title: RGD conjugates of the H2dedpa scaffold: synthesis, labeling and imaging with 68Ga.
abstract: BACKGROUND
  The rekindled interest in the (68)Ga generator as an attractive positron emission tomography generator system has led us and others to investigate novel chelate systems for (68)Ga. We have previously reported our findings with the acyclic, rapidly coordinating chelate H(2)dedpa and its model derivatives.
  
  
  METHODS
  In this report, we describe the synthesis of the corresponding bifunctional chelate scaffolds (H(2)dp-bb-NCS and H(2)dp-N-NCS) as well as the radiolabeling properties, transferrin stability, binding to the target using in vitro cell models and in vivo behavior the corresponding conjugates with the α(v)β(3) targeting cyclic pentapeptide cRGDyK (monomeric H(2)RGD-1 and dimeric H(2)RGD-2).
  
  
  RESULTS
  The ability of the conjugated ligands to coordinate Ga isotopes within 10 min at room temperature at concentrations of 1 nmol was confirmed. Complex [(67)Ga(RGD-1)](+) was more stable (92% after 2 h) than [(67)Ga(RGD-2)](+) (73% after 2 h) in a transferrin challenge experiment. IC(50) values for both conjugates (H(2)RGD-1 and H(2)RGD-2) and nonconjugated RGD were determined in a cell-based competitive binding assay with (125)I-echistatin using U87MG cells, where enhanced specific binding was observed for the multivalent H(2)RGD-2 conjugate compared to the monovalent H(2)RGD-1 and nonconjugated cRGDyK. The U87MG cell line was also used to generate subcutaneous xenograft tumors on RAG2M mice, which were used to evaluate the in vivo properties of [(68)Ga(RGD-1)](+) and [(68)Ga(RGD-2)](+). After 2 h of dynamic imaging, both block and nonblock mice were sacrificed to collect select organs at the 2-h time point. Although the uptake is specific, as judged from the ratios of nonblock to block (2.36 with [(67)Ga(RGD-1)](+), 1.46 with [(67)Ga(RGD-2)](+)), both conjugates display high uptake in blood.
  
  
  CONCLUSIONS
  We have successfully synthesized and applied the first bifunctional versions of H(2)dedpa for conjugation to a targeting vector and subsequent imaging of the corresponding conjugates.
authors.affiliation: Medicinal Inorganic Chemistry Group, Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, BC, Canada.
authors.forename: Eszter
authors.initials: E
authors.lastname: Boros
authors.forename: Cara L
authors.initials: CL
authors.lastname: Ferreira
authors.forename: Donald T T
authors.initials: DT
authors.lastname: Yapp
authors.forename: Rajanvir K
authors.initials: RK
authors.lastname: Gill
authors.forename: Eric W
authors.initials: EW
authors.lastname: Price
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Adam
authors.forename: Chris
authors.initials: C
authors.lastname: Orvig
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D045744:Cell Line, Tumor; D002614:Chelating Agents / Q000737:chemistry*; D060326:Chemistry Techniques, Synthetic; D003432:Cross-Linking Reagents / Q000737:chemistry*; D005029:Ethylenediamines / Q000737:chemistry*; D005710:Gallium Radioisotopes; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000378:metabolism; D007553:Isotope Labeling; D008297:Male; D051379:Mice; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000378:metabolism / Q000493:pharmacokinetics; D010848:Picolinic Acids / Q000737:chemistry*; D011854:Radiochemistry
chemical_list: D002614:Chelating Agents; D003432:Cross-Linking Reagents; D005029:Ethylenediamines; D005710:Gallium Radioisotopes; D039302:Integrin alphaVbeta3; D009842:Oligopeptides; D010848:Picolinic Acids; C047981:arginyl-glycyl-aspartic acid