Abstract
In recent years, copper-64 and copper-67 have been considered as a useful theranostic pair in nuclear medicine, due to their favourable and complementary decay properties. As $^{67}Cu$ and $^{64}Cu$ are chemically identical, development of both existing and new bifunctional chelators for $^{64}Cu$ imaging agents can be readily adapted for the $^{67}Cu$-radionuclide. In this study, we explored the use of photoactivatable copper chelators based on the asymmetric bis(thiosemicarbazone) scaffold, H$_2$ATSM/en, for the photoradiolabelling of protein. Photoactivatable $^{64}$CuATSM-derivatives were prepared by both direct synthesis and transmetallation from the corresponding $^{nat}$Zn complex. Then, irradiation with UV light in the presence of a protein of interest in a pH buffered aqueous solution afforded the $^{64}Cu$-labelled protein conjugates in decay-corrected radiochemical yield of 86.9 ± 1.0% via the transmetallation method and 35.3 ± 1.7% from the direct radiolabelling method. This study successfully demonstrates the viability of photochemically induced conjugation methods for the development of copper-based radiotracers for potential applications in diagnostic positron emission tomography (PET) imaging and targeted radionuclide therapy.