Utilizing PET and MALDI Imaging for Discovery of a Targeted Probe for Brain Endocannabinoid α/ß-Hydrolase Domain 6 (ABHD6).

Multimodal imaging provides rich biological information, which can be exploited to study drug activity, disease associated phenotypes, and pharmacological responses. Here we show discovery and validation of a new probe targeting the endocannabinoid α/ß-hydrolase domain 6 (ABHD6) enzyme by utilizing positron emission tomography (PET) and matrix-assisted laser desorption/ionization (MALDI) imaging. [18F]JZP-MA-11 as the first PET ligand for in vivo imaging of the ABHD6 is reported and specific uptake in ABHD6-rich peripheral tissues and major brain regions was demonstrated using PET. A proof-of-concept study in nonhuman primate confirmed brain uptake. In vivo pharmacological response upon ABHD6 inhibition was observed by MALDI imaging. These synergistic imaging efforts used to identify biological information cannot be obtained by a single imaging modality and hold promise for improving the understanding of ABHD6-mediated endocannabinoid metabolism in peripheral and central nervous system disorders.

Synthesis and evaluation of 6-[18F]fluoro-3-(pyridin-3-yl)-1H-indole as potential PET tracer for targeting tryptophane 2, 3-dioxygenase (TDO).

INTRODUCTION: The increase in expression of tryptophan 2, 3-dioxygenases (TDO) and indoleamine 2,3-dioxygenase (IDO) have been reported as potential tumor biomarkers. TDO and IDO are enzymes that catalyze the first and rate-limiting step of the kynurenine pathway. Positron emitting tomography (PET) tracers investigating the kynurenine pathway may allow for the detection of different disease pathologies in vivo including cancer. However, current PET tracers being developed for TDO and IDO have suffered from either multi-step low yielding syntheses or de-fluorination of the tracer in vivo. RESULTS: TDO inhibitors based on 6-fluoroindole with C3 substituents are a class of small molecules that have been shown to bind to TDO effectively, restore tryptophan concentration and decrease the production of immunosuppressive metabolites. The compound 6-fluoro-3-(pyridine-3-yl)-1H-indole has been reported to have high in vitro affinity for TDO. Herein we report the fully automated radiosynthesis of 6-[18F]fluoro-3-(pyridine-3-yl)-1H-indole [18F]4 using a copper-mediated nucleophilic 18F-fluorination resulting in a non-corrected yield of 5 to 6% of the tracer with a radiochemical purity of >99% after 4 h. Small animal dynamic PET/CT imaging of [18F]4 intravenously injected into normal C57BL/6 mice revealed rapid accumulation in heart and brain, reaching maximum occupancy in heart (10.9% ID/g) and brain (8.1% ID/g) at 1.75 min and 2.25 min, respectively. Furthermore, these in vivo studies revealed no de-fluorination of the tracer, as evidence by the absence of [18F]fluoride accumulation in bone. CONCLUSION: In vitro studies demonstrate that 4 has good affinity for hTDO and the radiolabeled analogue [18F]4 can be synthesized with suitable radiochemical yields. [18F]4 demonstrates good uptake in the brain and the radiolabeled compound shows no de-fluorination in vivo in C57BL/6 mice.

Efficient Distribution of a Novel Zirconium-89 Labeled Anti-cd20 Antibody Following Subcutaneous and Intravenous Administration in Control and Experimental Autoimmune Encephalomyelitis-Variant Mice.

Objective: To investigate the imaging and biodistribution of a novel zirconium-89 (89Zr)-labeled mouse anti-cd20 monoclonal antibody (mAb) in control and experimental autoimmune encephalomyelitis (EAE) mice following subcutaneous (s. c.) and intravenous (i.v.) administration. Background: Anti-cd20-mediated B-cell depletion using mAbs is a promising therapy for multiple sclerosis. Recombinant human myelin oligodendrocyte glycoprotein (rhMOG)-induced EAE involves B-cell-mediated inflammation and demyelination in mice. Design/Methods: C57BL/6J mice (n = 39) were EAE-induced using rhMOG. On Day 14 post EAE induction, 89Zr-labeled-anti-cd20 mAb was injected in control and EAE mice in the right lower flank (s.c.) or tail vein (i.v.). Positron emission tomography/computed tomography (PET/CT) imaging and gamma counting (ex vivo) were performed on Days 1, 3, and 7 to quantify tracer accumulation in the major organs, lymphatics, and central nervous system (CNS). A preliminary study was conducted in healthy mice to elucidate full and early kinetics of the tracer that were subsequently applied in the EAE and control mice study. Results:89Zr-labeled anti-cd20 mAb was effectively absorbed from s.c. and i.v. injection sites and distributed to all major organs in the EAE and control mice. There was a good correlation between in vivo PET/CT data and ex vivo quantification of biodistribution of the tracer. From gamma counting studies, initial tracer uptake within the lymphatic system was found to be higher in the draining lymph nodes (inguinal or subiliac and sciatic) following s.c. vs. i.v. administration; within the CNS a significantly higher tracer uptake was observed at 24 h in the cerebellum, cerebrum, and thoracic spinal cord (p < 0.05 for all) following s.c. vs. i.v. administration. Conclusions: The preclinical data suggest that initial tracer uptake was significantly higher in the draining lymph nodes (subiliac and sciatic) and parts of CNS (the cerebellum and cerebrum) when administered s.c. compared with i.v in EAE mice.