Synthesis and quality control of S11 C-methyl-L-cysteine: A New Amino Acid PET Tracer for Cancer Imaging

Objective 11C-MCYS is a tumor imaging agent,as an analogue of 11C-MET.We expore the method and quality control of 11C-MCYS.Methods 11CO2 was produced by 14N(p,α)11C nuclear reactions,which was delivered to the radiochemical laboratory.11CO2 was trapped and released into the synthesis module.Production of 11CH3I consisted of the reduction of 11CO2 with LiAlH4,hydrolysis of the intermediately formed organometallic complex and subsequent iodination of 11C-methanol with hydrogen iodide.11CH3I was delivered to a Sep-Pak plus C18 cartridge previously loaded with a solution of L-cysteine(2-3mg) dissolved in NaOH 0.5mol/L in ethanol/water 50/50(v/v,0.210ml).11C-MCYS was eluted with NaH 2PO4 0.05mol/L buffer(5ml,pH 3-4) and collected in a vented sterile vial.Contents and analytical methods of quality control for 11C-MCYS were investigated.Results 11CH3I was prepared routinely in our laboratories by utilizing a simple remotely controlled chemical module.The uncorrected radiochemical yield of 11CH 3I was 60-70% from 11CO 2 and the synthesis time was 8-10min after release of 11CO 2.11C-MCYS was prepared by adopting on-column methylation described above.The uncorrected radiochemical yield of 11C-MCYS was 60%-70% with the synthesis time of 2 min.The radiochemical purity of 11C-MCYS was above 98%,and the total synthesis time about 12 min.Conlusion It is easy to perform the automated synthesis of 11C-MCYS.All quality criteria of 11C-MCYS met the requirements of the positron radio-pharmaceuticals.