Synergistic Effect of AJW200, a von Willebrand Factor Neutralizing Antibody with Low Dose (0.9 mg/mg) Thrombolytic Therapy Following Embolic Stroke in Rabbits.

The von Willebrand factor (vWF) is an acute stroke response protein involved in platelet aggregation, adhesion, inflammation, and thrombus formation, responses that occur following an ischemic stroke. We hypothesize that administration of an anti-vWF antibody (anti-vWF-Ab) may be used as adjunctive therapy with tissue plasminogen activator (tPA) to promote behavioral improvement following an embolic stroke. In this proof-of-concept study, which used a blinded and randomized design, we studied delayed treatment with the anti-vWF-Ab, AJW200 (0.30 mg/kg), alone or in combination with a rabbit low-dose of tPA (0.9 mg/kg) using the rabbit small clot embolic stroke model (RSCEM) with behavioral function as the primary clinically relevant endpoint. To evaluate the quantitative relationship between clot burden in brain and clinical scores, so that an effective stroke dose (P₅₀) could be calculated, logistic sigmoidal quantal analysis curves were constructed. A beneficial treatment significantly increases P₅₀ compared to control. The effect of antibody administration, either alone or with low dose tPA was compared to a "positive control", a standard rabbit optimized dose of tPA (3.3 mg/kg), as a measure of the maximum improvement potential in the RSCEM. The anti-vWF-Ab, AJW200, or control IgG were administered IV 1 hour following embolization, and behavior was measured 48 hours later. AJW200 plus low-dose tPA significantly increased the P₅₀ value by 74% (p<0.05, t=2.612) and 81% (p<0.05, t=2.519) compared to low dose tPA or IgG, respectively, but not the AJW200 group (p>0.05). AJW200 increased the P₅₀ value by 28%, (p>0.05) compared to the control IgG-treated group. Standard dose tPA increased the P₅₀ value by 154% (p<0.05). Statistically, the combination response for AJW200 plus low-dose tPA was not significantly different from standard dose tPA (p=0.26). This study shows that the concomitant administration of the anti-vWF-Ab AJW200 with low dose tPA is synergistic and results in significantly improved behavioral function following embolic stroke. We postulate that neutralization of vWF may suppress or attenuate one or more aspects of the acute phase stroke cascade response including suppression of inflammatory response and reduced leukocyte adhesion.