Development of [11C]MFTC for PET Imaging of Fatty Acid Amide Hydrolase in Rat and Monkey Brains

We developed 2-methylpyridin-3-yl-4-(5-(2-fluorophenyl)-4H-1,2,4-triazol-3-yl)piperidine-1-[((11))C]carboxylate ([((11))C]MFTC) as a promising PET tracer for in vivo imaging of fatty acid amide hydrolase (FAAH) in rat and monkey brains. [((11))C]MFTC was synthesized by reacting 3-hydroxy-2-methylpyridine (2) with [((11))C]phosgene ([((11))C]COCl2), followed by reacting with 4-(5-(2-fluorophenyl)-4H-1,2,4-triazol-3-yl)piperidine (3), with a 20 +/- 4.6% radiochemical yield (decay-corrected, n = 30) based on [((11))C]CO2 and 40 min synthesis time from the end of bombardment. A biodistribution study in mice showed high uptake of radioactivity in FAAH-rich organs, including the lung, liver, and kidneys. Positron emission tomography (PET) summation images of rat brains showed high radioactivity in the frontal cortex, cerebellum, and hippocampus, which was consistent with the regional distribution pattern of FAAH in rodent brain. Pretreatment with MFTC or FAAH-selective URB597 significantly reduced the uptake in the brain. PET imaging of monkey brain showed relatively high uptake in the whole brain, particularly in the occipital cortex, which was also inhibited by treatment with MFTC or URB597. More than 96% of the total radioactivity was irreversible in the brain homogenate of rats 5 min after the radiotracer injection. The specific in vivo FAAH binding indicates that [((11))C]MFTC is a promising PET tracer for visualizing FAAH in the brain.