A decade after the discovery of RNAi mechanism in 1993, the pharmaceutical sector heavily invested in the research and development of siRNA therapy. There are several advantages that this therapy has over small molecules and antibodies. It can be administered quarterly or every six months. Another advantage is that, unlike small molecule and monoclonal antibodies that need to recognize specific conformation of a protein, siRNA functions by Watson-Crick basepairing with mRNA. Therefore, any target molecule that needs to be treated with high affinity and specificity can be selected if the right nucleotide sequence is available. One of the biggest challenges researchers needed to overcome was the identification and establishment of a delivery system through which the therapies would enter the body. And that the immune system often mistakes the RNAi therapies as remnants of infectious agents, which can trigger an immune response. Animal models did not accurately represent the degree of immune response that was seen in humans and despite the promise in the treatment investors divested away from RNAi.
However, there were a few companies that continued with the development of RNAi therapy for humans. Alnylam Pharmaceuticals, Sirna Therapeutics and Dicerna Pharmaceuticals are few of the companies still working on bringing RNAi therapies to market. It was learned that almost all siRNA therapies administered in the bloodstream accumulated in the liver. That is why most of the early drug targets were diseases that affected the liver. Repeated developmental work also shed light on improving the chemical composition of the RNA molecule to reduce the immune response, subsequently causing little to no side effects. Listed below are some of approved therapies or therapies in pipeline.