[11C]YM-202074 was synthesized by N-[11C]methylation of its desmethyl precursor with [11C]methyl iodide. The in vitro and in vivo brain regional distributions were determined in rats using autoradiography and PET, respectively.
[11C]YM-202074 (262–630 MBq, n=5) was obtained with radiochemical purity of >98 % and specific activity of 27–52 GBq/μmol at the end of synthesis, starting from [11C]CO2 of 19.3–21.5 GBq. In vitro autoradiographic results showed that the high specific binding of [11C]YM-202074 for mGluR1 was presented in the cerebellum, thalamus and hippocampus, which are known as mGluR1-rich regions. In ex vivo autoradiography and PET studies, the radioligand was specifically distributed in the cerebellum, although the uptake was low. Furthermore, the regional distribution was fairly uniform in the whole brain by pretreatment with JNJ16259685 (a mGluR1 antagonist). However, radiometabolite(s) was detected in the brain.
From these results, especially considering the low brain uptake and the influx of radiometabolite(s) into brain, [11C]YM-202074 may not be a useful PET ligand for in vivo imaging of mGluR1 in the brain.
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