title: BR55: a lipopeptide-based VEGFR2-targeted ultrasound contrast agent for molecular imaging of angiogenesis.
abstract: OBJECTIVE
  BR55, an ultrasound contrast agent functionalized with a heterodimer peptide targeting the vascular endothelial growth factor receptor 2 (VEGFR2), was evaluated in vitro and in vivo, demonstrating its potential for specific tumor detection.
  
  
  METHODS
  The targeted contrast agent was prepared by incorporation of a biospecific lipopeptide into the microbubble membrane. Experiments were performed in vitro to demonstrate the binding capacities of BR55 microbubbles on immobilized receptor proteins and on various endothelial or transfected cells expressing VEGFR2. The performance of BR55 microbubbles was compared with that of streptavidin-conjugated microbubbles targeted to the same receptor by coupling them to a biotinylated antibody. The specificity of BR55 binding to human and mouse endothelial cells was determined in competition experiments with the free lipopeptide, vascular endothelial growth factor (VEGF), or a VEGFR2-specific antibody. Molecular ultrasound imaging of VEGFR2 was performed in an orthotopic breast tumor model in rats using a nondestructive, contrast-specific imaging mode.
  
  
  RESULTS
  BR55 was shown to bind specifically to the immobilized recombinant VEGFR2 under flow (dynamic conditions). BR55 accumulation on the target over time was similar to that of microbubbles bearing a specific antibody. BR55 avidly bound to cells expressing VEGFR2, and the pattern of microbubble distribution was correlated with the pattern of receptor expression determined by immunocytochemistry. The binding of targeted microbubbles on cells was competed off by an excess of free lipopeptide, the natural ligand (VEGF) and by a VEGFR2-specific antibody (P < 0.001). Although selected for the human receptor, the VEGFR2-binding lipopeptide was also shown to recognize the rodent receptor. Tumor perfusion was assessed during the vascular phase of BR55, and then the malignant lesion was highlighted by specific accumulation of the targeted microbubbles on tumoral endothelium. The presence of VEGFR2 was confirmed by immunofluorescence staining of tumor cryosections.
  
  
  CONCLUSIONS
  VEGFR2-targeted ultrasound contrast agents such as BR55 will likely prove useful in human for the early detection of tumors as well as for the assessment of response to specific treatments.
authors.affiliation: Bracco Research SA, Geneva, Switzerland; and daggerThe Ernst Felder Laboratories, Bracco Research USA, Inc., Princeton, NJ, USA. sibylle.pochon@brg.bracco.com
authors.forename: Sibylle
authors.initials: S
authors.lastname: Pochon
authors.forename: Isabelle
authors.initials: I
authors.lastname: Tardy
authors.forename: Philippe
authors.initials: P
authors.lastname: Bussat
authors.forename: Thierry
authors.initials: T
authors.lastname: Bettinger
authors.forename: Jean
authors.initials: J
authors.lastname: Brochot
authors.forename: Mathew
authors.initials: M
authors.lastname: von Wronski
authors.forename: Lisa
authors.initials: L
authors.lastname: Passantino
authors.forename: Michel
authors.initials: M
authors.lastname: Schneider
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000098:blood supply* / Q000000981:diagnostic imaging* / Q000188:drug therapy; D045744:Cell Line, Tumor; D003287:Contrast Media / Q000493:pharmacokinetics; D016503:Drug Delivery Systems / Q000379:methods; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D055666:Lipopeptides / Q000493:pharmacokinetics*; D051379:Mice; D045423:Microbubbles; D015336:Molecular Probe Techniques; D009389:Neovascularization, Pathologic / Q000000981:diagnostic imaging* / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014463:Ultrasonography; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism*
chemical_list: D003287:Contrast Media; D055666:Lipopeptides; D040301:Vascular Endothelial Growth Factor Receptor-2