It is vital for researchers occupied in drug discovery to evaluate parameters of DDIs for the development of safe and effective drug candidates. Creative Bioarray offers TDI assays, including IC50 shift and Kinact/KI assay. We deliver accurate data and detailed experimental protocols to meet your needs.

CYP450 TDI Assay Introduction

• Why CYP450 TDI Assay?
• It is widely accepted that the current therapy of multi-drugs inescapably increases the likelihood of drug-drug interactions (DDI). Serious DDIs are a significant risk for new molecular entities (NCE).
• A large proportion of adverse drug reactions in the clinic can be attributed to drug-drug interactions. Most cited pharmacokinetic DDIs have involved cytochrome P450s (CYPs), responsible for metabolizing 80% of drugs.
• The forms of CYP inhibition can be roughly divided into two categories. One of them is the inhibition of CYP activity mediated by the drug itself (direct inhibition, DI). Another form is the inhibition mediated by the metabolites derived from the drug (time-dependent inhibition, TDI). In most cases, the inhibition caused by the time-dependent inhibition is irreversible.
• The consequences of irreversible inhibition are considered to be more severe than reversible inhibition. IC50 shift assay is possible to distinguish between reversible and irreversible inhibition. The kinact and KI values determined can be used to predict the risk of drug-drug interactions.
• The relationship between IC50 shift and kinact/ KI

CYP450 time-dependent inhibition IC50 shift assay can identify reversible and time-dependent inhibitors. IC50 values often quantify the potential of enzyme-inhibiting drugs. The IC50 change test is currently the standard method used for the preliminary evaluation of TDI.

However, with IC50 shift assay, problems can arise when dealing with irreversible or mechanism-based inhibitors (MBI). The IC50 value of MBI is time-dependent and can cause serious issues when ranking the inhibitory potential of different compounds. Therefore, most studies and ranking schemes associated with MBI depend on the inhibition constant (KI) and enzyme inactivation rate (kinact) instead of the IC50 value.

The kinact/KI assay determines the Kinetic constant of time-dependent inhibition. kinact is the maximum rate of enzyme inactivation at the saturation concentration of the inhibitor, while KI is the concentration of the inhibitor, which gives half of the maximum rate of inactivation. The experimental conditions are determined based on previously performed assays, such as P450 reversible inhibition and time-dependent inhibition: single point or IC50 shift.