The cytochrome P450s (CYPs) are a superfamily of isoforms that play an important role in the oxidative metabolism of drugs. Each CYP isoform possesses a characteristic broad spectrum of catalytic activities of substrates. When two or more drugs are administered at the same time, the possibility of drug interactions exists. The ability of a single CYP to metabolize multiple substrates is responsible for the large number of drug interactions associated with CYP inhibition. With the increasing number of new therapeutic agents on the market and the trend of drug combination, in vitro CYP-related metabolic studies are considered to be cost-effective in predicting the potential clinical drug-drug interactions (DDIs).
Creative Bioarray evaluates drug candidates as direct, time-dependent or metabolism-dependent inhibitors by using human liver microsomes, recombinant CYP enzymes or human hepatocytes. Our design allows us to screen for inhibition due to the drug added to the test system, as well as inhibition due to metabolites formed during pre-incubation. This design features low protein concentrations and short incubation times, minimizing errors caused by protein binding, metabolic instability and excessive metabolism of the marker substrate.
Direct inhibition, sometimes referred to as reversible inhibition, is the most basic form of enzyme inhibition. It measures enzyme activity by increasing the concentration of inhibitor, without a pre-incubation step. This is a classic in vitro inhibition assay that yields an IC50 as the result.
TDI refers to the changes in enzyme inhibition during in vitro incubation or in vivo dosing period. TDI is usually measured by comparing the potency (IC50) in direct inhibition to potency after 30 minutes pre-incubation in the absence of NADPH. The resulting IC50 will be significantly lower than that in the direct inhibition assay.
MDI can be observed when the product of the metabolic reaction is a more potent inhibitor than the parent compound. MDI is measured by introducing a 30 minute pre-incubation in the presence of NADPH. Once MDI is detected, the apparent inactivation constant (KI) and the maximal inactivation rate constant (Kinact) are determined to estimate the potential DDI risk.
|CYP1A2||Phenacetin O-dealkylation||a-Naphthoflavone, Furafylline|
|CYP2A6||Coumarin 7-hydroxylation||Fluvoxamine, Methoxsalen|
|CYP2B6||Efavirenz 8-hydroxylation, Bupropion hydroxylation||Sertraline, Phencyclidine, Thiotepa, Ticlopidine|
|CYP2C8||Amodiaquine N-dealkylation, Paclitaxel 6a-hydroxylation||Montelukast, Quercetin, Phenelzine|
|CYP2C9||Diclofenac 4-hydroxylation||Sulfaphenazole, Tienilic acid|
|CYP2C19||S-Mephenytoin 4-hydroxylation||S-(+)-N-3-benzyl-nirvanol, Nootkatone, Ticlopidine|
|CYP2D6||Dextromethorphan O-demethylation||Quinidine, Paroxetine|
|CYP3A4/5||Testosterone 6ß-hydroxylation, Midazolam 1-hydroxylation||Itraconazole, Ketoconazole, Azamulin, Troleandomycin, Verapamil|
All of our CYP inhibition assays can be ordered separately or in combination. Please talk to us now about the experimental design that best suits your needs.