Inhibiting glutamine metabolism has been proposed as a potential treatment strategy for improving non-alcoholic steatohepatitis (NASH). However, effective methods for assessing dynamic metabolic responses during interventions targeting glutaminolysis have not yet emerged. Here, we developed a positron emission tomography (PET) imaging platform using l-[5-¹¹C]glutamine ([¹¹C]Gln) and evaluated its efficacy in NASH mice undergoing metabolic therapy with bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide (BPTES), a glutaminase 1 (GLS1) inhibitor that intervenes in the first and rate-limiting step of glutaminolysis. PET imaging with [¹¹C]Gln effectively delineated the pharmacokinetics of l-glutamine, capturing its temporal-spatial pattern of action within the body. Furthermore, [¹¹C]Gln PET imaging revealed a significant increase in hepatic uptake in methionine and choline deficient (MCD)-fed NASH mice, whereas systemic therapeutic interventions with BPTES reduced the hepatic avidity of [¹¹C]Gln in MCD-fed mice. This reduction in [¹¹C]Gln uptake correlated with a decrease in GLS1 burden and improvements in liver damage, indicating the efficacy of BPTES in mitigating NASH-related metabolic abnormalities. These results suggest that [¹¹C]Gln PET imaging can serve as a noninvasive diagnostic platform for whole-body, real-time tracking of responses of glutaminolysis to GLS1 manipulation in NASH, and it may be a valuable tool for the clinical management of patients with NASH undergoing glutaminolysis-based metabolic therapy.

As a serine hydrolase, monoacylglycerol lipase (MAGL) is principally responsible for the metabolism of 2-arachidonoylglycerol (2-AG) in the central nervous system (CNS), leading to the formation of arachidonic acid (AA). Dysfunction of MAGL has been associated with multiple CNS disorders and symptoms, including neuroinflammation, cognitive impairment, epileptogenesis, nociception and neurodegenerative diseases. Inhibition of MAGL provides a promising therapeutic direction for the treatment of these conditions, and a MAGL positron emission tomography (PET) probe would greatly facilitate preclinical and clinical development of MAGL inhibitors. Herein, we design and synthesize a small library of fluoropyridyl-containing MAGL inhibitor candidates. Pharmacological evaluation of these candidates by activity-based protein profiling identified