Development of Tyrosine-Based RadiotracerTc99m-N4-Tyrosine for Breast Cancer Imaging

Abstract

The purpose of this study was to develop an efficient way to synthesizeTc99m-O-[3-(1,4,8,11-tetraazabicyclohexadecane)-propyl]-tyrosine (Tc99m-N4-Tyrosine), a novel amino acid-based radiotracer, and evaluate its potential in breast cancer gamma imaging. Precursor N4-Tyrosine was synthesized using a 5-step procedure, and its total synthesis yield was 38%. It was successfully labeled withTc99mwith high radiochemical purity (>95%). Cellular uptake ofTc99m-N4-Tyrosine was much higher than that ofTc99m-N4 and the clinical gold standard18F-2-deoxy-2-fluoro-glucose (18F-FDG) in rat breast tumor cellsin vitro. Tissue uptake and dosimetry estimation in normal rats revealed thatTc99m-N4-Tyrosine could be safely administered to humans. Evaluation in breast tumor-bearing rats showed that althoughTc99m-N4-Tyrosine appeared to be inferior to18F-FDG in distinguishing breast tumor tissue from chemical-induced inflammatory tissue, it had high tumor-to-muscle uptake ratios and could detect breast tumors clearly by planar scintigraphic imaging.Tc99m-N4-Tyrosine could thus be a useful radiotracer for use in breast tumor diagnostic imaging.