Radiolabeling of multimeric neurotensin(8-13) analogs with the short-lived positron emitter fluorine-18

Three methods for 18F-labeling of dimeric and tetrameric neurotensin(8-13) derivatives were evaluated with respect to the labeling yield and the required peptide amounts. Labeling using N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) gave low radiochemical yield for the dimeric peptides. Coupling of the tetramer with [18F]SFB was not successful. High yields were obtained for labeling of the aminooxy-functionalized neurotensin(8-13) dimer using 4-[18F]fluorobenzaldehyde ([18F]FBA) whilst coupling of the corresponding tetramer gave only low yields. Labeling of sulfydryl-functionalized neurotensin(8-13) derivatives using the maleinimide 4-[18F]fluorobenzaldehyde-O-[6-(2,5-dioxo-2,5-dihydro-pyrrol-1-yl)-hexyl] -oxime ([18F]FBAM) resulted in high radiochemical yields for both, the dimer and the tetramer. Therefore, [18F]FBAM seems to be the most suitable 18F-labeling agent for multivalent neurotensin(8-13) derivatives