title: A Targeting Microbubble for Ultrasound Molecular Imaging.
abstract: BACKGROUND
  Microbubbles conjugated with targeting ligands are used as contrast agents for ultrasound molecular imaging. However, they often contain immunogenic (strept)avidin, which impedes application in humans. Although targeting bubbles not employing the biotin-(strept)avidin conjugation chemistry have been explored, only a few reached the stage of ultrasound imaging in vivo, none were reported/evaluated to show all three of the following properties desired for clinical applications: (i) low degree of non-specific bubble retention in more than one non-reticuloendothelial tissue; (ii) effective for real-time imaging; and (iii) effective for acoustic quantification of molecular targets to a high degree of quantification. Furthermore, disclosures of the compositions and methodologies enabling reproduction of the bubbles are often withheld.
  
  
  OBJECTIVE
  To develop and evaluate a targeting microbubble based on maleimide-thiol conjugation chemistry for ultrasound molecular imaging.
  
  
  RESULTS
  Microbubbles with a previously unreported generic (non-targeting components) composition were grafted with anti-E-selectin F(ab')2 using maleimide-thiol conjugation, to produce E-selectin targeting microbubbles. The resulting targeting bubbles showed high specificity to E-selectin in vitro and in vivo. Non-specific bubble retention was minimal in at least three non-reticuloendothelial tissues with inflammation (mouse heart, kidneys, cremaster). The bubbles were effective for real-time ultrasound imaging of E-selectin expression in the inflamed mouse heart and kidneys, using a clinical ultrasound scanner. The acoustic signal intensity of the targeted bubbles retained in the heart correlated strongly with the level of E-selectin expression (|r|≥0.8), demonstrating a high degree of non-invasive molecular quantification.
  
  
  CONCLUSIONS
  Targeting microbubbles for ultrasound molecular imaging, based on maleimide-thiol conjugation chemistry and the generic composition described, may possess properties (i)-(iii) desired for clinical applications.
authors.affiliation: National Heart and Lung Institute, Imperial College London, London, United Kingdom; Department of Cardiology, Hammersmith Hospital, London, United Kingdom; Imaging Sciences Department, Medical Research Council, Imperial College London, London, United Kingdom.
authors.forename: James Shue-Min
authors.initials: JS
authors.lastname: Yeh
authors.affiliation: Imaging Sciences Department, Medical Research Council, Imperial College London, London, United Kingdom; Department of Chemistry, Imperial College London, London, United Kingdom.
authors.forename: Charles A
authors.initials: CA
authors.lastname: Sennoga
authors.affiliation: National Heart and Lung Institute, Imperial College London, London, United Kingdom.
authors.forename: Ellen
authors.initials: E
authors.lastname: McConnell
authors.affiliation: Imaging Sciences Department, Medical Research Council, Imperial College London, London, United Kingdom.
authors.forename: Robert
authors.initials: R
authors.lastname: Eckersley
authors.affiliation: Department of Bioengineering, Imperial College London, London, United Kingdom.
authors.forename: Meng-Xing
authors.initials: MX
authors.lastname: Tang
authors.affiliation: National Heart and Lung Institute, Imperial College London, London, United Kingdom; William Harvey Research Institute, Queen Mary, University of London, London, United Kingdom.
authors.forename: Sussan
authors.initials: S
authors.lastname: Nourshargh
authors.affiliation: Department of Chemistry, Imperial College London, London, United Kingdom.
authors.forename: John M
authors.initials: JM
authors.lastname: Seddon
authors.affiliation: National Heart and Lung Institute, Imperial College London, London, United Kingdom.
authors.forename: Dorian O
authors.initials: DO
authors.lastname: Haskard
authors.affiliation: National Heart and Lung Institute, Imperial College London, London, United Kingdom; Department of Cardiology, Hammersmith Hospital, London, United Kingdom.
authors.forename: Petros
authors.initials: P
authors.lastname: Nihoyannopoulos
mesh_terms: D000818:Animals; D019040:E-Selectin / Q000032:analysis* / Q000276:immunology; D004452:Echocardiography; D018796:Immunoconjugates / Q000737:chemistry* / Q000276:immunology; D007249:Inflammation / Q000000981:diagnostic imaging* / Q000276:immunology; D007668:Kidney / Q000000981:diagnostic imaging / Q000276:immunology; D008297:Male; D008301:Maleimides / Q000737:chemistry; D008810:Mice, Inbred C57BL; D045423:Microbubbles; D057054:Molecular Imaging / Q000379:methods*; D009206:Myocardium / Q000276:immunology / Q000473:pathology; D051381:Rats; D013438:Sulfhydryl Compounds / Q000737:chemistry
chemical_list: D019040:E-Selectin; D018796:Immunoconjugates; D008301:Maleimides; D013438:Sulfhydryl Compounds; C043592:maleimide