Development of a bifunctional chelating agent containing isothiocyanate residue for one step F-18 labeling of peptides and application for RGD labeling

We report herein a novel isothiocyanate active ligand for fluorine-18 labeling prepared by four step synthesis. It can be conjugated to a target molecule containing an amino functional group under weak basic conditions by way of thiourea bond formation. We explored the application of synthesized ligand by conjugating to well known α_vβ₃ integrin targeting peptide, c(RGDyK). The conjugated peptide showed good radiochemical yield and efficiency with an excellent radiochemical purity (97.1 ± 1.2%) in a short reaction time (10 min). Labeled peptide showed excellent in vitro and in vivo stability (>95%). α_vβ₃ integrin specific tumor uptake was observed both in biodistribution and small animal microPET studies on α_vβ₃-positive U87MG (human glioma cells) xenograft bearing mice. In general, successful application of synthesized ligand for labeling of RGD peptide could facilitate the possibility of using this ligand for labeling peptides containing an amino functional group.