Determination of the binding epitope of RGD-peptidomimetics to αvβ3 and α(IIb)β3 integrin-rich intact cells by NMR and computational studies.

NMR experiments (transferred NOE and Saturation Transfer Difference) were used to shed light on the binding epitope of RGD peptidomimetics 1-3 with integrins αvβ3 and α(IIb)β3, expressed on the membrane of ECV304 bladder cancer cells and human platelets, respectively. The NMR results were supported by docking calculations of 1-3 in the active sites of αvβ3 and α(IIb)β3 integrin receptors and were compared to the results of competitive αvβ3 receptor binding assays and competitive ECV304 cell adhesion experiments. While cis RGD ligand 1 interacts mainly with the α integrin subunit through its basic guanidine group, trans RGD ligands 2 and 3 are able to interact with both the α and β integrin subunits via an electrostatic clamp.