RT Journal Article
SR Electronic
T1 The Glucose-Dependent Insulinotropic Polypeptide Receptor: A Novel Target for Neuroendocrine Tumor Imaging—First Preclinical Studies
JF Journal of Nuclear Medicine
JO J Nucl Med
FD Society of Nuclear Medicine
SP 976
OP 982
DO 10.2967/jnumed.113.133744
VO 55
IS 6
A1 Gourni, Eleni
A1 Waser, Beatrice
A1 Clerc, Pascal
A1 Fourmy, Daniel
A1 Reubi, Jean Claude
A1 Maecke, Helmut R.
YR 2014
UL http://jnm.snmjournals.org/content/55/6/976.abstract
AB A new family of peptide receptors, the incretin receptor family, overexpressed on many neuroendocrine tumors (NETs) is of great importance because it may enable the in vivo peptide-based receptor targeting of a category of NETs that does not express the somatostatin receptor. Impressive in vivo diagnostic data were published for glucagonlike peptide 1 receptor–targeting radiopeptides. Recently, promising in vitro data have appeared for the second member of the incretin family, the glucose-dependent insulinotropic polypeptide (GIP) receptor. This prompted us to develop and evaluate a new class of radioligands with the potential to be used for the in vivo targeting of GIP receptor–positive tumors. Methods: GIP(1–42) was modified C-terminally, and the truncated peptides [Lys30(aminohexanoic acid [Ahx]-DOTA)]GIP(1–30)NH2 (EG1), [Lys16(Ahx-DOTA)]GIP(1–30)NH2 (EG2), and [Nle14, Lys30(Ahx-DOTA)]GIP(1–30)NH2 (EG4) were conjugated with Ahx-DOTA via the Lys16 and Lys30 side chains. Their inhibitory concentration of 50% (IC50) was determined using [125I-Tyr10]GIP(1–30) as radioligand and GIP(1–30) as control peptide. The DOTA conjugates were labeled with 111In and 68Ga. In vitro evaluation included saturation and internalization studies using the pancreatic endocrine cell line INR1G9 transfected with the human GIP receptor (INR1G9-hGIPr). The in vivo evaluation consisted of biodistribution and PET imaging studies on nude mice bearing INR1G9-hGIPr tumors. Results: Binding studies (IC50 and saturation studies) showed high affinity toward GIP receptor for the GIP conjugates. Specific in vitro internalization was found, and almost the entire cell-associated activity was internalized (>90% of the cell-bound activity), supporting the agonist potency of the 111In-vectors. 111In-EG4 and 68Ga-EG4 were shown to specifically target INR1G9-hGIPr xenografts, with tumor uptake of 10.4% ± 2.2% and 17.0% ± 4.4% injected activity/g, 1 h after injection, respectively. Kidneys showed the highest uptake, which could be reduced by approximately 40%–50% with a modified-fluid-gelatin plasma substitute or an inhibitor of the serine protease dipeptidyl peptidase 4. The PET images clearly visualized the tumor. Conclusion: The evaluation of EG4 as a proof-of-principle radioligand indicated the feasibility of imaging GIP receptor–positive tumors. These results prompt us to continue the development of this family of radioligands for imaging of a broad spectrum of NETs.