The development of stimuli-responsive drug carrier systems enabling to deliver high doses of anti-cancer drugs to tumor tissues is still urgently needed. In this study, we report the preparation of reduction-responsive methoxypolyethylene glycol-block-(poly(L-lysine)-co-poly(L-tyrosine)) (mPEG-b-(PLL-co-PLY)) nanoparticles (NPs) exhibiting sizes smaller than 100 nm and high drug loading content (DLC) of doxorubicin (DOX) by selecting the Lys and Tyr residues as the polypeptide building blocks. The disulfide-cross-linked mPEG-b-(PLL-co-PLY) assemblies with sizes can be tuned by varying the polypeptide composition followed by subsequent disulfide-cross-linking. Cytotoxicity assays showed that the Dox-loaded NPs exhibited efficient cell internalization and proliferation inhibition toward cancer cells, whereas the copolymers exhibited low hemolysis to human red blood cells and excellent biocompatibility to both normal and cancer cells. The enhanced internalization and cytotoxicity of DOX-NPs can be possible due to their small size and their reduction-responsive property. Anticancer studies using C57BL/6 mice bearing LLC tumor model showed that the DOX-loaded NPs significantly suppressed tumor growth and prolonged the survival of tumor-bearing mice without obvious body weight loss and damage to major organs. This approach provides a platform for developing stimuli-responsive, polypeptide-based drug delivery systems with high DLC for cancer treatment.
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