Evaluation of Cu-64 and Ga-68 Radiolabeled Glucagon-Like Peptide-1 Receptor Agonists as PET Tracers for Pancreatic β cell Imaging

PurposeCopper-64 (Cu-64) and Galium-68 (Ga-68) radiolabeled DO3A and NODA conjugates of exendin-4 were used for preclinical imaging of pancreatic β cells via targeting of glucagon-like peptide-1 receptor (GLP-1R).ProceduresDO3A-VS- and NODA-VS-tagged Cys40exendin-4 (DO3A-VS-Cys40-exendin-4 and NODA-VS-Cys40-exendin-4, respectively) were labeled with Cu-64 and Ga-68 using standard techniques. Biodistribution and dynamic positron emission tomography (PET) were carried out in normal Sprague–Dawley (SD) rats. Ex vivo autoradiography imaging was conducted with freshly frozen pancreatic thin sections.ResultsDO3A-VS- and NODA-VS-Cys40-exendin-4 analogues were labeled with Cu-64 and Ga-68 to a specific activity of 518.7 ± 3.7 Ci/mmol (19.19 ± 0.14 TBq/mmol) and radiochemical yield above 98 %. Biodistribution data demonstrated pancreatic uptake of 0.11 ± 0.02 %ID/g for [64Cu]DO3A-VS-, 0.14 ± 0.02 %ID/g for [64Cu]NODA-VS-, 0.11 ± 0.03 for [68Ga]DO3A-VS-, and 0.26 ± 0.03 for [68Ga]NODA-VS-Cys40-exendin-4. Excess exendin-4 and exendin-(9–39)-amide displaced all four Cu-64 and Ga-68 labeled exendin-4 derivatives in blocking studies.Conclusions[64Cu]/[68Ga]DO3A-VS-Cys40- and [64Cu]/[68Ga]NODA-VS-Cys40-exendin-4 can be used as PET imaging agents specific for GLP-1R expressed on β cells. Here, we report the first evidence of pancreatic uptake visualized with exendin-4 derivative in a rat animal model via in vivo dynamic PET imaging.