Classics in Neuroimaging: Radioligands for the Vesicular Monoamine Transporter 2.

Positron emission tomography (PET) studies of the monoamine neurotransmitter systems in the human brain employ a variety of radiotracers targeting the many receptors, transporters, and enzymes present in monoaminergic neurons. One of these is the vesicular monoamine transporter 2 (VMAT2), the protein responsible for the energy-dependent accumulation of monoamines into synaptic vesicles. The development of in vivo imaging radiotracers for VMAT2 is a story of starting with a well-characterized clinically used drug (tetrabenazine) which had a pharmacologically active metabolite: that metabolite that was in stepwise fashion refined and modified to provide both carbon-11 and fluorine-18 labeled VMAT2 radiotracers that are now used for human PET studies of neurodegenerative and psychiatric diseases. The design approach taken, which involved understanding the metabolism of the radiotracers and identification of the optimal ligand stereochemistry, are representative of important steps in the general concepts behind successful in vivo radiotracer design for brain imaging agents.