Abstract
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Objectives In comparison to somatostatin receptor scintigraphy (SRS), gastrin receptor scintigraphy (GRS) using 111In-DTPA-Minigastrin (MG0) showed added value in diagnosing neuroendocrine tumors (NET). We investigated whether the 68Ga-labeled gastrin analogue DOTA-MG0 is also suited for GRS with positron emission tomography (PET) which could help to improve image quality.
Methods Targeting of CCK2/gastrin receptor positive tumors with DOTA-MG0 labeled with either 111In or 68Ga in vitro was investigated using the AR42J rat tumor cell line. Biodistribution was examined in BALB/c nude mice with a subcutaneous AR42J tumor. To determine specificity of uptake, a 100-fold excess of cold peptide was co-injected. In vivo PET imaging was performed using an Inveon® preclinical PET/CT scanner.
Results In vitro studies showed high receptor affinity (IC50 = 5.0 nM), specific binding and rapid internalization kinetics of 111In-DOTA-MG0. Biodistribution studies revealed high tumor uptake of 111In-DOTA-MG0: 6.5 ± 1.4 %ID/g. Co-administration of an excess unlabelled peptide blocked the tumour uptake (0.74 ± 0.03 %ID/g), indicating that the tumour uptake is specific.The biodistribution of 68Ga-DOTA-MG0 similar to that of 111In-DOTA-MG0, subcutaneous tumors were clearly visualized by small animal PET imaging with 5 MBq 68Ga-DOTA-MG0.
Conclusions 111In and 68Ga-labelled DOTA-MG0 specifically accumulate in CCK2/gastrin receptor positive AR42J tumors with similar biodistribution. Subcutaneous AR42J tumors were clearly visualized by small animal PET. Therefore, 68Ga-DOTA-MG0 might be a promising tracer for PET imaging of CCK2/gastrin receptor positive tumors in humans.
- © 2009 by Society of Nuclear Medicine