Hiroyasu Hirose1, Toshifumi Kimura1, Megumu Okada1,
Yoshiki Itoh1, Fumiaki Ishida1,
Nobuo Mochizuki2, Tadayuki Nishibe2 and Masaru Nishikibe1,*
1TsukubaﾊResearch Institute, Banyu Pharmaceutical Co., Ltd.,
Okubo 3, Tsukuba 300-2611, Japan
2OdawaraﾊResearch Center, Nippon Soda Co., Ltd., Takada 345,
Odawara 250-0280, Japan
*ﾊ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ﾊ3 isozyme with an IC50 value of
0.039ﾊ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ﾊtimes more potent than those of cilostazol. In a rat
carotid arterial thrombosis model, intraduodenally administered NSP-513
(0.1ﾊmg/kg), cilostazol (30ﾊmg/kg) and aspirin (30ﾊmg/kg) reduced thrombus
formation by 75%, 66% and 48%, respectively. However, intravenously administered
dipyridamole (10ﾊ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ﾊ3 inhibitory effect of NSP-513 may
make this compound useful for assessing the physiological role of PDEﾊ3.
Keywords: NSP-513, Phosphodiesterase 3, Arterial thrombosis, Platelet
aggregation