Received for publication January 29, 2008.
Revised February 25, 2008.
Accepted for publication March 5, 2008.

COMPARISON OF IMMORTALIZED Fa2N-4 CELLS AND HUMAN HEPATOCYTES AS IN VITRO MODELS FOR CYTOCHROME P450 INDUCTION

Abstract

Fa2N-4 cells have been proposed as a tool to identify CYP3A4 inducers. To evaluate whether Fa2N-4 cells are a reliable surrogate for cryopreserved human hepatocytes, we assessed the basal mRNA expression of 64 drug disposition genes in Fa2N-4 cells. Significant differences were found in the expression of major drug metabolizing enzymes, nuclear receptors and transporters between both cell types. Importantly, the expression of constitutive androstane receptor (CAR) and several hepatic uptake transporters were significantly lower (>50-fold) in Fa2N-4 cells, while the expression of pregnane-X-receptor (PXR) and aryl hydrocarbon receptor (AhR) were similar between Fa2N-4 cells and human hepatocytes. Using an optimized induction assay for Fa2N-4 cells, CYP3A4 induction by rifampicin, the prototypical PXR-activator, increased from 1.5-to 7-fold at the level of functional activity. With nine selected compounds, which are known inducers of CYP3A4 either via activation of PXR, CAR, or both, we evaluated CYP3A4 and CYP2B6 mRNA induction using Fa2N-4 cells and human hepatocytes. No response was observed in Fa2N-4 cells treated with the selective CAR activators CITCO and artemisinin. CYP3A4 and -2B6 induction in Fa2N-4 cells were also low for phenytoin, phenobarbital, and efavirenz, which are dual activators of PXR/CAR. This was in agreement with the lack of expression of CAR. The EC50 value for rifampicin-mediated CYP3A4 induction was 10-fold higher than in human hepatocytes. This could be attributed to the low expression of hepatic organic anion transporting polypeptide OATP1B1 and OATP1B3 in Fa2N-4 cells. In summary, our findings identify limitations of Fa2N4-cells as a predictive induction model.

Key words: ABC transporters, Ah receptor, CAR, CYP induction, CYP3A, drug interactions, drug-drug interactions, enzyme induction, hepatocytes, PXR