Chemical vectors for gene delivery: a current review on polymers, peptides and lipids containing histidine or imidazole as nucleic acids carriers

Chemical vectors for gene delivery: uptake and intracellular trafficking

Chemical vectors for non-viral gene delivery are based on engineered DNA nanoparticles produced with various range of macromolecules suitable to mimic some viral functions required for gene transfer. Many efforts have been undertaken these past years to identify cellular barriers that have to be passed for this issue. Here, we summarize the current status of knowledge on the uptake mechanism of DNA nanoparticles made with polymers and liposomes, their endosomal escape, cytosolic diffusion, and nuclear import of pDNA. Studies reported these past years regarding pDNA nanoparticles endocytosis indicated that there is no clear evident relationship between the ways of entry and the transfection efficiency. By contrast, the sequestration of pDNA in intracellular vesicles and the low number of pDNA close to the nuclear envelop are identified as the major intracellular barriers. So, intensive investigations to increase the cytosolic delivery of pDNA and its migration toward nuclear pores make sense to bring the transfection efficiency closer to that of viruses.

siRNA applications in nanomedicine

The ability to specifically silence genes using RNA interference (RNAi) has wide therapeutic applications for the treatment of disease or the augmentation of tissue formation. RNAi is the sequence-specific gene silencing mediated by a 21-25 nucleotide double-stranded small interfering RNA (siRNA) molecule. siRNAs are incorporated into the RNA-induced silencing complex (RISC), which mediates mRNA sequence-specific binding and cleavage. Although RNAi has the potential to be a powerful therapeutic drug, its delivery remains a major limitation. The generation of nanosized particles is being investigated to enhance the delivery of siRNA-based drugs. These nanoparticles are generally designed to overcome one or more of the barriers encountered by the siRNA when trafficked to the cytosol. In this review, we will discuss recent advances in the design of delivery strategies for siRNA, focusing our attention to those strategies that have had in vivo success or have introduced novel functionality that allowed enhanced intracellular trafficking and/or cellular targeting. First, we will discuss the different barriers that must be overcome for efficient siRNA delivery. Second, we will discuss the approaches for siRNA delivery by size including direct modification of siRNAs (less than 10 nm), self-assembled particles based on cationic polymers and cationic lipids (100-300 nm), neutral liposomes (<200 nm), and macroscale matrices that contain naked siRNA or siRNA loaded nanoparticles (>100 microm). Finally, we will briefly discuss recent in vivo therapeutic success.

Incorporation of 2,3-diaminopropionic acid into linear cationic amphipathic peptides produces pH-sensitive vectors

Nonviral vectors that harness the change in pH in endosomes, are increasingly being used to deliver cargoes, including nucleic acids, into mammalian cells. Here we present evidence that the pK(a) of the beta-NH(2) in 2,3-diaminopropionic acid (Dap) is sufficiently lowered, when Dap is incorporated into peptides, that its protonation state is sensitive to the pH changes that occur during endosomal acidification. The lowered pK(a) of around 6.3 is stabilized by the increased electron-withdrawing effect of the peptide bonds, by intermolecular hydrogen bonding and from contributions arising from the peptide conformation. These include mixed polar/apolar environments, Coulombic interactions and intermolecular hydrogen bonding. Changes in the charged state are therefore expected between pH 5 and 7, and large-scale conformational changes are observed in Dap-rich peptides, in contrast to analogues containing lysine or ornithine, when the pH is altered through this range. These physical properties confer a robust gene-delivery capability on designed cationic amphipathic peptides that incorporate Dap.

Accelerated Achilles tendon healing by PDGF gene delivery with mesoporous silica nanoparticles

We report the ability of amino- and carboxyl-modified MCM-41 mesoporous silica nanoparticles (MSN) to deliver gene in vivo in rat Achilles tendons, despite their inefficiency to transfect primary tenocytes in culture. We show that luciferase activity lasted for at least 2 weeks in tendons injected with these MSN and a plasmid DNA (pDNA) encoding the luciferase reporter gene. By contrast, in tendons injected with naked plasmid, the luciferase expression decreased as a function of time and became hardly detectable after 2 weeks. Interestingly, there were neither signs of inflammation nor necrosis in tendon, kidney, heart and liver of rat weekly injected with pDNA/MSN formulation during 1.5 months. Our main data concern the acceleration of Achilles tendons healing by PDGF-B gene transfer using MSN. Biomechanical properties and histological analyses clearly indicate that tendons treated with MSN and PDGF gene healed significantly faster than untreated tendons and those treated with pPDGF alone.

Recent trends in non-viral vector-mediated gene delivery

Nucleic acids-based next generation biopharmaceuticals (i.e., pDNA, oligonucleotides, short interfering RNA) are potential pioneering materials to cope with various incurable diseases. However, several biological barriers present a challenge for efficient gene delivery. On the other hand, developments in nanotechnology now offer numerous non-viral vectors that have been fabricated and found capable of transmitting the biopharmaceuticals into the cell and even into specific subcellular compartments like mitochondria. This overview illustrates cellular barriers and current status of non-viral gene vectors, i.e., lipoplexes, liposomes, polyplexes, and nanoparticles, to relocate therapeutic DNA-based nanomedicine into the target cell. Despite the awesome impact of physical methods (i.e., ultrasound, electroporation), chemical methods have been shown to accomplish high-level and safe transgene expression. Further comprehension of barriers and the mechanism of cellular uptake will facilitate development of nucleic acids-based nanotherapy for alleviation of various disorders.

Mesomorphic imidazolium salts: new vectors for efficient siRNA transfection

The preparation of chloride (1(n)) and bromide (2(n)) derivatives of 1-methyl-3-[3,4-bis(alkoxy)benzyl]-4H-imidazolium with n = 6, 12, 16, 18 is described. The two series of salts possess a rich thermotropic mesomorphism, chain-length dependent. Thus, a lamellar smectic A phase, a bicontinuous cubic Ia3d phase, and a columnar hexagonal liquid crystalline mesophase are induced as a function of increasing chain length. The mesomorphic properties were studied by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction, and with the support of dilatometry and molecular dynamics, models for the various supramolecular arrangements of the salts are proposed. Such cationic amphiphiles were expected to be candidate molecules to design a new delivery reagent for nucleic acid transfection, particularly for short interfering RNA (siRNA). The use of an RNA interference mechanism, by introduction into cells by transfection of chemically synthesized siRNAs, is a powerful method for gene silencing studies. To exploit the potential of these amphilic imidazolium salts, these molecules were formulated with cohelper lipids and tested for their efficacy to deliver active siRNAs. Our results show high transfection efficacy of our formulated compounds and high silencing efficiency with more than 80% inhibition of the targeted gene at 10 nM siRNA concentration. Taken together our results show the potency of amphiphilic imidazolium salts as a new generation of transfection reagents for RNA interference.

Understanding microRNAs in neurodegeneration

Interest in the functions of microRNAs (miRNAs) in the nervous system has recently expanded to include their roles in neurodegeneration. Investigations have begun to reveal the influence of miRNAs on both neuronal survival and the accumulation of toxic proteins that are associated with neurodegeneration, and are providing clues as to how these toxic proteins can influence miRNA expression.

The promiscuous mGlu5 receptor--a range of partners for therapeutic possibilities?

The issue of non-specific effects for potential therapeutics is particularly salient in neurological/psychiatric disorders, where adverse drug reactions could impair critical brain functions. The issue of specificity is not limited to candidate molecules, as receptor targets themselves often influence physiological as well as pathological outcomes. Metabotropic glutamate receptor 5 (mGlu5) is an example of a "promiscuous" receptor target that has been implicated in addiction, but also many other processes. However, if receptor modulation could be restricted to specific pathways/brain regions, mGlu5 may still prove to be a viable therapeutic target for various indications. Using this premise, a number of possible methods to refine drug development strategy are discussed, including exploiting specific interactions of mGlu5 with other receptors to narrow the influence of pharmacological agents, and also the use of RNA interference targeted to specific cells/regions of the brain.

Delivery of magic bullets: on the still rocky road to gene therapy

In this issue, the promises, problems and current progress towards gene therapy are examined in a themed set of six reviews. These cover the major methodologies deployed over the last twenty to thirty years to deliver a gene or other potentially therapeutic molecules into an organism. Initial enthusiasm and optimism concerning the prospects for gene therapy and more generally, the delivery of magic bullets, arose after the pioneering discoveries of monoclonal antibodies and retroviral infection during the 1970's and were fuelled by strategies to make synthetic viruses and the advent of chemical vectors over the succeeding twenty years. However, despite significant advances, to date, the early hopes of widespread gene therapy still remain largely unfulfilled.

Lipid-based nanoparticles as pharmaceutical drug carriers: from concepts to clinic

In recent years, various nanotechnology platforms in the area of medical biology, including both diagnostics and therapy, have gained remarkable attention. Moreover, research and development of engineered multifunctional nanoparticles as pharmaceutical drug carriers have spurred exponential growth in applications to medicine in the last decade. Design principles of these nanoparticles, including nanoemulsions, dendrimers, nano-gold, liposomes, drug-carrier conjugates, antibody-drug complexes, and magnetic nanoparticles, are primarily based on unique assemblies of synthetic, natural, or biological components, including but not limited to synthetic polymers, metal ions, oils, and lipids as their building blocks. However, the potential success of these particles in the clinic relies on consideration of important parameters such as nanoparticle fabrication strategies, their physical properties, drug loading efficiencies, drug release potential, and, most importantly, minimum toxicity of the carrier itself. Among these, lipid-based nanoparticles bear the advantage of being the least toxic for in vivo applications, and significant progress has been made in the area of DNA/RNA and drug delivery using lipid-based nanoassemblies. In this review, we will primarily focus on the recent advances and updates on lipid-based nanoparticles for their projected applications in drug delivery. We begin with a review of current activities in the field of liposomes (the so-called honorary nanoparticles), and challenging issues of targeting and triggering will be discussed in detail. We will further describe nanoparticles derived from a novel class of amphipathic lipids called bolaamphiphiles with unique lipid assembly features that have been recently examined as drug/DNA delivery vehicles. Finally, an overview of an emerging novel class of particles (based on lipid components other than phospholipids), solid lipid nanoparticles and nanostructured lipid carriers will be presented. We conclude with a few examples of clinically successful formulations of currently available lipid-based nanoparticles.