Introduction: Vesicular monoamine transporters 2 (VMAT2) in the brain serve as transporter for packaging monoamine in vesicles for normal CNS neurotransmission. Several VMAT2 imaging agents, [11C]-(+)-DTBZ, dihydrotetrabenazine and [18F]FP-(+)-DTBZ (9-O-fluoropropyl-(+)-dihydro tetrabenazine, a.k.a. [18F]AV-133), are useful for studying the changes in brain function related to monoamine transmission by in vivo imaging. Deuterated analogs have been reported targeting VMAT2 binding sites.
Methods: A novel deuterated [18F]9-O-hexaduterofluoropropyl-(+)-dihydrotetrabenazine, [18F]D6-FP-(+)-DTBZ, [18F]1, was prepared as a VMAT2 imaging agent. This 18F agent which targeted VMAT2 was evaluated by in vitro binding, in vivo biodistribution and microPET imaging studies in rodents.
Results: The one step radiolabeling reaction led to the desired [18F]D6-FP-(+)-DTBZ, [18F]1, which showed excellent binding affinity to VMAT2 (Ki=0.32±0.07nM) comparable to that of FP-(+)-DTBZ (Ki=0.33±0.02nM) using [18F]FP-(+)-DTBZ and rat striatum membrane homogenates. In vivo biodistribution in normal rats showed that 1, exhibited excellent brain uptake and comparable high ratio of striatum to cerebellum (target/background) ratio at 1h after injection (ratio of 6.05±0.43 vs 5.66±0.72 for [18F]FP-(+)-DTBZ vs [18F]1, respectively). MicroPET imaging studies in rats further confirm that the striatum with high VMAT2 concentration was clearly delineated in normal rat brain after iv injection of [18F]1. We observed minor changes of metabolism in rat plasma between these two agents; however, the changes showed little effect on regional brain uptake and retention.
Conclusions: The results reported here lend support for using [18F]D6-FP-(+)-DTBZ, [18F]1, as in vivo PET imaging agent for VMAT2 binding in the brain.
Keywords: (18)F; Brain; Deuterium; In vivo metabolism; Monoamine transporter; PET imaging agent.
Copyright © 2017. Published by Elsevier Inc.