In vivo targeting of c-Met using a non-standard macrocyclic peptide in gastric carcinoma

Development of c-Met targeting probes based on specifically designed peptides with high affinity and stability could help enhance diagnostic efficacy and therapeutic effects in c-Met positive cancers. The Random non-standard Peptides Integrated Discovery (RaPID) system for synthesizing natural product-like macrocyclic peptides via in vitro translation-based selection has recently emerged to overcome the shortcomings of traditional peptide synthesis. Here, we developed non-standard macrocyclic peptides specific to c-Met, and examined the cancer-targeting efficiency of fluorescein-labeled (FL) anti-c-Met peptides, referred to as aML5-FL and aMD4-FL, both in vitro and in vivo. The aML5-FL effectively targeted SNU-638 gastric cancer cells with high c-Met expression, compared to the aMD4-FL due to its high affinity. After intravenous administration of aML5-FL in a tumor xenograft mouse model, FL signal intensity in the extracted SNU-638 tumors was higher than that in SNU-216 tumors. This study provides preclinical data for the usefulness of novel non-standard macrocyclic peptides developed by the RaPID system for specific biomarker imaging.