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Contrast Media & Molecular Imaging
Volume 2017 (2017), Article ID 6873684, 10 pages
Research Article

High Contrast PET Imaging of GRPR Expression in Prostate Cancer Using Cobalt-Labeled Bombesin Antagonist RM26

1Division of Molecular Imaging, Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden
2PET & Cyclotron Unit, Department of Nuclear Medicine, Odense University Hospital, Odense, Denmark
3Department of Clinical Research, University of Southern Denmark, Odense, Denmark
4Division of Organic Pharmaceutical Chemistry, Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden
5Science for Life Laboratory, Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden
6Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden

Correspondence should be addressed to Anna Orlova

Received 22 April 2017; Accepted 22 June 2017; Published 10 August 2017

Academic Editor: Ralf Schirrmacher

Copyright © 2017 Bogdan Mitran 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.


High gastrin releasing peptide receptor (GRPR) expression is associated with numerous cancers including prostate and breast cancer. The aim of the current study was to develop a 55Co-labeled PET agent based on GRPR antagonist RM26 for visualization of GRPR-expressing tumors. Labeling with 57Co and 55Co, stability, binding specificity, and in vitro and in vivo characteristics of 57Co-NOTA-PEG2-RM26 were studied. NOTA-PEG2-RM26 was successfully radiolabeled with 57Co and 55Co with high yields and demonstrated high stability. The radiopeptide showed retained binding specificity to GRPR in vitro and in vivo. 57Co-NOTA-PEG2-RM26 biodistribution in mice was characterized by rapid clearance of radioactivity from blood and normal non-GRPR-expressing organs and low hepatic uptake. The clearance was predominantly renal with a low degree of radioactivity reabsorption. Tumor-to-blood ratios were approximately 200 (3 h pi) and 1000 (24 h pi). The favorable biodistribution of cobalt-labeled NOTA-PEG2-RM26 translated into high contrast preclinical PET/CT (using 55Co) and SPECT/CT (using 57Co) images of PC-3 xenografts. The initial biological results suggest that 55Co-NOTA-PEG2-RM26 is a promising tracer for PET visualization of GRPR-expressing tumors.