Table of Contents
International Journal of Molecular Imaging
Volume 2014, Article ID 507012, 10 pages
http://dx.doi.org/10.1155/2014/507012
Research Article

Ex Vivo Characterization of a Novel Iodine-123-Labelled Aminomethylchroman as a Potential Agonist Ligand for SPECT Imaging of Dopamine D2/3 Receptors

1Department of Nuclear Medicine, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, Netherlands
2SyMO-Chem BV, Den Dolech 2, 5612 AZ Eindhoven, Netherlands
3GE Healthcare, De Rondom 8, 5612 AP Eindhoven, Netherlands
4Department of Pharmacology, Johannes Gutenberg University, Obere Zahlbacher Straße 67, 55101 Mainz, Germany
5Department of Nuclear Medicine and Molecular Imaging, University Medical Center Groningen, University of Groningen, Hanzeplein 1, 9713 GZ Groningen, Netherlands

Received 29 July 2014; Revised 18 November 2014; Accepted 27 November 2014; Published 25 December 2014

Academic Editor: Adriaan A. Lammertsma

Copyright © 2014 Jan-Peter van Wieringen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

For imaging of dopamine D2/3 receptors, agonist tracers are favoured over antagonists because they are more sensitive to detection of dopamine release and because they may selectively label the high-affinity receptor state. We have developed novel D2/3 receptor selective agonists that can be radiolabelled with [123I], which label is advantageous over most other labels, such as carbon-11, as it has a longer half-life. Particularly, we considered (R) N-[7-hydroxychroman-2-yl]-methyl 4-iodobenzyl amine (compound 1) as an attractive candidate for development as it shows high binding affinity to D2/3 receptors in vitro, and here we report on the characterization of this first [123I]-labelled D2/3 receptor agonist radiopharmaceutical intended for SPECT imaging. The appropriate tin precursor for [123I]-1 was developed and was successfully radiolabelled with iodine-123 giving a moderate yield (30–35%) and a good purity (>95%) for [123I]-1. In biodistribution experiments in Wistar rats intravenous injection of [123I]-1 resulted in a fast brain uptake, where the observed binding in the D2/3 receptor-rich striatum was slightly higher than that in the cerebellum 30 min to 4 h p.i. Storage phosphor imaging experiments, however, did not show specific D2/3 receptor binding. In conclusion, despite promising in vitro data for 1, neither specific ex vivo binding nor high signal-to-noise ratios were found in rodents for [123I]-1.