Development of a tail vein transection bleeding model in fully anaesthetized haemophilia A mice - characterization of two novel FVIII molecules.

Introduction: The tail tip bleeding model and the tail vein transection survival model in mice are important tools for assessment of in vivo effect in haemostasis research. While the tail vein transection model exhibits the best sensitivity to pharmacological intervention it uses death or near-death as endpoint which is fully avoided in the tail tip bleeding model. Aim: The aim of this study was to develop a new tail bleeding model maintaining the sensitivity of the previous survival model but avoiding death/near-death as endpoint. Methods: Combining the two existing tail bleeding models we developed an optimized version of the survival model with full anaesthetic coverage and short duration of experiments. Using this model, we characterized the effect of turoctocog alfa, a B-domain truncated FVIII molecule (NovoEight (R)), as well as the prolonged half-life version of the same molecule (turoctocog alfa pegol, N8-GP). Results: Data showed that the model was sensitive to clinically relevant doses of both turoctocog alfa as well as N8-GP when dosed for 'on demand' treatment. The model also correctly identified a longer duration of effect for N8-GP compared with turoctocog alfa. Moreover, the model allowed the use of mice of both genders and was reproducible over time. Conclusion: The optimized tail vein transection bleeding model is sensitive to standard as well as half-life prolonged FVIII molecules and should be a valuable alternative to both the tail tip bleeding model, enhancing sensitivity to pharmacological intervention, as well as to the previously used tail vein transection survival model, avoiding death or near-death as endpoint.