The aptamer ARC1779 blocks von Willebrand factor-dependent platelet function in patients with thrombotic thrombocytopenic purpura ex vivo.
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.
Mayr
Florian B
FB
Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.
Knöbl
Paul
P
Jilma
Bernd
B
Siller-Matula
Jolanta M
JM
Wagner
Patricia G
PG
Schaub
Robert G
RG
Gilbert
James C
JC
Jilma-Stohlawetz
Petra
P
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*
C526287:ARC 1779; D052157:Aptamers, Nucleotide; D014841:von Willebrand Factor