Comparing two TAG-72 binding peptides previously identified by phage display as potential imaging agents
Department of Radiology, Division of Nuclear Medicine
Amino Acid Sequence; Animals; Antigens, Neoplasm; Biotinylation; Gene Expression Regulation, Neoplastic; Glycoproteins; HT29 Cells; Humans; Mice; Molecular Sequence Data; Neoplasms; Organotechnetium Compounds; *Peptide Library; Peptides
Amino Acids, Peptides, and Proteins | Medicinal and Pharmaceutical Chemistry | Neoplasms | Oncology | Radiology
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.
phage display, TAG-72, tumor imaging, peptide biomarker
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Citation: Nucl Med Commun. 2011 Oct;32(10):920-4. doi: 10.1097/MNM.0b013e328348fc64. Link to article on publisher's site
Nuclear medicine communications
Chen, Ling; Wang, Yi; Cheng, Dengfeng; Dou, Shuping; Liu, Xinrong; Liu, Guozheng; Hnatowich, Donald J.; and Rusckowski, Mary, "Comparing two TAG-72 binding peptides previously identified by phage display as potential imaging agents" (2011). Radiology Publications and Presentations. 44.