title: Ex vivo evaluation of anti-GPVI antibody in cynomolgus monkeys: dissociation between anti-platelet aggregatory effect and bleeding time.
abstract: Recent progress in the understanding of thrombus formation has suggested an important role of glycoprotein (GP)VI. In contrast to its pivotal role in collagen-induced platelet activation, it has been suggested that its blockade does not induce massive bleeding tendency. To demonstrate the dissociation between inhibitory effect on platelet aggregation and bleeding by GPVI blockade, we examined the effects of Fab fragment of OM2, an anti-human GPVI monoclonal antibody on ex vivo collagen-induced platelet aggregation and skin bleeding time after intravenous injection in cynomolgus monkeys. In a dose-escalation study, OM2 potently (> 80%) inhibited collagen-induced platelet aggregation at the cumulative dose of 0.2 mg/kg with a slight prolongation of bleeding time (1.3 times baseline value). Furthermore, at 18.8 mg/kg, the highest dose tested, prolongation of bleeding time was still mild (1.9 times). In contrast, abciximab, Fab fragment of anti-GPIIb/IIIa antibody prolonged bleeding time by 5.0 times at 0.35 mg/kg, the lowest effective dose on platelet aggregation. In a pharmacodynamic study, a bolus injection of OM2 at 0.4 mg/kg produced potent inhibition of collagen-induced aggregation up to six hours after injection, showing longer half-life than that of abciximab. The injection of OM2 Fab did not induce thrombocytopenia and GPVI depletion in monkeys. These results suggest that blockade of GPVI by antibody can exert a potent inhibitory effect on collagen-induced platelet aggregation with a milder prolongation of bleeding time than blockade of GPIIb/IIIa. This study indicates that OM2 has the potential to be developed as a new class of therapeutic tool.
authors.affiliation: Otsuka Maryland Medicinal Laboratories, Rockville, MD 20850, USA.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Hisao
authors.initials: H
authors.lastname: Takizawa
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Nakama
authors.forename: Xiaoqi
authors.initials: X
authors.lastname: Gong
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Yamada
authors.forename: Narendra N
authors.initials: NN
authors.lastname: Tandon
authors.forename: Junichi
authors.initials: J
authors.lastname: Kambayashi
mesh_terms: D000818:Animals; D000906:Antibodies / Q000737:chemistry*; D001760:Bleeding Time / Q000379:methods*; D015153:Blotting, Western; D003094:Collagen / Q000737:chemistry; D007074:Immunoglobulin G / Q000737:chemistry; D008252:Macaca fascicularis; D010973:Platelet Adhesiveness; D010974:Platelet Aggregation; D010979:Platelet Function Tests / Q000379:methods*; D010980:Platelet Membrane Glycoproteins / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*; D013997:Time Factors
chemical_list: D000906:Antibodies; D007074:Immunoglobulin G; D010980:Platelet Membrane Glycoproteins; C098341:platelet membrane glycoprotein VI; D003094:Collagen