title: Biological evaluation of an ornithine-modified (99m)Tc-labeled RGD peptide as an angiogenesis imaging agent.
abstract: BACKGROUND
  Radiolabeled RGD peptides that specifically target integrin α(ν)β(3) have great potential in early tumor detection through noninvasive monitoring of tumor angiogenesis. Based on previous findings of our group on radiopeptides containing positively charged aminoacids, we developed a new cyclic cRGDfK derivative, c(RGDfK)-(Orn)(3)-CGG. This new peptide availing the polar linker (Orn)(3) and the (99m)Tc-chelating moiety CGG (Cys-Gly-Gly) is appropriately designed for (99m)Tc-labeling, as well as consequent conjugation onto nanoparticles.
  
  
  METHODS
  A tumor imaging agent, c(RGDfK)-(Orn)(3)-[CGG-(99m)Tc], is evaluated with regard to its radiochemical, radiobiological and imaging characteristics.
  
  
  RESULTS
  The complex c(RGDfK)-(Orn)(3)-[CGG-(99m)Tc] was obtained in high radiochemical yield (>98%) and was stable in vitro and ex vivo. It presented identical to the respective, fully analytically characterized (185/187)Re complex retention time in RP-HPLC. In contrary to other RGD derivatives, we showed that the new radiopeptide exhibits kidney uptake and urine excretion due to the ornithine linker. High tumor uptake (3.87±0.48% ID/g at 60 min p.i.) was observed and was maintained relatively high even at 24 h p.i. (1.83±0.05 % ID/g), thus providing well-defined scintigraphic imaging. Accumulation in other organs was negligible. Blocking experiments indicated target specificity for integrin receptors in U87MG glioblastoma cells.
  
  
  CONCLUSIONS
  Due to its relatively high tumor uptake, renal elimination and negligible abdominal localization, the new (99m)Tc-RGD peptide is considered promising in the field of imaging α(ν)β(3)-positive tumors. However, the preparation of multifunctional SPECT/MRI contrast agents (RGD-conjugated nanoparticles) for dual modality imaging of integrin expressing tumors should be further investigated.
authors.affiliation: Department of Medical Physics, School of Medicine, University of Patras, P.O. BOX: 132 73, GR 265 04, Rion, Greece.
authors.forename: Irene
authors.initials: I
authors.lastname: Tsiapa
authors.forename: George
authors.initials: G
authors.lastname: Loudos
authors.forename: Alexandra
authors.initials: A
authors.lastname: Varvarigou
authors.forename: Eirini
authors.initials: E
authors.lastname: Fragogeorgi
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Psimadas
authors.forename: Theodoros
authors.initials: T
authors.lastname: Tsotakos
authors.forename: Stavros
authors.initials: S
authors.lastname: Xanthopoulos
authors.forename: Dimitris
authors.initials: D
authors.lastname: Mihailidis
authors.forename: Penelope
authors.initials: P
authors.lastname: Bouziotis
authors.forename: George C
authors.initials: GC
authors.lastname: Nikiforidis
authors.forename: George C
authors.initials: GC
authors.lastname: Kagadis
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D004355:Drug Stability; D005260:Female; D006801:Humans; D007553:Isotope Labeling; D008279:Magnetic Resonance Imaging; D051379:Mice; D009389:Neovascularization, Pathologic / Q000175:diagnosis* / Q000000981:diagnostic imaging; D009842:Oligopeptides / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics; D009952:Ornithine / Q000737:chemistry*; D011786:Quality Control; D012211:Rhenium; D013667:Technetium; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D009842:Oligopeptides; D012211:Rhenium; D013667:Technetium; C047981:arginyl-glycyl-aspartic acid; D009952:Ornithine