Hiroyasu Hirose1, Toshifumi Kimura1, Megumu Okada1,
Yoshiki Itoh1, Fumiaki Ishida1,
Nobuo Mochizuki2, Tadayuki Nishibe2 and Masaru Nishikibe1,*
1Tsukuba Research Institute, Banyu Pharmaceutical Co., Ltd., Okubo 3, Tsukuba 300-2611, Japan
2Odawara Research Center, Nippon Soda Co., Ltd., Takada 345, Odawara 250-0280, Japan
* To whom reprint requests should be addressed.
Abstract: We investigated the effects of NSP-513, (R)-4,5-dihydro-5-methyl-6-[4-(2-propyl-3-oxo-1-cyclohexenyl)amino] phenyl-3(2H)-pyridazinone, on phosphodiesterase (PDE) isozyme activities, in vitro platelet aggregation and in vivo thrombus formation. NSP-513 selectively inhibited human platelet PDE 3 isozyme with an IC50 value of 0.039 mM. In an in vitro human platelet aggregation assay, the IC50 values (mM) of NSP-513 for platelet aggregation induced by collagen, U-46619, arachidonic acid, adenosine diphosphate (ADP), epinephrine and thrombin were 0.31, 0.25, 0.082, 0.66, 0.23 and 0.73, respectively. In a mouse pulmonary thromboembolism model, orally administered NSP-513 showed in vivo antithrombotic effects that were 320 to 470 times more potent than those of cilostazol. In a rat carotid arterial thrombosis model, intraduodenally administered NSP-513 (0.1 mg/kg), cilostazol (30 mg/kg) and aspirin (30 mg/kg) reduced thrombus formation by 75%, 66% and 48%, respectively. However, intravenously administered dipyridamole (10 mg/kg) did not significantly prevent thrombus formation. These results demonstrate that NSP-513 has the potential to prevent not only in vitro platelet aggregation but also in vivo thrombus formation and indicate that the highly selective PDE 3 inhibitory effect of NSP-513 may make this compound useful for assessing the physiological role of PDE 3.
Keywords: NSP-513, Phosphodiesterase 3, Arterial thrombosis, Platelet aggregation