EFFECTS OF DU-176B, A NOVEL DIRECT FACTOR XA INHIBITOR, ON PROTHROMBINASE ACTIVITY AND PLATELET AGGREGATION IN VITRO
Abstract number: P-T-642
Shibano1 T., Tsuji1 N., Kito1 F., Fukuda1 T., Furugohri1 T., Morishima1 Y.
1New Product Research Lab II, Daiichi Pharmaceutical Co., Ltd., Tokyo, Japan
How-to-cite Shibano T, Tsuji N, Kito F, Fukuda T, Furugohri T, Morishima Y. EFFECTS OF DU-176B, A NOVEL DIRECT FACTOR XA INHIBITOR, ON PROTHROMBINASE ACTIVITY AND PLATELET AGGREGATION IN VITRO. J Thromb Haemost 2007; 5 Supplement 2: P-T-642
Introduction: DU-176b is a competitive and highly selective direct factor Xa (FXa) inhibitor (Ki for free FXa = 0.561 nM, Ki for thrombin = 6000 nM). In the coagulation cascade, FXa is complexed with FVa and calcium ion on the surface of membrane phospholipids, and converts prothrombin into thrombin. Therefore inhibition of prothrombinase (PTase) activity is critical to exert anticoagulant effects. Platelet aggregation also contributes to thrombus formation.
Objectives: To determine the effects of DU-176b on PTase activity and human platelet aggregation in vitro.
Methods: PTase complex was formed by mixing of human FXa, FVa, CaCl2, and phospholipids. DU-176b was added to the mixture and the reaction was initiated by the addition of prothrombin. The concentration of generated thrombin was measured by amidolysis of S-2238. Ki value was calculated with Lineweaver-Burk plot. Collagen-, ADP-, and U46619-induced platelet aggregation was determined in human platelet rich plasma. Thrombin-induced platelet aggregation was assayed using washed platelets. DU-176b was added to platelet suspension and the reaction was started by the addition of agonists. Maximum aggregation was measured.
Results: DU-176b concentration-dependently suppressed generation of thrombin from prothrombin by PTase, which is a physiological reaction in the coagulation cascade. The Ki was 2.98 nM. The mode of inhibition was non-competitive/mixed-type. DU-176b did not impair platelet aggregation by collagen, ADP, and U46619. Thrombin induced platelet aggregation was inhibited by high concentrations of DU-176b (IC50 = 2.90 mM), reflecting its weak anti-thrombin activity.
Conclusions: DU-176b potently inhibited FXa in the physiological complex and is selective to the coagulation system.
To cite this abstract use the following format:
Journal of Thrombosis and Haemostasis 2007; Volume 5, Supplement 2: abstract number
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