CYP TDI – IC50 Shift

CYP enzymes have been shown to be subjective to time-dependent inhibition (TDI), a kinetic phenomenon where inhibition increases with incubation time between the inhibitor and the enzyme (or HLM). A major subset of TDI by a chemical compound is mechanism-based inhibition (MBI) in which the compound is a CYP “substrate“and subsequently inactivates the CYP enzyme during the catalytic cycle by an irreversible or quasi-irreversible mechanism to the active site.

In early drug discovery, knowing the mechanism of TDI will inform medicinal chemists on how to remove this property through drug design and optimization. TDI information is required for accurate DDI prediction, as the amount of CYP enzyme available becomes time-dependent in the presence of TDI.

Assay Methodology

Quintara Discovery can conduct time-dependent inhibition assays for CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 (two probe substrates) using human hepatic microsomes. In the standard assay format, the test compound is preincubated with HLM in the presence and absence of NADPH for 30 min. Subsequently an excess of CYP substrate is added to initiate the CYP-catalyzed reaction, and the IC50 values of the compounds are obtained. The ratio of the two IC50 values (+/- NADPH) is an indicator of potential time-dependent inhibition.

Time-Dependent Inhibition – IC50 Shift: Standard Assay Conditions (Customizable)

CYP Isoforms
CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 (other isoforms are available)

Pooled human liver microsomes

Testing Compound Concentration
0, 0.25xIC50, 0.5xIC50, 0.75xIC50, 1xIC50, 2.5xIC50, 5xIC50, 10xIC50

0 and 30 min +/- NADPH

Known time-dependent inhibitors

Detection Method
Specific metabolites by LC-MS/MS

IC50, Standard error of IC50, IC50 Shift, Report

Turnaround Time
2-3 days

Compound requirements
2 mg solid