title: Preclinical Evaluation of a P2X7 Receptor-Selective Radiotracer: PET Studies in a Rat Model with Local Overexpression of the Human P2X7 Receptor and in Nonhuman Primates.
abstract: The P2X7 receptor (P2X7R) orchestrates neuroinflammation, and this is the basis for an increased interest in the development of antagonists inhibiting P2X7R function in the brain. This study provides the preclinical evaluation of (11)C-JNJ-54173717, a PET tracer for P2X7R in both rats and nonhuman primates.
  
  
  
  (11)C-JNJ-54173717 is a high-affinity radiotracer for the human P2X7R (hP2X7R). Biodistribution and radiometabolite studies were performed. Viral vectors encoding either enhanced green fluorescent protein-hP2X7R or 3flag-hP2X7R were engineered and validated in cell culture. hP2X7R was regionally overexpressed in the rat striatum after stereotactic injection of viral vectors. Dynamic small-animal PET studies were performed in vector-injected rats and in healthy monkeys using (11)C-JNJ-54173717.
  
  
  
  The affinity of JNJ-54173717 was 1.6 ± 0.1 nM in a rat cortex P2X7R membrane binding assay. In a functional assay at the recombinant human and rat P2X7R orthologs, the half maximal inhibitory concentration (IC50) of JNJ-54173717 was 4.2 ± 0.01 nM and 7.6 ± 0.01 nM, respectively. The rat biodistribution study showed that (11)C-JNJ-54173717 crossed the blood-brain barrier and was cleared from plasma mainly via the hepatobiliary pathway. A polar radiometabolite was found in rat plasma. No radiometabolites were detected in rat brain. Dynamic small-animal PET showed binding of (11)C-JNJ-54173717 in the striatum expressing hP2X7R, with rapid washout from the noninjected control striatum and other brain regions. Likewise, (11)C-JNJ-54173717 PET signal was blocked by a chemically distinct P2X7R ligand, indicating specific binding to P2X7R in the monkey brain.
  
  
  
  JNJ-54173717 is a high-affinity P2X7R antagonist. An animal rat model stably expressing hP2X7R was developed and validated, identifying favorable characteristics for (11)C-JNJ-54173717 as a PET radioligand for in vivo visualization of hP2X7R. (11)C-JNJ-54173717 selectively visualized P2X7R in the monkey brain, and this radioligand will be further evaluated in a clinical setting to study P2X7R expression levels in neurodegenerative disorders.
authors.affiliation: Laboratory for Radiopharmacy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Leuven, Belgium Laboratory for Molecular Virology and Gene Therapy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Leuven, Belgium.
authors.forename: Dieter
authors.initials: D
authors.lastname: Ory
authors.affiliation: Laboratory for Radiopharmacy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Leuven, Belgium.
authors.forename: Sofie
authors.initials: S
authors.lastname: Celen
authors.affiliation: Laboratory for Molecular Virology and Gene Therapy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Leuven, Belgium Leuven Viral Vector Core, KU Leuven, Leuven, Belgium.
authors.forename: Rik
authors.initials: R
authors.lastname: Gijsbers
authors.affiliation: Leuven Viral Vector Core, KU Leuven, Leuven, Belgium Laboratory for Neurobiology and Gene Therapy, Department of Neurosciences, KU Leuven, Leuven, Belgium.
authors.forename: Chris
authors.initials: C
authors.lastname: Van Den Haute
authors.affiliation: Nuclear Medicine and Molecular Imaging, Department of Imaging and Pathology, University Hospital and KU Leuven, Leuven, Belgium.
authors.forename: Andrey
authors.initials: A
authors.lastname: Postnov
authors.affiliation: Nuclear Medicine and Molecular Imaging, Department of Imaging and Pathology, University Hospital and KU Leuven, Leuven, Belgium.
authors.forename: Michel
authors.initials: M
authors.lastname: Koole
authors.affiliation: Nuclear Medicine and Molecular Imaging, Department of Imaging and Pathology, University Hospital and KU Leuven, Leuven, Belgium.
authors.forename: Caroline
authors.initials: C
authors.lastname: Vandeputte
authors.affiliation: Janssen Research and Development, Discovery Sciences, a Division of Janssen-Cilag, Toledo, Spain.
authors.forename: José-Ignacio
authors.initials: JI
authors.lastname: Andrés
authors.affiliation: Janssen Research and Development, Discovery Sciences, a Division of Janssen-Cilag, Toledo, Spain.
authors.forename: Jesus
authors.initials: J
authors.lastname: Alcazar
authors.affiliation: Janssen Research and Development, Discovery Sciences, a Division of Janssen-Cilag, Toledo, Spain.
authors.forename: Meri
authors.initials: M
authors.lastname: De Angelis
authors.affiliation: Janssen Research and Development, Discovery Sciences, a Division of Janssen-Cilag, Toledo, Spain.
authors.forename: Xavier
authors.initials: X
authors.lastname: Langlois
authors.affiliation: Janssen Research and Development, Discovery Sciences, a Division of Janssen-Cilag, Toledo, Spain Janssen Research and Development, LLC, San Diego, California.
authors.forename: Anindya
authors.initials: A
authors.lastname: Bhattacharya
authors.affiliation: Janssen Research and Development, Neuroscience Discovery, a Division of Janssen Pharmaceutica Nevada, Beerse, Belgium; and.
authors.forename: Mark
authors.initials: M
authors.lastname: Schmidt
authors.affiliation: Janssen Research and Development, LLC, San Diego, California.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Letavic
authors.affiliation: Laboratory for Neuro- and Psychophysiology, Department of Neurosciences, KU Leuven, Leuven, Belgium.
authors.forename: Wim
authors.initials: W
authors.lastname: Vanduffel
authors.affiliation: Nuclear Medicine and Molecular Imaging, Department of Imaging and Pathology, University Hospital and KU Leuven, Leuven, Belgium.
authors.forename: Koen
authors.initials: K
authors.lastname: Van Laere
authors.affiliation: Laboratory for Radiopharmacy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Leuven, Belgium.
authors.forename: Alfons
authors.initials: A
authors.lastname: Verbruggen
authors.affiliation: Laboratory for Molecular Virology and Gene Therapy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Leuven, Belgium.
authors.forename: Zeger
authors.initials: Z
authors.lastname: Debyser
authors.affiliation: Laboratory for Radiopharmacy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Leuven, Belgium Guy.Bormans@pharm.kuleuven.be.
authors.forename: Guy
authors.initials: G
authors.lastname: Bormans
mesh_terms: D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism*; D005260:Female; D006801:Humans; D008253:Macaca mulatta; D008297:Male; D008657:Metabolic Clearance Rate; D057054:Molecular Imaging / Q000379:methods*; D009928:Organ Specificity; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D051381:Rats; D055647:Rats, Transgenic; D017208:Rats, Wistar; D058486:Receptors, Purinergic P2X7 / Q000378:metabolism*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D015854:Up-Regulation
chemical_list: C546468:P2RX7 protein, human; D019275:Radiopharmaceuticals; D058486:Receptors, Purinergic P2X7
keywords: P2X7 receptor; PET; neuroinflammation; non-human primate; viral vector