A humanized monoclonal antibody against vWF A1 domain inhibits vWF:RiCof activity and platelet adhesion in human volunteers

Abstract number: OC328

Machin^* S. J., Clarke† C., Ikemura‡ O., Kageyama§ S., Mackie^* I. J., Talbot† J. A., Ikeda¶ Y., Gyotoku§ Y.

§Ajinomoto Co., Inc, Japan; ‡Ajinomoto Pharmaceuticals Europe Ltd, UK; ¶Department of Internal Medicine, Keio University, Japan †Medeval Ltd, UK; ^*University College London, UK;

AJW200 (Ajinomoto, Japan) is a humanized IgG4 monoclonal antibody directed against the A1 domain of von Willebrand factor (vWF), which specifically inhibits vWF and platelet GPIb receptor interactions, resulting in inhibition of platelet adhesion, aggregation and activation at high shear stress. It inhibits arterial thrombus formation at high shear stress in dogs, without prolonging the bleeding time. In a randomized, double blind study, placebo, 0.01, 0.03, or 0.05 mg kg^-1 AJW200, were infused iv, into 24 healthy normal male subjects (age 20–45 years). Serial venous blood samples were collected before and up to 28 days after infusion. No clinically significant adverse events were recorded and there was no evidence of immunogenicity (by anti-AJW200 antibody and complement C3 assays). PK data, mean (SD) showed: C_max 204.8 (34.4), 586.2 (86.9), 833.2 (96.6) ng mL^-1; T_max 1.0 (0.6), 0.92 (0.2), 0.57 (0.26) h; T/2 23.5 (7.9), 24.3 (8.8), 27.2 (8.7) h, for 0.01, 0.03 and 0.05 mg kg^-1 AJW200, respectively. The maximum vWF occupancy by AJW200 was 19.4 (2.9), 51.0 (8.3) and 62.4 (4.7)%, for the 3 doses and there was a correlation between vWF occupancy and plasma AJW200 concentration. Ristocetin cofactor (RiCof) assays, showed a significant reduction at 1 h post infusion compared to baseline: 58 (22) vs. 110 (25)%, P < 0.0005 and 34 (16) vs. 116 (41)%, P < 0.005, at 0.03 and 0.05 mg kg^-1, respectively, lasting for up to 12 h. There were no significant changes in vWF:Ag, FVIII, vWF multimeric pattern or vWF cleaving protease activity. The template bleeding time (BT) was unchanged at all times and doses of AJW200. The PFA-100 (Dade Behring) showed prolonged closure times 1 h post infusion with both CADP: 146 (22) vs. 82 (10) and 202 (78) vs. 80 (19) s, P < 0.01; and CEPI: 182 (28) vs. 108 (16) and 233 (56) vs. 107 (19) s, P < 0.01 cartridges, at 0.03 and 0.05 mg kg^-1 AJW200, respectively. This effect lasted for 3–6 h with the lower and up to 12 h for the higher dose. The RiCof and PFA-100 responses showed dose dependent inhibition and the magnitude of the effect appeared to be related to the baseline vWF level. AJW200 was well tolerated, showing good inhibition of vWF RiCof activity and PFA-100 responses, without prolonging the skin bleeding time in healthy volunteers, and merits further clinical studies for thrombotic disorders such as acute TTP, acute coronary syndromes and stroke. This is the first study to demonstrate the effect of a monoclonal antibody that blocks GPIb/vWF in humans.