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Modern subunit vaccines with purified or recombinant antigens are important alternatives to the traditional vaccines. However, there remains a big challenge to elicit potent antibody production and CD8 T cell response. Nanoparticle-based antigen delivery systems have emerged as an innovative strategy to improve the efficacy of subunit vaccines. The present study reported self-assembled cationic micelles based on poly(ethylene glycol)-b-poly(L-lysine)-b-poly(L-leucine) (PEG-PLL-PLLeu) hybrid polypeptides as a simple and potent vaccine delivery system. The results showed that the PEG-PLL-PLLeu micelles spontaneously encapsulated OVA antigens with great loading capacity (LC=55%) and stability. More importantly, the polypeptide micelle formulations robustly enhanced vaccine-induced antibody production by 70-90 fold, which could be due to their capability of inducing dendritic cell maturation, enhancing antigen uptake and presentation, as well as promoting germinal center formation. Furthermore, the polypeptide micelles could simultaneously encapsulate OVA and polyriboinosinic: polyribocytidylic acid (PIC), a TLR3 agonist, to synergistically augment tumor specific cytotoxic-T-lymphocyte (CTL) response. Hence, the polypeptide micelle-based antigen delivery system could be a robust adjuvant to enhance vaccine-induced immune responses., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Combination of two or more therapeutic strategies with different mechanisms can cooperatively impede tumor growth. Co-delivery of chemotherapeutic drug and small interfering RNA (siRNA) within a single nanoparticle (NP) provides a rational strategy for combined cancer therapy. Here, we prepared polypeptide micelle nanoparticles (NPs) of a triblock copolymer poly(ethylene glycol)-b-poly(l-lysine)-b-poly(l-leucine) (PEG-PLL-PLLeu) to systemically codeliver docetaxel (DTX) and siRNA-Bcl-2 for an effective drug/gene vector. The hydrophobic PLLeu core entrapped with anticancer drugs, while the PLL polypeptide cationic backbone allowed for electrostatic interaction with the negatively charged siRNA. The resulting micelle NP exhibited very stable, good biocompatible and excellent passive targeted properties. The micelle complexes with siRNA-Bcl-2 effectively knocked down the expression of Bcl-2 mRNA and protein. Moreover, the co-delivery system of DTX and siRNA-Bcl-2 (DTX-siRNA-NPs) obviously down-regulation of the anti-apoptotic Bcl-2 gene and enhanced antitumor activity with a smaller dose of DTX, resulting the significantly inhibited tumor growth of MCF-7 xenograft murine model as compared to the individual siRNA and only DTX treatments. Our results demonstrated well-defined PEG-PLL-PLLeu polypeptide cationic micelles with the excellent synergistic effect of DTX and siRNA-Bcl-2 in combined cancer therapy., (Crown Copyright © 2013. Published by Elsevier Ltd. All rights reserved.)

Developing safe and effective nonviral gene vector is highly crucial for successful gene therapy. In the present study, we designed a series of biodegradable micelles based on hybrid polypeptide copolymers of poly(ethylene glycol)-b-poly(l-lysine)-b-poly(l-leucine) (PEG-PLL-PLLeu) for efficient gene delivery. A group of amphiphilic PEG-PLL-PLLeu hybrid polypeptide copolymers were synthesized by ring-opening polymerization of N-carboxyanhydride, and the chemical structure of each copolymer was characterized by (1)H NMR and FT-IR spectroscopy measurement. The PEG-PLL-PLLeu micelles were positively charged with tunable sizes ranging from 40 to 90 nm depending on the length of PLL and PLLeu segment. Compared with PEG-PLL copolymers, PEG-PLL-PLLeu micelles demonstrated significantly higher transfection efficiency and less cytotoxicity. Furthermore, the transfection efficiency and biocompatibility of the micelles can be simultaneously improved by tuning the length of PLL and PLLeu segments. The transfection efficiency of PEG-PLL-PLLeu micelles in vivo was two to three times higher than that of PEI(25k), which was attributable to their capability of promoting DNA condensation and cell internalization as well as successful lysosome escape. Hence well-defined PEG-PLL-PLLeu micelles would serve as highly effective nonviral vectors for in vivo gene delivery.