Assessing the Functional Redundancy between P-gp and BCRP in Controlling the Brain Distribution and Biliary Excretion of Dual Substrates with PET Imaging in Mice

Blood-brain barrier transporters: a translational consideration for CNS delivery of neurotherapeutics

INTRODUCTION

Successful neuropharmacology requires optimization of CNS drug delivery and, by extension, free drug concentrations at brain molecular targets. Detailed assessment of blood-brain barrier (BBB) physiological characteristics is necessary to achieve this goal. The 'next frontier' in CNS drug delivery is targeting BBB uptake transporters, an approach that requires evaluation of brain endothelial cell transport processes so that effective drug accumulation and improved therapeutic efficacy can occur.

AREAS COVERED

BBB permeability of drugs is governed by tight junction protein complexes (i.e., physical barrier) and transporters/enzymes (i.e., biochemical barrier). For most therapeutics, a component of blood-to-brain transport involves passive transcellular diffusion. Small molecule drugs that do not possess acceptable physicochemical characteristics for passive permeability may utilize putative membrane transporters for CNS uptake. While both uptake and efflux transport mechanisms are expressed at the brain microvascular endothelium, uptake transporters can be targeted for optimization of brain drug delivery and improved treatment of neurological disease states.

EXPERT OPINION

Uptake transporters represent a unique opportunity to optimize brain drug delivery by leveraging the endogenous biology of the BBB. A rigorous understanding of these transporters is required to improve translation from the bench to clinical trials and stimulate the development of new treatment paradigms for neurological diseases.

The influence of verapamil on the pharmacokinetics of the pan-HER tyrosine kinase inhibitor neratinib in rats: the role of P-glycoprotein-mediated efflux

Neratinib, an irreversible pan-HER tyrosine kinase inhibitor, has been approved for the treatment of HER2-positive (HER2⁺) early-stage and brain metastatic breast cancer. Thus far, the pharmacology effects and pharmacodynamics of neratinib have been well studied. However, the disposition of neratinib and its influencing factors in vivo remain unclear. P-glycoprotein (P-gp), one of the most extensively studied transporters, substantially restricts penetration of drugs into the body or deeper compartments (i.e., blood-brain barrier, BBB), regarding drug resistance and drug-drug interactions. Thereby, the aim of this study was to investigate the influence of verapamil (a P-gp inhibitor) on the pharmacokinetics of neratinib in rats. Here, we have established a high specific, selective and sensitive ultra-performance liquid chromatography-tandem mass spectrometric (UPLC-MS/MS) method to quantify plasma concentrations of neratinib in rats. Pharmacokinetic results showed that verapamil significantly increased the system exposure of neratinib, as C_max increased by 2.09-fold and AUC_0-t increased by 1.64-fold, respectively. Additionally, the in vitro transport of neratinib was evaluated using Madin-Darby canine kidney II (MDCK II) and human MDR1 gene overexpressed MDCK (MDCK-MDR1) cell line models. As a result, the net flux ratio was over than 2 and decreased over 50% by verapamil, suggesting that neratinib was a substrate of P-gp. Hence, our findings have highlighted the important role of P-gp in the system exposure of neratinib in vivo, and drug-drug interaction should be considered when coadministration of P-gp inhibitors with neratinib. These findings may support the further clinical development and application of neratinib.

The effects of cyclosporine A or activated charcoal co-administration on the pharmacokinetics of enrofloxacin in chickens

The study aimed to investigate the possible role of efflux transporter proteins in the pharmacokinetics of enrofloxacin (ENR) in broilers in the model of co-administration of activated charcoal (AC) or cyclosporine A (CsA). The concentrations of enrofloxacin and its metabolite ciprofloxacin were analyzed by liquid chromatography-mass spectrometry (LC-MS/MS) and population approach was used for pharmacokinetic analysis. It was found that body weight has a significant effect on the volume of distribution in the central compartment and on the systemic clearance. Oral AC increased the systemic clearance of intravenously administered ENR suggesting some role of enterohepatic recirculation. For orally administered ENR, CsA increased the area under the curve which can be explained by the inhibition of efflux transporters. Metabolism of the antibacterial drug was not affected by cyclosporine. The data suggest a role of efflux transporter proteins in the pharmacokinetics of drugs in chickens and drug-drug interactions have to be considered when substrates and modulators of these transporters are co-administered.

Impact of P-gp and BCRP on pulmonary drug disposition assessed by PET imaging in rats

P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are two efflux transporters which are expressed in the apical (i.e. airway lumen-facing) membranes of lung epithelial cells. To assess the influence of P-gp and BCRP on the pulmonary disposition of inhaled drugs, we performed positron emission tomography (PET) imaging in rats after intratracheal aerosolization of two model P-gp/BCRP substrate radiotracers (i.e. [¹¹C]erlotinib and [¹¹C]tariquidar). We studied rat groups in which both transporters were active (i.e. wild-type rats), either of the two transporters was inactive (Abcb1a/b^(-/-) and Abcg2^(-/-) rats) or both transporters were inactive (Abcg2^(-/-) rats in which pulmonary P-gp activity was inhibited by treatment with unlabeled tariquidar). PET-measured lung distribution data were compared with brain-to-plasma radioactivity concentration ratios measured in a gamma counter at the end of the PET scan. For [¹¹C]erlotinib, lung exposure (AUC_lungs) was moderately but not significantly increased in Abcb1a/b^(-/-) rats (1.6-fold) and Abcg2^(-/-) rats (1.5-fold), and markedly (3.6-fold, p < 0.0001) increased in tariquidar-treated Abcg2^(-/-) rats, compared to wild-type rats. Similarly, the brain uptake of [¹¹C]erlotinib was substantially (4.5-fold, p < 0.0001) increased when both P-gp and BCRP activities were impaired. For [¹¹C]tariquidar, differences in AUC_lungs between groups pointed into a similar direction as for [¹¹C]erlotinib, but were less pronounced and lacked statistical significance. Our study demonstrates functional P-gp and BCRP activity in vivo in the lungs and further suggests functional redundancy between P-gp and BCRP in limiting the pulmonary uptake of a model P-gp/BCRP substrate, analogous to the blood-brain barrier. Our results suggest that pulmonary efflux transporters are important for the efficacy and safety of inhaled drugs and that their modulation may be exploited in order to improve the pharmacokinetic and pharmacodynamic performance of pulmonary delivered drugs.

Regulation of Blood-Brain Barrier Transporters by Transforming Growth Factor-β/Activin Receptor-Like Kinase 1 Signaling: Relevance to the Brain Disposition of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Inhibitors (i.e., Statins)

Our laboratory has shown that activation of transforming growth factor- β (TGF- β )/activin receptor-like kinase 1 (ALK1) signaling can increase protein expression and transport activity of organic anion transporting polypeptide 1a4 (Oatp1a4) at the blood-brain barrier (BBB). These results are relevant to treatment of ischemic stroke because Oatp transport substrates such as 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (i.e., statins) improve functional neurologic outcomes in patients. Advancement of our work requires determination if TGF- β /ALK1 signaling alters Oatp1a4 functional expression differently across brain regions and if such disparities affect central nervous system (CNS) statin disposition. Therefore, we studied regulation of Oatp1a4 by the TGF- β /ALK1 pathway, in vivo, in rat brain microvessels isolated from cerebral cortex, hippocampus, and cerebellum using the ALK1 agonist bone morphogenetic protein-9 (BMP-9) and the ALK1 inhibitor 4-[6-[4-(1-piperazinyl)phenyl]pyrazolo[1,5-a]pyrimidin-3-yl]quinoline dihydrochloride 193189. We showed that Oatp1a4 protein expression and brain distribution of three currently marketed statin drugs (i.e., atorvastatin, pravastatin, and rosuvastatin) were increased in cortex relative to hippocampus and cerebellum. Additionally, BMP-9 treatment enhanced Oatp-mediated statin transport in cortical tissue but not in hippocampus or cerebellum. Although brain drug delivery is also dependent upon efflux transporters, such as P-glycoprotein and/or Breast Cancer Resistance Protein, our data showed that administration of BMP-9 did not alter the relative contribution of these transporters to CNS disposition of statins. Overall, this study provides evidence for differential regulation of Oatp1a4 by TGF- β /ALK1 signaling across brain regions, knowledge that is critical for development of therapeutic strategies to target Oatps at the BBB for CNS drug delivery. SIGNIFICANCE STATEMENT: Organic anion transporting polypeptides (Oatps) represent transporter targets for brain drug delivery. We have shown that Oatp1a4 statin uptake is higher in cortex versus hippocampus and cerebellum. Additionally, we report that the transforming growth factor- β /activin receptor-like kinase 1 agonist bone morphogenetic protein-9 increases Oatp1a4 functional expression, but not efflux transporters P-glycoprotein and Breast Cancer Resistance Protein, in cortical brain microvessels. Overall, this study provides critical data that will advance treatment for neurological diseases where drug development has been challenging.