RGD peptides are a class of short peptides containing arginine-glycine-aspartic acid (Arg-Gly-Asp), （This sequence enables custom peptide synthesis in the laboratory））which are widely present in living organisms. Among them, extracellular matrix (ECM) and adhesion proteins in blood are the most abundant in the human body. Common proteins containing RGD sequence mainly include fibrin (fibrinogen, Fg), laminogen (vitronectin, Vn), collagen (collagen) and the like. RGD peptides act as recognition sites for the interaction of integrins and their ligands, mediating cell-ECM and cell-to-cell adhesion. At the same time, it has the function of signal transduction. At present, the research on RGD mainly focuses on the effect of RGD peptide on platelet function, the application of RGD peptide in antithrombotic drugs, the research of RGD peptide in the induction and regeneration of bone tissue, the research of RGD peptide in tumor metastasis and neovascularization, and Application in tumor targeted therapy.

Most linear RGD peptides have short half-lives in circulation, and their therapeutic efficacy and biological activity are not ideal. In order to obtain satisfactory antitumor effects, high doses of linear peptides containing RGD sequences are often required, which undoubtedly increases the cost of treatment and may lead to unnecessary adverse reactions. Therefore, increasing the stability of peptide compounds and improving the biological activity of peptides is the goal of transforming RGD peptides. Studies have shown that changing the main or partial structure of the peptide to a circular structure can increase the stability of linear peptides. The circular RGD polypeptide containing two disulfide bonds has the strongest inhibitory effect on tumor neovascular endothelial cells, which is 20 times that of the circular RGD polypeptide containing a single disulfide bond and 200 times that of the linear RGD polypeptide. Coupling RGD peptides with other compounds is also one of the ways to increase peptide stability. After the RGD sequence peptide is coupled with polyacids, anticancer drugs, PEG, PEU, EAA, CEMA and other conjugates, its anti-cell adhesion and anti-tumor metastasis capabilities are enhanced