Repository logo
 

Radiosynthesis of (R,S)-[18 F]GE387: A Potential PET Radiotracer for Imaging Translocator Protein 18 kDa (TSPO) with Low Binding Sensitivity to the Human Gene Polymorphism rs6971.

Published version
Peer-reviewed

Change log

Authors

Qiao, Luxi 
Fisher, Emily 
McMurray, Lindsay 
Milicevic Sephton, Selena  ORCID logo  https://orcid.org/0000-0002-1105-6726
Hird, Matthew 

Abstract

Translocator protein (TSPO) is a biomarker of neuroinflammation, which is a hallmark of many neurodegenerative diseases and has been exploited as a positron emission tomography (PET) target. Carbon-11-labelled PK11195 remains the most applied agent for imaging TSPO, despite its short-lived isotope and low brain permeability. Second-generation radiotracers show variance in affinity amongst subjects (low-, mixed-, and high-affinity binders) caused by the genetic polymorphism (rs6971) of the TSPO gene. To overcome these limitations, a new structural scaffold was explored based on the TSPO pharmacophore, and the analogue with a low-affinity binder/high-affinity binder (LAB/HAB) ratio similar (1.2 vs. 1.3) to that of (R)-[11 C]PK11195 was investigated. The synthesis of the reference compound was accomplished in six steps and 9 % overall yield, and the precursor was prepared in eight steps and 8 % overall yield. The chiral separation of the reference and precursor compounds was performed using supercritical fluid chromatography with >95 % ee. The absolute configuration was determined by circular dichroism. Optimisation of reaction conditions for manual radiolabelling revealed acetonitrile as a preferred solvent at 100 °C. Automation of this radiolabelling method provided R and S enantiomers in respective 21.3±16.7 and 25.6±7.1 % decay-corrected yields and molar activities of 55.8±35.6 and 63.5±39.5 GBq μmol-1 (n=3). Injection of the racemic analogue into a healthy rat confirmed passage through the blood-brain barrier.

Description

Keywords

PET imaging, TSPO receptor, [18F]GE180, [18F]GE387, neuroinflammation biomarkers, Animals, Fluorine Radioisotopes, Humans, Polymorphism, Genetic, Positron-Emission Tomography, Proof of Concept Study, Protein Binding, Radiopharmaceuticals, Rats, Receptors, GABA, Stereoisomerism

Journal Title

ChemMedChem

Conference Name

Journal ISSN

1860-7179
1860-7187

Volume Title

14

Publisher

Wiley
Sponsorship
Medical Research Council (MR/K02308X/1)
This work was supported by Medical Research Council (UK) grant awards RG46503 (LM, MH, XZ) and RG70550 (EF), National Institute of Health Research (UK), Cambridge Biomedical Research Unit in Dementia (EF, NKR) and the Herchel Smith Fellowship programme (LQ).