Synthesis and evaluation of O-(3-[ 18F]fluoropropyl)-L-tyrosine as an oncologic PET tracer

O-(3-[ 18F]fluoropropyl)-L-tyrosine (FPT), an analogue of O-(2-[ 18F]fluoroethyl)-L-tyrosine (FET) as an amino acid tracer for tumor imaging with positron emission tomography (PET), was synthesized and evaluated. FPT was prepared by [ 18F]fluoropropylation of L-tyrosine in a two-step procedure. Biodistribution of FPT was determined in normal mice. FPT, FET and [ 18F]fluorine-2-deoxy-D-glucose (FDG) uptake studies were performed in mice bearing S18 fibrosarcoma and S. aureus-inoculated mice. Also, carcinoma-bearing mice and S. aureus-inoculated mice were imaged using FPT PET imaging compared with FET and FDG PET imaging. Synthesis of FPT was accompished in about 60 min with an overall radiochemical yield of 25-30% (without decay correction) by manual operation. High uptake and long retention time of FPT and FET in kidney, liver, lung, blood, etc., and low uptake in brain were found. Furthermore, high FPT, FET and FDG uptake in tumor, and almost no FPT and FET uptake in inflammatory tissue, in contrast, high FDG uptake in inflammatory tissue, were observed. In conclusion, FPT is easy to prepare and superior to FDG in the differentiation of tumor and inflammation, and seems to be a potential amino acid tracer like FET for tumors imaging with PET.