Cyclo(-RGDfK) is a potent and selective inhibitor of integrin αvβ3 with IC50 of 0.94 nM. Cyclo specifically targets tumor microvasculature and cancer cells by binding to αvβ3 integrin on the cell surface.

αvβ3 integrin:0.94 nM.

Cyclo (-RGDfK-) has a high affinity for purified integrin (Kd: 41.70 nM). It is reacting with HEK293(β3) cells moderately. The micelles modified by Cyclo(-RGDfK-) show strong affinity to T-24 cells and strong inhibitory effect on the proliferation of T-24 cells.

In athymic mice bearing α(v)β(3)-integrin-positive C6 gliomas, Cyclo (-RGDfK-) modification induces less tumor metabolic activity, less tumor progression, fewer intratumoral vessels.

Isolated Integrin Binding Assays.:Purified integrin (1 μg/mL; 4℃) is used to coat 96-well microtitre plates, which are then blocked with bovine serum albumin (BSA) (3% in 1 mM CaCl2, 1 mM MgCl2,10 pM MnCl2, 100 mM NaC1,50 mM Tris-hydroxymethyl-aminomethane; pH 7.4), and incubated (3 h at 30 ℃) with biotinylated ligands (1 pg/mL in binding buffer: 0.1% BSA, 1 mM CaCl2,1 mM MgCl2, 10 μM MnCl2, 100 mM NaCl, 50 mM Tris-hydroxymethyl-aminomethane; pH 7.4) in the presence or absence of serially diluted peptides. After washing (3×5 min with binding buffer), the bound biotinylated ligand is detected with alkaline-phosphatase conjugated goat anti-biotin antibodies (1 μg/mL; 1 h, 37℃), using p-nitrophenyl phosphate as chromogen. Cyclo (-RGDfK) binding in the absence of competitor is defined as 100% signal; binding to blocked wells in the absence of integrin is defined as 0%. Concentrations of Cyclo (-RGDfK) required for 50% inhibition of signal (IC50 values) are estimated graphically.