ANTITHROMBOTIC EFFECT OF A HUMANIZED ANTI-GPIIB IIIA MONOCLONAL-ANTIBODY, YM207, IN A PHOTOCHEMICALLY INDUCED THROMBOSIS MODEL IN MONKEYS/

We investigated the antithrombotic effects of a F(ab')(2) fragment of a humanized anti-platelet glycoprotein (GP) IIb/IIIa monoclonal antibo dy, YM207, in a platelet-rich thrombosis model. Thrombus was induced i n a mesenteric venule of squirrel monkeys by irradiation with filtered light in combination with i.v. administration of a fluorescent dye (s odium fluorescein). Time to occlusive thrombus formation was significa ntly prolonged by i.v. bolus injection of 0.3 mg/kg of YM207. At doses of 1 mg/kg and 3 mg/kg, complete occlusion did not occur during 60 mi n of the observation. Platelet aggregation in platelet-rich plasma was inhibited by YM207 at doses 0.3 mg/kg or more. A good correlation was obtained between inhibition of platelet aggregation and the percentag e of GPIIb/IIIa receptors blocked by YM207. Bleeding time was signific antly prolonged at a dose of 3 mg/kg. Platelet counts showed no signif icant change. These results suggest that YM207 is effective in prevent ing platelet-rich thrombus formation without inducing the prolongation of bleeding time or a significant decrease in platelet count. YM207 m ay be a useful therapeutic agent for the treatment of thrombotic disor ders.