Selective induction of P-glycoprotein at the CNS barriers during symptomatic stage of an ALS animal model

Abstract

P-glycoprotein (P-gp), Breast cancer resistance protein (BCRP) and Multidrug resistance-associated protein 2 (MRP2) residing at the blood-brain barrier (BBB) and the blood-spinal cord barrier (BSCB) are major obstacles for drug delivery to the Central Nervous System (CNS). Disease-induced changes of these xenobiotic transporters at the CNS barriers have been previously documented. Changes in the functional expression of these transporters at the CNS barriers would limit the clinical efficacy of therapeutic agents targeting the CNS. In this study, we characterized the changes in expression and efflux activity of P-gp, BCRP and MRP2 at the BBB and BSCB of an amyotrophic lateral sclerosis (ALS) SOD1-G93A transgenic rat model across the three stages of disease progression: pre-onset, onset and symptomatic. Up-regulation of P-gp and BCRP at the BBB and BSCB during disease progression of ALS would reduce drug entry to the CNS, while any decreases in transport activity would increase drug entry. In SOD rats at the ALS symptomatic stage, we observed increases in both P-gp transport activity and expression compared to age-matched wildtypes. BCRP and MRP2 levels were unchanged in these animals. Immunohistochemical analysis in brain and spinal cord capillaries of SOD rats from all three ALS stages and age-matched wildtypes showed no differences in nuclear localization of a known P-gp regulator, nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB). It suggests that NFκB may have a limited role during P-gp induction observed in our study and additional signaling pathways could be responsible for this response. Our observations imply that novel pharmacological approaches for treating ALS require selecting drugs that are not P-gp substrates in order to improve therapeutic efficacy in the CNS during ALS progression.

Functional Expression of P-glycoprotein and Organic Anion Transporting Polypeptides at the Blood-Brain Barrier: Understanding Transport Mechanisms for Improved CNS Drug Delivery?

“…Targeting P-gp with small molecules has been challenging because first and second P-gp inhibitors have exhibited toxicity issues as well as inhibition of CYP3A4 and other transporters, respectively (30,31,40). Future advances in targeting P-gp for CNS drug delivery are likely to involve targeting of regulatory pathways (95, 96) or transporter trafficking in brain microvascular endothelial cells (45). We propose an alternative approach to optimization of CNS drug delivery via targeting of endogenous SLC uptake transporters expressed at the BBB, such as Oatps.…”

Blood–Brain Barrier Driven Pharmacoresistance in Amyotrophic Lateral Sclerosis and Challenges for Effective Drug Therapies

“…Following these initial findings, the same lab further reported that protein and mRNA levels of Abcb1 and Abcg2 were selectively increased in the spinal cord and cerebral capillaries of SOD1-G93A mice models of ALS (4). Subsequently, other groups reported increased expression of P-gp, but not BCRP in the mutant SOD1-G86R mouse and SOD1-G93A rat models of ALS (34,35). P-gp overexpression may limit the ability of investigational drugs that are P-gp substrates to cross the BBB and reach the brain in therapeutic concentrations, therefore adversely impacting their efficacy.…”

P-glycoprotein Expression Is Upregulated in a Pre-Clinical Model of Traumatic Brain Injury

“…Pgp expression has been extensively examined in the context of cancer and other diseases due to its prominent role in limiting the action of disease-modifying therapeutic drugs. 7,9,10,[30][31][32][33][34][35][36][37][38][39] Most of these studies have used commercial Pgp antibodies. Similar to that reported previously for other Pgp antibodies, [40][41][42][43][44] our validation results using KO mice revealed that some tested antibodies had poor specificity, and caution must be taken when interpreting results of studies using these antibodies.…”