RADIOISOTOPES

We are developing new protein probes for in vivo radionuclide imaging using HaloTag® interchangeable labeling system. The selective and rapid bond formation between the HaloTag protein and HaloTag ligands can be applied to a more sophisticated labeling method for protein probes as a substitute of avidin–biotin interaction. For this purpose, we propose to use HaloTag-fusion proteins, which comprise targeting domain and HaloTag domain. In this study, we synthesized 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)–HaloTag ligands that could chelate radioactive metals useful for in vivo imaging. DOTA–HaloTag ligands were actually labeled with ¹¹¹In efficiently, and the labeled ligands were successfully conjugated to a POH protein, which is a protein probe designed for imaging of hypoxia inducible factor-1α activity. The obtained ¹¹¹In-labeled HaloTag-POH protein probes actually accumulated in implanted tumors in mice, which were visualized by single photon emission computed tomography (SPECT).