Development and validation of cyclic peptide probe for gastric cancer based on phage display technique

Cancer-targeting diagnostics should have a sensitive and specific binding affinity. To achieve this, biomarker development is critical. This study aimed to develop and validate a 7-mer cyclic peptide probe that can target gastric cancer. We developed this probe based on LGR5 (leucine-rich repeat-containing G-protein coupled receptor 5)-specific targeting, which is a marker for gastric cancer stem cells. An LGR5 targeting peptide sequence that was developed using phage display technology resulted in a cyclic peptide, C-YLASRVH-C (named YLA). We conjugated this peptide with fluorescent probes to validate its specific targeting ability for gastric cancer. The fluorescence-labeled YLA peptide exhibited 3.0-fold higher fluorescence intensity in a gastric cancer cell line (MKN45) than it did in a normal cell line (CCD841 cells). In contrast, pancreatic and colorectal cancer cells did not show significant fluorescence intensity with the YLA peptide. To verify its tumor-targeting affinity, we developed a control peptide, C-YLASAVH-C (named YLASA) using an ALA scanning experiment. Whole-body imaging of a gastric cancer xenograft model showed higher fluorescence intensity of tumors in the YLA peptide group than in the control peptide group. Moreover, ex vivo imaging of tumor tissues exhibited 6.8-fold higher fluorescence intensity in the YLA peptide group compared to that in the YLASA control peptide group. In conclusion, we confirmed that the YLA peptide probe functions as a specific diagnostic probe for gastric cancer. We anticipate that it will play a theranostic role through further development.