In Vitro and In Vivo Characterization of Three 68Ga- and 111In-Labeled Peptides for Cholecystokinin Receptor Imaging:

Cholecystokinin (CCK) receptors are overexpressed in several human tumor types, such as medullary thyroid carcinomas and small cell lung cancers. Several ligands for the CCK2 receptor (CCK2R) have been developed for radionuclide targeting of these tumors. In this study, we evaluated whether radiolabeled DOTA-sCCK8 and its stabilized derivative, DOTA-sCCK8[Phe2(p-CH2SO3H), Nle3,6], are suitable for imaging of CCK2R-positive tumors, using DOTA-MG0 as a reference. In vivo targeting of CCK2R-positive tumors with DOTA-sCCK8, DOTA-sCCK8[Phe2(p-CH2SO3H), Nle3,6], and DOTA-MG0, labeled with 111In or 68Ga, was evaluated in BALB/c nude mice with a subcutaneous A431-CCK2R tumor. Biodistribution studies and single-photon emission computed tomography (SPECT) and positron emission tomography (PET) were performed at 1 hour postinjection. All peptides specifically accreted in the CCK2R-expressing tumors. Both 111In-DOTA-sCCK8 and 111In-DOTA-sCCK8[Phe2(p-CH2SO3H), Nle3,6] showed good tumor retention (4.65% ID/g and 5.44% ...