Similarities and differences in the practice and use of time-dependent inhibition studies in drug discovery and development
Common Practices (≥75% concordance in responses) | Divergent Practices (<75% concordance in responses) |
|---|---|
| Strategic aspects | |
| All assess TDI during drug discovery/development continuum | Timing of definitive assays for clinical DDI predictions ranges from lead optimization through phase 1 |
| TDI data are used for predicting DDI | |
| No common cut-off values for TDI data for further progression of NMEs | |
| Use of various study designs for TDI assessment in drug discovery (e.g., IC50 shift vs. % activity loss at single NME concentration, etc.) | |
| No common consideration of structural alerts | |
| Technical aspects | |
| Pooled human liver microsomes (100%) | Dilution used during IC50 shift determinations range from no dilution to greater than 10-fold |
| Major P450 enzymes tested (Fig. 4) | |
| LC/MS/MS for measurement of probe substrates (100%) | Number of NME concentrations used to determine inactivation parameters (6 or greater) |
| Solvent control at each time point (- test article + NADPH) are used (100%) | |
| Number of time points used (4 to >6) | |
| Determine the log-linear phase of enzyme inactivation (100%) | Data analysis |
| Conduct control incubations without NADPH | Log-linear regression (kobs) followed by nonlinear fitting to determine KI and kinact parameters |
| Replicate determinations of KI and kinact are conducted | |
| Positive controls are included | Reciprocal plot (e.g., Kitz-Wilson) to estimate KI amd kinact |
| Test article depletion not measured | Global nonlinear regression |
| Use of TDI data | |
| Current models cannot accurately predict DDI due to TDI | Various models (static vs. dynamic, inclusion of gut first-pass vs. no gut first pass, etc.) are used for predicting DDI risk based on KI and kinact values |
| Existing models can categorize compounds as weak, moderate, or potent clinical DDI risks | |
| DDI predictions to decide whether to conduct a DDI study and inform its design | Various values used as surrogates for [I]in vivo (e.g. Cmax, free vs. total, etc.) |
|
| Microsomal and plasma protein binding corrections used by some |
LC/MS/MS, liquid chromatography/tandem mass spectrometry.