Comparing two TAG-72 binding peptides previously identified by phage display as potential imaging agents.

Abstract

AIM:

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.

MATERIALS AND 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.

CONCLUSION:

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: Ling Chen, Yi Wang, Dengfeng Cheng, Shuping Dou, Xinrong Liu, Guozheng Liu, Donald J Hnatowich, Mary Rusckowski
• Journal: Nuclear medicine communications (Nucl Med Commun) Vol. 32 Issue 10 Pg. 920-4 (Oct 2011) ISSN: 1473-5628 [Electronic] England
• PMID: 21876403 (Publication Type: Comparative Study, Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Antigens, Neoplasm
• Glycoproteins
• Organotechnetium Compounds
• Peptide Library
• Peptides
• tumor-associated antigen 72

Topics

• Amino Acid Sequence
• Animals
• Antigens, Neoplasm (metabolism)
• Biotinylation
• Gene Expression Regulation, Neoplastic
• Glycoproteins (metabolism)
• HT29 Cells
• Humans
• Mice
• Molecular Sequence Data
• Neoplasms (diagnosis, metabolism)
• Organotechnetium Compounds
• Peptide Library
• Peptides (chemistry, metabolism, pharmacokinetics)