Preparation and characterization of RGD tumour-homing-peptide-modified plasminogen K5

Plasminogen K5 (kringle 5) has strong inhibitory effects on endothelial-cell proliferation and migration. It was reported that K5 can reduce tumour neovascularization, resulting in clinically relevant antitumour effects. To determine whether addition of a tumour-targeting peptide could improve the tumour homing and antitumour activities of K5, we genetically modified K5 with an RGD (Arg-Gly-Asp) motif, which is a ligand with high affinity for αvβ₃ and αvβ₅ integrins. The fusion protein RGD-K5 was expressed in the Pichia pastoris system and the biological activity of RGD-K5 was assessed in vitro and in vivo. The results showed that the RGD-K5 exhibited a more potent effect of inhibiting endothelial cell proliferation and migration compared with that of traditional K5. RGD-K5 also displayed stronger anti-angiogenic activity in a CAM (chick chorioallantoic membrane) assay. Furthermore, RGD-K5 also showed stronger anti-angiogenic and antitumour effects in B16F10 melanoma-bearing mice compared with traditional K5. In conclusion, the biological activity of K5 can be further improved by the addition of a tumour-homing peptide, and the RGD-K5 may prove to be a promising novel candidate for cancer therapy.