Gold nanoparticles capped with polyethyleneimine for enhanced siRNA delivery

Five years of siRNA delivery: spotlight on gold nanoparticles

Gold nanoparticles have become widely used in scientific research due to their unique physical and chemical properties. In the last several years their use as siRNA delivery agents has been investigated. Here, progress made using gold nanoparticles for siRNA delivery is described and the different strategies employed are compared.

Nano-biolistics: a method of biolistic transfection of cells and tissues using a gene gun with novel nanometer-sized projectiles

Background

Biolistic transfection is proving an increasingly popular method of incorporating DNA or RNA into cells that are difficult to transfect using traditional methods. The technique routinely uses 'microparticles', which are ~1 μm diameter projectiles, fired into tissues using pressurised gas. These microparticles are efficient at delivering DNA into cells, but cannot efficiently transfect small cells and may cause significant tissue damage, thus limiting their potential usefulness. Here we describe the use of 40 nm diameter projectiles - nanoparticles - in biolistic transfections to determine if they are a suitable alternative to microparticles.

Results

Examination of transfection efficiencies in HEK293 cells, using a range of conditions including different DNA concentrations and different preparation procedures, reveals similar behaviour of microparticles and nanoparticles. The use of nanoparticles, however, resulted in ~30% fewer damaged HEK293 cells following transfection. Biolistic transfection of mouse ear tissue revealed similar depth penetration for the two types of particles, and also showed that < 10% of nuclei were damaged in nanoparticle-transfected samples, compared to > 20% in microparticle-transfected samples. Visualising details of small cellular structures was also considerably enhanced when using nanoparticles.

Conclusions

We conclude that nanoparticles are as efficient for biolistic transfection as microparticles, and are more appropriate for use in small cells, when examining cellular structures and/or where tissue damage is a problem.

Cell transcytosing poly-arginine coated magnetic nanovector for safe and effective siRNA delivery

Lack of safe and effective carriers for delivery of RNA therapeutics remains a barrier to its broad clinical application. We report the development of a cell tanscytosing magnetic nanovector engineered as an siRNA carrier. Iron oxide nanoparticles were modified with poly(ethylene glycol) (PEG), small interfering RNA (siRNA), and a cationic polymer layer. Three nanovector formulations with cationic polymer coatings of poly-arginine (pArg), polylysine (pLys), and polyethylenimine (PEI), respectively, were prepared. The three nanovector formulations where evaluated for safety and ability to promote gene silencing in three types of cancer cells C6/GFP(+), MCF7/GFP(+), and TC2/GFP(+), mimicking human cancers of the brain, breast, and prostate, respectively. Cell viability and fluorescence quantification assays revealed that pArg-coated nanovectors were most effective in promoting gene knockdown and least toxic of the three nanovector formulations tested. Transmission electron microscopy (TEM) imaging of nanovector treated cells further demonstrated that pArg-coated nanovectors enter cells through cell transcytosis, while pLys and PEI coated nanovectors enter cells endocytosis. Our findings suggest that NPs engineered to exploit the cell transcytosis intracellular trafficking pathway may offer a more safe and efficient route for siRNA delivery.

A brain-targeted rabies virus glycoprotein-disulfide linked PEI nanocarrier for delivery of neurogenic microRNA

Recent advances in efficient microRNA (miRNA) delivery techniques using brain-targeted nanoparticles offer critical information for understanding the functional role of miRNAs in vivo, and for supporting targeted gene therapy in terms of treating miRNA-associated neurological diseases. Here, we report the rabies virus glycoprotein (RVG)-labeled non-toxic SSPEI nanomaterials capable of neuron-specific miR-124a delivery to neuron in vivo. The RVG-labeled BPEI-SS (RVG-SSPEI) nanocarrier showed less toxicity in acetylcholine receptor-positive Neuro2a cells, and electrostatic interaction of RVG-SSPEI with miR-124a exhibited optimal transfection efficacy. The RVG-SSPEI polymer specifically targeted Neuro2a using cy5.5-miR-124a mixed with RVG-SSPEI. The functional action of miR-124a oligomers released from polyplexes in the cytoplasmic region was evaluated by a reporter vector containing a miR-124a -binding sequence, and showed a significantly reduced reporter signal in a dose-dependent manner. Cy5.5-miR-124a/RVG-SSPEI- injected into mice via tail veins displayed the enhanced accumulation of miR-124a in the isolated brain. Hindrance of the efficient penetration of neuronal cells by size limitation of the miR-124a/RVG-SSPEI improved with the help of mannitol through blood-brain barrier disruption. These findings indicated that the RVG peptide combined with mannitol infusion using SSPEI polymer for neuron-specific targeting in vivo is sufficient to deliver neurogenic microRNA into the brain.

Dual-emission fluorescent silica nanoparticle-based probe for ultrasensitive detection of Cu2+

An effective dual-emission fluorescent silica nanoparticle-based probe has been constructed for rapid and ultrasensitive detection of Cu(2+). In this nanoprobe, a dye-doped silica core served as a reference signal, thus providing a built-in correction for environmental effects. A response dye was covalently grafted on the surface of the silica nanoparticles through a chelating reagent for Cu(2+). The fluorescence of the response dye could be selectively quenched in the presence of Cu(2+), accompanied by a visual orange-to-green color switch of the nanoprobe. The nanoprobe provided an effective platform for reliable detection of Cu(2+) with a detection limit as low as 10 nM, which is nearly 2 × 10(3) times lower than the maximum level (∼20 μM) of Cu(2+) in drinking water permitted by the U.S. Environmental Protection Agency (EPA). The high sensitivity was attributed to the strong chelation of Cu(2+) with polyethyleneimine (PEI) and a signal amplification effect. The nanoprobe constructed by this method was very stable, enabling the rapid detection of Cu(2+) in real water samples. Good linear correlations were obtained over the concentration range from 1 × 10(-7) to 8 × 10(-7) (R(2) = 0.99) with recoveries of 103.8-99.14% and 95.5-95.14% for industrial wastewater and lake water, respectively. Additionally, the long-wavelength emission of the response dye can avoid the interference of the autofluorescence of the biosystems, which facilitated their applications in monitoring Cu(2+) in cells. Furthermore, the nanoprobe showed a good reversibility; the fluorescence can be switched "off" and "on" by an addition of Cu(2+) and EDTA, respectively.

Effective gene silencing by multilayered siRNA-coated gold nanoparticles

Small interfering RNA (siRNA) has been widely proposed to treat various diseases by silencing genes, but its delivery remains a challenge. A well controlled assembly approach is applied to prepare a protease-assisted nanodelivery system. Protease-degradable poly-L-lysine (PLL) and siRNA are fabricated onto gold nanoparticles (AuNPs), by alternating the charged polyelectrolytes. In this study, up to 4 layers of PLL and 3 layers of siRNA (sR3P) are coated. Due to the slow degradation of PLL, the incorporated siRNA is released gradually and shows extended gene-silencing effects. Importantly, the inhibition effect in cells is found to correlate with the number of siRNA layers.

Quantum dot-antisense oligonucleotide conjugates for multifunctional gene transfection, mRNA regulation, and tracking of biological processes

It was demonstrated that oligonucleotides, independent of their base sequence and length, could effectively induce the cellular uptake of mercapto acid-capped CdTe QDs after the oligonucleotides were covalently attached on the surface of the QDs. Following these experimental observations, a conjugate composed of covalently linked anti-survivin antisense oligonucleotides (ASON) and CdTe QDs was designed and synthesized. Then, the survivin mRNA down-regulation and the apoptosis of HeLa cells induced by ASON were studied. Systematic experimental results revealed that CdTe-ASON could effectively induce the apoptosis of HeLa cells, while CdTe QDs offered the possibility to visualize the specific intracellular localization of the CdTe-ASON probes strongly associated with their biological functions.

Maximization of loading and stability of ssDNA:iron oxide nanoparticle complexes formed through electrostatic interaction

The use of inorganic nanoparticles (NPs) as vectors for the delivery of oligonucleotides for in vitro and in vivo applications is rapidly gaining momentum. Some of the reasons making them especially good candidates for this purpose are their ease of synthesis in a range of sizes and surface coatings, their propensity to penetrate cell membranes, their stability and biocompatibility, and their unique size-dependent physical properties that impart additional diagnostic and therapeutic tools. Notwithstanding these notable attributes, a major obstacle to their practical use is given by the typically low oligonucleotide loading levels attainable through conventional bioconjugation procedures. This shortcoming is especially worrisome as toxicity concerns have been associated with codelivery of NPs. In this paper we are analytically analyzing the formation of electrostatic complexes between negatively charged ssDNA and positively charged iron oxide nanoparticles (SPIO-NP) with the purpose of identifying the optimal conditions leading to stable formulations at high oligo loading levels. The formation and loading levels of ssDNA:SPIO-NP complexes have been investigated at different oligo:NP ratios and under different ionic strengths through dynamic light scattering, fluorescence quenching experiments, and pull-down assays. Through these studies we have identified optimal conditions for attaining maximal oligo loading levels, and we are proposing a simple model to explain an unusual behavior observed in the formation of the complexes. Finally, we introduce an alternative loading method relying on the electrostatic coloading of an oligo sequence in the presence of a negatively charged PEGylated block copolymer, yielding very stable and high loading PEGylated ssDNA:SPIO-NPs. The findings that we are reporting are of general validity, and similar conditions could be easily translated to the electrostatic formation of ssDNA:NP complexes consisting of different NP materials and sizes.

Gene silencing mediated by magnetic lipospheres tagged with small interfering RNA

Lipospheres made from soy bean oil and a combination of the cationic lipid Metafectene and the helper lipid dioleoylphosphatidyl-ethanolamine were functionalized with magnetic nanoparticles (NPs) and small interfering RNA (siRNA). The resulting magnetic lipospheres loaded with siRNA are proven here as efficient nonviral vectors for gene silencing. Embedding magnetic NPs in the shell of lipospheres allows for magnetic force-assisted transfection (magnetofection) as well as magnetic targeting in both static and fluidic conditions mimicking the bloodstream.

pH-Sensitive siRNA nanovector for targeted gene silencing and cytotoxic effect in cancer cells

A small interfering RNA (siRNA) nanovector with dual targeting specificity and dual therapeutic effect is developed for targeted cancer imaging and therapy. The nanovector is composed of an iron oxide magnetic nanoparticle core coated with three different functional molecules: polyethyleneimine (PEI), siRNA, and chlorotoxin (CTX). The primary amine group of PEI is blocked with citraconic anhydride that is removable at acidic conditions, not only to increase its biocompatibility at physiological conditions but also to elicit a pH-sensitive cytotoxic effect in the acidic tumor microenvironment. The PEI is covalently immobilized on the nanovector via a disulfide linkage that is cleavable after cellular internalization of the nanovector. CTX as a tumor-specific targeting ligand and siRNA as a therapeutic payload are conjugated on the nanovector via a flexible and hydrophilic PEG linker for targeted gene silencing in cancer cells. With a size of ∼60 nm, the nanovector exhibits long-term stability and good magnetic property for magnetic resonance imaging. The multifunctional nanovector exhibits both significant cytotoxic and gene silencing effects at acidic pH conditions for C6 glioma cells, but not at physiological pH conditions. Our results suggest that this nanovector system could be safely used as a potential therapeutic agent for targeted treatment of glioma as well as other cancers.

Gold nanoparticles delivery in mammalian live cells: a critical review

Functional nanomaterials have recently attracted strong interest from the biology community, not only as potential drug delivery vehicles or diagnostic tools, but also as optical nanomaterials. This is illustrated by the explosion of publications in the field with more than 2,000 publications in the last 2 years (4,000 papers since 2000; from ISI Web of Knowledge, 'nanoparticle and cell' hit). Such a publication boom in this novel interdisciplinary field has resulted in papers of unequal standard, partly because it is challenging to assemble the required expertise in chemistry, physics, and biology in a single team. As an extreme example, several papers published in physical chemistry journals claim intracellular delivery of nanoparticles, but show pictures of cells that are, to the expert biologist, evidently dead (and therefore permeable). To attain proper cellular applications using nanomaterials, it is critical not only to achieve efficient delivery in healthy cells, but also to control the intracellular availability and the fate of the nanomaterial. This is still an open challenge that will only be met by innovative delivery methods combined with rigorous and quantitative characterization of the uptake and the fate of the nanoparticles. This review mainly focuses on gold nanoparticles and discusses the various approaches to nanoparticle delivery, including surface chemical modifications and several methods used to facilitate cellular uptake and endosomal escape. We will also review the main detection methods and how their optimum use can inform about intracellular localization, efficiency of delivery, and integrity of the surface capping.