Synthesis of a new bifunctional chelating agent for one step F-18 labeling and implementation in labeling of [F-18]AlF-NODA-RGD peptide for tumor angiogenesis imaging

Objectives For the general application of improved F-18 biomolecule labeling, we synthesized a bifunctional chelating agent containing isothiocyanate and NODA moieties for [F-18]AlF method.1 It can be conjugated onto a target molecule containing an amino functional group under mild basic conditions by formation of thiourea bond. We explored the application of synthesized agent by conjugating to a well-known αvβ3 integrin targeting peptide, c(RGDyK).

Methods Active ligand NODA-SCN was synthesized in four steps. Extended amino group of lysine in c(RGDyK) was conjugated with active ligand under basic condition (pH ~9). Conjugated product (NODA-SCN-RGD) was purified by prep-HPLC. Ligand conjugated peptide was labeled with freshly prepared [F-18](AlF)2+. Labeling efficiency was tested using ITLC. Biodistribution of [F-18]AlF-NODA-SCN-RGD was studied in nude balb/c mice bearing glioma xenografts at 60 min. Small animal PET images were obtained after 1 and 2 hr post-injection of the labeled agent.

Results NODA-SCN was synthesized with overall good yield (>50%). 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%). αvβ3 integrin specific tumor uptake was observed both in biodistribution (4.41 ± 0.98 %ID/g at 60 min p.i) and small animal microPET (SUV of 7.42 ± 0.49) studies. These values reduced significantly in the blocking study with co-injection of cold c(RGD)yK (3 mg/kg), which shows the specificity of labeled peptide.

Conclusions We developed a bifunctional chelating agent NODA-SCN for labeling peptides with F-18 using an AlF method. Successful application of the agent for F-18 labeling of RGD peptide demonstrated the feasibility of this ligand as a general protein and peptide labeling agent.

Research Support This research was partly supported by the Converging Research Center Program (2010K001055) and National Research Laboratory Program (R0A-2008-000-20116-0) through the Ministry of Education, Sciences and Technology