Knocking down barriers: advances in siRNA delivery

• Published in: Nature reviews. Drug discovery Vol. 8; no. 2; pp. 129 - 138
• Main Authors: Anderson, Daniel G, Whitehead, Kathryn A, Langer, Robert
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-02-2009; Nature Publishing Group
• Subjects: Animals; Bioavailability; Biomedical and Life Sciences; Biomedicine; Biotechnology; Caenorhabditis elegans; Cancer Research; Clinical Trials as Topic; Drug Delivery Systems - methods; Drug Delivery Systems - trends; Gene expression; Humans; Liposomes; Medicinal Chemistry; Molecular Medicine; Nanoparticles - administration & dosage; Pharmacokinetics; Pharmacology/Toxicology; Respiratory syncytial virus; review-article; RNA Interference - drug effects; RNA Interference - physiology; RNA, Small Interfering - administration & dosage; RNA, Small Interfering - pharmacology; United States
• ISSN: 1474-1776; 1474-1784; 1474-1784; 1474-1776
• DOI: 10.1038/nrd2742

Key Points
RNA interference (RNAi) is a fundamental pathway in eukaryotic cells by which sequence-specific small interfering RNA (siRNA) is able to silence genes through the destruction of complementary mRNA. RNAi is an important therapeutic tool that can be used to silence aberrant endogenous genes or to knockdown genes essential to the proliferation of infectious organisms.
Delivery remains the central challenge to the therapeutic application of RNAi technology. Before siRNA can take effect in the cytoplasm of a target cell, it must be transported through the body to the target site without undergoing clearance or degradation.
Currently, the most effective synthetic, non-viral delivery agents of siRNA are lipids, lipid-like materials and polymers.
Various cationic agents including stable nucleic acid–lipid particles, lipidoids, cyclodextrin polymers and polyethyleneimine polymers have been used to achieve the successful systemic delivery of siRNA in mammals without inducing significant toxicity.
Direct conjugation of delivery agents to siRNA can facilitate delivery. For example, cholesterol-modified siRNA enables targeting to the liver.
RNAi therapeutics have progressed to the clinic, where studies are being conducted to determine siRNA efficacy in treating several diseases, including age-related macular degeneration and respiratory syncytial virus.
Moving forward, it will be important to pay close attention to the potential nonspecific immunostimulatory effects of siRNA. Modifications to siRNA can be used to minimize stimulation of the immune system, and an increased emphasis must be placed on performing proper controls to ensure that therapeutic effects are sequence-specific.
RNA interference holds vast potential as a therapeutic strategy for both disease prevention and treatment, but its use has so far been hampered by a lack of safe and effective delivery techniques. In their Review, Anderson and colleagues discuss the challenges associated with small interfering RNA delivery and highlight promising novel synthetic delivery agents.
In the 10 years that have passed since the Nobel prize-winning discovery of RNA interference (RNAi), billions of dollars have been invested in the therapeutic application of gene silencing in humans. Today, there are promising data from ongoing clinical trials for the treatment of age-related macular degeneration and respiratory syncytial virus. Despite these early successes, however, the widespread use of RNAi therapeutics for disease prevention and treatment requires the development of clinically suitable, safe and effective drug delivery vehicles. Here, we provide an update on the progress of RNAi therapeutics and highlight novel synthetic materials for the encapsulation and intracellular delivery of nucleic acids.