Small interfering RNAs, or siRNAs, the molecules that mediate RNAi, can be synthesized chemically in the lab and then introduced into cells, opening up enormous possibilities for using siRNAs as potential drug candidates. Potential advantages of siRNA drugs include:

The ability to harness a natural pathway: RNAi is a natural pathway to control gene expression. This natural pathway can be harnessed to create a new class of innovative medicines.

The ability to target virtually any protein: A key limitation of traditional medicines is that they can only target certain classes of protein. Targets for currently marketed small-molecule drugs include G-protein-coupled receptors, ion channels, enzymes and nuclear hormone receptors. Despite much effort, attempts to find small-molecule drugs targeting other classes of proteins have been largely unsuccessful. The range of targets for protein drugs, such as monoclonal antibodies, is also limited, mainly to cell-surface receptors or to circulating proteins. In contrast, given the sequenced human genome, it is possible to design siRNAs for each and every gene/mRNA. This opens up the possibility of developing siRNA drugs for proteins that do not fit into the so-called "druggable target classes."

Acting "upstream" of today's medicines: With RNAi therapeutics, it is possible to block the production of disease-causing proteins before they are made. This affords the opportunity to provide greater efficacy in disease control and intervention. The RNAi approach is like "stopping a flood by turning off the faucet" as compared with today's medicines that "simply mop up the floor."

Simplified discovery of drug candidates: Identification of appropriate drug candidates can be more straightforward using siRNAs. In contrast to the extensive lead optimization steps required in small molecule and protein drug discovery, RNAi drug candidates can be identified using bioinformatic tools to select sequences complementary to the target mRNA. The process of choosing an RNAi-based drug candidate may simply involve the synthesis and testing of a relatively small number of siRNAs.