Silencing neurodegenerative disease: bringing RNA interference to the clinic

Biomaterial-based delivery of nucleic acids for tissue regeneration

Gene therapy is a promising novel method of tissue regeneration by stimulating or inhibiting key signaling pathways. However, their therapeutic applications in vivo are largely limited by several physiological obstacles, such as degradation of nucleases, impermeability of cell membranes, and transport to the desired intracellular compartments. Biomaterial-based gene delivery systems can overcome the problems of stability and local drug delivery, and can temporarily control the overexpression of therapeutic genes, leading to the local production of physiologically relevant levels of regulatory factors. But the gene delivery of biomaterials for tissue regeneration relies on multi-factor design. This review aims to outline the impact of gene delivery methods, therapeutic genes and biomaterials selection on this strategy, emphatically introduce the latest developments in the design of gene delivery vehicles based on biomaterials, summarize the mechanism of nucleic acid for tissue regeneration, and explore the strategies of nucleic acid delivery vehicles for various tissue regeneration.

Localised non-viral delivery of nucleic acids for nerve regeneration in injured nervous systems

Axons damaged by traumatic injuries are often unable to spontaneously regenerate in the adult central nervous system (CNS). Although the peripheral nervous system (PNS) has some regenerative capacity, its ability to regrow remains limited across large lesion gaps due to scar tissue formation. Nucleic acid therapy holds the potential of improving regeneration by enhancing the intrinsic growth ability of neurons and overcoming the inhibitory environment that prevents neurite outgrowth. Nucleic acids modulate gene expression by over-expression of neuronal growth factor or silencing growth-inhibitory molecules. Although in vitro outcomes appear promising, the lack of efficient non-viral nucleic acid delivery methods to the nervous system has limited the application of nucleic acid therapeutics to patients. Here, we review the recent development of efficient non-viral nucleic acid delivery platforms, as applied to the nervous system, including the transfection vectors and carriers used, as well as matrices and scaffolds that are currently used. Additionally, we will discuss possible improvements for localised nucleic acid delivery.

Novel siRNA delivery strategy: a new "strand" in CNS translational medicine?

RNA interference has been envisaged as a powerful tool for molecular and clinical investigation with a great potential for clinical applications. In recent years, increased understanding of cancer biology and stem cell biology has dramatically accelerated the development of technology for cell and gene therapy in these areas. This paper is a review of the most recent report of innovative use of siRNA to benefit several central nervous system diseases. Furthermore, a description is made of innovative strategies of delivery into the brain by means of viral and non-viral vectors with high potential for translation into clinical use. Problems are also highlighted that might hamper the transition from bench to bed, analyzing the lack of reliable preclinical models with predictive validity and the lack of effective delivery systems, which are able to overcome biological barriers and specifically reach the brain site of action.

Targeting Viral Heart Disease by RNA Interference

Viral heart disease (VHD) is an important clinical disease entity both in pediatric as well as adult cardiology. Coxsackieviruses (CVBs) are considered an important cause for VHD in both populations. VHD may lead to dilated cardiomyopathy and heart failure which can ultimately require heart transplantation. However, no specific treatment modality is so far available. We and others have shown that coxsackieviral replication and cytotoxicity can be successfully targeted by RNA interference, thus leading to increased cell viability and even prolongation of survival in vivo. However, considerable limitations have to be solved before this novel therapeutic approach may enter the clinical trials arena.

Technology insight: therapeutic RNA interference--how far from the neurology clinic?

As an evolutionarily conserved cellular pathway to regulate endogenous gene expression, RNA interference (RNAi) has been implicated in diverse biological processes. Biologists now routinely exploit this cellular pathway to suppress virtually any target gene in a sequence-specific manner, including dominantly acting genes that cause incurable neurodegenerative disorders. The development of RNAi as potential therapy for such diseases has generated considerable interest, partly because of the success of early studies of therapeutic RNAi in rodent models for a range of neurodegenerative diseases. In this article, we review the progress of RNAi therapy to date, and assess the challenges ahead for the application of such therapy to neurodegenerative diseases. We discuss the various strategies that might be used to achieve this goal, outline the preclinical studies that have already been completed, and highlight the experimental questions that need to be answered before human clinical trials can begin.

Nonviral approaches for neuronal delivery of nucleic acids

The delivery of therapeutic nucleic acids to neurons has the potential to treat neurological disease and spinal cord injury. While select viral vectors have shown promise as gene carriers to neurons, their potential as therapeutic agents is limited by their toxicity and immunogenicity, their broad tropism, and the cost of large-scale formulation. Nonviral vectors are an attractive alternative in that they offer improved safety profiles compared to viruses, are less expensive to produce, and can be targeted to specific neuronal subpopulations. However, most nonviral vectors suffer from significantly lower transfection efficiencies than neurotropic viruses, severely limiting their utility in neuron-targeted delivery applications. To realize the potential of nonviral delivery technology in neurons, vectors must be designed to overcome a series of extra- and intracellular barriers. In this article, we describe the challenges preventing successful nonviral delivery of nucleic acids to neurons and review strategies aimed at overcoming these challenges.

Therapeutic RNA interference for neurodegenerative diseases: From promise to progress

RNA interference (RNAi) has emerged as a powerful tool to manipulate gene expression in the laboratory. Due to its remarkable discriminating properties, individual genes, or even alleles can be targeted with exquisite specificity in cultured cells or living animals. Among its many potential biomedical applications, silencing of disease-linked genes stands out as a promising therapeutic strategy for many incurable disorders. Neurodegenerative diseases represent one of the more attractive targets for the development of therapeutic RNAi. In this group of diseases, the progressive loss of neurons leads to the gradual appearance of disabling neurological symptoms and premature death. Currently available therapies aim to improve the symptoms but not to halt the process of neurodegeneration. The increasing prevalence and economic burden of some of these diseases, such as Alzheimer's disease (AD) or Parkinson's disease (PD), has boosted the efforts invested in the development of interventions, such as RNAi, aimed at altering their natural course. This review will summarize where we stand in the therapeutic application of RNAi for neurodegenerative diseases. The basic principles of RNAi will be reviewed, focusing on features important for its therapeutic manipulation. Subsequently, a stepwise strategy for the development of therapeutic RNAi will be presented. Finally, the different preclinical trials of therapeutic RNAi completed in disease models will be summarized, stressing the experimental questions that need to be addressed before planning application in human disease.

Gene transfer therapy for neurodegenerative disorders

Recent advances in gene transfer technology have led to promising new therapies for neurodegenerative disorders. This article will review methods of gene transfer therapy and applications of these techniques to both genetic and sporadic neurodegenerative illnesses. The article will focus on Parkinson's disease, Huntington's disease, and Alzheimer's disease. Several promising gene therapy approaches to these diseases are being pursued both in animal models and in early human trials. Initial safety-tolerability results from these trials appear promising. It is therefore likely that the number of human trials of gene therapy for neurodegenerative disorders will increase over the coming years.

Interfering antiviral immunity: application, subversion, hope?

RNA interference (RNAi), initially recognized as a natural antiviral mechanism in plants, has rapidly emerged as an invaluable tool to suppress gene expression in a sequence-specific manner in all organisms, including mammals. Its potential to inhibit the replication of a variety of viruses has been demonstrated in vitro and in vivo in mouse and monkey models. These results have generated profound interest in the use of this technology as a potential treatment strategy for viral infections for which vaccines and drugs are unavailable or inadequate. In this review, we discuss the progress made within the past 2–3 years towards harnessing the potential of RNAi for clinical application in viral infections and the hurdles that have yet to be overcome.