In vitro antihepadnaviral activities of combinations of penciclovir, lamivudine, and adefovir

Antiviral Chemotherapy in Avian Medicine-A Review

This review article describes the current knowledge about the use of antiviral chemotherapeutics in avian species, such as farm poultry and companion birds. Specific therapeutics are described in alphabetical order including classic antiviral drugs, such as acyclovir, abacavir, adefovir, amantadine, didanosine, entecavir, ganciclovir, interferon, lamivudine, penciclovir, famciclovir, oseltamivir, ribavirin, and zidovudine, repurposed drugs, such as ivermectin and nitazoxanide, which were originally used as antiparasitic drugs, and some others substances showing antiviral activity, such as ampligen, azo derivates, docosanol, fluoroarabinosylpyrimidine nucleosides, and novel peptides. Most of them have only been used for research purposes and are not widely used in clinical practice because of a lack of essential pharmacokinetic and safety data. Suggested future research directions are also highlighted.

Animal Models of Hepatitis B Virus Infection-Success, Challenges, and Future Directions

Chronic hepatitis B virus (HBV) infection affects more than 250 million people worldwide, which greatly increases the risk for terminal liver diseases, such as liver cirrhosis and hepatocellular carcinoma (HCC). Even though current approved antiviral therapies, including pegylated type I interferon (IFN) and nucleos(t)ide analogs, can effectively suppress viremia, HBV infection is rarely cured. Since HBV exhibits a narrow species tropism and robustly infects only humans and higher primates, progress in HBV research and preclinical testing of antiviral drugs has been hampered by the scarcity of suitable animal models. Fortunately, a series of surrogate animal models have been developed for the study of HBV. An increased understanding of the barriers towards interspecies transmission has aided in the development of human chimeric mice and has greatly paved the way for HBV research in vivo, and for evaluating potential therapies of chronic hepatitis B. In this review, we summarize the currently available animal models for research of HBV and HBV-related hepadnaviruses, and we discuss challenges and future directions for improvement.

Animal models of HBV infection

The mechanisms determining hepatitis B virus (HBV) persistence and pathogenesis are not fully elucidated, but appear to be multi-factorial. Current medication to repress viral replication is available; however, the unique replication strategies employed by HBV enable the virus to persist within the infected hepatocytes. Consequently, cure is rarely achieved. Progresses in HBV research and preclinical testing of antiviral agents have been limited by the narrow species- and tissue-tropism of the virus, the paucity of infection models available and the restrictions imposed by the use of chimpanzees, the only animals fully susceptible to HBV infection. Mice are not HBV permissive but major efforts have focused on the development of mouse models of HBV replication and infection, such as the generation of humanized mice. By presenting the different animal models available, this review will highlight the most important and clinically relevant findings that have been retrieved from the respective systems.

siRNA combinations mediate greater suppression of hepatitis B virus replication in mice

Hepatitis B virus (HBV) infection is a major world-wide health problem. The major obstacles for current anti-HBV therapy are the low efficacy and the occurrence of drug resistant HBV mutations. Recent studies have demonstrated that combination therapy can enhance antiviral efficacy and overcome shortcomings of established drugs. In this study, the inhibitory effect mediated by combination of siRNAs targeting different sites of HBV in transgenic mice was analyzed. HBsAg and HBeAg in the sera of the mice were analyzed by enzyme-linked immunoadsorbent assay, HBV DNA by real-time PCR and HBV mRNA by RT-PCR. Our data demonstrated that all the three siRNAs employed showed marked anti-HBV effects. The expression of HBsAg and the replication of HBV DNA could be specifically inhibited in a dose-dependent manner by siRNAs. Furthermore, combination of siRNAs compared with individual use of each siRNA, exerted a stronger inhibition on antigen expression and viral replication, even though the final concentration of siRNA used for therapy was the same. Secreted HBsAg and HBeAg in the serum of mice treated with siRNA combination were reduced by 96.7 and 96.6 %, respectively. Immunohistochemical detection of liver tissue revealed 91 % reduction of HBsAg-positive cells in the combination therapy group. The combination of siRNAs caused a greater inhibition in the levels of viral mRNA and DNA (90 and 87.7 %) relative to the control group. It was noted that the siRNA3 showed stronger inhibition of cccDNA (78.6 %). Our results revealed that combination of siRNAs mediated a stronger inhibition of viral replication and antigen expression in transgenic mice than single siRNAs.

Combination versus sequential monotherapy in chronic HBV infection: a mathematical approach

Sequential monotherapy is the most widely used therapeutic approach in the treatment of hepatitis B virus (HBV) chronic infection. Unfortunately, under therapy, in some patients the hepatitis virus mutates and gives rise to variants which are drug resistant. We wonder whether those patients would have benefited from the choice of combination therapy instead of sequential monotherapy. To study the action of these two therapeutic approaches and to explain the emergence of drug resistance, we propose a stochastic model for the infection within a patient who is treated with two drugs, either sequentially or contemporaneously, and who, under the first kind of therapy develops a strain of the virus which is resistant to both drugs. Our stochastic model has a deterministic approximation which is a slight modification of a classic three-strain model. We discuss why stochastic simulations are more suitable than the study of the deterministic approximation, when modelling the rise of mutations (this is mainly due to the amplitude of the stochastic fluctuations). We run stochastic simulations with suitable parameters and compare the time when, under the two therapeutic approaches, the resistant strain first reaches detectability in the serum viral load. Our results show that the best choice is to start an early combination therapy, which allows one to stay drug resistance free for a longer time and in many cases leads to viral eradication.

⁹⁹mTc-N4amG: synthesis biodistribution and imaging in breast tumor-bearing rodents

(99m)Tc-N4-guanine ((99m)Tc-N4amG) was synthesized and evaluated in this study. Cellular uptake and cellular fraction studies were performed to evaluate the cell penetrating ability. Biodistribution and planar imaging were conducted in breast tumor-bearing rats. Up to 17%ID uptake was observed in cellular uptake study with 40% of (99m)Tc-N4amG was accumulated in the nucleus. Biodistribution and scintigraphic imaging studies showed increased tumor/muscle count density ratios as a function of time. Our results demonstrate the feasibility of using (99m)Tc-N4amG in tumor specific imaging.

Experimental models and therapeutic approaches for HBV

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. In spite of the existence of an effective vaccine, approximately 360 million people are chronically infected worldwide, who are at high risk of developing liver cirrhosis and hepatocellular carcinoma. Although current therapeutic regimens can efficiently suppress viral replication, the unique replication strategies employed by HBV permit the virus to persist within the infected hepatocytes. As a consequence, relapse of viral activity is commonly observed after cessation of treatment with polymerase inhibitors. The narrow host range of HBV has hindered progresses in understanding specific steps of HBV replication and the development of more effective therapeutic strategies aiming at achieving sustained viral control and, eventually, virus eradication. This review will focus on summarizing recent advances obtained with well-established and more innovative experimental models, giving emphasis on the strength of the different systems as tools for elucidating distinct aspects of HBV persistence and for the development of new therapeutic approaches.

Evaluation of the in vitro anti-HBV activity of clevudine in combination with other nucleoside/nucleotide inhibitors

BACKGROUND

To reduce the incidence of drug resistance and to maintain viral suppression, patients chronically infected with HBV might require combination therapy using two or more drugs with different resistance profiles. We investigated the activity of clevudine (CLV) in combination with other nucleoside/nucleotide analogues to determine if these combinations were compatible in vitro.

METHODS

Using the HepAD38 cell line, which expresses wild-type HBV, and a real-time PCR assay, we tested the anti-HBV activity of CLV in combination with entecavir, lamivudine, adefovir, tenofovir and telbivudine (TBV). We evaluated the uptake and phosphorylation of CLV in the presence of TBV, using HepAD38 cells and primary hepatocytes to determine the effect of TBV on the phosphorylation of CLV and vice versa. Phosphorylation of TBV and CLV to their corresponding monophosphate by deoxycytidine kinase, thymidine kinase-1 and thymidine kinase-2, and the phosphorylation of TBV monophosphate and CLV monophosphate by thymidylate kinase was evaluated and compared.

RESULTS

When CLV was combined with entecavir, lamivudine, adefovir or tenofovir, a synergistic antiviral effect was observed; however, the combination of CLV and TBV gave an antagonistic antiviral response. The results of in vitro metabolism and enzyme studies suggest that the antagonism observed with the CLV/TBV combination involves competition for uptake and phosphorylation.

CONCLUSIONS

The results of our studies demonstrate that combination treatments can provide enhanced antiviral activity and, when used in conjunction with appropriate metabolic investigations, provide a rational basis for the design and development of combination regimens for treating chronic HBV infection.

Anti-hepatitis B virus activity in vitro of combinations of tenofovir with nucleoside/nucleotide analogues

BACKGROUND

Long-term management of some chronic hepatitis B patients might require combination therapy using drugs with distinct resistance profiles to sustain viral suppression and to reduce the resistance-associated failure. Tenofovir disoproxil fumarate (TDF), approved for hepatitis B virus (HBV) and HIV-1 treatment, is active against wildtype HBV and HBV containing YMDD mutations, which confer resistance to emtricitabine (FTC), lamivudine (3TC) and telbivudine (LdT) and contribute to entecavir (ETV) resistance. We therefore evaluated the in vitro anti-HBV activity of tenofovir (TFV), the active parent drug of TDF, combined with FTC, 3TC, ETV, LdT and adefovir (AFV).

METHODS

The anti-HBV activities of the compounds were tested using the AD38 cell line that expresses wild-type HBV from a tetracycline-controllable promoter. Intracellular HBV DNA levels were quantified using real-time PCR assay and cytotoxicities were assessed with XTT assays. The antiviral data of the drug combinations were evaluated using MacSynergy analyses on the basis of the Bliss independence model as well as isobologram analyses on the basis of the Loewe additivity theory.

RESULTS

All drug combinations tested, FTC+TFV, 3TC+TFV, ETV+TFV, LdT+TFV and AFV+TFV, showed additive antiviral interactions as analysed by MacSynergy. Isobologram analyses revealed that these combination pairs were additive, with the exception of FTC+TFV, which demonstrated slight synergistic activity. No cytotoxic or antagonistic effects were observed with any of the combinations tested.

CONCLUSIONS

The combination of TFV with FTC, 3TC, ETV, LdT or AFV had additive to slightly synergistic anti-HBV effects in vitro. These results support the use of TDF as a component in combination regimens with currently available anti-HBV nucleoside analogues.

Combination of small interfering RNAs mediates greater suppression on hepatitis B virus cccDNA in HepG2.2.15 cells

AIM: To observe the inhibition of hepatitis B virus (HBV) replication and expression in HepG2.2.15 cells by combination of small interfering RNAs (siRNAs).

METHODS: Recombinant plasmid psil-HBV was constructed and transfected into HepG2.2.15 cells. At 48 h, 72 h and 96 h after transfection, culture media were collected and cells were harvested for HBV replication assay. HBsAg and HBeAg in the cell culture medium were detected by enzyme-linked immunoadsorbent assay (ELISA). Intracellular viral DNA and covalently closed circular DNA (cccDNA) were quantified by real-time polymerase chain reaction (PCR). HBV viral mRNA was reverse transcribed and quantified by reverse-transcript PCR (RT-PCR).

RESULTS: siRNAs showed marked anti-HBV effects. siRNAs could specifically inhibit the expression of HBsAg and the replication of HBV DNA in a dose-dependent manner. Furthermore, combination of siRNAs, compared with individual use of each siRNA, exerted a stronger inhibition on antigen expression and viral replication. More importantly, combination of siRNAs significantly suppressed HBV cccDNA amplification.

CONCLUSION: Combination of siRNAs mediates a stronger inhibition on viral replication and antigen expression in HepG2.2.15 cells, especially on cccDNA amplification.

Systematic review: combination therapies for treatment-naïve chronic hepatitis B

BACKGROUND

There is a renewed interest in use of combination therapies in treatment-naïve chronic hepatitis B (CHB) because of limitations of monotherapies.

AIM

To discuss the current status of combination therapies in treatment-naïve CHB.

METHODS

PubMed search was done using 'combination', 'sequential' and 'chronic hepatitis B' as the search terms.

RESULTS

The two most popular combination therapies include 'combination of nucleos(t)ide analogues' and 'combination of interferons and nucleos(t)ide analogues'. Combination therapies using two nucleos(t)ide analogues do not lead to higher long-term efficacy. However, addition of a nucleos(t)ide analogue with a good resistance profile to a nucleos(t)ide analogue with a lower genetic barrier to resistance decreases the risk of emergent resistance to the latter. Greater sustained virological, biochemical and seroconversion rates are observed with addition of lamivudine to conventional interferon, but pegylated-interferon monotherapy is equally effective as combination with lamivudine. Again, resistance to lamivudine is lower with its combination with interferons.

CONCLUSIONS

The answer to the question whether hepatitis B can be treated better with combination or monotherapy remains largely unknown. Additional trials are warranted of combination therapies of peginterferon and potent nucleos(t)ide analogues or therapies with the combined use of nucleos(t)ide analogues or immunomodulators.

The case for combination antiviral therapy for chronic hepatitis B virus infection

The treatment of hepatitis B virus (HBV) infection has been revolutionised in the past decade by the increased availability of effective antiviral agents. Many studies have shown the benefits of single agent therapy, but there is an alarming and rising rate of viral resistance, and clear evidence that viruses that harbour resistant mutations can cause liver disease and death. Current national guidelines for the treatment of HBV recommend a programme that starts with monotherapy, followed by sequential monotherapy or add-on therapy for those infections in which mutations have arisen. Very few studies starting with combination therapy have been undertaken, so there is little evidence of the clinical benefit of this approach to treatment. The studies that have been done have been short term and have concentrated on clinical parameters rather than virological resistance, which is likely to be the key determinant in the longer term. We argue that we should not wait for the evidence to use combination therapy for the treatment of HBV, since such trials may never be done and it would take several years for a benefit to become apparent. In the meantime, multidrug-resistant strains continue to hinder HBV control.

96 weeks combination of adefovir dipivoxil plus emtricitabine vs. adefovir dipivoxil monotherapy in the treatment of chronic hepatitis B

BACKGROUND/AIMS

In order to prevent the occurrence of drug-resistant mutants associated with treatment for chronic hepatitis B virus (HBV) infection, combination therapy is being developed. To determine the efficacy of adefovir dipivoxil (ADV) plus emtricitabine (FTC) combination therapy in chronic HBV infection.

METHODS

Thirty treatment-nai ve, HBeAg-positive patients were randomized to combination ADV plus FTC (n=14) or ADV plus placebo monotherapy (n=16) for 96 weeks. HBV DNA was measured by polymerase chain reaction. Treatment was stopped in those with HBeAg seroconversion.

RESULTS

The median decrease in HBV DNA at week 96 was higher in the combination group (-5.30 vs. -3.98 log(10)copies/ml, p=0.05). More patients in the combination group had normalization of alanine aminotransaminase and HBV DNA<300 copies/ml at week 96 when compared with the monotherapy group [11 of the 14 patients (78.6%) vs. 6 of the 16 patients (37.5%), p=0.03]. However, HBeAg seroconversion at week 96 was similar in the 2 groups [2/14 (14.3%) vs. 4/16 (25.0%), p=NS]. No ADV or FTC resistance was detected at week 96. In those with HBeAg seroconversion, 50.0% had post-treatment relapse.

CONCLUSIONS

Combination ADV plus FTC resulted in more potent suppression of HBV DNA over 96 weeks of therapy.

Why do we not yet have combination chemotherapy for chronic hepatitis B?

Despite the emergence of multidrug-resistant strains of hepatitis B virus (HBV) and previous success with combination therapy for other chronic viral infections, we are still using sequential monotherapy for chronic HBV infection. Antiviral-resistant HBV can result in major life-threatening complications. We now have complementary drugs, such as lamivudine and adefovir dipivoxil, with fundamentally different structures and associated with different signature resistance mutations, with adefovir dipivoxil showing antiviral activity against most lamivudine-resistant strains. Studies of combination therapy to date have used traditional endpoints--short-term reduction of HBV DNA levels and HBeAg seroconversion--rather than evolution of resistance. There is now an emerging body of data suggesting that combination therapy can decrease antiviral resistance in HBV infection, the endpoint likely to be of greatest long-term importance, and, rather than adding or replacing an antiviral agent after resistance develops, it is likely to be more effective in treatment-naive patients.

Adefovir dipivoxil monotherapy and combination therapy with lamivudine for the treatment of chronic hepatitis B in an Asian population

AIM

To determine differences in Chinese patients treated with adefovir (ADV) monotherapy or ADV in combination with lamivudine (3TC) after development of resistance to 3TC, with respect to biochemical improvement, HBV DNA suppression and development of subsequent ADV resistance.

METHODS

All hepatitis B patients with 3TC resistance treated with ADV for 3 months or more at our centre were included, and monitored 3-6 monthly for biochemical and virological response, and development of ADV resistance.

RESULTS

A total of 56 patients were included, 50% switched to ADV monotherapy and 50% received combination 3TC/ADV therapy. Median follow-up was 15.5 months. Normalization of alanine aminotransferase (ALT) occurred in 25 (89%) patients in the ADV group compared with 24 (86%) in the 3TC/ADV group (P = 0.686). Virological response (VR) was achieved in seven (35%) patients in the ADV group at 12 months compared with five (28%) in the 3TC/ADV group (P = 0.637). By 24 months, seven (64%) patients in the ADV group achieved VR compared with two (40%) in the 3TC/ADV group (P = 0.377). Cumulative probability of developing genotypic ADV resistance in the ADV group at 24 months was 18% compared with 7% in the 3TC/ADV group (P = 0.94).

CONCLUSION

There was no obvious improvement in ALT normalization and virological suppression or reduction in the development of ADV-resistant mutations with 3TC/ADV therapy compared with ADV monotherapy. Further studies with longer follow-ups are required to determine whether combination 3TC/ADV therapy will reduce the emergence of ADV resistance compared with ADV monotherapy.

Pharmacokinetics of telbivudine in healthy subjects and absence of drug interaction with lamivudine or adefovir dipivoxil

Two phase I studies were conducted to assess the plasma pharmacokinetics of telbivudine and potential drug-drug interactions between telbivudine (200 or 600 mg/day) and lamivudine (100 mg/day) or adefovir dipivoxil (10 mg/day) in healthy subjects. Study drugs were administered orally. The pharmacokinetics of telbivudine were characterized by rapid absorption with biphasic disposition. The maximum concentrations in plasma (Cmax) were reached at median times ranging from 2.5 to 3.0 h after dosing. Mean single-dose Cmax and area under the plasma concentration-time curve from time zero to infinity (AUC0-infinity) were 1.1 and 2.9 microg/ml and 7.4 and 21.8 microg . h/ml for the 200- and 600-mg telbivudine doses, respectively. Steady state was reached after daily dosing for 5 to 7 days. The mean steady-state Cmax and area under the plasma concentration-time curve over the dosing interval (AUCtau) were 1.2 and 3.4 microg/ml and 8.9 and 27.5 microg . h/ml for the 200- and 600-mg telbivudine repeat doses, respectively. The steady-state AUCtau of telbivudine was 23 to 57% higher than the single-dose values. Concomitant lamivudine or adefovir dipivoxil did not appear to significantly alter the steady-state plasma pharmacokinetics of telbivudine; the geometric mean ratios and associated 90% confidence interval (CI) for the AUCtau of telbivudine alone versus in combination were 106.3% (92.0 to 122.8%) and 98.6% (86.4 to 112.5%) when coadministered with lamivudine and adefovir dipivoxil, respectively. Similarly, the steady-state plasma pharmacokinetics of lamivudine or adefovir were not markedly affected by the coadministration of telbivudine; the geometric mean ratios and associated 90% CI, alone versus in combination with telbivudine, were 99.0% (87.1 to 112.4%) and 92.2% (84.0 to 101.1%), respectively, for the lamivudine and adefovir AUCtau values. Moreover, the combination regimens studied were well tolerated in all subjects. The results from these studies provide pharmacologic support for combination therapy or therapy switching involving telbivudine, lamivudine, and adefovir dipivoxil for the treatment of chronic hepatitis B virus infection.

Antiviral effect of Phyllanthus nanus ethanolic extract against hepatitis B virus (HBV) by expression microarray analysis

Ethanolic extract of Phyllanthus nanus (P. nanus) treatment exhibited potent antiviral activity against Hepatitis B virus (HBV). The effects of these extracts on HBV in the HBV genome integrated cell lines--Alexander cells and HepG2 2.2.15 cells were examined. Experimental results showed that the ethanolic extract of P. nanus produced suppressive effect on HBsAg secretion and HBsAg mRNA expression. The extract also inhibited HBV replication as measured by HBV DNA level in vitro. In addition, using a duck HBV (DHBV) primary culture model, the P. nanus ethanolic extract suppressed viral replication of DHBV in DHBV infected primary duck hepatocytes. The gene expression pattern in Alexander cells that had been treated with the ethanolic extract of P. nanus was also revealed by microarray techniques. The microarray results indicated that there was up-regulation of expression of several genes, including annexin A7 (Axn7). The subcellular localization of Axn7 and anti-HBV effect of Axn7 over-expression in Alexander cells were also investigated. Results showed that expression of Axn7-GFP fusion protein are localized around the secretory vesicles and could cause a decrease in HBsAg secretion in Alexander cells. Axn7 protein might play an important role in the medicinal effect of the active principle(s) of P. nanus.

Modeling infection with hepatitis B viruses in vivo

Hepatitis B virus (HBV) is a human-specific liver pathogen whose viral cycle and mechanisms of pathogenesis are not yet fully understood. Along with invaluable infection studies in chimpanzees, avian and mammalian HBV-related viruses continue to offer ample opportunities for studies in their natural hosts. Yet, none of these hosts are commonly used laboratory animals; the lack of reliable in vitro infection systems and convenient animal models has severely hampered progress in HBV research. The need to perform studies in HBV-permissive hepatocytes has led researchers to create new, challenging human–mouse chimera infection models. The types of animal models currently available to perform infection studies with HBV are presented and discussed in this review.

Inhibition of hepatitis B virus DNA replicative intermediate forms by recombinant interferon-gamma

AIM

To evaluate the in vitro anti-HBV activity of recombinant human IFN-gamma, alone and in combination with lamivudine.

METHODS

A recombinant baculovirus-HBV/HepG2 culture system was developed which could support productive HBV infection in vitro. Expression of HBsAg and HBeAg in infected HepG2 culture medium was detected by commercial enzyme immunoassays. HBV DNA replication intermediates were detected in infected cells by Southern hybridization and viral DNA load was determined by dot hybridization.

RESULTS

IFN-gamma at 0.1 to 5 microg/L efficiently down regulated HBsAg expression in transduced HepG2 cells. At 5 microg/L, IFN-gamma also suppressed HBV DNA replication in these cells. While treatment with a combination of lamivudine and IFN-gamma showed no additive effect, sequential treatment first with lamivudine and then IFN-gamma was found to be promising. In this culture system the best HBV suppression was observed with a pulse of 2 micromol/L lamivudine for two days, followed by 1 microg/L IFN-gamma for another four days. Compared to treatment with lamivudine alone, the sequential use of 0.2 micromol/L lamivudine for two days, followed by 5 microg/L IFN-gamma for six days showed a 72% reduction in HBV cccDNA pool.

CONCLUSION

This in vitro study warrants further evaluation of a combination of IFN-gamma and lamivudine, especially in IFN-alpha non-responder chronic hepatitis B patients. A reduced duration of lamivudine treatment would also restrict the emergence of drug-resistant HBV mutants.

Hepatitis B virus drug resistance: mechanism and clinical implications for the prevention of treatment failure

Hepatitis B virus (HBV) infection remains a major public health problem worldwide. Recently, the research efforts to identify new inhibitors enabled the development of antiviral agents to treat patients chronically infected by HBV. In clinical practice, the use of nucleoside analogs, which inhibit viral polymerase activity, induces suppression of viral replication accompanied by an improvement in biochemical and histological conditions in most patients. However, many clinical studies revealed the emergence of drug-resistant mutants during extended treatment. This review focuses on the mechanism of HBV drug-resistant mutant selection and on the clinical implications of HBV drug resistance for the prevention of treatment failure.

Antisense oligonucleotides targeted against asialoglycoprotein receptor 1 block human hepatitis B virus replication

Chronic hepatitis B virus (HBV) infection is a major worldwide public health problem. Better therapeutics and treatment strategies are urgently needed because of ineffective clinical treatment. Our previous study showed that asialoglycoprotein receptor 1 (ASGPR1) was upregulated by HBV but downregulated by lamivudine in HepG2.2.15 cells. It has also been reported that ASGPR is a candidate receptor for HBV attachment to hepatocytes. Therefore, as a major subunit of ASGPR, ASGPR1, might be a potential target for anti-HBV drugs. To validate this hypothesis, antisense oligonucleiotides (ASODNs) were used to downregulate ASGPR1 level in HepG2.2.15 cells. By using the MFOLD web server and BLAST searches, five ASODNs theoretically targeting ASGPR1 were selected. After 72 h post-transfection, HBV-DNA level in cell medium were examined by real-time polymerase chain reaction (PCR). Hepatitis B surface antigen (HBsAg) and Hepatitis B e antigen (HBeAg) were detected using enzyme-linked immunosorbent assay (ELISA). ASGPR1 mRNA and protein level were measured by semi-quantitative reverse transcriptase (RT)-PCR and Western blot analysis respectively. The results showed that ASODN2 significantly downregulated ASGPR1 level. It also reduced HBV-DNA, HBsAg and HBeAg level in cell medium as observed with lamivudine. In contrast, the sense sequence and scrambled sequence of ASODN2 had no effect on ASGPR1 and HBV markers in HepG2.2.15 cells. This indicated that ASODN2 could specifically reduce HBV replication in vitro. Additionally, cell proliferation and apoptosis assay suggested that downregulation of ASGPR1 did not affect cell viability. We, therefore, proposed that ASODNs targeted against ASGPR1 could block HBV replication without the influence of other changes, and ASGPR1 could be targeted for anti-HBV drug development.

Animal models for the study of HBV replication and its variants

Enormous progresses in hepatitis B virus research have been made through the identification of avian and mammalian HBV related viruses, which offer ample opportunities for studies in naturally occurring hosts. However, none of these natural hosts belongs to the commonly used laboratory animals, and the development of various mouse strains carrying HBV transgenes offered unique opportunities to investigate some mechanisms of viral pathogenesis. Furthermore, the need to perform infection studies in a system harbouring HBV-permissive hepatocytes has lately led researchers to create new challenging human mouse chimera models of HBV infection. In this review, we will overview the type of animal models currently available in hepadnavirus research.

Clevudine for the treatment of chronic hepatitis B virus infection

Chronic hepatitis B virus (HBV) infection is a major health problem that is responsible for < or = 1 million deaths and 500,000 cases of hepatocellular carcinoma worldwide each year. Drugs that are currently approved by the FDA for the treatment of chronic HBV consist of two groups: the immunomodulators, such as conventional IFN-alpha and pegylated IFN-alpha2a; and nucleoside/nucleotide analogues, such as lamivudine, adefovir dipivoxil and entecavir. However, due to the limitations of these agents, newer agents with improved efficacy are currently being developed. One nucleoside/nucleotide analogue that is drawing a wide range of interest is clevudine, which is an analogue of the unnatural beta-L configuration. In the woodchuck hepatitis virus (WHV), clevudine 10 mg/kg has proven to be effective in suppressing viral replication with < or = 9 log10 decreases in WHV. At this dose, a significant reduction of intrahepatic WHV RNA and covalently closed circular WHV DNA levels can also be observed. Treatment with clevudine 10 mg/kg can confer additional antiviral benefit in the form of a more sustained reduction in WHV replication, serum woodchuck hepatitis surface antigen and intrahepatic woodchuck hepatitis core antigen expression following the withdrawal of clevudine. In humans, clevudine 10, 50, 100 or 200 mg/day for 28 days can reduce the median HBV DNA by -2.5, -2.7, -3 and -2.6 log10, respectively. More importantly, this suppression of antiviral activity is maintained at 12 and 24 weeks post treatment. Based on the early results of clevudine, more large-scale human studies with clevudine monotherapy or combination therapy is eagerly awaited.

Viral kinetics in patients with lamivudine-resistant hepatitis B during adefovir-lamivudine combination therapy

BACKGROUND/AIMS

Mathematical analysis of viral kinetics during lamivudine-adefovir combination therapy has not yet been performed in patients with lamivudine-resistant hepatitis B.

METHODS

In 8 patients with lamivudine-resistant hepatitis B, adefovir dipivoxil (10 mg/day) was added to ongoing lamivudine. Viral decay during the first 8 weeks of combination therapy was described by a biphasic model to determine the efficacy: epsilon, of blocking viral production, the clearance: c, of free virus, and the loss of infected cells: delta.

RESULTS

Median epsilon was 98%, median c was 0.7/day, and median delta was 0.07/day. No significant association was found between viral kinetic and baseline parameters and virologic and biochemical treatment response. When compared with viral kinetic constants reported for higher dose adefovir dipivoxil monotherapy, epsilon was lower (P=0.026) and delta was higher (P=0.008) in this study whereas c did not differ between both studies.

CONCLUSIONS

Although a recent study did not show any differences in the reduction of HBV DNA comparing monotherapy with adefovir dipivoxil to adefovir-lamivudine combination therapy in patients with lamivudine-resistant chronic hepatitis B, mathematical analysis of early viral kinetics suggests an additional effect of lamivudine on the infected cell loss during adefovir-lamivudine combination therapy.

Combination of nucleoside analogues in the treatment of chronic hepatitis B virus infection: lesson from experimental models

Owing to the persistence of hepatitis B virus (HBV) and the selection of drug-resistant mutants, a new concept of antiviral therapy for chronic hepatitis B relies on the combination of nucleoside analogues. In experimental models of HBV infection, several key points concerning these combinations were addressed. (i) Is it possible to achieve a synergic antiviral effect with polymerase inhibitors? (ii) Is it possible to impact on intracellular viral covalently closed circular DNA? (iii) What is the impact of the cross-resistance patterns of the different nucleoside analogues? (iv) What is the effect of viral load suppression on the restoration of specific antiviral cellular responses? The clinical impact of these key issues is discussed in the perspective of new clinical trials.

Review article: Nucleoside analogues for the treatment of chronic hepatitis B

Current accepted treatment for chronic hepatitis B uses either the immunomodulator interferon alpha or nucleoside analogues lamivudine or adefovir. Interferon has side effects which mean it is often poorly tolerated. Long-term use of lamivudine is associated with increasing viral resistance for each year it is taken and the rebound viraemia that can occur when the drug is stopped is also of concern to many. Adefovir appears to have less of the resistance issues of lamivudine but is still a relatively new drug and at present its use is principally limited to patients with lamivudine-resistant disease. A number of other nucleoside analogues are currently being developed with some now at the stage of early clinical trials. A proportion share the significant resistance problems of lamivudine but many appear to have more potent anti-viral effect than the drugs currently available. If some of these newer anti-viral agents are approved for use in chronic hepatitis B, the potential for prolonged suppression of hepatitis B virus replication with resultant stabilization or improvement in liver disease may be achieved.

Intramolecular stacking interactions in ternary copper(II) complexes formed by a heteroaromatic amine and 9-[2-(2-phosphonoethoxy)ethyl]adenine, a relative of the antiviral nucleotide analogue 9-[2-(phosphonomethoxy)ethyl]adenine☆

The stability constants of the mixed-ligand complexes formed between Cu(Arm)2+, where Arm=2,2'-bipyridine (Bpy) or 1,10-phenanthroline (Phen), and the dianions of 9-[2-(2-phosphonoethoxy)ethyl]adenine (PEEA2-) and (2-phosphonoethoxy)ethane (PEE2-), also known as [2-(2-ethoxy)ethyl]phosphonate, were determined by potentiometric pH titrations in aqueous solution (25 degrees C; I=0.1 M, NaNO3). The ternary Cu(Arm)(PEEA) complexes are considerably more stable than the corresponding Cu(Arm)(R-PO3) species, where R-PO3(2-) represents a phosph(on)ate ligand with a group R that is unable to participate in any kind of interaction within the complexes. The increased stability is attributed to intramolecular stack formation in the Cu(Arm)(PEEA) complexes and also, to a smaller extent, to the formation of 6-membered chelates involving the ether oxygen atom present in the -CH2-O-CH2-CH2-PO3(2-) residue of PEEA2-. This latter interaction is separately quantified by studying the ternary Cu(Arm)(PEE) complexes which can form the 6-membered chelates but where no intramolecular ligand-ligand stacking is possible. Application of these results allows a quantitative analysis of the intramolecular equilibria involving three structurally different Cu(Arm)(PEEA) species; e.g., of the Cu(Bpy)(PEEA) system about 11% exist with the metal ion solely coordinated to the phosphonate group, 4% as a 6-membered chelate involving the ether oxygen atom of the -CH2-O-CH2CH2-PO3(2-) residue, and 85% with an intramolecular stack between the adenine moiety of PEEA2- and the aromatic rings of Bpy. In addition, the Cu(Arm)(PEEA) complexes may be protonated, leading to Cu(Arm)(H;PEEA)+ species for which it is concluded that the proton is located at the phosphonate group and that the complexes are mainly formed (50 and 70%) by a stacking adduct between Cu(Arm)2+ and the adenine residue of H(PEEA)-. Finally, the stacking properties of adenosine 5'-monophosphate (AMP2-), of the dianion of 9-[2-(phophonomethoxy)ethyl]adenine (PMEA2-) and of several of its analogues (=PA2-) are compared in their ternary Cu(Arm)(AMP) and Cu(Arm)(PA) systems. Conclusions regarding the antiviral properties of several acyclic nucleoside phosphonates are shortly discussed.

Combinations of adefovir with nucleoside analogs produce additive antiviral effects against hepatitis B virus in vitro

Combination therapies may be required for long-term management of some patients chronically infected with hepatitis B virus (HBV). Adefovir is a nucleotide analog that has similar activity against wild-type and lamivudine-resistant HBV. In contrast to lamivudine, clinical resistance to the prodrug adefovir dipivoxil emerges infrequently. Based on its clinical efficacy and low frequency of resistance, adefovir dipivoxil may form an important component of combination regimens. We therefore investigated the in vitro antiviral efficacy of combinations of adefovir with other nucleoside analogs (lamivudine, entecavir, emtricitabine [FTC],and telbivudine [L-dT]) and the nucleotide analog tenofovir. Using a novel stable cell line that expresses high levels of wild-type HBV, we assayed the antiviral activity of each drug alone and in combination with adefovir. All two-drug combinations resulted in greater antiviral effects than treatments with single agents and could be characterized as additive by the Bliss independence model. Analysis using the Loewe additivity model indicated that adefovir exerted additive antiviral effects when combined with lamivudine, FTC, or L-dT and moderately synergistic effects when combined with entecavir or tenofovir. There was no evidence of cytotoxicity with any of the drugs when used alone or in combination at the tested doses.

Renal excretion mechanisms of the antiviral nucleoside analogue AM 188 IN the rat isolated perfused kidney

1. AM 188 is an antiviral guanosine analogue that undergoes extensive renal excretion in humans. The present study was designed to investigate the disposition of AM 188 over a range of concentrations in the rat isolated perfused kidney (IPK) to explore the mechanisms involved in its renal handling. 2. Right kidneys of male Sprague-Dawley rats (n = 23) were isolated and perfused in recirculating mode with Krebs'-Henseleit (pH 7.4) buffer containing 0.65% bovine serum albumin, 3.6% dextran, amino acids and glucose. [14C]-Inulin was added to the perfusate reservoir to permit estimation of glomerular filtration rate (GFR). [3H]-AM 188 and unlabelled AM 188 were added to the perfusate as a bolus initially, followed by a constant rate of infusion at 5, 25, 125, 500 or 1000 microg/min to achieve initial target perfusate concentrations of 1, 5, 25, 100 or 200 microg/mL, respectively. During the 130 min over which AM 188 was infused, urine was collected in 10 min intervals (commencing 10 min after the bolus dose) and perfusate was collected at the mid-point of these intervals to permit calculation of the renal clearance (CLR) of AM 188. Binding of AM 188 in perfusate, measured using ultrafiltration, was negligible. 3. The bolus dose and infusion regimen produced relatively stable AM 188 concentrations in perfusate in the 5, 25 and 125 micro g/min groups and progressively increasing concentrations in the 500 and 1000 microg/min groups. High-pressure liquid chromatography analysis of IPK perfusate and urine suggested that there was no or negligible metabolism of AM 188 in the kidney. The CLR/GFR ratio for AM 188 (mean+/-SD) was 5.76 +/- 1.57, 5.99 +/- 0.52, 6.02 +/- 1.47, 3.38 +/- 0.26 and 1.08 +/- 0.42 in the 5, 25, 125, 500 and 1000 microg/min groups, respectively, showing significant reductions at the two highest infusion rates (P < 0.05). Although there was no difference between the five groups in the distribution of AM 188 between kidney tissue and perfusate (KT/P), at the end of perfusion the corresponding urine-to-tissue concentration ratio declined significantly in the 1000 microg/min group. 4. AM 188 undergoes substantial net renal secretion over a wide range of perfusate concentrations. A reduction in renal clearance at perfusate concentrations above 25 microg/mL could be due to saturation of carrier-mediated transport at the brush border membrane and/or a solubility limitation leading to precipitation of AM 188 in tubular cells and/or tubular urine.

Selection of a hepatitis B virus strain resistant to adefovir in a liver transplantation patient

BACKGROUND/AIMS

In contrast to lamivudine, adefovir dipivoxil (ADV) therapy is associated with delayed and infrequent selection of drug resistant hepatitis B virus (HBV).

METHODS

A 52 year-old man was treated with lamivudine for an HBV recurrence on his liver graft. A viral breakthrough was observed and the patient received ADV. Serum HBV DNA decreased rapidly and lamivudine was discontinued while ADV monotherapy was maintained. Serum HBV DNA levels remained suppressed until a second breakthrough was observed. Lamivudine was then reintroduced together with ADV, and serum HBV DNA became undetectable by polymerase chain reaction.

RESULTS

Sequence analyses of the HBV polymerase gene revealed a sequential selection of lamivudine resistance mutations L180M+M204V, followed by a reversion to wild-type, and subsequently the selection of a novel adefovir resistance mutation N236T. Phenotypic analyses in cell culture assays demonstrated that the HBV isolates at the time of ADV breakthrough had reduced susceptibility to ADV. This mutant remained sensitive to lamivudine, entecavir and emtricitabine in vitro.

CONCLUSIONS

We describe the first case of sequential selection of lamivudine and adefovir resistant strains of HBV in a liver transplantation patient. The selection of the N236T polymerase mutant was associated with resistance to ADV but remained sensitive to lamivudine in vitro and in vivo.

Resistance to adefovir dipivoxil therapy associated with the selection of a novel mutation in the HBV polymerase

BACKGROUND & AIMS

Adefovir dipivoxil effectively inhibits both hepatitis B virus (HBV) replication and disease activity in patients with chronic hepatitis B. Resistance to treatment was not observed in 2 recent large placebo-controlled 48-week studies with this drug. The aim of this study was to characterize adefovir resistance in a patient who developed clinical and virologic evidence of breakthrough during a 96-week course of treatment.

METHODS

HBV DNA was PCR amplified and sequenced. Phenotypic studies used patient-derived HBV as well as specific mutations created by site-directed mutagenesis of a HBV/baculovirus recombinant.

RESULTS

Following the commencement of treatment with adefovir dipivoxil, the patient initially responded with a 2.4 log(10) decrease in serum HBV DNA and normalization of alanine aminotransaminase levels by week 16. During the second year of treatment, however, serum HBV DNA rose progressively, eventually returning to near-pretreatment levels. This increase in viral replication was associated with a marked increase in alanine aminotransferase and mild changes in bilirubin, albumin, and prothrombin time. Comparison of pretreatment and posttreatment HBV DNA by polymerase chain reaction sequencing identified a novel asparagine to threonine mutation at residue rt236 in domain D of the HBV polymerase. In vitro testing of a laboratory strain encoding the rtN236T mutation and testing of patient-derived virus confirmed that the rtN236T substitution caused a marked reduction in susceptibility to adefovir.

CONCLUSIONS

The development of this novel mutation in the HBV polymerase confers resistance to adefovir dipivoxil. The patient responded to subsequent lamivudine therapy, achieving normalization of alanine aminotransferase and a significant decrease in serum HBV DNA.

Hepatitis B virus-induced defect of monocyte-derived dendritic cells leads to impaired T helper type 1 response in vitro: mechanisms for viral immune escape

Dendritic cells (DC) are the most potent antigen-presenting cells and play a central role in the induction of antiviral immune responses. Recently, we have shown that monocyte-derived DC (MoDC) from patients with chronic hepatitis B virus (HBV) infection are functionally impaired. In our present study MoDC from healthy subjects were propagated in vitro and inoculated with HBV particles to investigate the precise mechanisms that underly MoDC dysfunction. T-cell proliferation assays revealed an impaired allostimulatory capacity of HBV-inoculated MoDC (HBV-MoDC) as well as a lower potential of stimulating autologous T cells against a recall antigen in comparison to control-MoDC. Interleukin-2, tumour necrosis factor-alpha and interferon-gamma production by T cells in proliferation assays with HBV-MoDC was significantly lower than with control-MoDC and correlated with lower IL-12 production in HBV-MoDC cultures. The presence of the nucleoside analogue lamivudine (3TC), an inhibitor of HBV replication, restored impaired allostimulatory function of HBV-MoDC and up-regulated major histocompatibility complex class II expression. These results show that HBV infection compromises the antigen-presenting function of MoDC with concomitant impairment of T helper cell type 1 responses. This may play an important role for viral immune escape leading to chronic HBV infection. However, 3TC treatment can overcome HBV-MoDC-related T-cell hyporeactivity and this underscores its important role in enhanced immune responses to HBV.

Inhibition of hepatitis B virus replication in vivo by nucleoside analogues and siRNA

BACKGROUND & AIMS

Hepatitis B virus (HBV) causes acute and chronic infections that may result in severe liver diseases. Animal models to study new treatment options in vivo have several drawbacks. Therefore, we were interested to establish a new small animal model in which HBV replication and especially new treatment options can be studied easily.

METHODS

Naked DNA of an HBV replication competent vector was transferred via tail vein into NMRI mice. HBV replication was studied in serum and liver of the animals. HBV replication was modulated by treatment through siRNA and nucleoside analogues.

RESULTS

Tail vein transfer of a HBV replication competent construct resulted in expression of HBV-specific transcripts in the liver, and up to 10% of hepatocytes became HBc- and HBsAg-positive. HBeAg, HBsAg, and viral DNA could be detected in the serum of the animals, followed by the induction of HBV-specific cellular immune responses. Nucleoside treatment of the mice resulted in reduced polymerase activity in the liver. Additionally, siRNA transfer in the animals led to a significant reduction of HBsAg and/or eventually HBeAg expression, which was dependent on the localization of the complementary sequence in the HBV genome.

CONCLUSIONS

We have established a mouse model to study HBV replication and to investigate new and existing treatment approaches in vivo. Interestingly, siRNA seems a promising innovative treatment option to inhibit specifically HBV replication in vivo.

Treatment of chronic hepatitis B: current challenges and future directions

The clinical management of chronic hepatitis B infection has entered a new era with the introduction and widespread use of oral nucleoside analogues such as lamivudine and nucleotides such as adefovir dipivoxil. From this, new challenges have now emerged in terms of preventing antiviral drug resistance, promoting viral clearance and improving long-term survival. For example, the natural history of nucleoside or nucleotide analogue-associated hepatitis B virus resistant mutants has yet to be determined. Furthermore, the increasing prevalence of HBeAg negative disease with its reduced response to current therapies represents an ongoing challenge to attempts to improve standard of care. There is increasing recognition of the pivotal role that viral load and genotype, and their complex interactions with the host immune response, play in determining the outcome of these treatment interventions. The purpose of this paper is to highlight several key factors that should be considered in the context of future clinical research and management of chronic hepatitis B.

Effects of pyrimidine and purine analog combinations in the duck hepatitis B virus infection model

To design new strategies of antiviral therapy for chronic hepatitis B, we have evaluated the antiviral activity of the combination of amdoxovir (DAPD), emtricitabine [(-)FTC], and clevudine (L-FMAU) in the duck hepatitis B virus (DHBV) model. Using their triphosphate (TP) derivatives in a cell-free system expressing a wild-type active DHBV reverse transcriptase (RT), the three dual combinations exhibited a greater additive inhibitory effect on viral minus-strand DNA synthesis than the single drugs, according to the Bliss independence model. Both dual combinations with DAPD TP were the most efficient while the triple combination increased the inhibitory effect on the DHBV RT activity in comparison with the dual association, however, without additive effect. Postinoculation treatment of experimentally infected primary duck hepatocytes showed that dual and triple combinations potently inhibited viral DNA synthesis during treatment but did not inhibit the reinitiation of viral DNA synthesis after treatment cessation. Preinoculation treatment with the same combinations exhibited antiviral effects on intracellular viral DNA replication, but it was unable to prevent the initial covalently closed circular DNA (cccDNA) formation. Short-term in vivo treatment in acutely infected ducklings showed that the dual combinations were more-potent inhibitors of virus production than the single treatments, with the L-FMAU and FTC combination being the most potent. A longer administration of L-FMAU and FTC for 4 weeks efficiently suppressed viremia and viral replication. However, no viral clearance from the liver was observed, suggesting that the enhanced antiviral effect of this combination was not sufficient for cccDNA suppression and HBV eradication from infected cells.

Synthesis and acid-base properties of (1H-benzimidazol-2-yl-methyl)phosphonate (Bimp2-). Evidence for intramolecular hydrogen-bond formation in aqueous solution between (N-1)H and the phosphonate group

The synthesis of (1H-benzimidazol-2-yl-methyl)phosphonic acid, H2(Bimp)+/-, is described: 2-chloromethylbenzimidazole was reacted with ethylchloroformate to give 1-carboethoxy-2-chloromethylbenzimidazole which was treated with trimethyl phosphite and after hydrolysis with aqueous HBr H2(Bimp)+/- was obtained. In H2(Bimp)+/- one proton is at the N-3 site and the other at the phosphonate group; both acidity constants were determined in aqueous solution by potentiometric pH titrations (25 degrees C; I = 0.1 M, NaNO3) and this furnished the pKa values of 5.37 +/- 0.02 and 7.41 +/- 0.02, respectively. The acidity constant for the release of the primary proton from the P(O)(OH)2 group of H3(Bimp)+ was estimated: pKa = 1.5 +/- 0.2. Moreover, Bimp2- can be further deprotonated at its neutral (N-1/N-3)H site to give the benzimidazolate residue, but this reaction occurs only in strongly alkaline solution (KOH); application of the H_ scale developed by G. Yagil (J. Phys. Chem., 1967, 71, 1034) together with UV spectrophotometric measurements gave pKa = 14.65 +/- 0.12. Comparisons with acidity constants taken from the literature show that this latter pKa value is far too large and this allows the conclusion that an intramolecular hydrogen bond is formed between the (N-1/N-3)H site and the phosphonate group of Bimp2-; the formation degree of this hydrogen-bonded isomer is estimated to be 98 +/- 2%. The general relevance of this and the other results are shortly discussed and the species distribution for the Bimp system in dependence on pH is provided.

Adefovir Dipivoxil

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Effect of the G1896A precore mutation on drug sensitivity and replication yield of lamivudine-resistant HBV in vitro

Hepatitis B e antigen (HBeAg) negative chronic hepatitis B (CHB) is frequently caused by a mutation (G1896A) in the hepatitis B virus (HBV) precore (PC) reading frame that creates a stop codon, causing premature termination of the PC protein. During lamivudine treatment, drug resistance develops at a similar rate in HBeAg positive and HBeAg negative CHB. Lamivudine-resistant HBV mutants have been shown to replicate inefficiently in vitro in the absence of PC mutations, but it is unknown whether the presence of PC mutations affects replication efficiency or antiviral sensitivity. This study utilized the recombinant HBV baculovirus system to address these issues. HBV baculoviruses encoding the G1896A PC stop codon mutation were generated in wild-type (WT) and lamivudine-resistant (rtM204I and rtL180M + rtM204V) backgrounds, resulting in a panel of 6 related recombinant baculoviruses. In vitro assays were performed to compare the sensitivities of the PC mutant viruses with lamivudine and adefovir and to compare relative replication yields. The PC mutation did not significantly affect sensitivities to either adefovir or lamivudine. WT HBV and PC mutant HBV showed similar replication yields, whereas the replication yields of the lamivudine-resistant mutants were greatly reduced in HBeAg positive HBVs, confirming previous observations. However, the presence of the PC mutation was found to compensate for the replication deficiency in each of the lamivudine-resistant mutants, increasing the replication yields of each virus. In conclusion, the PC stop codon mutation appears to increase the replication efficacy of lamivudine-resistant virus but does not affect in vitro drug sensitivity.

Phenylpropenamide derivatives AT-61 and AT-130 inhibit replication of wild-type and lamivudine-resistant strains of hepatitis B virus in vitro

The phenylpropenamide derivatives AT-61 and AT-130 are nonnucleoside analogue inhibitors of hepatitis B virus (HBV) replication. They inhibited the replication of wild-type HBV with 50% inhibitory concentrations of 21.2 +/- 9.5 and 2.40 +/- 0.92 micro M, respectively, compared to 0.064 +/- 0.020 micro M lamivudine. There were no significant differences in sensitivity between wild-type and nucleoside analogue-resistant (rtL180M, rtM204I, and rtL180M + rtM204V) HBV.

Inhibitory activity of dioxolane purine analogs on wild-type and lamivudine-resistant mutants of hepadnaviruses

To design combination strategies for chronic hepatitis B therapy, we evaluated in vitro the inhibitory activity of 4 nucleoside analogs, (-)FTC, L-FMAU, DXG, and DAPD, in comparison with lamivudine (3TC) and PMEA. In a cell-free assay for the expression of wild-type duck hepatitis B virus (DHBV) reverse transcriptase, DAPD-TP was found to be the most active on viral minus strand DNA synthesis, including the priming reaction, followed by 3TC-TP, (-)FTC-TP, and DXG-TP, whereas L-FMAU-TP was a weak inhibitor. In cell culture experiments, important differences in drug concentration allowing a 50% inhibition of viral replication or polymerase activity (IC50s) were observed depending on the cell type used, showing that antiviral effect of nucleoside analogs may depend on their intracellular metabolism. IC50s obtained for wild-type DHBV replication in primary duck hepatocytes were much lower than with DHBV transfected LMH cells. IC50s were also significantly lower in the 2.2.1.5 and HepG2 cells compared with HBV transfected HuH7 cells. Moreover, L-FMAU inhibited preferentially HBV plus strand DNA synthesis in these cell lines. The antiviral effect of these inhibitors was also evaluated against 3TC-resistant mutants of the DHBV and HBV polymerases. These mutants were found to be cross resistant to (-)FTC. By contrast, the double DHBV polymerase mutant was sensitive to DXG-TP and DAPD-TP. Moreover, both purine analogs remained active against DHBV and HBV 3TC-resistant mutants in transfected LMH and HepG2 cells, respectively. In conclusion, the unique mechanism of action of these new inhibitors warrants further evaluation in experimental models to determine their capacity to delay or prevent the selection of drug resistant mutants.

Viral dynamics in chronic hepatitis B patients treated with lamivudine, lamivudine-famciclovir or lamivudine-ganciclovir

BACKGROUND

Prolonged nucleoside analogue therapy has been shown to reduce viral replication and normalize serum transaminases in the majority of chronic hepatitis B patients. However, from a theoretical point of view, monotherapy with lamivudine (a cytosine nucleoside analogue) will probably not result in eradication of hepatitis B virus. A prolonged course of lamivudine therapy would be needed to clear the virus from the liver. The occurrence of mutations, in combination with continuing low-grade viral replication in a number of patients, will prevent elimination of the virus from the liver. However, combination therapy with more than one nucleoside analogue could possibly overcome the disadvantages of monotherapy.

PATIENTS AND METHODS

In this study, we report on 12 patients who were evaluated by means of a mathematical model during lamivudine monotherapy and lamivudine-famciclovir and lamivudine-ganciclovir therapy.

RESULTS

There was no difference in the parameters representing blocking of viral production (epsilon = 93%, 95% and 86%, respectively), turnover of free virus (half-life of 16 h, 10 h and 12 h, respectively) and turnover of infected hepatocytes (half-life of 9 days, 7 days and 4 days, respectively) between the lamivudine, lamivudine-famciclovir and lamivudine-ganciclovir treatment groups.

CONCLUSIONS

Although our study group is small, we do not think the drug combinations used offer a major advantage over lamivudine monotherapy. Different combinations of nucleoside analogues need to be studied in order to obtain a major breakthrough in this treatment strategy.