PET Imaging with S-[(11)C]Methyl-L-Cysteine and L-[Methyl-(11)C]Methionine in Rat Models of Glioma, Glioma Radiotherapy, and Neuroinflammation.

PURPOSE: S-[(11)C]-methyl-L-cysteine ([(11)C]MCYS) has been claimed to offer higher tumor selectivity than L-[methyl- (11)C]methionine ([(11)C]MET). We examined this claim in animal models. PROCEDURES: Rats with implanted untreated (n = 10) or irradiated (n = 7, 1 × 25 Gy, on day 8) orthotopic gliomas were scanned after 6, 9, and 12 days, using positron emission tomography. Rats with striatal injections of saline (n = 9) or bacterial lipopolysaccharide (n = 9) were scanned after 3 days. RESULTS: Uptake of the two tracers in untreated gliomas was similar. [(11)C]MCYS was not accumulated in salivary glands, nasal epithelium, and healing wounds, in contrast to [(11)C]MET, but showed 40 % higher accumulation in the healthy brain. Both tracers showed a reduced tumor uptake 4 days after irradiation and minor accumulation in inflamed striatum. [(11)C]MCYS indicated higher lesion volumes than [(11)C]MET (untreated tumor + 47 %; irradiated tumor up to + 500 %; LPS-inflamed striatum + 240 %). CONCLUSIONS: [(11)C]MCYS was less accumulated in some non-tumor tissues than [(11)C]MET, but showed lower tumor-to-brain contrast.