Synthesis of 11C-labelled (R)-OHDMI and CFMME and their evaluation as candidate radioligands for imaging central norepinephrine transporters with PET.
(R)-1-(10,11-Dihydro-dibenzo[b,f]azepin-5-yl)-3-methylamino-propan-2-ol ((R)-OHDMI) and (S,S)-1-cyclopentyl-2-(5-fluoro-2-methoxy-phenyl)-1-morpholin-2-yl-ethanol (CFMME) were synthesized and found to be potent inhibitors of norepinephrine reuptake. Each was labelled efficiently in its methyl group with carbon-11 (t(1/2)=20.4 min) as a prospective radioligand for imaging brain norepinephrine transporters (NET) with positron emission tomography (PET). The uptake and distribution of radioactivity in brain following intravenous injection of each radioligand into cynomolgus monkey was examined in vivo with PET. After injection of (R)-[(11)C]OHDMI, the maximal whole brain uptake of radioactivity was very low (1.1% of injected dose; I.D.). For occipital cortex, thalamus, lower brainstem, mesencephalon and cerebellum, radioactivity ratios to striatum at 93 min after radioligand injection were 1.35, 1.35, 1.2, 1.2 and 1.0, respectively. After injection of [(11)C]CFMME, radioactivity readily entered brain (3.5% I.D.). Ratios of radioactivity to cerebellum at 93 min for thalamus, occipital cortex, region of locus coeruleus, mesencephalon and striatum were 1.35, 1.3, 1.3, 1.2 and 1.2, respectively. Radioactive metabolites in plasma were measured by radio-HPLC. (R)-[(11)C]OHDMI represented 75% of plasma radioactivity at 4 min after injection and 6% at 30 min. After injection of [(11)C]CFMME, 84% of the radioactivity in plasma represented parent at 4 min and 20% at 30 min. Since the two new hydroxylated radioligands provide only modest regional differentiation in brain uptake and form potentially troublesome lipophilic radioactive metabolites, they are concluded to be inferior to existing radioligands, such as (S,S)-[(11)C]MeNER, (S,S)-[(18)F]FMeNER-D(2) and (S,S)-[(18)F]FRB-D(4), for the study of brain NETs with PET in vivo.
Schou
Magnus
M
Karolinska Institutet, Department of Clinical Neuroscience, Psychiatry Section, Karolinska Hospital, S-17176 Stockholm, Sweden. magnus.schou@ki.se
Pike
Victor W
VW
Sóvágó
Judit
J
Gulyás
Balázs
B
Gallagher
Peter T
PT
Dobson
David R
DR
Walter
Magnus W
MW
Rudyk
Helene
H
Farde
Lars
L
Halldin
Christer
C
D000818:Animals; D001381:Azepines / Q000138:chemical synthesis*; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism; D002250:Carbon Radioisotopes; D002851:Chromatography, High Pressure Liquid; D000431:Ethanol / Q000031:analogs & derivatives* / Q000138:chemical synthesis; D007202:Indicators and Reagents; D008252:Macaca fascicularis; D009025:Morpholines / Q000138:chemical synthesis*; D017072:Neostriatum / Q000000981:diagnostic imaging / Q000378:metabolism; D050484:Norepinephrine Plasma Membrane Transport Proteins / Q000378:metabolism*; D049268:Positron-Emission Tomography; D020005:Propanols / Q000138:chemical synthesis*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis*; D013788:Thalamus / Q000000981:diagnostic imaging / Q000378:metabolism
C517755:1-(10,11-dihydro-dibenzo(b,f)azepin-5-yl)-3-methylamino-propan-2-ol; C517756:1-cyclopentyl-2-(5-fluoro-2-methoxy-phenyl)-1-morpholin-2-yl-ethanol; D001381:Azepines; D002250:Carbon Radioisotopes; D007202:Indicators and Reagents; D009025:Morpholines; D050484:Norepinephrine Plasma Membrane Transport Proteins; D020005:Propanols; D019275:Radiopharmaceuticals; D000431:Ethanol