Development Of A Novel Antithrombotic Therapy Targeting Platelet Gpib Alpha: Assessment Of Anfibatide In Vitro And In Phase I Clinical Trial

Platelet adhesion and aggregation are critical for hemostasis and atherothrombosis. Interaction between the GPIb complex and VWF initiates platelet adhesion and contributes to complete vessel occlusion, particularly at sites of stenosis. However, no therapeutic targeting this pathway has been developed. Previously, we demonstrated in murine thrombosis models that Anfibatide, a snake venom-derived GPIbα antagonist, inhibited botrocetin-induced VWF-GPIbα binding and inhibited thrombus formation in vitro and in vivo, without significantly activating platelets or changing bleeding. We subsequently hypothesized that Anfibatide would be a safe and potent anti-thrombotic agent in humans. We tested Anfibatide with human platelets in vitro and conducted the first anti-GPIbα phase I clinical trial with 94 healthy volunteers. In vitro, Anfibatide inhibited ristocetin-induced and low dose thrombin-induced human platelet aggregation. Surface plasmon resonance studies showed that Anfibatide binds to GPIbα and blocks binding of both VWF A1 domain and thrombin. In ex vivo perfusion chambers, Anfibatide strongly inhibited human platelet adhesion, aggregation, and thrombus formation on a collagen-coated surface, especially at high shear flow conditions. Importantly, Anfibatide effectively dissolved the preformed thrombi in perfusion chambers. Anfibatide incubation with human whole blood did not significantly change coagulation parameters measured by thromboelastography. After treating volunteers with Anfibatide, no serious adverse events, premature discontinuations due to adverse events, or deaths occurred during the study. Anfibatide bound to 95% of GPIb and inhibited 90% of platelet aggregation without prolonging activated partial thromboplastin time, prothrombin time, thrombin time, or bleeding time. There was no bleeding tendency, no alteration of platelet count, and no detectable anti-Anfibatide antibodies. In conclusion, Anfibatide provides anti-thrombotic effects through inhibition of both GPIbα-VWF and GPIbα-thrombin interactions. These results demonstrate that Anfibatide is a safe and potent anti-platelet reagent with great potential for future anti-thrombotic therapy.