Inhibition of tissue factor pathway inhibitor (TFPI) by ARC19499 improves clotting of hemophiliac blood

Abstract

Inhibition of tissue factor pathway inhibitor (TFPI) is a novel promising treatment concept for haemophilia. Ex vivo experiments examined the concentration-effect relationship of TFPI inhibition by ARC19499, a potent and specific inhibitor of TFPI. Clot formation was assessed by rotational thromboelastometry (ROTEM) and thrombin generation by calibrated automated thrombography (CAT) in blood and plasma samples from patients with congenital haemophiliaA (N=33) and B (N=6), acquired haemophiliaA (N=1), and healthy male controls (N=27). Clotting was significantly compromised in patients vs. controls. Measured FVIII activity levels in haemophiliacs correlated with parameters assessed by the CAT assay (except lagtime) and the clotting time assessed by the ROTEM.ARC19499 displayed a concentration dependent pro-haemostatic effect in both assays. ARC19499 normalized ROTEM clotting parameters and rendered CAT patterns of haemophilia samples practically indistinguishable from those of controls. ROTEM results with or without corn trypsin inhibitor were consistent. Effective concentrations of ARC19499 started at 2 nM, with maximum effects achieved at >60 nM. In an acquired haemophilia patient ARC19499 worked synergistically with FEIBA (factor VIII inhibitor bypassing activity) pre-treatment. Similarly, in blood spiked with a FVIII antibody, simulating a state of acquired haemophilia, ARC19499 restored normal coagulation. In summary, the anti-TFPI aptamer ARC19499 effectively enhanced ex vivo coagulation of patients with congenital or acquired haemophilia supporting further evaluation in clinical trials as a treatment for haemophilia.