title: Design, synthesis and evaluation in an LPS rodent model of neuroinflammation of a novel18F-labelled PET tracer targeting P2X7.
abstract: BACKGROUND
  The P2X7 receptor has been shown to play a fundamental role in the initiation and sustenance of the inflammatory cascade. The development of a novel fluorine-18 PET tracer superior and with a longer half-life to those currently available is a promising step towards harnessing the therapeutic and diagnostic potential offered by this target. Inspired by the known antagonist A-804598, the present study outlines the design via molecular docking, synthesis and biological evaluation of the novel P2X7 tracer [18F]EFB. The tracer was radiolabelled via a three-step procedure, in vitro binding assessed in P2X7-transfected HEK293 and in B16 cells by calcium influx assays and an initial preclinical evaluation was performed in a lipopolysaccharide (LPS)-injected rat model of neuroinflammation.
  
  
  RESULTS
  The novel tracer [18F]EFB was synthesised in 210 min in 3-5% decay-corrected radiochemical yield (DC RCY), >99% radiochemical purity (RCP) and >300 GBq/μmol and fully characterised. Functional assays showed that the compound binds with nM Kito human, rat and mouse P2X7 receptors. In vivo, [18F]EFB displayed a desirable distribution profile, and while it showed low blood-brain barrier penetration, brain uptake was quantifiable and displayed significantly higher mean longitudinal uptake in inflamed versus control rat CNS regions.
  
  
  CONCLUSIONS
  [18F]EFB demonstrates strong in vitro affinity to human and rodent P2X7 and limited yet quantifiable BBB penetration. Considering the initial promising in vivo data in an LPS rat model with elevated P2X7 expression, this work constitutes an important step in the development of a radiotracer useful for the diagnosis and monitoring of clinical disorders with associated neuroinflammatory processes.
authors.affiliation: Department of Imaging Sciences and Biomedical Engineering, King's College London, St Thomas' Hospital, 4th floor Lambeth Wing, SE1 7EH, London, UK.
authors.forename: Enrico Raffaele
authors.initials: ER
authors.lastname: Fantoni
authors.affiliation: School of Pharmacy, Medicinal Chemistry Unit, University of Camerino, via S. Agostino 1, 62032, Camerino, MC, Italy.
authors.forename: Diego
authors.initials: D
authors.lastname: Dal Ben
authors.affiliation: Prof Francesco Di Virgilio and Dr Simonetta Falzoni, Dipartimento di Morfologia, Chirurgia e Medicina Sperimentale, Sezione di Patologia, Oncologia e Biologia Sperimentale, University of Ferrara, Ferrara, Italy.
authors.forename: Simonetta
authors.initials: S
authors.lastname: Falzoni
authors.affiliation: Prof Francesco Di Virgilio and Dr Simonetta Falzoni, Dipartimento di Morfologia, Chirurgia e Medicina Sperimentale, Sezione di Patologia, Oncologia e Biologia Sperimentale, University of Ferrara, Ferrara, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Di Virgilio
authors.affiliation: Department of Psychiatry, Warneford Hospital, University of Oxford, Warneford Lane, Oxford, OX3 7JX, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Lovestone
authors.affiliation: Department of Imaging Sciences and Biomedical Engineering, King's College London, St Thomas' Hospital, 4th floor Lambeth Wing, SE1 7EH, London, UK. antony.gee@kcl.ac.uk.
authors.forename: Antony
authors.initials: A
authors.lastname: Gee
keywords: EFB; F-18; LPS; Molecular modelling; P2X7; Radiosynthesis