Synthesis, structural and in vitro studies of well-dispersed monomethoxy-poly(ethylene glycol)-honokiol conjugate micelles.

Honokiol, an active principle extracted from Magnolia officinalis, has great potential as a cancer treatment. However, its poor water solubility greatly hampers its delivery to the tumor sites at an effective concentration. In this study, an amphiphilic polymer-drug conjugate was successfully prepared by condensation of low molecular weight monomethoxy-poly(ethylene glycol) (MPEG)-2000 with honokiol (HK) through an ester linkage to increase the hydrophilicity of honokiol. The MPEG-honokiol (MPEG-HK) conjugate prepared formed nano-sized micelles, with a mean particle size of less than 20 nm (MPEG-HK, 360 µg ml(-1)) in water, which could be well dispersed in water. The nanoparticles obtained were characterized by particle size distribution, morphology and zeta potential. The stability and hydrolysis profile of the polymeric pro-drug in phosphate-buffered saline (PBS) and plasma were also studied and the results showed that only 20% of the conjugated honokiol was released in 2.0 h in beagle dog plasma, while in PBS the time required to reach 20% of honokiol release was >200 h. Meanwhile, the inhibitory activity of the honokiol conjugate was found to be retained in vitro against LL/2 cell lines with an IC50 value of 10.7 µg ml(-1). These results suggest that the polymer-drug conjugate provides a potential new approach to hydrophobic drugs, such as honokiol, in formulation design.