Cyclooxygenase 2 and the kidney :

The cyclooxygenase (COX) enzymes catalyze a key step in the conversion of arachidonate to PGH2, the immediate substrate for a series of cell specific prostaglandin and thromboxane synthases. Prostaglandins play critical roles in numerous biologic processes, including the regulation of immune function, kidney development, reproductive biology, and gastrointestinal integrity. There are two COX isoforms, which differ mainly in their pattern of expression. COX-1 is expressed in most tissues, whereas COX-2 usually is absent, but is induced by numerous physiologic stimuli. Surprisingly, disruption of Cox1 (Ptgs1) in the mouse did not result in gastrointestinal abnormalities. cox-2 (Ptgs2) null mice show reproductive anomalies and defects in kidney development. Epidemiologic, animal, and human data indicate that NSAIDs, inhibitors of cyclooxygenase, are chemopreventive for colon cancer. COX-2 is overexpressed in 50% of benign polyps and 80-85% of adenocarcinomas. Offspring from cox-2 null by Apcdelta716 matings exhibit an 86% reduction in polyp number when compared to offspring from control animals, thus providing genetic evidence that COX-2 contributes to tumor formation or growth. The in vivo mechanism by which COX-2 affects tumor growth has not been determined. It is possible that both tumor and stromally derived COX-2 could influence tumor angiogenesis and/ or immune function.

A series of sulfonamide-containing 1,5-diarylpyrazole derivatives were prepared and evaluated for their ability to block cyclooxygenase-2 (COX-2) in vitro and in vivo. Extensive structure-activity relationship (SAR) work was carried out within this series, and a number of potent and selective inhibitors of COX-2 were identified. Since an early structural lead (1f, SC-236) exhibited an unacceptably long plasma half-life, a number of pyrazole analogs containing potential metabolic sites were evaluated further in vivo in an effort to identify compounds with acceptable pharmacokinetic profiles. This work led to the identification of 1i (4-[5-(4-methylphenyl)-3-(trifluoromethyl)- H-pyrazol-1-yl]benzenesulfonamide, SC-58635, celecoxib), which is currently in phase III clinical trials for the treatment of rheumatoid arthritis and osteoarthritis.

Cyclooxygenase (COX) has two isoforms. Generally, COX 1 is constitutively expressed in most tissues, where it maintains physiological processes; inducible COX 2 is considered a pro-inflammatory enzyme and a chief target for the treatment of inflammatory diseases. Here we present evidence that COX 2 may have anti-inflammatory properties. In carrageenin-induced pleurisy in rats, the predominant cells at 2 hours are polymorphonuclear leucocytes, whereas mononuclear cells dominate from 24 hours until resolution at 48 hours. In this model, COX 2 protein expression peaked initially at 2 hours, associated with maximal prostaglandin E2 synthesis. However, at 48 hours there was a second increase in COX 2 expression, 350% greater than that at 2 hours. Paradoxically, this coincided with inflammatory resolution and was associated with minimal prostaglandin E2 synthesis. In contrast, levels of prostaglandin D2, and 15deoxy delta(12-14)prostaglandin J2 were high at 2 hours, decreased as inflammation increased, but were increased again at 48 hours. The selective COX 2 inhibitor NS-398 and the dual COX 1/COX 2 inhibitor indomethacin inhibited inflammation at 2 hours but significantly exacerbated inflammation at 48 hours. This exacerbation was associated with reduced exudate prostaglandin D2 and 15deoxy delta(12-14)prostaglandin J2 concentrations, and was reversed by replacement of these prostaglandins. Thus, COX 2 may be pro-inflammatory during the early phase of a carrageenin-induced pleurisy, dominated by polymorphonuclear leucocytes, but may aid resolution at the later, mononuclear cell-dominated phase by generating an alternative set of anti-inflammatory prostaglandins.