The idea of using RNAi in therapeutic applications would be to administer these small genetic sequences to "knock down" the activity of certain, aberrant genes. Because they function on the basis of genetic complementation, RNAi therapies should be highly specific. Such specificity is key for limiting side effects, which are often caused when drugs stray to the wrong target.
As with almost all novel technologies (and, in particular, genetic ones), researchers will not have an EZ-Pass in attempting to translate RNAi to the clinic. In a recent issue of Nature (and a corresponding news story by Andrew Pollack in the NYTimes on April 2), researchers reported that any sequence consisting of 21 or so nucleotides could trigger a physiological effect (angiogenesis inhibition) in mice through a generic mechanism, the "Toll-like Receptor 3" pathway. The study is particularly troubling, because it suggests that RNAi (or, at least certain types of RNAi) might be prone to worrisome side-effects.
According to Pollack, at least five such drugs are presently being tested in human beings. (photo credit: pbo31, 2005)