Abstract 1941: The Anti Von Willebrand Factor Aptamer ARC1779 Effectively Inhibits Platelet Activation and Adhesion
Objectives Immediately after vessel wall damage, plasma von Willebrand factor (VWF) binds to exposed collagen and laminin, enabling the subsequent adhesion of platelets to immobilized VWF via glycoprotein (GP) Ibα. The GPIbα-VWF interaction is able to withstand high (arterial and intrastenotic) shear conditions, rendering this mechanism crucial for the initiation of hemostatic and thrombotic processes in the arterial circulation. In addition, released VWF promotes platelet activation. We have generated a nuclease-resistant anti-VWF A1 domain aptamer, ARC1779. Aptamers are nucleic acid molecules with high affinity and specificity due to the ability to fold into unique three dimensional structures. We examined the ability of ARC1779 to inhibit these platelet activation processes.
Methods and Results Botrocetin-induced aggregation of platelet-rich plasma (IC90 ~100–300 nM) and shear force-induced platelet aggregation in whole blood (IC95 ~100 nM) were inhibited by ARC1779. Platelet adhesion was assessed under high shear conditions (1500/s) in a parallel plate flow chamber using calcein orange labeled platelets. ARC1779 at a concentration range of 7.5 nM − 375 nM produced a concentration dependent inhibition of platelet adhesion with an IC50 of 7.5 nM and IC90 of 75 nM. Almost complete abolition of platelet adhesion was achieved with 400 nM of the aptamer. Firm adhesion of platelets was assessed by monitoring time of adhesion of randomly selected adherent platelets treated with 200 nM of ARC1779. The time that ARC1779 treated platelets remained attached was significantly reduced compared to untreated platelets (p<0.001). The occlusion time after electrical injury of carotid arteries in cynomolgus macaques was assessed and found to be significantly prolonged during ARC1779 treatment. At a concentration of 700 nM, ARC1779 inhibited occlusion of the injured carotid arteries as effectively as the GPIIb/IIIa antagonist abciximab at 1300 nM. The bleeding time was significantly shorter with ARC1779 than with abciximab.
Conclusions ARC1779 constitutes a promising novel anti-platelet agent for various thrombotic indications.