Inhibition of gene expression in mice muscle by in vivo electrically mediated siRNA delivery

Importance of the electrophoresis and pulse energy for siRNA-mediated gene silencing by electroporation in differentiated primary human myotubes

BACKGROUND

Electrotransfection is based on application of high-voltage pulses that transiently increase membrane permeability, which enables delivery of DNA and RNA in vitro and in vivo. Its advantage in applications such as gene therapy and vaccination is that it does not use viral vectors. Skeletal muscles are among the most commonly used target tissues. While siRNA delivery into undifferentiated myoblasts is very efficient, electrotransfection of siRNA into differentiated myotubes presents a challenge. Our aim was to develop efficient protocol for electroporation-based siRNA delivery in cultured primary human myotubes and to identify crucial mechanisms and parameters that would enable faster optimization of electrotransfection in various cell lines.

RESULTS

We established optimal electroporation parameters for efficient siRNA delivery in cultured myotubes and achieved efficient knock-down of HIF-1α while preserving cells viability. The results show that electropermeabilization is a crucial step for siRNA electrotransfection in myotubes. Decrease in viability was observed for higher electric energy of the pulses, conversely lower pulse energy enabled higher electrotransfection silencing yield. Experimental data together with the theoretical analysis demonstrate that siRNA electrotransfer is a complex process where electropermeabilization, electrophoresis, siRNA translocation, and viability are all functions of pulsing parameters. However, despite this complexity, we demonstrated that pulse parameters for efficient delivery of small molecule such as PI, can be used as a starting point for optimization of electroporation parameters for siRNA delivery into cells in vitro if viability is preserved.

CONCLUSIONS

The optimized experimental protocol provides the basis for application of electrotransfer for silencing of various target genes in cultured human myotubes and more broadly for electrotransfection of various primary cell and cell lines. Together with the theoretical analysis our data offer new insights into mechanisms that underlie electroporation-based delivery of short RNA molecules, which can aid to faster optimisation of the pulse parameters in vitro and in vivo.

Efficient Downregulation of Alk4 in Skeletal Muscle After Systemic Treatment with Conjugated siRNAs in a Mouse Model for Duchenne Muscular Dystrophy

Downregulation of genes involved in the secondary pathology of Duchenne muscular dystrophy, for example, inflammation, fibrosis, and adiposis, is an interesting approach to ameliorate degeneration of muscle and replacement by fibrotic and adiposis tissue. Small interfering RNAs (siRNAs) are able to downregulate target genes, however, delivery of siRNAs to skeletal muscle still remains a challenge. We investigated delivery of fully chemically modified, cholesterol-conjugated siRNAs targeting Alk4, a nontherapeutic target that is expressed highly in muscle. We observed that a single intravenous or intraperitoneal (IP) injection of 10 mg/kg resulted in significant downregulation of Alk4 mRNA expression in skeletal muscles in both wild-type and mdx mice. Treatment with multiple IP injections of 10 mg/kg led to an overall reduction of Alk4 expression, reaching significance in tibialis anterior (39.7% ± 6.2%), diaphragm (32.7% ± 5.8%), and liver (41.3% ± 29.9%) in mdx mice. Doubling of the siRNA dose did not further increase mRNA silencing in muscles of mdx mice. The chemically modified conjugated siRNAs used in this study are very promising for delivery to both nondystrophic and dystrophic muscles and could have major implications for treatment of muscular dystrophy pathology.

Modified fibrin hydrogel for sustained delivery of RNAi lipopolyplexes in skeletal muscle

RNA interference is a promising therapeutical approach presently hindered by delivery concerns such as rapid RNA degradation and targeting of individual tissues. Injectable hydrogels are one potentially simple and direct route towards overcoming these barriers. Here we report on the utility of a combination of a mildly modified form of the clinically utilised fibrin hydrogel with Invivofectamine^® 3.0, a lipid nonviral transfection vector, for local and sustained release. PEGylation of fibrin allowed for controlled release of small interfering RNA (siRNA)-lipopolyplexes for at least 10 days and greatly increased the stability of fibrin in vitro and in vivo. A 3D cell culture model and a release study showed transfection efficacy of siRNA-lipopolyplexes was retained for a minimum of 7 days. Injection in conjunction with PEGylated-fibrinogen significantly increased retention of siRNA-lipopolyplexes in mouse skeletal muscle and enhanced knockdown of myostatin mRNA that correlated with muscle growth. Thus, the increased efficacy observed here for the combination of a lipid nanoparticle, the only type of nonviral vector approved for the clinic, with fibrin, might allow for more rapid translation of injectable hydrogel-based RNA interference.

Targeted Delivery for Neurodegenerative Disorders Using Gene Therapy Vectors: Gene Next Therapeutic Goals

The technique of gene therapy, ever since its advent nearly fifty years ago, has been utilized by scientists as a potential treatment option for various disorders. This review discusses some of the major neurodegenerative diseases (NDDs) like Alzheimer's disease (AD), Parkinson's Disease (PD), Motor neuron diseases (MND), Spinal Muscular Atrophy (SMA), Huntington's Disease (HD), Multiple Sclerosis (MS), etc. and their underlying genetic mechanisms along with the role that gene therapy can play in combating them. The pathogenesis and the molecular mechanisms specifying the altered gene expression of each of these NDDs have also been discussed in elaboration. The use of gene therapy vectors can prove to be an effective tool in the field of curative modern medicine for the generations to come. Therefore, consistent efforts and progressive research towards its implementation can provide us with powerful treatment options for disease conditions that have so far been considered as incurable.

Silencing Myostatin Using Cholesterol-conjugated siRNAs Induces Muscle Growth

Short interfering RNAs (siRNAs) are a valuable tool for gene silencing with applications in both target validation and therapeutics. Many advances have recently been made to improve potency and specificity, and reduce toxicity and immunostimulation. However, siRNA delivery to a variety of tissues remains an obstacle for this technology. To date, siRNA delivery to muscle has only been achieved by local administration or by methods with limited potential use in the clinic. We report systemic delivery of a highly chemically modified cholesterol-conjugated siRNA targeting muscle-specific gene myostatin (Mstn) to a full range of muscles in mice. Following a single intravenous injection, we observe 85–95% knockdown of Mstn mRNA in skeletal muscle and >65% reduction in circulating Mstn protein sustained for >21 days. This level of Mstn knockdown is also accompanied by a functional effect on skeletal muscle, with animals showing an increase in muscle mass, size, and strength. The cholesterol-conjugated siRNA platform described here could have major implications for treatment of a variety of muscle disorders, including muscular atrophic diseases, muscular dystrophy, and type II diabetes.

Powering up the molecular therapy of RNA interference by novel nanoparticles

With more suitable for disease treatment due to reduced cellular toxicity, higher loading capacity, and better biocompatibility, nanoparticle-based siRNA delivery systems have proved to be more potent, higher specific and less toxic than the traditional drug therapy.

Electroporation Enhanced Effect of Dystrophin Splice Switching PNA Oligomers in Normal and Dystrophic Muscle

Peptide nucleic acid (PNA) is a synthetic DNA mimic that has shown potential for discovery of novel splice switching antisense drugs. However, in vivo cellular delivery has been a limiting factor for development, and only few successful studies have been reported. As a possible modality for improvement of in vivo cellular availability, we have investigated the effect of electrotransfer upon intramuscular (i.m.) PNA administration in vivo. Antisense PNA targeting exon 23 of the murine dystrophin gene was administered by i.m. injection to the tibialis anterior (TA) muscle of normal NMRI and dystrophic mdx mice with or without electroporation. At low, single PNA doses (1.5, 3, or 10 µg/TA), electroporation augmented the antisense exon skipping induced by an unmodified PNA by twofold to fourfold in healthy mouse muscle with optimized electric parameters, measured after 7 days. The PNA splice switching was detected at the RNA level up to 4 weeks after a single-dose treatment. In dystrophic muscles of the MDX mouse, electroporation increased the number of dystrophin-positive fibers about 2.5-fold at 2 weeks after a single PNA administration compared to injection only. In conclusion, we find that electroporation can enhance PNA antisense effects in muscle tissue.

Mechanisms of transfer of bioactive molecules through the cell membrane by electroporation

A short review of biophysical mechanisms for electrotransfer of bioactive molecules through the cell membrane by using electroporation is presented. The concept of transient hydrophilic aqueous pores and membrane electroporation mechanisms of single cells and cells in suspension models are analyzed. Alongside the theoretical approach, some peculiarities of drug and gene electrotransfer into cells and applications in clinical trials are discussed.

Controlled Endolysosomal Release of Agents by pH-responsive Polymer Blend Particles

PURPOSE

A key step of delivering extracellular agents to its intracellular target is to escape from endosomal/lysosomal compartments, while minimizing the release of digestive enzymes that may compromise cellular functions. In this study, we examined the intracellular distribution of both fluorecent cargoes and enzymes by a particle delivery platform made from the controlled blending of poly(lactic-co-glycolic acid) (PLGA) and a random pH-sensitive copolymer.

METHODS

We utilized both microscopic and biochemical methods to semi-quantitatively assess how the composition of blend particles affects the level of endosomal escape of cargos of various sizes and enzymes into the cytosolic space.

RESULTS

We demonstrated that these polymeric particles enabled the controlled delivery of cargos into the cytosolic space that was more dependent on the cargo size and less on the composition of blend particles. Blend particles did not induce the rupture of endosomal/lysosomal compartments and released less than 20% of endosomal/lysosomal enzymes.

CONCLUSIONS

This study provides insight into understanding the efficacy and safety of a delivery system for intracellular delivery of biologics and drugs. Blend particles offer a potential platform to target intracellular compartments while potentially minimizing cellular toxicity.

Targeted electro-delivery of oligonucleotides for RNA interference: siRNA and antimiR

For more than a decade, the understanding of RNA interference (RNAi) has been a growing field of interest. Micro-RNAs (miRNAs) are small regulatory RNAs that play an important role in disease development and progression and therefore represent a potential new class of therapeutic targets. However, delivery of RNAi-based oligonucleotides is one of the most challenging hurdles to RNAi-based drug development. Electropermeabilization (EP) is recognized as a successful non-viral method to transfer nucleic acids into living cells both in vitro and in vivo. EP is the direct application of electric pulses to cells or tissues that transiently permeabilize plasma membranes, allowing the efficient delivery of exogenous molecules. The present review focused on the mechanism of RNAi-based oligonucleotides electrotransfer, from cellular uptake to intracellular distribution. Biophysical theories on oligonucleotide electrotransfer will be also presented. The advantages and few drawbacks of EP-mediated delivery will also be discussed.

Protein phosphatase 2C-alpha knockdown reduces angiotensin II-mediated skeletal muscle wasting via restoration of mitochondrial recycling and function

Background

Circulating angiotensin II (AngII) is elevated in congestive heart failure (CHF), and leads to skeletal muscle wasting, which is strongly associated with poor patient outcomes. We previously found that AngII upregulates protein phosphatase 2C-alpha (PP2Cα) and dephosphorylates AMP-activated protein kinase (AMPK), a critical regulator of cellular metabolism, in skeletal muscle.

Methods

To determine the role of PP2Cα in AngII-induced wasting, gastrocnemius (Gas) muscles of FVB mice were injected with scrambled or PP2Cα siRNA and mice were infused with saline or AngII for 4 days.

Results

Knockdown of PP2Cα reduced AngII wasting, blocked AngII upregulation of PP2Cα, increased p-T172-AMPK, and inhibited AngII-mediated reductions in peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), nuclear respiratory factor 1 (NRF1), mitochondrial transcription factor A (TFAM), in complex IV activity, and in ATP levels. AngII impaired the rate of autophagy as determined by a 2.4-fold increase in p62/SQSTM1 (p62) accumulation. This induction was reduced by PP2Cα knockdown, which also increased beclin-1 expression and microtubule-associated protein 1 light chain 3 (LC3)-II conversion in AngII-infused Gas. AngII reduced activating S555 phosphorylation of UNC-51-like kinase 1 (ULK1), a critical regulator of autophagosome formation, and increased inhibitory S757 ULK1 phosphorylation and these effects were prevented by PP2Cα siRNA.

Conclusions

AngII inhibited AMPK activity and reduced PGC-1α and TFAM expression (thereby inhibiting mitochondrial biogenesis) and impaired ULK1 activation and autophagy (thereby also inhibiting clearance of damaged mitochondria), resulting in mitochondrial dysfunction, decreased ATP, and wasting. Knockdown of PP2Cα normalized AMPK activity, PGC-1α, NRF1, and TFAM levels and blocked AngII inhibition of ULK1, leading to improved mitochondrial biogenesis/recycling/function, energy production, and inhibition of AngII-induced wasting. These results demonstrate novel effects of AngII on cellular metabolism that are likely critical in mediating the muscle wasting that is a hallmark of CHF.

Direct imaging of siRNA electrotransfer at the single-cell level

Short interfering RNAs (siRNAs) represent new potential therapeutic tools owing to their capacity to induce strong, sequence-specific, gene silencing in cells. Electropulsation is one of the physical methods successfully used to transfer siRNA into living cells in vitro and in vivo. Although this approach is proved to be effective for silencing gene expression by RNA interference, very little is known about the basic processes supporting siRNA transfer. In this study, we investigated, by direct visualization at the single-cell level, the electro-delivery of Alexa Fluor 546-labeled siRNA into murine melanoma cells stably expressing the enhanced green fluorescent protein (EGFP) as a target gene. The electrotransfer of siRNA was quantified by time-lapse fluorescence microscopy and was correlated with the silencing of EGFP expression. A direct transfer into the cell cytoplasm of the negatively charged siRNA was observed across the plasma membrane exclusively on the side facing the cathode. The oligonucleotide then freely diffused across the cytosol. Therefore, we show that the electric field pulse acts on both the permeabilization of the cell plasma membrane and on the electrophoretic drag of the negatively charged siRNA molecules from the bulk phase into the cytoplasm. The mechanism involved was clearly specific for the physicochemical properties of the electrotransferred molecule and was different from that observed with the electro-transfer of small molecules or plasmid DNA.

Insulin and wound healing

Skin is a dynamic and complex organ that relies on the interaction of different cell types, biomacromolecules and signaling molecules. Injury triggers a cascade of events designed to quickly restore skin integrity. Depending on the size and severity of the wound, extensive physiological and metabolic changes can occur, resulting in impaired wound healing and increased morbidity resulting in higher rates of death. While wound dressings provide a temporary barrier, they are inherently incapable of significantly restoring metabolic upsets, post-burn insulin resistance, and impaired wound healing in patients with extensive burns. Exogenous insulin application has therefore been investigated as a potential therapeutic intervention for nearly a century to improve wound recovery. This review will highlight the important achievements that demonstrate insulin's ability to stimulate cellular migration and burn wound recovery, as well as providing a perspective on future therapeutic applications and research directions.

siRNA delivery via electropulsation: a review of the basic processes

Due to their capacity for inducing strong and sequence specific gene silencing in cells, small interfering RNAs (siRNAs) are now recognized not only as powerful experimental tools for basic research in Molecular biology but with promising potentials in therapeutic development. Delivery is a bottleneck in many studies. There is a common opinion that full potential of siRNA as therapeutic agent will not be attained until better methodologies for its targeted intracellular delivery to cells and tissues are developed. Electropulsation (EP) is one of the physical methods successfully used to transfer siRNA into living cells in vitro and in vivo. This review will describe how siRNA electrotransfer obeys characterized biophysical processes (cell-size-dependent electropermeabilization, electrophoretic drag) with a strong control of a low loss of viability. Protocols can be easily adjusted by a proper setting of the electrical parameters and pulsing buffers. EP can be easily directly applied on animals. Preclinical studies showed that electropermeabilization brings a direct cytoplasmic distribution of siRNA and an efficient silencing of the targeted protein expression. EP appears as a promising tool for clinical applications of gene silencing. A panel of successful trials will be given.

Microprecision delivery of oligonucleotides in a 3D tissue model and its characterization using optical imaging

Despite significant potential of oligonucleotides (ONs) for therapeutic and diagnostic applications, rapid and widespread intracellular delivery of ONs in cells situated in tissues such as skin, head and neck cavity, and eye has not been achieved. This study was aimed at evaluating the synergistic combination of microneedle (MN) arrays and biochemical approaches for localized intratissue delivery of oligonucleotides in living cells in 3D tissue models. This synergistic combination was based on the ability of MNs to precisely deliver ONs into tissues to achieve widespread distribution, and the ability of biochemical agents (streptolysin O (SLO) and cholesterol conjugation to ONs) to enhance intracellular ON delivery. The results of this study demonstrate that ON probes were uniformly coated on microneedle arrays and were efficiently released from the microneedle surface upon insertion in tissue phantoms. Co-insertion of microneedles coated with ONs and SLO into 3D tissue models resulted in delivery of ONs into both the cytoplasm and nucleus of cells. Within a short incubation time (35 min), ONs were observed both laterally and along the depth of a 3D tissue up to a distance of 500 μm from the microneedle insertion point. Similar widespread intratissue distribution of ONs was achieved upon delivery of ON-cholesterol conjugates. Uniformity of ON delivery in tissues improved with longer incubation times (24 h) postinsertion. Using cholesterol-conjugated ONs, delivery of ON probes was limited to the cytoplasm of cells within a tissue. Finally, delivery of cholesterol-conjugated anti-GFP ON resulted in reduction of GFP expression in HeLa cells. In summary, the results of this study provide a novel approach for efficient intracellular delivery of ONs in tissues.

Delivery of RNAi-Based Oligonucleotides by Electropermeabilization

For more than a decade, understanding of RNA interference (RNAi) has been a growing field of interest. The potent gene silencing ability that small oligonucleotides have offers new perspectives for cancer therapeutics. One of the present limits is that many biological barriers exist for their efficient delivery into target cells or tissues. Electropermeabilization (EP) is one of the physical methods successfully used to transfer small oligonucleotides into cells or tissues. EP consists in the direct application of calibrated electric pulses to cells or tissues that transiently permeabilize the plasma membranes, allowing efficient in vitro and in vivo cytoplasmic delivery of exogenous molecules. The present review reports on the type of therapeutic RNAi-based oligonucleotides that can be electrotransferred, the mechanism(s) of their electrotransfer and the technical settings for pre-clinical purposes.

RNAi-based nanomedicines for targeted personalized therapy

RNA interference (RNAi) has just made it through the pipeline to clinical trials. However, in order for RNAi to serve as an ideal personalized therapeutics and be clinically approved-safe, specific, and potent strategies must be devised for efficient delivery of RNAi payloads to specific cell types, which despite the immense potential, remains a challenge. Through evaluating the recent reported studies in this field, we introduce the progress in designing targeted nano-scaled strategies that are anticipated to overcome the delivery drawbacks and along with the exciting "omics" discipline to personalize RNAi-based therapeutics.

Chemically modified oligonucleotide-increased stability negatively correlates with its efficacy despite efficient electrotransfer

Despite great potential for disease treatment, small interfering RNA (siRNA) development has been hampered due to its poor stability and the lack of efficient delivery method. To overcome the sensitivity, new generations of chemically modified oligonucleotides have been developed such as the locked nucleic acid (LNA). LNA substitution in an siRNA sequence (siLNA) is supposed to increase its stability and its affinity for its complementary sequence. The purpose of this study was to evaluate the potential benefit of an anti-GFP siLNA using the biophysical delivery method electropermeabilization. We used two types of electrical conditions: electrochemotherapy (ECT), a condition for efficient transfer of small molecules in clinics, and electrogenotherapy (EGT), a condition for efficient transfer of macromolecules. We first confirmed that siLNA was indeed more stable in mouse serum than unmodified siRNA. After determining the ECT and EGT optimal electrical parameters for a human colorectal carcinoma cell line (HCT-116) expressing eGFP, we showed that modifications of siRNA do not interfere with electrotransfer efficiency. However, despite its higher stability and its high electrotransfer efficacy, siLNA was less efficient for eGFP silencing compared to the electrotransferred, unmodified siRNA regardless of the electrical conditions used. Our study highlighted the care that is needed when designing chemically modified oligonucleotides.

Single cell electroporation using microfluidic devices

Electroporation is a powerful technique to increase the permeability of cell membranes and subsequently introduce foreign materials into cells. Pores are created in the cell membrane upon application of an electric field (kV/cm). Most applications employ bulk electroporation, at the scale of 1 mL of cells (ca. one million cells). However, recent progresses have shown the interest to miniaturize the technique to a single cell. Single cell electroporation is achieved either using microelectrodes which are placed in close vicinity to one cell, or in a microfluidic format. We focus here on this second approach, where individual cells are trapped in micrometer-size structures within a microchip, exposed in situ to a high electric field and loaded with either a dye (proof-of-principle experiments) or a plasmid. Specifically, we present one device that includes an array of independent electroporation sites for customized and successive poration of nine cells. The different steps of the single cell electroporation protocol are detailed including cell sample preparation, cell trapping, actual cell poration and on-chip detection of pore formation. Electroporation is illustrated here with the transport of dyes through the plasma membrane, the transfection of cells with GFP-encoding plasmids, and the study of the ERK1 signaling pathway using a GFP-ERK1 protein construct expressed by the cells after their transfection with the corresponding plasmid. This last example highlights the power of microfluidics with the implementation of various steps of a process (cell poration, culture, imaging) performed at the single cell level, on a single device.

shRNA-mediated gene knockdown in skeletal muscle

RNA interference appears as a promising tool for therapeutic gene silencing to block protein expression. A long-lived silencing is obtained through the in situ expression of shRNA. A safe approach is to use a physical method such as in vivo electropulsation with plate electrodes. This is presently validated in muscles by the in vivo coelectrotransfer of plasmids specifically coding for expression and silencing of a fluorescent protein. No long-lived tissue damage is observed by the proper choice of the electric pulsing parameters and the amount of injected plasmids. Using a noninvasive fluorescence imaging assay, electrodelivery in mouse muscles is observed to induce complete silencing over more than 2 months in a specific way. The proper choices of the plasmids (sequence, promoter, and relative amounts) appear as key parameters in the successful long-term silencing.

Skeletal muscle IP3R1 receptors amplify physiological and pathological synaptic calcium signals

Ca(2+) release from internal stores is critical for mediating both normal and pathological intracellular Ca(2+) signaling. Recent studies suggest that the inositol 1,4,5-triphosphate (IP(3)) receptor mediates Ca(2+) release from internal stores upon cholinergic activation of the neuromuscular junction (NMJ) in both physiological and pathological conditions. Here, we report that the type I IP(3) receptor (IP(3)R(1))-mediated Ca(2+) release plays a crucial role in synaptic gene expression, development, and neuromuscular transmission, as well as mediating degeneration during excessive cholinergic activation. We found that IP(3)R(1)-mediated Ca(2+) release plays a key role in early development of the NMJ, homeostatic regulation of neuromuscular transmission, and synaptic gene expression. Reducing IP(3)R(1)-mediated Ca(2+) release via siRNA knockdown or IP(3)R blockers in C2C12 cells decreased calpain activity and prevented agonist-induced acetylcholine receptor (AChR) cluster dispersal. In fully developed NMJ in adult muscle, IP(3)R(1) knockdown or blockade effectively increased synaptic strength at presynaptic and postsynaptic sites by increasing both quantal release and expression of AChR subunits and other NMJ-specific genes in a pattern resembling muscle denervation. Moreover, in two mouse models of cholinergic overactivity and NMJ Ca(2+) overload, anti-cholinesterase toxicity and the slow-channel myasthenic syndrome (SCS), IP(3)R(1) knockdown eliminated NMJ Ca(2+) overload, pathological activation of calpain and caspase proteases, and markers of DNA damage at subsynaptic nuclei, and improved both neuromuscular transmission and clinical measures of motor function. Thus, blockade or genetic silencing of muscle IP(3)R(1) may be an effective and well tolerated therapeutic strategy in SCS and other conditions of excitotoxicity or Ca(2+) overload.

Using drug-excipient interactions for siRNA delivery

SiRNA is the trigger of RNA interference, a mechanism discovered in the late 1990s. To release the therapeutic potential of this versatile but large and fragile molecule, excipients are used which either interact by electrostatic interaction, passively encapsulate siRNA or are covalently attached to enable specific and safe delivery of the drug substance. Controlling the delicate balance between protective complexation and release of siRNA at the right point and time is done by understanding excipients–siRNA interactions. These can be lipids, polymers such as PEI, PLGA, Chitosans, Cyclodextrins, as well as aptamers and peptides. This review describes the mechanisms of interaction of the most commonly used siRNA delivery vehicles, and looks at the results of their clinical and preclinical studies.

Evaluation of the ability of two transfection reagents to deliver small interfering RNA molecules to equine and guinea pig cartilage in vitro

OBJECTIVE

To evaluate 2 commercially available transfection reagents for transfection efficiency and distribution of small interfering RNA (siRNA) molecules to chondrocytes in monolayer cultures and full-thickness cartilage explants from guinea pigs and horses.

SAMPLE

Cartilage explants from 5 one-month-old and 3 adult guinea pigs and 5 adult clinically normal horses.

PROCEDURES

Monolayer chondrocytes and uniform cartilage explants were exposed to 1 of 2 siRNA transfection complexes according to manufacturers' protocols (1μM [1×]). Additionally, monolayer chondrocytes were exposed to 2× the suggested amount of a proprietary siRNA molecule. Full-thickness cartilage explants were treated with 1× (1μM), 2× (2μM), and 4× (4μM) or 1× (0.13μM), 4× (0.52μM), and 8× (1.04μM) the recommended concentrations of the proprietary siRNA and the cationic liposome siRNA, respectively, in equivalent media volumes. Use of fluorescent siRNA duplexes allowed quantification of transfected cells via flow cytometry and direct visualization of the depth and distribution of in situ transfection via fluorescent microscopy.

RESULTS

With both transfection reagents, > 90% of monolayer chondrocytes were transfected. In explants, only use of the proprietary molecule achieved > 50% transfection efficiency, whereas use of the cationic liposome achieved < 20%. Only the proprietary molecule-treated cartilage consistently contained fluorescent cells throughout all zones; the cationic liposome-transfected chondrocytes were restricted to explant surfaces.

CONCLUSIONS AND CLINICAL RELEVANCE

Robust transfection of chondrocytes in monolayer was achieved with both reagents, but only use of the proprietary molecule attained effective full-thickness transfection of explants that may allow relevant transcript reduction via RNAi.

Strategies for in vivo delivery of siRNAs: recent progress

RNA interference (RNAi) is a post-transcriptional gene-silencing mechanism that involves the degradation of messenger RNA in a highly sequence-specific manner. Double-stranded small interfering RNA (siRNA), consisting of 21-25 nucleotides, can induce RNAi and inhibit the expression of target proteins. Therefore, siRNA is considered a promising therapeutic for treatment of a variety of diseases, including genetic and viral diseases, and cancer. Clinical trials of siRNA are ongoing or have been planned, although some issues need to be addressed. For example, cellular uptake of naked siRNA is extremely low due to its polyanionic nature. Furthermore, siRNA is easily degraded by enzymes in blood, tissues, and cells. Several types of chemically modified siRNA have been produced and investigated to improve stability; these have involved modification of the siRNA backbone, the sugar moiety, and the nucleotide bases of antisense and/or sense strands. Because the accumulation at the target site after administration is extremely low, even if stability is improved, an effective delivery system is required to induce RNAi at the site of action. Delivery strategies can be categorized into physical methods, conjugation methods, and drug delivery system carrier-mediated methods. Physical techniques can enhance siRNA uptake at a specific tissue site using electroporation, pressure, mechanical massage, etc. Terminal modification of siRNAs can enhance their resistance to degradation by exonucleases in serum and tissue. Moreover, modification with a suitable ligand can achieve targeted delivery. Several types of carrier for drug delivery have been developed for siRNA in addition to traditional cationic liposome and cationic polymer systems. Ultrasound and microbubbles or liposomal bubbles have also been used in combination with a carrier for siRNA delivery. New materials with unique characteristics such as carbon nanotubes, gold nanoparticles, and gold nanorods have attracted attention as innovative carriers for siRNA.

Sustained prolonged topical delivery of bioactive human insulin for potential treatment of cutaneous wounds

Skin damaged by heat, radiation, or chemical exposure is difficult to treat and slow to heal. Indeed full restoration of the tissue is difficult to obtain. Sub-dermal insulin injection was recently shown to stimulate wound healing of the skin by accelerating wound closure, stimulating angiogenesis and inducing a regenerative process of healing. We have developed a topical delivery vehicle that is capable of releasing therapeutic levels of bioactive insulin for several weeks with the potential to stimulate and sustain healing. By encapsulating the crystalline form of insulin within poly(d,l-lactide-co-glycolide) microspheres, we succeeded in stabilizing and then releasing bioactive insulin for up to 25 days. To measure bioactivity we used Rat L6 myofibroblasts, stimulated them with this slow release insulin and determined activation of the receptors on the cell surface by quantifying AKT phosphorylation. There was only a minor and gradual decrease in AKT phosphorylation over time. To determine whether the slow release insulin could stimulate keratinocyte migration, wounding was simulated by scratching confluent cultures of human keratinocytes (HaCaT). Coverage of the scratch "wounds" was significantly faster in the presence of insulin released from microspheres than in the insulin-free control. Extended and sustained topical delivery of active insulin from a stable protein crystal-based reservoir shows promise in promoting tissue healing.

Delivery systems for the direct application of siRNAs to induce RNA interference (RNAi) in vivo

RNA interference (RNAi) is a powerful method for specific gene silencing which may also lead to promising novel therapeutic strategies. It is mediated through small interfering RNAs (siRNAs) which sequence-specifically trigger the cleavage and subsequent degradation of their target mRNA. One critical factor is the ability to deliver intact siRNAs into target cells/organs in vivo. This review highlights the mechanism of RNAi and the guidelines for the design of optimal siRNAs. It gives an overview of studies based on the systemic or local application of naked siRNAs or the use of various nonviral siRNA delivery systems. One promising avenue is the the complexation of siRNAs with the polyethylenimine (PEI), which efficiently stabilizes siRNAs and, upon systemic administration, leads to the delivery of the intact siRNAs into different organs. The antitumorigenic effects of PEI/siRNA-mediated in vivo gene-targeting of tumor-relevant proteins like in mouse tumor xenograft models are described.

Numerical study of the electroporation pulse shape effect on molecular uptake of biological cells

Background

In order to reduce the side-effects of chemotherapy, combined chemotherapy-electroporation (electrochemotherapy) has been suggested. Electroporation, application of appropriate electric pulses to biological cells, can significantly enhance molecular uptake of cells due to formation of transient pores in the cell membrane. It was experimentally demonstrated that the efficiency of electroporation is under the control of electric pulse parameters. However, the theoretical basis for these experimental results is not fully explained. In order to predict the outcome of experiments and optimize the efficiency of electroporation before each treatment, we developed a model to investigate the effect of pulse shape on efficiency of electroporation.

Results

Our model is based on a developed chemical-kinetics scheme and trapezium barrier model, while self-consistency was taken into account. This model is further supplemented with a molecular transport model to acquire the molecular uptake of cells. The investigated pulse shapes in this study were unipolar rectangular pulses with different rise and fall times, triangular, sinusoidal and bipolar rectangular pulses and also sinusoidal modulated unipolar pulses with different percentages of modulation. The obtained results from our modelling and simulations are in good agreement with previously published experimental results.

Conclusions

We therefore conclude that this model can be used to predict the effects of arbitrarily shaped electroporation pulses on cell membrane conductivity and molecular transport across the cell membrane.

RNAi as a new therapeutic strategy against HCV

Hepatitis C virus is a major cause of liver associated diseases all over the world. Irrespective of the significant advances in the current therapy, drugs and vaccines are restricted with many factors such as toxicity, complexity, cost and resistance. New technologies particularly RNA interference (RNAi) mediated by small interfering RNA (siRNA) have become more and more interesting and effective therapeutic entities to silence pathogenic gene products associated with disease, including cancer, viral infections and autoimmune disorders. RNAi works at a posttranscriptional level by targeting mRNA as a mean for inhibiting the synthesis of the encoded protein. Several reports have indicated the efficiency and specificity of synthetic and vector based siRNAs inhibiting HCV replication. In the present review, we focused on the recent development in the potential use and issues regarding siRNA as a therapy for HCV.

Electroporation and ultrasound enhanced non-viral gene delivery in vitro and in vivo

Non-viral vectors are less efficient than the use of viral vectors for delivery of genetic material to cells in vitro and especially in vivo. However, viral vectors involve the use of foreign proteins that can stimulate both the innate and acquired immune response. In contrast, plasmid DNA can be delivered without carrier proteins and is non-immunogenic. Plasmid gene delivery can be enhanced by the use of physical methods that aid the passage of the plasmid through the cell membrane. Electroporation and microbubble-enhanced ultrasound are two of the most effective physical delivery methods and these can be applied to a range of different cell types in vitro and a broad range of tissues in vivo. Both techniques also have the advantage that, unlike viral vectors, they can be used to target specific tissues with systemic delivery. Although electroporation is often the more efficient of the two, microbubble-enhanced ultrasound causes less damage and is less invasive. This review provides an introduction to the methodology and summarises the range of cells and tissues that have been genetically modified using these techniques.

Nonviral methods for siRNA delivery

RNA interference (RNAi) as a mechanism to selectively degrade mRNA (mRNA) expression has emerged as a potential novel approach for drug target validation and the study of functional genomics. Small interfering RNAs (siRNA) therapeutics has developed rapidly and already there are clinical trials ongoing or planned. Although other challenges remain, delivery strategies for siRNA become the main hurdle that must be resolved prior to the full-scale clinical development of siRNA therapeutics. This review provides an overview of the current delivery strategies for synthetic siRNA, focusing on the targeted, self-assembled nanoparticles which show potential to become a useful and efficient tool in cancer therapy.

Variability of the minimal transmembrane voltage resulting in detectable membrane electroporation

We present a study of the variability of the minimal transmembrane voltage resulting in detectable electroporation of the plasma membrane of spherical and irregularly shaped CHO cells (we denote this voltage by ITVc). Electroporation was detected by monitoring the influx of Ca(2+), and the transmembrane voltage was computed on a 3D finite-elements model of each cell constructed from its cross-section images. We found that ITVc was highly variable, particularly in irregularly shaped cells, where it ranged from 512-1028 mV. We show that this range is much too large to be an artifact due to numerical errors and experimental inaccuracies, implying that for cells of the same type and exposed to the same number of pulses with the same duration, the value of ITVc can differ considerably from one cell to another. We also observed that larger cells are in many cases characterized by a higher ITVc than a smaller one. This is in qualitative agreement with the reports that higher membrane curvature facilitates electroporation, but quantitative considerations suggest that the observed variability of ITVc cannot be attributed entirely to the differences in membrane curvature.

Sustained long-term RNA interference in nucleus pulposus cells in vivo mediated by unmodified small interfering RNA

RNA interference (RNAi) technology has recently emerged as an important biological strategy for gene silencing. Previously, the efficacies of RNAi in cultured nucleus pulposus cells in vitro have been reported. However, RNAi in the disc in vivo has never been reported. Therefore, the aims of the present study were to establish a method for RNAi in the disc in vivo and to evaluate the applicability of this technique for endogenous genes in the intervertebral discs using Fas Ligand (FasL) as a representative endogenous gene. To evaluate the efficacy of RNAi in vivo, two reporter luciferase plasmids (Firefly and Renilla) were used. These plasmids and unmodified short interference RNA (siRNA) duplex for targeting Firefly luciferase were co-transfected into coccygeal intervertebral disc of Sprague-Dawley rats in vivo using the ultrasound gene transfer technique. To evaluate the RNAi of the endogenous gene in vivo, siRNAs targeting rat FasL were transfected with the same technique. Non-specific siRNA was used as the negative control. The discs receiving no siRNAs were used as the control. The inhibitory effect of Firefly luciferase against Renilla luciferase was obtained using the results of dual-luciferase assay. Down-regulation of endogenous FasL was calculated by the data from real-time PCR. Our results showed that siRNA for Firefly luciferase can dramatically down-regulate the Firefly luciferase gene expression in vivo compared with Renilla luciferase. The inhibitory effects were maintained for at least 24 weeks and at 24 weeks post transfection, the inhibitory rate was 80% compared with the control group. Furthermore, the siRNA co-transfection group inhibited endogenous FasL expression by 53% compared with the control group. The present study demonstrates long-term down-regulation mediated by unmodified siRNA is possible not only for the exogenous reporter gene, but also for endogenous FasL expression in rat discs in vivo. This application of RNAi might be promising as a local therapy for disc degeneration and associated disorders by down-regulating some of the genes that are harmful for the normal physiology of the disc and may cause disc degeneration.

Transmembrane voltage analyses in spheroidal cells in response to an intense ultrashort electrical pulse

Self-consistent evaluations of both the transmembrane potential (TMP) and possible electroporation density across membrane of spheroidal cells in response to ultrashort, high-intensity pulses are reported and discussed. Most treatments in the literature have been based on spherical cells, and this represents a step towards more realistic analyses. The present study couples the Laplace equation with Smoluchowski theory of pore formation, to yield dynamic membrane conductivities that influence the TMP. It is shown that the TMP induced by pulsed external voltages can be substantial higher in oblate spheroids as compared to spherical or prolate spheroidal cells. Flattening of the surface area in oblate spheroids leads to both higher electric fields seen by the membrane, and allows a great fraction of the surface area to be porated. This suggests that biomedical applications such as drug delivery and electrochemotherapy could work best for flatter-shaped cells, and secondary field-enabled orienting would be beneficial. Results for arbitrary field orientations and different cell sizes have also been presented.

A histone deacetylase 4/myogenin positive feedback loop coordinates denervation-dependent gene induction and suppression

Muscle activity contributes to formation of the neuromuscular junction and affects muscle metabolism and contractile properties through regulated gene expression. However, the mechanisms coordinating these diverse activity-regulated processes remain poorly characterized. Recently, it was reported that histone deacetylase 4 (HDAC4) can mediate denervation-induced myogenin and nicotinic acetylcholine receptor gene expression. Here, we report that HDAC4 is not only necessary for denervation-dependent induction of genes involved in synaptogenesis (nicotinic acetylcholine receptor and muscle-specific receptor tyrosine kinase) but also for denervation-dependent suppression of genes involved in glycolysis (muscle-specific enolase and phosphofructokinase). In addition, HDAC4 differentially regulates genes involved in muscle fiber type specification by inducing myosin heavy chain IIA and suppressing myosin heavy chain IIB. Consistent with these regulated gene profiles, HDAC4 is enriched in fast oxidative fibers of innervated tibialis anterior muscle and HDAC4 knockdown enhances glycolysis in cultured myotubes. HDAC4 mediates gene induction indirectly by suppressing the expression of Dach2 and MITR that function as myogenin gene corepressors. In contrast, HDAC4 is directly recruited to myocyte enhancer factor 2 sites within target promoters to mediate gene suppression. Finally, we discovered an HDAC4/myogenin positive feedback loop that coordinates gene induction and repression underlying muscle phenotypic changes after muscle denervation.

siRNA, miRNA, and shRNA: in vivo Applications

RNA interference (RNAi), an accurate and potent gene-silencing method, was first experimentally documented in 1998 in Caenorhabditis elegans by Fire et al., who subsequently were awarded the 2006 Nobel Prize in Physiology/Medicine. Subsequent RNAi studies have demonstrated the clinical potential of synthetic small interfering RNAs (siRNAs) or short hairpin RNAs (shRNAs) in dental diseases, eye diseases, cancer, metabolic diseases, neurodegenerative disorders, and other illnesses. siRNAs are generally from 21 to 25 base-pairs (bp) in length and have sequence-homology-driven gene-knockdown capability. RNAi offers researchers an effortless tool for investigating biological systems by selectively silencing genes. Key technical aspects—such as optimization of selectivity, stability, in vivo delivery, efficacy, and safety—need to be investigated before RNAi can become a successful therapeutic strategy. Nevertheless, this area shows a huge potential for the pharmaceutical industry around the globe. Interestingly, recent studies have shown that the small RNA molecules, either indigenously produced as microRNAs (miRNAs) or exogenously administered synthetic dsRNAs, could effectively activate a particular gene in a sequence-specific manner instead of silencing it. This novel, but still uncharacterized, phenomenon has been termed ‘RNA activation’ (RNAa). In this review, we analyze these research findings and discussed the in vivo applications of siRNAs, miRNAs, and shRNAs.

A retrovirus-based system to stably silence GDF-8 expression and enhance myogenic differentiation in human rhabdomyosarcoma cells

BACKGROUND

Myostatin, also called GDF-8, a secreted growth and differentiating factor that belongs to the transforming growth factor-beta superfamily, is a known negative regulator of myogenesis in vivo. Overexpression of GDF-8 contributes to the lack of differentiation in human rhabdomyosarcoma (RMS) cells. We investigated whether a retrovirus-based RNA interference (RNAi) system against GDF-8 expression in human RMS cells would enhance myogenic differentiation.

METHODS

A retrovirus-based RNAi system was developed that utilized the U6-RNA polymerase III promoter to drive efficient expression and deliver the GDF8-specific short hairpin RNAs (shRNAs) in human RMS cell A204. In this system, the retrovirus vector was integrated into the host cell genome and allowed stable expression of shRNAs. GDF-8 expression was determined by real-time polymerase chain reaction and western blotting analysis. An 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was performed to determine the cell proliferation. Myogenic differentiation markers were monitored by western blotting analysis. Cell cycle and apoptosis was determined by propidium iodide staining and analysed in a flow cytometer.

RESULTS

In the siGDF8 A204 cell pools, the levels of both GDF-8 mRNA and protein were dramatically reduced by this RNAi system. In differentiation conditions, inhibition of myostatin synthesis led to enhanced cell cycle withdrawal, consequently stimulated myogenic differentiation and increased the rate of tumor cell apoptosis.

CONCLUSIONS

The results demonstrate that deactivation of myostatin by using retrovirus-based RNAi thus may be useful for therapy in rhabdomyosarcomas.

Delivery of siRNA into the cytoplasm by liposomal bubbles and ultrasound

Small interfering RNA (siRNA) is expected to be a novel therapeutic tool, however, its utilization has been limited by inefficient delivery systems. Recently, we have developed novel polyethyleneglycol modified liposomes (Bubble liposomes; BL) entrapping an ultrasound (US) imaging gas, which can work as a gene delivery tool with US exposure. In this study, we investigated whether the BL were suitable for the delivery of siRNA. BL efficiently delivered siRNA with only 10 s of exposure to US in vitro. Specific gene silencing effects could be achieved well even in the presence of serum or with the disruption of endocytosis. We suggest that siRNA is directly introduced into the cytoplasm by the BL and US and the mechanism enables effective transfection within a short time and in the presence of high serum. Transfection of siRNA into the tibialis muscles with BL and US was also performed. The gene-silencing effect could be sustained for more than 3 weeks. Thus, BL could be a useful siRNA delivery tool in vitro and in vivo.

Gene silencing by RNAi in mouse Sertoli cells

BACKGROUND

RNA interference (RNAi) is a valuable tool in the investigation of gene function. The purpose of this study was to examine the availability, target cell types and efficiency of RNAi in the mouse seminiferous epithelium.

METHODS

The experimental model was based on transgenic mice expressing EGFP (enhanced green fluorescent protein). RNAi was induced by in vivo transfection of plasmid vectors encoding for short hairpin RNAs (shRNAs) targeting EGFP. shRNAs were transfected in vivo by microinjection into the seminiferous tubules via the rete testis followed by square wave electroporation. As a transfection reporter, expression of red fluorescent protein (HcRed 1) was used. Cell types, the efficiency of both transfections and RNAi were all evaluated.

RESULTS

Sertoli cells were the main transfected cells. A reduction of about 40% in the level of EGFP protein was detected in cells successfully transfected both in vivo and in vitro. However, the efficiency of in vivo transfection was low.

CONCLUSION

In adult seminiferous epithelial cells, in vivo post-transcriptional gene silencing mediated by RNAi via shRNA is efficient in Sertoli cells. Similar levels of RNAi were detected both in vivo and in vitro. This also indicates that Sertoli cells have the necessary silencing machinery to repress the expression of endogenous genes via RNAi.

RNA interference: an emerging generation of biologicals

RNA interference (RNAi) is a mechanism displayed by most eukaryotic cells to rid themselves of foreign double‐stranded RNA molecules. RNAi has now been demonstrated to function in mammalian cells to alter gene expression, and has been used as a means for genetic discovery as well as a possible strategy for genetic correction. RNAi was first described in animal cells by Fire and colleagues in the nematode, Caenorhabditis elegans. Knowledge of RNAi mechanism in mammalian cell in 2001 brought a storm in the field of drug discovery. During the past few years scientists all over the world are focusing on exploiting the therapeutic potential of RNAi for identifying a new class of therapeutics. The applications of RNAi in medicine are unlimited because all cells possess RNAi machinery and hence all genes can be potential targets for therapy. RNAi can be developed as an endogenous host defense mechanism against many infections and diseases. Several studies have demonstrated therapeutic benefits of small interfering RNAs and micro RNAs in animal models. This has led to the rapid advancement of the technique from research discovery to clinical trials.

In vivo silencing of a molecular target by short interfering RNA electroporation: tumor vascularization correlates to delivery efficiency

Screening for a molecular target for cancer therapy requires multiple steps, of which an important one is evaluation of the knockdown effect of the target molecule on pregrown xenograft tumors. However, methods currently used for local administration of knockdown reagents, such as short interfering RNA (siRNA), are not satisfactory as to simplicity and efficiency. We established an electroporation method involving a constant voltage and "plate and fork" type electrodes and used it for in vivo delivery of siRNA. The delivery efficiency correlated to the electric current. The electric current correlated to the microvascular density and vascular endothelial growth factor (VEGF) expression and exhibited a threshold that guaranteed efficient delivery. Consequently, we showed that the vascularization and VEGF expression in tumors determined the efficiency of delivery of siRNA by electroporation. VEGF was chosen as a model target. VEGF siRNA electroporation suppressed the growth of tumors exhibiting high VEGF expression to less than 10% of the control level, but it had no effect on low VEGF-expressing tumors. Notably, a long interval (20 days) of electroporation was enough to obtain a satisfactory effect. Systemically injected siRNA could also be delivered into tumors by this method. Our data will provide the technical basis for in vivo electroporation, and this simple and efficient siRNA delivery method is applicable to in vivo comprehensive screening for a molecular target.

Long-lasting In vivo Gene Silencing by Electrotransfer of shRNA Expressing Plasmid

RNA interference appears as a promising tool for therapeutic gene silencing. A key limit is the delivery of the siRNA. A safe approach is to use a physical method such as in vivo electropulsation with contact electrodes. Getting a long lived silencing can be better approached by using the in situ expression of shRNA. This is presently obtained by using co-electrotransfer of specific plasmids coding for expression and silencing of a fluorescent protein. Using a non invasive fluorescence imaging assay, electrodelivery in mouse muscles is observed to induce complete silencing over more than two months in a specific way. The proper choices of the plasmids (sequence and relative amounts) and of the electric pulsing conditions appear as key parameters in the successful silencing.

Control of muscle mitochondria by insulin entails activation of Akt2-mtNOS pathway: implications for the metabolic syndrome

Background

In the metabolic syndrome with hyperinsulinemia, mitochondrial inhibition facilitates muscle fat and glycogen accumulation and accelerates its progression. In the last decade, nitric oxide (NO) emerged as a typical mitochondrial modulator by reversibly inhibiting citochrome oxidase and oxygen utilization. We wondered whether insulin-operated signaling pathways modulate mitochondrial respiration via NO, to alternatively release complete glucose oxidation to CO₂ and H₂O or to drive glucose storage to glycogen.

Methodology/Principal Findings

We illustrate here that NO produced by translocated nNOS (mtNOS) is the insulin-signaling molecule that controls mitochondrial oxygen utilization. We evoke a hyperinsulinemic-normoglycemic non-invasive clamp by subcutaneously injecting adult male rats with long-lasting human insulin glargine that remains stable in plasma by several hours. At a precise concentration, insulin increased phospho-Akt2 that translocates to mitochondria and determines in situ phosphorylation and substantial cooperative mtNOS activation (+4–8 fold, P<.05), high NO, and a lowering of mitochondrial oxygen uptake and resting metabolic rate (−25 to −60%, P<.05). Comparing in vivo insulin metabolic effects on gastrocnemius muscles by direct electroporation of siRNA nNOS or empty vector in the two legs of the same animal, confirmed that in the silenced muscles disrupted mtNOS allows higher oxygen uptake and complete (U-¹⁴C)-glucose utilization respect to normal mtNOS in the vector-treated ones (respectively 37±3 vs 10±1 µmolO₂/h.g tissue and 13±1 vs 7.2±1 µmol ³H₂O/h.g tissue, P<.05), which reciprocally restricted glycogen-synthesis by a half.

Conclusions/Significance

These evidences show that after energy replenishment, insulin depresses mitochondrial respiration in skeletal muscle via NO which permits substrates to be deposited as macromolecules; at discrete hyperinsulinemia, persistent mtNOS activation could contribute to mitochondrial dysfunction with insulin resistance and obesity and therefore, to the progression of the metabolic syndrome.

Nonviral delivery of synthetic siRNAs in vivo

Sequence-specific gene silencing using small interfering RNA (siRNA) is a Nobel prize-winning technology that is now being evaluated in clinical trials as a potentially novel therapeutic strategy. This article provides an overview of the major pharmaceutical challenges facing siRNA therapeutics, focusing on the delivery strategies for synthetic siRNA duplexes in vivo, as this remains one of the most important issues to be resolved. This article also highlights the importance of understanding the genocompatibility/toxicogenomics of siRNA delivery reagents in terms of their impact on gene-silencing activity and specificity. Collectively, this information is essential for the selection of optimally acting siRNA delivery system combinations for the many proposed applications of RNA interference.

Delivering small interfering RNA for novel therapeutics

The gene silencing capability of RNA interference (RNAi) is being used to study individual gene's biological function and role in biochemical pathways. However, the efficacy of RNAi depends upon efficient delivery of the intermediates of RNAi, small interfering RNA (siRNA) oligonucleotides. The delivery challenge is even greater when the aim is to inhibit the expression of target genes in disease tissues. In vivo delivery of siRNA is complicated and challenging, and recent works on various animal disease models and early successes in human clinical trials are enlightening the tremendous potential of RNAi therapeutics. In this chapter, the latest developments of in vivo delivery of siRNA and the critical issues related to this effort are addressed.