Non-clinical pharmacokinetics and pharmacodynamics of rVIII-SingleChain, a novel recombinant single-chain factor VIII.

INTRODUCTION: rVIII-SingleChain (CSL627), a novel recombinant coagulation factor VIII (FVIII), is under investigation in a phase I/III clinical programme (AFFINITY) for the treatment of haemophilia A. Non-clinical studies were conducted to investigate the pharmacokinetic/pharmacodynamic profile of rVIII-SingleChain in comparison with full-length recombinant FVIII. MATERIALS AND METHODS: Binding affinity of rVIII-SingleChain for von Willebrand factor was investigated by surface plasmon resonance analysis. The pharmacokinetic profile of rVIII-SingleChain was compared with a marketed full-length recombinant FVIII concentrate (Advate(®)) in haemophilia A mice, von Willebrand factor knock-out mice, Crl:CD (SD) rats, rabbits and cynomolgus monkeys. Systemic FVIII activity or antigen levels were recorded. Procoagulant activity was measured in an FeCl3-induced arterial occlusion model and by recording thrombin generation activity (ex vivo) after administration of 200-250 IU/kg rVIII-SingleChain or full-length FVIII to haemophilia A mice. RESULTS: rVIII-SingleChain displayed a high affinity for von Willebrand factor (KD=44 pM vs. 139 pM for full-length recombinant FVIII). In all animal species tested, rVIII-SingleChain had more favourable pharmacokinetic properties than full-length recombinant FVIII: clearance was decreased and area under the curve and terminal half-life were enhanced vs. full-length recombinant FVIII, while in vivo recovery and volume of distribution were equivalent. rVIII-SingleChain showed a prolonged thrombin generation potential and prolonged procoagulant activity vs. full-length recombinant FVIII in an FeCl3-induced arterial occlusion model. CONCLUSIONS: rVIII-SingleChain had a higher affinity for von Willebrand factor than full-length recombinant FVIII and displayed favourable pharmacokinetic/pharmacodynamic properties in non-clinical models.

C1-esterase inhibitor treatment: preclinical safety aspects on the potential prothrombotic risk.

Human plasma-derived C1-esterase inhibitor (C1-INH) is an efficacious and safe treatment for hereditary angioedema. However, thrombotic events in subjects treated with C1-INH at recommended or off-label, high doses have been reported. In this study, we addressed the potential prothrombotic risk of C1-INH treatment in high doses using a non-clinical rabbit model. Following intravenous infusion of C1-INH to rabbits at doses up to 800 IU/kg, the exposure and the pharmacodynamic efficacy of C1-INH in rabbits were confirmed by activity measurements of C1-esterase, and coagulation factors XIa and XIIa, respectively. Potential prothrombotic effects were assessed following induction of venous and arterial thrombosis using in vivo models of venous and arterial stasis, complemented by various in vitro assays of coagulation markers. Administration of C1-INH at doses up to 800 IU/kg did not potentiate thrombus formation during venous stasis. In contrast, inhibition of arterial occlusion was observed upon C1-INH administration when compared with isotonic saline treatment, indicating antithrombotic rather than prothrombotic activity of high dose C1-INH treatment in vivo. This was further confirmed in vitro by decreased thrombin generation, increased activated partial thromboplastin time, clotting time and clot formation time, and inhibition of platelet aggregation. No relevant changes in fibrinolysis or in the levels of thrombin-antithrombin complexes, and prothrombin fragment 1+2 were observed upon high dose C1-INH treatment. The data suggest that treatment of healthy rabbits with high doses of C1-INH could potentially inhibit coagulation and thrombus formation rather than induce a prothrombotic risk.

Preclinical efficacy and safety of rVIII-SingleChain (CSL627), a novel recombinant single-chain factor VIII.

INTRODUCTION: The preclinical efficacy and safety of rVIII-SingleChain (CSL627), a novel recombinant single-chain factor VIII, was assessed in a series of animal studies. MATERIALS AND METHODS: In the tail-clip bleeding model, hemophilia A mice were injected with escalating doses (1-150 IU/kg) of rVIII-SingleChain, B-domain deleted (BDD) rFVIII (ReFacto AF(®)), or full-length rFVIII products (Advate(®), Helixate(®)). Total blood loss and the percentage of animals in which hemostasis occurred were assessed in this observer-blinded, randomized study. In a second non-randomized study in hemophilia A mice, thromboelastographic analysis, thrombin generation, and activated partial thromboplastin time assays were performed. General safety and toxicity were assessed in three animal species, including determination of the prothrombotic potential of rVIII-SingleChain in a rabbit venous thrombosis model. RESULTS: Under acute bleeding conditions, the effect of rVIII-SingleChain on total blood loss and hemostasis was indistinguishable from BDD and full-length rFVIII. rVIII-SingleChain and full-length rFVIII (both 20 IU/kg) corrected thromboelastographic parameters, activated partial thromboplastin time, and thrombin generation to a similar degree in hemophilia A mice. In a thrombosis model, the effect of rVIII-SingleChain on thrombus incidence was non-significant and comparable to BDD rFVIII at doses up to 500 IU/kg. Treatment with rVIII-SingleChain did not cause anaphylactic reaction or local intolerance in safety and toxicity studies, and demonstrated an excellent overall safety profile. CONCLUSIONS: rVIII-SingleChain showed convincing hemostatic efficacy and excellent tolerability in animal studies, warranting continued investigation in human Phase I/III trials (AFFINITY).