In vivo imaging of human MDR1 Transcription in the Brain and Spine of MDR1-Luciferase Reporter Mice

Authors

Kazuto Yasuda, St. Jude Children's Research Hospital
Cynthia Cline, St. Jude Children's Research Hospital
Yvonne S. Lin, University of Washington
Rachel Scheib, St. Jude Children's Research Hospital
Samit Ganguly, St. Jude Children's Research Hospital
Ranjit K. Thirumaran, St. Jude Children's Research Hospital
Amarjit Chaudhry, St. Jude Children's Research Hospital
Richard B. Kim, Western UniversityFollow
Erin G. Tirona, Western University
R. H.J. Mathijssen, Erasmus MC
A. Sparreboom, St. Jude Children's Research Hospital

Document Type

Article

Publication Date

11-1-2015

Journal

Drug Metabolism and Disposition

Volume

43

Issue

11

First Page

1646

Last Page

1654

URL with Digital Object Identifier

10.1124/dmd.115.065078

Abstract

P-glycoprotein (Pgp) [the product of the MDR1 (ABCB1) gene] at the blood-brain barrier (BBB) limits central nervous system (CNS) entry of many prescribed drugs, contributing to the poor success rate of CNS drug candidates. Modulating Pgp expression could improve drug delivery into the brain; however, assays to predict regulation of human BBB Pgp are lacking. We developed a transgenic mouse model to monitor human MDR1 transcription in the brain and spinal cord in vivo. A reporter construct consisting of ∼10 kb of the human MDR1 promoter controlling the firefly luciferase gene was used to generate a transgenic mouse line (MDR1-luc). Fluorescence in situ hybridization localized the MDR1-luciferase transgene on chromosome 3. Reporter gene expression was monitored with an in vivo imaging system following D-luciferin injection. Basal expression was detectable in the brain, and treatment with activators of the constitutive androstane, pregnane X, and glucocorticoid receptors induced brain and spinal MDR1-luc transcription. Since D-luciferin is a substrate of ABCG2, the feasibility of improving D-luciferin brain accumulation (and luciferase signal) was tested by coadministering the dual ABCB1/ABCG2 inhibitor elacridar. The brain and spine MDR1-luc signal intensity was increased by elacridar treatment, suggesting enhanced D-luciferin brain bioavailability. There was regional heterogeneity in MDR1 transcription (cortex > cerebellum) that coincided with higher mouse Pgp protein expression. We confirmed luciferase expression in brain vessel endothelial cells by ex vivo analysis of tissue luciferase protein expression. We conclude that the MDR1-luc mouse provides a unique in vivo system to visualize MDR1 CNS expression and regulation.