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

Area of Science:

• Biotechnology
• Molecular Imaging
• Oncology

Background:

• Tumor-associated glycoprotein 72 (TAG-72) is a validated target for cancer therapy and diagnostics.
• Phage display technology enables the identification of specific peptide binders to tumor antigens.
• Development of targeted imaging agents is crucial for early cancer detection and treatment monitoring.

Purpose of the Study:

• To assess the in vitro and in vivo targeting capabilities of two TAG-72 binding peptides (A2-6 and A3-10).
• To compare the binding affinity and tumor accumulation properties of the selected peptides.
• To evaluate their potential as diagnostic imaging agents for TAG-72 positive cancers.

Main Methods:

• Peptides A2-6 and A3-10 were radiolabeled with technetium-99m ((99m)Tc) or biotinylated.
• In vitro specificity was confirmed using flow cytometry and competitive binding assays with TAG-72 positive (LS-174T) and negative (HT-29) cells.
• In vivo biodistribution and tumor visualization were assessed in mice using small-animal SPECT/CT imaging.

Main Results:

• Both peptides exhibited specific binding to TAG-72 positive LS-174T cells, with A2-6 showing higher binding affinity (IC50 = 46.5 nmol/l) than A3-10 (IC50 = 420 nmol/l).
• In vivo imaging revealed clear tumor visibility for both (99m)Tc-labeled peptides within 60 minutes.
• Tumor accumulation was higher for the A3-10 peptide, despite its lower binding affinity, with significant uptake also observed in kidneys and gallbladder.

Conclusions:

• The A3-10 peptide demonstrated favorable specific binding and tumor accumulation characteristics, making it a promising candidate for further development.
• While A2-6 had higher binding affinity, A3-10's overall performance suggests its potential as a novel imaging agent for TAG-72 positive cancers.
• These findings support the utility of phage-selected peptides for targeted cancer diagnostics.