Synthesis and characterization of a novel 68Ga-labeled p-bromobenzyl lysine-urea-ODAP PSMA inhibitor.

Prostate-specific membrane antigen (PSMA) has been proved as a specific target for diagnosis and treatment of prostate cancer (PCa). Recently, oxalyldiaminopropionic acid (ODAP)-Urea-based ligands showed the potential as a new scaffold for developing radiotracers to image PCa. In this study, we synthesized seven ODAP-Urea-Lys derivatives characterized with p-bromobenzyl group conjugated to lysine. The ligands showed medium-to-high potency, with Ki values ranging from 27.9 nM to 0.94 nM. The ligands could be efficiently radiolabeled with 68Ga, in high purity. Radioligands were stable and showed PSMA specific cellular uptake, in PSMA++ LNCaP cells and PSMA+ 22Rv1 cells over PSMA- PC3 cells. MicroPET imaging was performed in 22Rv1 tumor-bearing mice and 68Ga-ligand-1 showed the best characteristics among the seven ligands, with the highest tumor uptake (SUVmax: 0.56 ± 0.07). A biodistribution study was also performed. ODAP-Urea-Lys-p-bromobenzyl could be used to image prostate cancer in vivo, and the ligands could have high binding potency. The future investigation is still necessary to improve the tumor-specific uptake of this class of ligands and reducing the non-specific uptake in normal organs.