Therapeutic application of RNAi in viral disease

Abstract

RNA interference (RNAi) is believed to have a great potential as an antiviral approach against multiple disease causing viruses such as HIV, HBV, HCV influenza. The major reason for its promise as a therapeutic is because of its absolute specificity in silencing the target, which in turn is dictated by the exact complementarity of the target sequence to siRNA/shRNA, which are the small molecule mediators of RNAi. However, this feature also turns out to be a limitation since many viruses such as HIV undergo mutations that would lead to their escape from the inhibitory effects of RNAi. As a result, it becomes necessary to identify highly conserved nucleotide sequences that are relatively less prone to mutations due to their important roles in the viral life cycle, so that they can serve as efficient RNAi targets. In a multi panel study, we have identified and demonstrated the advantage of targeting conserved nucleotide regions in two totally unrelated viral families. In the first study, we have shown that a single shRNA targeting a highly conserved region that maps to the vif gene of HIV can not only inhibit the corresponding viral strain but can also provide very effective protection against multiple clades of the virus in primary human T cells, the major cell type infected by HIV. In our second study, by designing a siRNA to a highly conserved region in the envelope gene of encephalitic flaviviruses, we again establish that a single siRNA can protect mice against fatal encephalitis caused by two different viral species- Japanese encephalitis virus and West Nile virus. Our results underscore the importance of using conserved target regions for RNAi-mediated therapeutic applications, to not just achieve a broad-based viral intervention but to also suppress the possible emergence of mutant viral species.