In this work, PEG chains were grafted to PAMAM dendrimer G4

In this work, PEG chains were grafted to PAMAM dendrimer G4.0 via bis-aryl hydrazone linkages. cells, this new vector has been shown to be capable of both transfecting more cells and inducing higher ERK6 gene expression than the parent dendrimer. This work demonstrates that the use of the BAH linkage in coupling of PEG to the dendrimer helps maintain or increase the buffering capacity of the functionalized dendrimer and results in enhanced transfection. Keywords:bis-aryl hydrazone linkage, buffering capacity, dendrimer, gene delivery, polyethylene glycol, PEGylation == 1. Introduction == Synthetic non-viral vectors, particularly cationic polymers, have attracted considerable attention for gene transfer as they can potentially avoid toxicity and immunogenicity, provide high DNA transporting capacity, achieve prolonged gene expression, and allow low-cost manufacturing.15However, the lack of adequate functions to overcome multiple extra- and intra-cellular barriers is the major reason why synthetic vectors are far less efficient than viral vectors and have limited clinical power to date. The evolving understanding of potential barriers to gene delivery, for example polyplex unpackaging,6,7has led to development of a number of synthetic vectors having various functionalities to improve gene transfection efficiency. Developing multifunctional non-viral vectors has become an important goal in order to endow them with transfection efficiency approaching that of viral vectors. Amine-terminated polyamidoamine (PAMAM) dendrimers appear to be an ideal class of building blocks for developing multifunctional vectors, not only because of their well-defined highly branched structures and a number of surface groups available for assembly of many different types of functional entities but because of a number of inherent properties desired for gene RIPK1-IN-3 delivery.818Polycationic dendrimers can stably form polyplexes with nucleic acids and facilitate their efficient internalization, RIPK1-IN-3 mainly through endocytosis. The endocytic pathway begins near the physiological pH of 7.4, drops to a lower pH (5.56.0) in endosomes, and methods pH 5.0 in lysosomes.19Owing to the large buffering capacity conferred by a number of primary surface amines and tertiary amines inside RIPK1-IN-3 the core, dendrimers can act as a proton-sponge to facilitate the escape of polyplexes from endosomes or lysosomes in an acidic environment.4 In addition to the extensive use of commercially available PAMAM dendrimers, a number of new or engineered PAMAM dendritic structures, such as PEGylated PAMAM dendrimers, reducible hyperbranched poly(amidoamine)s with disulfide bonds,20polycationic PAMAM esters with grafted arginines,21and PAMAM dendrimers with a new core,22,23have been developed as new RIPK1-IN-3 vectors for enhanced gene transfection. PAMAM dendrimers with polyethylene glycol (PEG) arms, namely PEGylated PAMAM dendrimers, are a group of dendrimer derivatives that have important biomedical and pharmaceutical applications.24The incorporation of PEG chains into the dendritic structure can yield a number of biologically and pharmacokinetically desirable properties such as improved biocompatibility, reduced immunogenicity, prolonged half-life, increased water solubility, and enhanced structural stability, as reported in previous work.2531The use of PEGylated PAMAM dendrimers for gene transfection has been exhibited. Luo et al. conjugated PEG to PAMAM dendrimer generation 5 (G5.0) via a stable amide linkage and observed its high efficiency in transfecting Chinese hamster ovarian cells.32Recent work by Qi et al. revealed that the degree of PEGylation is an important variable affecting the transfection efficiency of PEGylated PAMAM dendrimers.33PAMAM-block-PEG-block-PAMAM34and transferrin-coupled PAMAM-PEG25have also been developed to enhance transfection efficiency and specificity, respectively. Because of the occupancy of the primary surface amine groups, surface modification of amine-terminated dendrimers by PEG potentially impairs the buffering capacity of the altered dendrimer, which, in turn, may result in unsatisfactory transfection efficiency.4To make sure high transfection efficiency, high weight ratios of vector to plasmid are therefore needed, for example 2501200:1 (w:w) for PAMAM dendrimer G5.0 conjugated with 14 PEG chains (MW=3400 gmol1) through amide bonds.32Although RIPK1-IN-3 a viable approach is to minimize the degree of dendrimer surface modification, this strategy becomes questionable, particularly when a high degree of PEGylation is needed in order to keep the vector nontoxic for a long term and/or when the assembly of more functional groups is necessary for making.