Received for publication July 29, 2005.
Revised January 11, 2006.
Accepted for publication January 11, 2006.

Empirical validation of a rat in vitro organ slice model as a tool for in vivo clearance prediction

Abstract

Tissue slices have been shown to be a valuable tool to predict metabolism of novel drugs. However, besides the numerous advantages of their use for this purpose, also some potential draw-backs exist including reported poor penetration of drugs into the inner cell layers of slices and loss of metabolic capacity during prolonged incubation leading to under-prediction of metabolic clearance. In the present study we empirically identified (and quantified) sources of under-prediction using rat tissue slices of lung, intestine, kidney and liver and found that thin liver slices (⁺/_-100 µm) metabolized model substrates (7-hydroxycoumarin, testosterone, warfarin, 7-ethoxycoumarin, midazolam, haloperidol and quinidine) as rapidly as isolated hepatocytes. Furthermore, it was found that organ slices remain metabolically active for sufficient periods of incubation enabling study of the kinetics of low clearance compounds. In addition, we determined the influence of albumin on the clearance prediction of 6 model substrates. For 3 of these substrates the intrinsic clearance in the presence of albumin was approximately 3 times higher than that obtained from incubations without albumin, but corrected for f_u. This resulted into a much more accurate prediction of in vivo whole body metabolic clearance for these compounds. Taken together, these results show that draw-backs of the use of slices for clearance prediction are largely surmountable. Provided that thin liver slices and physiological albumin concentration are used, whole body metabolic clearance is predicted with acceptable (2-fold) accuracy with organ slices. These results emphasize the applicability of organ slices in this field of research.

Key words: drug clearance, in vitro-in vivo prediction, pharmacokinetics, protein binding

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