Critical issues in delivery of RNAi therapeutics in vivo.

: RNA interference (RNAi) is a fundamental mechanism of gene regulation and has been harnessed to produce a new class of drugs for treatment of various diseases. A key issue in these applications is how to effectively deliver RNAi therapeutics into target cells. This review is focused on advances in RNA delivery in vivo. To achieve it, novel strategies have been developed to enhance stability of RNA in cells and tissues, overcome barriers to transport of RNA or its carriers in the body, and reduce immunogenicity and cytotoxicity of treatment. Approaches to RNA delivery are divided into three categories in this review: biological, chemical, and physical. Advantages and disadvantages of each method are discussed. At present, effective delivery of RNAi therapeutics in vivo is still a challenge although significant advances have been made in this field.