Maintaining the silence: reflections on long-term RNAi (original) (raw)

A status report on RNAi therapeutics

Silence, 2010

Fire and Mello initiated the current explosion of interest in RNA interference (RNAi) biology with their seminal work in Caenorhabditis elegans. These observations were closely followed by the demonstration of RNAi in Drosophila melanogaster. However, the full potential of these new discoveries only became clear when Tuschl and colleagues showed that 21-22 bp RNA duplexes with 3" overhangs, termed small interfering (si)RNAs, could reliably execute RNAi in a range of mammalian cells. Soon afterwards, it became clear that many different human cell types had endogenous machinery, the RNA-induced silencing complex (RISC), which could be harnessed to silence any gene in the genome. Beyond the availability of a novel way to dissect biology, an important target validation tool was now available. More importantly, two key properties of the RNAi pathway -sequence-mediated specificity and potency -suggested that RNAi might be the most important pharmacological advance since the advent of protein therapeutics. The implications were profound. One could now envisage selecting disease-associated targets at will and expect to suppress proteins that had remained intractable to inhibition by conventional methods, such as small molecules. This review attempts to summarize the current understanding on siRNA lead discovery, the delivery of RNAi therapeutics, typical in vivo pharmacological profiles, preclinical safety evaluation and an overview of the 14 programs that have already entered clinical practice.

RNAi through short interfering RNA (siRNAs) as a Novel Therapeutic Strategy

Since RNA interference (RNAi) was discovered in the late 1990s, it has evolved as a powerful and widely used strategy for the efficient silencing of genes. RNAi relies on the action of small interfering RNAs (siRNAs) which are incorporated into a complex termed RNA-induced silencing complex (RISC) and guide RISC to its cleavage site on the target mRNA. Thus, the efficiency of RNAi in vitro and in vivo is determined by the efficacy and intracellular presence of specific siRNA molecules. In vivo, the delivery of siRNAs is a major obstacle in the development of RNAi-based strategies also for clinical applications. Various approaches have been explored for the administration of RNAi in different pathological disorders. This review highlights criteria for the development of optimal siRNAs as well as strategies for siRNA stabilization and in vivo delivery. Different routes of siRNA administration and various siRNA formulations are discussed. The second part of the review provides a comprehensive overview on siRNA-mediated in vivo gene targeting in proof-of-principle studies as well as for the treatment of various pathologies including e.g. viral infection, cancer, liver and renal failure, CNS disorders and pathological ocular neovascularization.

The silent treatment: siRNAs as small molecule drugs

Gene Therapy, 2006

As soon as RNA interference (RNAi) was found to work in mammalian cells, research quickly focused on harnessing this powerful endogenous and specific mechanism of gene silencing for human therapy. RNAi uses small RNAs, less than 30 nucleotides in length, to suppress expression of genes with complementary sequences. Two strategies can introduce small RNAs into the cytoplasm of cells, where they are active -a drug approach where doublestranded RNAs are administered in complexes designed for intracellular delivery and a gene therapy approach to express precursor RNAs from viral vectors. Phase I clinical studies have already begun to test the therapeutic potential of small RNA drugs that silence disease-related genes by RNAi. This review will discuss progress in developing and testing small RNAi-based drugs and potential obstacles.

Therapeutic siRNA: principles, challenges, and strategies

The Yale journal of biology and medicine, 2012

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 facin...

Overcoming Barriers for siRNA Therapeutics: From Bench to Bedside

Pharmaceuticals

The RNA interference (RNAi) pathway possesses immense potential in silencing any gene in human cells. Small interfering RNA (siRNA) can efficiently trigger RNAi silencing of specific genes. FDA Approval of siRNA therapeutics in recent years garnered a new hope in siRNA therapeutics. However, their therapeutic use is limited by several challenges. siRNAs, being negatively charged, are membrane-impermeable and highly unstable in the systemic circulation. In this review, we have comprehensively discussed the extracellular barriers, including enzymatic degradation of siRNAs by serum endonucleases and RNAases, rapid renal clearance, membrane impermeability, and activation of the immune system. Besides, we have thoroughly described the intracellular barriers such as endosomal trap and off-target effects of siRNAs. Moreover, we have reported most of the strategies and techniques in overcoming these barriers, followed by critical comments in translating these molecules from bench to bedside.

siRNA – AN EXCELLENT TECHNIQUE FOR DOWNREGULATION OF GENE EXPRESSION

RNA interference (RNAi) was originally described in the nematode worm Caenorhabditis elegans as a response to double-stranded RNA (dsRNA), in which target mRNAs are degraded in a sequence-specific manner. Short sermon molecules can be prepared by direct chemical synthesis or transcription driven by RNA polymerase promoters. After recent discovery the use of small interfering RNA (siRNA) has become a powerful tool in silencing highly over expressed oncogenes in cancer. Now siRNA technology holds promise as a novel therapeutic modality for targeted silencing of cancer genes especially for those proteins that cannot be targeted by small inhibitors. However, clinical applications of siRNA-based therapeutics relay on the successful delivery of primary and metastatic tumors and remains as a great challenge. Designing and then chemically stabilizing the siRNA and can stabilize and improve the drug properties of siRNA therapeutics by using specific chemical modifications. A chemogenomics approach towards novel target discovery combined with RNAi-based screening is facilitating the robust, improved discovery of new targeted therapies. These approaches have strong potential to provide better cancer drug targets using a combination of short interfering RNA (siRNA) libraries and pre-existing chemotherapies, as well as a combination of siRNAs and novel compound libraries. RNAi is one of the most recent discoveries of a naturally occurring mechanism of gene regulation that is triggered by the introduction of double-stranded RNA into a cell. Designed to specifically knock down the expression of genes harboring a particular target sequence, and they represent an exciting therapeutic potential for inhibiting gene expression