Drug discovery and development of antiviral agents for the treatment of chronic hepatitis B virus infection

Anti-hepatitis B virus activities of triterpenoid saponin compound from Potentilla anserine L

The Tibetan herb Potentilla anserina L. has been widely used in China for many thousands of years to treat hepatitis-B. Bioassay-guided fractionation of the ethanol extract of the rhizomes led to the isolation of a triterpenoid saponin (TS) that was determined to be 2alpha,3beta,19alpha-trihydroxyurs-12-en-28-oic acid beta-D-glucopyranosyl ester. Using models of HBV infection, this compound was evaluated for its effect on HBV antigene expression in the 2.2.15 cell line in vitro and anti-hepatitis B virus (HBV) activities in Peking ducklings in vivo. Results showed that it could decrease the expression levels of HBsAg, HBeAg and HBVDNA in the 2.2.15 cell culture and the inhibitory effect was not due to the cytotoxity of the triterpenoid saponin. The antiviral study in vivo on Peking ducklings also demonstrated that this compound inhibits duck hepatitis B virus (DHBV) DNA replication.

Inhibitory effect of oxymatrine on serum hepatitis B virus DNA in HBV transgenic mice

AIM: To study the inhibitory effect of oxymatrine on serum hepatitis B virus (HBV) DNA in HBV transgenic mice.

METHODS: HBV transgenic mice model was established by microinjection, and identified by HBV DNA integration and replication. Transgenic mice with replicating HBV were divided into 3 groups, and injected with normal saline (group A, n = 9), 50 mg/kg (group B, n = 8) and 100 mg/kg (group C, n = 9) oxymatrine intraperitoneally once a day for 30 d, respectively. Quantitation of serum HBV DNA in HBV transgenic mice was performed by competitive polymerase chain reaction (PCR) in combination with DNA hybridization quantitative detection technique before and after treatment.

RESULTS: Compared with pre-treatment, the serum HBV DNA in group A (F = 1.04, P = 0.9612) and group B (F = 1.13, P = 0.8739) had no changes after treatment. However, in group C serum HBV DNA was significantly decreased (F = 13.97, P = 0.0012). The serum HBV DNA after treatment was lower in group C than in groups B and A (F = 8.65, P = 0.0068; F = 12.35, P = 0.0018; respectively). The serum HBV DNA after treatment was lower in group B than in group A, but there was no statistical significance (F = 1.43, P = 0.652).

CONCLUSION: Oxymatrine has inhibitory effects on serum HBV DNA in HBV transgenic mice.

Lethiferous effects of a recombinant vector carrying thymidine kinase suicide gene on 2.2.15 cells via a self-modulating mechanism

AIM: To determine the lethiferous effects of a recombinant vector carrying thymidine kinase (TK) suicide gene on 2.2.15 cells and the possible self-modulating mechanism.

METHODS: A self-modulated expressive plasmid pcDNA3-SCITK was constructed by inserting the fragments carrying hepatitis B virus antisense-S (HBV-anti-S) gene, hepatitis C virus core (HCV-C) gene, internal ribosome entry site (IRES) element of HCV and TK gene into the eukaryotic vector pcDNA3, in which the expression of TK suicide gene was controlled by the HBV S gene transcription. 2.2.15 cells that carry the full HBV genome and stably express series of HBV antigen were transfected with pcDNA₃-SCITK or vector pcDNA₃-SCI which was used as the mock plasmid. The HepG2 cells transfected with pcDNA₃-SCITK were functioned as the negative control. All the transfected cells were incubated in DMEM medium supplemented with 10 μg/mL. of ganciclovir (GCV). The HBsAg levels in the supernatant of cell culture were detected by ELISA on the 1^st, 3^rd and 6^th day post-transfection. Meanwhile, the morphology of tranfected cells was recorded by the photograph and the survival cell ratio was assessed by the trypan blue exclusion test on the 6^th day post-transfection.

RESULTS: The structural accuracy of pcDNA₃-SCITK was confirmed by restriction endonuclease digestion, PCR with specific primers and DNA sequencing. The HBsAg levels in the supernatant of transfected 2.2.15 cell culture were significantly decreased on the 6^th day post-transfection as compared with that of the mock control (P < 0.05). The lethiferous effect of pcDNA₃-SCITK expression on 2.2.15 cells was initially noted on the 3^rd day after transfection and aggravated on the 6^th day post transfection, in which the majority of transfected 2.2.15 cells were observed shrunken, round in shape and even dead. With assessment by the trypan blue exclusion test, the survival cell ratio on the 6^th day post transfection was 95% in the negative control and only 11% in the experimental group.

CONCLUSION: The results indicate that suicide gene expression of pcDNA₃-SCITK can only respond to HBV-S gene transcription, which may be potentially useful in the treatment of HBV infection and its related liver malignancies.

Evaluation of mitochondrial DNA content and enzyme levels in tenofovir DF-treated rats, rhesus monkeys and woodchucks

The antiviral compound tenofovir DF (Gilead Sciences) was evaluated for possible mitochondrial toxicity in rats, rhesus monkeys and woodchucks. Animals were treated by oral gavage with tenofovir DF, and the levels of mitochondrial enzymes cytochrome c oxidase and citrate synthase were assayed. In rats (6/group) treated daily for 28 days with 300 mg/kg tenofovir DF the enzyme levels were unchanged versus control in liver, kidney, and skeletal muscle. In a parallel study, rats (6/group) were treated with 40 mg/kg of the antiviral adefovir dipivoxil (Gilead Sciences) and enzyme levels were also unchanged versus control. In rhesus monkeys (6/group) treated daily with 30 mg/kg or 250 mg/kg tenofovir DF for 56 days, and in woodchucks (6/group) treated daily with 15 mg/kg or 50mg/kg tenofovir DF for 90 days, the enzyme levels were unchanged in liver, kidney, skeletal muscle and cardiac muscle. Mitochondrial DNA (mtDNA) content was determined in tissue from treated versus control animals by utilizing a quantitative real-time PCR (QPCR) technique, where the relative ratios of mitochondrial cytochrome b gene to the genomic actin gene were measured. The relative mtDNA content from rats, rhesus monkeys and woodchucks were unchanged in the various treatment groups. Variations in mtDNA content between animals in the same treatment group were noted. The actual species-dependent mitochondria/genomic ratios were estimated from the QPCR assay. In summary, treatment with tenofovir DF, or with adefovir dipivoxil, did not affect mtDNA content or level of mitochondrial enzymes, and no liver, muscle or renal microscopic abnormalities were observed in tenofovir-treated animals.