Assay Method Information

Assay Name:  Enzyme Inhibition Assay
Description:  CYP P450: Inhibitory activities of test compounds on 5 major isoforms of CYP P450 were evaluated by using pooled human liver microsome (HLM, purchased from BD Gentest) and selective substrates for those isoforms. Those CYP isoforms and their corresponding probe substrates are as follows: CYP1A2 (phenacetin, 30 μM), CYP2C9 (tolutamide, 100 μM), CYP2C19 (S-mephenytoin, 40 μM), CYP2D6 (dextromethorphan, 5 μM) and CYP3A4 (midazolam, 1 μM). All probe substrates were used at concentrations near or below their Kms. For experiment, a reaction mixture of test compound at 10 μM or in serial dilution, CYP probe substrate described above and 0.2 mg/mL pooled HLM in phosphate buffer, pH 7.4 in a final volume of 200 μL was pre-incubated at 37° C. for 10 minutes in triplicate. The reaction was initiated by addition of NADPH at final concentration of 1 mM. The reaction was terminated after 10 minutes (CYP1A2, CYP2D6 and CYP3A4) or 30 minutes (CYP2C9 and CYP2C19) by addition of 100 μL ice-cold acetonitrile with internal standard (IS). The samples were then centrifuged at 13,000 rpm and the supernatants were injected to LC-MS/MS (Agilent Technologies) to quantify the concentration of the specific metabolites of the probe substrates formed by individual CYP450 isoforms. The inhibition ratio is calculated as:(M t −M 0)/M water×100%in which Mt and M0 represent the concentrations of the specific probe substrate metabolite, which was formed by individual CYP450 isoform, at the beginning and end of the reaction in the presence of test compound; while Mwater represents the concentration of the specific metabolite at the end of the reaction in the absence of test compound.
Affinity data for this assay

If you find an error in this entry please send us an E-mail