Biocompatibility, drug release, and anti-tumor effect of pH-sensitive micelles prepared from poly(2-ethyl-2-oxazoline)-poly(DL-lactide) block copolymers

Various ratios PEOz-PDLLA diblock copolymers were synthesized through ring-opening polymerization of DL-lactide initiated by monohydroxyl terminated poly(2-ethyl-2-oxazoline) (PEOz-OH). The chemical composition and molar mass of the resulting copolymers were determined by using NMR and GPC. Spherical micelles with a diameter from 104 to 136 nm were obtained via self-assembly of PEOz-PDLLA in water, as evidenced by TEM and DLS. The CMC of copolymers was well below 0.01 mg/mL, and showed a decreasing trend with increase of PDLLA block length. A two-step procedure was applied to encapsulate curcumin taken as a hydrophobic model drug. Copolymers with longer PDLLA block exhibit enhanced drug loading capacity. In vitro drug release was carried out in phosphate buffered saline (PBS) at physiological and slightly acidic pH values. A pH-sensitive biphasic drug release behavior was detected with an initial burst release followed by slower prolonged release. Lower pH or shorter PDLLA block length leads to higher drug release rate because of faster degradation of micelles. Hemo- and cytocompatibility studies illustrated the excellent biocompatibility of PEOz-PDLLA micelles. MTT assay showed a significant cytotoxicity of curcumin-loaded micelles against A549 lung cancer cells. Therefore, it can be inferred that PEOz-PDLLA block copolymers with outstanding biocompatibility, controllable drug loading performance, and prolonged drug release present a good potential as nano-carrier of hydrophobic drugs.