Received for publication January 14, 2008.
Revised March 17, 2008.
Accepted for publication March 17, 2008.

Integrated in vitro analysis for the in vivo prediction of cytochrome P450 mediated drug-drug interactions

Abstract

Unbound IC₅₀ (IC_50,u) values of 15 drugs were determined in 8 recombinantly expressed human CYPs and human hepatocytes, and the data used to simulate clinical area under the plasma concentration-time curve changes (AUC) upon co-administration with prototypic CYP2D6 substrates. Significant differences in IC_50,u values between enzymes sources were observed for quinidine (0.02 µM in rCYP2D6 vs. 0.5 µM in hepatocytes) and propafenone (0.02 vs. 4.1 µM). The relative contribution of individual CYPs towards the oxidative metabolism of clinical probes desipramine, imipramine, tolterodine, propranolol and metoprolol were estimated via determinations of CL_int using rCYPs. Simulated AUC were compared to those observed in vivo via the ratios of unbound inhibitor concentration at the entrance to the liver to inhibition constants determined against rCYPs ([I]_in,u:K_i) and incorporating parallel substrate elimination pathways. For this dataset, there were 20% false negatives (observed AUC 2, predicted AUC < 2), 77% correct predictions and 3% false positives. The [I]_in,u:K_i approach thus appears relatively successful at estimating the degree of clinical interactions and can be incorporated into drug discovery strategies. Using Simcyp ADME simulator^® there were 3% false negatives, 94% correct simulations and 3% false positives. False negative predictions were rationalised as a result of mechanism-based inhibition, production of inhibitory metabolites and/or hepatic uptake. Integrating inhibition and reaction phenotyping data from automated rCYP screens has shown applicability to predict the occurrence and degree of in vivo DDI and such data may identify the clinical consequences for candidate drugs as both 'perpetrators' and 'victims' of CYP mediated interactions.

Key words: CYP inhibition, CYP2D, drug discovery, drug interactions, drug-drug interactions, enzyme inhibitors, hepatocytes, isolated hepatocytes, mechanism-based inhibition, recombinant proteins

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