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Chronic infection with the hepatitis B virus (HBV) occurs in approximately 6% of the world's population and carriers of the virus are at risk for complicating hepatocellular carcinoma. Current treatment options have limited efficacy and chronic HBV infection is likely to remain a significant global medical problem for many years to come. Silencing HBV gene expression by harnessing RNA interference (RNAi) presents an attractive option for development of novel and effective anti HBV agents. However, despite significant and rapid progress, further refinement of existing technologies is necessary before clinical application of RNAi-based HBV therapies is realised. Limiting off target effects, improvement of delivery efficiency, dose regulation, and preventing reactivation of viral replication are some of the hurdles that need to be overcome. To address this we assessed the usefulness of the recently described class of altritol-containing synthetic siRNAs (ANA siRNAs), which were administered as lipoplexes and tested in vivo in a stringent HBV transgenic mouse model. Our observations show that ANA siRNAs are capable of silencing of HBV replication in vivo. Importantly, non specific immunostimulation was observed with unmodified siRNAs, and this undesirable effect was significantly attenuated by ANA modification. Inhibition of HBV replication of approximately 50% was achieved without evidence for induction of toxicity. These results augur well for future application of ANA siRNA therapeutic lipoplexes.

Harnessing RNA interference (RNAi) to inhibit hepatitis B virus (HBV) gene expression has promising application to therapy. Here we describe a new hepatotropic nontoxic lipid-based vector system that is used to deliver chemically unmodified small interfering RNA (siRNA) sequences to the liver. Anti HBV formulations were generated by condensation of siRNA (A component) with cationic liposomes (B component) to form AB core particles. These core particles incorporate an aminoxy cholesteryl lipid for convenient surface postcoupling of polyethylene glycol (PEG; C component, stealth/biocompatibility polymer) to give triggered PEGylated siRNA-nanoparticles (also known as siRNA-ABC nanoparticles) with uniform small sizes of 80−100 nm in diameter. The oxime linkage that results from PEG coupling is pH sensitive and was included to facilitate acidic pH-triggered release of nucleic acids from endosomes. Nanoparticle-mediated siRNA delivery results in HBV replication knockdown in cell culture and in murine hydrodynamic injection models in vivo. Furthermore repeated systemic administration of triggered PEGylated siRNA-nanoparticles to HBV transgenic mice results in the suppression of markers of HBV replication by up to 3-fold relative to controls over a 28 day period. This compares favorably to silencing effects seen during lamivudine treatment. Collectively these observations indicate that our PEGylated siRNA-nanoparticles may have valuable applications in RNAi-based HBV therapy.

Developments in vector design using tissue-specific and tumor-specific promoters have led to significant improvements in tumor-targeting strategies. These developments combined with the ability to monitor gene expression by molecular imaging have facilitated the detection and prolonged monitoring of disease progression in small-animal models. Bioluminescence imaging offers a convenient and sensitive platform for monitoring gene expression patterns in preclinical models of gene therapy. Targeting a specific subset of cells/tissues via systemic delivery of vectors would be highly beneficial in gene therapy protocols. Using a two-step transcriptional amplification (TSTA)-based lentiviral vector (LV-TSTA), we demonstrate specific targeting of prostate tumors in vivo after systemic administration of lentivirus. Four days after intravenous administration of LV-TSTA into adult severe combined immunodeficient (SCID) mice (n = 5) carrying subcutaneous prostate tumors, we found significant levels of transduction at the tumor site when compared with other organs (p < 0.05). Gene expression was sustained in the tumor for up to 3 weeks (7.3 × 104 ± 2 × 104 photons/ sec/cm2/steradian (p/sec/cm2/sr) on day 4 and 7.0 × 104 ± 4 × 104 p/sec/cm2/sr on day 21). Low levels of transduction were also observed in the spleen and liver (5.0 × 102 ± 1.7 × 102 p/sec/cm2/sr). The results from this study support the use of TSTA-based lentiviral vectors for prostate tumor targeting after systemic delivery. Noninvasive imaging using such vectors should be useful for monitoring long-term gene expression in gene therapy applications.

ABSTRACTThe ability of entecavir (ETV) to inhibit Duck hepatitis B virus(DHBV) infection in duck hepatocytes and ducklings was examined using lamivudine (3TC) as a comparator drug. ETV exhibited antiviral activity (50% effective concentration [EC50], 0.13 nM) in DHBV-infected duck hepatocytes that was >1,000-fold more potent than that of 3TC (EC50, 138 nM). A 21-day treatment of ducklings with 1 mg of ETV per kg of body weight per day by oral gavage resulted in a mean reduction of log103.1 in serum DHBV DNA levels. Daily treatment with 0.1 mg of ETV/kg was nearly as effective, achieving an average viral DNA level decrease of log102.1. Reducing the daily dose of ETV to only 0.01 mg/kg resulted in an average viral DNA level decrease of log100.97. Daily treatment with 25 mg of 3TC/kg resulted in an average viral DNA level decrease of log100.66, compared to the log100.20 drop seen for ducklings given the vehicle alone. ETV was also more effective in decreasing the DHBV DNA levels in duck livers after 21 days of treatment, causing average drops of log101.41, log100.76, and log100.26 for dose levels of 1.0, 0.1, and 0.01 mg/kg, respectively, compared to a decrease of log100.06 for 3TC at a dose level of 25 mg/kg. Levels of viral covalently closed circular DNA in the treatment group receiving 1 mg of ETV/kg were reduced compared to those in the vehicle-treated group. ETV and 3TC were both well tolerated in all treated animals. These results show that ETV is a highly potent and effective antiviral in the DHBV duck model.