The cyclooxygenase (COX) enzymes (COX-1 and COX-2) catalyze the bis-oxygenation of free arachidonic acid to prostaglandin (PG) H2, the precursor of other PGs and thromboxane (Tx). SC-560 is a selective COX-1 inhibitor with an IC50 value of 9 nM. It shows much less inhibitory potency against COX-2 with an IC50 value of 6.3 μM[3]. SC-560 decreased COX-1-dependent TxB2 production in human platelets with an IC50 value of 2.5 nM. It also reduced COX-2-dependent PGE2 synthesis in LPS-stimulated human monocytes with an IC50 value of 1.8 nM[4]. Oral administration of SC-560 (10 or 30 mg/kg) one hour before the whole blood assay inhibited ionophore-stimulated TxB2 production in rats. Oral dosing with SC-560 (0.1-100 mg/kg) blocked the production of TxB2 in a concentration-dependent manner in rat inflamed skin. SC-560 at 100 mg/kg showed 40% inhibition on PGE2 production in LPS-induced rat air pouch. It also efficiently inhibited PGE2 synthesis in stomach mucosa with an ED50 value of 0.2 mg/kg. However, 30 mg/kg SC-560 exhibited no significant effect on the onset of edema or hyperalgesia[3].
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