Inhibition of RNA virus infections with peptide-conjugated morpholino oligomers

RNA virus infections cause immense human disease burdens globally, and few effective antiviral drugs are available for their treatment. Peptide-conjugated phosphorodiamidate morpholino oligomers (PPMO) are nuclease resistant and water-soluble single-stranded-DNA-analogues that can enter cells readily and act as steric-blocking antisense agents through stable duplex formation with complementary RNA. Recently there have been a number of publications documenting sequence-specific and dose-dependent inhibition of non-retroviral RNA virus infections by PPMO in both cell culture and murine experimental systems. PPMO have suppressed viral titers by several orders of magnitude in cell cultures, and have reduced viral replication in and/or increased survivorship of mice experimentally infected with poliovirus, coxsackievirus B3, dengue virus, West Nile virus, Venezuelan Equine encephalitis virus, respiratory syncytial virus, Ebola virus and influenza A virus. Along with evaluating PPMO efficacy and toxicity, these studies also explored PPMO mechanism of action, pharmacologic properties and the generation and characterization of resistant virus. Effective PPMO target sites in viral RNA have included regions of highly conserved sequence thought to be important in the pre-initiation or initiation of translation, or in long-range RNA-RNA interactions involved in viral RNA synthesis. These studies provide guidance for the design of steric-blocking antisense agents against RNA viruses, insights into viral molecular biology and novel strategies for the development of antiviral therapeutics. The purpose of this review is to summarize notable findings from the reports documenting antiviral activity by PPMO, with a focus on the specific regions of viral RNA that provided the most effective targets for PPMO-based inhibition of viral replication.