RNAi therapeutics: principles, prospects and challenges

Abstract

RNA interference (RNAi) was discovered less than a decade ago and already there are human clinical trials in progress or planned. A major advantage of RNAi versus other antisense based approaches for therapeutic applications is that it utilizes cellular machinery that efficiently allows targeting of complementary transcripts, often resulting in highly potent down-regulation of gene expression. Despite the excitement about this remarkable biological process for sequence specific gene regulation, there are a number of hurdles and concerns that must be overcome prior to making RNAi a real therapeutic modality, which include off-target effects, triggering of type I interferon responses, and effective delivery in vivo. This review discusses mechanistic aspects of RNAi, the potential problem areas and solutions and therapeutic applications. It is anticipated that RNAi will be a major therapeutic modality within the next several years, and clearly warrants intense investigation to fully understand the mechanisms involved.

Figure 1

The left hand side shows a schematic diagram of the mammalian RNAi pathway and formation of small interfering RNAs (siRNA) that mediates homology-dependent target mRNA degradation in the cytoplasm though the RNA-induced silencing complex (RISC). The right hand side shows different entry point for artificial DNA-based (marked in red) or RNA-based (marked in blue) siRNA drugs that enters and activates RISC for gene silencing.

Figure 2

The left hand side shows various non-targeted or targeted in vivo delivery strategies for RNA-based siRNA drugs. The right hand side shows a schematic diagram of either a DNA-based pol-III or pol-II promoted shRNA expression cassettes. These shRNA expression units can by delivered by viral or non-viral methods to the target tissue, as illustrated by gene transfer using lentiviral vector technology.