68Ga-labelled exendin-3, a new agent for the detection of insulinomas with PET.

Abstract

PURPOSE:

Insulinomas are neuroendocrine tumours derived from pancreatic beta-cells. The glucagon-like peptide 1 receptor (GLP-1R) is expressed with a high incidence (>90%) and high density in insulinomas. Glucagon-like peptide 1 (GLP-1), the natural ligand of GLP-1R, is rapidly degraded in vivo. A more stable agonist of GLP-1R is exendin-3. We investigated imaging of insulinomas with DOTA-conjugated exendin-3 labelled with (68)Ga.

METHODS:

Targeting of insulinomas with [Lys(40)(DOTA)]exendin-3 labelled with either (111)In or (68)Ga was investigated in vitro using insulinoma tumour cells (INS-1). [Lys(40)((111)In-DTPA)]Exendin-3 was used as a reference in this study. In vivo targeting was investigated in BALB/c nude mice with subcutaneous INS-1 tumours. PET imaging was performed using a preclinical PET/CT scanner.

RESULTS:

In vitro exendin-3 specifically bound and was internalized by GLP-1R-positive cells. In BALB/c nude mice with subcutaneous INS-1 tumours a high uptake of [Lys(40)((111)In-DTPA)]exendin-3 in the tumour was observed (33.5 +/- 11.6%ID/g at 4 h after injection). Uptake was specific, as determined by coinjection of an excess of unlabelled [Lys(40)]exendin-3 (1.8 +/- 0.1%ID/g). The pancreas also exhibited high and specific uptake (11.3 +/- 1.0%ID/g). High uptake was also found in the kidneys (144 +/- 24%ID/g) and this uptake was not receptor-mediated. In this murine tumour model optimal targeting of the GLP-1R expressing tumour was obtained at exendin doses < or =0.1 microg. Remarkably, tumour uptake of (68)Ga-labelled [Lys(40)(DOTA)]exendin-3 was lower (8.9 +/- 3.1%ID/g) than tumour uptake of (111)In-labelled [Lys(40)(DTPA)]exendin-3 (25.4 +/- 7.2%ID/g). The subcutaneous tumours were clearly visualized by small-animal PET imaging after injection of 3 MBq of [Lys(40)((68)Ga-DOTA)]exendin-3.

CONCLUSION:

[Lys(40)((68)Ga-DOTA)]Exendin-3 specifically accumulates in insulinomas, although the uptake is lower than that of [Lys(40)((111)In-DTPA)]exendin-3. Therefore, [Lys(40)((68)Ga-DOTA)]exendin-3 is a promising tracer to visualize insulinomas with PET.

• Authors: Maarten Brom, Wim J G Oyen, Lieke Joosten, Martin Gotthardt, Otto C Boerman
• Journal: European journal of nuclear medicine and molecular imaging (Eur J Nucl Med Mol Imaging) Vol. 37 Issue 7 Pg. 1345-55 (Jul 2010) ISSN: 1619-7089 [Electronic] Germany
• PMID: 20111963 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Gallium Radioisotopes
• Heterocyclic Compounds, 1-Ring
• Peptides
• exendin 3
• 1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid
• Pentetic Acid
• Lysine

Topics

• Amino Acid Sequence
• Animals
• Biological Transport
• Cell Line, Tumor
• Dose-Response Relationship, Drug
• Female
• Gallium Radioisotopes
• Heterocyclic Compounds, 1-Ring (chemistry)
• Inhibitory Concentration 50
• Injections
• Insulinoma (diagnostic imaging, metabolism)
• Kinetics
• Lysine (chemistry)
• Mice
• Molecular Sequence Data
• Pentetic Acid (chemistry)
• Peptides (chemistry, metabolism, pharmacokinetics)
• Positron-Emission Tomography (methods)
• Rats