In vivo PET Imaging of [11C]CIMBI-5, a 5-HT2AR Agonist Radiotracer in Nonhuman Primates
DOI:
https://doi.org/10.18433/jpps30329Abstract
Purpose: 5-HT2AR exists in high and low affinity states. Agonist PET tracers measure binding to the active high affinity site and thus provide a functionally relevant measure of the receptor. Limited in vivo data have been reported so far for a comparison of agonist versus antagonist tracers for 5-HT2AR used as a proof of principle for measurement of high and low affinity states of this receptor. We compared the in vivo binding of [11C]CIMBI-5, a 5-HT2AR agonist, and of the antagonist [11C]M100907, in monkeys and baboons. Methods: [11C]CIMBI-5 and [11C]M100907 baseline PET scans were performed in anesthetized male baboons (n=2) and male vervet monkeys (n=2) with an ECAT EXACT HR+ and GE 64-slice PET/CT Discovery VCT scanners. Blocking studies were performed in vervet monkeys by pretreatment with MDL100907 (0.5 mg/kg, i.v.) 60 minutes prior to the scan. Regional distribution volumes and binding potentials were calculated for each ROI using the likelihood estimation in graphical analysis and Logan plot, with either plasma input function or reference region as input, and simplified reference tissue model approaches. Results: PET imaging of [11C]CIMBI-5 in baboons and monkeys showed the highest binding in 5-HT2AR-rich cortical regions, while the lowest binding was observed in cerebellum, consistent with the expected distribution of 5-HT2AR. Very low free fractions and rapid metabolism were observed for [11C]CIMBI-5 in baboon plasma. Binding potential values for [11C]CIMBI-5 were 25-33% lower than those for [11C]MDL100907 in the considered brain regions. Conclusion: The lower binding potential of [11C]CIMBI-5 in comparison to [11C]MDL100907 is likely due to the preferential binding of the former to the high affinity site in vivo in contrast to the antagonist, [11C]MDL100907, which binds to both high and low affinity sites.Downloads
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Philip H. Elsinga, PhD
Department of Nuclear Medicine and
Molecular Imaging, University Medical Center
Groningen, University of Groningen,
Groningen, The Netherlands
E-mail: p.h.elsinga@umcg.nl
Min-Jeong Kim, M.D., Ph.D. Molecular Imaging Branch,
National Institute of Mental Health
Center Drive, Bldg. 10, Rm B1D43 Bethesda, MD 20892-1026, USA
Tel: 301-451-8894
Fax: 301-480-3610
Email: min-jeong.kim@nih.gov
Dr. Jogesh Mukherji, PhD
Associate Professor, Department of Psychiatry & Human Behavior
Director of Radiopharmaceutical Development
Senior Chemist, Brain Imaging Center 162 Irvine Hall, University of California-Irvine, CA
E-mail: mukherjj@uci.edu
Neil Vasdev, Ph.D.
Director, Azrieli Centre for Neuro-Radiochemistry
Associate Director & Chief Radiochemist, Research Imaging Centre
Centre for Addiction and Mental Health
College St, Toronto, ON, M5T 1R8
Tel: 416-535-8501 ext. 30988; Email: neil.vasdev@utoronto.ca
Luc Zimmer
Université Claude Bernard Lyon 1, Lyon Neuroscience Research Center, INSERM, CNRS, 69500, Bron, France
CERMEP-Imaging Platform, 69677, Bron, France
Hospices Civils de Lyon, 69002, Lyon, France
zimmer@univ-lyon1.fr
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