Pharmacology of a selective cyclooxygenase-2 inhibitor, HN-56249: a novel compound exhibiting a marked preference for the human enzyme in intact cells.

HN-56249 (3-(2,4-dichlorothiophenoxy)-4-methylsulfonylamino-benzenesu lfonamide), a highly selective cyclooxygenase (COX)-2 inhibitor, is the prototype of a novel series of COX inhibitors comprising bicyclic arylethersulfonamides; of this series HN-56249 is the most potent and selective human COX-2 inhibitor. HN-56249 inhibited platelet aggregation as a measure of COX-1 activity only moderately (IC50 26.5+/-1.7 microM). In LPS-stimulated monocytic cells the release of prostaglandin (PG) F1alpha as a measure of COX-2 was markedly inhibited (IC50 0.027+/-0.001 microM). Thus, HN-56249 showed an approximately 1000-fold selectivity for COX-2 in intact cells. In whole blood assays HN-56249 showed a potent inhibitory activity for COX-2 (IC50 0.78+/-0.37 microM) only. COX-1 was only weakly inhibited (IC50 867+/-181 microM). Hence, HN-56249 exhibited a greater than 1000-fold selectivity for whole blood COX-2. HN-56249 surpassed the COX-2 selectivities of the COX-2 selective inhibitors 3-cyclohexyloxy-4-methylsulfonylamino-nitrobenzene (NS-398) and 6-(2,4-difluorophenoxy)-5-methyl-sulfonylamino-1-indanone (flosulide) in the intact cell assays by eight- and threefold, respectively, and in the whole blood assays by approximately 40-fold. Following i.v. administration HN-56249 inhibited carrageenan-induced rat paw oedema only moderately (ID50 26.2+/-5.7 mg/kg, mean +/- SEM), approximately tenfold less potent than indomethacin (ID50 2.1+/-0.2 mg/kg, mean +/- SEM). After oral administration HN-56249 reversed thermal hyperalgesia in the carrageenan-induced rat paw oedema test, however, some 30-fold less potently than diclofenac. Comparing the inhibitory potency of HN-56249 against human COX-2 with that against murine COX-2 in intact cells revealed a 300-fold selectivity for the human enzyme. Similar effects were observed with other COX-2-selective arylethersulfonamides. In contrast, non-COX-2-selective arylethersulfonamides, including a highly selective COX-1 inhibitor, inhibited human and murine COX-2 approximately equipotently. In conclusion, HN-56249 is a novel potent and highly selective COX-2 inhibitor with a marked preference for the human COX-2 enzyme in vitro. Despite excellent bioavailability and the long plasma half-life of HN-56249, anti-inflammatory effects in rodents were only moderate. We suggest these differing in vitro-in vivo effects observed could be due to significant inflammatory prostaglandin synthesis by COX-1, or to the genetic differences between human and rodent COX-2, or to both.

The analgesic NSAID lornoxicam inhibits cyclooxygenase (COX)-1/-2, inducible nitric oxide synthase (iNOS), and the formation of interleukin (IL)-6 in vitro.

OBJECTIVE: To investigate anti-inflammatory effects of lornoxicam in vitro on COX-1/COX-2, on NO formation from iNOS and on the formation of the pro-inflammatory cytokines TNF-alpha, IL-1beta, IL-6, and IL-8. MATERIALS AND METHODS: COX-1 inhibition in intact cells was assessed employing two systems: measurement of aggregation in human washed platelets and assessment of TXB2 formation in HEL cells. COX-2 inhibition was assessed by measuring 6-keto-PGF1alpha in supernatants of intact cells of LPS-stimulated J774.2 cells (murine) and of Mono Mac 6 cells (human). In whole blood inhibition of COX-1 was performed by measuring TXB2 formation after clotting, and COX-2 inhibition was examined in LPS-stimulated whole blood cultures. The reduction of NO levels as a measure of the inhibition of cellular NO formation was assayed in supernatants of LPS-stimulated RAW 264.7 cells using the Griess reaction. Compound influence on the formation ofTNF-alpha, IL-1beta, IL-6, and IL-8 was examined using LPS-stimulated monocytic cells (THP-1) and measurement of cytokine concentrations by specific ELISAs. RESULTS: In intact human cells, lornoxicam showed a balanced inhibition of COX-1/-2 exhibiting the lowest IC50 (0.005 microM/0.008 microM) of the large panel of NSAIDs tested. Similar results were obtained in the whole blood for COX-1/-2. NO formation was dose-dependently inhibited by lornoxicam (IC50 of 65 microM) whereas piroxicam, diclofenac, ibuprofen, ketorolac and naproxen inhibited the NO formation markedly less. Indomethacin was approximately equipotent with lornoxicam. In stimulated monocytic cells (THP-1), lornoxicam showed a marked inhibition of IL-6 formation (IC50 54 microM) while the formation ofTNF-alpha, IL-1beta and IL-8 was only moderately affected. CONCLUSIONS: Of the panel of NSAIDs tested, lornoxicam was found to be the most potent balanced inhibitor of human COX-1/-2. The equipotent COX-isoenzyme inhibition by lornoxicam is complemented by a marked inhibition of IL-6 production and of iNOS-derived NO formation. The in vitro activities described support the marked anti-inflammatory and analgesic activities of lornoxicam found in animal models as well as in clinical studies.