The preparation of shikonin-based nanomedicine with robust GSH-responsiveness

Shikonin (SHK), an active naphthoquinone pigment isolated from the root of Chinese herbal medicine has been proven to have a significant therapeutic effect on breast cancer. However, the poor water solubility as well as the lack of tumor targeting restrict the practice application of SHK molecules as chemotherapeutic agents. Here, SHK drugs were chemically conjugated to polyethylene glycol (PEG) molecules via a disulfide bond (referred to as SHK-SS-PEG) through a facile one-step strategy. The conjugates exhibited an excellent water solubility of 12.96 mM, which is ca. 7807 times as high as that of pure SHK drugs. Noteworthily, the conjugates can self-assemble into spherical micelles with an average particle size of 106 nm, facilitating in vivo delivery as well as the accumulation in tumor tissues based on the enhanced permeability and retention (EPR) effect. Moreover, the disulfide bond enables rapid cleavage of micelles and efficient release of SHK molecules from the conjugates in response to reduced Glutathione (GSH) overexpressed within tumor cells. Thanks to the GSH-responsiveness release of SHK, the conjugate-based micelles (containing 6 μM SHK) resulted in the cell killing rate of 73 % for the MCF-7 breast cancer cells after 48 h incubation, which is 45 % higher than that for the HUVEC normal cells. All these collective beneficial properties make the SHK-SS-PEG conjugate a promising candidate for the treatment of many types of cancers.