Automated Radiosynthesis and Bio-distribution of ¹⁸FFluoromethyl Choline

To develop a rapid and automated synthetic method for making ¹⁸FFluoromethyl choline （¹⁸F-FCH）, the automatic synthesis module from Sumitomo corporation was used to synthesize ¹⁸F-FCH, the bio-distribution in normal mice and the PET/CT imaging on pancreatic tumor xenograft murine models were also evaluated. CH₂Br₂ was used as precursor, intermediate product of ¹⁸FCH₂Br was produced by the gaseous reaction with ¹⁸F^-. Then, the ¹⁸FCH2OTf, more reactive ¹⁸F fluotomethylating agent than the ¹⁸FCH2Br, was converted on-line by passing ¹⁸FCH₂Br through a heated Ag-Triflate column. ¹⁸FC₂H₄SO₃CF₃ reacted with N, N-dimethylaminoethanol (DMAE) on SEP-PAK C-18 cartridge, followed by purification on SEP-PAK Accell CM cartridge. The ¹⁸F-FCH was intravenously injected into mice, the mice were sacrificed at 5, 10, 30, 60, 90, 120 minutes post injection respectively. The major organs were removed and weighed before radioactive γ-counting. PET/CT imaging was carried out at 10 minutes after injection of ¹⁸F-FCH in nude mice xenografted with pancreatic cancer. The results showed that ¹⁸Ffluorocholine was produced from ¹⁸Ffluoride in overall radiochemical yields of （25±5）% (uncorrected, n=23) in 32 minutes, radiochemical purity was higher than 97%. The biodistribution datas showed high uptake in liver, kidney, low uptake in brain, lung, muscle and rapid clearance in blood. Most organs reached its radioactive peak within 5 minutes and then decreasing or in a relatively stable state. The bio-distribution of ¹⁸F-FCH was similar with the reported data of ¹¹C-choline. PET/CT imaging showed high accumulation in the kidney, liver and spleen, however, the uptake of ¹⁸F-FCH in the pancreatic cancer was very low. It has very low potential as a positive pancreatic cancer imaging agent. This new automated synthesis technique provides high and reproducible yields that could be dedicated for routine use.