Hybrid Polymeric Nanomaterials for siRNA Delivery and Imaging

A combined nanomaterials‐based approach for simultaneous therapy and molecular imaging has powerful potential for efficient treatment and monitoring the prognosis of incurable diseases such as malignant tumors or degenerative diseases. Recent developments of hybrid polymeric nanomaterials for siRNA delivery and imaging are highlighted. A particular focus is on various conjugation and formulation strategies of how to incorporate siRNA and imaging agents onto the surface of functionally active polymer‐coated inorganic nanomaterials such as iron oxide, gold, and quantum‐dot nanoparticles for theranostic applications. These multifunctional nanocarriers may allow real‐time tracking of siRNA as well as visualization of its therapeutic effects in vitro and in vivo.

     

Adsorption of DNA onto anionic lipid surfaces

Currently self-assembled DNA delivery systems composed of DNA multivalent cations and anionic lipids are considered to be promising tools for gene therapy. These systems become an alternative to traditional cationic lipid–DNA complexes because of their low cytotoxicity lipids. However, currently these nonviral gene delivery methods exhibit low transfection efficiencies. This feature is in large part due to the poorly understood DNA complexation mechanisms at the molecular level. It is well-known that the adsorption of DNA onto like charged lipid surfaces requires the presence of multivalent cations that act as bridges between DNA and anionic lipids. Unfortunately, the molecular mechanisms behind such adsorption phenomenon still remain unclear. Accordingly a historical background of experimental evidence related to adsorption and complexation of DNA onto anionic lipid surfaces mediated by different multivalent cations is firstly reviewed. Next, recent experiments aimed to characterise the interfacial adsorption of DNA onto a model anionic phospholipid monolayer mediated by Ca^2 + (including AFM images) are discussed. Afterwards, modelling studies of DNA adsorption onto charged surfaces are summarised before presenting preliminary results obtained from both CG and all-atomic MD computer simulations. Our results allow us to establish the optimal conditions for cation-mediated adsorption of DNA onto negatively charged surfaces. Moreover, atomistic simulations provide an excellent framework to understand the interaction between DNA and anionic lipids in the presence of divalent cations. Accordingly,our simulation results in conjunction go beyond the macroscopic picture in which DNA is stuck to anionic membranes by using multivalent cations that form glue layers between them. Structural aspects of the DNA adsorption and molecular binding between the different charged groups from DNA and lipids in the presenceof divalent cations are reported in the last part of the study. Although this research work is far from biomedical applications, we truly believe that scientific advances in this line will assist, at least in part, in the rationaldesign and development of optimal carrier systems for genes and applicable to other drugs.     

A Biodegradable Polymersome Containing Bcl‐xL siRNA and Doxorubicin as a Dual Delivery Vehicle for a Synergistic Anticancer Effect

Combined cancer treatment via co‐delivery of siRNAs and an anticancer drug can be a promising strategy due to the synergistic effect of simultaneously minimizing gene/drug administration. In this study, Bcl‐xL siRNA and doxorubicin (DOX) are encapsulated into designed methoxy‐poly(ethylene glycol)‐block‐poly(D ,L ‐lactic acid) (mPEG‐b‐PLA) block copolymer polymersomes (PSomes). A study of the cytotoxicity of Bcl‐xL siRNA and DOX co‐encapsulated PSomes (CPSomes) shows more inhibited proliferation of MKN‐45 and MKN‐28 human gastric cancer cell lines than only gene‐ and drug‐loaded ones. Consequently, these results demonstrate that co‐delivery of genes and drugs using PSomes results in a synergistic efficacy and indicates the potential of PSomes as efficient nanocarriers for combined cancer therapy.

     

Preparation of poly(glutamic acid) shielding micelles self-assembled from polylysine-b-polyphenylalanine for gene and drug codelivery

A novel amphiphilic cationic block copolymer polylysine-b-polyphenylalanine(PLL-b-PPhe) was synthesized and self-assembled into micelles in aqueous solution,then shielded with poly(glutamic acid)(marked as PG/PLL-b-PPhe) to codeliver gene and drug for combination cancer therapy.Here,doxorubicin(DOX) was selected to be loaded into PLL-b-PPhe micelles and the drug loading efficiency was 8.0%.The drug release studies revealed that the PLL-b-PPhe micelles were pH sensitive and the released DOX could reach to 53.0%,65.0%,72.0% at pH 7.4,6.8 and 5.0,respectively.In order to reduce positive charge and cytotoxicity of PLL-b-PPhe micelles,PG was used as shelding,simultaneously condensed with Bcl2 siRNA to form gene carrier system.Compared with PEI,PG/PLL-b-PPhe had excellent gene transfection efficiency,especially when the molar ratio of PLL to PPhe was 30:60 and the mixed mass ratio of PLL-b-PPhe to gene was 5:1.More importantly,DOX and Bcl2 siRNA gene codelivery system displayed remarkable cytotoxicity against B16 F10 cells.Confocal laser scanning microscopy(CLSM) and flow cytometry were used to characterize endocytosis of the codelivery system,and confirmed that both DOX and Bcl2 siRNA had been endocytosed into B16 F10 cells.The above results indicated that gene and drug codelivery was a promising strategy in future cancer therapy.