Search

Integrin targeting, arginine-glycine-aspartic acid (RGD)-based nanocarriers have been widely used for tumor imaging, the monitoring of tumor development, and the delivery of anti-cancer drugs. However, the thermodynamics of an RGD-integrin formation and dissociation associated with binding dynamics, affinity, and stability remains unclear. Here, we probed the binding strength of the binary complex to live pancreatic cancer cells using single-molecule binding force spectroscopy methods, in which the RGD peptides were functionalized on a force probe tip through the PEG-based bifunctional linker molecules. While the density of integrin α(V) receptors on the cell surface varies more than two-fold from cell line to cell line, the individual RGD-integrin complexes exhibited a cell type-independent, monovalent bond strength. The load-dependent, bond strength of multivalent RGD-integrin interactions scaled sublinearly with increasing bond number, consistent with the noncooperative, parallel bond model. Furthermore, the multivalent bonds ruptured sequentially either by one or in multiples, and the force strength was comparable with the synchronous rupture force. Comparison of energy landscapes of the bond number revealed a substantial decrease of kinetic off rates for multivalent bonds, along with the increased width of the potential well and the increased potential barrier height between bound and unbound state, enhancing the stability of the multivalent bonds between them.