Cardiovascular Pharmacology
Biochemical and pharmacological profile of darexaban, an oral direct factor Xa inhibitor

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Abstract

Darexaban (YM150) is an oral factor Xa inhibitor developed for the prophylaxis of venous and arterial thromboembolic disease. This study was conducted to investigate the biochemical and pharmacological profiles of darexaban and its active metabolite darexaban glucuronide (YM-222714), which predominantly determines the antithrombotic effect after oral administration of darexaban. In vitro activity was evaluated by enzyme and coagulation assays, and a prothrombin activation assay using reconstituted prothrombinase or whole blood clot. In vivo effects were examined in venous thrombosis, arterio–venous (A–V) shunt thrombosis, and bleeding models in rats. Both darexaban and darexaban glucuronide competitively and selectively inhibited human factor Xa with Ki values of 0.031 and 0.020 μM, respectively. They showed anticoagulant activity in human plasma, with doubling concentrations of darexaban and darexaban glucuronide for prothrombin time of 1.2 and 0.95 μM, respectively. Anticoagulant activity was independent of antithrombin. Darexaban and darexaban glucuronide inhibited the prothrombin activation induced by prothrombinase complex or whole blood clot with similar potency to free factor Xa. In contrast, prothrombinase- and clot-induced prothrombin activation were resistant to inhibition by enoxaparin. In venous and A–V shunt thrombosis models in rats, darexaban strongly suppressed thrombus formation without affecting bleeding time, with ID50 values of 0.97 and 16.7 mg/kg, respectively. Warfarin also suppressed thrombus formation in these models, but caused a marked prolongation of bleeding time at antithrombotic dose. In conclusion, darexaban is a selective and direct factor Xa inhibitor and a promising oral anticoagulant for the prophylaxis and treatment of thromboembolic diseases.

Introduction

Anticoagulant agents are widely used for the prevention and treatment of venous thromboembolism, stroke prevention in patients with atrial fibrillation, and for the acute management of patients with acute coronary syndrome. Thanks to their rapid onset of action, heparins are used for the initial treatment of thromboembolism, but are unsuitable for long-term therapy because they must be given parenterally (Hirsh et al., 2008). Warfarin is administered orally, but its use is associated with many clinical problems such as a narrow therapeutic window, slow onset of action, multiple food and drug interactions, and genetic variation in metabolism. These problems in turn result in the need for routine coagulation monitoring and frequent dose adjustment to maintain safe and effective warfarin levels (Ansell et al., 2008). New anticoagulants with a simpler and more convenient use have therefore been sought.

Factor Xa is a pivotal blood coagulation factor that is common to both the extrinsic and intrinsic coagulation cascades. Inhibition of factor Xa is therefore an attractive strategy for the prophylaxis and treatment of thromboembolic diseases (Eikelboom and Weitz, 2010). Darexaban (formerly called YM150) is a new oral factor Xa inhibitor which has been developed for the prophylaxis of venous and arterial thromboembolic disease. Darexaban is rapidly absorbed and extensively metabolized to darexaban glucuronide (YM-222714), the main active metabolite of darexaban which predominantly determines its antithrombotic effect (Groenendaal et al., 2010). In clinical studies in patients following total hip replacement, darexaban showed good tolerability and a dose-related decrease in venous thromboembolism incidence without compromising safety regarding major bleeding events (Eriksson et al., 2007, Eriksson et al., 2010).

Here, we investigated the in vitro profiles of darexaban and darexaban glucuronide in comparison to those of heparins. We also examined the in vivo antithrombotic effects of darexaban in rat thrombosis models and its effects on coagulation time and bleeding time in comparison to those of warfarin.

Section snippets

Reagents

Darexaban and darexaban glucuronide were synthesized by Astellas Pharma Inc. (Ibaraki, Japan) (Fig. 1). Heparin sodium was purchased from Ajinomoto Pharmaceuticals Co., Ltd. (Tokyo, Japan); enoxaparin sodium (Lovenox®) from Sanofi-aventis (Paris, France); and warfarin from Sigma (St. Louis, MO, USA). Factor Xa, factor VIIa, and factor XIIaβ were from Enzyme Research Laboratories Inc. (South Bend, IN, USA); prothrombin, factor Va, factor IXa, and factor XIa from Haematologic Technologies, Inc.

Enzyme assays

Both darexaban and darexaban glucuronide inhibited human factor Xa activity in a concentration-dependent manner, with Ki values of 0.031 ± 0.003 and 0.020 ± 0.001 μM, respectively. The Lineweaver–Burk plot indicated that these compounds were competitive inhibitors against human factor Xa (Fig. 2). Both compounds slightly inhibited plasma kallikrein (Ki: 11 ± 0.73 and 17 ± 0.87 μM), but with Ki values 350- and 850-fold lower than that against factor Xa, respectively. Ki values for the other serine

Discussion

The present study showed that darexaban and its active metabolite darexaban glucuronide are selective and direct factor Xa inhibitors. They also inhibit factor Xa within the prothrombinase complex and whole blood clot. In rat models of thrombosis, darexaban strongly inhibited thrombus formation without affecting bleeding time. These findings suggest that the anticoagulant profile of darexaban is preferable to those of conventional anticoagulants, heparins and warfarin.

Clinical studies have

Acknowledgments

We gratefully acknowledge the help of Drs. Shunichiro Hachiya, Tsukasa Ishihara, Keizo Sugasawa, Hiroyuki Koshio, and Fukushi Hirayama in the synthesis of darexaban and darexaban glucuronide. We also thank Drs. Masao Sasamata, Keiji Miyata, and Nobuo Seki for their interest and encouragement.

References (23)

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