title: Noninvasive visualization and quantification of tumor αVβ3 integrin expression using a novel positron emission tomography probe, 64Cu-cyclam-RAFT-c(-RGDfK-)4.
abstract: BACKGROUND
  The α(V)β(3) integrin is a well-known transmembrane receptor involved in tumor invasion, angiogenesis and metastasis. Our aim was to evaluate a novel positron emission tomography (PET) probe, (64)Cu-cyclam-RAFT-c(-RGDfK-)(4), for noninvasive visualization and quantification of α(V)β(3) integrin expression.
  
  
  METHODS
  RAFT-c(-RGDfK-)(4), a tetrameric cyclic Arg-Gly-Asp (RGD)-based peptide, was conjugated with a bifunctional chelator, 1,4,8,11-tetraazacyclotetradecane (cyclam), radiolabeled with the positron emitter (64)Cu and evaluated in vitro by cell binding and competitive inhibition assays and in vivo by biodistribution and receptor blocking studies, and PET imaging. The following cell lines, human embryonic kidney HEK293(β(1)) [α(V)β(3)-negative] and HEK293(β(3)) [α(V)β(3)-overexpressing] and human glioblastoma U87MG [naturally expressing α(V)β(3)], together with their subcutaneous xenografts in athymic nude mice, were used for the present study. The expression levels of α(V)β(3) on these cell lines and tumor xenografts were analyzed by flow cytometry and sodium dodecyl sulfate-polyacrylamide gel electrophoresis/autoradiography, respectively.
  
  
  RESULTS
  (64)Cu-cyclam-RAFT-c(-RGDfK-)(4) demonstrated the in vitro and in vivo specificity for the α(V)β(3) integrin and displayed rapid blood clearance, predominantly renal excretion and low uptake in nontumor tissues. Tumor uptake of (64)Cu-cyclam-RAFT-c(-RGDfK-)(4) (3 h postinjection) in HEK293(β(3)) (high levels of α(V)β(3)), U87MG (moderate levels of α(V)β(3)) and HEK293(β(1)) (undetectable levels of α(V)β(3)) tumors was 9.35%±1.19%, 3.46%±0.45% and 1.18%±0.30% injected dose per gram, respectively, with a strong and positive correlation with the tumor α(V)β(3) expression levels (correlation coefficient=0.967; P<.0001). Positron emission tomographic images showed that α(V)β(3)-positive tumors were clearly visualized with high tumor-to-background contrast, and agreed well with the biodistribution results.
  
  
  CONCLUSIONS
  (64)Cu-cyclam-RAFT-c(-RGDfK-)(4) exhibits potential for noninvasively quantifying α(V)β(3) expression.
authors.affiliation: Molecular Imaging Center, National Institute of Radiological Sciences, Chiba 263-8555, Japan.
authors.forename: Zhao-Hui
authors.initials: ZH
authors.lastname: Jin
authors.forename: Takako
authors.initials: T
authors.lastname: Furukawa
authors.forename: Mathieu
authors.initials: M
authors.lastname: Galibert
authors.forename: Didier
authors.initials: D
authors.lastname: Boturyn
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Coll
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Fukumura
authors.forename: Tsuneo
authors.initials: T
authors.lastname: Saga
authors.forename: Pascal
authors.initials: P
authors.lastname: Dumy
authors.forename: Yasuhisa
authors.initials: Y
authors.lastname: Fujibayashi
mesh_terms: D000818:Animals; D001692:Biological Transport; D045744:Cell Line, Tumor; D056831:Coordination Complexes / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics; D004355:Drug Stability; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D057809:HEK293 Cells; D006207:Half-Life; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D009369:Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism*; D009842:Oligopeptides / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics; D010456:Peptides, Cyclic / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics; D049268:Positron-Emission Tomography / Q000379:methods*
chemical_list: C560405:64Cu-cyclam-RAFT-cyclo(arginyl-glycyl-aspartyl-phenylalanyl-lysyl)4; D056831:Coordination Complexes; D039302:Integrin alphaVbeta3; D009842:Oligopeptides; D010456:Peptides, Cyclic; C047981:arginyl-glycyl-aspartic acid