Estimation of acute flurbiprofen and ketoprofen toxicity in rat gastric mucosa at therapy-relevant doses.

OBJECTIVE: Since assessment of the acute gastrotoxicity of nonsteroidal antiinflammatory drugs (NSAIDs) in rats requires high doses of the drugs, we sought to establish an experimental model with which this adverse NSAID effect can be estimated at therapy-relevant doses. METHODS: The study was performed with racemic flurbiprofen-trometamol (R/S-FBP), its pure enantiomers S-FBP and R-FBP, and racemic ketoprofen-trometamol (R/S-KP). Two hours after administration of FBP or KP to Sprague-Dawley rats, HCl (0.5 M, 10 ml/kg) was given intragastrically (IG), and the haemorrhagic lesion area in the gastric mucosa quantified 1 h post-HCI. RESULTS: FBP amplified gastric acid injury in a dose-related manner, the rank order of potency being S-FBP > R/S-FBP >> R-FBP. While less than 1 micromol/kg S-FBP and R/S-FBP aggravated acid injury, doses up to 50 micromol/kg failed to cause appreciable damage without subsequent HCl challenge. Similar observations were made with R/S-KP which at doses of > or = 1 micromol/kg aggravated gastric acid injury. There was no significant difference in the gastrotoxicity of FBP when the drug was administered subcutaneously or IG, whereas subcutaneously injected R/S-KP was slightly more toxic than IG R/S-KP. CONCLUSIONS: These data show that FBP- and KP-induced amplification of acid injury in the rat gastric mucosa is a sensitive assay whereby, with single drug dosing, the gastrotoxic potential of these and other NSAIDs may be estimated at therapy-relevant doses that in humans threaten mucosal integrity only following chronic use.

Intestinal toxicity of ketoprofen-trometamol vs its enantiomers in rat. Role of oxidative stress.

OBJECTIVE: Gastrointestinal damage and bleeding are the major side effects of non-steroidal anti-inflammatory drugs (NSAID), however the mechanisms of this ulcerogenic action are not fully understood. It has recently been proposed that neutrophil-and oxygen radical-dependent microvascular injuries may be important prime events that lead to mucosal injury. In addition, other factors like bile flow, intact bacterial flora or feeding conditions may contribute to the formation of lesions. Ketoprofen is a NSAID that exists as a pair of R(-) and S (+) enantiomers; like other 2-arylpropionic acids, its anti-inflammatory effects resides almost exclusively in the S (+) isomer. The present study was undertaken to explore the role of oxidative stress in the pathogenesis of intestinal injury induced by oral administration of racemic ketoprofen and its enantiomers given as their water soluble tromethamine salts. MATERIAL AND METHODS: Evaluation of intestinal damage and activities of oxidative stress related enzymes such as myeloperoxidase (MPO), xanthine-oxidase (XO) and superoxide dismutase (SOD) were studied in an experimental animal model using refed rats. RESULTS: After the oral treatment followed by a refeeding period of 24 h, ketoprofen (100, 50, 25 mg/Kg b.w.) dose-dependently caused longitudinal ulcers on the mesenteric side of the middle and lower intestine lumen. The intestinal toxicity caused by S(+)-ketoprofen was significantly lower than the effect observed after racemate and R(-) enantiomer treatments (P <0.001), though the bioinversion of R(-)-ketoprofen to S(+)-enantiomer that occurs in the rat has to be considered. XO activity was unaffected by the studied drugs. Enhanced enteropathy by the racemate and its R (-)-enantiomer was correlated with a significant increase of MPO activity as an index of neutrophil infiltration, and a decrease in SOD activity (p<0.05 Vs control). S(+)-ketoprofen did not significantly change these parameters. CONCLUSIONS: These results suggest that reactive oxygen metabolites can contribute significantly to the development of intestinal lesions, and that R(-)-ketoprofen present in racemic preparations can enhance the toxic intestinal effects of S (+)-enantiomer via modification of neutrophil migration and oxidative stress.

Modeling cyclooxygenase inhibition. Implication of active site hydration on the selectivity of ketoprofen analogues.

Molecular modeling studies performed on the two cyclooxygenase isozymes (COXs) suggest that active site hydration is crucial for understanding inhibitor selectivity. In this work, models have been constructed considering some implicit water molecules, placed in the position suggested by GRID, that participate in the dynamic hydrogen-bonding network at the polar active site entrance together with protein residues 355, 524, 120, and 513. The selectivity observed for ketoprofen (1) and the structural analogues 2 and 3 may be rationalized in terms of such implicit hydration.

Synthesis and pharmacological evaluation of new 4-2-(7-heterocyclemethoxynaftalen-2-ylmethoxy)ethylbenzoic acids as LTD(4)-antagonists.

A group of new 4-[2-(7-heterocyclemethoxynaftalen-2-ylmethoxy)ethyl]benzoic acids have been synthesized and pharmacologically evaluated as LTD(4)-antagonists. Thiazole derivatives, especially 4-[2-[7-(4-cyclobutylthiazole-2-ylmethoxyl)naphthalen- 2-ylmetho-xy]et hyl]benzoic acid, present considerable activity and improved pharmacokinetic profiles in comparison with our quinoline containing lead molecule confirming the interest of our compounds as potentially oral antiasthmatics and that the 4-alkylthiazole system can be considered as bioisosteric of the quinoline ring at least in our series of compounds.

Derivation of pharmacophore and CoMFA models for leukotriene D(4) receptor antagonists of the quinolinyl(bridged)aryl series.

The present work focuses on the study of the three-dimensional (3D) structural requirements for the leukotriene D(4) (LTD(4)) antagonistic activity of compounds having the basic quinolinyl(bridged)aryl framework. An approach combining pharmacophore mapping, molecule alignment, and CoMFA models was used to derive a hypothesis for a series of LTD(4) antagonists having the basic diaryl-bridged framework. In this compound series, the produced pharmacophore hypotheses have shown to yield molecule alignments suitable to derive valuable CoMFA models. Model selection focused on (1) obtention of coherent modeling results, (2) consistency with the available SAR data, and (3) ability to predict the activity of an independent set of congeneric molecules. This approach resulted in a combined pharmacophore and CoMFA model that can generally represent the antagonistic activity within a log unit of the measured value for compounds of the series. The resulting pharmacophore (model C) consists of an acidic or negative ionizable function (AC), a hydrogen-bond acceptor (HBA), and three hydrophobic regions (HY) and produces chemically meaningful alignments with the most active compounds of the series mapping the pharmacophore in a extended energetically favorable conformation.

Analysis of antinociceptive effects of flurbiprofen enantiomers in a rat model of arthritic pain.

The potential antinociceptive effects of the S(+)- and R(-)-enantiomers of flurbiprofen (SFB and RFB, respectively) were investigated when given intravenously to rats using the pain-induced functional impairment model in the rat (PIFIR), an animal model of arthritic pain. Groups of 6 rats received either vehicle or the enantiomer in turn and antinociception was determined by evaluating the dose-response curves over time. Although SFB and RFB produced dose-dependent effects with similar efficacy (SFB: 277.4 +/- 29.9 au and RFB: 293.5 +/- 20.1 au), the R(-)-enantiomer was unable to produce any antinociceptive action when assessed at the same dose ranges as SFB. It was necessary to increase the dose of RFB by 100 times to produce similar antinociception. Accordingly, S(+)-flurbiprofen was 100-fold more potent (ED50 = 0.33 +/- 0.13 mg/kg) than its antipode R(-)-(ED50 = 30.0 +/- 1.7 mg/kg). SFB generated from metabolic inversion (> 1%) after i.v. dosage of RFB, as well as impurities of SFB present in RFB preparations, tend to confirm the hypothesis that the efficacy of RFB achieved at 100 mg/kg, similar to that observed with 1 mg/kg of SFB, is attributable to SFB.

Structural basis of the dynamic mechanism of ligand binding to cyclooxygenase.

Molecular modeling studies performed on the two cyclooxygenase (COX) isozymes suggest that the cavity at the mouth of the active site on the membrane domain that may act as an actual binding site of COX ligands. Actual docking of different inhibitors at this site provides a structural basis to explain the dynamics of COX inhibition.

Analgesic, antiinflammatory, and antipyretic effects of S(+)-ketoprofen in vivo.

Many studies indicate that the S-enantiomers of arylpropionic (APA) nonsteroidal antiinflammatory drugs (NSAIDs) are the pharmacologically active enantiomers. S(+)-ketoprofen (dexketoprofen) stereoselectively inhibits cyclooxygenase (COX) in vitro but very little is known about the differential activity of ketoprofen enantiomers in vivo. We examined the analgesic, antiinflammatory, and antipyretic activities of S(+)-ketoprofen in rats and mice. First, we measured the antinociceptive action of S(+)-ketoprofen in abdominal pain models. After intravenous administration. 0.5 mg/kg S(+)-ketoprofen inhibited 92.1+/-2.2% of writhing in mice. Stereoselectivity in the activity was detected; intravenous administration of the R(-)-enantiomer resulted in no statistically significant activity in a dose range of 0.15-1 mg/kg. Similar results were obtained after oral administration in mice. In the rat, S(+)-ketoprofen was a more potent analgesic than diclofenac by both intravenous and oral administration. There was no significant difference between the analgesic effect of S(+)-ketoprofen treatment and the twofold dose of the racemic form in both the mouse and rat models. Second, we measured the antiinflammatory activity of S(+)-ketoprofen using a carrageenan-induced paw edema model in the rat. Intravenous administration of 5 mg/kg of S(+)-ketoprofen almost completely inhibited edema formation. After oral administration, S(+)-ketoprofen is both more potent and effective than diclofenac. Third, we measured antipyretic activity. S(+)-ketoprofen showed a marked antipyretic action (ED50 = 1.6 mg/kg) and was the most potent of the NSAIDs tested. S(+)-ketoprofen is a potent antiinflammatory, analgesic, and antipyretic agent in vivo, consistent with its potent anti-COX activity.

Antinociceptive effects of S(+)-ketoprofen and other analgesic drugs in a rat model of pain induced by uric acid.

We investigated the antinociceptive properties of dexketoprofen trometamol [S(+)-ketoprofen tromethamine salt; SKP], a new analgesic, antiinflammatory drug, using the pain-induced functional impairment model in the rat (PIFIR), an animal model of arthritic pain. SKP was compared with racemic ketoprofen tromethamine salt (rac-KP), R(-)-ketoprofen tromethamine salt (RKP), ketorolac (KET), and morphine (MOR). We also assessed the effects of flurbiprofen (rac-FB) and its enantiomers (SFB and RFB) in the same model. Groups of six rats received either vehicle or analgesic drug and antinociception was evaluated by evaluating the dose-response curves over time. SKP was an effective antinociceptive drug in this model and was almost equally potent by either oral or intracerebroventricular administration. The oral potency of SKP was similar to that of oral KET and greater than that of oral MOR. No significant differences were observed between racemic ketoprofen and its enantiomers when administered orally. In the rat, significant bioinversion of RKP to SKP occurs when RKP is given orally. After oral administration of RKP, SKP was detectable in 30 min and surpassed the concentration of RKP after 3 h. Nevertheless, when the compounds were given intracerebroventricularly, some stereoselectivity in favor of SKP was observed. Stereoselectivity was observed with flurbiprofen, an analogue of ketoprofen that does not undergo significant metabolic inversion. Whereas SFB was an effective antinociceptive, RFB had no antinociceptive effect at the doses tested when given either orally or intracerebroventricularly.

Bioavailability of S(+)-ketoprofen after oral administration of different mixtures of ketoprofen enantiomers to dogs.

Recent reports have disagreed on whether the bioavailability of S(+)-ketoprofen is affected by the presence of R(-)-ketoprofen. To examine this directly, we designed a randomized crossover study in beagle dogs. [14C]-S(+)-ketoprofen trometamol and R(-)-ketoprofen trometamol were administered in the following percentage ratios: A, 99:1; B, 95:5; C, 90:10; D, 70:30; E, 50:50. Treatments were administered as a single oral dose of 1 mg/kg tromnetamol salt. Each of eight dogs received all five combinations in random order with a 1-week wash-out period between doses. Blood samples were taken before drug administration and at regular intervals for 240 min after dosing. A progressive increase in the plasma concentration of [14C]-S(+)-ketoprofen was observed on going from treatment E (lowest dose of Senantiomer) to treatments containing the highest doses of [14C]-S(+)-ketoprofen. When the pharmacokinetic calculations were normalized to the dose of [14C]-S(+)-ketoprofen, we found no statistically significant differences among the normalized AUC and Cmax values of the five treatments. Therefore, S(+)-ketoprofen absorption was linear and was not influenced by the presence of R(-)-ketoprofen. Furthermore, there were no significant differences in tmax values among treatments, indicating that the rate of S(+)-ketoprofen absorption was also unaffected by the presence of R(-)-ketoprofen.

Intestinal ulcerogenic effect of S(+)-ketoprofen in the rat.

Nonsteroidal antiinflammatory drugs (NSAIDs) inhibit prostaglandin synthesis in the gastrointestinal mucosa, which can lead not only to stomach ulcers but also ulcers in the small and large intestines. Ulcers of the small intestine are less common than those of the stomach, but intestinal lesions are more life threatening. Although the R(-)-enantiomers of the arylpropionic acid (APA) class of NSAIDs are assumed to lack the toxic effects of cyclooxygenase inhibition, they may contribute to the ulcerogenicity of racemates. We have examined the intestinal ulcerogenic effects of single oral doses of S(+)-ketoprofen compared with racemic ketoprofen in the small intestine and cecum of rats. The toxicity in the small intestine was measured as the weight ratio between portions of intestine showing lesions and the total weight of the tissue. Toxicity in the cecum was evaluated by measuring the size of the ulcers. S(+)-ketoprofen had no significant ulcerogenic effect at 10 or 20 mg/kg. However, racemic ketoprofen was clearly ulcerogenic in the small intestine and cecum at the 40 mg dose. R(-)-ketoprofen at 20 mg/kg does not show any effect in the cecum and only limited ulcerogenesis in the small intestine: The latter effect may be the result of racemic inversion. Therefore, the ulcerogenic action of racemic ketoprofen can be interpreted as a synergism between S(+)- and R(-)-ketoprofen. The mechanism of this synergism is not well understood but may be a general feature of APA NSAIDs.

Pharmacokinetics of dexketoprofen trometamol in healthy volunteers after single and repeated oral doses.

The pharmacokinetics of dexketoprofen trometamol were evaluated in two studies using healthy volunteers. In the first study, the relative bioavailability of a single oral capsule of dexketoprofen free acid 25 mg or dexketoprofen trometamol 25 mg (given as 37 mg of the trometamol salt) was compared to ketoprofen 50 mg in 18 healthy volunteers. In the second study, the pharmacokinetics and tolerability of oral dexketoprofen trometamol in tablet form were evaluated after either a single 25 mg dose (24 volunteers) or a repeated dose of 25 mg twice daily for 7 days (12 volunteers). The absorption of dexketoprofen from dexketoprofen trometamol capsules was bioequivalent to that of ketoprofen. On the other hand, the extent of absorption of dexketoprofen free acid was significantly lower than that for ketoprofen. Dexketoprofen trometamol showed the most rapid absorption rate, with highest Cmax and shortest t(max) values, whereas dexketoprofen free acid had the slowest absorption rate, and ketoprofen had an intermediate absorption rate. After repeated-dose administration of dexketoprofen trometamol, the pharmacokinetic parameters were similar to those obtained after single doses, indicating that no drug accumulation occurred. Dexketoprofen trometamol was well tolerated, with no clinically relevant adverse events reported.

Clinical comparison of dexketoprofen trometamol, ketoprofen, and placebo in postoperative dental pain.

The efficacy and tolerability of single doses of dexketoprofen trometamol 12.5 mg, 25 mg, and 50 mg and ketoprofen 50 mg were compared in this double-blind, randomized, placebo-controlled study of 210 patients with moderate to severe pain after removal of one mandibular impacted third molar tooth. Pain intensity and pain relief were monitored for 6 h after administration of medication using visual analogue and verbal rating scales. All four active treatments were significantly more effective than placebo (P < 0.001). Dexketoprofen 25 mg and 50 mg produced an analgesic effect within 30 min of administration and their effect persisted for 6 h. Ketoprofen 50 mg produced a level of analgesia similar to those of the higher doses of dexketoprofen trometamol, but it had a slower onset. The 12.5-mg dose of dexketoprofen trometamol was significantly superior to placebo but produced a lower level and shorter duration of analgesia compared to the other active treatments. There were no significant differences between 25 and 50 mg of dexketoprofen trometamol in any measure of analgesic efficacy. No serious adverse events were observed and there were no significant differences in the incidence of adverse events among treatment groups. These results demonstrate that dexketoprofen trometamol 25 mg is at least as effective as the racemic ketoprofen 50 mg in the treatment of postsurgical dental pain. The more rapid onset of action compared to ketoprofen suggests that dexketoprofen trometamol is more appropriate for treatment of acute pain.

The effect of food and an antacid on the bioavailability of dexketoprofen trometamol.

This randomized three-way, crossover pharmacokinetic study was performed to determine whether food or an antacid alters the bioavailability of dexketoprofen trometamol. A total of 24 healthy volunteers received three single 25 mg doses of dexketoprofen trometamol administered either in fasting condition, after an antacid (Maalox), or after a high-fat breakfast. Each volunteer received the three treatments in a randomized order, with a 7-day washout period between treatments. Blood samples were taken at regular intervals up to 24 h after dose. Plasma dexketoprofen concentrotions were determined by HPLC and the main outcome measures were area under curve of concentration vs. time (AUC0-infinity), maximal plasma concentration (Cmax), and time to reach maximal concentration (t(max)). Administration of an antacid 10 min before dexketoprofen trometamol had no clinically relevant effect on any of the pharmacokinetic parameters. Food did not alter the extent of absorption of dexketoprofen trometamol, but t(max) was significantly increased and C(max). significantly decreased compared with the fasting state. In conclusion, we can state that neither antacid nor food has a significant effect on the overall bioavailability of dexketoprofen trometamol.

Clinical comparison of dexketoprofen trometamol and dipyrone in postoperative dental pain.

A total of 125 outpatients with moderate to severe pain after surgical removal of one impacted third molar were randomly assigned to receive dexketoprofen trometamol 12.5 or 25 mg or dipyrone 575 mg. For first-dose assessments, patients rated their pain intensity and its relief at regular intervals. From 60 min post dose to the end of the 6-h observation period, both doses of dexketoprofen trometamol had higher pain relief scores than dipyrone: Between 3 and 6 h the differences were statistically significant. In addition, peak measures (PIDmax and PARmax) were statistically superior after both doses of dexketoprofen trometamol compared to dipyrone. The overall efficacy assessed at the end of the first-dose phase was rated as good or excellent by 90%, 83.3%, and 70% of patients receiving dexketoprofen trometamol 25 mg, dexketoprofen trometamol 12.5 mg, and dipyrone, respectively. The number of patients who required remedication during the 6-h period was significantly lower in both dexketoprofen groups. Repeated-dose data were also obtained. No significant differences were found in the efficacy after repeated doses, the number of doses taken, or the mean time elapsed between doses. The overall efficacy at the end of the repeated-dose phase was rated as good or excellent by 84.2%, 66.7%, and 70% of patients receiving dexketoprofen trometamol 25 mg, dexketoprofen trometamol 12.5 mg, and dipyrone, respectively. The frequency of adverse events was similar for all treatments and no serious adverse events were reported during the study.

Comparison of the efficacy and tolerability of dexketoprofen and ketoprofen in the treatment of primary dysmenorrhea.

Dexketoprofen, the pure S(+)-enantiomer of ketoprofen, is a promising new analgesic, but few clinical trials have yet examined its efficacy and tolerability. In this study, patients with a history of primary dysmenorrhea were treated with dexketoprofen doses of 12.5 and 25 mg, ketoprofen 50 mg, and placebo using a randomized, four-way crossover design. Efficacy analyses showed that dexketoprofen 12.5 and 25 mg and racemic ketoprofen 50 mg significantly reduced pain intensity compared with placebo from 1 h after dose to 4-6 h after dose. Interestingly, dexketoprofen at 12.5 mg was significantly superior to placebo at 30 min after dose. Mean pain relief scores also demonstrated that both doses of dexketoprofen and racemic ketoprofen were significantly superior to placebo at 1-6 h after the first dose. No indices of analgesic efficacy showed any significant differences between the two doses of dexketoprofen or between dexketoprofen and ketoprofen. After repeated dose administration, similar results were obtained. There were no significant effects of any treatment on activities of daily living, menstrual flow, or associated symptoms. Dexketoprofen was effective, well tolerated, and had no difference in the incidence of adverse events compared to ketoprofen or placebo.

Comparison of dexketoprofen trometamol and ketoprofen in the treatment of osteoarthritis of the knee.

Dexketoprofen, the active enantiomer of the racemic compound ketoprofen, is a new nonsteroidal antiinflammatory drug (NSAID) of the arylpropionate family. The efficacy and safety of dexketoprofen trometamol were compared with the equivalent enantiomeric dose of ketoprofen in a multicenter, randomized, double-blind 3-week trial of adult outpatients with pain due to osteoarthritis of the knee. After a washout period of 7-15 days, patients were randomly assigned to receive either dexketoprofen trometamol 25 mg tid (N = 89) or ketoprofen 50 mg tid (N = 94). Of the 183 patients enrolled, two were lost to follow-up. At the end of treatment (3 weeks), the main efficacy outcome measures were significantly better in the dexketoprofen trometamol group than in the ketoprofen group. In addition, overall physician assessment indicated that 75% of the dexketoprofen group had improved compared with 50% of the ketoprofen patients. There were fewer adverse events in the dexketoprofen treatment group, but the difference did not reach statistical significance. These results demonstrate that dexketoprofen trometamol 25 mg tid is more effective than ketoprofen 50 mg tid in short-term symptomatic treatment of knee osteoarthritis and suggest that the tolerability of dexketoprofen trometamol is more favorable than ketoprofen. Therefore, the substitution of dexketoprofen for racemic ketoprofen may be advantageous in clinical practice.

Stereoselective inhibition of rat brain cyclooxygenase by dexketoprofen.

Although it has been assumed that the effects of nonsteroidal antiinflammatory drugs (NSAIDs) are mainly the result of their action on local synthesis of prostaglandins, there is growing evidence to suggest that they may also exert a central analgesic action. Some authors have suggested that inhibition of prostaglandin synthesis in the brain could contribute to the analgesic action. The effect of dexketoprofen trometamol (tromethamine salt of the enantiomer (+)-S-ketoprofen) on prostaglandin synthesis was investigated in rat brain fragments and in cyclooxygenase preparations from rat brain microsomes. Effects of the (-)-R-enantiomer and the racemic mixture were also evaluated. Significant levels of prostaglandin F2 alpha (PGF2 alpha) were synthesized in rat brain fragments after 10 min of incubation at 37 degrees C. Dexketoprofen was found to be a potent inhibitor of this PGF2 alpha production in rat brain (IC50 = 6.2 nM), and it completely suppressed PGF2 alpha production at 1 microM concentration. In addition, inhibition of PGF2 alpha synthesis by dexketoprofen was highly stereoselective since the enantiomer (-)-R-ketoprofen was significantly less potent (IC50 = 294 nM); with this enantiomer, even at high concentrations such as 1 microM, less than 60% inhibition was achieved. These results correlated with those obtained in the study of racemic ketoprofen and its enantiomers on cyclooxygenase activity of rat brain microsomes, where dexketoprofen also inhibited enzymatic activity stereoselectively. IC50 values obtained for dexketoprofen, (-)-R-ketoprofen, and rac-ketoprofen were 3.5 microM, 45.3 microM, and 5.8 microM, respectively. The above results could be related to the potent analgesic effect of dexketoprofen observed in vivo, which was also stereoselective. Taken together, these findings suggest that prostaglandin synthesis inhibition in rat brain by dexketoprofen could be associated, at least in part, with the analgesic effect of this NSAID.

Comparative molecular modeling study of the three-dimensional structures of prostaglandin endoperoxide H2 synthase 1 and 2 (COX-1 and COX-2).

To understand the structural features that dictate the selectivity of diverse nonsteroidal antiinflammatory drugs for the two isoforms of the human prostaglandin H2 synthase (PGHS), the three-dimensional (3D) structure of human COX-2 was assessed by means of sequence homology modeling. The ovine COX-1 structure, solved by X-ray diffraction methods and sharing a 61% sequence identity with human COX-2, was used as template. Both structures were energy minimized using the AMBER 4.0 force field with a dielectric constant of 4r. (S)-Flurbiprofen, a nonselective COX inhibitor, and SC-558, a COX-2-selective ligand, were docked at the cyclooxygenase binding site in both isozymes, evidencing the role of different residues in the ligand-protein interaction. The 3D structures of the constructed four ligand-enzyme complexes were refined by energy minimization. Molecular dynamics simulations were also carried out, to understand more deeply the structural origins of the selectivity. Distances calculated during the dynamics process between the different ligands and the interacting residues of the two PGHS isozymes provided evidence of the flexible nature of the cyclooxygenase active site, permitting the identification of different conserved and nonconserved residues as responsible for ligand selectivity.

Differential effect of alkyl chain-modified ether lipids on protein kinase C autophosphorylation and histone phosphorylation.

Analogues of 1-O-octadecyl-2-O-methyl-rac-glycerol-3-phosphocholine (ET-18-OMe), containing a carbonyl group at different positions in the alkyl chain and/or a pentylammonium group in sn-3 of glycerol, were evaluated as inhibitors of protein kinase C (PKC; EC 2.7.1.37). The presence of a carbonyl group in the alkyl chain of Et-18-OMe had a dual role in decreasing the inhibitory effect on histone phosphorylation and activating this reaction at low concentrations of compound. The optimal stimulatory effect was observed with the compound having the carbonyl function in C-7 of the alkyl chain. In contrast, all of these compounds were only inhibitors of PKC autophosphorylation, its potency decreasing progressively with the distance between the carbonyl group and the sn-1 position of glycerol. Replacement of the phosphocholine group of ET-18-OMe by a pentamethylene trimethylammonium group maintained the inhibitory effect on histone phosphorylation and autophosphorylation of PKC, and the simultaneous introduction of a ketone group in C-7 of the alkyl chain did not decrease any of these effects. The effects of all these analogues on PKC autophosphorylation, but not on histone phosphorylation, correlated quite well with their known antiproliferative activity on human tumor cell lines and membranolytic activity.