Abstract
West Nile (WN) and St. Louis encephalitis (SLE) viruses can cause fatal neurological infection and currently there is neither a specific treatment nor an approved vaccine for these infections. In our earlier studies, we have reported that siRNAs can be developed as broad-spectrum antivirals for the treatment of infection caused by related viruses and that a small peptide called RVG-9R can deliver siRNA to neuronal cells as well as macrophages. To increase the repertoire of broad-spectrum antiflaviviral siRNAs, we screened 25 siRNAs targeting conserved regions in the viral genome. Five siRNAs were found to inhibit both WNV and SLE replication in vitro reflecting broad-spectrum antiviral activity and one of these was also validated in vivo. In addition, we also show that RVG-9R delivers siRNA to macrophages and dendritic cells, resulting in effective suppression of virus replication. Mice were challenged intraperitoneally (i.p.) with West Nile virus (WNV) and treated i.v. with siRNA/peptide complex. The peritoneal macrophages isolated on day 3 post infection were isolated and transferred to new hosts. Mice receiving macrophages from the anti-viral siRNA treated mice failed to develop any disease while the control mice transferred with irrelevant siRNA treated mice all died of encephalitis. These studies suggest that early suppression of viral replication in macrophages and dendritic cells by RVG-9R-mediated siRNA delivery is key to preventing the development of a fatal neurological disease.
Highlights
West Nile (WN), Japanese B encephalitis (JE) and St
Since flaviviruses are thought to first multiply in dendritic cells and macrophages before spreading to the brain [12,13,14] in this study we tested if RVG-9R is able to deliver siRNA to macrophages to suppress the early virus replication in these cells
Identification of broad-spectrum antiflaviviral siRNAs We have previously shown that a siRNA (FVEjw) targeting highly conserved region in the viral envelope gene could inhibit the replication of both JEV and West Nile virus (WNV) [15]
Summary
West Nile (WN), Japanese B encephalitis (JE) and St. Louis encephalitis (SLE) viruses are mosquito-borne flaviviruses that can cause a devastating acute neurological illness with up to 30% mortality and permanent neurological disabilities in the survivors [1]. Delivering effective quantities of siRNAs into the right target cells in vivo through clinically feasible methods represents a major challenge for the successful development of RNAi-based therapeutics [9]. Our recent studies suggest that a small peptide derived from the rabies virus glycoprotein fused to a highly positively charged 9-mer polyarginine residues (RVG-9R) can provide a tool for siRNA delivery to neuronal cells as well as macrophages [10,11]. Since flaviviruses are thought to first multiply in dendritic cells and macrophages before spreading to the brain [12,13,14] in this study we tested if RVG-9R is able to deliver siRNA to macrophages to suppress the early virus replication in these cells. To expand the repertoire of broad-spectrum siRNAs capable of suppressing multiple flaviviruses, we tested a panel of 25 siRNAs targeting relatively conserved genomic regions
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