SC-560 is a member of the diaryl heterocycle class of cyclooxygenase (COX) inhibitors which includes celecoxib (Celebrex?) and rofecoxib (Vioxx?). However, unlike these selective COX-2 inhibitors, SC-560 is a selective inhibitor of COX-1. Using human recombinant enzymes, the IC50 value for SC-560 with respect to COX-1 is 9 nM, while the corresponding IC50 value for COX-2 is 6.3 μM. Thus, SC-560 shows 700-fold selectivity for the COX-1 enzyme. SC-560 is orally active in the rat, where 10 mg/kg completely abolishes the ionophore-induced production of thromboxane B2 in whole blood. However, SC-560 is ineffective in the treatment of inflammation in models such as the LPS-induced rat air-pouch model, in which the COX-2 generated prostaglandins play a significant role in the inflammatory process. In whole cells, however, SC-560 appears to act as a non-selective COX inhibitor. The mechanism of the selective versus non-selective effects of SC-560 in a cell-free environment compared whole cells has not been elucidated.
