Antiviral agents for hepatitis B

Hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC): molecular mechanisms and novel paradigms

Chronic hepatitis B (HBV) infection is a major risk factor for hepatocellular carcinoma (HCC). Most HCCs complicate the evolution of an active or inactive cirrhosis. However, some tumors occur on livers with minimal histological changes; the prevalence of such cases varies from one geographical region to the other, being much higher in the Southern half of Africa (around 40% of HCCs) than in Asia, America and Europe, where at least 90% of HCCs are associated in the cirrhosis. This heterogeneity is probably a reflection of different environmental and genetic factors. This review will summarise the current knowledge on the mechanisms involved in HBV-related liver carcinogenesis. It will show in particular how viruses can be viewed as tools to discover and dissect new cellular pathways involved in cancer development and emphasize the potential synergistic effects between HBV and hepatitis C virus (HCV), as well as between viral infections and other environmental factors, such as alcohol.

Immunotherapy of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death, with over a million new cases annually. It is generally advanced upon detection due to underlying liver disease, which further complicates treatment. Most of the therapeutic strategies in current use (surgery, transplantation, irradiation or chemotherapy) are either palliative or only of benefit to a small percentage of patients. This article reviews the biology of HCC, including many of the molecular changes and mechanisms leading to HCC development. This article discusses the recent innovative strategies to interfere with the progression of HCC, including novel gene therapy strategies. The most recent data supporting the use of immunotherapy for hepatocellular cancer is reviewed in detail.

Identification of woodchuck class I MHC antigens using monoclonal antibodies

Two class I major histocompatibility complex (MHC) proteins with molecular masses of 43- and 39-kDa were identified in the cell surface membranes of normal woodchucks using a newly developed antiwoodchuck class I monoclonal antibody (mAb) B1b.B9 and immunoblotting. B1b.B9 was generated by immunizing mice with viable woodchuck peripheral blood mononuclear cells and was selected for anti-class I MHC reactivity using a cellular enzyme-linked immunoassay, indirect immunofluorescence on tissue sections and flow cytofluorimetry. The distribution pattern of class I MHC antigen on woodchuck lymphoid cells was found to be similar to that reported in other species. Also, the antigen expression on normal woodchuck hepatocytes was comparable to that observed on normal human liver parenchymal cells; thus, the antigen was not detected on hepatocytes by staining of liver tissue sections, but was found by indirect immunofluorescence staining of isolated liver cells. Western blot analysis of the plasma membranes from normal woodchuck hepatocytes revealed the presence of a single species of class I MHC heavy chain protein with a molecular mass of 43-kDa, whereas splenocyte plasma membranes showed intense expression of a 43-kDa species, as well as the presence of a 39-kDa protein. The 39- and 43-kDa proteins were extracted with Triton X-114 to the hydrophobic protein phase, suggesting that they both contain a hydrophobic transmembrane domain. The data obtained indicate that the B1b.B9 identifies a nonpolymorphic epitope of woodchuck class I MHC heavy chains, providing an important reagent for the study of the pathogenesis of hepatitis B virus infection in a woodchuck model.

Prospectives on the treatment of chronic hepatitis B and chronic hepatitis C with thymic peptides and antiviral agents

At the present time, interferon is considered the only effective therapeutic approach in the treatment of both chronic hepatitis B and chronic hepatitis C. It is clear that the disappointing response rates in both chronic hepatitis B and C place added emphasis on efforts to identify alternative forms of therapy. In addition to the development of other antiviral agents including the nucleoside analogs which might prove more effective and have fewer associated side-effects, other agents currently under investigation include thymic peptides such as thymosin alpha 1. In the future, the therapeutic approach to the treatment of chronic hepatitis B and C may consist of combination therapy using perhaps an immune modulator and an antiviral agent or, several antiviral drugs. Alternatively, there is indication that cellular targeting systems with delivery of the toxic material to the specific cell containing the virus may be more effective, while minimizing side-effects. Finally, there are agents such as ursodeoxycholic acid which perhaps, makes bile less toxic and can be used as adjunctive therapy with improvement in liver chemistry values. The treatment of chronic hepatitis B and chronic hepatitis C has shifted in emphasis form the concept of treating liver disease towards that of treating viral infections which happen to effect primarily the liver.

The in vitro anti-hepatitis B virus activity of FIAU [1-(2'-deoxy-2'-fluoro-1-beta-D-arabinofuranosyl-5-iodo)uracil] is selective, reversible, and determined, at least in part, by the host cell

A human hepatoblastoma cell line was stably transfected with a head-to-tail dimer of the Hepatitis B virus (HBV), subtype adw, genome to generate a cell line which produces HBV. FIAU [1-(2'-deoxy-2'-fluoro-1-beta-D-arabinofuranosyl-5-iodo)uracil] inhibited viral replication in these cells with an IC50 of 0.90 microM, as determined by PCR analysis of extracellular Dane particle DNA, and displayed a 50% cytotoxic concentration (TC50) of 344.3 microM, as determined using the MTT assay. The selectivity index of FIAU (TC50/IC50) was 382.6. In cells incubated for 10 days with FIAU (100 microM) and then incubated with drug-free media with daily media changes for 7 days, viral DNA replication was markedly inhibited but resumed within 24 h after drug removal, demonstrating that the in vitro anti-HBV activity of FIAU is reversible. Both the antiviral activity and cytotoxicity of FIAU were reversed by the addition of equimolar to 10-fold excess molar concentrations of thymidine. The de-iodinated metabolite of FIAU, FAU, had only marginal anti-HBV activity at 100 microM, indicating that this metabolite does not contribute significantly to the activity of FIAU. The examination of intracellular viral DNA replicative intermediates revealed that FIAU was 2000-fold more active against duck HBV DNA replication in human hepatoma cells (IC50 = 0.075 microM) than against this same virus in chicken liver cells (IC50 = 156 microM). FIAU was anabolized to a 25-fold greater extent in human hepatoma cells than in chicken cells, indicating that the anti-HBV activity of this nucleoside analog is dependent, in part, on its phosphorylation by the host cell.