The
EphB2 receptor is known to be overexpressed in various types of
cancer and is therefore a promising target for
tumor cell imaging by positron emission tomography (PET). In this regard, imaging could facilitate the early detection of EphB2-overexpressing
tumors, monitoring responses to
therapy directed toward EphB2, and thus improvement in patient outcomes. We report the synthesis and evaluation of several fluorine-18-labeled
peptides containing the SNEW amino acid motif, with high affinity for the
EphB2 receptor, for their potential as radiotracers in the non-invasive imaging of
cancer using PET. For the purposes of radiofluorination, EphB2-antagonistic SNEW
peptides were varied at the C terminus by the introduction of
L-cysteine, and further by
alkyne- or
azide-modified
amino acids. In addition, two novel bifunctional and bioorthogonal labeling building blocks [(18)F]AFP and [(18)F]
BFP were applied, and their capacity to introduce
fluorine-18 was compared with that of the established building block [(18)F]FBAM.
Copper-assisted Huisgen 1,3-dipolar cycloaddition, which belongs to the set of bioorthogonal click chemistry reactions, was used to introduce both novel building blocks into
azide- or
alkyne-modified SNEW
peptides under mild conditions. Finally, the depletion of
copper immediately after radiolabeling is a highly important step of this novel methodology.