More than 20 years ago, FRANKEL et al. extracted the trans-activating transcriptional activator (TAT) protein from human immunodeficiency virus 1 and found that it has the activity of penetrating the cell membrane. After that, a large number of short peptides with similar activities were found. , These short peptides are called cell penetrating peptides (cell penetrating peptides, CPP), also called protein transduction domain. Compared with electroporation, magnetic transfection, lipofection and viral vectors, cell-penetrating peptides have been obtained due to their advantages of high penetration efficiency, low cytotoxicity, and the ability to carry various biologically active molecules (including nanoparticles). Widespread attention by researchers

Cell-penetrating peptides Peptides with specific membrane-penetrating functions can be synthesized in a peptide company by custom peptide synthesis. There have been debates on the specific membrane-penetrating mechanism of cell-penetrating peptides, and it is generally believed that there are two main ways of penetrating the membrane: endocytosis and direct transmembrane without endocytosis. At present, most experimental studies support endocytosis to penetrate the membrane, but the cargo molecules (CPP and bioactive molecules) that enter the cell through endocytosis are bound in vesicles (endosomes) and cannot function, and are long-term Trapped in vesicles, the acidic environment of the vesicles and lysosomes and the various enzymes they contain can further inactivate or degrade cargo molecules. Therefore, vesicle binding after cell-penetrating peptides enter cells has become a major problem in the application of cell-penetrating peptides.

The main solution to this problem is to rupture the endocytosed vesicles to release the cargo molecules by appropriate methods, such as by adding additional vesicle leakage-promoting agents or modifying the penetrating peptides with disrupted vesicle membranes structure, etc. The vesicle leakage-promoting reagents discovered so far include pyrene butyric acid, polycationic peptide dffAT, etc. Co-incubating oligomeric arginine penetrating peptides with them shows that all of them can improve the endosomal escape rate of penetrating peptides at the cellular level . distribution in the cytoplasm, but also significantly increased the toxicity of cell-penetrating peptides. In addition, some researchers have used the strategy of protonation of the imidazole group of histidine in an acidic environment to promote the swelling and rupture of endocytic vesicles to increase the endosomal escape of cell-penetrating peptides. In addition to the above strategies, some researchers have fused CPP with liposomes, and used liposomes to fuse with endocytic vesicle membranes under acidic conditions to promote the endosomal escape of cargo molecules.