Development of a new thiol-reactive prosthetic group for site-specific labeling of biomolecules with radioactive iodine

In this report, we describe the radiosynthesis of a new thiol-targeting prosthetic group for efficient radioactive iodine labeling of biomolecules. Radioiodination using the precursor 3 was performed to obtain I-125-labeled tetrazole 4b with high radiochemical yield (73%) and radiochemical purity. Using the radiolabeled 4b, a single free cysteine containing peptide and human serum albumin were labeled with I-125 in modest-to-good radiochemical yields (65-99%) under mildly reactive conditions. A biodistribution study of [I-125]7 in normal ICR mice exhibited lower thyroid uptake values than those of I-125-labeled human serum albumin prepared via a traditional radiolabeling method. Thus, [I-125]7 could be employed as an effective radiotracer for molecular imaging and biodistribution studies. The results clearly demonstrate that 4b has the potential to be effectively implemented as a prosthetic group in the preparation of radiolabeled biomolecules.