Nucleic acid-based drugs against the highly pathogenic H5N1 avian influenza virus infection

Background: Highly pathogenic H5N1 avian influenza virus (HPAIV) continues to cause serious global concerns because it threathens the poultry industry and causes loss of human lives. The ability of HPAIV to mutate and develop resistance to antiviral drugs and vaccines necessitates the development of novel drugs and vaccines, including those which are nucleic acid-based. Liposome-encapsulated Poly ICLC (a ds RNA and a toll-like receptor-3 [TLR-3] agonist) and antisense oligonucleotides are examples of nucleic acid-based drugs which can be safe and efficacious against HPAIV. Methods: Using a lethal Balb/c mouse model, liposome-encapsulated Poly ICLC and antisense oligonucleotides (directed against the hemagglutinin protein) were evaluated for their prophylactic or therapeutic efficacy against a wild strain (influenza A/H5N1/chicken/Henan/2005) of HPAIV. Liposome-encapsulated Poly ICLC were administered intranasally at day -3 and day -1 prior to HPAIV challenge, and antisense oligonucleotides were administered intranasally at 4 and 8 hours post virus challenge. Antiviral efficacies were determined by comparing the survival rates of drug-treated mice at day 14 post infection compared to control saline group. Results: Depending to various challenge doses of HPAIV, liposome-encapsulated Poly ICLC administered intranasally provided 67-100% protection when given at up to 24 and 48 hrs prior to virus challenge. RT-PCR analysis of lungs tissues of LE Poly ICLC treated mice indicated up-regulation of TLR-3 and antiviral interferons (-α, - β and -γ) mRNAs production. Treatment of mice with antisense oligonucleotides administered to mice at 4 and 8 hours post infection were completely protected against a 10 lethal dose virus challenge with influenza A/H5N1/chicken/Henan/2005, or with influenza A/PR/8/34 (H1N1). However, therapeutic efficacy of antisense oligonucleotide decreased when treatment with antisense was delayed beyond 8 hours post infection. Conclusion: Liposome-encapsulated Poly ICLC provided high level of protection in mice against lethal doses of HPAIV, and against a seasonal strain of influenza A/PR/8/34 virus (H1N1). Activation of TLR-3 signaling pathway can provide broad-spectrum protection against various strains of influenza virus, regardless of mutations. Post-exposure treatment of HPAIV can be achieved through silencing of influenza virus gene expression using virus-specific antisense oligonucleotides. These findings support the potential role of nucleic acid-based drugs for prevention and treatment of HPAIV.