RGD-4C, an arginine-glycine-aspartic acid peptide (ACDCRGDCFC), exhibits integrin binding activity. The primary integrin recognition site in extracellular matrix proteins, the Arg-Gly-Asp (RGD) sequence, allows peptides with this sequence to mimic matrix proteins' recognition specificity. As an αv-integrin ligand, RGD-4C can be conjugated with bioactive molecules to demonstrate antitumor effects in animal models [1] [2] [3].