Radiosynthesis and evaluation of an (18)F–labeled silicon containing exendin-4 peptide as a PET probe for imaging insulinoma

BACKGROUND: Analogues of exendin-4 have been radiolabeled for imaging the glucagon-like peptide type 1 receptors (GLP-1R) which are overexpressed in insulinoma. The aim of this research was to synthesize an (18)F–labeled silicon containing exendin-4 peptide ((18)F-2) and to evaluate its in vitro and in vivo behavior in CHL-GLP-1 receptor positive tumor-bearing mice. (18)F–labeled silicon containing exendin-4 peptide ((18)F-2) was prepared via one-step nucleophilic substitution of a silane precursor with (18)F–fluoride in the presence of acetic acid and K222. (18)F-2 was then administered to tumor-bearing mice for PET imaging and ex vivo biodistribution experiments. RESULTS: (18)F-2 was produced in a radiochemical yield (decay corrected) of 1.5% and a molar activity of max. 16 GBq/μmol. The GLP-1R positive tumors were clearly visualized by PET imaging. Biodistribution studies showed reduced uptake of (18)F-2 in the kidneys compared to radiometal labeled exendin-4 derivatives. The radiotracer showed specific tumour uptake which remained steady over 2 h. CONCLUSIONS: This exendin-4 analogue, (18)F-2, is a potential probe for imaging GLP-1R positive tumors.