Abstract
Background: High expression of glucagon-like peptide-1 receptor (GLP-1R) in insulinoma supplies a potential drug target for tumor imaging. Exendin-4 can specifically bind to GLP-1R as an agonist and its analogs are extensively used in receptor imaging studies.Purpose: A new GLP-1R imaging agent, [18F]AlF-NOTA-MAL-Cys39-exendin-4, was designed and prepared for insulinoma imaging.Methods: Cys39-exendin-4 was conjugated with NOTA-MAL, then the compound was radiolabeled with [18F]AlF complex to obtained [18F]AlF-NOTA-MAL-Cys39-exendin-4. The tumor-targeting characters of the tracer were evaluated in INS-1 cells and BALB/c nude mice models.Results: [18F]AlF-NOTA-MAL-Cys39-exendin-4 can be efficiently produced with a yield of 17.5 ± 3.2% (non-decay corrected) and radiochemical purity of >95%. The IC50 value of displacement [18F]AlF-NOTA-MAL-Cys39-exendin-4 with Cys39-exendin-4 was 13.52 ± 1.36 nM. PET images showed excellent tumor visualization with high uptake (9.15 ± 1.6%ID/g at 30 min and 7.74 ± 0.87%ID/g at 60 min). The tumor to muscle, pancreas and liver ratios were 63.25, 3.85 and 7.29 at 60 min after injection. GLP-1R binding specificity was demonstrated by co-injection with an excess of unlabeled Cys39-exendin-4 and the tumor uptake was found to be reduced significantly.Conclusion: [18F]AlF-NOTA-MAL-Cys39-exendin-4 shows favorable characteristics for insulinoma imaging and may be translated to clinical studies.
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