title: Mechanistic insights from comparing intrinsic clearance values between human liver microsomes and hepatocytes to guide drug design.
abstract: Metabolic stability of drug candidates are often determined in both liver microsome and hepatocyte assays. Comparison of intrinsic clearance values between the two assays provides additional information to guide drug design. Intrinsic clearance values from human liver microsomes and hepatocytes were compared for a set of commercial drugs with known metabolic pathways and transporter characteristics. The results showed that for compounds that were predominately metabolized by CYP mediated mechanisms, the intrinsic clearance values from the two assays were comparable. For compounds with non-CYP pathways, such as UGT and AO, intrinsic clearance was faster in hepatocytes than in microsomes. Substrates of uptake or efflux transporters in this study did not have significant differences of intrinsic clearance between microsomes and hepatocytes, when uptake into the hepatocytes was not the rate-limiting step. When hepatic uptake was rate limiting, intrinsic clearance in microsomes was faster than that in hepatocytes, which was more prevalent for compounds with rapid metabolism. Low passive permeability can limit the exposure to drug molecules to the metabolizing enzymes in the hepatocytes in relationship to the rate of metabolism. The faster the rate of metabolism, the higher permeability is needed for molecule to enter the cells and not becoming rate-limiting. The findings are very useful for drug discovery programs to gain additional insights on mechanistic information to help drug design without added experiments. Follow-up studies can then be designed to address specific questions.
authors: Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc., Groton, CT 06340, USA. LI.DI@PFIZER.COM
authors: Li
authors: L
authors: Di
authors: Christopher
authors: C
authors: Keefer
authors: Dennis O
authors: DO
authors: Scott
authors: Timothy J
authors: TJ
authors: Strelevitz
authors: George
authors: G
authors: Chang
authors: Yi-An
authors: YA
authors: Bi
authors: Yurong
authors: Y
authors: Lai
authors: Jonathon
authors: J
authors: Duckworth
authors: Katherine
authors: K
authors: Fenner
authors: Matthew D
authors: MD
authors: Troutman
authors: R Scott
authors: RS
authors: Obach
mesh_terms: D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D015195:Drug Design; D055808:Drug Discovery; D015507:Drugs, Investigational / Q000378:metabolism* / Q000493:pharmacokinetics; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology*; D057166:High-Throughput Screening Assays; D006801:Humans; D007700:Kinetics; D008657:Metabolic Clearance Rate; D053858:Metabolic Networks and Pathways; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D008954:Models, Biological; D055553:Prescription Drugs / Q000378:metabolism* / Q000493:pharmacokinetics
chemical_list: D002352:Carrier Proteins; D015507:Drugs, Investigational; D055553:Prescription Drugs; D003577:Cytochrome P-450 Enzyme System