Review article: Success and failure of nucleoside and nucleotide analogues in chronic hepatitis B

Synthesis of C-4-Substituted Steviol Derivatives and Their Inhibitory Effects against Hepatitis B Virus

ent-13-Hydroxykaur-16-ene-19-N-butylureide (6) was one of 33 synthesized C-4-substituted steviol derivatives that were evaluated for their effects on hepatitis B virus (HBV) surface antigen (HBsAg) secretion. The IC₅₀ (16.9 μM) and SI (57.7) values for inhibiting HBV DNA replication of compound 6 were greater than those of the reference compound, lamivudine (3-TC; IC₅₀: 107.5 μM; SI: 22.0). Thus, the anti-HBV mechanism of 6 was investigated, and it specifically inhibited viral gene expression and reduced viral DNA levels, as well as potently attenuated all of the viral promoter activity of HBV-expressing Huh7 cells. Examination of cellular signaling pathways found that 6 inhibited the activities of the nuclear factor (NF)-κB- and activator protein (AP)-1 element-containing promoters, but had no effects on AP-2 or interferon-stimulated response element (ISRE)-containing promoters in HBV-expressing cells. Meanwhile, it significantly eliminated NF-κB and extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) signaling-related protein levels and inhibited their phosphorylation in HBV-transfected Huh7 cells. The inhibitory potency of 6 against HBV DNA replication was reversed by cotransfecting the NF-κB p65 expression plasmid. Using the MAPK-specific activator anisomycin also reversed the inhibitory effect of 6 on viral DNA replication. The present findings suggest that the anti-HBV mechanism of 6 is partly mediated through the NF-κB and MAPK signaling pathways.

Isothiafludine, a novel non-nucleoside compound, inhibits hepatitis B virus replication through blocking pregenomic RNA encapsidation

AIM

To investigate the action of isothiafludine (NZ-4), a derivative of bis-heterocycle tandem pairs from the natural product leucamide A, on the replication cycle of hepatitis B virus (HBV) in vitro and in vivo.

METHODS

HBV replication cycle was monitored in HepG2.2.15 cells using qPCR, qRT-PCR, and Southern and Northern blotting. HBV protein expression and capsid assembly were detected using Western blotting and native agarose gel electrophoresis analysis. The interaction of pregenomic RNA (pgRNA) and the core protein was investigated by RNA immunoprecipitation. To evaluate the anti-HBV effect of NZ-4 in vivo, DHBV-infected ducks were orally administered NZ-4 (25, 50 or 100 mg·kg⁻¹·d⁻¹) for 15 d.

RESULTS

NZ-4 suppressed intracellular HBV replication in HepG2.2.15 cells with an IC₅₀ value of 1.33 μmol/L, whereas the compound inhibited the cell viability with an IC₅₀ value of 50.4 μmol/L. Furthermore, NZ-4 was active against the replication of various drug-resistant HBV mutants, including 3TC/ETV-dual-resistant and ADV-resistant HBV mutants. NZ-4 (5, 10, 20 μmol/L) concentration-dependently reduced the encapsidated HBV pgRNA, resulting in the assembly of replication-deficient capsids in HepG2.2.15 cells. Oral administration of NZ-4 dose-dependently inhibited DHBV DNA replication in the DHBV-infected ducks.

CONCLUSION

NZ-4 inhibits HBV replication by interfering with the interaction between pgRNA and HBcAg in the capsid assembly process, thus increasing the replication-deficient HBV capsids. Such mechanism of action might provide a new therapeutic strategy to combat HBV infection.

Current status of antiviral therapy for hepatitis B

Chronic hepatitis B (CHB) is a major public health problem affecting up to 400 million people globally. Complications of CHB including liver failure and hepatocellular carcinoma result in 1.2 million deaths per year, making CHB the 10th leading cause of mortality worldwide. The natural history of CHB is variable and complex. The past decade witnessed important developments for the therapy of hepatitis B and marked the new era of oral therapy. The ultimate goal of CHB therapy is to arrest the progression of liver injury and to prevent the development of liver failure and hepatocellular carcinoma. Currently, six agents are approved for the treatment of CHB. Each of these agents, given as monotherapy, has been shown to produce virological, biochemical, and histological benefits for both HBeAg positive and negative CHB. There are, however, limitations in spite of their efficacy. The significant side-effect profile of interferon, for example, limits its long-term use. The approved oral agents are tolerable with prolonged use but drug resistance could limit long-term monotherapy. To date, combination therapy with nucleoside analogue and pegylated interferon or two nucleos(t)ide analogues given for one year does not show superiority in durability of response compared to monotherapy. Ongoing research effort is critical to identify the ideal hepatitis B therapy that is safe, effective, and produces durable response with a finite course of therapy. It is equally important to conduct a well designed, prospective natural history study to identify predictors of disease progression. This will accurately guide treatment strategy for this important disease.

Clinical profile, genotype and management updates of hepatitis B virus

Hepatitis B virus (HBV) is a well known agent of acute and chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. Around 400 million people worldwide carrier of HBV of which more than 250 million reside in Asia, and 1-2 million people have died from it. It has a partially double-stranded DNA, having 3.2-kb genome size and replicate via reverse transcription of RNA intermediate. In the natural history or during the antiviral therapy of chronic HBV infection, seroconversion from HBeAg to anti-HBeAg is usually accompanied by a decrease in viral replication and remission of liver disease. Based on genomic sequence data HBV is classified into eight genotypes A-H and four major serotypes ayw, ayr, adw and adr on the basis of complete genome and S gene sequence analysis. Genotypes and serotypes are useful tools in understanding the epidemiology of HBV infection. HBV genotypes have distinct geographical distributions. The HBV variants appear during HBeAg seroconversion and they bring mutations in the precore region (PC) that prevent HBeAg synthesis. Another common HBeAg variant is the basal core promoter mutant (BCP) characterized by point mutation in the promoter of both HBeAg mRNA and core protein mRNA. The most frequent core promoter mutation is the double A1762T and G1764A nucleotide exchange, which results in a substantial decrease in HBeAg expression but enhanced viral genome replication. The approved antiviral drugs such as Interferon, lamivudine, adefovir dipivoxil, entecavir and telbivudine for purpose of treating chronic HBV infection is to prevent or stop the progression of liver injury by suppressing viral replication or eliminating infection. Sustained losses of viral markers of active viral replication (HBeAg and HBV DNA) are the standard end point of the therapies.

Full-length hepatitis B virus sequences from naïve patients with fluctuation of viral load during ADV monotherapy

The reasons for adefovir dipivoxil (ADV) treatment failures appear diverse. Few studies have reported full-length hepatitis B virus (HBV) genome in patients with ADV treatment failures. The patients were from a phase III clinical trial that investigated the antiviral response to ADV in China. Seven patients had increase in HBV-DNA (>1 log(10) copies/ml above on-treatment nadir) at week 52. The serum HBV-DNA levels were above 10(4)copies/ml at week 92 in four of them. Sixteen full-length HBV genomes from the four patients at four time points were sequenced using cloning sequencing method. The frequency of substitutions at week 52 was higher than at weeks 28(16 wt) and 92(80). HBV-DNA reduction was correlated negatively with the frequency of substitutions at the three time points. No published ADV-resistant mutations were detected. The mutations, including substitutions in immunogenic epitopes and conserved sites of the polymerase gene, were frequent during ADV treatment. Amino acid deletions in X gene and basal core promoter/pre-core mutations appeared before or during ADV treatment. The substitutions in immunogenic epitopes (mainly of the surface gene) and conserved sites of the polymerase gene other than ADV-resistant mutations may have influenced antiviral efficacy in the study. More potent antiviral drugs may be important to rescue individual patients and for public health safety. It is needed to study how these substitutions influence HBV replication, disease progression, and antiviral treatment efficacy.

Advances in the diagnosis and treatment of hepatitis B

PURPOSE OF REVIEW

Hepatitis B virus is responsible for much morbidity and mortality worldwide. Although the armament of drugs licensed for its treatment grows, it is increasingly apparent that the efficacy of these drugs is dependent upon much more that their pharmacology.

RECENT FINDINGS

A better understanding of the natural history of chronic hepatitis B infection together with recent advances in the molecular biology of antiviral resistance have given added dimensions to physicians' decision-making thought processes.

SUMMARY

The present review outlines the recent advances in diagnostic testing that enable a better understanding of an individual patient's phase of illness and also how such information can update treatment choices better. In the second part of this review, the licensed therapies and their relative merits are discussed, as is their role in managing resistance to antiviral therapy.

Pseudomonas exotoxin antisense RNA selectively kills hepatitis B virus infected cells

AIM: To present an approach for selectively killing retrovirus-infected cells that combines the toxicity of Pseudomonas exotoxin (PE) and the presence of reverse transcriptase (RT) in infected cells.

METHODS: PE antisense toxin RNA has palindromic stem loops at its 5’ and 3’ ends enabling self-primed generation of cDNA in the presence of RT. The RT activity expressed in retrovirus-infected cells converts “antisense-toxin-RNA” into a lethal toxin gene exclusively in these cells.

RESULTS: Using cotransfection studies with PE-expressing RNAs and β-gal expressing reporter plasmids, we show that, in HepG2 and HepG2.2.15 hepatoma cells as well as in duck hepatitis B virus (DHBV) infected cells, HBV or DHBV-polymerase reverse transcribe a lethal cDNA copy of an antisense toxin RNA, which is composed of sequences complementary to a PE gene and eukaryotic transcription and translation signals.

CONCLUSION: This finding may have important implications as a novel therapeutic strategy aimed at the elimination of HBV infection.