Preclinical characteristics of rVIII-SingleChain in clinical development

The novel coagulation factor VIII molecule, rVIII-SingleChain, is composed of covalently bonded heavy and light chains to improve product characteristics, and thus FVIII therapy by enhancing molecular stability. The two-chain endogenous FVIII represents a labile configuration, although 95% of circulating FVIII is complexed with von Willebrand factor (VWF). This complex determines FVIII stability, its half-life and was shown to influence its presentation to the immune system. Yet, the unmet medical need for an improved FVIII therapy, that offers a reduced potential for immunogenicity combined with a more convenient dosing frequency is driven by a high incidence of inhibitory antibody development and an inherently short half-life of FVIII. Non-clinical studies were conducted to investigate whether enhanced integrity can translate into improved pharmacological characteristics of rVIII-SingleChain in non-clinical models. In comparison to marketed two-chain, full-length rFVIII the binding affinity of rVIII-SingleChain for VWF and its stability were investigated in vitro. In animals, the PK properties of rVIII-SingleChain, its procoagulant activity and immunogenicity potential to induce anti-FVIII antibodies was explored. Compared to full-length rFVIII, rVIII-SingleChain displayed a high affinity for VWF and a markedly enhanced molecular stability. Similarly, rVIII-SingleChain had more favorable PK properties, and thereby showed a prolonged thrombin generation potential and procoagulant activity. Furthermore, in FVIII knock-out mice rVIII-SingleChain induced a lower anti-FVIII antibody response. This potential for reduced immunogenicity is investigated employing different ex vivo human immune model systems. These non-clinical results warrant further exploration whether such improved molecular properties may translate into clinical benefit in hemophilia A patients