Prediction of human pharmacokinetics of activated recombinant factor VII and B-domain truncated factor VIII from animal population pharmacokinetic models of haemophilia

Rotational thromboelastometry can predict the probability of bleeding events in a translational rat model of haemophilia A following gene-based FVIIa prophylaxis

INTRODUCTION

Monitoring of clinical effectiveness of bypassing agents in haemophilia patients is hampered by the lack of validated laboratory assays. Thromboelastography (TEG) and rotational thromboelastometry (ROTEM) have been evaluated for predicting clinical effectiveness of bypassing agents, however, with limited success.

AIM

Application of a longitudinal model-based approach may allow for a quantitative characterization of the link between ROTEM parameters and the probability of bleeding events.

METHODS

We analyse longitudinal data from haemophilia A rats receiving gene-based FVIIa prophylaxis in terms of total circulatory levels of FVII/FVIIa, clotting time (CT) measured using ROTEM and the probability of bleeding events.

RESULTS

Using population pharmacokinetic-pharmacodynamic (PKPD) modelling, a PK-CT-repeated time-to-event (RTTE) model was developed composed of three submodels (a) a FVII/FVIIa PK model, (b) a PK-CT model describing the relationship between predicted FVIIa expression and CT and (c) a RTTE model describing the probability of bleeding events as a function of CT. The developed PK-CT-RTTE model accurately described the vector dose-dependent plasma concentration-time profile of total FVII/FVIIa and the exposure-response relationship between AAV-derived FVIIa expression and CT. Importantly, the developed model accurately described the occurrence of bleeding events over time in a quantitative manner, revealing a linear relationship between predicted change from baseline CT and the probability of bleeding events.

CONCLUSION

Using PK-CT-RTTE modelling, we demonstrated that ROTEM parameters can accurately predict the probability of bleeding events in a translational animal model of haemophilia A.

Impact of capacity-limited binding on recombinant factor VIII and von Willebrand factor pharmacokinetics in hemophilia A rats

Essentials Knowledge of the interplay between FVIII and VWF pharmacokinetics (PK) is lacking. We characterized the capacity-limited PK of FVIII and VWF. The PK model described the PK of FVIII and VWF over a broad range of rFVIII doses. High-dose rFVIII treatment can reduce the endogenous VWF levels.

BACKGROUND

Understanding of the pharmacokinetics (PK) interplay between factor VIII (FVIII) and von Willebrand factor (VWF) following high-dose FVIII treatment is lacking.

OBJECTIVES

To characterize the PK of recombinant FVIII (rFVIII), VWF, and the rFVIII:VWF complex in hemophilia A rats following intravenous administration of rFVIII using PK modeling. A second aim was to investigate the effect of high daily dosing and constant expression of rFVIII on VWF exposure using PK simulations.

METHODS

We developed a population PK model based on the principles of target-mediated drug disposition modeling, using data on total rFVIII and VWF plasma concentrations, and the rFVIII:VWF complex luminescent oxygen channeling immunoassay signal in hemophilia A rats following intravenous administration of rFVIII (17.5, 100, 1000, and 5000 IU kg-1 ). Additionally, we evaluated the influence of high-dose rFVIII treatment on the exposure of VWF using PK simulations.

RESULTS

The plasma concentration-time profiles of total rFVIII and VWF, and the luminescent oxygen channeling immunoassay signal-time profiles of the rFVIII:VWF complex were adequately described using a two-compartment quasi-steady-state target-mediated drug disposition model (Kss  = 0.14 nmol L-1 ). The elimination half-life of the rFVIII:VWF complex was dependent on the unbound plasma concentration of rFVIII. Additionally, we showed that high-dose rFVIII treatment may significantly reduce the endogenous VWF levels.

CONCLUSIONS

We developed a population-based PK model describing the time-course of total rFVIII, total VWF, and the rFVIII:VWF complex over a broad range of rFVIII doses in hemophilia A rats.