title: The aptamer ARC1779 blocks von Willebrand factor-dependent platelet function in patients with thrombotic thrombocytopenic purpura ex vivo.
abstract: BACKGROUND
  In thrombotic thrombocytopenic purpura (TTP), ultralarge von Willebrand factor (VWF) multimers bind platelet (PLT) glycoprotein Ib and lead to the formation of disseminated fibrin-poor, VWF-rich PLT thrombi. The aptamer ARC1779 blocks binding of the VWF A1 domain to PLT glycoprotein Ib. We evaluated whether ARC1779 inhibits the excessive VWF activity and VWF-mediated PLT function in patients with TTP.
  
  
  METHODS
  We studied the ex vivo concentration response curves for ARC1779 on PLT function analyzer (PFA-100, Dade Behring) and cone-and-plate analyzer (CPA, Impact-R) PLT function tests, agonist-induced PLT aggregation, and VWF activity of TTP patients (n = 11, three in acute phase and eight in remission) and healthy controls (n = 44).
  
  
  RESULTS
  VWF activity and VWF-dependent PLT plug formation were increased in TTP patients relative to healthy controls, but agonist-induced PLT aggregation was not. ARC1779 blocked collagen/adenosine 5'-diphosphate (ADP)-induced PLT plug formation as measured by PFA-100 with an inhibitory concentration (IC)(100) of approximately 1 microg/mL in citrate-anticoagulated samples and approximately 3 to 4 microg/mL in hirudin-anticoagulated samples. A similar concentration of ARC1779 was necessary to block shear-dependent PLT adhesion in both TTP patients and healthy controls using the CPA assay (IC(100) of approx. 1 microg/mL for both). ARC1779 blocked VWF activity with an IC(90) of approximately 3 to 4 microg/mL in all subjects, but did not inhibit PLT aggregation by ADP, collagen, or arachidonic acid even at concentrations much greater than those that fully inhibited VWF-dependent PLT function.
  
  
  CONCLUSIONS
  ARC1779 potently and specifically inhibits VWF activity and VWF-dependent PLT function. ARC1779 may be a promising novel therapeutic for the treatment of TTP.
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.
authors.forename: Florian B
authors.initials: FB
authors.lastname: Mayr
authors.forename: Paul
authors.initials: P
authors.lastname: Knöbl
authors.forename: Bernd
authors.initials: B
authors.lastname: Jilma
authors.forename: Jolanta M
authors.initials: JM
authors.lastname: Siller-Matula
authors.forename: Patricia G
authors.initials: PG
authors.lastname: Wagner
authors.forename: Robert G
authors.initials: RG
authors.lastname: Schaub
authors.forename: James C
authors.initials: JC
authors.lastname: Gilbert
authors.forename: Petra
authors.initials: P
authors.lastname: Jilma-Stohlawetz
mesh_terms: D000328:Adult; D052157:Aptamers, Nucleotide; D001792:Blood Platelets / Q000187:drug effects* / Q000502:physiology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010974:Platelet Aggregation / Q000187:drug effects; D011697:Purpura, Thrombotic Thrombocytopenic / Q000097:blood / Q000188:drug therapy*; D014841:von Willebrand Factor / Q000037:antagonists & inhibitors*
chemical_list: C526287:ARC 1779; D052157:Aptamers, Nucleotide; D014841:von Willebrand Factor