In vitro phosphodiesterase 10A (PDE10A) binding in whole hemisphere human brain using the PET radioligand [18F]MNI-659.

Highly specific and sensitive biomarkers for pathologies related to dysfunctions in the basal ganglia circuit are of great value to assess therapeutic efficacy not only clinically to establish an early diagnosis, but also in terms of monitoring the efficacy of therapeutic interventions and decelerated neurodegeneration. The phosphodiesterase 10A (PDE10A) enzyme plays a central role in striatal signaling and is implicated in several neuropsychiatric disorders involving striatal pathology, such as Huntingtońs disease (HD) and schizophrenia. Inhibition of PDE10A activates the neurons in the striatum and consequently leads to alteration of behavioral aspects modulated by the striatal circuit. [18F]MNI-659, (2-(2-(3-(4-(2-[18F]fluoroethoxy)phenyl)-7-methyl-4-oxo-3,4-dihydroquinazolin-2-yl)ethyl)-4-isopropoxyisoindoline-1,3-dione), is a newly developed PET radioligand that shows a high binding to PDE10A in the human brain in vivo. In the present study, we examined the in vitro binding of [18F]MNI-659 in human postmortem brain to gain a better understanding of the presence, density, disease-related alterations and therapy related to changes in PDE10A expression. The results show high specific binding of [18F]MNI-659 in the caudate nucleus, putamen and the hippocampal formation. Low specific [18F]MNI-659 binding was detected in nucleus accumbens in comparison to the caudate nucleus and putamen. In vitro binding studies with [18F]MNI-659 will facilitate in elucidating better understanding of the role of PDE10A activity in health and disease that may lead to new diagnostic opportunities in HD.