The practical advantages of using the mouse in pharmacokinetic (PK) studies of human recombinant proteins are many and obvious. However, the relevance of studying human proteins in a mouse model is always questionable. The aims of the present study were i) to investigate if the mouse can be used as a model for PK studies of human FVIIa and FVIIa analogues by comparing the clearance of human recombinant FVIIa (hFVIIa) and murine recombinant FVIIa (mFVIIa), and ii) to study the roles of tissue factor (TF) in clearance of FVIIa.

Eighteen NMRI mice were given a single intravenous 1 mg/kg dose of FVIIa or derivative containing trace amounts of iodinated FVIIa or derivative. Eye blood was sampled from anaesthetized mice in the interval of 0–8 h post administration. A sparse sampling schedule was employed in that three blood samples were taken pr. time point and three samples were drawn pr. mouse. The FVIIa plasma concentration was determined from the radioactivity measured by a γ-counter. The PK parameters were calculated by a 2-compartmental method using the WinNonlin software (Pharsight Corporation, USA), and the data was analyzed in one-way ANOVA test.

The pharmacokinetic profile for both proteins was best determined by a 2-compartment analysis. The PK parameters obtained for the two proteins were statistically indistinguishable and showed a rapid distribution phase followed by a slower terminal half-life. The following values were obtained for hFVIIa and mFVIIa: T½ (distribution) was 0.38 h for hFVIIa and 0.71 h for mFVIIa, while a T½ (elimination) of 4.85 h was found for hFVIIa and 5.53 h for mFVIIa. Total clearance values of 34.7 ml/kg/h and 32.8 ml/kg/h were obtained for hFVIIa for mFVIIa, respectively. The volumes of distribution for the two proteins were also statistically indistinguishable, being 220.1 ml/kg for hFVIIa and 203.9 ml/kg for mFVIIa. No significant difference was thus observed between hFVIIa and mFVIIa in terms of the PK parameters including the terminal half-lives. These data might indicate that human FVIIa and murine FVIIa are cleared by the same mechanism(s) in mice, suggesting that the mouse is a valid model for PK studies of human FVIIa and derivatives thereof.

The similar PK profiles for hFVIIa and mFVIIa observed further indicated a TF-independent clearance mechanism of FVIIa. Relative to mFVIIa the affinity of hFVIIa for mTF is known to be markedly decreased (

Petersen LC et. al. Thromb Res. 2005;116:75–85
). Involvement of TF binding in clearance was therefore expected to result in different PK profiles for the two proteins; hence in a mouse model one would expect hFVIIa to be cleared at a much slower rate than mFVIIa. Since this was not the case, this study suggests a TF-independent mechanism of FVIIa clearance in mice.

Our studies suggest that the mice can be used as a model to evaluate the PK profile of human FVIIa, and that TF is not involved in the clearance mechanisms of FVIIa.

Topics:
magnetic resonance imaging, mice, pharmacokinetics, recombinant coagulation factor viia, recombinant proteins, single-dose regimen, thromboplastin, half-life, eye, radioactivity

Disclosures: PhD student.; Stock options.

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2006, The American Society of Hematology
2006
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