pgp - publications

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1. J Pharmacol Toxicol Methods. 2012 Feb 26. [Epub ahead of print]

Determining P-glycoprotein-drug interactions: Evaluation of reconstituted
P-glycoprotein in a liposomal system and LLC-MDR1 polarized cell monolayers.

Melchior DL, Sharom FJ, Evers R, Wright GE, Chu JW, Wright SE, Chu X, Yabut J.

GLSynthesis Inc., One Innovation Drive, Worcester, Massachusetts 01605 USA.

INTRODUCTION: P-Glycoprotein (ABCB1, MDR1) is a multidrug efflux pump that is a
member of the ATP-binding cassette (ABC) superfamily. Many drugs in common
clinical use are either substrates or inhibitors of this transporter.
Quantitative details of P-glycoprotein inhibition by pharmaceutical agents are
essential for assessment of their pharmacokinetic behavior and prevention of
negative patient reactions. Cell-based systems have been widely used for
determination of drug interactions with P-glycoprotein, but they suffer from
several disadvantages, and results are often widely variable between
laboratories. We aimed to demonstrate that a novel liposomal system employing
contemporary biochemical methodologies could measure the ability of clinically
used drugs to inhibit the P-glycoprotein pump. To accomplish this we compared
results with those of cell-based approaches. METHODS: Purified
transport-competent hamster Abcb1a P-glycoprotein was reconstituted into a
unilamellar liposomal system, Fluorosome-trans-pgp, whose aqueous interior
contains fluorescent drug sensors. This provides a well-defined system for
measuring P-glycoprotein transport inhibition by test drugs in real time using
rapid fluorescence-based technology. RESULTS: Inhibition of ATP-driven transport
by Fluorosome-trans-pgp employed a panel of 46 representative drugs. Resulting
IC(50) values correlated well (r(2)=0.80) with K(d) values for drug binding to
purified P-glycoprotein. They also showed a similar trend to transport inhibition
data obtained using LLC-MDR1 cell monolayers. Fluorosome-trans-pgp IC(50) values
were in agreement with published results of digoxin drug-drug interaction studies
in humans. DISCUSSION: This novel approach using a liposomal system and
fluorescence-based technology is shown to be suitable to study whether marketed
drugs and drug candidates are P-glycoprotein inhibitors. The assay is rapid,
allowing a 7-point IC(50) determination in <6min, and requires minimal quantities
of test drug. The method is amenable to robotics and offers a cost advantage
relative to conventional cell-based assays. The well-defined nature of this assay
also obviates many of the inherent complications and ambiguities of cell-based
systems.

Copyright © 2012 Elsevier Inc. All rights reserved.

PMID: 22394995 [PubMed - as supplied by publisher]