title: Understanding the clinical pharmacokinetics of a GABAA partial agonist by application of in vitro tools.
abstract: 1. 4-Oxo-4,5,6,7-tetrahydro-1H-indole-3-carboxylic acid (4-methylaminomethyl-phenyl)-amide (1), developed for general anxiety disorder, was discontinued from clinical development due to unsuitable oral pharmacokinetics. 2. In humans, (1) demonstrated an unacceptable high apparent oral clearance (Cl(p)/F) that also demonstrated a supraproportional dose-exposure relationship. Secondary peaks in the plasma concentration-time profile suggested possible enterohepatic recirculation of (1). A combination of in vitro mechanistic tools was applied to better understand the processes underlying these complex clinical pharmacokinetic profiles of (1). 3. In metabolism experiments, (1) was shown to be a substrate of monoamine oxidase A (MAO-A) as well as being metabolized by cytochrome P450. The former appeared to be a high K(M) process with a high capacity, while the latter showed saturation between 1 and 10 microM, consistent with the supraproportional dose-exposure relationship. 4. In a sandwich-cultured hepatocyte model, (1) was shown to be a substrate for both uptake and efflux into the canicular space, which is consistent with the observation of pharmacokinetics suggestive of enterohepatic recirculation. Finally, in human epithelial colon adenocarcinoma cell line (Caco-2) and Madin-Darby canine kidney cells transwell flux experiments, (1) was shown to have relatively low permeability and a basolateral-to-apical flux ratio consistent with the activity of P-glycoprotein. 5. In combination, a compounding of the contributions of MAO-A, hepatic uptake and efflux transporters, and P-glycoprotein to the disposition of (1) may underlie the low oral exposure, saturable clearance, and aberrant concentration versus time profiles observed for this compound in humans.
authors.affiliation: Department of Pharmacokinetics, Pharmacodynamics and Metabolism, Pfizer Global Research and Development, Groton/New London Laboratories, Pfizer Inc., Groton, CT 06340, USA. aarti.sawant@pfizer.com
authors.forename: Aarti D
authors.initials: AD
authors.lastname: Sawant
authors.forename: E L
authors.initials: EL
authors.lastname: Miller
authors.forename: D B
authors.initials: DB
authors.lastname: Duignan
authors.forename: J
authors.initials: J
authors.lastname: Brodfuehrer
authors.forename: S M
authors.initials: SM
authors.lastname: Winter
authors.forename: F R
authors.initials: FR
authors.lastname: Nelson
authors.forename: A
authors.initials: A
authors.lastname: Kamel
authors.forename: R S
authors.initials: RS
authors.lastname: Obach
authors.forename: A D N
authors.initials: AD
authors.lastname: Vaz
mesh_terms: D000813:Anilides / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics*; D000818:Animals; D014151:Anti-Anxiety Agents / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D058785:GABA-A Receptor Agonists; D006801:Humans; D066298:In Vitro Techniques; D007211:Indoles / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics*; D008099:Liver / Q000378:metabolism; D015394:Molecular Structure; D008995:Monoamine Oxidase / Q000378:metabolism
chemical_list: C551633:4-oxo-4,5,6,7-tetrahydro-1H-indole-3-carboxylic acid (4-methylaminomethylphenyl)amide; D000813:Anilides; D014151:Anti-Anxiety Agents; D058785:GABA-A Receptor Agonists; D007211:Indoles; D003577:Cytochrome P-450 Enzyme System; D008995:Monoamine Oxidase