IN VIVO SCREENING OF CHEMICAL MODIFICATIONS OF siRNAs FOR EFFECT ON THE INNATE IMMUNE RESPONSE IN FISH

Abstract Due to their sequence specific gene silencing activity siRNAs are regarded as promising new active compounds in gene medicine and functional studies. But one serious problem with delivering siRNAs as treatment is the now well-established non-specific activities of some RNAs duplexes. Cellular reactions towards double stranded RNAs include the 2´-5´ oligoadenylate synthetase system, the protein kinase R, RIG-I and Toll-like receptor activated pathways all resulting in antiviral defence mechanism. We have previously shown that antiviral innate immune reactions against injected siRNAs could be detected in vivo as reduced susceptibility to a fish pathogenic virus. This protection corresponded with an interferon response. Here we use this fish model to screen siRNAs containing various chemical modifications of the RNA backbone and find that is possible to differentiate between the antiviral activities of these duplexes. We conclude that the fish in vivo model is a potent tool for gaining insight into the overall triggering of antiviral reactions by siRNAs in vertebrates. The perspective is to learn how to avoid triggering of non-specific antiviral responses and still allow uptake of siRNAs into RISC for specific gene silencing.