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Radiosynthesis and Radiotracer Properties of a 7-(2-[18F]Fluoroethoxy)-6-methoxypyrrolidinylquinazoline for Imaging of Phosphodiesterase 10A with PET

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Author(s): Uta Funke | Winnie Deuther-Conrad | Gregor Schwan | Aurélie Maisonial | Matthias Scheunemann | Steffen Fischer | Achim Hiller | Detlef Briel | Peter Brust

Journal: Pharmaceuticals
ISSN 1424-8247

Volume: 5;
Issue: 2;
Start page: 169;
Date: 2012;
Original page

Keywords: PDE10A | quinazoline | fluorine-18 | positron emission tomography | PET

ABSTRACT
Phosphodiesterase 10A (PDE10A) is a key enzyme of intracellular signal transduction which is involved in the regulation of neurotransmission. The molecular imaging of PDE10A by PET is expected to allow a better understanding of physiological and pathological processes related to PDE10A expression and function in the brain. The aim of this study was to develop a new 18F-labeled PDE10A ligand based on a 6,7-dimethoxy-4-pyrrolidinylquinazoline and to evaluate its properties in biodistribution studies. Nucleophilic substitution of the 7-tosyloxy-analogue led to the 7-[18F]fluoroethoxy-derivative [18F]IV with radiochemical yields of 25% ± 9% (n = 9), high radiochemical purity of ≥99% and specific activities of 110–1,100 GBq/μmol. [18F]IV showed moderate PDE10A affinity (KD,PDE10A = 14 nM) and high metabolic stability in the brain of female CD-1 mice, wherein the radioligand entered rapidly with a peak uptake of 2.3% ID/g in striatum at 5 min p.i. However, ex vivo autoradiographic and in vivo blocking studies revealed no target specific accumulation and demonstrated [18F]IV to be inapplicable for imaging PDE10A with PET.
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