Inhibition of Von Willebrand Factor (VWF) by ARC1779 Normalizes Von Willebrand Factor/FVIII Levels and Corrects Thrombocytopenia in VWD Type 2b Patients,

Infusion of the anti-VWF aptamer ARC1779 effectively elevated platelet counts in some patients with congenital thrombocytopenic purpura, and blunted the platelet drop induced by desmopressin in patients with type 2b von Willebrand disease (VWD). Thus, we hypothesized that ARC1779 may increase VWF levels and correct thrombocytopenia by blocking the hyperactive VWF A1 domain in type 2b VWD.

Thrombocytopenic patients suffering from type 2b VWD received intravenous infusions of ARC1779 (4 mcg/kg/min) for 72 hours in a prospective clinical trial. Patients were monitored using previsouly published assays (Thromb Haemost. 2010;104:563–70). Data are provided as median and the range and were tested for significance by repeated measures analysis of variance.

All patients had moderate thrombocytopenia, low levels of VWF:RCo, VWF:CBA, FVIII:C, and collagen/ADP closure times >300s (platelet function analyzer PFA-100). ARC1779 was well tolerated and safe even in a patient who suffered from active chronic gastrointestinal bleeding due to angiodysplasias before start of infusion. Plasma concentrations of ARC1779 increased to 76 mcg/mL (59–130) which suppressed free VWF A1 domains in the REAADS assay to a minimum of <3 to 5%. Consistent with the estimated in vivo half-life of VWF, VWF/FVIII levels increased as early as 12h after start of infusion, peaked near the end of infusion, and returned to baseline at follow-up. That was best exemplified by VWF:RCo levels which increased from 32% (26–45%) 10-fold to 367% (215–418%) 8h after end of infusion, and decreased again to 33% (20–40%) during follow up. Similarly VWF:CBA levels increased 16-fold (8 to 69-fold), VWF: Ag levels 5.2 fold (3 to 27-fold), and FVIII levels 4.3 fold (3 to 6-fold). Most importantly inhibition of hyperactive VWF rapidly increased platelet counts from 40/nL (38–58/nL) to a maximum of 146/nL (107–248/nL). This was observed although patients were suffering from chronic liver disease due to hepatitis C infection or associated immune thrombocytopenia, which could have blunted the platelet response. All changes were statistically significant (p<0.007).

This clinical trial underscores the therapeutic efficacy of the VWF A1 antagonist aptamer ARC1779. ARC1779 significantly increases VWF/FVIII levels and most importantly improves or even corrects thrombocytopenia in VWD type 2b patients. This could facilitate (i) the collection of autologous platelets for platelet transfusions pre-operatively or (ii) interferon therapy in patients whose HCV therapy could not be initiated or had to be stopped due to thrombocytopenia. As angiodysplasias may be caused by defective or deficient VWF (Blood 2011;117:1071–80), it may also be tempting to further investigate the potential of chronic anti-VWF aptamer therapy to treat angiodysplasia.

Knoebl:Archemix Corp.: Consultancy. Pabinger:Archemix Corp.: Consultancy. Gilbert:Archemix Corp.: previous employment. Schaub:Archemix Corp.: Consultancy, previous employment. Jilma:Archemix Corp.: Consultancy, Research Funding.