PH-Sensitive Pro-Drug Based On Unimolecular Micelle

Amphiphilic polymeric micelles are popular as drug carriers to cure cancer.But they could been easily influenced by external circumstance and released the drug long before they arrive at the tumor tissue.We synthesized a novel unimolecular micelle polyamidoamine-graft-poly?methylacrylic hydrazide?-graft-poly[3-dimethyl?methacryloyloxyethyl?ammonium propanesulfonate????-PNHNH₂-PDMAPS?,which is constructed with dendrimer PAMAM as hydrophobic core,PDMAPS as hydrophilic shell.The pro-drug ???-Phyd-DOX-PDMAPS was obtained through the dynamic covalent reaction of the hydrazide of ???-PNHNH₂-PDMAPS and the carbanyl group of anti-cancer drug doxorubicin?DOX?.The PAMAM core made the polymer unimolecular micelle and were stable with the change of the external environment such as concentration,salt concentration and pH and so on.Zwitterionic polymer PDMAPS improved the biocompatibility of the unimolecular micelle,showed great ability to resist nonspecific protein adsorption and decreased the biotoxicity of the nanocarrier.DOX was bonded through hydrazone bond and could be released via pH stimulus.First,dendrimer PAMAM were prepared by alternative Michael addition and amidation reaction,then it was turned into macroinitiator ???-Br via the amidation reaction with 2-bromoisobutyryl bromide?BIBB?and triethylamine as acid-binding agent.The ATRP was taken place with ???-Br as macroinitiator,CuBr/bpy as catalyst system and MMA/DMAPS as monomer to obtain the polymer ???-PMMA-PDMAPS.After hydrazinolysis,the polymer became ???-PNHNH₂-PDMAPS.The structure of the polymer was confirmed by proton nuclear magnetic resonance spectroscopy?1H-NMR?and fourier transform-infrared spectroscopy?FT-IR?.Zetasizer was used to study the size change of unimolecular micelles in different time,concentration and salt concentration and the size change of unimolecular micelles mixed with protein.It turned out that unimolecular micelle ???-PNHNH₂-PDMAPS show great stability and ability to resist nonspecific protein adsorption.The pro-drug ???-Phyd-DOX-PDMAPS was obtained through the dynamic covalent reaction of ???-PNHNH₂-PDMAPS and DOX.The drug loading content?DLC?and drug loading efficiency?DLE?was determined by ultraviolet and visible spectrophotometer?UV-vis?and was significantly higher than that of the micelle without dynamic bond.The in vitro drug release of pro-drug was proceed under two pH conditions?pH=5.0 and pH=7.4?.While the drug could be released consistently and more than 80% DOX was released after 24 h at pH=5.0,only less than 10% DOX was released at pH=7.4,lower than that of DOX@ ???-PDMAPS.The biology experiments showed that unimolecular micelle had no cytotoxicity.The pro-drug could be endocytosed by HepG2 cells and could kill the cancer cell effectively.To sum up,the pro-drug ???-Phyd-DOX-PDMAPS are significative in the drug delivery field.