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Krzyczmonik A, Grafinger KE, Keller T, Pfeifer L, Forsback S, Haaparanta-Solin M, Gouverneur V, López-Picón F, Solin O. Evaluation of [ 18F]FMTEB in Sprague Dawley rats as a PET tracer for metabotropic glutamate receptor 5. Nucl Med Biol 2023; 116-117:108309. [PMID: 36521341 DOI: 10.1016/j.nucmedbio.2022.108309] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2022] [Revised: 10/31/2022] [Accepted: 11/17/2022] [Indexed: 11/27/2022]
Abstract
INTRODUCTION [18F]FMTEB, along with other tracers, was developed as a promising PET radioligand for imaging metabotropic glutamate receptor subtype 5 (mGluR5). Despite favorable preliminary results, it has not been used further for studies of mGluR5. This paper presents an in-depth preclinical evaluation of [18F]FMTEB in healthy Sprague Dawley rats. METHODS [18F]FMTEB was synthesized from a boronic ester precursor using copper-mediated fluorination. In vivo PET imaging was performed on six rats, of which three were pre-treated with a high affinity mGluR5 receptor antagonist. An additional 18 rats were used for ex vivo experiments for metabolite analyses in plasma, brain and urine, and for biodistribution and ex vivo brain autoradiography at different time points. RESULTS [18F]FMTEB was synthesized in adequate radiochemical yield and a molar activity of 154 ± 64 GBq/μmol. Both in vivo imaging and ex vivo brain autoradiography showed high specificity for mGluR5, and the blocking experiments showed a clear decrease in radioactivity in mGluR5-rich brain areas. Metabolite analyses confirmed fast metabolism of the tracer in plasma. The percentage of parent compound in brain tissue exceeded 90 % up to 90 min after injection. CONCLUSION [18F]FMTEB produced via copper-mediated 18F-fluorination fulfilled the requirements for preclinical evaluation in rats. The absence of specific uptake in cerebellum and absence of defluorination of the tracer allowed cerebellum to be used as a reference tissue. Due to the fast kinetics in rats, the region-to-cerebellum ratios equilibrated within 30 min. These results prove [18F]FMTEB to be a good candidate for mapping mGluR5 in rat brain and a suitable alternative to [18F]FPEB.
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Affiliation(s)
- Anna Krzyczmonik
- Turku PET Centre, Radiopharmaceutical Chemistry Laboratory, University of Turku, Turku, Finland
| | - Katharina E Grafinger
- Turku PET Centre, Preclinical Imaging, University of Turku, Turku, Finland; MediCity Research Laboratory, University of Turku, Turku, Finland
| | - Thomas Keller
- Turku PET Centre, Radiopharmaceutical Chemistry Laboratory, University of Turku, Turku, Finland
| | - Lukas Pfeifer
- University of Oxford, Chemistry Research Laboratory, Oxford, United Kingdom
| | - Sarita Forsback
- Turku PET Centre, Radiopharmaceutical Chemistry Laboratory, University of Turku, Turku, Finland; Department of Chemistry, University of Turku, Turku, Finland
| | - Merja Haaparanta-Solin
- Turku PET Centre, Preclinical Imaging, University of Turku, Turku, Finland; MediCity Research Laboratory, University of Turku, Turku, Finland
| | | | - Francisco López-Picón
- Turku PET Centre, Preclinical Imaging, University of Turku, Turku, Finland; MediCity Research Laboratory, University of Turku, Turku, Finland
| | - Olof Solin
- Turku PET Centre, Radiopharmaceutical Chemistry Laboratory, University of Turku, Turku, Finland; Department of Chemistry, University of Turku, Turku, Finland; Turku PET Centre, Accelerator Laboratory, Åbo Akademi University, Turku, Finland.
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