Amphiphilic Poly(ethylene glycol)-Cholesterol Conjugate: Stable Micellar Formulation for Efficient Loading and Effective Intracellular Delivery of Curcumin

A biodegradable and biocompatible micellar-based drug delivery system was developed using amphiphilic methoxy-poly(ethylene glycol)-cholesterol (C1) and poly(ethylene glycol)-S-S-cholesterol (C2) conjugates and applied to the tumoral release of the water-insoluble drug curcumin. These synthesized surfactants C1 and C2 were found to form stable micelles (CMC ∼ 6 μM) and an average hydrodynamic size of around 20-25 nm. The curcumin-encapsulated C1 micelle was formulated by a solvent evaporation method. A very high drug encapsulation efficiency (EE) of ∼88% and a drug loading (DL) capacity of ∼9% were determined for both the micelles. From the reduced rate of curcumin degradation and differential scanning calorimetry (DSC) analysis, the stability of the curcumin-loaded C1 micelle was found to be higher than that of the unloaded micelle, which confirmed a more compact structural arrangement in the presence of hydrophobic curcumin. A pH-sensitive release of curcumin (faster release with decrease in pH) was observed for the curcumin-loaded C1 micelle, attributed to the diffusion and relaxation/erosion of micellar aggregates. To achieve reduction environment-sensitive drug release, a disulfide (S-S) chemical linkage-incorporated mPEG-cholesterol conjugate (C2) was synthesized, which was found to show glutathione-responsive faster release of curcumin. The in vitro experiments carried out in SCC9 oral cancer cell lines showed that the blank C1 and C2 micelles were noncytotoxic at lower concentrations (<50 μM), while curcumin-loaded C1 and C2 micelles inhibited the proliferation and promoted the apoptosis. An increased in vitro cytotoxicity was observed for curcumin-loaded micelles compared to that of curcumin itself, demonstrating a better cell penetration efficacy of the micelle. These results were further supplemented by the in vivo anticancer analysis of the curcumin-loaded C1 and C2 micellar formulations using the mice xenograft model. Notably, curcumin-loaded C2 micelles showed a significantly stronger apoptotic effect in xenograft mice compared to curcumin-loaded C1 micelles, indicating the GSH environment-sensitive drug release and improved bioavailability. In conclusion, the mPEG-cholesterol C1 and C2 micellar system with the advantages of small size, high encapsulation efficiency, high drug loading, simple preparing technique, biocompatibility, and good in vitro and in vivo performance may have the potential to be used as a drug carrier for sustained and stimuli-responsive release of the hydrophobic drug curcumin.