title: Comparing two TAG-72 binding peptides previously identified by phage display as potential imaging agents.
abstract: OBJECTIVE
  To evaluate the targeting property in vitro and in vivo of two tumor-associated glycoprotein 72 (TAG-72) binding peptides, previously identified in this laboratory by phage selection using different elution conditions.
  
  
  METHODS
  The peptides GGVSCMQTSPVCENNL (A2-6) and NPGTCKDKWEICLLNGG (A3-10) were radiolabeled with technetium-99m ((99m)Tc) using N-hydroxysuccinimidyl-S-acetyl-mercaptoacetyltriglycine (NHS-MAG(3)) as a chelator or were biotinylated. The specificity of the two peptides for the TAG-72 positive LS-174T cancer cells was demonstrated in vitro both by flow cytometry analysis using the biotinylated peptides and by competitive binding using the (99m)Tc-labeled peptides. The in-vivo biodistributions of the peptides were evaluated in TAG-72 positive LS-174T tumor-bearing mice by small-animal single photon emission computed tomography/computed tomography imaging.
  
  
  RESULTS
  As evidence of specific binding, both peptides showed a significant increase in percentage binding with increasing peptide concentration by flow cytometry analysis to LS-174T cells, but not to TAG-72 negative HT-29 cells. The (99m)Tc-labeled A2-6 peptide bound LS-174T cells with an inhibition constant at 50% of 46.5 nmol/l compared with 420 nmol/l for the A3-10 peptide. In mice, accumulation of both peptides was highest in kidneys and gallbladder. Tumors were clearly visible by single photon emission computed tomography imaging for both (99m)Tc-labeled peptides through 60 min, although the tumor accumulation was higher for the A3-10 peptide.
  
  
  CONCLUSIONS
  The A3-10 peptide, with lower, yet reasonable binding affinity compared with the A2-6 peptide, showed sufficiently favorable specific binding and tumor accumulation to be considered further as a potential imaging agent for TAG-72 positive cancers.
authors.affiliation: Division of Nuclear Medicine, Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts, USA.
authors.forename: Ling
authors.initials: L
authors.lastname: Chen
authors.forename: Yi
authors.initials: Y
authors.lastname: Wang
authors.forename: Dengfeng
authors.initials: D
authors.lastname: Cheng
authors.forename: Shuping
authors.initials: S
authors.lastname: Dou
authors.forename: Xinrong
authors.initials: X
authors.lastname: Liu
authors.forename: Guozheng
authors.initials: G
authors.lastname: Liu
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Hnatowich
authors.forename: Mary
authors.initials: M
authors.lastname: Rusckowski
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism*; D019921:Biotinylation; D015972:Gene Expression Regulation, Neoplastic; D006023:Glycoproteins / Q000378:metabolism*; D019073:HT29 Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009369:Neoplasms / Q000175:diagnosis / Q000378:metabolism; D015609:Organotechnetium Compounds; D019151:Peptide Library; D010455:Peptides / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics
chemical_list: D000951:Antigens, Neoplasm; D006023:Glycoproteins; D015609:Organotechnetium Compounds; D019151:Peptide Library; D010455:Peptides; C047052:tumor-associated antigen 72