Acid‐Labile Copolymer Micelles Cross‐Linked by a Twin Ortho Ester Cross‐Linking Agent: Synthesis, Characterization, and Evaluation

Abstract

In this work, a series of poly(ethylene glycol)‐block‐poly(N‐succinimidyl methacrylate) (PEG‐b‐PNSM) micelles with different length of PNSM are prepared by self‐assembly in phosphate buffer. In situ cross‐linked micelles (CLM) with high stability at neutral pH are obtained by adding a pH‐sensitive cross‐linker bearing two five‐membered ortho ester rings, 2‐{4‐[2‐(2‐amino‐ethoxy)‐[1,3]dioxolan‐4‐ylmethoxymethyl]‐[1,3]dioxolan‐2‐yloxy}‐thylamine. Nile Red as a model drug is easily loaded into CLM, and the release rate accelerate at acidic environments (pH 5). Cytotoxicity of PEG‐b‐PNSM and CLM against NIH3T3 cells is determined and favorable biocompatibility is possessed. Confocal laser scanning microscopy study shows that Nile Red‐loaded CLM has excellent cellular uptake by MCF‐7 cells. Paclitaxel (PTX) is successfully encapsulated into the cross‐linked micelles. In vitro cytotoxicity of free PTX, and PTX‐loaded CLM causes almost the same potency in killing MCF‐7 cells. These results suggest that cross‐linked micelles can be a potential vehicle for delivering hydrophobic anticancer drugs to tumors.