Two novel monoclonal antibodies to VWFA3 inhibit VWF-collagen and VWF-platelet interactions.

Summary. Background: The interaction of collagen-von Willebrand factor (VWF)-GPIb is essential for platelet adhesion, especially under high shear conditions. VWF, which acts as a bridge between platelets and exposed subendothelium, interacts with collagen through its A3 domain, which is a new target for the antithrombotic agent. Objective: To develop functional blockers that specifically inhibit VWF-dependent adhesion of platelets to collagen under high shear stress. Methods: To develop murine antihuman VWF A3 monoclonal antibodies (mAbs) by standard hybridoma technology, and characterize their abilities to block interactions between VWF A3 and collagen as well as platelet function. Results: Thirty anti-VWF-A3 mAbs were obtained. Among them, two mAbs, designated as SZ-123 and SZ-125, were found to inhibit VWF-collagen type III interaction. SZ-123 and SZ-125 inhibited the binding of purified human VWF (1.5 or 3 μg mL−1) to human placenta collagen type III (IC50 = 0.07 ± 0.02 and 0.15 ± 0.03 μg mL−1, respectively) or to calf skin collagen type III (IC50 = 0.48 ± 0.06 and 0.51 ± 0.07 μg mL−1, respectively) coated on plates. Under flow shear condition (1000 s−1), SZ-123 and SZ-125 inhibited platelet adhesion on human placenta collagen- or calf skin collagen-coated surfaces. Both mAbs also inhibited platelet aggregation induced by ristocetin, botrocetin or bovine plasma. Conclusions: SZ-123 and SZ-125 inhibited VWF-collagen and VWF-platelet interactions.