Cyclic AMP and cyclic GMP phosphodiesterase inhibition by an antiplatelet agent, 6-[(3-methylene-2-oxo-5-phenyl-5-tetrahydrofuranyl) methoxy]quinolinone (CCT-62)

The antiplatelet activity of (6-[(3-methylene-2-oxo-5-phenyl-5- tetrahydrofuranyl) methoxy]quinolinone) (CCT-62) was determined in vitro in rabbit platelets. CCT-62 inhibited rabbit platelet aggregation and ATP release caused by thrombin (0.1 U/ml), platelet-activating factor (2 ng/ml), collagen (10 μg/ml), arachidonic acid (100 μM), and 9,11-dideoxy-9α, 11α- methanoepoxy prostaglandin F(2α) (1 μM) in a concentration-dependent manner. The IC₅₀ values for platelet aggregation were 18.4 ± 4.5, 10.1 ± 1.6, 3.0 ± 0.9, 1.5 ± 0.3 and 1.0 ± 0.3 μM, respectively. In addition, CCT-62 disaggregated the clumped platelets caused by these aggregation inducers. It also inhibited phosphoinositide breakdown and intracellular calcium elevation induced by the above platelet aggregation inducers. CCT-62 increased intracellular cyclic AMP and cyclic GMP levels in a concentration- and time-dependent manner. Furthermore, it potentiated cyclic AMP formation caused by prostaglandin E₁ but not that caused by 3-isobutyl-1- methylxanthine. CCT-62 did not affect adenylate or guanylate cyclase but inhibited cyclic AMP- and cyclic GMP-phosphodiesterase activities. The antiplatelet effect of CCT-62 was reversed by a protein kinase A inhibitor, N-[2-(P-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H89). This data clearly indicated that CCT-62 is an inhibitor of phosphodiesterases and that its antiplatelet effect is mainly mediated by elevation of cyclic AMP levels.