Assessment of ex vivo Pharmacodynamic Markers during Inhibition of Thrombosis by CI-1031 (ZK-807834), a Novel Direct Factor Xa Inhibitor

Abstract

CI-1031 (ZK-807834) is a novel, synthetic factor Xa (FXa) inhibitor with a Ki of 0.11 nM against human FXa. In human plasma in vitro, CI-1031 doubled PT and aPTT at 0.23 and 0.49 µM, respectively. The in vivo antithrombotic effect of CI-1031 was evaluated in a veno-venous shunt model of thrombosis in anesthetized rabbits. After thrombus formation was verified in the first shunts, rabbits received either vehicle or CI-1031 intravenously (bolus injection of 60, 240, or 480 µg/kg followed by an infusion of 2, 8, or 16 µg/kg/min for 140 min, respectively). The second shunts were inserted after 20 min of infusion of CI-1031 or vehicle. CI-1031 dose-dependently prolonged time to occlusion (TTO) in the second shunts (35 ± 21, 62 ± 24, and 120 ± 0 min for the three dose groups, respectively, vs. 10 ± 1 min for vehicle). Thrombus mass (TM) was reduced in a dose-dependent manner by CI-1031 (42 ± 7, 27 ± 6, and 18 ± 4 mg vs. 50 ± 4 mg for vehicle). Maximal TM reduction was 70% with an IC₅₀ of 0.6 µg/ml. Among all the coagulation parameters tested, PT had the best correlation with plasma CI- 1031 concentration (r = 0.97). Ex vivo plasma anti-FXa activity was also well correlated with plasma concentration of CI-1031 and with PT (r = 0.96 and 0.98, respectively). These results indicate that CI-1031, which is currently undergoing clinical evaluation, is an effective antithrombotic compound with a favorable efficacy-to-bleeding ratio. In addition, CI-1031 concentration in plasma can be monitored using PT or anti-Xa assays, thereby providing reliable methods to ensure safe and accurate dose titration of CI-1031.