Design, activity determination and 99mTc labeling of cyclic RGD dimer for targeting integrin αVβ3

This paper was to design a cyclic RGD (Arg-Gly-Asp) peptide tumor inhibitor with high affinity to integrin α_vβ₃ receptor by molecular docking technique, determinate the characteristics of the cRGD dimer in vitro and prepare ^99mTc-cRGD dimer tumor probe. cRGD molecule library was built and an optimal structure of cRGD peptide with the best score that was Cys-Arg-Gly-Asp-(D)Ser-Cys was screened out using DOCK procedure of V-life software. A dimer containing two cRGD peptides linked by Tyr-(D) Ser-Lys-(D)Ser-Ser and with a side chain Gly-Gly-(D)Ala-Gly on lysine residue was synthesisized and ^99mTc-cRGD dimer was prepared. The radiolabeled efficiency, stability, water-soluble and affinity of cRGD dimer in vitro were evaluated. Under the reaction condition of room temperature, 1g/L SnCl₂·2H₂O and the 30 min of reaction time, ^99mTc labeling efficiency reached (87.42±3.21) % With Sephadex G10 purification, the radiochemical purity was no less than 95%. In both mediums of saline and fresh human serum, the radiochemical purity kept high stability at room temperature and 37 °C. The equilibrium dissociation constant (Kd) to U87MG human glioma cells was determined and the octanol-water partition coefficient was mearsured. The Kd value is (3.867+0.052)×10^-9 mol/L and octanol-water partition coefficient log P value is -1.96±0.01. This in vitro study provides evidence that cRGD peptide screened by computer-aided drug design (CADD) system can bind to integrin αvβ3 with high affinity, and may be a potential candidate radiotracer for integrin αvβ3-positive tumors imaging.