The acute antihyperalgesic action of nonsteroidal, anti-inflammatory drugs and release of spinal prostaglandin E2 is mediated by the inhibition of constitutive spinal cyclooxygenase-2 (COX-2) but not COX-1.

Western blots show the constitutive expression of COX-1 and COX-2 in the rat spinal dorsal and ventral horns and in the dorsal root ganglia. Using selective inhibitors of cyclooxygenase (COX) isozymes, we show that in rats with chronic indwelling intrathecal catheters the acute thermal hyperalgesia evoked by the spinal delivery of substance P (SP; 20 nmol) or NMDA (2 nmol) and the thermal hyperalgesia induced by the injection of carrageenan into the paw are suppressed by intrathecal and systemic COX-2 inhibitors. The intrathecal effects are dose-dependent and stereospecific. In contrast, a COX-1 inhibitor given systemically, but not spinally, reduced carrageenan-evoked thermal hyperalgesia but had no effect by any route with spinal SP hyperalgesia. Using intrathecal loop dialysis catheters, we showed that intrathecal SP would enhance the release of prostaglandin E(2) (PGE(2)). This intrathecally evoked release of spinal PGE(2) was diminished by systemic delivery of nonspecific COX and COX-2-selective inhibitors, but not a COX-1-selective inhibitor. Given at systemic doses that block SP- and carrageenan-evoked hyperalgesia, COX-2, but not COX-1, inhibitors reduced spinal SP-evoked PGE(2) release. Thus, constitutive spinal COX-2, but not COX-1, is an important contributor to the acute antihyperalgesic effects of spinal as well as systemic COX-2 inhibitors.

A three-step kinetic mechanism for selective inhibition of cyclo-oxygenase-2 by diarylheterocyclic inhibitors.

Cyclo-oxygenase (COX) enzymes are the targets for non-steroidal anti-inflammatory drugs (NSAIDs). These drugs demonstrate a variety of inhibitory mechanisms, which include simple competitive, as well as slow binding and irreversible inhibition. In general, most NSAIDs inhibit COX-1 and -2 by similar mechanisms. A unique class of diarylheterocyclic inhibitors has been developed that is highly selective for COX-2 by virtue of distinct inhibitory mechanisms for each isoenzyme. Several of these inhibitors, with varying selectivity, have been utilized to probe the mechanisms of COX inhibition. Results from analysis of both steady-state and time-dependent inhibition were compared. A generalized mechanism for inhibition, consisting of three sequential reversible steps, can account for the various types of kinetic behaviour observed with these inhibitors.

Cox-2-specific inhibitors: definition of a new therapeutic concept.

Nonsteroidal anti-inflammatory drugs have been a mainstay in the treatment of inflammatory diseases such as rheumatoid arthritis. However, these agents can result in severe and occasionally life-threatening adverse effects that can limit therapeutic benefit. Progress toward safer anti-inflammatory therapy was aided by the discovery that cyclooxygenase (COX) exists as two isozymes, COX-1 and COX-2. Both isozymes form prostaglandins that support physiologic functions; however, the formation of proinflammatory prostaglandins is catalyzed by COX-2. Inhibition of COX-2 accounts for the anti-inflammatory and analgesic action of NSAIDs; however, concurrent inhibition of COX-1 inhibits prostaglandin-dependent mechanisms such as gastroduodenal mucosal defense and platelet aggregation. This inhibition is the basis of the gastrointestinal toxicity and bleeding characteristic of these drugs. These findings led to the hypothesis that agents that selectively inhibit COX-2 would possess anti-inflammatory and analgesic action but would spare COX-1, thereby avoiding adverse effects in the gastrointestinal tract and platelets. Selective COX-2 inhibitors are now available. The novelty of these agents has raised questions in the medical community as to what constitutes selectivity for COX-2. This review outlines the criteria that must be met to characterize a compound as COX-2-specific. Clinical evidence of clear improvement in gastrointestinal tolerability and safety must be demonstrated in addition to complementary evidence of COX-2 selectivity obtained from enzyme, biochemical, and clinical pharmacology evaluations.

Selective cyclooxygenase-2 inhibitors: heteroaryl modified 1,2-diarylimidazoles are potent, orally active antiinflammatory agents.

A series of heteroaryl modified 1,2-diarylimidazoles has been synthesized and found to be potent and highly selective (1000-9000-fold) inhibitors of the human COX-2. 3-Pyridyl derived COX-2 selective inhibitor (25) exhibited excellent activity in acute (carrageenan induced paw edema, ED(50) = 5.4 mg/kg) and chronic (adjuvant induced arthritis, ED(50) = 0.25 mg/kg) models of inflammation. The relatively long half-life of 25 in rat and dog prompted investigation of the pyridyl and other heteroaromatic systems containing potential metabolic functionalities. A number of substituted pyridyl and thiazole containing compounds (e.g., 44, 46, 54, 76, and 78) demonstrated excellent oral activity in every efficacy model evaluated. Several orally active diarylimidazoles exhibited desirable pharmacokinetics profiles and showed no GI toxicity in the rat up to 100 mg/kg in both acute and chronic models. The paper describes facile and practical syntheses of the targeted diarylimidazoles. The structure-activity relationships and antiinflammatory properties of a series of diarylimidazoles are discussed.

Effects of celecoxib and naproxen on renal function in the elderly.

OBJECTIVE: To compare the effects of celecoxib, a cyclooxygenase 2-specific inhibitor, with the nonspecific cyclooxygenase 1 and 2 inhibitor naproxen on renal function in 29 healthy elderly subjects in a single-blind, randomized, crossover study. METHODS: Subjects received either celecoxib, 200 mg twice daily, for 5 days followed by celecoxib, 400 mg twice daily, for the next 5 days, or they received naproxen, 500 mg twice daily, for 10 days. After a 7-day washout, subjects were crossed over to receive the other regimen. RESULTS: After the first dose, the trend was for a greater decrease in glomerular filtration rate with naproxen (-5.31 mL/min per 1.73 m2) compared with celecoxib (-0.86 mL/min per 1.73 m2). The treatment difference became statistically significant on day 6 (-7.53 vs -1.11 mL/min per 1.73 m2 for naproxen and celecoxib, respectively; P=.004). Urinary prostaglandin E2 and 6-keto-prostaglandin F1alpha excretion was significantly reduced from baseline across the treatment interval with both celecoxib and naproxen (P< or =.04). There were no significant differences in prostaglandin excretion between these 2 agents (P> or =.07). Small, transient decreases (P<.05) in urinary sodium excretion were observed after the initiation of both celecoxib and naproxen treatment. Sodium excretion values returned to baseline by the end of the study. CONCLUSIONS: The results indicate that cyclooxygenase 2-specific inhibition in healthy elderly subjects may spare renal hemodynamic function, although the effects on sodium excretion, as well as urinary prostaglandin E2 and 6-keto-prostaglandin F1alpha excretion, appear to be similar to those of nonspecific cyclooxygenase inhibitors such as naproxen.

Effects of celecoxib, a novel cyclooxygenase-2 inhibitor, on platelet function in healthy adults: a randomized, controlled trial.

Conventional nonsteroidal anti-inflammatory drugs (NSAIDs) nonspecifically inhibit cyclooxygenase-1 (COX-1), an enzyme critical to normal platelet function, and COX-2, which mediates inflammatory response mechanisms. Celecoxib, an antiarthritic agent that inhibits COX-2 but spares COX-1 at therapeutic doses, is expected to have minimal effects on platelet function. A double-blind, randomized, placebo-controlled study of 10 days' duration was conducted in 24 healthy adults to compare the effects on platelet function of a supratherapeutic dose of celecoxib (600 mg bid) with a standard dose of naproxen (500 mg bid), a conventional NSAID. Ex vivo platelet aggregation in response to standard agonists (collagen, arachidonate, or U46619 [a thromboxane A2 receptor agonist]), bleeding time, and serum thromboxane B2 (TxB2) level were measured. Unlike celecoxib or placebo, naproxen produced statistically significant reductions in platelet aggregation and serum TxB2 levels and increased bleeding time. The results indicate that even at supratherapeutic doses, celecoxib will not interfere with normal mechanisms of platelet aggregation and hemostasis, supporting the premise that celecoxib is COX-1 sparing relative to conventional NSAIDs.

Anti-inflammatory and upper gastrointestinal effects of celecoxib in rheumatoid arthritis: a randomized controlled trial.

CONTEXT: In vitro studies have shown that celecoxib inhibits cyclooxygenase 2 (COX-2) but not COX-1, suggesting that this drug may have anti-inflammatory and analgesic activity without adverse upper gastrointestinal (GI) tract effects that result from COX-1 inhibition. OBJECTIVE: To test whether celecoxib has efficacy as an anti-inflammatory and analgesic with reduced GI tract mucosal damage compared with conventional nonsteroidal anti-inflammatory drugs in patients with rheumatoid arthritis. DESIGN: Randomized, multicenter, placebo-controlled, double-blind trial lasting 12 weeks, with follow-up at weeks 2, 6, and 12, from September 1996 thorugh February 1998. SETTING: Seventy-nine clinical sites in the United States and Canada. PATIENTS: A total of 1149 patients aged 18 years or older with symptomatic rheumatoid arthritis who met inclusion criteria were randomized; 688 (60%) of these completed the study. INTERVENTIONS: Patients were randomized to receive celecoxib, 100 mg, 200 mg, or 400 mg twice per day (n = 240, 235, and 218, respectively); naproxen, 500 mg twice per day (n = 225); or placebo (n = 231). MAIN OUTCOME MEASURES: Improvement in signs and symptoms of rheumatoid arthritis as assessed using standard measures of efficacy and GI tract safety as assessed by upper GI tract endoscopy before and after treatment, compared among treatment groups. RESULTS: All dosages of celecoxib and naproxen significantly improved the signs and symptoms of arthritis compared with placebo. Maximal anti-inflammatory and analgesic activity was evident within 2 weeks of initiating treatment and was sustained throughout the 12 weeks. The incidence of endoscopically determined gastroduodenal ulcers in placebo-treated patients was 4 (4%) of 99, and the incidences across all dosages of celecoxib were not significantly different (P>.40): 9 (6%) of 148 with 100 mg twice per day, 6 (4%) of 145 with 200 mg twice per day, and 8 (6%) of 130 with 400 mg twice per day. In contrast, the incidence with naproxen was 36 (26%) of 137, significantly greater than either placebo or celecoxib (P<.001). The overall incidences of GI tract adverse effects were 19% for placebo; 28%, 25%, and 26% for celecoxib 100 mg, 200 mg, and 400 mg twice per day, respectively; and 31 % for naproxen. CONCLUSION: In this study, all dosages of celecoxib were efficacious in the treatment of rheumatoid arthritis and did not affect COX-1 activity in the GI tract mucosa as evidenced by less frequent incidence of endoscopic ulcers compared with naproxen.

Celecoxib versus diclofenac in long-term management of rheumatoid arthritis: randomised double-blind comparison.

BACKGROUND: Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclo-oxygenase (COX), which leads to suppression of COX-1-mediated production of gastrointestinal-protective prostaglandins. Gastrointestinal injury is a common outcome. We compared the efficacy, safety, and tolerability of long-term therapy with celecoxib, a COX-1 sparing inhibitor of COX-2, with diclofenac, a non-specific COX inhibitor. METHODS: 655 patients with adult-onset rheumatoid arthritis of at least 6 months' duration were randomly assigned oral celecoxib 200 mg twice daily or diclofenac SR 75 mg twice daily for 24 weeks. Anti-inflammatory and analgesic activity and tolerability were assessed at baseline, every 4 weeks, and at week 24. We assessed gastrointestinal safety by upper-gastrointestinal endoscopy within 7 days of the last treatment dose at centres where the procedure was available. Analysis was by intention-to-treat. FINDINGS: 430 patients underwent endoscopy (celecoxib n=212, diclofenac n=218). The two drugs were similar in management of rheumatoid arthritis pain and inflammation. Gastroduodenal ulcers were detected endoscopically in 33 (15%) patients treated with diclofenac and in eight (4%) in the celecoxib group (p<0.001). The rate of withdrawal for any gastrointestinal-related adverse event, most commonly abdominal pain, diarrhoea, and dyspepsia, was nearly three times higher in the diclofenac-treated group than in the celecoxib group (16 vs 6%; p<0.001). INTERPRETATION: Celecoxib showed sustained anti-inflammatory and analgesic activity similar to diclofenac, with a lower frequency of upper gastrointestinal ulceration or gastrointestinal adverse events, and tolerability was better.

Treatment of osteoarthritis with celecoxib, a cyclooxygenase-2 inhibitor: a randomized controlled trial.

OBJECTIVE: To compare the efficacy and safety of celecoxib, a cyclooxygenase-2 (COX-2) inhibitor, with those of naproxen, a nonsteroidal anti-inflammatory drug (NSAID), and placebo in the treatment of osteoarthritis of the knee. METHODS: In this multicenter, randomized, double-blind, placebo-controlled trial, 1003 patients with symptomatic osteoarthritis of the knee were randomly assigned to receive celecoxib at doses of 50, 100, or 200 mg twice a day; naproxen, 500 mg twice a day; or placebo for 12 weeks. Patients were evaluated with standard measures of efficacy 2 to 7 days after discontinuing previous NSAID or analgesic therapy and after 2, 6, and 12 weeks of treatment with the study drug. RESULTS: Celecoxib treatment led to significant improvement in the signs and symptoms of osteoarthritis as determined by all efficacy measures. Significant pain relief occurred within 2 days of the initiation of treatment, and maximum anti-inflammatory and analgesic activity, evident within 2 weeks, was sustained throughout the 12-week study. All celecoxib doses were efficacious compared with placebo, although the 50-mg twice-daily dosage regimen was minimally effective. The higher doses of celecoxib (100 and 200 mg twice a day) were similarly efficacious, and the magnitude of improvement observed with these dosing regimens was comparable to that seen with naproxen at a dose of 500 mg twice a day. All doses of celecoxib and naproxen were well tolerated. CONCLUSION: COX-2 inhibition with celecoxib is an effective approach for the treatment of osteoarthritis, as seen by clinical improvement in signs and symptoms comparable to treatment with naproxen.

Kinetic basis for selective inhibition of cyclo-oxygenases.

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the formation of prostaglandins by cyclo-oxygenases (COX). The discovery of a second COX isoform (COX-2) associated with inflammation led to agents that selectively inhibit COX-2, e.g. celecoxib. We evaluated the kinetics of inhibition of celecoxib and several NSAIDs. Celecoxib displays classic competitive kinetics on COX-1 (Ki=10-16 microM). An initial competitive interaction with COX-2 can also be discerned with celecoxib (Ki=11-15 microM), followed by a time-dependent interaction leading to potent inhibition, characterized as inactivation (Kinact=0.03-0.5 s-1). Half-maximal inhibition (IC50) using end-point assays reflects the competitive component on COX-1 (IC50=4-19 microM) and the inactivation component on COX-2 (IC50=0.003-0.006 microM). NSAIDs exhibit four distinct modes of COX inhibition based on kinetic behaviour: (1) competitive, e.g. ibuprofen; (2) weak binding, time-dependent, e.g. naproxen, oxicams; (3) tight binding, time-dependent, e.g. indomethacin; (4) covalent, e.g. aspirin. In addition, most NSAIDs display different kinetic behaviour for each isoform. Weakly binding inhibitors show variable behaviour in enzyme assays, with apparent inhibitory activity being markedly influenced by experimental conditions; determination of kinetic constants with this class is unreliable and IC50 values are strongly dependent on assay conditions. Although IC50 determinations are useful for structure/activity analyses, the complex and distinct mechanisms of enzyme inhibition of each COX isoform by the NSAIDs renders comparison of inhibitory activity on COX-1 and COX-2 using IC50 ratios of questionable validity.

Transformation of intestinal epithelial cells by chronic TGF-beta1 treatment results in downregulation of the type II TGF-beta receptor and induction of cyclooxygenase-2.

The precise role of TGF-beta in colorectal carcinogenesis is not clear. The purpose of this study was to determine the phenotypic alterations caused by chronic exposure to TGF-beta in non-transformed intestinal epithelial (RIE-1) cells. Growth of RIE-1 cells was inhibited by >75% following TGF-beta1 treatment for 7 days, after which the cells resumed a normal growth despite the presence of TGF-beta1. These 'TGF-beta-resistant' cells (RIE-Tr) were continuously exposed to TGF-beta for >50 days. Unlike the parental RIE cells, RIE-Tr cells lost contact inhibition, formed foci in culture, grew in soft agarose. RIE-Tr cells demonstrated TGF-beta-dependent invasive potential in an in vitro assay and were resistant to Matrigel and Na-butyrate-induced apoptosis. The RIE-Tr cells were also tumorigenic in nude mice. The transformed phenotype of RIE-Tr cells was associated with a 95% decrease in the level of the type II TGF-beta receptor (TbetaRII) protein, a 40-fold increase in cyclooxygenase-2 (COX-2) protein, and 5.9-fold increase in the production of prostacyclin. Most RIE-Tr subclones that expressed low levels of TbetaRII and high levels of COX-2 were tumorigenic. Those subclones that express abundant TbetaRII and low levels of COX-2 were not tumorigenic in nude mice. A selective COX-2 inhibitor inhibited RIE-Tr cell growth in culture and tumor growth in nude mice. The reduced expression of TbetaRII, increased expression of COX-2, and the ability to form colonies in Matrigel were all reversible upon withdrawal of exogenous TGF-beta1 for the RIE-Tr cells.

Pharmacological analysis of cyclooxygenase-1 in inflammation.

The enzymes cyclooxygenase-1 and cyclooxygenase-2 (COX-1 and COX-2) catalyze the conversion of arachidonic acid to prostaglandin (PG) H2, the precursor of PGs and thromboxane. These lipid mediators play important roles in inflammation and pain and in normal physiological functions. While there are abundant data indicating that the inducible isoform, COX-2, is important in inflammation and pain, the constitutively expressed isoform, COX-1, has also been suggested to play a role in inflammatory processes. To address the latter question pharmacologically, we used a highly selective COX-1 inhibitor, SC-560 (COX-1 IC50 = 0.009 microM; COX-2 IC50 = 6.3 microM). SC-560 inhibited COX-1-derived platelet thromboxane B2, gastric PGE2, and dermal PGE2 production, indicating that it was orally active, but did not inhibit COX-2-derived PGs in the lipopolysaccharide-induced rat air pouch. Therapeutic or prophylactic administration of SC-560 in the rat carrageenan footpad model did not affect acute inflammation or hyperalgesia at doses that markedly inhibited in vivo COX-1 activity. By contrast, celecoxib, a selective COX-2 inhibitor, was anti-inflammatory and analgesic in this model. Paradoxically, both SC-560 and celecoxib reduced paw PGs to equivalent levels. Increased levels of PGs were found in the cerebrospinal fluid after carrageenan injection and were markedly reduced by celecoxib, but were not affected by SC-560. These results suggest that, in addition to the role of peripherally produced PGs, there is a critical, centrally mediated neurological component to inflammatory pain that is mediated at least in part by COX-2.

Cyclooxygenase-2 inhibition prevents delayed death of CA1 hippocampal neurons following global ischemia.

The inducible isoform of the enzyme cyclooxygenase-2 (COX2) is an immediate early gene induced by synaptic activity in the brain. COX2 activity is an important mediator of inflammation, but it is not known whether COX2 activity is pathogenic in brain. To study the role of COX2 activity in ischemic injury in brain, expression of COX2 mRNA and protein and the effect of treatment with a COX2 inhibitor on neuronal survival in a rat model of global ischemia were determined. Expression of both COX2 mRNA and protein was increased after ischemia in CA1 hippocampal neurons before their death. There was increased survival of CA1 neurons in rats treated with the COX2-selective inhibitor SC58125 [1-[(4-methylsulfonyl) phenyl]-3-trifluoro-methyl-5-[(4-fluoro)phenyl] pyrazole] before or after global ischemia compared with vehicle controls. Furthermore, hippocampal prostaglandin E2 concentrations 24 h after global ischemia were decreased in drug-treated animals compared with vehicle-treated controls. These results suggest that COX2 activity contributes to CA1 neuronal death after global ischemia.

Preliminary study of the safety and efficacy of SC-58635, a novel cyclooxygenase 2 inhibitor: efficacy and safety in two placebo-controlled trials in osteoarthritis and rheumatoid arthritis, and studies of gastrointestinal and platelet effects.

OBJECTIVE: To investigate the efficacy and safety of SC-58635 (celecoxib), an antiinflammatory and analgesic agent that acts by selective cyclooxygenase 2 (COX-2) inhibition and is not expected to cause the typical gastrointestinal (GI), renal, and platelet-related side effects associated with inhibition of the COX-1 enzyme. METHODS: Four phase II trials were performed: a 2-week osteoarthritis efficacy trial, a 4-week rheumatoid arthritis efficacy trial, a 1-week endoscopic study of GI mucosal effects, and a 1-week study of effects on platelet function. RESULTS: The 2 arthritis trials identified SC-58635 dosage levels that were consistently effective in treating the signs and symptoms of arthritis and were distinguished from placebo on standard arthritis scales. In the upper GI endoscopy study, 19% of subjects receiving naproxen (6 of 32) developed gastric ulcers, whereas no ulcers occurred in subjects receiving SC-58635 or placebo. The study of platelet effects revealed no meaningful effect of SC-58635 on platelet aggregation or thromboxane B2 levels, whereas aspirin caused significant decreases in 2 of 3 platelet aggregation measures and thromboxane B2 levels. In all 4 trials, SC-58635 was well tolerated, with a safety profile similar to that of placebo. CONCLUSION: SC-58635 achieves analgesic and antiinflammatory efficacy in arthritis through selective COX-2 inhibition, without showing any evidence of 2 of the toxic effects of COX-1 inhibition associated with nonsteroidal antiinflammatory drugs.

Effect of COX-1 and COX-2 inhibition on induction and maintenance of carrageenan-evoked thermal hyperalgesia in rats.

Intrathecal administration of nonsteroidal anti-inflammatory drugs in the rat blocks the thermal hyperalgesia induced by tissue injury, which suggests a role for spinal cyclooxygenase (COX) products in this facilitated state. Two isozymes of the COX enzyme have been reported, COX-1 and COX-2, but the agents thus far examined are not isozyme selective. We examined the effects of intrathecally (i.t.) or systemically (i.p.) administered S(+)-ibuprofen (a nonselective COX inhibitor) or 1-[(4-methysulfonyl)phenyl]-3-tri-fluoromethyl-5-(4-fluorophenyl) pyrazole (SC58125; a COX-2 selective inhibitor) on carrageenan-induced thermal hyperalgesia (reduced hindpaw-withdrawal latency). The following observations were made: 1) Thermal hyperalgesia otherwise observed during the first 170 min was blocked in a dose-dependent manner by S(+)-ibuprofen or SC58125 administered i.t. or i.p. before carrageenan treatment. 2) Intraperitoneal, but not i.t., administration of either inhibitor after the establishment of hyperalgesia (170 min after carrageenan injection) reversed thermal hyperalgesia in a dose-dependent manner. Thus, the initial component of thermal hyperalgesia after tissue injury was blocked by systemic or spinal administration of both COX inhibitors, whereas established hyperalgesia was reversed only by systemic inhibitors. This study demonstrates that at least spinal COX-2, if not both COX-1 and COX-2, are necessary for the initiation of thermal hyperalgesia, whereas nonspinal sources of prostanoids (synthesized by COX-2 and perhaps also COX-1) are important for the maintenance of thermal hyperalgesia associated with tissue injury and inflammation.

Regulation of prostaglandin biosynthesis in vivo by glutathione.

Intraperitoneal administration of urate crystals to mice reduced subsequent macrophage conversion of arachidonic acid (AA) to prostaglandins (PGs) and 12-hydroxyeicosatetraenoic acid for up to 6 h. In contrast, levels of 12-hydroxyheptadecatrienoic acid (12-HHT) were markedly elevated. This metabolic profile was previously observed in vitro when recombinant cyclooxygenase (COX) enzymes were incubated with reduced glutathione (GSH). Analysis of peritoneal GSH levels revealed a fivefold elevation after urate crystal administration. The GSH synthesis inhibitor L-buthionine-[S,R]-sulfoximine partially reversed the urate crystal effect on both GSH elevation and PG synthesis. Moreover, addition of exogenous GSH to isolated peritoneal macrophages shifted AA metabolism from PGs to 12-HHT. Urate crystal administration reduced COX-1, but induced COX-2 expression in peritoneal cells. The reduction of COX-1 may contribute to the attenuation of PG synthesis after 1 and 2 h, but PG synthesis remained inhibited up to 6 h, when COX-2 levels were high. Overall, our results indicate that elevated GSH levels inhibit PG production in this model and provide in vivo evidence for the role of GSH in the regulation of PG biosynthesis.

A selective cyclooxygenase 2 inhibitor suppresses the growth of H-ras-transformed rat intestinal epithelial cells.

BACKGROUND & AIMS: Constitutive expression of cyclooxygenase 2 (COX-2) has been found in 85% of colorectal cancers. Ras mutations are found in 50% of colorectal adenocarcinomas. The aim of this study was to determine the role of COX-2 in ras-induced transformation in rat intestinal epithelial (RIE) cells. METHODS: Cell growth was determined by cell counts. The expression of COX-2 was examined by Northern and Western analyses. For tumorigenicity assays, cells were inoculated into dorsal subcutaneous tissue of athymic nude mice. DNA-fragmentation assays were performed to detect apoptosis. RESULTS: The expression of COX-2 was increased in RIE-Ras cells at both messenger RNA (9-fold) and protein (12-fold) levels. Prostaglandin I2 levels were elevated 2.15-fold in RIE-Ras cells. Serum deprivation further increased COX-2 expression 3.8-fold in RIE-Ras cells. Treatment with a selective COX-2 antagonist (SC58125) inhibited the growth of RIE-Ras cells through inhibition of cell proliferation and by induction of apoptosis. SC-58125 treatment reduced the colony formation in Matrigel by 83.0%. Intraperitoneal administration of SC-58125 suppressed RIE-Ras tumor growth in nude mice by 60.3% in 4 weeks. SC-58125 treatment also induced apoptosis in RIE-Ras cells as indicated by increased DNA fragmentation. CONCLUSIONS: Overexpression of COX-2 may contribute to tumorigenicity of ras-transformed intestinal epithelial cells. Selective inhibition of COX-2 activity inhibits growth of ras-transformed intestinal epithelial cells and induces apoptosis.

Cyclooxygenases and the central nervous system.

Prostaglandins (PGs) were first described in the brain by Samuelsson over 30 years ago (Samuelsson, 1964). Since then a large number of studies have shown that PGs are formed in regions of the brain and spinal cord in response to a variety of stimuli. The recent identification of two forms of cyclooxygenase (COX; Kujubu et al., 1991; Xie et al., 1991; Smith and DeWitt, 1996), both of which are expressed in the brain, along with superior tools for mapping COX distribution, has spurred a resurgence of interest in the role of PGs in the central nervous system (CNS). In this review we will describe new data in this area, focusing on the distribution and potential role of the COX isoforms in brain function and disease.

Effect of spinal cyclooxygenase inhibitors in rat using the formalin test and in vitro prostaglandin E2 release.

Spinally delivery of the non-specific cyclooxygenase inhibitor, S(+)-ibuprofen, reduces the second phase of the formalin test and the evoked release of prostaglandin E2 (prostaglandin E2) from rat spinal cord in vitro. Using two selective cyclooxygenase-2 inhibitors, SC58125 (1-[(4-methysufonyl)phenyl]-3-tri-fluoromethyl-5-(4-fluorophenyl)p yrazole) and SC-236 (4-[5-(4-chlorophenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfon amide), we observed that neither agent at the highest dose/concentration employed altered the second phase of the formalin test after intrathecal delivery or K+-evoked prostaglandin E2 release from spinal cord in vitro, although ibuprofen was effective in both models. These observations suggest that cyclooxygenase-2 may not be associated with spinal prostanoid synthesis acutely or with facilitated nociception which occurs within the limited time frame of the formalin test.