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Cytochrome P450 Inhibition in Human Liver Microsomes

Background

Co-administration of drugs can result in drug-drug interaction, as drugs compete for the same enzymes. Inhibition of CYP450 enzymes is a principal mechanism of metabolism-based drug-drug interactions and a common cause of adverse drug events. Therefore, one of the crucial properties in early drug discovery is the assessment of the potential of test compounds to inhibit a specific CYP450 isoform. This data is useful for further investigations of clinical drug-drug interactions (DDI).

The human liver microsomal assay is accepted as the ‘gold standard’ for in vitro DDI assessment as it is closest to the native enzyme environment. This assay is therefore used to characterise development compounds where data will be submitted to regulatory authorities.

Assay description

  • CYP450 isoforms
    CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP3A4

  • Compound concentration
    10µM (single point) or 0-100µM (IC50)

  • Compound requirements
    1-2 mg of dry matter

  • Incubation details
    isoform specific substrate (see Table 1)
    isoform specific time of incubation

  • Assay controls
    known isoform specific positive control
    (see Table 1 and Figure 1)

  • Detection method
    LC-MS/MS with internal standard
Table 1. CYP450 isoform specific substrates and positive controls

Figure 1. Comparison of IC50 values for CYP450 isoform specific positive control with literature values1,2,3
 
1 Obach 2006, J Pharmacol Exp Ther 316, 336
2 Zientek et al. 2008, J Pharmacol Toxicol Method 58, 206
3 Zambon et al. 2010, Drug Metabol Lett 4, 120

Assay details adjustable to client’s and/or project specific requests

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