Automatic synthesis of 18F-FB-RGD and evaluation of its biodistribution

Objective To evaluate the automatic synthesis of 18F-labeled cyclic RGD peptide c(RGDyK)and its biological distribution in the tumor-bearing mice. Methods N-succinimidyl-4-18 F-fluorobenzoate (18F-SFB) was automatically synthesized and then re-dissolved in acetonitrile (MeCN). The cyclic RGD peptide c(RGDyK) was mixed with an hydrous DMSO and N, N-diisopropyl ethylamine (DIPEA). 18F-FBRGD was obtained by the reaction of peptide solution with 18 F-SFB. The final product was purified by HPLC gradient separation system and solid-phase extraction method. The biodistribution study and competition test of N-4-18F- fluorobenzoyl-RGD (18F-FB-RGD) in the tumor-bearing mice was performed. Results The labeling yield of 18 F-FB-RGD was (33.6 ± 3.5)%. The synthesis time was 110 min. The radiochemical purity was more than 98%. The tumor uptake of 18F-FB-RGD was (3.43 ±0.15), (2.61 ±0.14), (2.11 ±0.13), and (1.79 ±0.18) %ID/g, respectively, at 30, 60, 90 and 120 min after injection. The ratio of tumor to muscle activity ranged from 4.26 ±0.69 to 5.80 ±0.78. The tumor uptake decreased dramatically after RGD blockage. The uptake was (0.46 ±0.21) %ID/g and (2.87 ±0.59) %ID/g in the blocked and unblocked mice, respectively, at 60 min after blockage. Conclusions 18 F-FB-RGD can be automatically synthesized and it may become a promising tumor imaging agent. Key words: RGD;  Isotope labeling;  Fluorine radioisotopes;  Chemical synthesis; Automation;  Neoplasm transplantation;  Mice