Abstract
Purpose
TRPC5 belongs to the mammalian superfamily of transient receptor potential (TRP) Ca2+-permeable cationic channels and it has been implicated in various CNS disorders. As part of our ongoing interest in the development of a PET radiotracer for imaging TRPC5, herein, we explored the radiosynthesis, and in vitro and in vivo evaluation of a new C-11 radiotracer [11C]HC070 in rodents and nonhuman primates.
Procedures
[11C]HC070 was radiolabeled utilizing the corresponding precursor and [11C]CH3I via N-methylation protocol. Ex vivo biodistribution study of [11C]HC070 was performed in Sprague–Dawley rats. In vitro autoradiography study was conducted for the rat brain sections to characterize the radiotracer distribution in the brain regionals. MicroPET brain imaging studies of [11C]HC070 were done for 129S1/SvImJ wild-type mice and 129S1/SvImJ TRPC5 knockout mice for 0–60-min dynamic data acquisition after intravenous administration of the radiotracer. Dynamic PET scans (0–120 min) for the brain of cynomolgus male macaques were performed after the radiotracer injection.
Results
[11C]HC070 was efficiently prepared with good radiochemical yield (45 ± 5%, n = 15), high chemical and radiochemical purity (> 99%), and high molar activity (320.6 ± 7.4 GBq/μmol, 8.6 ± 0.2 Ci/μmol) at the end of bombardment (EOB). Radiotracer [11C]HC070 has good solubility in the aqueous dose solution. The ex vivo biodistribution study showed that [11C]HC070 had a quick rat brain clearance. Autoradiography demonstrated that [11C]HC070 specifically binds to TRPC5-enriched regions in rat brain. MicroPET study showed the peak brain uptake (SUV value) was 0.63 in 129S1/SvImJ TRPC5 knockout mice compared to 1.13 in 129S1/SvImJ wild-type mice. PET study showed that [11C]HC070 has good brain uptake with maximum SUV of ~ 2.2 in the macaque brain, followed by rapid clearance.
Conclusions
Our data showed that [11C]HC070 is a TRPC5-specific radiotracer with high brain uptake and good brain washout pharmacokinetics in both rodents and nonhuman primates. The radiotracer is worth further investigating of its suitability to be a PET radiotracer for imaging TRPC5 in animals and human subjects in vivo.
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Acknowledgements
The authors gratefully thank William H. Margenau and Patrick Zerkel of Washington University Cyclotron Facilities for C-11 radioisotope production, Nikki Fettig of the Mallinckrodt Institute of Radiology Preclinical Imaging Facility, and Emily Williams, Emily Flores, and John Hood of nonhuman primate imaging facility for their assistance with microPET imaging studies. We appreciate Ms. Lynne Jones for proofreading the manuscript.
Funding
This work was financially supported by the USA National Institutes of Health (NIH) through the National Institute of Neurological Disorders and Stroke, the National Institute on Aging [NS103988, NS075527 and NS103957].
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All animal experiments were conducted in compliance with the Guide for the Care and Use of Laboratory Animals under Washington University’s Institutional Animal Care and Use Committee (IACUC)-approved protocols (20180188).
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Yu, Y., Jiang, H., Liang, Q. et al. Radiosynthesis and Evaluation of a C-11 Radiotracer for Transient Receptor Potential Canonical 5 in the Brain. Mol Imaging Biol 25, 334–342 (2023). https://doi.org/10.1007/s11307-022-01760-y
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DOI: https://doi.org/10.1007/s11307-022-01760-y