Synthesis and Evaluation of Fluorinated Aporphines: Potential Positron Emission Tomography Ligands for D2 Receptors
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ABSTRACT:
SUBMITTER: Sromek AW
PROVIDER: S-EPMC3110009 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Alterations in dopamine D(2)/D(3) receptor binding have been reported in schizophrenia, and a meta-analysis of imaging studies has shown a modest elevation in striatum. Newer radioligands now allow the assessment of these receptors in extrastriatal regions. We used positron emission tomography with [(18)F]fallypride to evaluate D(2)/D(3) receptors in both striatal and extrastriatal regions in schizophrenia.Twenty-one patients with schizophrenia and 22 matched healthy control subjects were scanned with an ECAT EXACT HR+ camera. Two-tissue compartment modeling and the reference tissue method gave binding potentials relative to nondisplaceable uptake, total plasma concentration, and free plasma concentration. These were compared between groups in five striatal and eight extrastriatal regions. Several regional volumes were lower in the patient group, and positron emission tomography data were corrected for partial volume effects.Binding potential values differed in three regions between groups. Values for binding potential relative to nondisplaceable uptake from two-tissue compartment modeling in patients and control subjects, respectively, were 28.7 ± 6.8 and 25.3 ± 4.3 in postcommissural caudate, 2.9 ± .7 and 2.6 ± .4 in thalamus, and 1.8 ± .5 and 2.1 ± .7 in uncus. Loss of D(2)/D(3) receptors with age was found in striatal and extrastriatal regions and was greater in neocortex.Our study found selective alterations in D(2)/D(3) receptors in striatal and extrastriatal regions, consistent with some but not all previously published reports. As previously shown for the striatum, a more sensitive imaging approach for studying the role of dopamine in the pathophysiology of schizophrenia might be assessment of neurotransmitter levels rather than D(2)/D(3) receptor levels in extrastriatal regions.
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Project description:Positron emission tomography (PET) coupled to an effective radioligand could provide an important tool for understanding possible links between neuropsychiatric disorders and brain NOP (nociceptin/orphanin FQ peptide) receptors. We sought to develop such a PET radioligand. High-affinity NOP ligands were synthesized based on a 3-(2'-fluoro-4',5'-dihydrospiro[piperidine-4,7'-thieno[2,3-c]pyran]-1-yl)-2(2-halobenzyl)-N-alkylpropanamide scaffold and from experimental screens in rats, with ex vivo LC-MS/MS measures, three ligands were identified for labeling with carbon-11 and evaluation with PET in monkey. Each ligand was labeled by (11)C-methylation of an N-desmethyl precursor and studied in monkey under baseline and NOP receptor-preblock conditions. The three radioligands, [(11)C](S)-10a-c, gave similar results. Baseline scans showed high entry of radioactivity into the brain to give a distribution reflecting that expected for NOP receptors. Preblock experiments showed high early peak levels of brain radioactivity, which rapidly declined to a much lower level than seen in baseline scans, thereby indicating a high level of receptor-specific binding in baseline experiments. Overall, [(11)C](S)-10c showed the most favorable receptor-specific signal and kinetics and is now selected for evaluation in human subjects.
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2011-11-01 | E-GEOD-21217 | biostudies-arrayexpress