Jun-Ichiro Kita

UR-3216: A New Generation Oral Platelet GPIIb / IIIa Antagonist

Various oral platelet GPIIb/IIIa receptor antagonists have undergone clinical investigations, but to date without success. Various factors have been proposed to explain their failure such as low affinity for the receptor, large peak/trough ratio, low bioavailability, partial agonist activity and pro-aggregatory effect. Efforts to discover a truly effective, safe, oral antagonist led to the discovery of UR-3216 (Fig. 1). The active form of UR-3216, UR-2922, possessed a high affinity for the human platelet receptor (K(d) <1 nM) with a slow dissociation rate (k(off)= 90 min) in vitro. UR-2922 induced no ligand-induced binding sites (LIBS) expression or prothrombotic activity in human platelets, distinctly different from orbofiban and other small molecule antagonists. To date, UR-2922 is the only high affinity GPIIb/IIIa antagonist without LIBS expression. In vivo characteristics of UR-3216 showed prolonged duration of efficacy (>24 h) with its favorable pharmacokinetic profile, superior to all the other oral GPIIb/IIIa antagonists. UR-3216 showed high bioavailability, rapid bioconversion to the active form and biliary excretion. UR-3216 is a novel, orally active GPIIb/IIIa antagonist of a new generation, which has substantially improved the crucial compounding factors and will be useful for the treatment of cardiovascular diseases.