Inhibitory Effect of Modified 5′-Capped Short RNA Fragments on Influenza Virus RNA Polymerase Gene Expression

We have shown previously that the 5′-capped short phosphodiester RNA fragments, Cap decoy, (Gm 12 nt) are potent inhibitors of influenza virus RNA polymerase gene expression. Here we investigate the modified capped RNA derivative containing phosphorothioate oligonucleotides (Cap decoy) as a potential influenza virus RNA polymerase inhibitor. The modified 5′-capped short phosphorothioate RNA fragments (Gms 12–15 nt) with the 5′-capped structure (m7GpppGm) were synthesized by T7 RNA polymerase. The 5′-capped short RNA fragments (Gms 12–15 nt) were encapsulated in liposome particulates and tested for their inhibitory effects on influenza virus RNA polymerase gene expression in the clone 76 cells. The 12–15 nt long Gms RNA fragments showed highly inhibitory effects. By contrast, the inhibitory effects of the 13 nt long short RNA fragments (Gm 13 nt) were considerably less in comparison with the 5′-capped short phosphorothioate RNA fragments (Gms 12–15 nt). In particular, the various Gms RNA chain lengths showed no significant differences in the inhibition of influenza virus RNA polymerase gene expression. Furthermore, the capped RNA with a phosphorothioate backbone was resistant to nuclease activity. These phosphorothioate RNA fragments exhibited higher inhibitory activity than the 5′-capped short RNA fragments (Gm 12 nt). These decoys may prove to be useful in anti-influenza virus therapeutics.