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.