In Vitro and In Vivo Characterization of Two C-11-Labeled PET Tracers for Vesicular Acetylcholine Transporter

Prashanth K. Padakanti, Xiang Zhang, Hongjun Jin, Jinquan Cui, Ruike Wang, Junfeng Li, Hubert P. Flores, Stanley M. Parsons, Joel S. Perlmutter, Zhude Tu

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

Purpose: The vesicular acetylcholine transporter (VAChT) is a specific biomarker for imaging presynaptic cholinergic neurons. Herein, two potent and selective 11C-labeled VAChT inhibitors were evaluated in rodents and nonhuman primates for imaging VAChT in vivo.

Procedures: For both (−)-[11C]2 and (−)-[11C]6, biodistribution, autoradiography, and metabolism studies were performed in male Sprague Dawley rats. Positron emission tomography (PET) brain studies with (−)-[11C]2 were performed in adult male cynomolgus macaques; 2 h dynamic data was acquired, and the regions of interest were drawn by co-registration of the PET images with the MRI.

Results: The resolved enantiomers (−)-2 and (−)-6 were very potent and selective for VAChT in vitro (Ki < 5 nM for VAChT with >35-fold selectivity for VAChT vs. σ receptors); both radioligands, (−)-[11C]2 and (−)-[11C]6, demonstrated high accumulation in the VAChT-enriched striatum of rats. (−)-[11C]2 had a higher striatum to cerebellum ratio of 2.4-fold at 60 min; at 30 min, striatal uptake reached 0.550 ± 0.086 %ID/g. Uptake was also specific and selective; following pretreatment with (±)-2, striatal uptake of (−)-[11C]2 in rats at 30 min decreased by 50 %, while pretreatment with a potent sigma ligand had no significant effect on striatal uptake in rats. In addition, (−)-[11C]2 displayed favorable in vivo stability in rat blood and brain. PET studies of (−)-[11C]2 in nonhuman primates indicate that it readily crosses the blood-brain barrier (BBB) and provides clear visualization of the striatum; striatal uptake reaches the maximum at 60 min, at which time the target to nontarget ratio reached ~2-fold.

Conclusions: The radioligand (−)-[11C]2 has high potential to be a suitable PET radioligand for imaging VAChT in the brain of living subjects.

Original languageEnglish
Pages (from-to)773-780
Number of pages8
JournalMolecular Imaging and Biology
Volume16
Issue number6
DOIs
StatePublished - Nov 18 2014

Keywords

  • Alzheimer’s disease
  • PET imaging
  • Radiotracer
  • VAChT
  • Vesamicol

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