He_2021_Nucl.Med.Biol_96-97_S36

Objectives: Monoacylglycerol lipase (MAGL) is the key enzyme for degradation of the most abundant brain endocannabinoid, 2-ara-chidonoylglycerol (2-AG). It is considered as an attractive drug target for oncological and psychiatric diseases [1]. During the last decade, several irreversible MAGL PET ligands have been disclosed, however, reversible MAGL radiotracers with sufficient brain penetration are barely reported. To the best of our knowledge, [18F]T-401 is the only available reversible MAGL tracer with moderate brain uptake in mice. In this study, we synthesized a series of reversible MAGL inhibitors based on the piperazinyl pyrrolidin-2-one core structure [2,3]. The most potent compounds were radiolabeled with either C-11 or F-18. Their utilities as PET imaging agents were evaluated. Methods: Novel series of piperazinyl pyrrolidin-2-one derivatives were designed and prepared via multi-step synthetic approaches. Their IC 50 values towards MAGL were determined by tracing the hydrolysis of natural substrate 2-AG. The most potent ligands YH132 and YH135 were labeled with C-11, and YH149 was labeled with F-18. In vitro autoradiography and PET imaging were performed in MAGL knockout and wild-type mice to evaluate their in vitro and in vivo specificity. [18F]YH149 was further evaluated in ex vivo biodistribution and drug-occupancy studies to assess its utility for imaging MAGL in the rodent brain. Results: IC50 values of the novel MAGL inhibitors ranged from 3 nM to 10.7 M. YH132 (IC50 = 6 nM),YH135 (IC50 = 18 nM), andYH149 (IC50 = 12 nM) that possess IC 50 values in a nano-molar range for human MAGL were further evaluated as radioligands. Both [11C]YH132 and [11C]YH135 showed high accumulation in MAGL-rich brain regions in in vitro autoradiographic studies. In PET studies using MAGL knock-out and wild-type mice, [11C]YH132 revealed higher brain permeability and specificity than [11C]YH135. Therefore, [18F]YH149, the F-18 labeled analog of YH132, was synthesized via copper-mediated fluorination. [18F]YH149 demonstrated excellent in vitro and in vivo specificity towards MAGL. The averaged PET image (12.5-52.5 min p.i.) was in high accordance with MAGL expression pattern in the mouse brain. In ex vivo biodistribution in mice, [18F]YH149 exhibited significantly higher brain uptake than the benchmark radiotracer [18F]T-401 at 30 min post-injection [2]. Blocking effects were observed in the brain and MAGL-expressive peripheral organs using PF-06795071, an irreversible MAGL inhibitor. Furthermore, the drug occupancy study indicated that [18F]YH149 can be used to determine the D50 value of PF-06795071 in the mouse brain. Conclusions: The fluorinated PET probe, [18F]YH149, revealed high in vitro/in vivo specificity towards MAGL and increased brain permeability compared to the previously reported reversible MAGL PET radiotracers. Preliminary results indicate that [18F]YH149 is a very promising PET tracer for imaging MAGL and capable to evaluate target occupancy in vivo