Erschienen in:
01.06.2011 | Short Communication
Value of the radiolabelled GLP-1 receptor antagonist exendin(9–39) for targeting of GLP-1 receptor-expressing pancreatic tissues in mice and humans
verfasst von:
Beatrice Waser, Jean Claude Reubi
Erschienen in:
European Journal of Nuclear Medicine and Molecular Imaging
|
Ausgabe 6/2011
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Abstract
Purpose
Radiolabelled glucagon-like peptide 1 (GLP-1) receptor agonists have recently been shown to successfully image benign insulinomas in patients. Moreover, it was recently reported that antagonist tracers were superior to agonist tracers for somatostatin and gastrin-releasing peptide receptor targeting of tumours. The present preclinical study determines therefore the value of an established GLP-1 receptor antagonist for the in vitro visualization of GLP-1 receptor-expressing tissues in mice and humans.
Methods
Receptor autoradiography studies with 125I-GLP-1(7–36)amide agonist or 125I-Bolton-Hunter-exendin(9–39) antagonist radioligands were performed in mice pancreas and insulinomas as well as in human insulinomas; competition experiments were performed in the presence of increasing concentration of GLP-1(7–36)amide or exendin(9–39).
Results
The antagonist 125I-Bolton-Hunter-exendin(9–39) labels mouse pancreatic β-cells and mouse insulinomas, but it does not label human pancreatic β-cells and insulinomas. High affinity displacement (IC50 approximately 2 nM) is observed in mouse β-cells and insulinomas with either the exendin(9–39) antagonist or GLP-1(7–36)amide agonist. For comparison, the agonist 125I-GLP-1(7–36)amide intensively labels mouse pancreatic β-cells, mouse insulinoma and human insulinomas; high affinity displacement is observed for the GLP-1(7–36)amide in all tissues; however, a 5 and 20 times lower affinity is found for exendin(9–39) in the mouse and human tissues, respectively.
Conclusion
This study reports a species-dependent behaviour of the GLP-1 receptor antagonist exendin(9–39) that can optimally target GLP-1 receptors in mice but not in human tissue. Due to its overly low binding affinity, this antagonist is an inadequate targeting agent for human GLP-1 receptor-expressing tissues, as opposed to the GLP-1 receptor agonist, GLP-1(7–36)amide.