Inhibition of influenza virus RNA polymerase by 5'-capped short RNA fragments.

We have demonstrated that 5'-capped short RNA fragments inhibit the expression of chloramphenicol acetyltransferase (CAT) in the murine 76 cell line, derived which expresses the genes for the RNA polymerases (PB1, PB2, and PA) and the nucleoprotein (NP) of influenza virus in response to treatment with dexamethasone. We have synthesized 5'-capped short RNA fragments (8-13 ntds long) with a 5'-capped structure (m7GpppGm) using T7 RNA polymerase. The 5'-capped short RNA fragments (8-13 ntds long) were encapsulated in liposomes and were tested for their inhibitory effect by a CAT-ELISA assay using the clone 76 cells. The RNA fragments that were 9-12 ntds long showed inhibitory effects. In particular, the 9 ntds long RNA fragment, was highly inhibitory. On the other hand, the inhibitory effect of the 13 ntds long RNA fragment was considerably decreased in comparison with the other short RNA fragments. The minimal RNA chain length required for priming activity was found to be 12 ntds long. Furthermore, the 5'-capped RNA fragments exhibited higher inhibitory activities than the antisense phosphorothioate oligonucleotide (PB2-AUG-as, 20 ntds long) complementary to the site of the PB2-AUG initiation codon. Liposome encapsulation protected the RNA fragments in serum-containing medium and substantially improved their cellular accumulation.