title: A new 18F-labeled fluoroacetylmorpholino derivative of vesamicol for neuroimaging of the vesicular acetylcholine transporter.
abstract: With the aim of producing selective radiotracers for in vivo imaging of the vesicular acetylcholine transporter (VAChT) using positron mission tomography (PET), here, we report synthesis and analysis of a new class of conformationally constrained vesamicol analogues with moderate lipophilicity. The sequential ring opening on trans-1,4-cyclohexadiene dioxide enabled an approach to synthesize 6-arylpiperidino-octahydrobenzo[1,4]oxazine-7-ols [morpholino vesamicols]. The radiosynthesis of the [18F]fluoroacetyl-substituted derivative ([18F]FAMV) was achieved starting from a corresponding bromo precursor [2-Bromo-1-[7-hydroxy-6-(4-phenyl-piperidin-1-yl)-octahydro-benzo[1,4]oxazin-4-yl]-ethanone] and using a modified commercial computer-controlled module system with a radiochemical yield of 27+/-4%, a high radiochemical purity (99%) and a specific activity of 35 GBq/micromol. In competitive binding assays using a PC12 cell line overexpressing VAChT and [3H]-(-) vesamicol, 2-fluoro-1-[7-hydroxy-6-(4-phenyl-piperidin-1-yl)-octahydro-benzo[1,4]oxazin-4-yl]-ethanone (FAMV) demonstrated a high selectivity for binding to VAChT (K(i): 39.9+/-5.9 nM) when compared to its binding to sigma 1/2 receptors (Ki>1500 nM). The compound showed a moderate lipophilicity (logD (pH 7)=1.9) and a plasma protein binding of 49%. The brain uptake of [18F]FAMV was about 0.1% injected dose per gram at 5 min after injection and decreased continuously with time. Notably, an increasing accumulation of radioactivity in the lateral brain ventricles was observed. After 1 h, the accumulation of [18F]FAMV, expressed as ratio to the cerebellum, was 4.5 for the striatum, 2.0 for the cortical and 1.5 for the hippocampal regions, measured on brain slices using ex vivo autoradiography. At the present time, 75% of [18F]FAMV in the plasma was shown to be metabolized to various hydrophilic compounds, as detected by high-performance liquid chromatography. The degradation of [18F]FAMV was also detected in brain extracts as early as 15 min post injection (p.i.) and increased to 50% at 1 h postinjection. In conclusion, although the chemical properties of [18F]FAMV and the selectivity of binding to VAChT appear to be promising indicators of a useful PET tracer for imaging VAChT, a low brain extraction, in combination with only moderate specific accumulation in cholinergic brain regions and an insufficient in vivo stability prevents the application of this compound for neuroimaging in humans.
authors.affiliation: Department of Nuclear Medicine, University of Leipzig, 04103 Leipzig, Germany. sord@medizin.uni-leipzig.de
authors.forename: Dietlind
authors.initials: D
authors.lastname: Sorger
authors.forename: Matthias
authors.initials: M
authors.lastname: Scheunemann
authors.forename: Udo
authors.initials: U
authors.lastname: Grossmann
authors.forename: Steffen
authors.initials: S
authors.lastname: Fischer
authors.forename: Johnny
authors.initials: J
authors.lastname: Vercouille
authors.forename: Achim
authors.initials: A
authors.lastname: Hiller
authors.forename: Barbara
authors.initials: B
authors.lastname: Wenzel
authors.forename: Ali
authors.initials: A
authors.lastname: Roghani
authors.forename: Reinhard
authors.initials: R
authors.lastname: Schliebs
authors.forename: Peter
authors.initials: P
authors.lastname: Brust
authors.forename: Osama
authors.initials: O
authors.lastname: Sabri
authors.forename: Jörg
authors.initials: J
authors.lastname: Steinbach
mesh_terms: D000818:Animals; D001345:Autoradiography; D001667:Binding, Competitive; D001921:Brain / Q000000981:diagnostic imaging*; D005260:Female; D005462:Fluorine Radioisotopes / Q000493:pharmacokinetics*; D007553:Isotope Labeling / Q000379:methods; D008657:Metabolic Clearance Rate; D009025:Morpholines / Q000737:chemistry* / Q000493:pharmacokinetics; D016716:PC12 Cells; D010880:Piperidines / Q000737:chemistry* / Q000493:pharmacokinetics*; D049268:Positron-Emission Tomography; D011485:Protein Binding; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D017480:Receptors, sigma / Q000037:antagonists & inhibitors; D050494:Vesicular Acetylcholine Transport Proteins / Q000037:antagonists & inhibitors*; D000097605:Sigma-1 Receptor
chemical_list: D005462:Fluorine Radioisotopes; D009025:Morpholines; D010880:Piperidines; D019275:Radiopharmaceuticals; D017480:Receptors, sigma; D050494:Vesicular Acetylcholine Transport Proteins; D000097605:Sigma-1 Receptor; C106107:sigma-2 receptor; C006189:vesamicol