Automated radiolabeling and in vivo evaluation of 18F-FDOPA

Objective To synthesize 18F-fluoro-L-3, 4-dihydroxyphenylalanine (18F-FDOPA) and evaluate its biodistribution and kinetics in mice, in order to explore its feasibility for insulinoma detection. Methods 18F-FDOPA was synthesized by a three-step nucleophilic reaction. Radiolabeling yield, radiochemical purity and stability in vitro were analyzed. Normal mice were scarified at 2, 5, 15, 30, 60 and 120 min postinjection to measure radioactive counts in main organs. Biodistribution and kinetics were evaluated by dynamic microPET in normal mice. The insulinoma tumor (INS-1) model was established and dynamic microPET was performed immediately after intravenous injection and stopped at 60 min. Region of interest (ROI) was drawn to access time-activity curve (TAC) in main organs and insulinoma. Results 18F-FDOPA was prepared with radiochemical yield of (11.0±0.4)%, radiochemical purity of (99.3±0.2)%. The radiochemical purity was still >99% after being stored for 120 min at room temperature. Predominant uptake of 18F-FDOPA was in the kidneys, and was cleared rapidly in blood. Pancreas showed stable uptake from 20 to 50 min, which was (5.98±0.71) percentage activity of injection dose per gram of tissue (%ID/g) at 20 min and (4.62±0.47) %ID/g at 50 min postinjection, respectively. 18F-FDOPA showed high affinity to tumor tissue of insulinoma ((11.42±0.70) %ID/g) at 2 min. Conclusions 18F-FDOPA could be easily synthesized in short total reaction time with high radiochemical purity and stability. Early phase imaging of 18F-FDOPA may be helpful for insulinoma detection. Key words: Levodopa; Isotope labeling; Fluorine radioisotopes; Insulinoma; Positron-emission tomography; Mice