High Affinity “Click” RGD Peptidomimetics as Radiolabeled Probes for Imaging αvβ3 Integrin

Non-peptidic RGD-mimic ligands were designed and synthesized by click chemistry between an arginine-azide mimic and an aspartic acid-alkyne mimic. Some of these molecules combine excellent in vitro properties (high αvβ3 affinity, selectivity, drug-like logD, high metabolic stability) with a variety of radiolabeling options (e.g. tritium and [18F]fluorine, plus compatibility with radio-iodination), not requiring the use of chelators or prosthetic groups. The binding mode of the resulting triazole RGD-mimics to αvβ3 or αIIbβ3 receptors was investigated by molecular modeling simulations. Compound 12 was successfully radiofluorinated and used for in vivo PET/CT studies in U87-tumour models, which showed only modest tumour uptake and retention, owing to rapid excretion. These results demonstrate that the novel click-RGD mimics are excellent radiolabeled probes for in vitro and cell-based studies on αvβ3 integrin, whereas further optimization of their pharmaco-kinetic and dynamic profile would be necessary for a successful use in in vivo imaging.