A numerical method for analysis of in vitro time-dependent inhibition data. Part 2. Application to experimental data

Area of Science:

• Pharmacology
• Drug Metabolism
• Enzyme Kinetics

Background:

• Time-dependent inhibition (TDI) of cytochrome P450 enzymes is a key factor in drug-drug interactions.
• Current methods for characterizing TDI kinetics involve determining the rate of enzyme loss (kobs) at various inhibitor concentrations ([I]) and replotting to find kinetic parameters (KI and kinact).

Purpose of the Study:

• To apply a novel numerical method, developed in a companion study, to analyze experimental in vitro TDI data.
• To assess the method's ability to model complex and atypical TDI kinetic schemes.

Main Methods:

• Application of a new numerical method to five experimental TDI datasets involving CYP2B6, CYP2C8, and CYP3A4.
• Utilizing complex kinetic models, including quasi-irreversible inhibition, partial inhibition, and multiple-inhibitor binding models, where necessary.

Main Results:

• None of the analyzed datasets exhibited Michaelis-Menten-only kinetics.
• The numerical method successfully fitted complex models to the experimental data, revealing quasi-irreversible and partial inhibition kinetics.
• Three datasets required a multiple-inhibitor binding model for accurate parameterization.

Conclusions:

• The developed numerical method is generally applicable for analyzing in vitro TDI data, even with complex and atypical kinetic profiles.
• This approach enhances the mechanistic and clinical understanding of drug-drug interactions driven by cytochrome P450 enzyme inhibition.