α-Amylase- and Redox-Responsive Nanoparticles for Tumor-Targeted Drug Delivery

Paclitaxel (PTX) is an effective antineoplastic agent and shows potent antitumor activity against a wide spectrum of cancers. Yet, the wide clinical use of PTX is limited by its poor aqueous solubility and the side effects associated with its current therapeutic formulation. To tackle these obstacles, we report, for the first time, α-amylase- and redox-responsive nanoparticles based on hydroxyethyl starch (HES) for the tumor-targeted delivery of PTX. PTX is conjugated onto HES by a redox-sensitive disulfide bond to form HES-SS-PTX, which was confirmed by results from NMR, high-performance liquid chromatography-mass spectrometry, and Fourier transform infrared spectrometry. The HES-SS-PTX conjugates assemble into stable and monodispersed nanoparticles (NPs), as characterized with Dynamic light scattering, transmission electron microscopy, and atomic force microscopy. In blood, α-amylase will degrade the HES shell and thus decrease the size of the HES-SS-PTX NPs, facilitating NP extravasation and penetration into the tumor. A pharmacokinetic study demonstrated that the HES-SS-PTX NPs have a longer half-life than that of the commercial PTX formulation (Taxol). As a consequence, HES-SS-PTX NPs accumulate more in the tumor compared with the extent of Taxol, as shown in an in vivo imaging study. Under reductive conditions, the HES-SS-PTX NPs could disassemble quickly as evidenced by their triggered collapse, burst drug release, and enhanced cytotoxicity against 4T1 tumor cells in the presence of a reducing agent. Collectively, the HES-SS-PTX NPs show improved in vivo antitumor efficacy (63.6 vs 52.4%) and reduced toxicity in 4T1 tumor-bearing mice compared with those of Taxol. These results highlight the advantages of HES-based α-amylase- and redox-responsive NPs, showing their great clinical translation potential for cancer chemotherapy.