Non-viral vectors for the mediation of RNAi

Though the delivery of siRNA into cells, tissues or organs remains to be a big obstacle for its applications, recently siRNA therapeutics has developed rapidly and already there are clinical trials ongoing or planned. Some non-viral vectors have attracted much more attention and shown the great potential for combating the delivery obstacle. As a novel class of lipid like materials lipidoids have the advantages of easy synthesis and large library of compounds. Cell penetrating peptides and chitosans have been used for the delivery of bioactive molecules for many years, but they are showing great promise for the delivery of siRNA. The hybrids of inorganic particles and the conjugates of siRNA have indicated the complex utilization different materials may provide another solution to the delivery problem. The most exciting thing is some clinical trials are undergoing, which provokes the hope of real curing method by using RNAi mediated by some non-viral vectors.     

Combinatorial library of lipidoids for in vitro DNA delivery

A combinatorial library of lipidoids was constructed and studied for in vitro gene delivery. The library of lipidoids was synthesized by reacting commercially available amines with lipophilic acrylates, acrylamides, or epoxides. Lipidoids derived from amine 86 (N,N-bis(2-hydroxyethyl)ethylene diamine) and amine 87 (N-(3-aminopropyl)diethaneamine) showed high efficiency in DNA delivery, some with a higher transfection efficiency than Lipofectamine 2000, a commonly used commercial gold standard for in vitro gene delivery. The structure-activity relationship between the lipidoids was further studied with respect to small variations in chemical structures and the resulting efficiency in DNA delivery in vitro. Since these lipidoids are easy to synthesize and do not require a colipid for efficient DNA delivery, they could offer an inexpensive but effective alternative to other commonly used commercial gene delivery carriers.     

RNA interference against viruses: strike and counterstrike

RNA interference (RNAi) is a conserved sequence-specific, gene-silencing mechanism that is induced by double-stranded RNA. RNAi holds great promise as a novel nucleic acid-based therapeutic against a wide variety of diseases, including cancer, infectious diseases and genetic disorders. Antiviral RNAi strategies have received much attention and several compounds are currently being tested in clinical trials. Although induced RNAi is able to trigger profound and specific inhibition of virus replication, it is becoming clear that RNAi therapeutics are not as straightforward as we had initially hoped. Difficulties concerning toxicity and delivery to the right cells that earlier hampered the development of antisense-based therapeutics may also apply to RNAi. In addition, there are indications that viruses have evolved ways to escape from RNAi. Proper consideration of all of these issues will be necessary in the design of RNAi-based therapeutics for successful clinical intervention of human pathogenic viruses.     

Opinion: miRNAs – The new wave of molecular cancer therapeutics

Cutting-edge advances in nanomedicine and the recent approval of two siRNA-based therapeutics by the Food and Drug Administration (FDA) has rekindled the interest in RNA interference (RNAi) as vehicles for the development of novel cancer therapeutics. In this perspective, we will briefly discuss how miRNAs are becoming the next-generation RNAi therapeutic, the advances in delivery vehicles for in vivo miRNA delivery, and where miRNA technology stands in terms of clinical translation.     

Small interfering RNA-mediated silencing induces target-dependent assembly of GW/P bodies

Gene silencing using small interfering RNA (siRNA) is a valuable laboratory tool and a promising approach to therapeutics for a variety of human diseases. Recently, RNA interference (RNAi) has been linked to cytoplasmic GW bodies (GWB). However, the correlation between RNAi and the formation of GWB, also known as mammalian processing bodies, remains unclear. In this report, we show that transfection of functional siRNA induced larger and greater numbers of GWB. This siRNA-induced increase of GWB depended on the endogenous expression of the target mRNA. Knockdown of GW182 or Ago2 demonstrated that the siRNA-induced increase of GWB required these two proteins and correlated with RNAi. Furthermore, knockdown of rck/p54 or LSm1 did not prevent the reassembly of GWB that were induced by and correlated with siRNA-mediated RNA silencing. We propose that RNAi is a key regulatory mechanism for the assembly of GWB, and in some cases, GWB may serve as markers for RNAi in mammalian cells.     

Clinical advances of siRNA therapeutics

Small interfering RNA (siRNA) enables efficient target gene silencing by employing a RNA interference (RNAi) mechanism, which can compromise gene expression and regulate gene activity by cleaving mRNA or repressing its translation. Twenty years after the discovery of RNAi in 1998, ONPATTRO? (patisiran) (Alnylam Pharmaceuticals, Inc.), a lipid formulated siRNA modality, was approved for the first time by United States Food and Drug Administration and the European Commission in 2018. With this milestone achievement, siRNA therapeutics will soar in the coming years. Here, we review the discovery and the mechanisms of RNAi, briefly describe the delivery technologies of siRNA, and summarize recent clinical advances of siRNA therapeutics.     

RNA interference trigger variants: getting the most out of RNA for RNA interference-based therapeutics

The manifestation of RNA interference (RNAi)-based therapeutics lies in safe and successful delivery of small interfering RNAs (siRNAs), the molecular entity that triggers and guides sequence-specific degradation of target mRNAs. Optimizing the chemistry and structure of siRNAs to achieve maximum efficacy is an important parameter in the development of siRNA therapeutics. The RNAi protein machinery can tolerate a variety of non-canonical modifications made to siRNAs, each of which imparts advantageous properties. Here, we review these modifications to siRNAs in pre-clinical and clinical studies.     

首例RNA干扰药物问世及该领域技术演化历程

近期,RNA干扰(RNAi)制药公司Alnylam开发的小干扰RNA (siRNA)药物ONPATTRO?美国食品与药物管理局和欧盟委员会批准上市,用于治疗成人患者的遗传性转甲状腺素蛋白淀粉样变性引起的多发性神经病变.这是全球第一款RNAi药物,该事件标志着人类继小分子化合物、单克隆抗体蛋白类药物后,在前沿生物制药领域实现了新的突破,意味着RNAi疗法从基础研究到临床治疗的开发全过程首次贯通,具有里程碑式的意义.本文概述了该药物及适应症的基本情况,介绍了RNAi发现历史、作用机理与药物特征,RNAi药物的研发历程,以及该领域关键技术的最新研究进展.     

RNA interference-mediated simultaneous silencing of four genes using cross-shaped RNA

The structural flexibility of RNA interference (RNAi)-triggering nucleic acids suggests that the design of unconventional RNAi trigger structures with novel features is possible. Here, we report a cross-shaped RNA duplex structure, termed quadruple interfering RNA (qiRNA), with multiple target gene silencing activity. qiRNA triggers the simultaneous down-regulation of four cellular target genes via an RNAi mechanism. In addition, qiRNA shows enhanced intracellular delivery and target gene silencing over conventional siRNA when complexed with jetPEI, a linear polyethyleneimine (PEI). We also show that the long antisense strand of qiRNA is incorporated intact into an RNA-induced silencing complex (RISC). This novel RNA scaffold further expands the repertoire of RNAi-triggering molecular structures and could be used in the development of therapeutics for various diseases including viral infections and cancer.     

The silent treatment: RNAi as a defense against virus infection in mammals

RNA interference (RNAi) is a mechanism for sequence-specific gene silencing guided by double-stranded RNA. In plants and insects it is well established that RNAi is instrumental in the response to viral infections; whether RNAi has a similar function in mammals is under intense investigation. Recent studies to address this question have identified some unanticipated interactions between the RNAi machinery and mammalian viruses. Furthermore, introduction of virus-specific small interfering RNAs (siRNAs) into cells, thus programming the RNAi machinery to target viruses, is an effective therapeutic approach to inhibit virus replication in vitro and in animal models. Although several issues remain to be addressed, such as delivery and viral escape, these findings hold tremendous potential for the development of RNAi-based antiviral therapeutics.     

Therapeutic siRNA: principles, challenges, and strategies

RNA interference (RNAi) is a remarkable endogenous regulatory pathway that can bring about sequence-specific gene silencing. If harnessed effectively, RNAi could result in a potent targeted therapeutic modality with applications ranging from viral diseases to cancer. The major barrier to realizing the full medicinal potential of RNAi is the difficulty of delivering effector molecules, such as small interfering RNAs (siRNAs), in vivo. An effective delivery strategy for siRNAs must address limitations that include poor stability and non-targeted biodistribution, while protecting against the stimulation of an undesirable innate immune response. The design of such a system requires rigorous understanding of all mechanisms involved. This article reviews the mechanistic principles of RNA interference, its potential, the greatest challenges for use in biomedical applications, and some of the work that has been done toward engineering delivery systems that overcome some of the hurdles facing siRNA-based therapeutics.     

Branched, tripartite-interfering RNAs silence multiple target genes with long guide strands

Structural modifications could provide classical small interfering RNA (siRNA) structure with several advantages, including reduced off-target effects and increased silencing activity. Thus, RNA interference (RNAi)-triggering molecules with diverse structural modifications have been investigated by introducing variations on duplex length and overhang structure. However, most of siRNA structural variants are based on the linear duplex structure. In this study, we introduce a branched, non-linear tripartite-interfering RNA (tiRNA) structure that could induce silencing of multiple target genes. Surprisingly, the gene silencing by tiRNA structure does not require Dicer-mediated processing into smaller RNA units, and the 38-nt-long guide strands can trigger specific gene silencing through the RNAi machinery in mammalian cells. tiRNA also shows improved gene silencing potency over the classical siRNA structure when complexed with cationic delivery vehicles due to the enhanced intracellular delivery. These results demonstrate that tiRNA is a novel RNA nanostructure for executing multi-target gene silencing with increased potency, which could be utilized as a structural platform to develop efficient anticancer or antiviral RNAi therapeutics.     

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.     

RNA interference for antiviral therapy

Silencing gene expression through a process known as RNA interference (RNAi) has been known in the plant world for many years. In recent years, knowledge of the prevalence of RNAi and the mechanism of gene silencing through RNAi has started to unfold. It is now believed that RNAi serves in part as an innate response against invading viral pathogens and, indeed, counter silencing mechanisms aimed at neutralizing RNAi have been found in various viral pathogens. During the past few years, it has been demonstrated that RNAi, induced by specifically designed double-stranded RNA (dsRNA) molecules, can silence gene expression of human viral pathogens both in acute and chronic viral infections. Furthermore, it is now apparent that in in vitro and in some in vivo models, the prospects for this technology in developing therapeutic applications are robust. However, many key questions and obstacles in the translation of RNAi into a potential therapeutic platform still remain, including the specificity and longevity of the silencing effect, and, most importantly, the delivery of the dsRNA that induces the system. It is expected that for the specific examples in which the delivery issue could be circumvented or resolved, RNAi may hold promise for the development of gene-specific therapeutics.     

Delivery of RNA Interference

Over the last few years, RNA Interference (RNAi), a naturally occurring mechanism of gene regulation conserved in plant and mammalian cells, has opened numerous novel opportunities for basic research across the field of biology. While RNAi has helped accelerate discovery and understanding of gene functions, it also has great potential as a therapeutic and potentially prophylactic modality. Challenging diseases failing conventional therapeutics could become treatable by specific silencing of key pathogenic genes. More specifically, therapeutic targets previously deemed “undruggable” by small molecules, are now coming within reach of RNAi based therapy. For RNAi to be effective and elicit gene silencing response, the double-stranded RNA molecules must be delivered to the target cell. Unfortunately, delivery of these RNA duplexes has been challenging, halting rapid development of RNAi-based therapies. In this review we present current advancements in the field of siRNA delivery methods, including the pros and cons of each method.     

RNA干扰(RNAi)文库研究进展

RNAi是由双链RNA(dsRNA)引发的转录后基因沉默现象,由dsRNA产生的小分子siRNA会导致生物体内同源转录产物特异性降解,是基因表达调控的重要方式之一。目前RNAi技术已发展成为遗传分析强有力的工具,在基因功能分析鉴定方面发挥越来越大的作用。构建大规模的RNAi文库进而转变成RNAi突变体库是功能基因组学研究的重要手段,因此如何利用简单经济的方法构建特定物种的高效RNAi文库就成为关键问题。综述了目前构建RNAi文库的不同方法以及每种构建方法的优点和存在的不足,为不同研究目的的RNAi文库的构建提供参考。     

Gel-based application of siRNA to human epithelial cancer cells induces RNAi-dependent apoptosis

Gene silencing by RNA interference (RNAi) operates at the level of mRNA that is targeted for destruction with exquisite sequence specificity. In principle, any disease-related mRNA sequence is a putative target for RNAi-based therapeutics. To develop this therapeutic potential, it is necessary to develop ways of inducing RNAi by clinically acceptable delivery procedures. Here, we ask if inducers of RNAi can be delivered to human cells via a gel-based medium. RNAi was induced using synthetic small interfering RNAs (siRNAs), which bypass the need for expression vectors and carry the added bonus of high potency and immediate efficacy. Established cultures of human cells of normal and tumor origin were overlaid with an agarose/liposome/siRNA gel formulation without adverse effects on cell viability or proliferation. Epithelial cancer cells (but not normal human fibroblasts) proved vulnerable to specific siRNAs delivered via the agarose/liposome/siRNA formulation. Moreover, proapoptotic siRNAs induced apoptosis of cervical carcinoma cells (treated with human papillomavirus [HPV] E7 siRNA) and of colorectal carcinoma cells (treated with Bcl-2 siRNA). Thus, we demonstrate successful topical gel-based delivery of inducers of RNAi to human epithelial cancer cells. Topical induction of RNAi opens an important new therapeutic approach for treatment of human diseases, including cervical cancer and other accessible disorders.     

RNAi therapeutics: a potential new class of pharmaceutical drugs

The rapid identification of highly specific and potent drug candidates continues to be a substantial challenge with traditional pharmaceutical approaches. Moreover, many targets have proven to be intractable to traditional small-molecule and protein approaches. Therapeutics based on RNA interference (RNAi) offer a powerful method for rapidly identifying specific and potent inhibitors of disease targets from all molecular classes. Numerous proof-of-concept studies in animal models of human disease demonstrate the broad potential application of RNAi therapeutics. The major challenge for successful drug development is identifying delivery strategies that can be translated to the clinic. With advances in this area and the commencement of multiple clinical trials with RNAi therapeutic candidates, a transformation in modern medicine may soon be realized.