Characterizing antiviral activity of adefovir dipivoxil in transgenic mice expressing hepatitis B virus

FDA-approved drug repurposing screen identifies inhibitors of SARS-CoV-2 pseudovirus entry

Background and purpose

The coronavirus disease 2019 (COVID-19) pandemic has devastated global health and the economy, underscoring the urgent need for extensive research into the mechanisms of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral entry and the development of effective therapeutic interventions.

Experimental approach

We established a cell line expressing human angiotensin-converting enzyme 2 (ACE2). We used it as a model of pseudotyped viral entry using murine leukemia virus (MLV) expressing SARS-CoV-2 spike (S) protein on its surface and firefly luciferase as a reporter. We screened an U.S. Food and Drug Administration (FDA)-approved compound library for inhibiting ACE2-dependent SARS-CoV-2 pseudotyped viral entry and identified several drug-repurposing candidates.

Key results

We identified 18 drugs and drug candidates, including 14 previously reported inhibitors of viral entry and four novel candidates. Pyridoxal 5'-phosphate, Dovitinib, Adefovir dipivoxil, and Biapenem potently inhibit ACE2-dependent viral entry with inhibitory concentration 50% (IC50) values of 57nM, 74 nM, 130 nM, and 183 nM, respectively.

Conclusion and implications

We identified four novel FDA-approved candidate drugs for anti-SARS-CoV-2 combination therapy. Our findings contribute to the growing body of evidence supporting drug repurposing as a viable strategy for rapidly developing COVID-19 treatments.

Preclinical animal models to evaluate therapeutic antiviral antibodies

Despite the availability of effective preventative vaccines and potent small-molecule antiviral drugs, effective non-toxic prophylactic and therapeutic measures are still lacking for many viruses. The use of monoclonal and polyclonal antibodies in an antiviral context could fill this gap and provide effective virus-specific medical interventions. In order to develop these therapeutic antibodies, preclinical animal models are of utmost importance. Due to the variability in viral pathogenesis, immunity and overall characteristics, the most representative animal model for human viral infection differs between virus species. Therefore, throughout the years researchers sought to find the ideal preclinical animal model for each virus. The most used animal models in preclinical research include rodents (mice, ferrets, …) and non-human primates (macaques, chimpanzee, ….). Currently, antibodies are tested for antiviral efficacy against a variety of viruses including different hepatitis viruses, human immunodeficiency virus (HIV), influenza viruses, respiratory syncytial virus (RSV), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and rabies virus. This review provides an overview of the current knowledge about the preclinical animal models that are used for the evaluation of therapeutic antibodies for the abovementioned viruses.

In Vivo Mouse Models for Hepatitis B Virus Infection and Their Application

Despite the availability of effective vaccination, hepatitis B virus (HBV) infection continues to be a major challenge worldwide. Research efforts are ongoing to find an effective cure for the estimated 250 million people chronically infected by HBV in recent years. The exceptionally limited host spectrum of HBV has limited the research progress. Thus, different HBV mouse models have been developed and used for studies on infection, immune responses, pathogenesis, and antiviral therapies. However, these mouse models have great limitations as no spread of HBV infection occurs in the mouse liver and no or only very mild hepatitis is present. Thus, the suitability of these mouse models for a given issue and the interpretation of the results need to be critically assessed. This review summarizes the currently available mouse models for HBV research, including hydrodynamic injection, viral vector-mediated transfection, recombinant covalently closed circular DNA (rc-cccDNA), transgenic, and liver humanized mouse models. We systematically discuss the characteristics of each model, with the main focus on hydrodynamic injection mouse model. The usefulness and limitations of each mouse model are discussed based on the published studies. This review summarizes the facts for considerations of the use and suitability of mouse model in future HBV studies.

Animal Models for the Study of Hepatitis B Virus Pathobiology and Immunity: Past, Present, and Future

Hepatitis B virus (HBV) infection is a global public health problem that plagues approximately 240 million people. Chronic hepatitis B (CHB) often leads to liver inflammation and aberrant repair which results in diseases ranging from liver fibrosis, cirrhosis, to hepatocellular carcinoma. Despite its narrow species tropism, researchers have established various in vivo models for HBV or its related viruses which have provided a wealth of knowledge on viral lifecycle, pathogenesis, and immunity. Here we briefly revisit over five decades of endeavor in animal model development for HBV and summarize their advantages and limitations. We also suggest directions for further improvements that are crucial for elucidation of the viral immune-evasion strategies and for development of novel therapeutics for a functional cure.

Modeling Hepatotropic Viral Infections: Cells vs. Animals

The lack of an appropriate platform for a better understanding of the molecular basis of hepatitis viruses and the absence of reliable models to identify novel therapeutic agents for a targeted treatment are the two major obstacles for launching efficient clinical protocols in different types of viral hepatitis. Viruses are obligate intracellular parasites, and the development of model systems for efficient viral replication is necessary for basic and applied studies. Viral hepatitis is a major health issue and a leading cause of morbidity and mortality. Despite the extensive efforts that have been made on fundamental and translational research, traditional models are not effective in representing this viral infection in a laboratory. In this review, we discuss in vitro cell-based models and in vivo animal models, with their strengths and weaknesses. In addition, the most important findings that have been retrieved from each model are described.

Investigation of the Structure and Dynamics of Antiviral Drug Adefovir Dipivoxil by Site-Specific Spin-Lattice Relaxation Time Measurements and Chemical Shift Anisotropy Tensor Measurements

Adefovir is regarded as a potential antiviral agent. However, it cannot be considered as a valuable drug candidate due to its high polarity that limits its permeability across the human intestinal mucosa. When the ribose phosphate group of adefovir is replaced by the isopolar phosphonomethyl ether functionality, it neutralizes the negative charge of the drug. This makes the drug lipid-soluble and potent to diffuse across the cell membrane. The prodrug adefovir dipivoxil is regarded as a potent antiviral drug against hepatitis B virus (HBV), human immunodeficiency virus (HIV), Rauscher murine leukemia virus (R-MuLV), murine cytomegalovirus (MCMV), herpes simplex virus (HSV), simian immunodeficiency virus (SIV), and feline immunodeficiency virus (FIV). The correlation between the structure and the dynamics of adefovir dipivoxil is determined by measuring the principal components of chemical shift anisotropy (CSA) tensor, site-specific spin-lattice relaxation time, and molecular correlation time at crystallographically different carbon nuclei sites. The CSA parameters, spin-lattice relaxation time, and molecular correlation time of phosphorous nucleus of the organophosphate group of adefovir dipivoxil molecule are also determined. The spin-lattice relaxation time of carbon nuclei varies from 1 to 107 s. The range of molecular correlation time also varies from 10-4 to 10-8 s. These remarkable diversities of motional dynamics of the molecules imply that there exist various motional degrees of freedom within this valuable drug and these motional degrees of freedom are independent of each other, which may be the reason for the biological activities exhibited by the drug. The correlation between structure and dynamics of such an important antiviral drug adefovir dipivoxil can be visualized by these types of extensive spectroscopic measurements, which will enlighten the path of inventing advanced medicine in the pharmaceutical industry, and it will also illuminate the understanding of the structure-activity relationships of antiviral drug.

Antiviral effects of a niobium-substituted heteropolytungstate on hepatitis B virus-transgenic mice

To study the efficacy of a polyoxometalate, Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O, as an antiviral treatment in HBV transgenic mice. HBV transgenic mice were treated with Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O by intragastric administration. Adefovir and distilled water were administered as controls. Serum HBV DNA, liver HBV RNA levels were measured by quantitative RT-PCR. Serum HBsAg levels were measured by ELISA. The hepatitis B virus surface antigen (HBsAg) in liver cells was detected by immunohistochemistry (IHC). Pathological changes in the liver tissues were also observed by light and electron microscopy. Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O significantly decreased serum HBsAg and HBV DNA levels. Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O resulted in a 98% decrease in serum HBV DNA at 28 days, from 4.3 log₁₀ copies/ml at baseline to 2.5 log₁₀ copies/ml after treatment, and the inhibition rate of HBV DNA was higher than ADV at the same dose. The HBV replication levels in each group slightly increased at 7 days after withdrawal, but rebounded slightly more in the Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O treatment group compared to the H₂ O control group (p < .05). There were no differences in HBV RNA levels. No significant differences were observed in the pathology, but there were decreased HBsAg levels in the Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O-treated group compared to the control group. The results demonstrated that Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O displayed potent anti-HBV activity in HBV transgenic mice and supported for future clinic study.

In Vivo Model Systems for Hepatitis B Virus Research

Hepatitis B virus (HBV) affects more than 257 million people globally, resulting in progressively worsening liver disease, manifesting as fibrosis, cirrhosis, and hepatocellular carcinoma. The exceptionally narrow species tropism of HBV restricts its natural hosts to humans and non-human primates, including chimpanzees, gorillas, gibbons, and orangutans. The unavailability of completely immunocompetent small-animal models has contributed to the lack of curative therapeutic interventions. Even though surrogates allow the study of closely related viruses, their host genetic backgrounds, immune responses, and molecular virology differ from those of HBV. Various different models, based on either pure murine or xenotransplantation systems, have been introduced over the past years, often making the choice of the optimal model for any given question challenging. Here, we offer a concise review of in vivo model systems employed to study HBV infection and steps in the HBV life cycle or pathogenesis.

Adefovir dipivoxil sensitizes colon cancer cells to vemurafenib by disrupting the KCTD12-CDK1 interaction

Vemurafenib is a B-Raf V600E inhibitor that exerts significant inhibitory effects in melanoma but not in colon cancer, and the mechanism of vemurafenib resistance remains unclear. In this study, bioinformatics analysis of gene profiles in cancer cells treated with vemurafenib or its analog revealed that cell cycle progression is significantly affected by vemurafenib. We found that CDK1 is stably activated in the vemurafenib-resistant (VR) colon cancer sublines that we established, indicating that CDK1 activation is responsible for vemurafenib resistance. As the KCTD12-CDK1 interaction is necessary for CDK1 activation, we screened an FDA-approved drug library consisting of 616 compounds and identified that adefovir dipivoxil (AD), a nucleoside analog for treatment of HBV infections, disrupts the CDK1-KCTD12 interaction and induces G2 phase arrest in the cell cycle. Functional assays demonstrated that AD significantly inhibited colon cancer cell proliferation and tumorigenesis both in vitro and in vivo with no observed side effects. Furthermore, AD sensitized vemurafenib-resistant colon cancer cells and tumor xenografts to vemurafenib. This study reveals that CDK1 activation induces vemurafenib resistance and that AD is a promising therapeutic strategy for colon cancer both as a single agent and in combination with vemurafenib.

Cell and Animal Models for Studying Hepatitis B Virus Infection and Drug Development

Many cell culture and animal models have been used to study hepatitis B virus (HBV) replication and its effects in the liver; these have facilitated development of strategies to control and clear chronic HBV infection. We discuss the advantages and limitations of systems for studying HBV and developing antiviral agents, along with recent advances. New and improved model systems are needed. Cell culture systems should be convenient, support efficient HBV infection, and reproduce responses of hepatocytes in the human body. We also need animals that are fully permissive to HBV infection, convenient for study, and recapitulate human immune responses to HBV and effects in the liver. High-throughput screening technologies could facilitate drug development based on findings from cell and animal models.

Activity of nucleic acid polymers in rodent models of HBV infection

Nucleic acid polymers (NAPs) block the release of HBsAg from infected hepatocytes. These compounds have been previously shown to have the unique ability to eliminate serum surface antigen in DHBV-infected Pekin ducks and achieve multilog reduction of HBsAg or HBsAg loss in patients with chronic HBV infection and HBV/HDV coinfection. In ducks and humans, the blockage of HBsAg release by NAPs occurs by the selective targeting of the assembly and/or secretion of subviral particles (SVPs). The clinically active NAP species REP 2055 and REP 2139 were investigated in other relevant animal models of HBV infection including woodchucks chronically infected with WHV, HBV transgenic mice and HBV infected SCID-Hu mice. The liver accumulation of REP 2139 in woodchucks following subcutaneous administration was examined and was found to be similar to that observed in mice and ducks. However, in woodchucks, NAP treatment was associated with only mild (36-79% relative to baseline) reductions in WHsAg (4/10 animals) after 3-5 weeks of treatment without changes in serum WHV DNA. In HBV infected SCID-Hu mice, REP 2055 treatment was not associated with any reduction of HBsAg, HBeAg or HBV DNA in the serum after 28 days of treatment. In HBV transgenic mice, no reductions in serum HBsAg were observed with REP 2139 with up to 12 weeks of treatment. In conclusion, the antiviral effects of NAPs in DHBV infected ducks and patients with chronic HBV infection were weak or absent in woodchuck and mouse models despite similar liver accumulation of NAPs in all these species, suggesting that the mechanisms of SVP assembly and or secretion present in rodent models differs from that in DHBV and chronic HBV infections.

Experimental in vitro and in vivo models for the study of human hepatitis B virus infection

Chronic infection with the hepatitis B virus (HBV) affects an estimate of 240 million people worldwide despite the availability of a preventive vaccine. Medication to repress viral replication is available but a cure is rarely achieved. The narrow species and tissue tropism of the virus and the lack of reliable in vitro models and laboratory animals susceptible to HBV infection, have limited research progress in the past. As a result, several aspects of the HBV life cycle as well as the network of virus host interactions occurring during the infection are not yet understood. Only recently, the identification of the functional cellular receptor enabling HBV entry has opened new possibilities to establish innovative infection systems. Regarding the in vivo models of HBV infection, the classical reference was the chimpanzee. However, because of the strongly restricted use of great apes for HBV research, major efforts have focused on the development of mouse models of HBV replication and infection such as the generation of humanized mice. This review summarizes the animal and cell culture based models currently available for the study of HBV biology. We will discuss the benefits and caveats of each model and present a selection of the most important findings that have been retrieved from the respective systems.

Modeling hepatitis B virus infection, immunopathology and therapy in mice

Despite the availability of a preventive vaccine, chronic hepatitis B virus (HBV) infection-induced liver diseases continue to be a major global public health problem. HBV naturally infects only humans and chimpanzees. This narrow host range has hindered our ability to study the characteristics of the virus and how it interacts with its host. It is thus important to establish small animal models to study HBV infection, persistence, clearance and the immunopathogenesis of chronic hepatitis B. In this review, we briefly summarize currently available animal models for HBV research, then focus on mouse models, especially the recently developed humanized mice that can support HBV infection and immunopathogenesis in vivo. This article is part of a symposium in Antiviral Research on "From the discovery of the Australia antigen to the development of new curative therapies for hepatitis B: an unfinished story."

Mouse models of hepatitis B virus infection comprising host-virus immunologic interactions

Hepatitis B virus (HBV) infection is one of the most prevalent infectious diseases associated with various human liver diseases, including acute, fulminant and chronic hepatitis; liver cirrhosis; and hepatocellular carcinoma. Despite the availability of an HBV vaccine and the development of antiviral therapies, there are still more than 350 million chronically infected people worldwide, approximately 5% of the world population. To understand the virus biology and pathogenesis in HBV-infected patients, several animal models have been developed to mimic hepatic HBV infection and the immune response against HBV, but the narrow host range of HBV infection and lack of a full immune response spectrum in animal models remain significant limitations. Accumulating evidence obtained from studies using a variety of mouse models that recapitulate hepatic HBV infection provides several clues for understanding host-virus immunologic interactions during HBV infection, whereas the determinants of the immune response required for HBV clearance are poorly defined. Therefore, adequate mouse models are urgently needed to elucidate the mechanism of HBV elimination and identify novel targets for antiviral therapies.

Mouse models of hepatitis B and delta virus infection

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. Therapeutic regimens currently available can efficiently suppress HBV replication; however, 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. Among the HBV chronically infected patients, more than 15million patients are estimated to be co-infected with the hepatitis delta virus (HDV), a defective satellite virus that needs the HBV envelope for propagation. No specific drugs are currently available against HDV, while nucleos(t)ide analogs are not effective against HDV replication. Since chronic HBV/HDV co-infection leads to the most severe form of chronic viral hepatitis in men, a better understanding of the molecular mechanisms of HDV-mediated pathogenesis and the development of improved therapeutic approaches is urgently needed. The obvious limitations imposed by the use of great apes and the paucity of robust experimental models of HBV infection have hindered progresses in understanding the complex network of virus-host interactions that are established in the course of HBV and HDV infections. This review focuses on summarizing recent advances obtained with well-established and more innovative experimental mouse models, giving emphasis on the strength of infection systems based on the reconstitution of the murine liver with human hepatocytes, as tools for elucidating the whole life cycle of HBV and HDV, as well as for studies on interactions with the infected human hepatocytes and for preclinical drug evaluation.

Potential of acyclic nucleoside phosphonates in the treatment of DNA virus and retrovirus infections

The acyclic nucleoside phosphonates [HPMPC: cidofovir, Vistide; PMEA: adefovir dipivoxil, Hepsera; and PMPA: tenofovir, Viread] have proven to be effective in vitro (cell culture systems) and in vivo (animal models and clinical studies) against a wide variety of DNA virus and retrovirus infections, for example, cidofovir against herpesvirus [herpes simplex virus type 1 and 2, varicella-zoster virus, cytomegalovirus, Epstein-Barr virus, human herpesvirus type 6, 7 and 8), polyoma-, papilloma-, adeno- and poxvirus (variola virus, cowpox virus, vaccinia virus, molluscum contagiosum virus and orf) infections; adefovir against herpesvirus, hepadnavirus [human hepatitis B virus] and retrovirus [HIV type-1 and 2, simian immunodeficiency virus and feline immunodeficiency virus] infections; and tenofovir against both hepadna- and retrovirus infections. Cidofovir has been officially approved for the treatment of cytomegalovirus retinitis in AIDS patients, tenofovir disoproxil fumarate (Viread) for the treatment of HIV infections (i.e., AIDS) and adefovir dipivoxil for the treatment of chronic hepatitis B.

Liver immune-pathogenesis and therapy of human liver tropic virus infection in humanized mouse models

Hepatitis B virus (HBV) and hepatitis C virus (HCV) infect and replicate primarily in human hepatocytes. Few reliable and easy accessible animal models are available for studying the immune system's contribution to the liver disease progression during hepatitis virus infection. Humanized mouse models reconstituted with human hematopoietic stem cells (HSCs) have been developed to study human immunology, human immunodeficiency virus 1 infection, and immunopathogenesis. However, a humanized mouse model engrafted with both human immune and human liver cells is needed to study infection and immunopathogenesis of HBV/HCV infection in vivo. We have recently developed the humanized mouse model with both human immune and human liver cells (AFC8-hu HSC/Hep) to study immunopathogenesis and therapy of HCV infection in vivo. In this review, we summarize the current models of HBV/HCV infection and their limitations in immunopathogenesis. We will then present our recent findings of HCV infection and immunopathogenesis in the AFC8-hu HSC/Hep mouse, which supports HCV infection, human T-cell response and associated liver pathogenesis. Inoculation of humanized mice with primary HCV isolates resulted in long-term HCV infection. HCV infection induced elevated infiltration of human immune cells in the livers of HCV-infected humanized mice. HCV infection also induced HCV-specific T-cell immune response in lymphoid tissues of humanized mice. Additionally, HCV infection induced liver fibrosis in humanized mice. Anti-human alpha smooth muscle actin (αSMA) staining showed elevated human hepatic stellate cell activation in HCV-infected humanized mice. We discuss the limitation and future improvements of the AFC8-hu HSC/Hep mouse model and its application in evaluating novel therapeutics, as well as studying both HCV and HBV infection, human immune responses, and associated human liver fibrosis and cancer.

Construction of a single lentiviral vector containing tetracycline-inducible Alb-uPA for transduction of uPA expression in murine hepatocytes

The SCID-beige/Alb-uPA mouse model is currently the best small animal model available for viral hepatitis infection studies [1]. But the construction procedure is often costly and time-consuming due to logistic and technical difficulties. Thus, the widespread application of these chimeric mice has been hampered [2]. In order to optimize the procedure, we constructed a single lentiviral vector containing modified tetracycline-regulated system to control Alb-uPA gene expression in the cultured hepatocytes. The modified albumin promoter controlled by tetracycline (Tet)-dependent transactivator rtTA2S-M2 was integrated into a lentiviral vector. The full-length uPA cDNA was inserted into another lentiviral vector containing PTight, a modified Tet-responsive promoter. Two vectors were then digested by specific enzymes and ligated by DNA ligase 4. The ligated DNA fragment was inserted into a modified pLKO.1 cloning vector and the final lentiviral vector was then successfully constructed. H2.35 cell, Lewis lung carcinoma, primary kidney, primary hepatic interstitial and CT26 cells were infected with recombinant lentivirus at selected MOI. The expression of uPA induced by DOX was detectable only in the infected H2.35 cells, which was confirmed by real-time PCR and Western blot analysis. Moreover, DOX induced uPA expression on the infected H2.35 cells in a dose-dependent manner. The constructed single lentiviral vector has many biological advantages, including that the interested gene expression under "Tet-on/off" system is controlled by DOX in a dose-depending fashion only in murine liver cells, which provides an advantage for simplifying generation of conditional transgenic animals.

Biological characteristics of the rtA181T/sW172* mutant strain of Hepatitis B virus in animal model

BACKGROUND

The effects of Hepatitis B virus (HBV) rtA181T/sW172* mutation on viral replication and pathogenicity was concerned recently. This study aimed to investigate the biological characteristics of rtA181T/sW172* mutant strain of HBV in animal model.

METHODS

The rtA181T/sW172* mutant plasmid was constructed using the pHBV4.1 (wild type HBV) as a template. The wild and mutant HBV replication mouse models were established utilizing a hydrodynamic technique. The titers of hepatitis B surface antigen (HBsAg), hepatitis B e antigen, and HBV DNA in serum, and the levels of HBsAg, hepatitis B core antigen(HBcAg), HBV DNA replication intermediates (HBV DNA RI) and HBV RNA in liver were measured after 1, 3, 5, 7, 10, 12 and 15 days of plasmid injection.

RESULTS

In wild-type HBV replication mouse model, serum HBsAg was high on day 1, 3, and 5, but became lower since day 7; while in mutant HBV mouse model, serum HBsAg was always at very low level. In liver tissues, HBV DNA RI of wild type HBV was detected on day 1 after transfection. The level subsequently peaked on day 3, gradually declined after day 5, and was almost undetectable on day 10. However, the HBV DNA RI levels of the mutant strain were always higher and lasted longer until day 15. Consistently, the expression levels of HBsAg and HBcAg in liver of the mutant group were significantly increased.

CONCLUSIONS

In the case of the HBV rtA181T/sW172* mutation, the secretion of serum HBsAg was impaired, whereas HBV DNA replication and HBsAg/HBcAg expression were increased in liver. These results suggest that the mutation can impair HBsAg secretion, and may cause the accumulation of viral core particles in liver.

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.

Breaking B and T cell tolerance using cationic lipid--DNA complexes (CLDC) as a vaccine adjuvant with hepatitis B virus (HBV) surface antigen in transgenic mice expressing HBV

Cationic lipid DNA complexes (CLDC), referred to here as JVRS-100, were evaluated as an adjuvant for hepatitis B surface antigen (HBsAg) for eliciting B and T cell responses in transgenic mice expressing hepatitis B virus (HBV). To confirm the immunogenicity of HBsAg+JVRS-1000, a study was conducted in C57BL/6 mice, the genetic background of the HBV transgenic mice used in the study. HBsAg+JVRS-100 elicited a T cell response and B cell response as evidenced by interferon-gamma (IFN-γ) secretion by re-stimulated splenocytes and anti-HBsAg IgG induction, respectively, whereas, HBsAg only elicited a B cell response. In HBV transgenic mice, HBsAg did not elicit either T or B cell responses, unlike the HBsAg+JVRS-100 that elicited both. Energix-B vaccine did perform better than the HBsAg by eliciting a B cell response in the transgenic mice, but it did not perform as HBsAg+JVRS-100 since it did not elicit a T cell response. The response by HBsAg+JVRS-100 was not sufficient to cause destruction of infected liver cells, but it did suppress HBV DNA non-cytolytically. From these results, JVRS-100 might be considered for further development as an adjuvant for HBV therapeutic vaccines.

Animal model for study of human hepatitis viruses

Human hepatitis B virus (HBV) and hepatitis C virus (HCV) infect only chimpanzees and humans. Analysis of both viruses has long been hampered by the absence of a small animal model. The recent development of human hepatocyte chimeric mice has enabled us to carry out studies on viral replication and cellular changes induced by replication of human hepatitis viruses. Various therapeutic agents have also been tested using this model. In the present review, we summarize published studies using chimeric mice and discuss the merits and shortcomings of this model.

Application of hepatitis B virus replication mouse model

AIM

To evaluate the value of the hepatitis B virus (HBV) replication mouse model with regard to several aspects of the study of HBV biology.

METHODS

To evaluate the HBV replication mouse model in detecting the efficacy of anti-HBV agents, the interferon inducer polyinosinic-polytidylin acid (polyIC) and nucleotide analogues adefovir and entecavir were administered to mice injected with wild type pHBV4.1, and the inhibiting effect of these agents on HBV DNA replication was evaluated. To identify the model's value in a replication ability study of HBV drug-resistant mutants and a HBx-minus mutant, telbivudine resistance mutants (rtM204I, ayw subtype), adefovir resistance mutants (rtA181V + rtN236T, ayw subtype) and HBx-minus mutants were injected respectively, and their corresponding HBV DNA replication intermediates in mouse liver were assessed.

RESULTS

Compared with the wild type HBV replication mouse model without antiviral agent treatment, the HBV DNA replication intermediates of the polyIC-treated group were decreased 1-fold; while in the entecavir- and adefovir-treated groups, the levels of HBV DNA replication intermediates were inhibited 13.6-fold and 1.4-fold, respectively. For the mouse models injected with telbivudine resistance mutant, adefovir resistance mutant and HBx-minus mutant, HBV DNA replication intermediates could still be detected, but the levels of HBV DNA replication intermediates of these mutants decreased 4.5-fold, 5.6-fold and 2.9-fold respectively, compared with the mouse model with wild type HBV plasmid.

CONCLUSION

The HBV replication mouse model we established was a useful and convenient tool to detect the efficacy of antiviral agents and to study the replication ability of HBV mutants in vivo.

Effect of oxymatrine on the replication cycle of hepatitis B virus in vitro

AIM: To determine the antiviral mechanism or target of oxymatrine against hepatitis B virus (HBV).

METHODS: HepG2.2.15 cells were incubated with culture medium containing 500 μg/mL of oxymatrine for 2 and 5 d. The surface antigen of HBV (HBsAg) and e antigen of HBV (HBeAg) in supernatant were determined by ELISA. HBV DNA in supernatant, and intracellular covalently closed circular DNA (cccDNA), relaxed circular DNA (rcDNA) and pregenomic RNA (pgRNA) were quantified by specific real-time polymerase chain reaction (PCR) or reverse transcription (RT)-PCR.

RESULTS: Treatment with oxymatrine for 2 d and 5 d reduced the production of HBV by the cell line, as indicated by the decline of HBsAg (22.67%, t = 5.439, P = 0.0322 and 22.39%, t = 5.376, P = 0.0329, respectively), HBeAg (55.34%, t = 9.859, P = 0.0101 and 43.97%, t = 14.080, P = 0.0050) and HBV DNA (40.75%, t = 4.570, P = 0.0447 and 75.32%, t = 14.460, P = 0.0047) in the supernatant. Intracellular cccDNA was also markedly reduced by 63.98% (t = 6.152, P = 0.0254) and 80.83% (t = 10.270, P = 0.0093), and intracellular rcDNA by 34.35% (t = 4.776, P = 0.0413) and 39.24% (t = 10.050, P = 0.0097). In contrast, intracellular pgRNA increased by 6.90-fold (t = 8.941, P = 0.0123) and 3.18-fold (t = 7.432, P = 0.0176) after 500 μg/mL of oxymatrine treatment for 2 d and 5 d, respectively.

CONCLUSION: Oxymatrine may inhibit the replication of HBV by interfering with the process of packaging pgRNA into the nucleocapsid, or inhibiting the activity of the viral DNA polymerase.

Alkoxyalkyl esters of 9-(s)-(3-hydroxy-2-phosphonomethoxypropyl) adenine are potent and selective inhibitors of hepatitis B virus (HBV) replication in vitro and in HBV transgenic mice in vivo

Alkoxyalkyl esters of acyclic nucleoside phosphonates have previously been shown to have increased antiviral activity when they are administered orally in animal models of viral diseases, including lethal infections with vaccinia virus, cowpox virus, ectromelia virus, murine cytomegalovirus, and adenovirus. 9-(S)-(3-Hydroxy-2-phosphonomethoxypropyl)adenine [(S)-HPMPA] was previously shown to have activity against hepatitis B virus (HBV) in vitro. To assess the effect of alkoxyalkyl esterification of (S)-HPMPA, we prepared the hexadecyloxypropyl (HDP), 15-methyl-hexadecyloxypropyl (15M-HDP), and octadecyloxyethyl (ODE) esters and compared their activities with the activity of adefovir dipivoxil in vitro and in vivo. Alkoxyalkyl esters of (S)-HPMPA were 6 to 20 times more active than unmodified (S)-HPMPA on the basis of their 50% effective concentrations in 2.2.15 cells. The increased antiviral activity appeared to be due in part to the increased uptake and conversion of HDP-(S)-HPMPA to HPMPA diphosphate observed in HepG2 cells in vitro. HDP-(S)-HPMPA retained full activity against HBV mutants resistant to lamivudine (L180M, M204V), but cross-resistance to a mutant resistant to adefovir (N236T) was detected. HDP-(S)-HPMPA is orally bioavailable and provides excellent liver exposure to the drug. Oral treatment of HBV transgenic mice with HDP-(S)-HPMPA, 15M-HDP-(S)-HPMPA, and ODE-(S)-HPMPA for 14 days reduced liver HBV DNA levels by roughly 1.5 log units, a response equivalent to that of adefovir dipivoxil.

Development of a real-time quantitative reverse transcriptase PCR assay for detection of the Friend leukemia virus load in murine plasma

Friend leukemia virus (FLV), a murine retrovirus, has been used as a model for elucidation of human immunodeficiency virus (HIV) immunopathogenesis and evaluation of anti-HIV drug effects for several decades. However, no method for direct detection of the plasma viral load has yet been reported. In this study, a TaqMan real-time quantitative reverse transcriptase PCR (qRT-PCR) assay was established for the rapid detection and quantitation of FLV. Measurement of the absolute FLV load was achieved through synthesis of a standard RNA from within the FLV envelope gene for generation of a standard curve. The assay allows quantitation over a range from 20 to 2 x 10(8) RNA copies per reaction in a two-step real-time quantitative reverse transcriptase PCR protocol. The relationships between the initially injected FLV dose and the plasma FLV load and spleen index were explored. Following this, the in vivo effects of zidovudine, adefovir dipivoxil, and entecavir on mice infected with FLV were evaluated. The results showed that the plasma FLV load was not proportional to the spleen index over the same FLV injection dosage series, although a trend was observed. When evaluated using plasma viral load, high dose (15 mg/(kg d)) adefovir dipivoxil was capable of significant inhibition of FLV replication in mice. The qRT-PCR assay described here allows specific, sensitive and direct detection of FLV and may also provide more precise measurement of FLV load.

Efficacy of cationic lipid-DNA complexes (CLDC) on hepatitis B virus in transgenic mice

Cationic lipid-DNA (non-coding) complexes (CLDC) are activators of the innate immune response that increase survival of rodents with some acute viral infections and cancers. CLDC were evaluated for their ability to impact viral DNA levels in transgenic mice carrying an infectious clone of hepatitis B virus (HBV). Mice used in the studies were diet-restricted as nursing pups from solid food, because the expression of HBV DNA in the liver was increased above background levels in some mice with this restriction. Survival surgery was performed on these mice to obtain liver biopsies from which to select animals with suitable levels of liver HBV DNA for entry into the experimental protocols. Intravenous administration of 5 microg/mouse of CLDC on days 1, 7 and 13 reduced liver HBV DNA to similar low levels achieved with the positive control, adefovir dipivoxil. In a subsequent experiment, the same treatment schedule was used to determine that the minimal effective CLDC dose was between 0.5 and 0.05 microg/mouse. Selective cytokines were increased in the livers of CLDC-treated compared to placebo-treated mice in a dose-responsive manner. CLDC were effective in reducing liver HBV DNA and could be considered for further evaluation in other hepatitis models.

Long-term inhibition of hepatitis B virus in transgenic mice by double-stranded adeno-associated virus 8-delivered short hairpin RNA

RNA interference (RNAi) was reported to block hepatitis B virus (HBV) gene expression and replication in vitro and in vivo. However, it remains a technical challenge for RNAi-based therapy to achieve long-term and complete inhibition effects in chronic HBV infection, which presumably requires more extensive and uniform transduction of the whole infected hepatocytes. To increase the in vivo transfection efficiency in liver, we used a double-stranded adeno-associated virus 8-pseudotyped vector (dsAAV2/8) to deliver shRNA. HBV transgenic mice were used as an animal model to evaluate the inhibition effects of the RNAi-based gene therapy. A single administration of dsAAV2/8 vector, carrying HBV-specific shRNA, effectively suppressed the steady level of HBV protein, mRNA and replicative DNA in liver of HBV transgenic mice, leading to up to 2-3 log(10) decrease in HBV load in the circulation. Significant HBV suppression sustained for at least 120 days after vector administration. The therapeutic effect of shRNA was target sequence dependent and did not involve activation of interferon. These results underscore the potential for developing RNAi-based therapy by dsAAV2/8 vector to treat HBV chronic infection, and possibly other persistent liver infections as well.

Antiviral effect of Chinese medicine jiaweisinisan in hepatitis B virus transgenic mice

AIM

To study the antiviral effect of Chinese medicine jiaweisinisan (JWSNS) on hepatitis B virus (HBV) infection in transgenic mice (TGM).

METHODS

Twenty two 6-8 wk old HBV TGM in the third generation were divided into TGM control group and TGM treated group randomly. The normal control group included ten normal BC 57L/6 mice at the same age. The mice in treated group were administrated with JWSNS at the concentration of 4 g/mL and the dosage of 50 g/kg per d for 30 d, while the mice in TGM control group and normal control group were administrated with normal saline at the same dosage and the same time. Polymerase chain reaction (PCR) was used to assess the contents of HBV DNA in serum of HBV TGM before and after treatments, whereas blot hybridization was utilized to measure the contents of HBV DNA in the liver of both HBV TGM and normal BC 57L/6 mice.

RESULTS

The levels of serum HBV DNA in TGM treated group were remarkably decreased after the treatment of JWSNS (7.662+/-0.78 vs 5.22+/-3.14, P < 0.05), while there was no obvious change after administration of normal saline in TGM control group (7.125+/-4.26 vs 8.932+/-5.12, P > 0.05). The OD values of HBV DNA in the livers of the mice in TGM treated group were significantly lower than those of TGM control group (0.274+/-0.096 vs 0.432+/-0.119, P < 0.01).

CONCLUSION

JWSNS exerts suppressive effects on HBV DNA in the serum and liver of TGM.

Preliminary study on the efficacy and safety of lamivudine and interferon alpha therapy in decreasing serum HBV DNA level in HBV positive transgenic mice during pregnancy

Previous studies reported that the HBV DNA level in maternal serum is an important risk factor for intrauterine infection. Two antiviral drugs, lamivudine (3TC) and interferon alpha (IFNalpha), are used extensively clinically to reduce maternal HBV DNA level, However, because of a lack of evidence on the efficacy and safety of these drugs during pregnancy, they are categorized as grade C which prevents their use during pregnancy. This study provides new data on the efficacy and safety of lamivudine and IFNalpha in HBV positive transgenic pregnant mice. In this study, transgenic mice with high titers of hepatitis B virus (HBV) were employed to study the antiviral effects of 3TC and IFNalpha during different gestation periods. The study also examined changes in several serological HBV markers, the effects of perinatal exposure to antiviral drugs on the mother and offspring, drug efficacy in reducing the level of HBV DNA in maternal blood, and the safety to both the mother and offspring. The main conclusion of the study is that a significant decrease in HBV DNA level can be obtained after treatment with lamivudine but not with IFNalpha. No adverse effects were observed in the maternal mice and the offsprings. This finding may provide a rationale for the potential use of lamivudine for the treatment of pregnant women as a safe and effective measure to reduce the level of maternal viremia.

A self-processing ribozyme cassette: utility against human papillomavirus 11 E6/E7 mRNA and hepatitis B virus

We have been developing a self-processing triple-ribozyme cassette, which consists of two cis-acting hammerhead ribozymes flanking an internal, trans-acting hammerhead ribozyme (ITRz). Here, the single ITRz was replaced by two contiguous ITRz (dITRz), and a short poly(A) tail was designed onto the 3' end of the liberated dITRz, to produce the "SNIP(AA)" cassette. Self-processing of the cassette appeared to proceed efficiently in cells: The only region of the cassette identified in cells was the liberated dITRz, with approximately 10-20% of the dITRz found within the nucleus. We tested this reagent against two therapeutically important targets, human papillomavirus 11 E6/E7 mRNA and hepatitis B virus (HBV). Library selection protocols were utilized to define accessible target sites, and ribozymes targeted to these sites were very active in vitro. Pairs of the selected ribozymes were then inserted into the SNIP(AA) cassette. SNIP(AA) constructs targeted to the E6/E7 mRNA were tested in cell culture using a cotransfection approach. Significant reductions were produced in E6/E7 target, with 80-90% reductions observed at 5 days following cotransfection. SNIP(AA) constructs targeted to HBV RNA were tested in vivo in a transgenic mouse model. SNIP(AA) constructs were packaged in liposomes, which were targeted to hepatocytes using asialofetuin, and administered ip. After 2 weeks, a >80% reduction in viral liver DNA was observed. Immunohistochemical staining for core antigen showed a similar decrease in the number of hepatocytes staining positively, compounded by a concomitant loss of residual staining intensity. These results demonstrate the in vivo utility of the self-processing SNIP(AA) cassette against HBV.

Anti-hepatitis B virus activity of ORI-9020, a novel phosphorothioate dinucleotide, in a transgenic mouse model

ORI-9020, a novel dinucleotide, evaluated in transgenic mice expressing hepatitis B virus (HBV), significantly reduced liver HBV DNA (P </= 0.001). Levels of HBeAg and HBsAg in serum and of HBcAg in liver were not affected by treatment. A minimal effective dosage was determined to be between 1.6 and 0.5 mg/kg of body weight/day, which was similar to that observed for adefovir dipivoxil.

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

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

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

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

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

Clinical potential of the acyclic nucleoside phosphonates cidofovir, adefovir, and tenofovir in treatment of DNA virus and retrovirus infections

The acyclic nucleoside phosphonates HPMPC (cidofovir), PMEA (adefovir), and PMPA (tenofovir) have proved to be effective in vitro (cell culture systems) and in vivo (animal models and clinical studies) against a wide variety of DNA virus and retrovirus infections: cidofovir against herpesvirus (herpes simplex virus types 1 and 2 varicella-zoster virus, cytomegalovirus [CMV], Epstein-Barr virus, and human herpesviruses 6, 7, and 8), polyomavirus, papillomavirus, adenovirus, and poxvirus (variola virus, cowpox virus, vaccinia virus, molluscum contagiosum virus, and orf virus) infections; adefovir against herpesvirus, hepadnavirus (human hepatitis B virus), and retrovirus (human immunodeficiency virus types 1 [HIV-1] and 2 [HIV-2], simian immunodeficiency virus, and feline immunodeficiency virus) infections; and tenofovir against both hepadnavirus and retrovirus infections. Cidofovir (Vistide) has been officially approved for the treatment of CMV retinitis in AIDS patients, tenofovir disoproxil fumarate (Viread) has been approved for the treatment of HIV infections (i.e., AIDS), and adefovir dipivoxil (Hepsera) has been approved for the treatment of chronic hepatitis B. Nephrotoxicity is the dose-limiting side effect for cidofovir (Vistide) when used intravenously (5 mg/kg); no toxic side effects have been described for adefovir dipivoxil and tenofovir disoproxil fumarate, at the approved doses (Hepsera at 10 mg orally daily and Viread at 300 mg orally daily).

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

AIM: To study the inhibitory effect of oxymatrine on HBsAg, HBeAg, and HBcAg expression in the liver tissue of HBV transgenic mice, and to further expound the mechanisms of oxymatrine anti-HBV.

METHODS: HBV transgenic mice models were established by microinjecting methods, and detected by HBV DNA integration and replication. Replicating HBV transgenic mice were divided into three groups: injected with normal saline (n = 9), 50 mg/kg (n = 8) and 100mg/kg (n = 9) oxymatrine intraperitonealy once a day for 30 d, respectively. After treatment, detection of HBsAg and HBeAg by ELISA, HBsAg and HBcAg by immunohistochemistry in the liver tissues was conducted.

RESULTS: Compared with group normal saline, HBsAg content in 50 mg/kg and 100 mg/kg oxymatrine decreased, but there was no statistic significance (F = 1.29, P>0.05). Compared with normal saline group, HBeAg content in 50 mg/kg and 100 mg/kg oxymatrine groups obviously decreased(F = 9.09, P < 0.01), but there was no obvious significance between 50 mg/kg and 100 mg/kg oxymatrine groups (F = 1.58, P> 0.05). The number of HbsAg-positive cells in the normal saline group, 50 mg/kg and 100 mg/kg oxymatrine had no changes in the liver tissues (x² = 1.61, P> 0.05). The number of HBcAg-positive cells in the liver tissues was significantly lower in the group of 100 mg/kg oxymatrine than that in the group of normal saline (x²= 4.73, P < 0.05), but the number between normal saline group and 50 mg/kg oxymatrine group, and between the groups of 50 mg/kg and 100 mg/kg oxymatrine had no obvious significance.

CONCLUSION: There is an inhibitory effect of oxymatrine on expression of hepatitis B virus in HBV transgenic mice.

Characterization of antiviral activity of entecavir in transgenic mice expressing hepatitis B virus

Entecavir (ETV), a cyclopentyl guanosine nucleoside analog, was evaluated in transgenic mice expressing hepatitis B virus (HBV). ETV administered orally once daily for 10 days at a dosage of 3.2mg/kg significantly (P<or=0.001) reduced liver HBV DNA in female mice from 5.9 to <0.82 pg of HBV DNA per microg of cellular DNA, and from 8.3 to <1.1 pg/microg in male mice. To compare the efficacy of ETV with other compounds previously evaluated in this model and with ETV activities in other animal models, the efficacy of serial one-half log dilutions of ETV were evaluated in both male and female mice to determine the minimal effective dose. End-point titration experiments resulted in a statistically significant HBV DNA reduction in the liver at concentrations of 0.032 and 0.1mg/kg per day in female and male mice, respectively. Viral liver RNA, and serum e (HBeAg), serum surface (HBsAg), and liver core antigens (HBcAg) were not affected by ETV treatment presumably because the antiviral target was viral polymerase activity and the HBV produced from the transgene was not capable of secondary rounds of infection in the mouse. ETV was well tolerated and no morbidity or mortality was observed during the 10-day study. Similar to other animal models, ETV displayed potent anti-HBV activity in this transgenic mouse model.

Distribution and anti-HBV effects of antisense oligodeoxynucleotides conjugated to galactosylated poly-L-lysine

AIM

To describe distribution of the phosphorothioated antisense oligodeoxynucleotides (PS-asODNs) conjugated to galactosylated poly-L-lysine (Gal-PLL) in mice, and to observe their effects on expression of HBV gene in the 2.2.15 cells and transgenic mice.

METHODS

According to the result of direct sequencing of PCR amplified products, a 16 mer phosphorothioate analogue of the antisense oligodeoxynucleotides (PS-asODNs) directed against the HBV U(5)-like region was conjugated to the hepatotropic Gal-PLL molecules. Its distribution was demonstrated using asODNs labeled with (32)P at the 5' terminus with a T4-polynucleotide Kinase. Its inhibition effect on HBV expression was observed in the transfected 2.2.15 cells and transgenic mice.

RESULTS

The Gal-PLL and asODNs could form stable complex at a molar ratio of 2:1. As shown in the HBV-transfected 2.2.15 cells, the inhibition effects of asODNs alone and asODNs conjugated to Gal-PLL, at 10 micromol/L for both, on HBsAg and HBeAg production were different,the former being 70 % and 58 %, respectively, and the latter being 96 % and 82 %, respectively. A more pronounced reduction was also observed in viral DNA load in the culture supernatant for the test with Gal-PLL-asODNs. Among many mouse organs, livers retained more asODNs molecules after administration. The preferential concentration in liver was found to be 52.14 % for Gal-PLL-asODNs, as high as 2.38-fold of that for asODNs (21.9 %). Both elements decreased gradually in liver, with 2.9 % of the former, 5.99 % of the latter retained 24 hours after the administration. The injection interval, therefore, was recommended to be 24 hours. In the transgenic mice, serum HBsAg decreased significantly (P<0.01) at the 12th day after administrating Gal-PLL- asODNs, the serum HBV DNA turned negative in 4 of the 6 mice.

CONCLUSION

Antisense oligodeoxynucleotides conjugated to Gal-PLL can be concentrated in liver and intaked by hepatocytic cells. This may result in specific inhibition of expression and replication of HBV in vitro and in vivo.

Adefovir Dipivoxil

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