Practical Tips

1. The compound must be compared to an "appropriate" positive control (see Table 5.7).

2. A compound is considered an inducer if it produces a response >2-fold over the base line.

3. Clinically relevant drug concentrations (at least three concentrations) or full dose response profiles should be used with at least one order of magnitude higher than Cmax.

4. Typically, CYP activity is used as a marker. Correlation between enzyme induction and increased mRNA levels have been established and it is more sensitive than activity determination. Also, when assessing a time-dependent inhibitor, CYP activity could be masked by the induction but mRNA levels are more indicative.

5. At least three different human hepatocytes individual donars should be tested.

6. Cryopreserved hepatocytes as well as freshly plated hepato-cytes could be used.

7. Other cell-based assays used for this purpose are (but not limited) HepG2 cell transfected with CYP3A4 and luciferase, Fa2N-4, and HepaRG.

8. It is important to assess cytotoxicity at every concentration of the test compound.

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