Improvement of spatial fibrin formation by the anti-TFPI aptamer BAX499: changing clot size by targeting extrinsic pathway initiation

J Thromb Haemost. 2011 Sep;9(9):1825-34. doi: 10.1111/j.1538-7836.2011.04412.x.


Background: Tissue factor pathway inhibitor (TFPI) is a major regulator of clotting initiation and a promising target for pro- and anticoagulation therapy. The aptamer BAX499 (formerly ARC19499) is a high-affinity specific TFPI antagonist designed to improve hemostasis. However, it is not clear how stimulation of coagulation onset by inactivating TFPI will affect spatial and temporal clot propagation.

Objective: To examine the BAX499 effect on clotting in a spatial, reaction-diffusion experimental system in comparison with that of recombinant activated factor VII (rVIIa).

Methods: Clotting in plasma activated by immobilized tissue factor (TF) was monitored by videomicroscopy.

Results: BAX499 dose-dependently improved coagulation in normal and hemophilia A plasma activated with TF at 2 pmole m(-2) by shortening lag time and increasing clot size by up to ~2-fold. The effect was TFPI specific as confirmed by experiments in TFPI-depleted plasma with or without TFPI supplementation. Clotting improvement was half-maximal at 0.7 nm of BAX499 and reached a plateau at 10 nm, remaining there at concentrations up to 1000 nm. The BAX499 effect decreased with TF surface density increase. RVIIa improved clotting in hemophilia A plasma activated with TF at 2 or 20 pmole m(-2) , both by shortening lag time and increasing spatial velocity of clot propagation; its effects were strongly concentration dependent.

Conclusions: BAX499 significantly improves spatial coagulation by inhibiting TFPI in a spatially localized manner that is different to that observed with rVIIa.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aptamers, Nucleotide / administration & dosage
  • Aptamers, Nucleotide / pharmacology*
  • Blood Coagulation / drug effects*
  • Blood Coagulation / physiology
  • Computer Simulation
  • Factor VIIa / administration & dosage
  • Factor VIIa / pharmacology
  • Fibrin / biosynthesis*
  • Hemophilia A / blood
  • Hemophilia A / drug therapy
  • Hemostasis / drug effects
  • Hemostasis / physiology
  • Humans
  • In Vitro Techniques
  • Lipoproteins / antagonists & inhibitors*
  • Lipoproteins / deficiency
  • Lipoproteins / physiology
  • Male
  • Microscopy, Video
  • Models, Biological
  • Recombinant Proteins / administration & dosage
  • Recombinant Proteins / pharmacology


  • Aptamers, Nucleotide
  • Lipoproteins
  • Recombinant Proteins
  • lipoprotein-associated coagulation inhibitor
  • Fibrin
  • Factor VIIa