Measurement of cyclosporin induced changes in P-glycoprotein function at the human blood-brain barrier using [18F]MC225 and PET.

INTRODUCTION: P-glycoprotein (P-gp) or multidrug-resistance protein is one of the most extensively studied efflux transporters at the blood-brain barrier (BBB). Changes in P-gp function are associated with several neurodegenerative and psychiatric diseases, including Alzheimer's disease, Parkinson's disease and schizophrenia and with the bioavailability of several pharmaceuticals in the brain, causing multi-drug resistance or side effects. PET imaging can be used to measure the P-gp function in vivo. This study aims to validate [ 18F]MC225 as specific P-gp PET tracer with the use of cyclosporin as selective P-gp inhibitor.

METHODS: Fourteen healthy volunteers (age 67 ± 5y) were included. Subjects underwent twice a 60 min dynamic [ 18F]MC225 (200MBq) PET scan with continuous arterial blood sampling and a cerebral T1-weighted MRI as anatomical reference. During the second scan, in five subjects, cyclosporin was administered in a dose of 2.5 mg/kg/hour, starting 30 min prior to the scan, to inhibit the BBB P-gp function. Tissue time-activity curves of preselected brain regions (Hammer's atlas) were fitted to a reversible two-tissue compartment model (2T4k) using the metabolite corrected plasma and uncorrected whole blood curves as input functions.

RESULTS: No significant difference was found in plasma kinetics, plasma curves, plasma-to-whole blood ratio, and the parent fraction of the baseline scans and scans after administration of cyclosporin. Volume of distribution values in whole brain grey matter showed a significant increase (6.18 ± 1.29 to 9.00 ± 1.29 mL·cm - 3,p = 0.03) after the administration of cyclosporin.

CONCLUSION: The outcomes of the current study reflect the potential ability of [ 18F]MC225 to measure cyclosporin induced changes in P-gp function at the human BBB in vivo.

TRIAL REGISTRATION: EudraCT 2020-001564-28.