drug, rofecoxib, using solid dispersion approach. Diverse carriers viz. polyethylene glycols (PEG 4000 and 6000), polyglycolized fatty acid ester (Gelucire 44/14), polyvinylpyrollidone K25 (PVP), poloxamers (Lutrol F127 and F68), polyols (mannitol, sorbitol), organic acid (citric acid) and hydrotropes (urea, nicotinamide) were investigated for the purpose. Phase-solubility studies revealed AL type of curves for each carrier, indicating linear increase in drug solubility with carrier concentration. The sign and magnitude of the thermodynamic parameter, Gibbs free energy of transfer, indicated spontaneity of solubilization process. All the solid dispersions showed dissolution improvement vis-à-vis pure drug to varying degrees, with citric acid, PVP and poloxamers as the most promising carriers. Mathematical modeling of in vitro dissolution data indicated the best fitting with Korsemeyer-Peppas model and the drug release kinetics primarily as Fickian diffusion. Solid state characterization of the drug-poloxamer binary system using XRD, FTIR, DSC and SEM techniques revealed distinct loss of drug crystallinity in the formulation, ostensibly accounting for enhancement in dissolution rate.

Rofecoxib attenuates both primary and secondary inflammatory hyperalgesia: a randomized, double blinded, placebo controlled crossover trial in the UV-B pain model

The analysis of drug's influence on peripheral and central sensitisation can give useful information about its mode of action and can lead to more efficacy in the treatment of pain. Peripheral inflammation is associated with peripheral expression and up-regulation of cyclooxygenase 2 (COX-2) in the CNS. The relative contribution of COX-2 mediated central sensitisation may be prominent under inflammatory conditions. In this randomized, double blinded, placebo controlled cross-over trial the effects of multidoses of the COX-2 selective inhibitor rofecoxib on primary and secondary hyperalgesia were evaluated in the UVB pain model. Twenty-four hours after local UVB irradiation at the upper leg of 42 healthy volunteers heat pain perception (HPPT) and heat pain tolerance thresholds (HPTT) were assessed within the inflammation. The area of secondary hyperalgesia was determined by pin prick test. Subjects received oral rofecoxib 50, 250, 500 mg or placebo. Pain testing was repeated after 3 and 6 h. Compared to placebo, rofecoxib significantly increased HPPT (1.55 and 1.08 degrees C, P<0.0001 and P=0.0333), HPTT (1.74 and 1.58 degrees C, P<0.0001 and P<0.0001), and reduced the mean area of secondary hyperalgesia by 15.6% (P=0.007) and 16.8% (P<0.001) after 3 and 6 h. No significant difference between the three dosage groups was observed. These data confirm peripheral effects of rofecoxib in a human inflammatory UV-B pain model and provide circumstantial evidence that even a standard clinical dose of rofecoxib reduces central hyperalgesia in inflammatory pain. We confirm that the effect of single oral dose of rofecoxib plateaus at 50 mg.

Pain and osteoarthritis: new drugs and mechanisms

PURPOSE OF REVIEW

This review discusses the recent literature on drugs used for symptomatic pain relief in patients with osteoarthritis (OA) as well as potential mechanisms underlying their pharmacologic action.

RECENT FINDINGS

Recent research has shed light on the molecular mechanisms underlying the contribution of prostaglandins to pain sensation. Moreover, the role of the enzymes cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) in inflammation and subsequent structural changes of joints has been clarified. Based on the COX-1/COX-2 hypothesis, various selective COX-2 inhibitors with improved gastrointestinal tolerability as compared with conventional nonsteroidal anti-inflammatory drugs (NSAIDs) have been established for the symptomatic treatment of OA in recent years. Rational therapy with these compounds should be based on their diverse pharmacokinetic characteristics. Among the traditional NSAIDs, the mode of action of aceclofenac has been recently clarified in that the compound was shown to elicit preferential inhibition of COX-2 as a result of limited but sustained biotransformation to diclofenac. Novel mechanisms have also been proposed to account for the action of acetaminophen. Finally, there is evidence from animal models to suggest that the dual LOX/COX inhibitor licofelone may stop disease progression in OA. Clinical studies are under way to establish this compound for treatment of OA.

SUMMARY

It is anticipated that new insights into the pathophysiology of OA as well as novel therapeutics will improve the pharmacologic options in OA.

Adverse oral reactions associated with the COX-2 inhibitor rofecoxib

Rofecoxib is an inhibitor of the enzyme cyclo-oxygenase 2 (COX-2) used as an analgesic and anti-inflammatory agent especially in rheumatoid arthritis and osteoarthritis. The adverse effects are generally less than with other anti-inflammatory drugs (NSAIDs), and no oral adverse reactions have been reported in the literature. We present three cases of oral lesions caused by rofecoxib. Extensive erosions appeared, which in all cases resolved on withdrawal of the drug.

Benefit-risk assessment of rofecoxib in the treatment of osteoarthritis

NSAIDs are widely used to treat pain and inflammation in osteoarthritis. Their use in this indication is generally intermittent and fluctuates with the intensity of the disease. Nonetheless, success of the therapy is frequently limited by injury to the gastrointestinal mucosa and complications such as bleeding, ulceration and perforation. A careful and detailed evaluation of these aspects in regard to the newly introduced NSAIDs is of considerable clinical importance. This review focuses on the NSAID rofecoxib, one of the selective cyclo-oxygenase (COX)-2 inhibitors, which are claimed to be as effective as nonselective NSAIDs with better gastrointestinal tolerability. Indeed, phase II, phase III and epidemiological studies have revealed that the efficacy of rofecoxib is comparable to that of conventional NSAIDs but with lower gastrointestinal toxicity, although this advantage may not be demonstrable in every patient. In patients treated with low-dose aspirin (acetylsalicylic acid) for cardiovascular prophylaxis, celecoxib (another selective COX-2 inhibitor) seems to have no obvious advantages over conventional NSAIDs, and similar conclusions may be applied to rofecoxib. A comparison of NSAID therapy +/- concomitant low-dose aspirin was not a primary outcome in this trial with celecoxib and there is thus a need for further studies which compare the gastrointestinal risk of a selective COX-2 inhibitor plus aspirin versus a conventional NSAID. Recent debate has emerged regarding the cardiovascular safety of rofecoxib. Although there is evidence both for and against higher cardiovascular risk with rofecoxib, a retrospective cohort study recently published suggested that there is no increased risk of acute myocardial infarction in the short-term when compared with non-selective NSAIDs. The renal toxicity of rofecoxib has been thoroughly investigated. Clinical studies revealed renal effects of rofecoxib similar to those of conventional NSAIDs. Since adverse effects increase with the degree of renal impairment, monitoring of renal function should be carried out in patients at risk. Although there are still insufficient data concerning certain important adverse effects of rofecoxib, this drug is becoming an important alternative in the therapy of osteoarthritis, especially in high-risk patients. Clinicians need to weigh up the benefits and risks of rofecoxib on a case-by-base basis.