title: In vitro cell studies of technetium-99m labeled RGD-HYNIC peptide, a comparison of tricine and EDDA as co-ligands.
abstract: The level of alpha(V)beta(3) integrins on endothelial cells is elevated in angiogenesis. The high binding specificity to alpha(V)beta(3) integrins of peptides containing Arg-Gly-Asp (RGD) residues suggests that the radiolabeled RGD peptides may be useful as tumor specific imaging agents. In this research, cyclised peptides containing Arg-Gly-Asp (RGD) and Arg-Gly-Glu (RGE, as control) residues were conjugated with HYNIC and labeled with (99m)Tc.
  
  
  OBJECTIVE
  The goal was to evaluate the influence of co-ligand, either tricine or ethylenediamine-N,N'-diacetic acid (EDDA) on protein and integrin binding and on cellular uptake in culture.
  
  
  METHODS
  The n-octanol/water partition coefficient, binding to bovine serum albumin (BSA) and human umbilical vein endothelial (HUVE) cells, and cell lysate distributions of the radiolabeled peptides were evaluated.
  
  
  RESULTS
  The co-ligands had a significant effect on the labeling efficiency of the HYNIC conjugates and on certain properties of the (99m)Tc complexes. The labeling efficiency with tricine was 10 fold higher and BSA binding was over 8 fold greater compared to EDDA. Both RGD labels showed higher (6 to 28 fold) binding to HUVE cells than that of the RGE labels, indicating binding specificity. After cell-lysis, only a small percentage of the total RGD label that accumulated in the cells was found bound to cellular proteins (9% of RGD/tricine and 5% of RGD/EDDA), implying that over 90% of the radiolabeled peptides were internalized for both radiolabeled RGDs. The number of the RGD molecules bound to proteins was estimated to be approximately three per cell, suggesting that only a small number of alpha(V)beta(3) integrin proteins are expressed on the cells.
  
  
  CONCLUSIONS
  Apart from the differences in radiolabeling, the only important effect of substituting EDDA for tricine as co-ligand on the HYNIC-peptides was the lower degree of serum protein binding. In spite of the lower serum protein binding potential, in vivo tumor accumulation of the RGD/EDDA may not be improved compared to RGD/tricine since quantitation of the cell binding results suggests that the number of alpha(V)beta(3) integrin proteins per cell might be limited.
authors.affiliation: Division of Nuclear Medicine, Department of Radiology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
authors.forename: Zi-Fen
authors.initials: ZF
authors.lastname: Su
authors.forename: Jiang
authors.initials: J
authors.lastname: He
authors.forename: Mary
authors.initials: M
authors.lastname: Rusckowski
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Hnatowich
mesh_terms: D001798:Blood Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D004492:Edetic Acid / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D004730:Endothelium, Vascular / Q000000981:diagnostic imaging / Q000378:metabolism*; D005998:Glycine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D006801:Humans; D006834:Hydrazines / Q000493:pharmacokinetics*; D016023:Integrins / Q000378:metabolism*; D008024:Ligands; D008657:Metabolic Clearance Rate; D009539:Nicotinic Acids / Q000493:pharmacokinetics*; D009842:Oligopeptides / Q000493:pharmacokinetics*; D011485:Protein Binding; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D013667:Technetium / Q000493:pharmacokinetics*; D014471:Umbilical Veins / Q000000981:diagnostic imaging / Q000378:metabolism
chemical_list: C120392:6-hydrazinopyridine-3-carboxylic acid; D001798:Blood Proteins; D006834:Hydrazines; D016023:Integrins; D008024:Ligands; D009539:Nicotinic Acids; D009842:Oligopeptides; D019275:Radiopharmaceuticals; C026058:EDDA; D013667:Technetium; C047981:arginyl-glycyl-aspartic acid; D004492:Edetic Acid; D005998:Glycine; C100184:tricine