Pharmacological Interruption of Acute Thrombus Formation with Minimal Hemorrhagic Complications by a Small Molecule Tissue Factor/Factor VIIa Inhibitor: Comparison to Factor Xa and Thrombin Inhibition in a Nonhuman Primate Thrombosis Model

Abstract

This study was designed to evaluate the antithrombotic efficacy and bleeding propensity of a selective, small-molecule inhibitor of tissue factor/factor VIIa (TF/VIIa) in comparison to smallmolecule, selective inhibitors of factor Xa and thrombin in a nonhuman primate model of thrombosis. Acute, spontaneous thrombus formation was induced by electrolytic injury to the intimal surface of a femoral blood vessel, which results in thrombus propagation at the injured site. The TF/FVIIa inhibitor 3-amino-5-[1- [2-({4-[amino(imino)methyl]benzyl}amino)-2-oxoethyl]-3-chloro-5-(isopropylamino)-6-oxo-1,6-dihydropyrazin-2-yl]benzoic acid dihydrochloride (PHA-927F) was fully effective in prevention of thrombosis-induced vessel occlusion at a dose of 400 g/kg/min, i.v., in the arterial vasculature (femoral artery). Neither the effective dose nor multiples up to 4.4-fold the effective arterial plasma concentration elicited any significant effect on bleeding time or blood loss from either the bleeding time site or the surgical (femoral isolation) site. Smallmolecule inhibitors of factor Xa or thrombin were effective arterial antithrombotic agents; however, in contrast to the TF/ FVIIa inhibitor, they both elicited substantial increases in bleeding propensity at the effective dose and at multiples of the effective plasma concentration. These data indicate that TF/ VIIa inhibition effectively prevented arterial thrombosis with less impact on bleeding parameters than equivalent doses of factor Xa and thrombin inhibitors.The most common cause of mortality in the United States and Western countries is cardiovascular disease, predominantly associated with acute coronary syndromes consisting of unstable angina, myocardial infarction, and sudden death (Braunwald et al., 1989). Acute coronary syndromes are associated with acute thrombus formation, often as the result of rupture of the thin fibrous cap of a vulnerable plaque. Upon plaque rupture, platelet activation occurs followed by a cascade of coagulation reactions as tissue factor is exposed to soluble factor VIIa in the blood (Moreno et al., 1996).Tissue factor initiates the extrinsic pathway of blood coagulation and is the obligate cofactor for activation of zymogen coagulation factor VII to the serine protease factor VIIa. The tissue factor/factor VIIa complex (TF/VIIa) initiates coagulation by activating the physiological substrates factor IX and factor X, ultimately leading to thrombin generation and fibrin deposition. Tissue factor is a cell surface-expressed glycoprotein that is composed of a 219-amino acid residue extracellular domain, a single transmembrane sequence, and a short cytoplasmic domain (Edgington et al., 1991). Tissue factor is primarily expressed in the media and adventitia of blood vessels forming a hemostatic envelope that surrounds the vessel.Following plaque rupture or vascular damage, such as occurs in hypertension, atherosclerosis, diabetes, smoking, and interventional procedures, such as balloon angioplasty, tissue factor is exposed to the blood a...

Tissue factor upregulation drives a thrombosis–inflammation circuit in relation to cardiovascular complications

“…Unlike FXa/FIIa inhibition or warfarin treatment that often accompanies bleeding episodes in clincical practice, such upstream downregulation specifically targets the inducible extrinsic hypercoagulation while leaving the intrinsic 'constitutive' coagulation of haemostatic function intact. A minimal or no bleeding episode has been reported in the upstream regulation by TF/ FVIIa inhibitors (PHA-927F, 280 FFR-rFVIIa 281 or Pyrid 282 ) in recent experimental trials and animal studies. Effective anti-inflammation could also be expected, resulting from the broad limitation of the generation of proinflammatory signals along the enhanced coagulation cascade.…”

Inhibitors of Factor VIIa/Tissue Factor

“…PHA-927F (Figure 2) was reported to inhibit FVIIa/TF with an IC 50 of 25 nmol/L and more than 3500-fold selectivity against thrombin and FXa. 7 Intravenous administration of PHA-927F in a nonhuman primate model of arterial injury model demonstrated dose-dependent inhibition of thrombus formation with markedly less bleeding when compared with a FXa inhibitor or thrombin inhibitor at the minimally efficacious dose or up to 4.4-fold multiples thereof. Other reports have followed of small molecule FVIIa/TF inhibitors demonstrating efficacy after intravenous dosing in monkeys 8,18,27 and lower species as well.…”

Recent Advances in the Discovery of Tissue Factor/Factor VIIa Inhibitors and Dual Inhibitors of Factor VIIa/Factor Xa

“…The studies demonstrate the ability of a small-molecule inhibitor of TF/FVIIa to inhibit or prevent thrombosis while having minimal effects on bleeding parameters. Separation of efficacy and bleeding propensity was not observed with the factor Xa and thrombin inhibitors used in this study, as bleeding increased significantly at the fully efficacious dose of the test compounds [22].…”

“…Preclinical studies of 20 in a non-human primate model of thrombosis were made to evaluate the antithrombotic efficacy of the agent and the risk of bleeding events [50]. Acute, spontaneous thrombus formation was induced by electrolytic injury to the intimal surface of a femoral blood vessel, which resulted in thrombus propagation at the injured site.…”