title: Use of a multistaged time-dependent inhibition assay to assess the impact of intestinal metabolism on drug-drug interaction potential.
abstract: In early discovery, compounds are often eliminated because of their potential to undergo metabolic activation and/or cytochrome P450 time-dependent inactivation (TDI). The blockbuster drug raloxifene is an example of a compound that would have been eliminated in the current paradigm. Despite raloxifene's in vitro bioactivation and TDI of CYP3A4, it is well tolerated in patients with no drug-drug interactions. This discordance is attributed to its presystemic glucuronidation, thereby decreasing the amount of unchanged raloxifene available for CYP3A inactivation. The current study used raloxifene as a model to assess the effect of hepatic and intestinal glucuronidation on the kinetic parameters of CYP3A4 inactivation. Therefore, a simple multistaged time-dependent inactivation using UDP-glucuronosyltransferase-enabled and -absent reactions was built to understand the impact of the gut metabolism on inactivation potential. The results of these experiments demonstrated a 2.7-fold change in inactivation efficiency of CYP3A4. Incorporation of these results into a simulated midazolam drug-drug interaction study showed very little change in the pharmacokinetic parameters of the victim drug. In contrast, the absence of glucuronidation resulted in a 4.1-fold increase in the area under the curve (AUC) of midazolam, when in the presence of raloxifene, hence providing an understanding of the impact of intestinal glucuronidation on raloxifene's time-dependent inhibition of CYP3A4 and also providing a validation of a simple in vitro experiment to assess the influence of gut metabolism on time-dependent inhibitors at the discovery phase.
authors: Pharmacokinetics, Pharmacodynamics, and Drug Metabolism, Pfizer Inc., La Jolla, California, USA. michael.zientek@pfizer.com
authors: Michael
authors: M
authors: Zientek
authors: Deepak
authors: D
authors: Dalvie
mesh_terms: D019540:Area Under Curve; D001711:Biotransformation / Q000187:drug effects; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism; D004347:Drug Interactions; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000187:drug effects*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008874:Midazolam / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology; D020849:Raloxifene Hydrochloride / Q000378:metabolism* / Q000493:pharmacokinetics / Q000494:pharmacology*
chemical_list: D020849:Raloxifene Hydrochloride; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D008874:Midazolam