Target Occupancy Study and Whole-Body Dosimetry With a MAGL PET Ligand 11C-PF-06809247 in Non-Human Primates

Abstract

\n Purpose\n\nMonoacylglycerol lipase (MAGL) is a key serine hydrolase which terminates endocannabinoid signaling and regulates arachidonic acid driven inflammatory responses within the central nervous system (CNS). To develop 11C-PF-06809247 into a clinically usable positron emission tomography (PET) radioligand, we assessed the brain target occupancy of a MAGL inhibitor using non-human primate (NHP). Additionally, we measured the whole-body distribution of 11C-PF-06809247 in NHP and estimated human effective radiation doses.\nMethods\n\nSeven cynomolgus monkeys were enrolled for brain PET measurements. Two PET measurements were performed in each NHP: one baseline and one pretreatment condition with intravenous administration of PF-06818883, a selective MAGL inhibitor, (total of seven doses between 0.01–1.27 mg/kg). Kinetic parameters K1, k2 and k3 were estimated by an irreversible two tissue compartment (2TC) model using metabolite corrected plasma radioactivity as the input function. Ki by 2TC and Patlak analysis were calculated. The target occupancy was calculated using Ki at baseline and pretreatment conditions. Two cynomolgus monkeys were enrolled for whole-body PET measurements. Estimates of the absorbed radiation dose in humans were calculated with OLINDA/EXM 1.1 using the adult male reference model.\nResults\n\nRadioactivity was decreased in all brain regions following pretreatment with PF-06818883. Occupancy was measured as 25.4%-100.5% in a dose dependent manner. Whole-body PET showed high uptake values in the liver, small intestine, kidney, and brain. The effective dose was calculated as 4.3 µSv/MBq.\nConclusion\n\n 11C-PF-06809247 is a promising PET ligand for further MAGL studies in human brain.