CYP Inhibition 

In the human body, Cytochrome P450 (CYP) enzymes play a major role in the metabolism of drugs and therefore, CYPs are primary targets in the assessment of drug-drug interactions.  Inhibition of CYPs can lead to altered metabolic capacity resulting in the inhibition of the metabolism of one, or both, drugs.  This can lead to potentially toxic accumulation of one, or both, drugs.  Therefore, it is crucial to assess the CYP inhibition potential of a test compound.  Our CYP Inhibition assays uses industry accepted substrates and human liver microsomes expressing the seven main cytochrome P450 isoforms (CYP1A, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6 and CYP3A4; other isoforms also available) to assess the decrease in metabolite formation.  This assay is performed in accordance with the FDA guidelines on Drug Interaction Studies.¹

Recombinant human microsomes containing the seven main CYPs (and other isoforms of your choosing if needed) are incubated with the industry accepted substrates and the controls/test compound.  The test compound is assessed at several concentrations.  The metabolite for each CYP is measured to determine the % inhibition and calculate an IC50.  Test compounds can be classified into three categories:

Strong Inhibitor:  IC50 < 1µM

Moderate Inhibitor:  IC50 between 1 and 10 µM

Weak/Non-Inhibitor:  IC50 > 10 µM

The graphs illustrate the inhibition of CYP1A isoforms using a strong inhibitor (alpha-naphthoflavone) in human hepatocyte microsomes.  Alpha-naphthoflavone is a strong inhibitor with an IC50 of ~0.1 μM.

IONTOX’s CYP inhibition study can be combined with our Human Dynamic Multiple Organ Plate to assess the effects of the tested compound or metabolites on subsequent tissues, such as the liver, kidney or lung.

1. FDA (2012) Draft Guidance for Industry: Drug Interaction Studies - Study Design, Data Analysis, Implications for Dosing, and Labeling Recommendations.