title: Plasma Protein Binding of Challenging Compounds.
abstract: Accurately determining fraction unbound (fu ) with currently available methods has been challenging for certain compounds. Inaccurate fu values can lead to the misinterpretation of important attributes of a drug candidate. Our analysis of over 2000 Pfizer drug discovery compounds showed no systematic bias in low or high fu precision using the equilibrium dialysis method. However, the accuracy of the plasma protein binding (PPB) estimate for highly bound compounds may be poor, should equilibrium not be fully achieved in the equilibrium dialysis assay. Here, a dilution method and a presaturation method were applied to accelerate equilibration for a set of challenging compounds. These improved methods demonstrate the ability to provide an accurate measurement of PPB for highly bound compounds with fu values much less than 1%. Therefore, we recommend that the actual experimental fu value be used for the prediction of drug-drug interaction potential and for the characterization of important drug candidate properties. Our recommendation calls into question the need for current regulatory guidelines that restrict the reporting of fu values below 1%.
authors.affiliation: Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, Connecticut, 06340.
authors.forename: Keith
authors.initials: K
authors.lastname: Riccardi
authors.affiliation: Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, Connecticut, 06340.
authors.forename: Shannon
authors.initials: S
authors.lastname: Cawley
authors.affiliation: Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, Connecticut, 06340.
authors.forename: Phillip D
authors.initials: PD
authors.lastname: Yates
authors.affiliation: Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, Connecticut, 06340.
authors.forename: Cheng
authors.initials: C
authors.lastname: Chang
authors.affiliation: Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, Connecticut, 06340.
authors.forename: Carrie
authors.initials: C
authors.lastname: Funk
authors.affiliation: Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, Connecticut, 06340.
authors.forename: Mark
authors.initials: M
authors.lastname: Niosi
authors.affiliation: Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, Connecticut, 06340.
authors.forename: Jian
authors.initials: J
authors.lastname: Lin
authors.affiliation: Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, Connecticut, 06340.
authors.forename: Li
authors.initials: L
authors.lastname: Di
mesh_terms: D000465:Algorithms; D000818:Animals; D001798:Blood Proteins / Q000378:metabolism*; D003956:Dialysis; D004285:Dogs; D004353:Drug Evaluation, Preclinical / Q000379:methods*; D004347:Drug Interactions; D004355:Drug Stability; D005260:Female; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008252:Macaca fascicularis; D008297:Male; D051379:Mice; D008954:Models, Biological; D051381:Rats; D015203:Reproducibility of Results; D054852:Small Molecule Libraries; D012995:Solubility
chemical_list: D001798:Blood Proteins; D054852:Small Molecule Libraries
keywords: albumin; alpha-1-acid glycoprotein; dilution method; drug interactions; equilibrium dialysis; in vitro models; nonspecific binding; presaturation method; protein binding