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 ⁶⁸Ga-N188 and validated its nectin-4 detection efficacy. However, the relatively short half-life and low positron emission rate of ⁶⁸Ga 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 ¹⁸F, which has a longer half-life and a higher positron emission rate, for PET imaging. Micro-PET/CT imaging-based screening showed that Al¹⁸F-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 Al¹⁸F-N231 had a good stability and safety profile in vivo. Biodistribution studies validated the specific binding of Al¹⁸F-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, Al¹⁸F-N231 has promising capability for noninvasive nectin-4 detection in vivo.