The synthesis and preclinical evaluation in rhesus monkey of [¹⁸F]MK-6577 and [¹¹C]CMPyPB glycine transporter 1 positron emission tomography radiotracers.

Terence G Hamill, Waisi Eng, Andrew Jennings, Richard Lewis, Steven Thomas, Suzanne Wood, Leslie Street, David Wisnoski, Scott Wolkenberg, Craig Lindsley, Sandra M Sanabria-Bohórquez, Shil Patel, Kerry Riffel, Christine Ryan, Jacquelynn Cook, Cyrille Sur, H Donald Burns, Richard Hargreaves

Index: Synapse 65(4) , 261-70, (2011)

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Abstract

Two positron emission tomography radiotracers for the glycine transporter 1 (GlyT1) are reported here. Each radiotracer is a propylsulfonamide-containing benzamide and was labeled with either carbon-11 or fluorine-18. [¹¹C]CMPyPB was synthesized by the alkylation of a 3-hydroxypyridine precursor using [¹¹C]MeI, and [¹⁸F]MK-6577 was synthesized by a nucleophilic aromatic substitution reaction using a 2-chloropyridine precursor. Each tracer shows good uptake into rhesus monkey brain with the expected distribution of highest uptake in the pons, thalamus, and cerebellum and lower uptake in the striatum and gray matter of the frontal cortex. In vivo blockade and chase studies of [¹⁸F]MK-6577 showed a large specific signal and reversible binding. In vitro autoradiographic studies with [¹⁸F]MK-6577 showed a large specific signal in both rhesus monkey and human brain slices and a distribution consistent with the in vivo results and those reported in the literature. In vivo metabolism studies in rhesus monkeys demonstrated that only more-polar metabolites are formed for each tracer. Of these two tracers, [¹⁸F]MK-6577 was more extensively characterized and is a promising clinical positron emission tomography tracer for imaging GlyT1 and for measuring GlyT1 occupancy of therapeutic compounds.Copyright © 2010 Wiley-Liss, Inc.