Abstract 631: Nonpeptide Factor XIa (FXIa) Inhibitor. In vitro Kinetic Evaluation and in vivo Studies of BMS-262084 on Arterial Thrombosis and Hemostasis in Rabbits
BMS-262084 is a 4-carboxy-2-azetidinone-containing irreversible inhibitor of FXIa. We evaluated the inhibition mechanism of BMS-262084, and its effects on thrombosis and hemostasis in rabbits. In vitro BMS-262084 acted as a mechanism-based inactivator of human FXIa with an inactivation constant (kassoc) of 2.5 ± 0.9 x 105 M−1s−1 (n = 4). The tripeptide substrate, L-pyroglutamyl-L-prolyl-L-arginine-p-nitroaniline, protects FXIa from inactivation by BMS-262084 in a competitive fashion consistent with active site irreversible inhibition. The relative kassoc values for BMS-262084 were slower with trypsin (4.2-fold), tryptase, (4.8-fold), plasma kallikrein (14-fold), urokinase (56-fold), FVIIa (250-fold), and > 300-fold slower for plasmin, FXa, FXIIa, FIXa, and thrombin, demonstrating that it is a more effective inactivator of FXIa compared to the other proteases studied. The kassoc for BMS-262084 with rabbit FXIa is 0.9 x 105 M−1 sec−1, similar to the human constant. In vivo we studied the effects of BMS-262084 in rabbit models of electrically-induced carotid arterial thrombosis and cuticle bleeding. BMS-262084 was infused IV from 1 h before artery injury or cuticle transection to the end of the experiment. Integrated carotid blood flow over 90 min (iCBF, % control) was used as a marker of the antithrombotic effect. BMS-262084 at 0.3, 1, 3 and 10 mg/kg/h IV increased iCBF to 23 ± 5, 51 ± 8, 70 ± 8 and 102 ± 9 %, respectively, vs. 11 ± 2 % in the vehicle-treated group (n = 3 to 6 per group). As expected with FXIa inhibition, BMS-262084 increased ex vivo activated partial thromboplastin time (aPTT) at 0.3, 1, 3 and 10 mg/kg/h by 1.4±0.1, 1.8±0.1, 2.3 ± 0.1 and 2.9 ± 0.4-fold, respectively, without changes in prothrombin time and thrombin time. The antithrombotic effect of BMS-262084 correlated with its ex vivo aPTT (r = 0.7, P<0.002, n=20), supporting the use of ex vivo aPTT as a biomarker. Bleeding times (percent change over control) at 3 and 10 mg/kg/h of BMS-262084 were 17 ± 4 and 52 ± 7 %, respectively. Aspirin at 3 mg/kg/h IV, a clinically-relevant dose, increased bleeding time by 67 ± 3 % (n = 6). These results suggest that a small molecule FXIa inhibitor may be useful for prevention of arterial thrombosis at doses that have aspirin-like effects on bleeding times.