Comparative inhibitory potential of differently modified antisense oligodeoxynucleotides on hepatitis C virus translation

Background A completely modified phosphorothioate antisense oligodeoxynucleotide (cS‐ODN 4) directed against nucleotides 326–348 of the hepatitis C virus (HCV) 5′ non‐coding region (NCR) efficiently inhibits viral gene expression. As cS‐ODN exerts undesired side‐effects in vivo, we synthesized partially modified ODN 4 that contained only six modified nucleotides which are located at the ODN termini or are scattered along the molecule. The tested modifications were polar phosphorothioates (S) and non‐polar methyl‐ (M) or benzylphosphonates (B). Results In an in vitro translation system, specific inhibition of HCV gene expression by M‐ODN 4 or B‐ODN 4 was observed if terminally modified ODN were used; the maximal inhibition was 92.3% ± 1.9% and 87.1% ± 3.7%, respectively, at 10 μmol L−1 concentration. S‐ODN 4 specifically suppressed viral translation irrespective of the location of the modifications, resulting in a maximal inhibition of 86.3% ± 3.3%. For all terminally modified ODNs the therapeutic index was high, with tB‐ODN 4 the second best at 3.8. Inhibition correlated with efficient RNase H‐associated cleavage of target RNA. In transient co‐transfection experiments of HepG2 cells with a reporter gene construct and the ODN, terminally modified B‐ODN 4 was the most effective and specific inhibitor. At a concentration of 5 μmol L−1 the suppression of HCV translation was 96.3% ± 0.7%. Conclusion These data demonstrate that terminally modified B‐ODN 4 is a potent inhibitor of HCV gene expression in vitro and in HepG2 cell culture and may be valuable for future antiviral treatment.