Targeting beta-3 integrin using a linear hexapeptide labeled with a near-infrared fluorescent molecular probe

Biomolecules containing the RGD peptide sequence are known to bind integrins with high affinity. Studies of hexa-and hepta-peptides labeled with a near-infrared fluorescent probe (cypate) showed that rearranging the glycine in a linear RGD peptide sequence to form the GRD analogue favored the uptake of the GRD compound by α_vβ₃ integrin receptor (ABIR)-positive A549 tumor cells and tissue. The internalization of the GRD compound in A549 cells and tumor uptake in mice were inhibited by ABIR-avid peptides, suggesting its recognition by this receptor. Further studies with functional blocking antibodies and β₃ knockout cells revealed that β₃ integrin mediates the internalization of the cypate-GRD peptide. Molecular modeling studies supported preferential interaction of the probe with the β₃ subunit of integrins relative to the α_v subunit. The results demonstrate that the cypate-GRD peptide targets β₃ integrin, thereby providing a strategy to monitor drug delivery and efficacy, and physiopathologic processes mediated by this protein.