5-[6-1 -(Cyclohexyl-1 H-tetrazol-5-YL)hexyl]-1,8-naphthyridin-2-(1H)-one, SC-44368, a Potent Anti-aggregatory Agent which Selectively Inhibits Platelet Cyclic AMP Phosphodiesterase.

SC-44368 (5-[6-(1-cyclohexyl-1H-tetrazol-5-y)hexyl]-1,8-naphthyridin-2(1H)-one) is a potent and selective competitive inhibitor of platelet cyclic AMP-dependent phosphodiesterase (cAMP-PDE) (Ki: 1.65 μM). For the phosphodiesterase isoenzyms from human platelets SC-44368 shows a 26-fold selectivity (IC50 ratio) for the inhibition of the cAMP-PDE over the cyclic GMP-dependent phosphodiesterase (cGMP-PDE). By comparison, 3-isobutyl-1-methyl-xanthine (IBMX) inhibited the cAMP-PDE and cGMP-PDE from human platelets with approximately equal efficacy. Broad inhibitory activity was evident against human platelet aggregatory responses in vitro. IC50 values of 18.1 ± 5.3 μM (25 nM platelet activating factor, PAF), 17.3 ± 3.0 μM (1.0 μg/ml collagen) and 24.2 ± 10.3 μM (1μM ADP) were obtained against maximum increases in platelet-rich plasma (PRP) light transmission achieved by each agonist. SC-44368 potentiated the prostacyclin-induced increase of intra-platelet cAMP levels but did not potentiate the sodium nitroprusside-induced increase of intraplatelet cGMP levels. In an ex vivo model of platelet aggregation SC-44368 (3 mg/kg, i.v.) produced a potent inhibition of collagen-induced platelet aggregation. SC-44368 produced only weak hypotensive activity in the rat. Thus, SC-44368 is a novel cAMP-PDE inhibitor which possesses potent, broad spectrum anti-aggregatory properties.