Phospholipase A2 Sensitive Liposomes for Delivery of Small Interfering RNA (siRNA)

Small interfering RNA (siRNA) is potent and highly specific for gene silencing and there is currently a lot of enthusiasm for developing siRNA into a drug. However, for most therapeutic applications of siRNA, delivery systems are needed. These delivery systems have multiple requirements and should on one hand ideally be stable carriers protecting the siRNA from degradation and on the other hand assist the siRNA in overcoming membrane barriers for intracellular delivery to the cytosol. Long-circulating liposomes, which are sensitive to secretory phospholipase A₂ (sPLA₂) are feasible delivery systems for systemic administration of drugs due to their passive targeting to pathological tissue via the enhanced permeability and retention (EPR) effect and their site-specific, enzyme-triggered release of encapsulated drug in response to sPLA₂ which exists locally at elevated levels at, e.g,. sites of inflammation. However, recent data suggest that endosomal membrane destabilizing approaches could be addressed to design sPLA₂-sensitive liposomes as successful delivery systems for siRNA to the RNA interference pathway in the cytoplasm upon systemic administration.     

Systemic siRNA delivery to leukocyte-implicated diseases

Short interfering RNA (siRNA), a small duplex of RNA fragment, has proved as an extremely useful research tool to interrogate gene functions in test tubes. However, the transformation of siRNAs from a functional genomic tool into a new therapeutic modality has been hindered by ineffective delivery methods for systemic administration. In this review, we will discuss the recent advances in formulating new delivery strategies that target siRNAs to specific cells following systemic administration. Special emphasis will be given to leukocytes, since siRNA delivery remains exceptionally challenging here due to the unavailability of effective delivery technologies. We will not only detail new platforms that utilize leukocyte integrins as receptor targets for siRNAs delivery, but also show how one of these strategies has been utilized for in vivo drug target validation of a novel anti-inflammatory target, cyclin D1, for inflammatory bowel diseases.     

Cellular Delivery of siRNA Mediated by Fusion-Active Virosomes

RNA interference is expected to have considerable potential for the development of novel specific therapeutic strategies. However, successful application of RNA interference in vivo will depend on the availability of efficient delivery systems for the introduction of small-interfering RNA (siRNA) into the appropriate target cells. This paper focuses on the use of reconstituted viral envelopes (“virosomes”), derived from influenza virus, as a carrier system for cellular delivery of siRNA. Complexed to cationic lipid, siRNA molecules could be efficiently encapsulated in influenza virosomes. Delivery to cultured cells was assessed on the basis of flow cytometry analysis using fluorescently labeled siRNA. Virosome-encapsulated siRNA directed against Green Fluorescent Protein (GFP) inhibited GFP fluorescence in cells transfected with a plasmid encoding GFP or in cells constitutively expressing GFP. Delivery of siRNA was dependent on the low-pH-induced membrane fusion activity of the virosomal hemagglutinin, supporting the notion that virosomes introduce their encapsulated siRNA into the cell cytosol through fusion of the virosomal membrane with the limiting membrane of cellular endosomes, after internalization of the virosomes by receptor-mediated endocytosis. It is concluded that virosomes represent a promising carrier system for cellular delivery of siRNA in vitro as well as in vivo.     

Cellular delivery of siRNA mediated by fusion-active virosomes

RNA interference is expected to have considerable potential for the development of novel specific therapeutic strategies. However, successful application of RNA interference in vivo will depend on the availability of efficient delivery systems for the introduction of small-interfering RNA (siRNA) into the appropriate target cells. This paper focuses on the use of reconstituted viral envelopes ("virosomes"), derived from influenza virus, as a carrier system for cellular delivery of siRNA. Complexed to cationic lipid, siRNA molecules could be efficiently encapsulated in influenza virosomes. Delivery to cultured cells was assessed on the basis of flow cytometry analysis using fluorescently labeled siRNA. Virosome-encapsulated siRNA directed against Green Fluorescent Protein (GFP) inhibited GFP fluorescence in cells transfected with a plasmid encoding GFP or in cells constitutively expressing GFP. Delivery of siRNA was dependent on the low-pH-induced membrane fusion activity of the virosomal hemagglutinin, supporting the notion that virosomes introduce their encapsulated siRNA into the cell cytosol through fusion of the virosomal membrane with the limiting membrane of cellular endosomes, after internalization of the virosomes by receptor-mediated endocytosis. It is concluded that virosomes represent a promising carrier system for cellular delivery of siRNA in vitro as well as in vivo.     

Atelocollagen-mediated systemic administration of myostatin-targeting siRNA improves muscular atrophy in caveolin-3-deficient mice

Small interfering RNA (siRNA)-mediated silencing of gene expression is rapidly becoming a powerful tool for molecular therapy. However, the rapid degradation of siRNAs and their limited duration of activity require efficient delivery methods. Atelocollagen (ATCOL)-mediated administration of siRNAs is a promising approach to disease treatment, including muscular atrophy. Herein, we report that ATCOL-mediated systemic administration of a myostatin-targeting siRNA into a caveolin-3-deficient mouse model of limb-girdle muscular dystrophy 1C (LGMD1C) induced a marked increase in muscle mass and a significant recovery of contractile force. These results provide evidence that ATCOL-mediated systemic administration of siRNAs may be a powerful therapeutic tool for disease treatment, including muscular atrophy.     

Novel polymerizable surfactants with pH-sensitive amphiphilicity and cell membrane disruption for efficient siRNA delivery

Small interfering RNA (siRNA) is a promising new therapeutic modality that can specifically silence disease-related genes. The main challenge for successful clinical development of therapeutic siRNA is the lack of efficient delivery systems. In this study, we have designed and synthesized a small library of novel multifunctional siRNA carriers, polymerizable surfactants with pH-sensitive amphiphilicity based on the hypothesis that pH-sensitive amphiphilicity and environmentally sensitive siRNA release can result in efficient siRNA delivery. The polymerizable surfactants comprise a protonatable amino head group, two cysteine residues, and two lipophilic tails. The surfactants demonstrated pH-sensitive amphiphilic hemolytic activity or cell membrane disruption with rat red blood cells. Most of the surfactants resulted in low hemolysis at pH 7.4 and high hemolysis at reduced pH (6.5 and 5.4). The pH-sensitive cell membrane disruption can facilitate endosomal-lysosomal escape of siRNA delivery systems at the endosomal-lysosomal pH. The surfactants formed compact nanoparticles (160-260 nm) with siRNA at N/P ratios of 8 and 10 via charge complexation with the amino head group, lipophilic condensation, and autoxidative polymerization of dithiols. The siRNA complexes with the surfactants demonstrated low cytotoxicity. The cellular siRNA delivery efficiency and RNAi activity of the surfactants correlated well with their pH-sensitive amphiphilic cell membrane disruption. The surfactants mediated 40-88% silencing of luciferase expression with 100 nM siRNA and 35-75% with 20 nM siRNA in U87-luc cells. Some of the surfactants resulted in similar or higher gene silencing efficiency than TransFast. EHCO with no hemolytic activity at pH 7.4 and 6.5 and high hemolytic activity at pH 5.4 resulted in the best siRNA delivery efficiency. The polymerizable surfactants with pH-sensitive amphiphilicity are promising for efficient siRNA delivery.     

Synergistic Transdermal Delivery of Biomacromolecules Using Sonophoresis after Microneedle Treatment

Transdermal drug delivery systems have been studied as an attractive alternative to conventional delivery routes. However, the outermost layer of the skin, the stratum corneum, acts as a primary barrier to drug delivery. A synergistic combination of microneedles (MNs) and low-frequency ultrasound (U) was used to enhance the penetration of siRNA and ovalbumin. The specific gene knockdown caused by siRNAs through the RNA interference pathway is more stable when delivered via the transdermal route. Ovalbumin, a representative adjuvant, causes a more efficient immune response in the skin because of the numerous immune cells in the skin. The synergistic transdermal delivery resulted in approximately 7 times and 15 times greater penetration of siRNA and ovalbumin respectively than in their respective negative controls, and histological analysis showed minimal invasion. Thus, as the synergistic transdermal delivery enhanced the penetration of biomacromolecules into the skin, this technique is expected to yield a promising technology for a transdermal drug delivery system.     

Current progress of siRNA/shRNA therapeutics in clinical trials

Through a mechanism known as RNA interference (RNAi), small interfering RNA (siRNA) molecules can target complementary mRNA strands for degradation, thus specifically inhibiting gene expression. The ability of siRNAs to inhibit gene expression offers a mechanism that can be exploited for novel therapeutics. Indeed, over the past decade, at least 21 siRNA therapeutics have been developed for more than a dozen diseases, including various cancers, viruses, and genetic disorders. Like other biological drugs, RNAi-based therapeutics often require a delivery vehicle to transport them to the targeted cells. Thus, the clinical advancement of numerous siRNA drugs has relied on the development of siRNA carriers, including biodegradable nanoparticles, lipids, bacteria, and attenuated viruses. Most therapies permit systemic delivery of the siRNA drug, while others use ex vivo delivery by autologous cell therapy. Advancements in bioengineering and nanotechnology have led to improved control of delivery and release of some siRNA therapeutics. Likewise, progress in molecular biology has allowed for improved design of the siRNA molecules. Here, we provide an overview of siRNA therapeutics in clinical trials, including their clinical progress, the challenges they have encountered, and the future they hold in the treatment of human diseases.     

Strategies for ocular siRNA delivery: Potential and limitations of non-viral nanocarriers

ABSTRACT: Controlling gene expression via small interfering RNA (siRNA) has opened the doors to a plethora of therapeutic possibilities, with many currently in the pipelines of drug development for various ocular diseases. Despite the potential of siRNA technologies, barriers to intracellular delivery significantly limit their clinical efficacy. However, recent progress in the field of drug delivery strongly suggests that targeted manipulation of gene expression via siRNA delivered through nanocarriers can have an enormous impact on improving therapeutic outcomes for ophthalmic applications. Particularly, synthetic nanocarriers have demonstrated their suitability as a customizable multifunctional platform for the targeted intracellular delivery of siRNA and other hydrophilic and hydrophobic drugs in ocular applications. We predict that synthetic nanocarriers will simultaneously increase drug bioavailability, while reducing side effects and the need for repeated intraocular injections. This review will discuss the recent advances in ocular siRNA delivery via non-viral nanocarriers and the potential and limitations of various strategies for the development of a 'universal' siRNA delivery system for clinical applications.     

siRNA纳米递送系统研究进展

小干扰RNA (small interfering RNA,siRNA)是RNA干扰的引发物,激发与之互补的目标mRNA沉默,对基因调控及疾病治疗有重要意义。siRNA作为药物需要克服血管屏障、实现细胞内吞及溶酶体逃逸,同时还需要避免核酸酶作用下发生降解。因此,设计合适的纳米载体以帮助siRNA成功递送进细胞并发挥作用是目前siRNA药物发展的重要目标。纳米载体的材料种类、尺寸、结构、表面修饰等精确设计是实现siRNA药物成功递送的重要因素。随着研究的深入和应用的发展,siRNA药物纳米载体的精确控制制备、精准靶向递送及多功能化取得了较好的成果。本文围绕siRNA药物纳米载体,对siRNA药物应用及其递送困难、siRNA药物纳米载体主要设计策略、目前siRNA药物上市情况进行介绍,同时对其未来发展方向进行展望。     

Human group III secreted phospholipase A2 promotes neuronal outgrowth and survival

Human sPLA2-III [group III secreted PLA2 (phospholipase A2)] is an atypical sPLA2 isoenzyme that consists of a central group III sPLA2 domain flanked by unique N- and C-terminal domains. In the present study, we found that sPLA2-III is expressed in neuronal cells, such as peripheral neuronal fibres, spinal DRG (dorsal root ganglia) neurons and cerebellar Purkinje cells. Adenoviral expression of sPLA2-III in PC12 cells (pheochromocytoma cells) or DRG explants facilitated neurite outgrowth, whereas expression of a catalytically inactive sPLA2-III mutant or use of sPLA2-III-directed siRNA (small interfering RNA) reduced NGF (nerve growth factor)-induced neuritogenesis. sPLA2-III also suppressed neuronal death induced by NGF deprivation. Lipid MS revealed that sPLA2-III overexpression increased the cellular level of lysophosphatidylcholine, a PLA2 reaction product with neuritogenic and neurotropic activities, whereas siRNA knockdown reduced the level of lysophosphatidylcholine. These observations suggest the potential contribution of sPLA2-III to neuronal differentiation and its function under certain conditions.     

Rigid nanoparticle-based delivery of anti-cancer siRNA: Challenges and opportunities

Gene therapy is a promising strategy to treat various genetic and acquired diseases. Small interfering RNA (siRNA) is a revolutionary tool for gene therapy and the analysis of gene function. However, the development of a safe, efficient, and targetable non-viral siRNA delivery system remains a major challenge in gene therapy. An ideal delivery system should be able to encapsulate and protect the siRNA cargo from serum proteins, exhibit target tissue and cell specificity, penetrate the cell membrane, and release its cargo in the desired intracellular compartment. Nanomedicine has the potential to deal with these challenges faced by siRNA delivery. The unique characteristics of rigid nanoparticles mostly inorganic nanoparticles and allotropes of carbon nanomaterials, including high surface area, facile surface modification, controllable size, and excellent magnetic/optical/electrical properties, make them promising candidates for targeted siRNA delivery. In this review, recent progresses on rigid nanoparticle-based siRNA delivery systems will be summarized.     

Physicochemical and biological characterization of targeted, nucleic acid-containing nanoparticles

Nucleic acid-based therapeutics have the potential to provide potent and highly specific treatments for a variety of human ailments. However, systemic delivery continues to be a significant hurdle to success. Multifunctional nanoparticles are being investigated as systemic, nonviral delivery systems, and here, we describe the physicochemical and biological characterization of cyclodextrin-containing polycations (CDP) and their nanoparticles formed with nucleic acids including plasmid DNA (pDNA) and small interfering RNA (siRNA). These polycation/nucleic acid complexes can be tuned by formulation conditions to yield particles with sizes ranging from 60 to 150 nm, zeta potentials from 10 to 30 mV, and molecular weights from approximately 7 x 107 to 1 x 109 g mol-1 as determined by light scattering techniques. Inclusion complexes formed between adamantane (AD)-containing molecules and the beta-cyclodextrin molecules enable the modular attachment of poly(ethylene glycol) (AD-PEG) conjugates for steric stabilization and targeting ligands (AD-PEG-transferrin) for cell-specific targeting. A 70 nm particle can contain approximately 10 000 CDP polymer chains, approximately 2000 siRNA molecules, approximately 4000 AD-PEG5000 molecules, and approximately 100 AD-PEG5000-Tf molecules; this represents a significant payload of siRNA and a large ratio of siRNA to targeting ligand (20:1). The particles protect the nucleic acid payload from nuclease degradation, do not aggregate at physiological salt concentrations, and cause minimal erythrocyte aggregation and complement fixation at the concentrations typically used for in vivo application. Uptake of the nucleic acid-containing particles by HeLa cells is measured by flow cytometry and visualized by confocal microscopy. Competitive uptake experiments show that the transferrin-targeted particles display enhanced affinity for the transferrin receptor through avidity effects (multiligand binding). Functional efficacy of the delivered pDNA and siRNA is demonstrated through luciferase reporter protein expression and knockdown, respectively. The analysis of the CDP delivery vehicle provides insights that can be applied to the design of targeted nucleic acid delivery vehicles in general.     

Targeting cyclin B1 through peptide-based delivery of siRNA prevents tumour growth

The development of short interfering RNA (siRNA), has provided great hope for therapeutic targeting of specific genes responsible for patholological disorders. However, the poor cellular uptake and bioavailability of siRNA remain a major obstacle to their clinical development and most strategies that propose to improve siRNA delivery remain limited for in vivo applications. In this study, we report a novel peptide-based approach, MPG-8 an improved variant of the amphipathic peptide carrier MPG, that forms nanoparticles with siRNA and promotes their efficient delivery into primary cell lines and in vivo upon intra-tumoral injection. Moreover, we show that functionalization of this carrier with cholesterol significantly improves tissue distribution and stability of siRNA in vivo, thereby enhancing the efficiency of this technology for systemic administration following intravenous injection without triggering any non-specific inflammatory response. We have validated the therapeutic potential of this strategy for cancer treatment by targeting cyclin B1 in mouse tumour models, and demonstrate that tumour growth is compromised. The robustness of the biological response achieved through this approach, infers that MPG 8-based technology holds a strong promise for therapeutic administration of siRNA.     

New paradigms on siRNA local application

Small interfering RNA (siRNA) functions through pairing with specific mRNA sequences and results in the mRNA’s degradation. It is a potential therapeutic approach for many diseases caused by altered gene expression. The delivery of siRNA is still a major problem due to its rapid degradation in the circulation. Various strategies have been proposed to help with the cellular uptake of siRNA and short or small hairpin RNA (shRNA). Here, we reviewed recently published data regarding local applications of siRNA. Compared with systemic delivery methods, local delivery of siRNA/shRNA has many advantages, such as targeting the specific tissues or organs, mimicking a gene knockout effect, or developing certain diseases models. The eye, brain, and tumor tissues are ‘hot’ target tissues/organs for local siRNA delivery. The siRNA can be delivered locally, in naked form, with chemical modifications, or in formulations with viral or non-viral vectors, such as liposomes and nanoparticles. This review provides a comprehensive overview of RNAi local administration and potential future applications in clinical treatment. [BMB Reports 2015; 48(3): 147-152]     

Rapid delivery of small interfering RNA by biosurfactant MEL-A-containing liposomes

The downregulation of gene expression by RNA interference holds great potential for genetic analysis and gene therapy. However, a more efficient delivery system for small interfering RNA (siRNA) into the target cells is required for wide fields such as cell biology, physiology, and clinical application. Non-viral vectors are stronger candidates than viral vectors because they are safer and easier to prepare. We have previously used a new method for gene transfection by combining cationic liposomes with the biosurfactant mannosylerythritol lipid-A (MEL-A). The novel MEL-A-containing cationic liposomes rapidly delivered DNA (plasmids and oligonucleotides) into the cytosol and nucleus through membrane fusion between liposomes and the plasma membrane, and consequently, enhanced the gene transfection efficiency. In this study, we determined the efficiency of MEL-A-containing cationic liposomes for siRNA delivery. We observed that exogenous and endogenous protein expression was suppressed by approximately 60% at 24 h after brief (30 min) incubation of target cells with MEL-A-containing cationic liposome/siRNA complexes. Confocal microscopic analysis showed that suppression of protein expression was caused by rapid siRNA delivery into the cytosol. We found that the MEL-A-containing cationic liposomes directly delivered siRNA into the cytoplasm by the membrane fusion in addition to endocytotic pathway whereas Lipofectamine™ RNAiMax delivered siRNA only by the endocytotic pathway. It seems that the ability to rapidly and directly deliver siRNA into the cytosol using MEL-A-containing cationic liposomes is able to reduce immune responses, cytotoxicity, and other side effects caused by viral vectors in clinical applications.     

基于核酸自组装纳米结构的siRNA药物递送研究进展

RNA干扰(RNA interference,RNAi)作为转录后调节机制,可靶向mRNA进行剪切降解从而发挥基因沉默效应.siRNA (small interference RNA)因其高效性和特异性而被广泛应用于药物研究中.目前,研究者们已开发了多种阳离子载体用于siRNA递送.但由于siRNA双链结构具有相对较强的刚性结构,且阴离子电荷密度较低,无法与阳离子载体形成稳定、致密的复合物,使得siRNA的应用仍面临诸多挑战,如细胞摄取率低、靶向特异性差、递送过程不稳定、潜在的细胞毒性以及易诱发免疫反应等.近年来,核酸自组装纳米结构由于其结构灵活且负电荷密度较高而受到广泛关注,有望实现siRNA药物的高效递送和基因沉默.本文综述了近年来基于核酸自组装纳米结构的siRNA递送的研究进展及其应用.     

siRNA associated with immunonanoparticles directed against cd99 antigen improves gene expression inhibition in vivo in Ewing's sarcoma

Ewing's sarcoma is a rare, mostly pediatric bone cancer that presents a chromosome abnormality called EWS/Fli‐1, responsible for the development of the tumor. In vivo, tumor growth can be inhibited specifically by delivering small interfering RNA (siRNA) associated with nanoparticles. The aim of the work was to design targeted nanoparticles against the cell membrane glycoprotein cd99, which is overexpressed in Ewing's sarcoma cells to improve siRNA delivery to tumor cells. Biotinylated poly(isobutylcyanoacrylate) nanoparticles were conceived as a platform to design targeted nanoparticles with biotinylated ligands and using the biotin–streptavidin coupling method. The targeted nanoparticles were validated in vivo for the targeted delivery of siRNA after systemic administration to mice bearing a tumor model of the Ewing's sarcoma. The expression of the gene responsible of Ewing's sarcoma was inhibited at 78% ± 6% by associating the siRNA with the cd99‐targeted nanoparticles compared with an inhibition of only 41% ± 9% achieved with the nontargeted nanoparticles. Copyright © 2013 John Wiley & Sons, Ltd.     

Small interfering RNA delivery and gene silencing using polymeric nanocarrier systems

The effectiveness of a drug is determined by the ability to migrate through the body and reach target sites in therapeutically relevant levels. Nanocarriers for delivery of bioactive agents are being developed at iNANO to maximise drug payload at target sites. The inclusion of “biological triggers” into the nanocarrier design is used for modulation of cellular nucleic acid trafficking and increased target interaction. Polymers were used to formulate nanocarriers in the size range 30–250 nm containing small interfering RNAs (siRNAs) for gene silencing applications. PAGE analysis showed the structural integrity of the siRNA was maintained during particle formation. In systems composed of bioresponsive polymers, nanocarrier disassembly and siRNA release under cellular conditions were shown, using Atomic Force Microscopy. The time course for siRNA uptake into NIH cells was visualised using confocal microscopy. In addition, siRNA localisation within cells could be modulated by the composition of the polymer used. The ability of the nanocarrier system to mediate gene expression was investigated in a cell line stably expressing enhanced green fluorescent protein (eGFP). Furthermore, the various delivery systems were tested in a mouse model stably expressing the eGFP protein using both nasal and intravenous delivery routes. The systems described in this work demonstrate an ability to transport siRNA into cells whilst maintaining siRNA functionality; essential properties for nanocarrier-based RNA interference strategies.