Biomedical subjects

John L Gerin

Publications and source records attributed to John L Gerin.

18 recordsLinked to original sources

PubMed2006

Native hepatitis B virions and capsids visualized by electron cryomicroscopy.

Hepatitis B virus (HBV) infects more than 350 million people, of which one million will die every year. The infectious virion is an enveloped capsid containing the viral polymerase and double-stranded DNA genome. The structure of the capsid assembled in vitro from expressed core protein has been studied intensively. However, little is known about the structure and assembly of native capsids present in infected cells, and even less is known about the structure of mature virions. We used electron cryomicroscopy (cryo-EM) and image analysis to examine HBV virions (Dane particles) isolated from patient serum and capsids positive and negative for HBV DNA isolated from the livers of transgenic mice. Both types of capsids assembled as icosahedral particles indistinguishable from previous image reconstructions of capsids. Likewise, the virions contained capsids with either T = 3 or T = 4 icosahedral symmetry. Projections extending from the lipid envelope were attributed to surface glycoproteins. Their packing was unexpectedly nonicosahedral but conformed to an ordered lattice. These structural features distinguish HBV from other enveloped viruses.

Animals↗

PubMed2006

Genetic changes in hepatitis delta virus from acutely and chronically infected woodchucks.

A woodchuck-derived hepatitis delta virus (HDV) inoculum was created by transfection of a genotype I HDV cDNA clone directly into the liver of a woodchuck that was chronically infected with woodchuck hepatitis virus. All woodchucks receiving this inoculum became positive for HDV RNA in serum, and 67% became chronically infected, similar to the rate of chronic HDV infection in humans. Analysis of HDV sequences obtained at 73 weeks postinfection indicated that changes had occurred at a rate of 0.5% per year; many of these modifications were consistent with editing by host RNA adenosine deaminase. The appearance of sequence changes, which were not evenly distributed on the genome, was correlated with the course of HDV infection. A limited number of modifications occurred in the consensus sequence of the viral genome that altered the sequence of the hepatitis delta antigen (HDAg). All chronically infected animals examined exhibited these changes 73 weeks following infection, but at earlier times, only one of the HDV carriers exhibited consensus sequence substitutions. On the other hand, sequence modifications in animals that eventually recovered from HDV infection were apparent after 27 weeks. The data are consistent with a model in which HDV sequence changes are selected by host immune responses. Chronic HDV infection in woodchucks may result from a delayed and weak immune response that is limited to a small number of epitopes on HDAg.

Acute Disease↗

PubMed2005

Clevudine inhibits hepatitis delta virus viremia: a pilot study of chronically infected woodchucks.

In a small controlled study, clevudine, a potent inhibitor of hepadnaviruses, including hepatitis B virus and woodchuck hepatitis virus, suppressed hepatitis delta virus (HDV) viremia in chronically infected woodchucks. Suppression was correlated with the marked reduction of woodchuck hepatitis virus surface antigen in individual animals, consistent with the concept that repression of surface antigen expression may be a useful antiviral strategy for HDV.

Animals↗

PubMed2005

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

Tenofovir disoproxil fumarate (TDF) is a nucleotide analogue approved for treatment of human immunodeficiency virus (HIV) infection. TDF also has been shown in vitro to inhibit replication of wild-type hepatitis B virus (HBV) and lamivudine-resistant HBV mutants and to inhibit lamivudine-resistant HBV in patients and HBV in patients coinfected with the HIV. Data on the in vivo efficacy of TDF against wild-type virus in non-HIV-coinfected or lamivudine-naïve chronic HBV-infected patients are lacking in the published literature. The antiviral effect of oral administration of TDF against chronic woodchuck hepatitis virus (WHV) infection, an established and predictive animal model for antiviral therapy, was evaluated in a placebo-controlled, dose-ranging study (doses, 0.5 to 15.0 mg/kg of body weight/day). Four weeks of once-daily treatment with TDF doses of 0.5, 1.5, or 5.0 mg/kg/day reduced serum WHV viremia significantly (0.2 to 1.5 log reduction from pretreatment level). No effects on the levels of anti-WHV core and anti-WHV surface antibodies in serum or on the concentrations of WHV RNA or WHV antigens in the liver of treated woodchucks were observed. Individual TDF-treated woodchucks demonstrated transient declines in WHV surface antigen serum antigenemia and, characteristically, these woodchucks also had transient declines in serum WHV viremia, intrahepatic WHV replication, and hepatic expression of WHV antigens. No evidence of toxicity was observed in any of the TDF-treated woodchucks. Following drug withdrawal there was prompt recrudescence of WHV viremia to pretreatment levels. It was concluded that oral administration of TDF for 4 weeks was safe and effective in the woodchuck model of chronic HBV infection.

Adenine↗

PubMed2004

Integration of woodchuck hepatitis and N-myc rearrangement determine size and histologic grade of hepatic tumors.

Integrations of woodchuck hepatitis virus (WHV) DNA and rearrangements of the N-myc 2 gene have been detected frequently in hepatocellular carcinoma (HCC) of Eastern woodchucks (Marmota monax) chronically infected with WHV. Fifty-five hepatocellular neoplasms and matched nontumor hepatic tissue specimens obtained postmortem from 13 chronic WHV carriers were analyzed and the frequency of WHV DNA integrations and of N-myc rearrangements compared in tumors of different size and histologic grade. Four small tumor nodules were classified histologically as adenomas and integrated sequences of WHV DNA were detected in two of the four tumor nodules. In one of the two nodules, there was evidence of N-myc rearrangement. Fifty-one neoplasms were classified as HCC. Seven were grade 1 HCCs. WHV DNA integrations were demonstrated in 43% but none had N-myc rearrangements. Twenty grade 2 HCCs had WHV DNA integrations in 80% and in 38% N-myc rearrangements were present. Twenty-four grade 3 HCCs had integrations of WHV DNA in 79% and N-myc rearrangements in 74%. In two other grade 3 HCCs, rearrangements of N-myc were detected in the absence of WHV DNA integrations. The 12 largest tumors in the series all were grade 2 or 3 HCCs, and in 83%, both WHV DNA integrations and N-myc rearrangements were demonstrated. In conclusion, molecular changes observed in this study suggest a progression of genetic alterations providing either a significant proliferative stimulation and/or a growth advantage in hepatocarcinogenesis of woodchucks with chronic WHV infection.

Animals↗

PubMed2004

Kinetics of viremia and acute liver injury in relation to outcome of neonatal woodchuck hepatitis virus infection.

The kinetics of serum viral responses and acute liver injury were studied during neonatal woodchuck hepatitis virus (WHV) infection in relation to the chronic or resolved outcome. The mean concentrations of serum WHV DNA and surface antigen were significantly higher by week 10 post infection in chronic infections compared to resolving infections, and diverged even further by the time of peak viral load development in serum (week 12). After week 12, these viral markers were detected less frequently with time and at lower concentrations in the resolved outcome. In both outcomes, mean serum activities of hepatic enzymes became increased significantly above baseline by weeks 10-12, peaked at week 14, and normalized by weeks 20-22, thus indicating transient acute liver injury. The increasing liver injury responses were comparable between outcomes at week 12, when serum viral load was markedly higher in the developing chronic infections. This suggested a deficiency in early non-cytolytic control of infection in the chronic outcome. At week 14, liver injury was significantly greater in the resolved outcome and associated with higher mean Fas ligand (FasL) and perforin messenger RNAs (mRNAs) in liver compared to the chronic outcome. This indicated greater immune-mediated killing of infected hepatocytes during resolution. Thus, chronicity as an outcome of neonatal WHV infection develops relatively early during the acute phase of infection due to reduced immune-mediated clearance of infected hepatocytes by both cytolytic and non-cytolytic processes.

Animals↗

PubMed2004

Cross-species hybridization: characterization of gene expression in woodchuck liver using human membrane arrays.

Total RNA from normal adult woodchucks was analyzed using membrane arrays containing human cDNA clones, and the gene expression patterns were compared to human liver. Various hybridization and wash conditions were examined. In both the woodchuck and human livers, 352 genes were identified as highly expressed (Z-scores > or =1.96). These genes represented numerous liver functions: transcription, RNA processing, signal transduction, protein synthesis and degradation, as well as enzymes. Several genes were selected and expression was verified by Northern blots for woodchuck liver. There were no false positives but 29 genes were identified as false negatives, expressed only in human liver. Possible reasons for these false negatives were the length and percentage of homology between the two species, differences in the distribution and types of mismatches, and the sequence region spotted on the array. These were assessed by examining expression of the transferrin gene in both species. A 200-fold range of RNA concentration (0.1-20 microg total RNA) was also examined and the optimal RNA concentration was determined to be 5 microg. Membranes were capable of being hybridized and reprobed at least five times. The study demonstrates that cross-species hybridization is a valid method for identifying gene expression in woodchuck liver.

Animals↗

PubMed2004

Suppression of lamivudine-resistant B-domain mutants by adefovir dipivoxil in the woodchuck hepatitis virus model.

Adult woodchucks (Marmota monax) chronically infected with woodchuck hepatitis virus (WHV) were treated orally with lamivudine (15 mg/kg per day) for 57 weeks. After 20 weeks of treatment a 2-3 log reduction in serum WHV DNA was detected. Serum titers of WHV then increased gradually, in the presence of lamivudine treatment, reaching pre-treatment values by week 40. Viral recrudescence was associated with development of mutations in the B domain of the WHV polymerase gene. Mutations observed in the highly conserved FLLA motif of the B domain were L564V, L565M, and A566T, with A566T being the most frequently observed. Beginning on week 57 of lamivudine treatment, one group (n = 3) was treated orally with adefovir dipivoxil at a dose of 15 mg/kg per day plus lamivudine, and a second group (n = 3) was treated with H2O placebo plus lamivudine. In woodchucks treated with adefovir dipivoxil, two had the A566T mutation, and one had both A566T and L565V. In the group maintained on lamivudine monotherapy, A566T alone was present in one animal, another carried both A566T and L565V, and in the third, no B-domain mutations were detected. There was a 4.5 log reduction in serum WHV DNA after 12 weeks of treatment with the adefovir/lamivudine combination, while in the lamivudine monotherapy controls, WHV DNA decreased by only 0.83 log (P > 0.001). A slight recurrence in serum titers of WHV DNA was observed one week after withdrawal of adefovir treatment but no further increase in viral load was observed during the remainder of the 12-week post-treatment follow-up period. The results demonstrate that supplemental adefovir dipivoxil treatment is effective in suppressing replication of lamivudine-resistant B-domain mutants in the woodchuck model of hepatitis B virus infection.

Adenine↗

PubMed2004

Hepatocellular carcinoma in the woodchuck model of hepatitis B virus infection.

The Eastern woodchuck ( Marmota monax ) harbors a DNA virus (Woodchuck hepatitis virus [WHV]) that is similar in structure and replicative life cycle to the human hepatitis B virus (HBV). Like HBV, WHV infects the liver and can cause acute and chronic hepatitis. Furthermore, chronic WHV infection in woodchucks usually leads to development of hepatocellular carcinoma (HCC) within the first 2-4 years of life. The woodchuck model has been important in the preclinical evaluation of safety and efficacy of the antiviral drugs now in use for treatment of HBV infection and continues to serve as an important, predictive model for innovative forms of therapy of hepatitis B using antiviral nucleosides and immune response modifiers alone or in combination. Almost all woodchucks that become chronic WHV carriers after experimental neonatal inoculation develop HCC with a median HCC-free survival of 24 months and a median life expectancy of 30-32 months. The woodchuck model of viral-induced HCC has been used effectively for the development of new imaging agents for enhancement of detection of hepatic neoplasms by ultrasound and magnetic resonance imaging. The chemoprevention of HCC using long-term antiviral nucleoside therapy has been shown in the woodchuck, and "proof of principal" has been established for some of the innovative, molecular methods for treatment of HCC. The model is available for fundamental investigations of the viral and molecular mechanisms responsible for hepatocarcinogenesis and should have substantial value for future development of innovative methods for chemoprevention and gene therapy of human HCC.

Animals↗

PubMed2004

Clevudine therapy with vaccine inhibits progression of chronic hepatitis and delays onset of hepatocellular carcinoma in chronic woodchuck hepatitis virus infection.

We examined a rational approach to therapy of chronic hepatitis B virus (HBV) infection that utilized the reduction of viral load combined with appropriately timed immune modulation/stimulation. In a placebo-controlled study, chronic woodchuck hepatitis virus (WHV) carrier woodchucks received clevudine (L-FMAU), previously shown to have especially potent and sustained antiviral activity in woodchucks, for 32 weeks followed by WHV surface antigen (WHsAg) alum-adjuvanted vaccine at 32, 36, 40 and 48 weeks. Clevudine induced significant reductions in viraemia, surface antigenaemia, hepatic WHV nucleic acids, and hepatic core and surface antigens. Viral replication markers remained markedly suppressed in 75% of the clevudine-treated woodchucks following drug withdrawal, but remained at high levels in the vaccine monotherapy and placebo groups. Combination drug and vaccine therapy had benefits based on sustained reduction of viraemia, antigenaemia, and hepatic WHV DNA and RNA; inhibition of progression of chronic hepatitis; reduced frequency of chronic liver injury; and delayed onset of hepatocellular carcinoma (HCC). Combination therapy contributed to prevention of HCC in up to 38% of treated carriers, although the growth rate of established HCC was not affected. This study demonstrates enhanced benefits of combination chemo-immunotherapy against viral load and disease progression in chronic hepadnaviral infection, and provides a platform for further development of such treatment regimens.

Animals↗

PubMed2003

Role of type 1 versus type 2 immune responses in liver during the onset of chronic woodchuck hepatitis virus infection.

Immune response messenger RNAs (mRNA) were compared in liver during self-limited (resolved) and chronic neonatal woodchuck hepatitis virus (WHV) infection. At week 14 postinfection (mid-acute phase), mRNAs for leukocyte markers (CD3, CD4, CD8), type 1 cytokines and related transcription factors (IFN-gamma, TNF-alpha, STAT4, T-bet), and IL-10 were increased in livers from resolving infections, but mRNAs of other type 1 (IL-2) and type 2 (IL-4, STAT6, and GATA3 markers remained at baseline levels. Increased coexpression of IFN-gamma and TNF-alpha mRNAs correlated in most cases with lower levels of intrahepatic WHV covalently closed circular DNA (cccDNA). At the same time point postinfection, livers from woodchucks that eventually progressed to chronic infection had baseline or slightly elevated levels of CD and type 1 mRNAs, which were significantly lower (or elevated less frequently) compared with resolving woodchucks. Earlier, at week 8, there were no differences between the two outcome settings. During these early time points and at a later stage in chronic infection (15 months), type 2 mRNAs in carrier liver remained at baseline levels or, when elevated, were never in excess of those in resolving woodchucks. In conclusion, the onset and maintenance of neonatal chronic WHV infection are not associated with antagonistic type 2 immunoregulation of type 1 responses in liver. Accordingly, chronicity develops in association with a primary deficiency in the intrahepatic CD responses, especially involving CD8(+) T lymphocytes, and in both extracellular (cytokine) and intracellular (transcriptional) type 1 response mediators. This has relevant implications for future treatment of chronic hepatitis B virus (HBV) infection in humans.

Animals↗

PubMed2003

Global screening for human viral pathogens.

We propose a system for continuing surveillance of viral pathogens circulating in large human populations. We base this system on the physical isolation of viruses from large pooled samples of human serum and plasma (e.g., discarded specimens from diagnostic laboratories), followed by shotgun sequencing of the resulting genomes. The technology for concentrating virions from 100-L volumes was developed previously at Oak Ridge National Laboratory, and the means for purifying and concentrating virions from volumes in microliters have been developed recently. At the same time, marine virologists have developed efficient methods for concentrating, amplifying, and sequencing complex viral mixtures obtained from the ocean. Given this existing technology base, we believe an integrated, automated, and contained system for surveillance of the human "virome" can be implemented within 1 to 2 years. Such a system could monitor the levels of known viruses in human populations, rapidly detect outbreaks, and systematically discover novel or variant human viruses.

Automation↗

PubMed2002

Real-time polymerase chain reaction assays for leukocyte CD and cytokine mRNAs of the Eastern woodchuck (Marmota monax).

Real-time polymerase chain reaction (PCR) assays were developed for woodchuck leukocyte cluster of differentiation (CD) and cytokine mRNA expression. Plasmid DNA standards of each marker (CD3, CD4, CD8, IL-2, IFN-gamma, TNF-alpha, IL-4, IL-10), and RNA standards from mitogen-stimulated woodchuck peripheral blood mononuclear cells (PBMCs) were used to validate and optimize the assays for TaqMan 7700 and iCycler PCR instruments. The complementary DNAs (cDNAs) produced by reverse transcription (RT) of RNA were quantified by real-time PCR against the plasmid DNA standards (6-8 log range) with detection of as few as 10-50 copies of amplicon cDNA per reaction. Analysis of unstimulated and concanavalin A-stimulated woodchuck PBMC demonstrated increased CD and cytokine mRNA expression following mitogenic activation. A liver sample from a woodchuck hepatitis virus (WHV) infected woodchuck with histologically confirmed acute hepatitis had increased intrahepatic CD and cytokine mRNAs compared to liver from an uninfected control woodchuck. The real-time PCR assays were highly specific for the woodchuck markers in PBMC and liver samples and were equally applicable for use in alternate real-time PCR instrumentation. These assays will enable the high-throughput analyses of mRNA markers during WHV infection, and thereby facilitate continued modelling of the immunopathogenesis and immunotherapy of human hepatitis B virus (HBV) infection.

Animals↗

PubMed2002

Mutations in the conserved woodchuck hepatitis virus polymerase FLLA and YMDD regions conferring resistance to lamivudine.

During more than 104 weeks of treatment with lamivudine (3TC) in chronic woodchuck hepatitis virus (WHV) carrier woodchucks, viral recrudescence occurred. Analysis of WHV DNA polymerase from woodchuck serum samples by PCR followed by DNA sequencing demonstrated that all samples were wild type at the conserved YMDD motif in domain C. Four of the six 3TC-treated woodchucks showed a mixture of the wild-type Ala (GCT) and the mutant Thr (ACT) at the conserved amino acid residue 566 (FLLA) in domain B of the WHV polymerase region. The appearance of the A566T mutation was temporally associated with viral recrudescence. This change is analogous with the amino acid 181 (FLLA) in HBV where 3TC selects for a change from Ala to Thr in humans. In the woodchuck, the Ala to Thr change in the polymerase gene results in a mutation of the WHV surface protein (amino acid 377) from Trp (TGG) to an opal codon (TGA), which may prematurely terminates the polypeptide. Three WHV molecular infectious clones were constructed to study this mutation in greater detail in vitro: A566T, analogous to A181T in HBV; M589V, analogous to the M204V in HBV; and the double mutant A566T/M589V, analogous to A181T/M204V in HBV. These mutants exhibited drug-sensitivity and replication profiles that paralleled those reported for analogous HBV variants. In transfected Huh7 cells, WHV containing the M589V mutation conferred at least 100-fold increased resistance to 3TC, but replicated approximately 5-fold less efficiently than wild-type virus as judged by both extracellular virus production and intracellular DNA replicative forms. In contrast, A566T mutant was approximately 10-fold more resistant to 3TC, replicated intracellularly as well as wild type, but produced 10-fold lower levels of virions than wild type. These findings are consistent with the observation that the A566T mutation alters the overlapping WHV surface antigen reading frame. WHV carrying mutations in the conserved YMDD motif, while not directly selected during lamivudine therapy in WHV carrier woodchucks, are replication competent in cell culture indicating the potential for their emergence in treated animals. These results further illustrate the utility of the WHV/woodchuck model to studies of HBV-drug resistance.

Amino Acid Sequence↗

PubMed2002

Immunization with surface antigen vaccine alone and after treatment with 1-(2-fluoro-5-methyl-beta-L-arabinofuranosyl)-uracil (L-FMAU) breaks humoral and cell-mediated immune tolerance in chronic woodchuck hepatitis virus infection.

Woodchucks chronically infected with the woodchuck hepatitis virus (WHV) were treated with the antiviral drug 1-(2-fluoro-5-methyl-beta-L-arabinofuranosyl)-uracil (L-FMAU) or placebo for 32 weeks. Half the woodchucks in each group then received four injections of surface antigen vaccine during the next 16 weeks. Vaccination alone elicited a low-level antibody response to surface antigen in most carriers but did not affect serum WHV DNA and surface antigen. Carriers treated first with L-FMAU to reduce serum WHV DNA and surface antigen and then vaccinated had a similar low-level antibody response to surface antigen. Following vaccinations, cell-mediated immunity to surface antigen was demonstrated in both groups, independent of serum viral and antigen load, but was significantly enhanced in woodchucks treated with L-FMAU and was broadened to include other viral antigens (core, e, and x antigens and selected core peptides). Cell-mediated immunity and antibody responses to surface antigen were observed after drug discontinuation in half of the carriers that received L-FMAU alone. Surface antigen vaccine alone or in combination with drug broke humoral and cell-mediated immune tolerance in chronic WHV infection, but the combination with drug was more effective. This suggested that a high viral and antigen load in carriers is important in maintaining immunologic tolerance during chronicity. The humoral and cellular immunity associated with the combination of L-FMAU and vaccine resembled that observed in self-limited WHV infection. Such combination therapy represents a potentially useful approach to the control of chronic hepatitis B virus infection in humans.

Animals↗

PubMed2002

Deficiencies in the acute-phase cell-mediated immune response to viral antigens are associated with development of chronic woodchuck hepatitis virus infection following neonatal inoculation.

In vitro proliferation of peripheral blood mononuclear cells was used to measure virus-specific cell-mediated immunity (vCMI) following neonatal woodchuck hepatitis virus (WHV) infection. Fifteen neonates were inoculated with the W8 strain of WHV. In 11, infection was resolved, and 4 became chronic carriers. Nineteen neonates were inoculated with the W7 strain and all became chronic carriers. Seven age-matched uninfected woodchucks served as controls. Virologic and vCMI profiles among the W8 and W7 infections were compared and related to the outcome of infection. Resolving woodchucks had robust, acute-phase vCMI to WHV antigens (core, surface, and x) and to several nonoverlapping core peptides. The acute-phase vCMI was associated temporally with the clearance of viral DNA and of surface antigen from serum at 14 to 22 weeks postinfection. In contrast, in approximately half of the W8 and W7 infections that progressed to chronicity, no significant acute-phase vCMI was detected. In the remaining carriers, acute-phase vCMI was observed, but it was less frequent and incomplete compared to that of resolved woodchucks. Serum viral load developed less rapidly in those carriers that had evidence of acute-phase vCMI, but it was still increased compared to that of resolving woodchucks. Thus, vigorous and multispecific acute-phase vCMI was associated with resolution of neonatal WHV infection. Absent or incomplete acute-phase vCMI was associated with the progression to chronic infection. By analogy, these results suggest that the onset of chronic hepatitis B virus (HBV) infection in humans may be associated with deficiencies in the primary T-cell response to acute HBV infection.

Acute Disease↗

PubMed2002

Immunogenic effects of woodchuck hepatitis virus surface antigen vaccine in combination with antiviral therapy: breaking of humoral and cellular immune tolerance in chronic woodchuck hepatitis virus infection.

OBJECTIVE: A rational treatment strategy for chronic hepatitis B virus (HBV) infection might involve the modulation of immunity after the reduction of viremia and antigenemia. This strategy was tested in woodchucks chronically infected with the woodchuck hepatitis virus (WHV) by combining antiviral treatment with 1-(2-fluoro-5-methyl-beta-L-arabinofuranosyl)-uracil (L-FMAU) and therapeutic vaccination with WHV surface antigen (WHsAg). METHODS: Chronic WHV carriers were treated with L-FMAU or placebo for 32 weeks. Half the woodchucks in each group then received four injections of a conventional WHsAg vaccine during the next 16 weeks. RESULTS: Vaccination alone elicited low-level antibody to WHsAg (anti-WHs) in most carriers but did not affect serum WHV DNA, WHsAg or liver enzyme responses. Carriers treated first with L-FMAU to reduce WHV DNA and WHsAg and then vaccinated developed similar low-level anti-WHs and normalized liver enzymes. Following vaccinations, WHsAg-specific cell-mediated immunity (CMI) was demonstrated in both groups, but was significantly enhanced in carriers treated with L-FMAU, and was broadened to include WHV core antigen (WHcAg) and selected peptide epitopes of WHcAg and WHsAg. Anti-WHs and associated CMI to WHcAg and WHsAg were observed after drug discontinuation in half of the carriers that received L-FMAU alone. CONCLUSIONS: Vaccination with WHsAg following treatment with L-FMAU disrupted virus-specific humoral and cell-mediated immune tolerance in chronic WHV infection and enhanced the immune response profiles beyond those seen with monotherapies alone. The combination therapy resulted in immune response profiles that resembled those observed during resolution of WHV infection. The results in woodchucks demonstrate the feasibility of using such a combination therapy for the control of chronic HBV infection in humans.

Animals↗

PubMed2002

Viral pharmacodynamic model for (-)-beta-2',3'-dideoxy-5-fluoro-3'-thiacytidine (emtricitabine) in chronically infected woodchucks.

There is a need for adequate models of virus depletion in animals and humans as a function of drug dose in order to plan starting dose regimens in the clinic for new antiretroviral nucleoside agents. An indirect response pharmacodynamic model was fitted to link the plasma pharmacokinetics from a 28 day treatment with the nucleoside reverse transcription inhibitor emtricitabine [(-)-FTC], with the resulting virus depletion and recovery profiles in woodchucks chronically infected with woodchuck hepatitis B virus. In this approach it is assumed that the virus is eliminated from serum in a first order fashion and that the fraction of serum virus load produced per day is inhibited by the accumulation of nucleoside triphosphate in a manner that could be described using a Hill equation. Nadir virus load values were inversely related to pretreatment virus load levels within each dose group. A median inhibitory concentration value of 1.5 microM for (-)-FTC triphosphate, previously measured against the isolated viral polymerase of woodchuck hepatitis, was used in model fitting. The fitted value for concentration exponent eta of 3.46 indicated a greater than linear sensitivity of virus inhibition with dose. Since the post-treatment virus rebound was much greater than predictions of an initial model, a dose-dependent rebound factor was incorporated in the final model. The rebound factor was maximal at the end of (-)-FTC treatment and decayed mono-exponentially with a rate constant Kreb of 0.11/day. The model inferred decay half-life of (-)-FTC triphosphate in the apparent 'effect compartment' of the model was similar to the half-life value previously estimated for human hepatitis B virus-infected hepatocytes. The model described adequately the virus depletion and recovery profiles for the dose range tested and could be adapted for the selection of starting doses for future animal and human studies with emtricitabine and other nucleoside analogues in development.

Animals↗