Antiviral effect of oral administration of tenofovir disoproxil fumarate in woodchucks with chronic woodchuck hepatitis virus infection

Discovery of orally bioavailable phosphonate prodrugs of potent ENPP1 inhibitors for cancer treatment

Ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1) is the dominant hydrolase of 2',3'-cyclic GMP-AMP (cGAMP). Inhibition of ENPP1 contributes to increased cGAMP concentration and stimulator of interferon gene (STING) activation, with the potential to boost immune response against cancer. ENPP1 is a promising therapeutic target in tumor immunotherapy. To date, orally bioavailable ENPP1 inhibitors with highly potent activity under physiological conditions have been rarely reported. Herein, we report our effort in the design and synthesis of two different series of ENPP1 inhibitors, and in the identification of a highly potent ENPP1 inhibitor 27 (IC50 = 1.2 nM at pH 7.5), which significantly enhanced the cGAMP-mediated STING activity in THP-1 cells. Phosphonate compound 27 has good preclinical pharmacokinetic profiles with low plasma clearance rate in mouse, rat, and dog. It has been developed as bis-POM prodrug 36 which successfully improves the oral bioavailability of 27. In the Pan02 syngeneic mouse model of pancreatic cancer, orally administered 36 showed synergistic effect in combination with radiotherapy.

Clinical Conundrum of Acute Hepatitis B With Concurrent Hepatitis E Infection Leading to Severe Acute Liver Injury

Acute liver injury in the setting of acute fulminant hepatitis caused by the hepatitis B virus (HBV) can occur both during primary infection and after chronic HBV reactivation. Guidelines recommend considering antiviral therapy in both cases. Antiviral therapy with a nucleoside analog may be beneficial in patients with acute liver failure from acute HBV infection, though not all studies have shown a benefit. This is a case of a 53-year-old woman with a past medical history of untreated hepatitis C with undetectable viral load and right breast cancer status post lumpectomy, who presented to the emergency department with complaints of yellowish skin and sclera discoloration with right upper quadrant pain for one week. She was a known intravenous drug abuser and binge alcohol user. Her labs were positive for hepatitis B, hepatitis E, and hepatitis C viruses. She also had elevated liver enzymes with hyperbilirubinemia showing severe acute liver injury. Computed tomography of the abdomen and pelvis with contrast was normal, and the abdominal ultrasound showed homogenous echotexture of the liver without a focal lesion. The patient was diagnosed with acute fulminant hepatitis B. After initial hemodynamic stabilization, N-acetylcysteine (NAC) and tenofovir were started, and transaminases were followed. Liver function tests showed a downtrend, and, in a few weeks, they came to baseline. Hepatitis B viral load became undetectable as well. Acute hepatitis B infection is seldom treated. The presented case depicts the use of tenofovir in the setting of severe acute liver injury due to hepatitis B. Starting antiviral therapy (especially tenofovir disoproxil fumarate) early in the disease course was shown to have very assuring results with complete resolution of symptoms and normalization of liver function tests. The treatment protocol for acute HBV deserves further investigation.

Disease Animal Models for Cancer Research

Despite nonanimal methods (NAMs) are more and more exploited and new NAMs are developed and validated, animal models are still used in cancer research. Animals are used at multiple levels, from understanding molecular traits and pathways, to mimicking clinical aspects of tumor progression, to drug testing. In vivo approaches are not trivial and involve cross-disciplinary knowledge: animal biology and physiology, genetics, pathology, and animal welfare.The aim of this chapter is not to list and address all animal models used in cancer research. Instead, the authors would like to guide experimenters in the strategies to adopt in both planning and performing in vivo experimental procedures, including the choice of cancer animal models.

Combination Treatment with the Vimentin-Targeting Antibody hzVSF and Tenofovir Suppresses Woodchuck Hepatitis Virus Infection in Woodchucks

Current treatment options for patients infected with hepatitis B virus (HBV) are suboptimal, because the approved drugs rarely induce cure due to the persistence of the viral DNA genome in the nucleus of infected hepatocytes, and are associated with either severe side effects (pegylated interferon-alpha) or require life-long administration (nucleos(t)ide analogs). We report here the evaluation of the safety and therapeutic efficacy of a novel, humanized antibody (hzVSF) in the woodchuck model of HBV infection. hzVSF has been shown to act as a viral entry inhibitor, most likely by suppressing vimentin-mediated endocytosis of virions. Targeting the increased vimentin expression on liver cells by hzVSF after infection with HBV or woodchuck hepatitis virus (WHV) was demonstrated initially. Thereafter, hzVSF safety was assessed in eight woodchucks naïve for WHV infection. Antiviral efficacy of hzVSF was evaluated subsequently in 24 chronic WHV carrier woodchucks by monotreatment with three ascending doses and in combination with tenofovir alafenamide fumarate (TAF). Consistent with the proposed blocking of WHV reinfection, intravenous hzVSF administration for 12 weeks resulted in a modest but transient reduction of viral replication and associated liver inflammation. In combination with oral TAF dosing, the antiviral effect of hzVSF was enhanced and sustained in half of the woodchucks with an antibody response to viral proteins. Thus, hzVSF safely but modestly alters chronic WHV infection in woodchucks; however, as a combination partner to TAF, its antiviral efficacy is markedly increased. The results of this preclinical study support future evaluation of this novel anti-HBV drug in patients.

Characterization of Seasonal Pharmacokinetic Variability in Woodchucks

The eastern woodchuck (Marmota monax) is a hibernating species extensively used as an in vivo efficacy model for chronic human hepatitis B virus infection. Under laboratory conditions, woodchucks develop a pseudohibernation condition; thus, the pharmacokinetics (PK) of small-molecule therapeutics may be affected by the seasonal change. The seasonal PK of four probe compounds were characterized over 12 months in seven male and nine female laboratory-maintained woodchucks. These compounds were selected to study changes in oxidative metabolism [antipyrine (AP)], glucuronidation [raltegravir (RTG)], renal clearance [lamivudine (3TC)], and hepatic function [indocyanine green (ICG)]. Seasonal changes in physiologic parameters and PK were determined. Seasonal body weight increases were ≥30%. Seasonal changes in body temperature and heart rate were <10%. The mean AP exposure remained unchanged from April to August 2017, followed by a significant increase (≥1.0-fold) from August to December and subsequent decrease to baseline at the end of study. A similar trend was observed in RTG and 3TC exposures. The ICG exposure remained unchanged. No significant sex difference in PK was observed, although female woodchucks appeared to be less susceptible to seasonal PK and body weight changes. Significant seasonal PK changes for AP, RTG, and 3TC indicate decreases in oxidative metabolism, phase II glucuronidation, and renal clearance during pseudohibernation. The lack of seasonal change in ICG exposure suggests there are no significant changes in hepatic function. This information can be used to optimize the scheduling of woodchuck studies to avoid seasonally driven variation in drug PK. SIGNIFICANCE STATEMENT: Woodchuck is a hibernating species and is commonly used as a nonclinical model of hepatitis B infection. Investigation of seasonal PK changes is perhaps of greater interest to pharmaceutical industry scientists, who use the woodchuck model to optimize the scheduling of woodchuck studies to avoid seasonally driven variation in drug PK and/or toxicity. This information is also valuable to drug metabolism and veterinary scientists in understanding woodchuck's seasonal metabolism and behavior under the pseudohibernation condition.

Nanoparticle Uptake in a Spontaneous and Immunocompetent Woodchuck Liver Cancer Model

There is a tremendous focus on the application of nanomaterials for the treatment of cancer. Nonprimate models are conventionally used to assess the biomedical utility of nanomaterials. However, these animals often lack an intact immunological background, and the tumors in these animals do not develop spontaneously. We introduce a preclinical woodchuck hepatitis virus-induced liver cancer model as a platform for nanoparticle (NP)-based in vivo experiments. Liver cancer development in these out-bred animals occurs as a result of persistent viral infection, mimicking human hepatitis B virus-induced HCC development. We highlight how this model addresses key gaps associated with other commonly used tumor models. We employed this model to (1) track organ biodistribution of gold NPs after intravenous administration, (2) examine their subcellular localization in the liver, (3) determine clearance kinetics, and (4) characterize the identity of hepatic macrophages that take up NPs using RNA-sequencing (RNA-seq). We found that the liver and spleen were the primary sites of NP accumulation. Subcellular analyses revealed accumulation of NPs in the lysosomes of CD14⁺ cells. Through RNA-seq, we uncovered that immunosuppressive macrophages within the woodchuck liver are the major cell type that take up injected NPs. The woodchuck-HCC model has the potential to be an invaluable tool to examine NP-based immune modifiers that promote host anti-tumor immunity.

Nucleic acid polymer REP 2139 and nucleos(T)ide analogues act synergistically against chronic hepadnaviral infection in vivo in Pekin ducks

Nucleic acid polymer (NAP) REP 2139 treatment was shown to block the release of viral surface antigen in duck HBV (DHBV)-infected ducks and in patients with chronic HBV or HBV/hepatitis D virus infection. In this preclinical study, a combination therapy consisting of REP 2139 with tenofovir disoproxil fumarate (TDF) and entecavir (ETV) was evaluated in vivo in the chronic DHBV infection model. DHBV-infected duck groups were treated as follows: normal saline (control); REP 2139 TDF; REP 2139 + TDF; and REP 2139 + TDF + ETV. After 4 weeks of treatment, all animals were followed for 8 weeks. Serum DHBsAg and anti-DHBsAg antibodies were monitored by enzyme-linked immunosorbent assay and viremia by qPCR. Total viral DNA and covalently closed circular DNA (cccDNA) were quantified in autopsy liver samples by qPCR. Intrahepatic DHBsAg was assessed at the end of follow-up by immunohistochemistry. On-treatment reduction of serum DHBsAg and viremia was more rapid when REP 2139 was combined with TDF or TDF and ETV, and, in contrast to TDF monotherapy, no viral rebound was observed after treatment cessation. Importantly, combination therapy resulted in a significant decrease in intrahepatic viral DNA (>3 log) and cccDNA (>2 log), which were tightly correlated with the clearance of DHBsAg in the liver.

CONCLUSION

Synergistic antiviral effects were observed when REP 2139 was combined with TDF or TDF + ETV leading to control of infection in blood and liver, associated with intrahepatic viral surface antigen elimination that persisted after treatment withdrawal. Our findings suggest the potential of developing such combination therapy for treatment of chronically infected patients in the absence of pegylated interferon. (Hepatology 2018;67:2127-2140).

Safety and efficacy of anti-PD-L1 therapy in the woodchuck model of HBV infection

Immune clearance of Hepatitis B virus (HBV) is characterized by broad and robust antiviral T cell responses, while virus-specific T cells in chronic hepatitis B (CHB) are rare and exhibit immune exhaustion that includes programmed-death-1 (PD-1) expression on virus-specific T cells. Thus, an immunotherapy able to expand and activate virus-specific T cells may have therapeutic benefit for CHB patients. Like HBV-infected patients, woodchucks infected with woodchuck hepatitis virus (WHV) can have increased hepatic expression of PD-1-ligand-1 (PD-L1), increased PD-1 on CD8+ T cells, and a limited number of virus-specific T cells with substantial individual variation in these parameters. We used woodchucks infected with WHV to assess the safety and efficacy of anti-PD-L1 monoclonal antibody therapy (αPD-L1) in a variety of WHV infection states. Experimentally-infected animals lacked PD-1 or PD-L1 upregulation compared to uninfected controls, and accordingly, αPD-L1 treatment in lab-infected animals had limited antiviral effects. In contrast, animals with naturally acquired WHV infections displayed elevated PD-1 and PD-L1. In these same animals, combination therapy with αPD-L1 and entecavir (ETV) improved control of viremia and antigenemia compared to ETV treatment alone, but with efficacy restricted to a minority of animals. Pre-treatment WHV surface antigen (sAg) level was identified as a statistically significant predictor of treatment response, while PD-1 expression on peripheral CD8+ T cells, T cell production of interferon gamma (IFN-γ) upon in vitro antigen stimulation (WHV ELISPOT), and circulating levels of liver enzymes were not. To further assess the safety of this strategy, αPD-L1 was tested in acute WHV infection to model the risk of liver damage when the extent of hepatic infection and antiviral immune responses were expected to be the greatest. No significant increase in serum markers of hepatic injury was observed over those in infected, untreated control animals. These data support a positive benefit/risk assessment for blockade of the PD-1:PD-L1 pathway in CHB patients and may help to identify patient groups most likely to benefit from treatment. Furthermore, the efficacy of αPD-L1 in only a minority of animals, as observed here, suggests that additional agents may be needed to achieve a more robust and consistent response leading to full sAg loss and durable responses through anti-sAg antibody seroconversion.

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.

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.

Tenofovir disoproxil fumarate in the treatment of chronic hepatitis B

The specific drugs available for chronic hepatitis B infection include standard and pegylated IFN-α, and nucleoside/nucleotide analogs that directly inhibit the reverse transcriptase. The main goal of current hepatitis B virus therapy is to achieve sustained suppression of viral replication to prevent the development of chronic liver disease, but favorable long-term tolerability and resistance profiles are also desirable. This article reviews the chemistry and the mechanisms of action of tenofovir disoproxil fumarate, but it also focuses on the related clinical trails designed to date, in which clinical efficacy has been analyzed attending to HBe antigen status. In addition, studies including patients that have been previously treated with lamivudine or adefovir are discussed.

[(Methyl)1-(11)c]-acetate metabolism in hepatocellular carcinoma

PURPOSE

Studies have established the value of [(methyl)1-(11)C]-acetate ([(11)C]Act) combined with 2-deoxy-2[(18)F]fluoro-D-glucose (FDG) for detecting hepatocellular carcinoma (HCC) using positron emission tomography (PET). In this study, the metabolic fate of [(11)C]Act in HCC was characterized.

METHODS

Experiments with acetic acid [1-(14)C] sodium salt ([(14)C]Act) were carried out on WCH-17 cells and freshly derived rat hepatocytes. PET scans with [(11)C]Act were also carried out on woodchucks with HCC before injection of [(14)C]Act. The radioactivity levels in different metabolites were quantified with thin-layer chromatography.

RESULTS

In WCH-17 cells, the predominant metabolite was phosphatidylcholine (PC). Regions of HCCs with the highest [(11)C]Act uptake had higher radioactivity accumulation in lipid-soluble compounds than surrounding hepatic tissues. In those regions, PC and triacylglycerol (TG) accumulated more radioactivity than in surrounding hepatic tissues.

CONCLUSIONS

High [(11)C]Act uptake in HCC is associated with increased de novo lipogenesis. PC and TG are the main metabolites into which the radioactive label from [(11)C]Act is incorporated in HCC.

Tenofovir improves the outcome in patients with spontaneous reactivation of hepatitis B presenting as acute-on-chronic liver failure

Spontaneous reactivation of chronic hepatitis B (CHB) is an important cause of acute-on-chronic liver failure (ACLF). Antiviral drugs may help reduce the high morbidity and mortality in such patients, especially in places where liver transplant is not available. The aim was to evaluate the efficacy of tenofovir and to determine the predictors of mortality in patients with spontaneous reactivation of CHB with ACLF. Consecutive patients of ACLF due to spontaneous reactivation of CHB were randomized to receive either tenofovir or placebo. The primary endpoint was survival at 3 months. Of the 90 patients with ACLF of different etiologies, 27 (26%) were due to reactivation of CHB and were enrolled. The median baseline hepatitis B virus (HBV) DNA level was 9 × 10(5) IU/mL. Fourteen patients received tenofovir and 13 placebo. At 3 months the probability of survival was higher in the tenofovir than the placebo group (8/14 [57%] versus 2/13 [15%], respectively; P = 0.03). The cause of death in the 15 patients was progressive liver failure leading to multiorgan failure. Liver transplantation could not be offered due to its nonavailability. In the surviving patients, there was a significant improvement in the Child-Turcotte Pugh (CTP) and model for endstage liver disease (MELD) scores and significant decline in the HBV DNA levels in the tenofovir group, whereas these parameters did not change significantly in the placebo group. More than 2 log reduction in HBV DNA levels at 2 weeks was found to be an independent predictor of survival.

CONCLUSION

Tenofovir significantly reduces HBV-DNA levels, improves CTP and MELD scores, and reduces mortality in patients with severe spontaneous reactivation of CHB presenting as ACLF. Reduction in HBV-DNA levels at 2 weeks should be a desirable goal and is a good predictor of survival.

Antiviral treatment of chronic hepatitis B virus (HBV) infections

While 25 compounds have been formally licensed for the treatment of HIV infection (AIDS), only seven licensed products are currently available for the treatment of chronic hepatitis B virus (HBV) infection: interferon-α, pegylated interferon-α, lamivudine, adefovir (dipivoxil), entecavir, telbivudine and tenofovir (disoproxil fumarate). In contrast to the treatment of HIV infections where the individual drugs are routinely used in combination, for the treatment of chronic HBV infection the individual drugs are generally used in monotherapy. In principle, combination drug therapy should allow reducing the likelihood of drug-resistant development.

Another ten stories in antiviral drug discovery (part C): "Old" and "new" antivirals, strategies, and perspectives

The ten stories told here deal with (i) ribavirin as an inhibitor of IMP dehydrogenase and (ii) ribavirin, in combination with pegylated interferon, as the present "standard of care" for hepatitis C; (iii) S-adenosylhomocysteine hydrolase inhibitors as antiviral agents; (iv) new adamantadine derivatives for the treatment of influenza A virus infections; (v) 5-substituted 2'-deoxyuridines (i.e. IDU, TFT) for the treatment of herpes simplex virus (HSV) infections; (vi) acyclic guanosine analogues (e.g. acyclovir) for the treatment of HSV infections; (vii) OMP decarboxylase inhibitors (i.e. pyrazofurin) and CTP synthetase inhibitors (i.e. cyclopentenylcytosine) as possible antiviral agents; (viii) the future of cidofovir (and alkoxyalkyl esters thereof) and ST-246 as potential antipoxvirus agents; (ix) the two decade journey from tivirapine to rilpivirine in the ultimate therapy of HIV infections; and (x) the extension of the therapeutic application of tenofovir disoproxil fumarate (Viread) to the treatment of hepatitis B virus infection, in addition to HIV infection.

Profound antiviral effect of oral administration of MIV-210 on chronic hepadnaviral infection in a woodchuck model of hepatitis B

MIV-210 is a prodrug of 3'-fluoro-2',3'-dideoxyguanosine with high oral bioavailability in humans and potent activity against hepatitis B virus (HBV). Woodchucks infected with woodchuck hepatitis virus (WHV) represent an accurate model of HBV infection that is utilized for evaluation of the efficacy and safety of novel anti-HBV agents. Oral administration of MIV-210 at 20 or 60 mg/kg of body weight/day induced a rapid virological response in chronically infected woodchucks, reducing serum WHV DNA levels by 4.75 log10 and 5.72 log10, respectively, in 2 weeks. A progressive decline in WHV viremia occurred throughout the 10-week therapy, giving final reductions of 7.23 log10 and 7.68 log10 in the 20- and 60-mg/kg/day groups, respectively. Further, a daily dose of 10 mg/kg decreased the serum WHV load 400-fold after 4 weeks of treatment, and a dose of 5 mg/kg/day was sufficient to maintain this antiviral effect during the following 6-week period. MIV-210 at 20 or 60 mg/kg/day reduced the liver WHV DNA load 200- to 2,500-fold from pretreatment levels and, importantly, led to a 2.0 log10 drop in the hepatic content of WHV covalently closed circular DNA. The treatment with 60 mg/kg/day was well tolerated. Liver biopsy specimens obtained after the 10-week treatment with 20 or 60 mg/kg/day and after the 10-week follow-up showed hepatocyte and mitochondrial ultrastructures comparable to those in the placebo-treated group. It was concluded that MIV-210 is highly effective against chronic WHV infection. These findings, together with the previously demonstrated inhibitory activity of MIV-210 against lamivudine-, adefovir-, and entecavir-resistant HBV variants, make MIV-210 a highly valuable candidate for further testing as an agent against chronic hepatitis B.

Pharmacotherapy of chronic viral hepatitis and hepatocellular carcinoma

BACKGROUND

Hepatitis B virus (HBV) is a major etiologic agent of chronic liver disease (CLD) and hepatocellular carcinoma. Drugs have been developed and shown to be effective against HBV replication. These treatments are often associated with the resolution of CLD. However, they are too expensive, not well tolerated, and result in the development of resistance when given as mono or salvage therapies. In addition, most of these drugs target only the virus polymerase.

OBJECTIVE

To revitalize the field, drugs with other targets and combination therapies need to be developed.

METHODS

Major advances in HBV and liver cancer drug development over the past decade, focusing on Phase III trials and FDA-approved compounds, are presented.

RESULTS/DISCUSSION

A number of potent nucleoside/nucleotide analogs are now available for treatment, but for the long-term management of CLD, the development of combination therapies will probably be required. Development of compounds with new virus targets will enhance the utility of combination therapies. Development of compounds to host targets altered prior to or after the development of liver cancer, as demonstrated by sorafenib, need to be developed. The goal is to devise drug cocktails that will yield sustained virus responses and halt disease progression and tumor development.

Antiviral effects of lamivudine, emtricitabine, adefovir dipivoxil, and tenofovir disoproxil fumarate administered orally alone and in combination to woodchucks with chronic woodchuck hepatitis virus infection

Adefovir dipivoxil (ADV) and tenofovir disoproxil fumarate (TDF) are nucleotide analogs that inhibit the replication of wild-type hepatitis B virus (HBV) and lamivudine (3TC)-resistant virus in HBV-infected patients, including those who are coinfected with human immunodeficiency virus. The combination of ADV or TDF with other nucleoside analogs is a proposed strategy for managing antiviral drug resistance during the treatment of chronic HBV infection. The antiviral effect of oral ADV or TDF, alone or in combination with 3TC or emtricitabine (FTC), against chronic woodchuck hepatitis virus (WHV) infection was evaluated in a placebo-controlled study in the woodchuck, an established and predictive model for antiviral therapy. Once-daily treatment for 48 weeks with ADV plus 3TC or TDF plus FTC significantly reduced serum WHV viremia levels from the pretreatment level by 6.2 log(10) and 6.1 log(10) genome equivalents/ml serum, respectively, followed by TDF plus 3TC (5.6 log(10) genome equivalents/ml), ADV alone (4.8 log(10) genome equivalents/ml), ADV plus FTC (one survivor) (4.4 log(10) genome equivalents/ml), TDF alone (2.9 log(10) genome equivalents/ml), 3TC alone (2.7 log(10) genome equivalents/ml), and FTC alone (2.0 log(10) genome equivalents/ml). Individual woodchucks across all treatment groups also demonstrated pronounced declines in serum WHV surface antigen, characteristically accompanied by declines in hepatic WHV replication and the hepatic expression of WHV antigens. Most woodchucks had prompt recrudescence of WHV replication after drug withdrawal, but individual woodchucks across treatment groups had sustained effects. No signs of toxicity were observed for any of the drugs or drug combinations administered. In conclusion, the oral administration of 3TC, FTC, ADV, and TDF alone and in combination was safe and effective in the woodchuck model of HBV infection.

Antiviral treatment of chronic hepatitis B virus infections: the past, the present and the future

A decade ago, standard therapy against chronic hepatitis B virus infections only consisted of lamivudine or IFN-alpha. Treatment with lamivudine and IFN has been compounded by, respectively, the emergence of drug-resistant virus strains and the appearance of serious side effects. In the last 10 years, hepatitis B treatment has made much progress. Several treatments are now licensed for the treatment of patients with chronic hepatitis B and others are under development. Here, we provide an overview of the potential and mode of action of anti-HBV agents that are currently available, and/or may become available in the near future. Foremost among these newer compounds are adefovir dipivoxil, entecavir and telbivudine.

The role of the woodchuck model in the treatment of hepatitis B virus infection

Experimental studies of animals with chronic hepadnavirus infection could provide valuable insight into optimal therapeutic strategies for individuals with chronic HBV infection. In this review, we focus on the contributions of the woodchuck model to our understanding of HBV biology and on its role in the development of antiviral drug. Furthermore, we consider the implications of studies focusing on the natural history of WHV infection for the management of HBV and the capacity of treatment to prevent complications of chronic hepatitis B infection.

Establishment and primary application of a mouse model with hepatitis B virus replication

AIM: To establish a rapid and convenient animal model with hepatitis B virus (HBV) replication.

METHODS: A naked DNA solution of HBV-replication-competent plasmid was transferred to BALB/C mice via the tail vein, using a hydrodynamic in vivo transfection procedure. After injection, these mice were sacrificed on d 1, 3, 4, 5, 7 and 10. HBV DNA replication intermediates in the liver were analyzed by Southern blot hybridization. The expression of hepatitis B core antigen (HBcAg) and hepatitis B surface antigen (HBsAg) in the liver was checked by immunohistochemistry. Serum HBsAg and hepatitis B e antigen (HBeAg) was detected by enzyme-linked immunosorbent assay (ELISA). Inhibition of HBV replication was compared in HBV replication model mice treated intraperitoneally with polyinosinic-polytidylin acid (polyIC) or phosphate-buffered saline (PBS).

RESULTS: After hydrodynamic in vivo transfection, HBV DNA replication intermediates in the mouse liver were detectable on d 1 and abundant on d 3 and 4, the levels were slightly decreased and remained relatively stable between d 5 and 7, and were almost undetectable on d 10. The expression patterns of HBcAg and HBsAg were similar to that of HBV replication intermediate DNA, except that they reached a peak on d 1 after injection. No obvious differences in HBV DNA replication intermediates were observed in the left, right and middle lobes of the liver. After treatment with polyIC, the level of HBV intermediate DNA in the liver was lower than that in the control mice injected with PBS.

CONCLUSION: A rapid and convenient mouse model with a high level of HBV replication was developed and used to investigate the inhibitory effect of polyIC on HBV replication, which provides a useful tool for future functional studies of the HBV genome.

Antiviral effect of orally administered (-)-beta-D-2-aminopurine dioxolane in woodchucks with chronic woodchuck hepatitis virus infection

(-)-beta-D-2-Aminopurine dioxolane (APD) is a nucleoside prodrug that is efficiently converted to 9-(beta-D-1,3-dioxolan-4-yl)guanine (DXG). DXG has antiviral activity in vitro against hepatitis B virus (HBV) but limited aqueous solubility, making it difficult to administer orally to HBV-infected individuals. APD is more water soluble than DXG and represents a promising prodrug for the delivery of DXG. A placebo-controlled, dose-ranging efficacy and pharmacokinetic study was conducted with woodchucks that were chronically infected with woodchuck hepatitis virus (WHV). APD was efficiently converted to DXG after oral and intravenous administrations of APD, with serum concentrations of DXG being higher following oral administration than following intravenous administration, suggestive of a considerable first-pass intestinal and/or hepatic metabolism. APD administered orally at 1, 3, 10, and 30 mg/kg of body weight per day for 4 weeks produced a dose-dependent antiviral response. Doses of 3 and 10 mg/kg/day reduced serum WHV viremia by 0.4 and 0.7 log(10) copies/ml, respectively. The 30-mg/kg/day dose resulted in a more pronounced, statistically significant decline in serum WHV viremia of 1.9 log(10) copies/ml and was associated with a 1.5-fold reduction in hepatic WHV DNA. Individual woodchucks within the highest APD dose group that had declines in serum WHV surface antigen levels, WHV viremia, and hepatic WHV DNA also had reductions in hepatic WHV RNA. There was a prompt recrudescence of WHV viremia following drug withdrawal. Therefore, oral administration of APD for 4 weeks was safe in the woodchuck model of chronic HBV infection, and the effect on serum WHV viremia was dose dependent.

Immunosuppression reactivates viral replication long after resolution of woodchuck hepatitis virus infection

Resolution of hepatitis B virus (HBV) infection is characterized by coordinated humoral and cellular immune responses. Immunity is durable over decades, protecting the host from reinfection and potential activation of residual HBV. Woodchucks infected at birth with woodchuck hepatitis virus (WHV) cleared viremia and developed antibodies to surface antigen (anti-WHs). Woodchucks became seronegative for anti-WHs 3-6 years later, but in some, WHV DNA was detected in serum, liver, and/or peripheral blood mononuclear cells (PBMCs). Those with WHV DNA had increased in vitro cellular immune responses to viral antigens, CD4 and CD8 markers, and Th1-type cytokines, suggesting active WHV-specific T lymphocytes. Immunosuppression for 12 weeks using cyclosporine A in such woodchucks resulted in transient reactivation of WHV replication. Serum of 1 woodchuck that became positive for WHV DNA during immunosuppression was inoculated into WHV-susceptible woodchucks, and a productive infection was demonstrated. The results indicate that after infection durable cellular immunity to WHV is essential for the long-term control of viral replication and is probably maintained by continuous priming from residual virus.

CONCLUSION

These experimental observations demonstrate the potential of immunosuppression to reactivate HBV after resolution of infection.

The woodchuck as an animal model for pathogenesis and therapy of chronic hepatitis B virus infection

This review describes the woodchuck and the woodchuck hepatitis virus (WHV) as an animal model for pathogenesis and therapy of chronic hepatitis B virus (HBV) infection and disease in humans. The establishment of woodchuck breeding colonies, and use of laboratory-reared woodchucks infected with defined WHV inocula, have enhanced our understanding of the virology and immunology of HBV infection and disease pathogenesis, including major sequelae like chronic hepatitis and hepatocellular carcinoma. The role of persistent WHV infection and of viral load on the natural history of infection and disease progression has been firmly established along the way. More recently, the model has shed new light on the role of host immune responses in these natural processes, and on how the immune system of the chronic carrier can be manipulated therapeutically to reduce or delay serious disease sequelae through induction of the recovery phenotype. The woodchuck is an outbred species and is not well defined immunologically due to a limitation of available host markers. However, the recent development of several key host response assays for woodchucks provides experimental opportunities for further mechanistic studies of outcome predictors in neonatal- and adult-acquired infections. Understanding the virological and immunological mechanisms responsible for resolution of self-limited infection, and for the onset and maintenance of chronic infection, will greatly facilitate the development of successful strategies for the therapeutic eradication of established chronic HBV infection. Likewise, the results of drug efficacy and toxicity studies in the chronic carrier woodchucks are predictive for responses of patients chronically infected with HBV. Therefore, chronic WHV carrier woodchucks provide a well-characterized mammalian model for preclinical evaluation of the safety and efficacy of drug candidates, experimental therapeutic vaccines, and immunomodulators for the treatment and prevention of HBV disease sequelae.

Intracellular metabolism and in vitro activity of tenofovir against hepatitis B virus

Tenofovir is an acyclic nucleotide analog with activity against human immunodeficiency virus (HIV) and hepatitis B virus (HBV). Tenofovir disoproxil fumarate (tenofovir DF), a bis-alkoxyester prodrug of tenofovir, is approved for the treatment of HIV and is currently being developed to treat chronic hepatitis B. In this report, we further characterize the in vitro activity of tenofovir against HBV as well as its metabolism in hepatic cells. We show that tenofovir is efficiently phosphorylated to tenofovir diphosphate (TFV-DP) in both HepG2 cells and primary human hepatocytes. TFV-DP has a long intracellular half-life (95 h) and is a potent and competitive inhibitor of HBV polymerase (Ki = 0.18 microM). Tenofovir has a 50% effective concentration of 1.1 microM against HBV in cell-based assays, and potency is improved > 50-fold by the addition of bis-isoproxil progroups. Tenofovir has previously demonstrated full activity against lamivudine-resistant HBV in vitro and clinically. Here we show that the major adefovir resistance mutation, rtN236T, confers three- to fourfold-reduced susceptibility to tenofovir in cell culture; the clinical significance of this susceptibility shift has not yet been determined. The rtA194T HBV polymerase mutation recently identified in tenofovir DF-treated HIV/HBV-coinfected patients did not confer in vitro resistance to tenofovir as a single mutation or in a lamivudine-resistant viral background. Overall, the antiviral and metabolic profile of tenofovir supports its development for the treatment of chronic hepatitis B.

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.