Synthesis of novel DOTA-/AAZTA-based bifunctional chelators: Solution thermodynamics, peptidomimetic conjugation, and radiopharmaceutical evaluation

Bifunctional chelators (BFCs), which link metallic radionuclide and a targeting vector, are some of the most crucial components of metallic radionuclide-based radiopharmaceuticals for positron-emission computed tomography (PET) imaging. In this study, we designed and synthesized two versatile BFCs, p-NCS-Ph-DE4TA and pNCS-Ph-AAZ4TA, and we conjugated them with a prostate-specific membrane antigen (PSMA) inhibitor. These two chelators showed high affinity for Ga (III) according to a study of the thermodynamics and kinetics and DFT calculations. The labeled PSMA targeted probes, [68Ga]Ga-p-NCS-Ph-DE4TA-PSMA and [68Ga]Ga-p-NCS-PhAAZ4TA-PSMA, maintained excellent stability in vitro, and they exhibited high specific activity when binding to PSMA. A PET/CT imaging study in mice bearing SMMC-7721 hepatocellular carcinoma xenografts demonstrated clear visualization of tumors with a high tumor uptake and low background level, indicating the excellent performance in vivo and specific activity when targeting hepatocellular carcinomas. In summary, p-NCS-PhDE4TA and p-NCS-Ph-AAZ4TA are leading developmental candidates for PET imaging for tumor diagnosis.