18F-radiolabeled GLP-1 analog exendin-4 for PET/CT imaging of insulinoma in small animals.

BACKGROUND: Insulinoma is a neuroendocrine tumor derived from the β cells of pancreatic islets. They are usually relatively inaccessible for surgical intervention. High expression levels of glucagon-like peptide-1 (GLP-1) receptor have been detected in insulinoma. AIM: The aim of the study was to evaluate the potential of F-radiolabeled GLP-1 analog exendin-4 for the diagnosis of insulinoma using PET/computed tomography imaging. MATERIALS AND METHODS: The GLP-1 receptor-specific molecular probe [F]FB-exendin-4 was prepared by the conjugation of exendin-4 and N-succinimidyl-4-[F] fluorobenzoate ([F]SFB). High expression of GLP-1 by the RIN-m5f insulinoma line and GLP-1 receptor specificity were evaluated by determining the saturation curve for in-vitro binding of I-radiolabeled exendin-4 and by investigation of the competitive binding between I-radiolabeled and unlabeled exendin-4. Further, the in-vivo biodistribution and micro-PET/computed tomography images of insulinoma-bearing mice were studied. RESULTS: An overall radiochemical yield of 35.6±2.3% (decay corrected, n=5) and specific radioactivity of around 30 GBq/µmol were achieved for [F]FB-exendin-4, and the radiochemical purity was over 98%. Both in-vitro and in-vivo studies confirmed the specificity of [F]FB-exendin-4 to insulinoma cells. CONCLUSION: [F]FB-exendin-4 has been found to be an effective molecular imaging probe for detecting insulinomas.