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 (<b>C1)</b> and poly(ethylene glycol)-S-S-cholesterol (<b>C2</b>) conjugates and applied to the tumoral release of the water-insoluble drug curcumin. These synthesized surfactants <b>C1</b> and <b>C2</b> 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 <b>C1</b> 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 <b>C1</b> 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 (<b>C2</b>) was synthesized, which was found to show glutathione-responsive faster release of curcumin. The <i>in vitro</i> experiments carried out in SCC9 oral cancer cell lines showed that the blank <b>C1</b> and <b>C2</b> micelles were noncytotoxic at lower concentrations (<50 μM), while curcumin-loaded <b>C1</b> and <b>C2</b> micelles inhibited the proliferation and promoted the apoptosis. An increased <i>in vitro</i> 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 <i>in vivo</i> anticancer analysis of the curcumin-loaded <b>C1</b> and <b>C2</b> micellar formulations using the mice xenograft model. Notably, curcumin-loaded <b>C2</b> micelles showed a significantly stronger apoptotic effect in xenograft mice compared to curcumin-loaded <b>C1</b> micelles, indicating the GSH environment-sensitive drug release and improved bioavailability. In conclusion, the mPEG-cholesterol <b>C1</b> and <b>C2</b> micellar system with the advantages of small size, high encapsulation efficiency, high drug loading, simple preparing technique, biocompatibility, and good <i>in vitro</i> and <i>in vivo</i> performance may have the potential to be used as a drug carrier for sustained and stimuli-responsive release of the hydrophobic drug curcumin.