RNAi as a Therapy
Alnylam is the leading company in the industry's efforts to harness the natural process of RNAi to create a whole new class of human therapeutics. If successfully developed, these RNAi therapeutics could represent breakthroughs in the treatment of human disease.
RNAi occurs in all human cells. As with other major biological technologies, such as recombinant DNA and monoclonal antibodies, the fact that RNAi is a natural biological pathway led many to believe that it could make a particularly safe and effective therapeutic platform.
RNAi is widely exploited by researchers and drug developers for biological research and drug target validation. It is therefore not surprising that there is growing interest in using RNAi as a therapeutic modality itself. RNAi therapeutics have been demonstrated to specifically silence genes with the expected outcome not only in cultured cells in vitro, but also in animal models of human disease and most recently in human clinical studies.
It is known that proteins are responsible for much of the physical and dynamic properties of a cell, and defects in their function or regulation contribute to — if not cause — most human diseases. The majority of drugs today are therefore designed to inactivate proteins, with most attempting to neutralize disease-associated proteins through direct binding without eliminating them.
Much of the interest in RNAi is based on the fact that the RNAi mechanism operates upstream of protein production by eliminating the messenger RNAs coding for such proteins. By way of analogy, the RNAi approach is akin to "stopping a flood by turning off the faucet" as compared with today's medicines that simply "mop up the floor." Moreover, as each messenger RNA is the template for the translation of multiple proteins, comparatively low amounts of an RNAi therapeutic should be effective in ablating protein function.
The RNAi interference process
Small interfering RNA (siRNA) is targeted to a specific gene. 
Within cells siRNA unwinds and is incorporated into RISC, a stable protein-RNA complex. 
siRNA is directed to a targeted messenger RNA (mRNA) that is known to be involved in a disease pathway.
The mRNA undergoes degradation, thereby interrupting the protein synthesis of the targeted gene.
