title: S-11C-methyl-L-cysteine: a new amino acid PET tracer for cancer imaging.
abstract: S-(11)C-methyl-L-cysteine ((11)C-MCYS), an analog of S-(11)C-methyl-L-methionine ((11)C-MET), can potentially serve as an amino acid PET tracer for tumor imaging. The aim of this study was to investigate the radiosynthesis and perform a biologic evaluation of (11)C-MCYS as a tumor imaging tracer. The results of the first human PET study are reported.
  
  
  METHODS
  (11)C-MCYS was prepared by (11)C-methylation of the precursor L-cysteine with (11)CH(3)I and purification on commercial C18 cartridges. In vitro competitive inhibition experiments were performed with Hepa1-6 hepatoma cell lines, and biodistribution of (11)C-MCYS was determined in normal mice. The incorporation of (11)C-MCYS into tissue proteins was investigated. In vivo (11)C-MCYS uptake studies were performed on hepatocellular carcinoma-bearing nude mice and inflammation models and compared with (11)C-MET PET and (18)F-FDG PET. In a human PET study, a patient with a recurrence of glioma after surgery was examined with (11)C-MCYS PET and (18)F-FDG PET.
  
  
  RESULTS
  The uncorrected radiochemical yield of (11)C-MCYS from (11)CH(3)I was more than 50% with a synthesis time of 2 min, the radiochemical purity of (11)C-MCYS was more than 99%, and the enantiomeric purity was more than 90%. In vitro studies showed that (11)C-MCYS transport was mediated through transport system L. Biodistribution studies demonstrated high uptake of (11)C-MCYS in the liver, stomach wall, and heart and low uptake of (11)C-MCYS in the brain. There was higher accumulation of (11)C-MCYS in the tumor than in the muscles. The tumor-to-muscle and inflammatory lesion-to-muscle ratios were 7.27 and 1.62, respectively, for (11)C-MCYS, 5.08 and 3.88, respectively, for (18)F-FDG, and 4.26 and 2.28, respectively, for (11)C-MET at 60 min after injection. Almost no (11)C-MCYS was incorporated into proteins. For the patient PET study, high uptake of (11)C-MCYS with true-positive results, but low uptake of (18)F-FDG with false-negative results, was found in the recurrent glioma.
  
  
  CONCLUSIONS
  Automated synthesis of (11)C-MCYS is easy to perform. (11)C-MCYS is superior to (11)C-MET and (18)F-FDG in the differentiation of tumor from inflammation and seems to have potential as an oncologic PET tracer for the diagnosis of solid tumors.
authors.affiliation: PET-CT Center, Department of Nuclear Medicine, First Affiliated Hospital, Sun Yat-Sen University, Guangzhou, China.
authors.forename: Huaifu
authors.initials: H
authors.lastname: Deng
authors.forename: Xiaolan
authors.initials: X
authors.lastname: Tang
authors.forename: Hongliang
authors.initials: H
authors.lastname: Wang
authors.forename: Ganghua
authors.initials: G
authors.lastname: Tang
authors.forename: Fuhua
authors.initials: F
authors.lastname: Wen
authors.forename: Xinchong
authors.initials: X
authors.lastname: Shi
authors.forename: Chang
authors.initials: C
authors.lastname: Yi
authors.forename: Kening
authors.initials: K
authors.lastname: Wu
authors.forename: Quanfei
authors.initials: Q
authors.lastname: Meng
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D045744:Cell Line, Tumor; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000493:pharmacokinetics; D005260:Female; D007553:Isotope Labeling; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009369:Neoplasms / Q000000981:diagnostic imaging*; D049268:Positron-Emission Tomography; D011506:Proteins / Q000378:metabolism; D011786:Quality Control; D011849:Radioactive Tracers; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D014018:Tissue Distribution; D051598:Whole Body Imaging
chemical_list: D011506:Proteins; D011849:Radioactive Tracers; D019275:Radiopharmaceuticals; C008425:S-methylcysteine; D003545:Cysteine