Polymeric micelles of poly(2-ethyl-2-oxazoline)-block-poly(ε-caprolactone) copolymer as a carrier for paclitaxel

Polymeric micelles based on amphiphilic block copolymers of poly(2-ethyl-2-oxazoline) (PEtOz) and poly(epsilon-caprolactone) (PCL) were prepared in an aqueous phase. The loading of paclitaxel into PEtOz-PCL micelles was confirmed by H-1-NMR spectra. Paclitaxel was efficiently loaded into PEtOz-PCL micelles using dialysis method, and the loading content of paclitaxel in micelles was in the range 0.5-7.6 wt.% depending on the block composition of block copolymers, organic solvent used in the dialysis, and feed weight ratio of paclitaxel to block copolymer. The higher the content of hydrophobic block in the block copolymers, the higher the loading efficiency of micelles for paclitaxel. When acetonitrile was used as solvent, a higher drug loading efficiency was obtained than with THF. The loading efficiency decreased with increasing feed weight ratio of paclitaxel to block copolymer from 0.1:1 to 0.2:1. The hydrodynamic diameters of paclitaxel-loaded micelles were in the range 18.3-23.4 nm with narrow size distribution. The hemolysis test of PEtOz-PCL performed in vitro indicated that the toxicity of PEtOz-PCLs to lipid membrane was not significant compared with Tween 80, and was comparable to that observed with Cremophore EL. The proliferation inhibition activity of paclitaxel-loaded micelles for KB human epidermoid carcinoma cells was also evaluated in vitro. Paclitaxel-entrapped polymeric micelles exhibited comparable activity to that observed with Cremophore EL-based paclitaxel formulations in inhibiting the growth of KB cells. (C) 2003 Elsevier Science B.V. All rights reserved.