Effect of RGD-4C position is more important than disulfide bonds on antiangiogenic activity of RGD-4C modified endostatin derived synthetic polypeptide.

ES-2 (IVRRADRAAVP), an endostatin-derived synthetic polypeptide, contains the amino acids 50-60 of endostatin from its N terminus, and it had no inhibitory effects on tumor growth in vivo. In order to increase the targeted delivery of ES-2 to tumors and further enhance the activity, the polypeptide RGD-4C (ACDCRGDCFC) was introduced into ES-2, and the effects of RGD-4C position and RGD-4C disulfide bonds on polypeptides activity were investigated. When RGD-4C polypeptides (with or without disulfide bonds) were introduced to the N-terminals of synthesized ES-2, the modified ES-2 showed significant antitumor activity in vivo. Cell proliferation and chicken chorioallantoic membrane (CAM) assay results showed that disulfide bonds had no significant effects on RGD-4C-modified ES-2 antiangiogenic activity. Furthermore, the target of modified peptides was integrin alpha5beta1, rather than integrin alphavbeta3 as previous studies mentioned.