Here, we report a fluorescent probe based on a macrocyclic peptide scaffold that specifically stains EpCAM-expressing MCF7 cells. The 14-mer macrocyclic peptide binding to the extracellular domain of EpCAM with a dissociation constant in the low nM range (1.7 nM) was discovered using the random non-standard peptide-integrated discovery system. Notably, this probe containing a fluorescence tag is less than 3000 Da in total and able to visualize nearly every live cell under high cell-density conditions, which was not achieved by the conventional mAb staining method. This suggests that the molecular probe based on the compact macrocyclic scaffold has great potentials as an imaging tool for the EpCAM biomarker as well as a delivery vehicle for drug conjugates.
Keywords: Cancer cell imaging; EpCAM; Fluorescent imaging probe; In vitro selection; Macrocyclic peptide.