Synthesis of amphiphilic copolymers containing zwitterionic sulfobetaine as pH and redox responsive drug carriers.

Amphiphilic poly(ɛ-caprolactone)-SS-poly(N,N-diethylaminoethyl methacrylate)-r-poly(N-(3-sulfopropyl)-N-methacrylate-N,N-diethylammonium-betaine) (PCL-SS-PDEASB) was designed and synthesized successfully. pH and redox dually responsive micelles were prepared based on the obtained copolymers, with zwitterionic sulfobetaines as hydrophilic shell, DEA as pH sensitive content and disulfide as redox responsive linkage. The micelle diameters were all less than 200 nm and the micelle diameter distributions were narrow. These micelles could be triggered by pH and redox condition. The drug release from the drug-loaded micelles displayed fastest under simultaneously acidic and reductive conditions. Results of in vitro cell toxicity evaluation showed that introduction of sulfobetaines could greatly decrease the toxicity of poly(ɛ-caprolactone)-SS-poly(N,N-diethylaminoethyl methacrylate) (PCL-SS-PDEA) micelles. DOX-loaded PCL-SS-PDEASB micelles showed higher efficiency to kill HeLa cells than DOX-loaded PCL-PDEASB micelles. Half inhibitory concentration (IC50) of DOX-loaded PCL-SS-PDEASB micelles decreased with the content of sulfobetaines increasing and was even closer to that of DOX·HCl. Thus, the pH and redox dually responsive biodegradable micelles generated by PCL-SS-PDEASB may be potential smart drug carriers for tumor targeted delivery.