New Bifunctional Chelator p-SCN-PhPr-NE3TA for Copper-64: Synthesis, Peptidomimetic Conjugation, Radiolabeling, and Evaluation for PET Imaging.

Bifunctional chelators play an important role in developing metallic radionuclide-based radiopharmaceuticals. In this study, a new bifunctional ligand, p-SCN-PhPr-NE3TA, was synthesized and conjugated to a very late antigen-4 targeting peptidomimetic, LLP2A, for evaluating its application in (64)Cu-based positron emission tomography (PET) imaging. The new ligand exhibited strong selective coordination of Cu(II), leading to a robust Cu complex, even in the presence of 10-fold Fe(III). The LLP2A conjugate of p-SCN-PhPr-NE3TA was prepared and successfully labeled with (64)Cu under mild conditions. The conjugate (64)Cu-NE3TA-PEG4-LLP2A showed significantly higher specific activity, compared with (64)Cu-NOTA-PEG4-LLP2A, while maintaining comparable serum stability. Subsequent biodistribution studies and PET imaging in mice bearing B16F10 xenografts confirmed its favorable in vivo performance and high tumor uptake with low background, rendering p-SCN-PhPr-NE3TA a promising bifunctional chelator for (64)Cu-based radiopharmaceuticals.