Abstract WP97: The Aptamer BT200 Blocks Von Willebrand Factor and Platelet Function in Blood of Stroke Patients

Background: The effect of conventional anti-platelet agents is limited in secondary stroke prevention, and their effects are further blunted under conditions of high shear stress in the presence of increased levels of circulating VWF. VWF mediates platelet adhesion to collagen under high shear stress and is thereby critically involved in thrombus formation at sites of stenotic extracranial intracranial arteries (reviewed by Buchtele et al. 2018). We have created a novel anti-VWF aptamer (BT200) which could be useful for secondary stroke prevention, because the anti-VWF aptamer ARC1779 effectively reduced cerebral embolization after carotid endarterectomy (Markus et al. 2011). Aims: To characterize the effects of BT200 in blood of patients with large artery atherosclerosis stroke. Methods: Blood samples were obtained from 30 patients with acute stroke Inhibition of VWF activity by BT200 was quantified by REAADS ELISA and VWF ristocetin cofactor activity (VWF:RCo), platelet function under high shear rates with the PFA-100, and ristocetin-induced platelet aggregation in whole blood. Results: The majority of stroke patients had elevated VWF:RCo levels (mean: 198%; range 55-330%). Of 15 patients receiving clopidogrel with or without aspirin, only two had a prolonged collagen adenosine diphosphate closure time (CADP-CT) >123s, and only one patient had a ristocetin induced aggregation of <20U. BT200 concentration dependently inhibited VWF activity to <3% and VWF dependent platelet function (p<0.001): BT200 invariably prolonged CADP-CT to target levels of >300s, and decreased aggregation to <20U in blood samples from all patients. Conclusions: BT200 effectively inhibits VWF activity and VWF-dependent platelet function in blood from patients with acute stroke. Results from this study proved useful for planning of the ongoing phase I and planned phase II trial.