Synthesis of ([C-11]carbonyl)raclopride and a comparison with ([C-11]methyl)raclopride in a monkey PET study
2015 (English)In: Nuclear Medicine and Biology, ISSN 0969-8051, E-ISSN 1872-9614, Vol. 42, no 11, 893-898 p.Article in journal (Refereed) Published
Introduction: The selective dopamine D-2 receptor antagonist raclopride is usually labeled with carbon-11 using [C-11]methyl iodide or [C-11]methyl triflate for use in the quantification of dopamine D-2 receptors in human brain. The aim of this work was to label raclopride at the carbonyl position using [C-11]carbon monoxide chemistry and to compare ([C-11]carbonyl)raclopride with ([C-11]methyl)raclopride in non-human primate (NHP) using PET with regard to quantitative outcome measurement, metabolism of the labeled tracers and protein binding. Methods: Palladium-mediated carbonylation using [C-11]carbon monoxide, 4,6-dichloro-2-iodo-3-methoxyphenol and (S)-(-)-2-aminomethyl-1-ethylpyrrolidine was applied in the synthesis of ([C-11]carbonyl)raclopride. The reaction was performed at atmospheric pressure using xantphos as supporting phosphine ligand and palladium (pi-cinnamyl) chloride dimer as the palladium source. ([C-11]Methyl)raclopride was prepared by a previously published method. In the PET study, two female cynomolgus monkeys were used under gas anesthesia of sevoflurane. A dynamic PET measurement was performed for 63 min with an HRRT PET camera after intravenous injection of ([C-11]carbonyl)raclopride and ([C-11]methyl)raclopride, respectively, during the same day. The order of injection of the two PET radioligands was changed between the two monkeys. The venous blood sample for measurement of protein binding was taken 3 min prior to the PET scan. Binding potential (BPND) of the putamen and caudate was calculated with SRTM using the cerebellum as a reference region. Results: The target compound ([C-11]carbonyl)raclopride was obtained with 50 +/- 5% decay corrected radiochemical yield and 95% radiochemical purity. The trapping efficiency (TE) of [C-11]carbon monoxide was 65 +/- 5% and the specific radioactivity of the final product was 34 +/- 1 GBq/mu mol after a 50 min of synthesis time. The radiochemical yield of ([C-11]methyl)raclopride was in the same range as published previously i.e. 50-60% and specific radioactivity of those two batches which were used in the present PET study were 192 GBq/mu mol and 638 GBq/mu mol respectively after a synthesis time of 32 min. In monkey PET studies, the percentage difference of BPND in putamen was <3% and that in caudate was <9% for the two radioligands. The plasma protein binding was 86.2 +/- 0.3% and 85.7 +/- 0.6% for ([C-11]carbonyl)raclopride and ([C-11]methyl)raclopride, respectively. The radiometabolite pattern was similar for both radioligands. Conclusion: Raclopride was C-11-labeled at the carbonyl position using a palladium-mediated [C-11]carbonylation reaction. A comparison between ([C-11]carbonyl)raclopride and ([C-11]merhyl)raclopride with regard to quantitative PET outcome measurements, metabolism of radioligands and protein binding in monkey was performed. The monkey PET study with ([C-11]carbonyl)raclopride showed similar results as for ([C-11]methyl)raclopride. The PET studies were performed on 2 subjects.
Place, publisher, year, edition, pages
2015. Vol. 42, no 11, 893-898 p.
([C-11]carbonyl)raclopride, (CO)-C-11, [C-11]aminocarbonylation, NHP, PET, radiometabolites
Radiology, Nuclear Medicine and Medical Imaging
IdentifiersURN: urn:nbn:se:uu:diva-266691DOI: 10.1016/j.nucmedbio.2015.07.003ISI: 000363073000012PubMedID: 26272268OAI: oai:DiVA.org:uu-266691DiVA: diva2:868912