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

S-[C-11]-methyl-L-cysteine ([C-11]MCYS) has been claimed to offer higher tumor selectivity than L-[methyl- C-11]methionine ([C-11]MET). We examined this claim in animal models. Rats with implanted untreated (n = 10) or irradiated (n = 7, 1 x 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. Uptake of the two tracers in untreated gliomas was similar. [C-11]MCYS was not accumulated in salivary glands, nasal epithelium, and healing wounds, in contrast to [C-11]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. [C-11]MCYS indicated higher lesion volumes than [C-11]MET (untreated tumor + 47 %; irradiated tumor up to + 500 %; LPS-inflamed striatum + 240 %). [C-11]MCYS was less accumulated in some non-tumor tissues than [C-11]MET, but showed lower tumor-to-brain contrast.