Cationic liposomes as non-viral carriers of gene medicines: resolved issues, open questions, and future promises

Solid lipid nanoparticles for retinal gene therapy: transfection and intracellular trafficking in RPE cells

Retinal pigment epithelial (RPE) cells are usually employed to study DNA systems for diseases related to problems in the retina. Solid lipid nanoparticles (SLNs) have been shown to be useful non-viral vectors for gene therapy. The objective of this work was to evaluate the transfection capacity of SLNs in the human retinal pigment epithelial established cell line (ARPE-19) in order to elucidate the potential application of this vector in the treatment of retinal diseases. Results showed a lower transfection level of SLNs in ARPE-19 cells than in HEK293 (2.5% vs. 14.9% EGFP positive cells at 72h post-transfection). Trafficking studies revealed a delay in cell uptake of the vectors in ARPE-19 cells. Differences in internalization process into the two cell lines studied explain, in part, the difference in the gene expression. The clathrin-mediated endocytosis in ARPE-19 cells directs the solid lipid nanoparticles to lysosomes; moreover, the low division rate of this cell line hampers the entrance of DNA into the nucleus. The knowledge of intracellular trafficking is very useful in order to design more efficient vectors taking into account the characteristics of the specific cell line to be transfected.

Cationic liposomal lipids: from gene carriers to cell signaling

Cationic lipids are positively charged amphiphilic molecules which, for most of them, form positively charged liposomes, sometimes in combination with a neutral helper lipid. Such liposomes are mainly used as efficient DNA, RNA or protein carriers for gene therapy or immunization trials. Over the past decade, significant progress has been made in the understanding of the cellular pathways and mechanisms involved in lipoplex-mediated gene transfection but the interaction of cationic lipids with cell components and the consequences of such an interaction on cell physiology remains poorly described. The data reported in the present review provide evidence that cationic lipids are not just carriers for molecular delivery into cells but do modify cellular pathways and stimulate immune or anti-inflammatory responses. Considering the wide number of cationic lipids currently available and the variety of cellular components that could be involved, it is likely that only a few cationic lipid-dependent functions have been identified so far.

Nonviral vector gene modification of stem cells for myocardial repair

Therapeutic angiogenesis and myogenesis restore perfusion of ischemic myocardium and improve left ventricular contractility. These therapeutic modalities must be considered as complementary rather than competing to exploit their advantages for optimal beneficial effects. The resistant nature of cardiomyocytes to gene transfection can be overcome by ex vivo delivery of therapeutic genes to the heart using genetically modified stem cells. This review article gives an overview of different vectors and delivery systems in general used for therapeutic gene delivery to the heart and provides a critical appreciation of the ex vivo gene delivery approach using genetically modified stem cells to achieve angiomyogenesis for the treatment of infarcted heart.

Lipophilic peptides for gene delivery

DNA transfections are widely performed in research laboratories and in vivo gene delivery holds the promise for curing many diseases. The synthetic carriers or vectors for DNA are typically cationic lipids. However, in biology, the recognition of nucleic acids by proteins involves both electrostatic and stacking contributions. As such we have prepared a series of new lipophilic peptide vectors that possess lysine and tryptophan amino acids for evaluation. These lipophilic peptides show minimal cytotoxicity and enhanced in vitro gene transfection activity.

Self-assembly approaches to nanomaterial encapsulation in viral protein cages

A perspective on abiotic material encapsulation inside virus capsids is provided. The emphasis is on the physical principles of virus assembly relevant to packaging, strategies for encapsulation and capsid modification, and on emerging applications.

Precisely defined protein-polymer conjugates: construction of synthetic DNA binding domains on proteins by using multivalent dendrons

Nature has evolved proteins and enzymes to carry out a wide range of sophisticated tasks. Proteins modified with functional polymers possess many desirable physical and chemical properties and have applications in nanobiotechnology. Here we describe multivalent Newkome-type polyamine dendrons that function as synthetic DNA binding domains, which can be conjugated with proteins. These polyamine dendrons employ naturally occurring spermine surface groups to bind DNA with high affinity and are attached onto protein surfaces in a site-specific manner to yield well-defined one-to-one protein-polymer conjugates, where the number of dendrons and their attachment site on the protein surface are precisely known. This precise structure is achieved by using N-maleimido-core dendrons that selectively react via 1,4-conjugate addition with a single free thiol group on the protein surface--either Cys-34 of bovine serum albumin (BSA) or a genetically engineered cysteine mutant of Class II hydrophobin (HFBI). This reaction can be conducted in mild aqueous solutions (pH 7.2-7.4) and at ambient temperature, resulting in BSA- and HFBI-dendron conjugates. The protein-dendron conjugates constitute a specific biosynthetic diblock copolymer and bind DNA with high affinity, as shown by ethidium bromide displacement assay. Importantly, even the low-molecular-weight first-generation polyamine dendron (1 kDa) can bind a large BSA protein (66.4 kDa) to DNA with relatively good affinity. Preliminary gene transfection, cytotoxicity, and self-assembly studies establish the relevance of this methodology for in vitro applications, such as gene therapy and surface patterning. These results encourage further developments in protein-dendron block copolymer-like conjugates and will allow the advance of functional biomimetic nanoscale materials.

Dramatic influence of the orientation of linker between hydrophilic and hydrophobic lipid moiety in liposomal gene delivery

A number of prior studies have demonstrated that the DNA-binding and gene transfection efficacies of cationic amphiphiles crucially depend on their various structural parameters including hydrophobic chain lengths, headgroup functionalities, and the nature of the linker-functionality used in tethering the polar headgroup and hydrophobic tails. However, to date addressing the issue of linker orientation remains unexplored in liposomal gene delivery. Toward probing the influence of linker orientation in cationic lipid mediated gene delivery, we have designed and synthesized two structurally isomeric remarkably similar cationic amphiphiles 1 and 2 bearing the same hydrophobic tails and the same polar headgroups connected by the same ester linker group. The only structural difference between the cationic amphiphiles 1 and 2 is the orientation of their linker ester functionality. While lipid 1 showed high gene transfer efficacies in multiple cultured animal cells, lipid 2 was essentially transfection incompetent. Findings in both transmission electron microscopic and dynamic laser light scattering studies revealed no significant size difference between the lipoplexes of lipids 1 and 2. Findings in confocal microscopic and fluorescence resonance energy transfer (FRET) experiments, taken together, support the notion that the remarkably higher gene transfer efficacies of lipid 1 compared to those of lipid 2 presumably originate from higher biomembrane fusogenicity of lipid 1 liposomes. Differential scanning calorimetry (DSC) and fluorescence anisotropy studies revealed a significantly higher gel-to-liquid crystalline temperature for the lipid 2 liposomes than that for lipid 1 liposomes. Findings in the dye entrapment experiment were also consistent with the higher rigidity of lipid 2/cholesterol (1:1 mole ratio) liposomes. Thus, the higher biomembrane fusibility of lipid 1 liposomes than that of lipid 2 liposomes presumably originates from the more rigid nature of lipid 2 cationic liposomes. Taken together, the present findings demonstrate for the first time that even as minor a structural variation as linker orientation reversal in cationic amphiphiles can profoundly influence DNA-binding characteristics, membrane rigidity, membrane fusibility, cellular uptake, and consequently gene delivery efficacies of cationic liposomes.