Recent development of nonviral gene delivery systems with virus-like structures and mechanisms

Polyplex micelles prepared from ω-cholesteryl PEG-polycation block copolymers for systemic gene delivery

Polyplex micelles formed with plasmid DNA (pDNA) and poly(ethylene glycol) (PEG)-block-poly{N-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} [PAsp(DET)] exhibit effective endosomal escaping properties based on di-protonation of diamine side chains with decreasing pH, which improves their transfection efficiency and thus are promising candidates for local in vivo gene transfer. Here, PEG-PAsp(DET) polyplex micelles were further improved as in vivo systemic vectors by introduction of cholesterol (Chole) into the ω-terminus of PEG-PAsp(DET) to obtain PEG-PAsp(DET)-Chole. Introduction of the cholesterol resulted in enhanced association of block copolymers with pDNA, which led to increased stability in proteinous medium and also in the blood stream after systemic injection compared to PEG-PAsp(DET) micelles. The synergistic effect between enhanced polymer association with pDNA and increased micelle stability of PEG-PAsp(DET)-Chole polyplex micelles led to high in vitro gene transfer even at relatively low concentrations, due to efficient cellular uptake and effective endosomal escape of block copolymers and pDNA. Finally, PEG-PAsp(DET)-Chole micelles achieved significant suppression of tumor growth following intravenous injection into mice bearing a subcutaneous pancreatic tumor using therapeutic pDNA encoding an anti-angiogenic protein. These results suggest that PEG-PAsp(DET)-Chole micelles can be effective systemic gene vectors for treatment of solid tumors.

AAV's anatomy: roadmap for optimizing vectors for translational success

Adeno-Associated Virus based vectors (rAAV) are advantageous for human gene therapy due to low inflammatory responses, lack of toxicity, natural persistence, and ability to transencapsidate the genome allowing large variations in vector biology and tropism. Over sixty clinical trials have been conducted using rAAV serotype 2 for gene delivery with a number demonstrating success in immunoprivileged sites, including the retina and the CNS. Furthermore, an increasing number of trials have been initiated utilizing other serotypes of AAV to exploit vector tropism, trafficking, and expression efficiency. While these trials have demonstrated success in safety with emerging success in clinical outcomes, one benefit has been identification of issues associated with vector administration in humans (e.g. the role of pre-existing antibody responses, loss of transgene expression in non-immunoprivileged sites, and low transgene expression levels). For these reasons, several strategies are being used to optimize rAAV vectors, ranging from addition of exogenous agents for immune evasion to optimization of the transgene cassette for enhanced therapeutic output. By far, the vast majority of approaches have focused on genetic manipulation of the viral capsid. These methods include rational mutagenesis, engineering of targeting peptides, generation of chimeric particles, library and directed evolution approaches, as well as immune evasion modifications. Overall, these modifications have created a new repertoire of AAV vectors with improved targeting, transgene expression, and immune evasion. Continued work in these areas should synergize strategies to improve capsids and transgene cassettes that will eventually lead to optimized vectors ideally suited for translational success.

Nonviral vectors for the delivery of small interfering RNAs to the CNS

While efficient methods for cell line transfection are well described, for primary neurons a high-yield method different from those relying on viral vectors is lacking. Viral vector-based primary neuronal infection has several drawbacks, including complexity of vector preparation, safety concerns and the generation of immune and inflammatory responses, when used in vivo. This article will cover the different approaches that are being used to efficiently deliver genetic material (both DNA and small interfering RNA) to neuronal tissue using nonviral vectors, including the use of cationic lipids, polyethylenimine derivatives, dendrimers, carbon nanotubes and the combination of carbon-made nanoparticles with dendrimers. The effectiveness, both in vivo and in vitro, of the different methods to deliver genetic material to neural tissue is discussed.

Physicochemical and biological properties of self-assembled antisense/poly(amidoamine) dendrimer nanoparticles: the effect of dendrimer generation and charge ratio

To gain a deeper understanding of the physicochemical phenomenon of self-assembled nanoparticles of different generations and ratios of poly (amidoamine) dendrimer (PAMAM) dendrimer and a short-stranded DNA (antisense oligonucleotide), multiple methods were used to characterize these nanoparticles including photon correlation spectroscopy (PCS); zeta potential measurement; and atomic force microscopy (AFM). PCS and AFM results revealed that, in contrast to larger molecules of DNA, smaller molecules produce more heterodisperse and large nanoparticles when they are condensed with a cationic dendrimer. AFM images also showed that such nanoparticles were spherical. The stability of the antisense content of the nanoparticles was investigated over different charge ratios using polyacrylamide gel electrophoresis. It was clear from such analyses that much more than charge neutrality point was required to obtain stable nanoparticles. For cell uptake, self-assembled nanoparticles were prepared with PAMAM G5 and 5’-FITC labeled antisense and the uptake experiment was carried out in T47D cell culture. This investigation also shows that the cytotoxicity of the nanoparticles was dependent upon the generation and charge ratio of the PAMAM dendrimer, and the antisense concentration had no significant effect on the cytotoxicity.

Thermo- and pH-responsive polymers in drug delivery

Stimuli-responsive polymers show a sharp change in properties upon a small or modest change in environmental condition, e.g. temperature, light, salt concentration or pH. This behaviour can be utilised for the preparation of so-called 'smart' drug delivery systems, which mimic biological response behaviour to a certain extent. The possible environmental conditions to use for this purpose are limited due to the biomedical setting of drug delivery as application. Different organs, tissues and cellular compartments may have large differences in pH, which makes the pH a suitable stimulus. Therefore the majority of examples, discussed in this paper, deal with pH-responsive drug delivery system. Thermo-responsive polymer is also covered to a large extent, as well as double-responsive system. The physico-chemical behaviour underlying the phase transition will be discussed in brief. Then selected examples of applications are described.