title: Single concentration loss of activity assay provides an improved assessment of drug-drug interaction risk compared to IC50-shift.
abstract: 1. The utility of two abbreviated, higher-throughput assays [IC50-shift and the loss of activity (LOA) assay] to evaluate time-dependent inhibition (TDI) of 24 structurally related compounds was compared. 2. Good correlation (R(2)  = 0.90) between % inhibition and kinact/KI suggested that the LOA assay has utility as an indicator of TDI potential. Weaker correlation was observed for the shifted IC50 (IC50(T = 30)) (R(2) = 0.61) and the fold-shift in IC50 (R(2) = 0.17). 3. Primary mechanism for poor correlation was depletion of active enzyme at concentrations > 1 μM leading to greater than predicted inhibition in the IC50-shift assay. 4. Previously reported strong correlations between IC50(T = 30) and kinact/KI were found to be dependent on potent TDI compounds with kinact/KI > 30; correlation was reduced for moderate inhibitors (kinact/KI < 30). LOA assay maintained good correlation even when strong TDI compounds were excluded. 5. LOA assay (% Inhibition at 30 min, 10 μM) was a good predictor of in vivo DDI (AUCr), providing a graded response with low potential for false negatives or positives. IC50-shift assay had bias for over-predicting in vivo DDI and was more likely to identify false positives.
authors.affiliation: a Department of Pharmacokinetics and Drug Metabolism , Amgen , South San Francisco , CA , USA.
authors.forename: Simon G
authors.initials: SG
authors.lastname: Wong
authors.affiliation: a Department of Pharmacokinetics and Drug Metabolism , Amgen , South San Francisco , CA , USA.
authors.forename: Mey
authors.initials: M
authors.lastname: Lee
authors.affiliation: a Department of Pharmacokinetics and Drug Metabolism , Amgen , South San Francisco , CA , USA.
authors.forename: Bradley K
authors.initials: BK
authors.lastname: Wong
mesh_terms: D001681:Biological Assay / Q000379:methods*; D004347:Drug Interactions; D020128:Inhibitory Concentration 50
keywords: Drug–drug interaction; IC50; IC50-shift; P450; mechanism-based inactivation; risk assessment; time-dependent inhibition