Preclinical Evaluation of an Al18F-Radiolabeled Bicyclic Peptide Targeting Nectin-4

Precisely assessing nectin-4 expression in tumors is important in identifying patients who may benefit from nectin-4-targeted therapies. In our previous work, we developed a bicyclic peptide-based nectin-4-targeting radiotracer 68 Ga–N188 and validated its nectin-4 detection efficacy. However, the relatively short half-life and low positron emission rate of 68 Ga limit its further application. In this study, we constructed three novel nectin-4-targeting ligands N230–232 based on a bicyclic peptide structure and labeled with radionuclide 18 F, which has a longer half-life and a higher positron emission rate, for PET imaging. Micro-PET/CT imaging-based screening showed that Al 18 F–N231 had the best imaging contrast with a tumor-to-muscle ratio of 10.97 ± 2.39. Further characterization demonstrated that ligand N231 had a high affinity to nectin-4 with a K d of 4.29 nM, and Al 18 F–N231 had a good stability and safety profile in vivo . Biodistribution studies validated the specific binding of Al 18 F–N231 to nectin-4 in vivo, with tumor uptake in the nectin-4 + SW780 tumor group being 1.45- and 3.75-fold higher than that in the nectin-4 – 5637 tumor group and blocking group, respectively. Based on the results of this work, Al 18 F–N231 has promising capability for noninvasive nectin-4 detection in vivo .