Evaluating the single-molecule interactions between targeted peptides and the receptors on living cell membrane

As potential ligands, targeted peptides have become an important part in the construction of intelligent drug delivery systems (DDSs). The targeting interaction of peptides with receptors is a key point affecting the efficacy of targeted nano-drugs. Herein, three common peptides (HAIYPRH (T7), YHWYGYTPQNVI (GE11), and RGD) that have been widely used in cancer targeted therapy and tumor diagnostics, targeting the corresponding receptors (transferrin receptor (TfR), epidermal growth factor receptor (EGFR), and α_νβ₃ integrin receptor), were selected as examples to study the targeting interacton on living cell surface at the single-molecule level by using single-molecule force spectroscopy (SMFS) based on atomic force microscopy (AFM). The dissociation activation energy in the absence of an external force (ΔG_β,0) of T7-TfR, GE11-EGFR, and RGD-α_νβ₃ integrin is evaluated at single-molecule level. Among these three peptide-receptor pairs, the T7-TfR bond is the most stable with a smaller dissociation kinetic rate constant at zero force (K_off), larger kinetic on-rate constant (K_on), and shorter interaction time (τ). Furthermore, T7 can target TfR even more effectively on A549 cell membrane after treatment with drugs. Our methodology can also be applicable to the study of other ligand targeted DDSs.