In vivo assessment and dosimetry of 2 novel PDE10A PET radiotracers in humans

Subtitle:$^{18}F$-MNI-659 and $^{18}F$-MNI-654

Phosphodiesterase (PDE) 10A is an enzyme involved in the regulation of cyclic adenosine monophosphate and cyclic guanosine monophosphate and is highly expressed in medium-sized spiny neurons of the striatum, making it an attractive target for novel therapies for a variety of neurologic and psychiatric disorders that involve striatal function. Potential ligands for PET imaging of PDE10A have been reported. Here, we report the first-in-human characterization of 2 new PDE10A radioligands, 2-(2-(3-(1-(2-fluoroethyl)-1H-indazol-6-yl)-7-methyl-4-oxo-3,4-dihydroquinazolin-2-yl)ethyl)-4-isopropoxyisoindoline-1,3-dione (18F-MNI-654) and 2-(2-(3-(4-(2-fluoroethoxy)phenyl)-7-methyl-4-oxo-3,4-dihydroquinazolin-2-yl)ethyl)-4-isopropoxyisoindoline-1,3-dione (18F-MNI-659), with the goal of selecting the best one for use in future studies interrogating pathophysiologic changes in neuropsychiatric disorders and aiding pharmaceutical development targeting PDE10A. Methods: Eleven healthy volunteers participated in this study (18F-MNI-654 testretest, 2 men; 18F-MNI-659 testretest, 4 men and 1 woman; 18F-MNI-659 dosimetry, 2 men and 2 women). Brain PET images were acquired over 5.5 h for 18F-MNI-654 and over 3.5 h for 18F-MNI-659, and pharmacokinetic modeling with plasma- and reference-region (cerebellar cortex)-based methods was performed. Whole-body PET images were acquired over 6 h for 18F-MNI-659 and radiation dosimetry estimated with OLINDA. Results: Both radiotracers were similarly metabolized, with about 20% of intact parent remaining at 120 min after injection. PET timeactivity data demonstrated that 18F-MNI-654 kinetics were much slower than 18F-MNI-659 kinetics. For 18F-MNI-659, there was good agreement between the Logan and simplified reference tissue models for nondisplaceable binding potential (BPND), supporting noninvasive quantification, with testretest variability less than 10% and intraclass correlation greater than 0.9. The 18F-MNI-659 effective dose was estimated at 0.024 mSv/MBq. Conclusion: PET imaging in the human brain with 2 novel PDE10A 18F tracers is being reported. Noninvasive quantification of 18F-MNI-659 with the simplified reference tissue model using the cerebellum as a reference is possible. In addition, 18F-MNI-659 kinetics are fast enough for a good estimate of BPND with 90 min of data, with values around 3.0 in the basal ganglia. Finally, 18F-MNI-659 dosimetry is favorable and consistent with values reported for other PET radiotracers currently used in humans.

Publication year:2014

Keywords:A1 Journal article

Accessibility:Closed