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

Combining Neratinib with CDK4/6, mTOR, and MEK Inhibitors in Models of HER2-positive Cancer

PURPOSE

Neratinib is an irreversible, pan-HER tyrosine kinase inhibitor that is FDA approved for HER2-overexpressing/amplified (HER2+) breast cancer. In this preclinical study, we explored the efficacy of neratinib in combination with inhibitors of downstream signaling in HER2+ cancers in vitro and in vivo.

EXPERIMENTAL DESIGN

Cell viability, colony formation assays, and Western blotting were used to determine the effect of neratinib in vitro. In vivo efficacy was assessed with patient-derived xenografts (PDX): two breast, two colorectal, and one esophageal cancer (with HER2 mutations). Four PDXs were derived from patients who received previous HER2-targeted therapy. Proteomics were assessed through reverse phase protein arrays and network-level adaptive responses were assessed through Target Score algorithm.

RESULTS

In HER2+ breast cancer cells, neratinib was synergistic with multiple agents, including mTOR inhibitors everolimus and sapanisertib, MEK inhibitor trametinib, CDK4/6 inhibitor palbociclib, and PI3Kα inhibitor alpelisib. We tested efficacy of neratinib with everolimus, trametinib, or palbociclib in five HER2+ PDXs. Neratinib combined with everolimus or trametinib led to a 100% increase in median event-free survival (EFS; tumor doubling time) in 25% (1/4) and 60% (3/5) of models, respectively, while neratinib with palbociclib increased EFS in all five models. Network analysis of adaptive responses demonstrated upregulation of EGFR and HER2 signaling in response to CDK4/6, mTOR, and MEK inhibition, possibly providing an explanation for the observed synergies with neratinib.

CONCLUSIONS

Taken together, our results provide strong preclinical evidence for combining neratinib with CDK4/6, mTOR, and MEK inhibitors for the treatment of HER2+ cancer.

Efficacy and cost-effectiveness of antiviral regimens for entecavir-resistant hepatitis B: A systematic review and network meta-analysis

BACKGROUND

Chronic hepatitis B (CHB) patients who had exposed to lamivudine (LAM) and telbivudine (LdT) had high risk of developing entecavir (ETV)-resistance after long-term treatment. We aimed to conduct a systematic review and a network meta-analysis on the efficacy and cost-effectiveness on antiviral regimens in CHB patients with ETV-resistance.

DATA SOURCES

We searched PubMed, EMBASE and Web of Science for studies on nucleos(t)ide analogues (NAs) treatment [including tenofovir disoproxil fumarate (TDF)-based rescue therapies, adefovir (ADV)-based rescue therapies and double-dose ETV therapy] in CHB patients with ETV-resistance. The network meta-analysis was conducted for 1-year complete virological response (CVR) and biological response (BR) rates using GeMTC and ADDIS. A cost-effective analysis was conducted to select an economic and effective treatment regimen based on the 1-year CVR rate.

RESULTS

A total of 6 studies were finally included in this analysis. The antiviral efficacy was estimated. On network meta-analysis, the 1-year CVR rate in ETV-TDF [odds ratio (OR)  = 22.30; 95 % confidence interval (CI): 2.78-241.93], LAM-TDF (OR  = 70.67; 95 % CI: 5.16-1307.45) and TDF (OR  = 16.90; 95 % CI: 2.28-186.30) groups were significantly higher than that in the ETV double-dose group; the 1-year CVR rate in the LAM-TDF group (OR  = 14.82; 95 % CI: 1.03-220.31) was significantly higher than that in the LAM/LdT-ADV group. The 1-year BR rate of ETV-TDF (OR = 28.68; 95 % CI: 1.70-1505.08) and TDF (OR = 21.79; 95 % CI: 1.43-1070.09) therapies were significantly higher than that of ETV double-dose therapy. TDF-based therapies had the highest possibility to achieve the CVR and BR at 1 year, in which LAM-TDF combined therapy was the most effective regimen. The ratio of cost/effectiveness for 1-year treatment was 8 526, 17 649, 20 651 Yuan in the TDF group, TDF-ETV group, and ETV-ADV group, respectively.

CONCLUSIONS

TDF-based combined therapies such as ETV-TDF and LAM-TDF therapies were the first-line treatment if financial condition is allowed.

Synergistic cytotoxic activity of cannabinoids from cannabis sativa against cutaneous T-cell lymphoma (CTCL) in-vitro and ex-vivo

Cannabis sativa produces hundreds of phytocannabinoids and terpenes. Mycosis fungoides (MF) is the most common type of cutaneous T-cell lymphoma (CTCL), characterized by patches, plaques and tumors. Sézary is a leukemic stage of CTCL presenting with erythroderma and the presence of neoplastic Sézary T-cells in peripheral blood. This study aimed to identify active compounds from whole cannabis extracts and their synergistic mixtures, and to assess respective cytotoxic activity against CTCL cells. Ethanol extracts of C. sativa were analyzed by high-performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GC/MS). Cytotoxic activity was determined using the XTT assay on My-La and HuT-78 cell lines as well as peripheral blood lymphocytes from Sézary patients (SPBL). Annexin V assay and fluorescence-activated cell sorting (FACS) were used to determine apoptosis and cell cycle. RNA sequencing and quantitative PCR were used to determine gene expression. Active cannabis compounds presenting high cytotoxic activity on My-La and HuT-78 cell lines were identified in crude extract fractions designated S4 and S5, and their synergistic mixture was specified. This mixture induced cell cycle arrest and cell apoptosis; a relatively selective apoptosis was also recorded on the malignant CD4⁺CD26^- SPBL cells. Significant cytotoxic activity of the corresponding mixture of pure phytocannabinoids further verified genuine interaction between S4 and S5. The gene expression profile was distinct in My-La and HuT-78 cells treated with the S4 and S5 synergistic mixture. We suggest that specifying formulations of synergistic active cannabis compounds and unraveling their modes of action may lead to new cannabis-based therapies.

Identification of Synergistic Interaction Between Cannabis-Derived Compounds for Cytotoxic Activity in Colorectal Cancer Cell Lines and Colon Polyps That Induces Apoptosis-Related Cell Death and Distinct Gene Expression

Introduction: Colorectal cancer remains the third most common cancer diagnosis and fourth leading cause of cancer-related mortality worldwide. Purified cannabinoids have been reported to prevent proliferation, metastasis, and induce apoptosis in a variety of cancer cell types. However, the active compounds from Cannabis sativa flowers and their interactions remain elusive.

Research Aim: This study was aimed to specify the cytotoxic effect of C. sativa-derived extracts on colon cancer cells and adenomatous polyps by identification of active compound(s) and characterization of their interaction.

Materials and Methods: Ethanol extracts of C. sativa were analyzed by high-performance liquid chromatography and gas chromatograph/mass spectrometry and their cytotoxic activity was determined using alamarBlue-based assay (Resazurin) and tetrazolium dye-based assay (XTT) on cancer and normal colon cell lines and on dysplastic adenomatous polyp cells. Annexin V Assay and fluorescence-activated cell sorting (FACS) were used to determine apoptosis and cell cycle, and RNA sequencing was used to determine gene expression.

Results: The unheated cannabis extracts (C2F), fraction 7 (F7), and fraction 3 (F3) had cytotoxic activity on colon cancer cells, but reduced activity on normal colon cell lines. Moreover, synergistic interaction was found between F7 and F3 and the latter contains mainly cannabigerolic acid. The F7 and F7+F3 cytotoxic activity involved cell apoptosis and cell cycle arrest in S or G0/G1 phases, respectively. RNA profiling identified 2283 differentially expressed genes in F7+F3 treatment, among them genes related to the Wnt signaling pathway and apoptosis-related genes. Moreover, F7, F3, and F7+F3 treatments induced cell death of polyp cells.

Conclusions:C. sativa compounds interact synergistically for cytotoxic activity against colon cancer cells and induce cell cycle arrest, apoptotic cell death, and distinct gene expression. F3, F7, and F7+F3 are also active on adenomatous polyps, suggesting possible future therapeutic value.

Combined effect of telmisartan and fluvastatin on arachidonic acid metabolism in human liver microsomes

1. Epoxyeicosatrienoic acids (EETs), metabolites of arachidonic acid (AA) via cytochrome P450s, have a protective effect on the cardiovascular system involving vasodilation. We have previously demonstrated that telmisartan (TEL) inhibits EETs production from AA in vitro. 2. The objectives of the study were to examine the inhibitory effect of fluvastatin (FLU), an inhibitor of CYP2C9, and the combined effect of TEL and FLU on the production of EETs using human liver microsomes. The combined effect of TEL and FLU was evaluated using two methods, the fixed concentration method and the fixed ratio method. 3. FLU significantly reduced total eicosanoids (sum of EETs and their subsequent metabolites dihydroxyeicosatrienoic acids) production at > 0.25 µM. The results of the fixed concentration method indicated that the addition of the other inhibitor resulted in significant reduction of the production of total eicosanoids in a concentration-dependent manner. In the fixed ratio method, the combination of TEL and FLU over all concentration ratios tested did not produce a horizontal shift in the dose response curves. 4. Our results showing an additive combined effect of TEL and FLU on AA metabolism, suggest that concomitant treatment with TEL and FLU would theoretically affect the vascular tone mediated by EETs from AA.

Novel antiviral activity and mechanism of bromocriptine as a Zika virus NS2B-NS3 protease inhibitor

Zika virus (ZIKV) infection is associated with congenital malformations in infected fetuses and severe neurological and other systemic complications in adults. There are currently limited anti-ZIKV treatment options that are readily available and safe for use in pregnancy. In this drug repurposing study, bromocriptine was found to have inhibitory effects on ZIKV replication in cytopathic effect inhibition, virus yield reduction, and plaque reduction assays. Time-of-drug-addition assay showed that bromocriptine exerted anti-ZIKV activity between 0 and 12 h post-ZIKV inoculation, corroborating with post-entry events in the virus replication cycle prior to budding. Our docking model showed that bromocriptine interacted with several active site residues of the proteolytic cavity involving H51 and S135 in the ZIKV-NS2B-NS3 protease protein, and might occupy the active site and inhibit the protease activity of the ZIKV-NS2B-NS3 protein. A fluorescence-based protease inhibition assay confirmed that bromocriptine inhibited ZIKV protease activity. Moreover, bromocriptine exhibited synergistic effect with interferon-α2b against ZIKV replication in cytopathic effect inhibition assay. The availability of per vagina administration of bromocriptine as suppositories or vaginoadhesive discs and the synergistic anti-ZIKV activity between bromocriptine and type I interferon may make bromocriptine a potentially useful and readily available treatment option for ZIKV infection. The anti-ZIKV effects of bromocriptine should be evaluated in a suitable animal model.

In vitro drug combination studies of Letermovir (AIC246, MK-8228) with approved anti-human cytomegalovirus (HCMV) and anti-HIV compounds in inhibition of HCMV and HIV replication

Despite modern prevention and treatment strategies, human cytomegalovirus (HCMV) remains a common opportunistic pathogen associated with serious morbidity and mortality in immunocompromised individuals, such as transplant recipients and AIDS patients. All drugs currently licensed for the treatment of HCMV infection target the viral DNA polymerase and are associated with severe toxicity issues and the emergence of drug resistance. Letermovir (AIC246, MK-8228) is a new anti-HCMV agent in clinical development that acts via a novel mode of action and has demonstrated anti-HCMV activity in vitro and in vivo. For the future, drug combination therapies, including letermovir, might be indicated under special medical conditions, such as the emergence of multidrug-resistant virus strains in transplant recipients or in HCMV-HIV-coinfected patients. Accordingly, knowledge of the compatibility of letermovir with other HCMV or HIV antivirals is of medical importance. Here, we evaluated the inhibition of HCMV replication by letermovir in combination with all currently approved HCMV antivirals using cell culture checkerboard assays. In addition, the effects of letermovir on the antiviral activities of selected HIV drugs, and vice versa, were analyzed. Using two different mathematical techniques to analyze the experimental data, (i) additive effects were observed for the combination of letermovir with anti-HCMV drugs and (ii) no interaction was found between letermovir and anti-HIV drugs. Since none of the tested drug combinations significantly antagonized letermovir efficacy (or vice versa), our findings suggest that letermovir may offer the potential for combination therapy with the tested HCMV and HIV drugs.

Comparison of the efficacies of entecavir 0.5 and 1.0 mg combined with adefovir in patients with chronic hepatitis B who had failed on prior nucleos(t)ide analogue treatments

Entecavir (ETV) plus adefovir (ADV) combination therapy is one of the useful treatment option for the patients with chronic hepatitis B (CHB) who had failed on prior nucleos(t) ide analogue (NA) treatments. This study compared the efficacies of the combinations of ETV 0.5 mg plus ADV and ETV 1.0 mg plus ADV in patients who had failed on prior multiple NA treatments. This retrospective analysis included 148 consecutive patients with CHB infection in Korea (n = 37 with ETV 0.5 mg plus ADV and n = 111 with ETV 1.0 mg plus ADV). The virological and biochemical responses were compared between the two groups. The cumulative probability of viral suppression of ETV 0.5 mg plus ADV was not inferior to that of ETV 1.0 mg plus ADV (hazard ratio [HR], 0.64; 95% confidence interval [CI], 0.38-1.08; P = 0.094). The changes in serum HBV DNA level in the ETV 0.5 mg plus ADV group were not different between the two groups over 12 months. Moreover, no significant difference was observed in acquiring ETV-resistant variants between the two groups during the treatment (HR, 0.95; P = 0.953). This study suggests the proof-of-concept that the lower dose of NA in combination with other NA might be the theoretical option for rescue combination therapy in patients with CHB who had failed on prior multiple NA treatments in order to reduce systemic exposure and possible side effects of NA.

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

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

Early Viral Kinetics with Telbivudine, Tenofovir or Combination of Both in Immunotolerant Patients with Hepatitis B e Antigen-Positive Chronic Hepatitis B

Introduction

Viral kinetics has proved useful in understanding antiviral potency, determining antiviral profiles and optimizing treatment strategy.

Methods

This was a randomized, open-label study comparing the viral kinetics in 46 hepatitis B e antigen-positive patients during 12-week treatment with telbivudine monotherapy, tenofovir monotherapy or the combination of telbivudine plus tenofovir. A standard biphasic mathematical model was used to compare hepatitis B virus (HBV) DNA decay parameters.

Results

Forty-six patients received telbivudine (n = 16), tenofovir (n = 14) or telbivudine plus tenofovir (n = 16). From baseline to Week 12, the mean (SD) reduction in HBV DNA levels was not significantly different between treatment groups: −3.9 (0.9) log₁₀ copies/mL in telbivudine group, −4.2 (0.7) log₁₀ copies/mL in tenofovir group, and −4.4 (1.0) log₁₀ copies/mL in combination group. No significant difference was observed among the three groups for viral clearance rate per day (0.97, 1.02, and 0.88, respectively) or for infected cell loss rate per day (0.04, 0.05, and 0.05, respectively). Antiviral efficiency in blocking viral production was similar in the monotherapy groups (median; 99.7% in telbivudine group and 99.4% in tenofovir group), but was slightly better and more homogeneous in the combination treatment group than in the monotherapy groups: mean (SD), 99.1% (0.8%) and 98.8% (1.6%), respectively (Wald–Wolfowitz test; P = 0.038). All treatments were well tolerated and no serious adverse event was reported during the study. Of the 46 patients in the safety population, 23 experienced adverse events. Most of the adverse events were not suspected to be related to the study drug by the investigators.

Conclusion

Monotherapy with telbivudine or tenofovir showed similar antiviral effectiveness in HBV DNA reduction and viral kinetics of HBV DNA decay. Efficiency in blocking viral production was slightly improved in the combination treatment group compared to the monotherapy groups.

Electronic supplementary material

The online version of this article (doi:10.1007/s40121-014-0039-5) contains supplementary material, which is available to authorized users.

In vitro activity and resistance profile of samatasvir, a novel NS5A replication inhibitor of hepatitis C virus

The hepatitis C virus (HCV) nonstructural 5A (NS5A) protein is a clinically validated target for drugs designed to treat chronic HCV infection. This study evaluated the in vitro activity, selectivity, and resistance profile of a novel anti-HCV compound, samatasvir (IDX719), alone and in combination with other antiviral agents. Samatasvir was effective and selective against infectious HCV and replicons, with 50% effective concentrations (EC50s) falling within a tight range of 2 to 24 pM in genotype 1 through 5 replicons and with a 10-fold EC50 shift in the presence of 40% human serum in the genotype 1b replicon. The EC90/EC50 ratio was low (2.6). A 50% cytotoxic concentration (CC50) of >100 μM provided a selectivity index of >5 × 10(7). Resistance selection experiments (with genotype 1a replicons) and testing against replicons bearing site-directed mutations (with genotype 1a and 1b replicons) identified NS5A amino acids 28, 30, 31, 32, and 93 as potential resistance loci, suggesting that samatasvir affects NS5A function. Samatasvir demonstrated an overall additive effect when combined with interferon alfa (IFN-α), ribavirin, representative HCV protease, and nonnucleoside polymerase inhibitors or the nucleotide prodrug IDX184. Samatasvir retained full activity in the presence of HIV and hepatitis B virus (HBV) antivirals and was not cross-resistant with HCV protease, nucleotide, and nonnucleoside polymerase inhibitor classes. Thus, samatasvir is a selective low-picomolar inhibitor of HCV replication in vitro and is a promising candidate for future combination therapies with other direct-acting antiviral drugs in HCV-infected patients.

Ribavirin inhibits in vitro hepatitis E virus replication through depletion of cellular GTP pools and is moderately synergistic with alpha interferon

Hepatitis E virus (HEV) is a common cause of acute hepatitis that results in high mortality in pregnant women and may establish chronic infections in immunocompromised patients. We demonstrate for the first time that alpha interferon (IFN-α) and ribavirin inhibit in vitro HEV replication in both a subgenomic replicon and an infectious culture system based on a genotype 3 strain. IFN-α showed a moderate but significant synergism with ribavirin. These findings corroborate the reported clinical effectiveness of both drugs. In addition, the antiviral activity of ribavirin against wild-type genotype 1, 2, and 3 strains was confirmed by immunofluorescence staining. Furthermore, the in vitro activity of ribavirin depends on depletion of intracellular GTP pools, which is evident from the facts that (i) other GTP-depleting agents (5-ethynyl-1-β-d-ribofuranosylimidazole-4-carboxamide [EICAR] and mycophenolic acid) inhibit viral replication, (ii) exogenously added guanosine reverses the antiviral effects, and (iii) a strong correlation (R(2) = 0.9998) exists between the antiviral activity and GTP depletion of ribavirin and other GTP-depleting agents.

Efficacy of adefovir-based combination therapy for patients with Lamivudine- and entecavir-resistant chronic hepatitis B virus infection

Treatment strategies for entecavir (ETV)-resistant chronic hepatitis B (CHB) patients are not yet well established. The aim of this study was to evaluate overall antiviral efficacy and to compare the efficacy of combination therapy with adefovir (ADV) plus nucleoside analogues (lamivudine [LAM], telbivudine [LdT], or ETV) in patients infected with LAM- and ETV-resistant hepatitis B virus (HBV) variants. Virologic, biochemical, and serologic responses during combination therapy with ADV plus nucleoside analogues were assessed. Propensity score analysis was used to select a matched group of patients for the comparison of rescue therapy regimens. A total of 67 consecutive patients were analyzed. Complete virologic suppression was achieved in 27 patients. The overall cumulative incidence of complete virologic suppression at month 24 was 47.4%: 44.3% in the LAM or LdT plus ADV group and 51.4% in the group given ETV and ADV. There was no significant difference between these two groups (P = 0.234). The cumulative incidences of complete virologic suppression were still comparable between the two groups selected and matched using the propensity score model (P = 0.419). Virologic breakthrough was observed in 9 patients, and rtA181V substitution was newly detected in one patient. Hepatitis B e antigen (HBeAg) negativity and lower baseline HBV DNA level were associated with complete virologic suppression in univariate analysis. In multivariate analysis, lower baseline HBV DNA level remained an independent predictor. In conclusion, combination therapy with ADV plus nucleoside analogues fails to show sufficient antiviral efficacy in CHB patients with resistance to both LAM and ETV. Further study is warranted to evaluate the efficacy of a more potent tenofovir-based regimen in such patients.

Efficacy of adefovir-based combination therapy for patients with Lamivudine- and entecavir-resistant chronic hepatitis B virus infection

Treatment strategies for entecavir (ETV)-resistant chronic hepatitis B (CHB) patients are not yet well established. The aim of this study was to evaluate overall antiviral efficacy and to compare the efficacy of combination therapy with adefovir (ADV) plus nucleoside analogues (lamivudine [LAM], telbivudine [LdT], or ETV) in patients infected with LAM- and ETV-resistant hepatitis B virus (HBV) variants. Virologic, biochemical, and serologic responses during combination therapy with ADV plus nucleoside analogues were assessed. Propensity score analysis was used to select a matched group of patients for the comparison of rescue therapy regimens. A total of 67 consecutive patients were analyzed. Complete virologic suppression was achieved in 27 patients. The overall cumulative incidence of complete virologic suppression at month 24 was 47.4%: 44.3% in the LAM or LdT plus ADV group and 51.4% in the group given ETV and ADV. There was no significant difference between these two groups (P = 0.234). The cumulative incidences of complete virologic suppression were still comparable between the two groups selected and matched using the propensity score model (P = 0.419). Virologic breakthrough was observed in 9 patients, and rtA181V substitution was newly detected in one patient. Hepatitis B e antigen (HBeAg) negativity and lower baseline HBV DNA level were associated with complete virologic suppression in univariate analysis. In multivariate analysis, lower baseline HBV DNA level remained an independent predictor. In conclusion, combination therapy with ADV plus nucleoside analogues fails to show sufficient antiviral efficacy in CHB patients with resistance to both LAM and ETV. Further study is warranted to evaluate the efficacy of a more potent tenofovir-based regimen in such patients.

Sulfamoylbenzamide derivatives inhibit the assembly of hepatitis B virus nucleocapsids

Chronic hepatitis B virus (HBV) infection, a serious public health problem leading to cirrhosis and hepatocellular carcinoma, is currently treated with either pegylated alpha interferon (pegIFN-α) or one of the five nucleos(t)ide analogue viral DNA polymerase inhibitors. However, neither pegIFN-α nor nucleos(t)ide analogues are capable of reliably curing the viral infection. In order to develop novel antiviral drugs against HBV, we established a cell-based screening assay by using an immortalized mouse hepatocyte-derived stable cell line supporting a high level of HBV replication in a tetracycline-inducible manner. Screening of a library consisting of 26,900 small molecules led to the discovery of a series of sulfamoylbenzamide (SBA) derivatives that significantly reduced the amount of cytoplasmic HBV DNA. Structure-activity relationship studies have thus far identified a group of fluorine-substituted SBAs with submicromolar antiviral activity against HBV in human hepatoma cells. Mechanistic analyses reveal that the compounds dose dependently inhibit the formation of pregenomic RNA (pgRNA)-containing nucleocapsids of HBV but not other animal hepadnaviruses, such as woodchuck hepatitis virus (WHV) and duck hepatitis B virus (DHBV). Moreover, heterologous genetic complementation studies of capsid protein, DNA polymerase, and pgRNA between HBV and WHV suggest that HBV capsid protein confers sensitivity to the SBAs. In summary, SBAs represent a novel chemical entity with superior activity and a unique antiviral mechanism and are thus warranted for further development as novel antiviral therapeutics for the treatment of chronic hepatitis B.

Absence of a Pharmacokinetic Interaction Between Entecavir and Adefovir

This study evaluated the effect of entecavir on the pharmacokinetics of adefovir and the effect of adefovir on the pharmacokinetics of entecavir using a fixed-sequence crossover design in healthy adult subjects. Subjects received 10 mg of adefovir once daily on days 1 to 4, 1 mg of entecavir on days 5 to 14, and 1 mg of entecavir plus 10 mg of adefovir on days 15 to 24. Pharmacokinetic assessments were performed on days 4 and 24 for adefovir and on days 14 and 24 for entecavir. The geometric mean ratios (90% confidence interval) for area under the plasma concentration-time curve in 1 dosing interval, peak plasma concentration, and 24-hour postdose plasma concentration of entecavir when coadministered with adefovir and of adefovir when coadministered with entecavir were within the prespecified 0.80 to 1.25 no-effect range. Entecavir and adefovir were well tolerated when administered in combination. Therefore, the pharmacokinetic data generated in this study indicate that entecavir and adefovir can be coadministered without the need for dosage adjustment.

Entecavir plus adefovir combination treatment for chronic hepatitis B patients after failure of nucleoside/nucleotide analogues

BACKGROUND

The combination of entecavir, a nucleoside analogue, and adefovir, a nucleotide analogue, would be a promising salvage treatment for chronic hepatitis B (CHB) patients who fail nucleoside/nucleotide analogue (NA) regimens.

METHODS

A total of 89 CHB patients who had failed NA regimens and were treated with entecavir plus adefovir combination for at least 12 months were included.

RESULTS

Mean baseline HBV DNA of patients was 6.16 ±1.44 log(10) IU/ml. Patients were classed by the number of previously failed NAs; 1 NA (lamivudine; n=15; Group 1), 2 NAs (lamivudine and either adefovir or entecavir; n=39; Group 2) and 3 NAs (lamivudine, adefovir and entecavir; n=35; Group 3). After 12 months of treatment, the mean reduction in HBV DNA was greater in Group 1 than in Group 2 or 3 (-5.81 ±1.71, -3.20 ±1.36 and -2.93 ±1.56 log(10) IU/ml, respectively; P<0.01). The rates of virological response (HBV DNA<2,000 IU/ml) were 100%, 79.5% and 34.3% (P<0.01), and the rates of complete virological response (HBV DNA<60 IU/ml) were 53.3%, 25.6% and 14.3% in Group 1, 2 and 3, respectively (P<0.01) at 12 months. Higher baseline HBV DNA (odds ratio =0.59; P=0.02) and increasing number of previously failed NAs (P<0.01) were independently associated with a lower rate of complete virological response at 12 months.

CONCLUSIONS

Entecavir plus adefovir combination treatment was effective in achieving virological response in CHB patients after failure of NAs. However, its effect progressively decreased as the number of previously failed NAs increased.

Treatment of HBeAg positive chronic hepatitis B: interferon or nucleoside analogues

Interferon alpha has restricted efficacy in as much as only a proportion of patients show a response. However, in appropriately selected HBeAg-positive and HBeAg-negative patients, sustained suppression of viral replication can be achieved, and HBeAg or even HBsAg seroconversion can be attained. Thus, finite course of interferon alpha can be successful, and offer an advantage to patient. Interferon (IFN) remains a benchmark therapy for chronic hepatitis B. The main advantages of IFN-α over nucleoside analogues are the absence of resistance and the possibility of immune-mediated clearance of hepatitis B. Unfortunately, side effects preclude the use of interferon alpha in substantial proportions of patients, and prolonged maintenance therapy to suppress hepatitis B virus (HBV) is not feasible. Nucleoside analogues are given by mouth, once per day, and the safety, potency and efficacy have improved and facilitated treatment. However, maintenance of long-term suppression is required for the majority of patients. In general, treatment of chronic hepatitis B should target patients with active disease and viral replication, preferably before the signs and symptoms of cirrhosis or significant injury has occurred. Current EASL guidelines suggest that treatment be based on the evaluation of three criteria: Serum aminotransferase levels, serum HBV DNA levels and histological grade and stage. Many questions remain unanswered on the optimal treatment of patients with chronic hepatitis B with a nucleoside vs interferon alpha. Both forms of treatment have benefits and the choice should be selected and tailored. Stopping or futility rules can be implemented in patients who fail interferon. Recent data suggest the safety and efficacy of nucleoside analogues in the third trimester of pregnancy to reduce the risk of transmission from mothers to their children.

Combination of N-methylisatin-β-thiosemicarbazone derivative (SCH16) with ribavirin and mycophenolic acid potentiates the antiviral activity of SCH16 against Japanese encephalitis virus in vitro

AIM

 To investigate the drug to drug interaction of N-methylisatin-β-thiosemicarbazone (MIBT) derivative (SCH16) with ribavirin, mycophenolic acid and pentoxifylline against Japanese encephalitis virus in vitro. Our earlier studies have reported significant antiviral activity of these compounds against Japanese encephalitis virus in vitro and in vivo.

METHODS AND RESULTS

 An in vitro drug to drug combination analysis was carried out to investigate whether or not the direct antiviral effect shown by the individual MIBT derivative could be effectively increased when lower concentrations of two compounds in combination were used. The results of this study showed that the combination of MIBT derivative (SCH16) with ribavirin or mycophenolic acid significantly enhanced the antiviral activity of SCH16 against JEV in vitro. In contrast, the combination of SCH16 and pentoxifylline resulted in antagonism.

CONCLUSION

 The antiviral activity showed by SCH16 was enhanced in the presence of ribavirin and mycophenolic acid.

SIGNIFICANCE AND IMPACT OF THE STUDY

 Studying the synergistic/additive interaction of the compounds in combination would help in lowering the effective concentration so as to overcome the concern of toxicity.

Randomized trial of entecavir plus adefovir in patients with lamivudine-resistant chronic hepatitis B who show suboptimal response to lamivudine plus adefovir

A substantial proportion of patients with lamivudine-resistant hepatitis B virus (HBV) show suboptimal virologic response during rescue combination treatment with lamivudine plus adefovir. In this randomized active-control trial, 90 patients with serum HBV DNA levels of >2,000 IU/ml after at least 24 weeks of treatment with lamivudine-plus-adefovir therapy for lamivudine-resistant HBV were randomized to combination treatment with entecavir plus adefovir (ETV+ADV, n = 45) or continuation of lamivudine plus adefovir (LAM+ADV, n = 45) for 52 weeks. At baseline, patients' mean serum HBV DNA level was 4.60 log(10) IU/ml (standard deviation [SD], 1.03). All 90 patients completed 52 weeks of treatment. At week 52, the proportion of patients with serum HBV DNA levels of <60 IU/ml, the primary endpoint, was significantly higher in the ETV+ADV group than in the LAM+ADV group (n = 13, 29%, versus n = 2, 4%, respectively; P = 0.004). The mean reduction in serum HBV DNA levels from baseline was significantly greater in the ETV+ADV group than in the LAM+ADV group (-2.2 log(10) IU/ml versus -0.6 log(10) IU/ml, respectively; P < 0.001). At week 52, additional mutations causing resistance to adefovir or entecavir were analyzed in all patients with detectable HBV DNA by restriction fragment mass polymorphism assays and detected in none of the ETV+ADV group but in 15% of patients in the LAM+ADV group (P = 0.018). Safety and adverse event profiles were similar in the two groups. In conclusion, entecavir-plus-adefovir combination therapy provides superior virologic response and favorable resistance profiles, compared with the continuing lamivudine-plus-adefovir combination, in patients with lamivudine-resistant HBV who fail to respond to lamivudine-plus-adefovir combination therapy.

INX-08189, a phosphoramidate prodrug of 6-O-methyl-2'-C-methyl guanosine, is a potent inhibitor of hepatitis C virus replication with excellent pharmacokinetic and pharmacodynamic properties

INX-08189 is an aryl-phosphoramidate of 6-O-methyl-2'-C-methyl guanosine. INX-08189 was highly potent in replicon assays, with a 50% effective concentration of 10±6 nM against hepatitis C genotype 1b at 72 h. The inhibitory effect on viral replication was rapid, with a 50% effective concentration (EC50) of 35±8 nM at 24 h. An intracellular 2'-C-methyl guanosine triphosphate (2'-C-MeGTP) concentration of 2.43±0.42 pmol/10(6) cells was sufficient to achieve 90% inhibition of viral replication. In vitro resistance studies confirmed that the S282T mutation in the NS5b gene conferred an approximately 10-fold reduction in sensitivity to INX-08189. However, the complete inhibition of S282T mutant replicons still could be achieved with an EC90 of 344±170 nM. Drug combination studies of INX-08189 and ribavirin indicated significant synergy in antiviral potency both in wild-type and S282T-expressing replicons. Genotype 1b replicons could be cleared after 14 days of culture when exposed to as little as 20 nM INX-08189. No evidence of mitochondrial toxicity was observed after 14 days of INX-08189 exposure in both HepG2 and CEM human cell lines. In vivo studies of rats and cynomolgus monkeys demonstrated that 2'-C-MeGTP concentrations in liver equivalent to the EC90 could be attained after a single oral dose of INX-08189. Rat liver 2'-C-MeGTP concentrations were proportional to dose, sustained for greater than 24 h, and correlated with plasma concentrations of the nucleoside metabolite 2'-C-methyl guanosine. The characteristics displayed by INX-08189 support its continued development as a clinical candidate for the treatment of chronic HCV infection.

Antiviral drugs for HBV liver disease

INTRODUCTION

Chronic hepatitis B (CHB) virus infection affects about 400 million people around the globe and is among the world's leading causes of death. The management of CHB has evolved rapidly, several therapeutic options are now available to prevent both progression of liver disease and anticipated liver morbidity and mortality.

AREAS COVERED

Current treatment modalities for CHB patients, together with suggestions from our own experience are summarized. The most relevant works published in recent years on pegylated interferon, nucleos(t)ides analogues (NUC) and the 2009 update of the American Association for the Study of Liver Diseases Practice Guidelines and the 2009 European Association for the Study of the Liver (EASL) Clinical Practice Guidelines on the management of chronic hepatitis B are discussed.

EXPERT OPINION

Pegylated interferon and NUC have advantages and limitations, as short-term interferon treatment induces a sustained virological response in a third of patients, whereas long-term suppressive therapy by NUC rapidly inhibits HBV replication in most patients but drug resistance and safety in the long-term will remain the most important unresolved questions. Careful evaluation of patient history, staging of liver disease and virological factors should guide the start of treatment and the choice to the most appropriate individualized treatment strategy in all CHB patients.

Telbivudine: a review of its use in compensated chronic hepatitis B

Telbivudine (Sebivo®; Tyzeka®) is a synthetic nucleoside analogue that inhibits replication of hepatitis B virus (HBV). It is used in the treatment of adults with chronic hepatitis B (CHB) with evidence of viral replication and persistently elevated serum ALT and/or AST levels, and/or histological evidence of active disease. Telbivudine is a potent antiviral that provides effective and sustained viral suppression in patients with compensated CHB. In clinical trials, treatment outcomes were improved significantly more with telbivudine 600 mg once daily than with lamivudine 100 mg or adefovir 10 mg once daily, and telbivudine-treated patients had significantly less viral resistance than lamivudine-treated patients. Increasing rates of hepatitis B e antigen (HBeAg) seroconversion were achieved in HBeAg-positive patients during periods of up to 4 years continuous telbivudine treatment, and seroconversion was durable in most patients throughout a 2-year, off-treatment follow-up, indicating the potential for a finite treatment period in this group of patients. Telbivudine is associated with a medium genetic barrier to resistance and, as patients with undetectable HBV DNA levels have significantly improved outcomes, it is recommended that HBV DNA levels are monitored at week 24 (and 6 monthly thereafter), with the addition of a nucleoside/nucleotide analogue without cross resistance (such as adefovir dipivoxil) if viraemia is present to reduce the risk of resistance (Roadmap concept). Telbivudine was generally well tolerated in clinical trials for periods of up to 4 years, and has a similar tolerability profile to that of lamivudine. A minority of telbivudine-treated patients experience creatinine kinase elevation, usually transient, and myopathy occurs rarely. In modelled cost effectiveness studies in several Asian countries, treatment with telbivudine Roadmap was cost effective in HBeAg-positive patients. Thus, telbivudine provides a valuable treatment option in CHB, particularly when administered using the Roadmap concept in HbeAg-positive patients.

A Review of Oral Antiretroviral Therapy for the Treatment of Chronic Hepatitis B

Objective:

To describe the current evidence for the use of oral antiretroviral (ARV) agents in the treatment of chronic hepatitis B (CHB).

Data Sources:

A search from 1950 to April 2010 was conducted using the databases PubMed and MEDLINE with the search terms chronic hepatitis B, lamivudine, entecavir, adefovir, telbivudine, tenofovir, emtricitabine, clevudine, and pradefovir. The search was limited to trials conducted in humans that were published in the English language.

Study Selection and Data Extraction:

Studies were included if they evaluated the use of oral ARVs in patients with CHB infection who were not coinfected with hepatitis C, hepatitis D, or HIV.

Data Synthesis:

Oral ARVs have revolutionized the treatment of CHB. Studies conducted comparing ARVs have favored entecavir and tenofovir with respect to their ability to decrease hepatitis B virus DNA viral load while minimizing the development of resistance. However, low seroconversion rates, recurrent viremia when ARV therapy is discontinued, and increased resistance rates with longer treatment durations limit the benefit of oral ARVs in the treatment of CHB. Combination therapy has been a suggested solution; however, studies have yet to prove additional benefit over currently recommended monotherapy.

Conclusions:

Oral ARVs should continue to be used in the treatment of CHB; however, research is needed to define the optimal duration of therapy, evaluate the utility of combination therapy, and explore novel targets within the hepatitis B life cycle.

The hepatitis C virus (HCV) NS4B RNA binding inhibitor clemizole is highly synergistic with HCV protease inhibitors

BACKGROUND

We recently identified a compound, clemizole hydrochloride, that inhibits NS4B's RNA binding and hepatitis C virus (HCV) replication. Although significant, clemizole's antiviral effect is moderate (50% effective concentration of 8 microM against an HCV genotype 2a clone). We hypothesized that the combination of clemizole with other anti-HCV agents can increase the antiviral effect over that achieved with each drug alone and could also decrease the emergence of viral resistance.

METHODS

Luciferase reporter-linked HCV replication assays were used to study the antiviral effects of drug combinations that included clemizole. Data were analyzed using Loewe additivity and Bliss independence models for synergy, and resistance studies were performed using HCV colony formation assays.

RESULTS

Clemizole's antiviral effect was highly synergistic with the HCV protease inhibitors SCH503034 and VX950, without toxicity. In contrast, combinations of clemizole with either interferon, ribavirin, or the nucleoside (NM283) and nonnucleoside (HCV796) HCV polymerase inhibitors were additive. Furthermore, combination of clemizole with SCH503034 decreased the frequency of drug-resistant mutants, compared with treatment with either drug alone. Finally, no cross-resistance to clemizole of SCH503034-resistant mutants (or vice versa) was observed.

CONCLUSIONS

Clemizole can yield high-level synergy with the protease inhibitor class. Inclusion of clemizole in future anti-HCV cocktails can represent an attractive paradigm for increasing current virologic response rates.

Effect of newer oral antiviral agents on future therapy of chronic hepatitis B

Long-term therapy with oral nucleoside/nucleotide analogues (NAs) is a favoured approach to the treatment of patients with chronic hepatitis B (CHB); however, all oral agents currently approved for the treatment of such patients are associated with some risk for drug resistance. This can lead to a rebound in HBV levels and, eventually, progressive liver disease. Combination therapy is one strategy that has the potential for enhanced antiviral effects and diminished or delayed resistance. The disadvantages of combination therapy include increased cost, the potential for drug interactions and increased toxicity. Additional therapeutic efficacy from combination therapy has not been demonstrated in clinical trials of HBV, and this approach might be less relevant now that potent NAs with excellent drug resistance profiles are available. However, it might be possible to identify subsets of patients (for example, those with extremely high viraemia or low baseline alanine aminotransferase levels) who derive added benefit from combination therapy. This review examines efficacy and resistance data for new low resistance oral NAs and clinical experience to date with de novo combination therapy in patients with CHB. The application of combination therapy in select populations of patients with CHB is also discussed.

Drug delivery systems and liver targeting for the improved pharmacotherapy of the hepatitis B virus (HBV) infection

In spite of the progress made in vaccine and antiviral therapy development, hepatitis B virus (HBV) infection is still the most common cause of liver cirrhosis and hepatocellular carcinoma, with more than 400 million people chronically infected worldwide. Antiviral therapy with nucleos(t)ide analogues and/or immunomodulating peptides is the only option to control and prevent the progression of the disease in chronic hepatitis B (CHB)-infected patients. So far, the current antiviral monotherapy remains unsatisfactory because of the low efficacy and the development of drug resistance mutants. Moreover, viral rebound is frequently observed following therapy cessation, since covalent closed circular DNA (cccDNA) is not removed from hepatocytes by antiviral therapy. First, this review describes the current pharmacotherapy for the management of CHB and the new drug candidates being investigated. Then, the challenges in the development of drug delivery systems for the targeting of antiviral drugs to the liver parenchyma are discussed. Finally, perspectives in the design of a more efficient pharmacotherapy to eradicate the virus from the host are addressed.

Safety and efficacy of telbivudine for the treatment of chronic hepatitis B

Telbivudine was recently approved for the treatment of chronic hepatitis B. Phase III studies indicated its antiviral potency with 6- to 6.5-log copies/mL reductions in hepatitis B DNA levels at year 1, comparable to other potent agents such as entecavir or tenofovir. Genotypic resistance rates, however, reached 25% at year 2 in hepatitis B e-antigen positive subjects and 11% in hepatitis B e-antigen negative subjects, preventing it from becoming a preferred first-line drug for hepatitis B. Furthermore, its signature resistance mutation (a change from methionine to isoleucine at position 204 in the reverse transcriptase domain of the hepatitis B polymerase) also confers cross-resistance to entecavir, lamivudine, and emtricitabine. Telbivudine is well tolerated, with elevations in creatine phosphokinase being the most common abnormality observed in clinical trials. Most often, elevations were asymptomatic. Future research in hepatitis B will focus on the best ways to use existing therapies, including telbivudine, sequentially or in combination in order to maximize viral suppression and minimize the development of antiviral resistance.

HIV Type-1 Entry Inhibitors with a New Mode of Action

Background:

The development of antiviral drugs has provided crucial new means to mitigate or relieve the debilitating effects of many viral pathogens. Regular use of these drugs has led to generation of resistant strains, making the control of many viral infections very difficult, particularly in HIV-seropositive and AIDS patients. A rich source for the discovery of new HIV infection inhibitors has been, and continues to be, the ‘mining’ of the large diversity of compounds already available in nature, and specifically those from botanical extracts.

Methods:

Using a newly developed direct binding assay with mass spectrometry technology (direct analysis in real-time time-of-flight mass spectrometry), we were able to show that compounds present in extracts of elderberry, cinnamon and green tea bind to and block HIV type-1 (HIV-1) infection in target cells.

Results:

The compounds that blocked HIV-1 infection were flavonoids and A-type proanthocyanidins. The 50% inhibitory concentration values of these extracts ranged from 0.5 to 201 µg/ml for four different HIV-1 serotypes. Interaction matrices with the elderberry extract and enfuvirtide, a peptide HIV-1 fusion inhibitor, revealed significant super additive effects. This indicates that the compounds in elderberry that prevent HIV-1 infection are likely to bind to viral glycoproteins other than gp41 (the binding site for enfuvirtide).

Conclusions:

Optimized elderberry, green tea and cinnamon extracts rich in certain flavonoid compounds were shown to block HIV-1 entry and infection in GHOST cells. As such, these types of botanical extracts could provide a starting point for the development of possible safe and reliable cotherapies for HIV-1-positive individuals, as well as for the identification of new small molecules as leading drug candidates for HIV-1 therapeutics and microbicides.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Telbivudine in the treatment of chronic hepatitis B

INTRODUCTION

The treatment of chronic hepatitis B virus (HBV) infection has been revolutionized in the past decade by the increased availability of effective antiviral agents. Telbivudine is an L-nucleoside that is structurally related to lamivudine and has recently been approved for use in patients with chronic HBV infection. Telbivudine is highly selective for HBV DNA and inhibits viral DNA synthesis with no effect on human DNA or other viruses. This article reviews the pharmacology, pharmacokinetics, therapeutic efficacy and safety of telbivudine, and discusses its place in the current armamentarium against HBV.

METHODS

Relevant publications were identified from searches of Medline and PubMed between 2000 and 2008, using the search terms "hepatitis B/HBV," "telbivudine/LdT," "beta-L-thymidine," "pharmacokinetics," "safety," "adverse events," and "resistance." The reference lists of retrieved articles were searched for relevant studies.

RESULTS

Phase 3 clinical studies demonstrate that telbivudine is superior to lamivudine over a 2-year period in hepatitis B e-antigen (HBeAg)-positive and HBeAg-negative patients. Telbivudine was associated with a statistically significantly greater reduction in HBV DNA, greater proportion of alanine aminotransferase normalization, and greater histological response than lamivudine. Furthermore, telbivudine use resulted in fewer cases of treatment failure and less virological resistance than lamivudine. However, after 2 years of therapy, telbivudine resistance was appreciable (25%) and considerably higher than that seen with other new antivirals such as tenofovir and entecavir. Overall, telbivudine was found to be safe, although grade 3 or 4 adverse events, including elevations in creatine kinase, were more commonly found in patients receiving telbivudine than lamivudine. Telbivudine is not active against lamivudine-resistant HBV.

CONCLUSIONS

Telbivudine is a new antiviral agent joining the armamentarium against HBV. It is superior to lamivudine in terms of therapeutic response and resistance profile. However, concerns about resistance with long-term use, along with inferior cost-effective analyses, have relegated telbivudine to a second-line agent in the management of chronic HBV infection.

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.

Hepatitis B: reflections on the current approach to antiviral therapy

This article summarizes the current state of antiviral therapy of hepatitis B with special attention given to areas that remain controversial or poorly defined. Strict adherence to liver association practice guidelines may result in missed opportunities to treat patients with significant underlying liver disease. In particular, recommended ALT thresholds may not appropriately reflect disease activity or degree of fibrosis. There is growing evidence that an alternative treatment paradigm for preventing late-stage disease complications may be indicated in highly viremic patients with early life exposure to hepatitis B. Pegylated interferon therapy is often a better choice for young to middle-aged patients with genotype A and B because of the higher rate of HBeAg seroconversion and a greater chance for HBsAg seroconversion in both HBeAg-positive and -negative patients as compared to nucleoside analogs. Nucleoside analog monotherapy is the current standard of care for many patients. However, long-term monotherapy results in resistance to a variable degree and sequential monotherapy may result in multi-drug resistant virus. Which patients would specifically benefit from early combination therapy also remains poorly defined. The rapidity and robustness of the suppression of HBV DNA while on a nucleoside analog should be monitored relatively early during treatment because it affects treatment outcome and the rate of resistance. While great progress has been made in treating hepatitis B, many important issues require further study.

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

BACKGROUND

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Role of tenofovir in the treatment of chronic HBV infection

Nucleoside analogues revolutionized the treatment of chronic HBV infection and have become the most important therapeutic option within the last decade. Currently, the nucleoside analogues lamivudine, telbivudine and entecavir, and the nucleotide analogue adefovir dipivoxil, are licensed. Tenofovir disoproxil fumarate (TDF) is another acyclic nucleotide analogue that has been successfully used in the treatment of HIV-infected patients, but has demonstrated significant antiviral activity in wild-type and lamivudine-resistant HBV infections. The use of TDF 300 mg/day leads to marked suppression of HBV replication below the detection limit in different patients groups with HBV mono- or HIV/HBV co-infection in most instances, and a remarkably high rate of hepatitis B e antigen loss and even hepatitis B surface antigen loss was found in small, uncontrolled studies. Belonging to the substance class of acyclic nucleotide analogues, TDF is not cross-resistant to nucleoside analogue resistance-associated mutations. In equal dosages, TDF has comparable antiviral potency as compared with its congender adefovir dipivoxil, but in clinical studies exhibits higher antiviral efficacy and generates a higher genetic barrier against the development of genotypic HBV resistance due to its approximately 24-fold higher dosage. Owing to the numerous newly developed compounds and as a consequence of the emerging problem of drug resistance, treatment concepts for chronic hepatitis B will certainly be modified in the future. Because of its quite favorable antiviral and safety properties, TDF will likely be highly regarded in the management of HBV infections in the future.

Efficacies of β-L-D4A against hepatitis B virus in 2.2.15 cells

AIM: To investigate the antiviral effect of beta-L-enantiomer of 2’,3’-didehydro-2’,3’-dideoxyadenosine (β-L-D4A) on 2.2.15 cells transfected with the hepatitis B virus (HBV) genome.

METHODS: Lamivudine (3TC) as a positive control. Then, HBV DNA in treated 2.2.15 cells and the Hepatitis B surface antigen (HBsAg) in the culture supernatants were detected to determine the inhibitory effect of β-L-D4A. At the same time, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) was used to detect the survival ratio of 2.2.15 cells.

RESULTS: β-L-D4A has a dose-dependent inhibitory effect on HBV DNA replication; this effect was apparent when the concentration was above 1 mol/L. When β-L-D4A was at the highest concentration, 100 mol/L, the HBsAg inhibition ratio was above 50%. The Therapeutic index (TI) of β-L-D4A was above 2.1.

CONCLUSION: β-L-D4A has a dose-dependent inhibitory effect on the replication of HBV DNA and the secretion of HBsAg at low toxicity.

Telbivudine

Telbivudine, the unmodified L-enantiomer of the naturally occurring nucleoside D-thymidine, is a potent synthetic nucleoside analogue. It acts as a hepatitis B virus (HBV) polymerase inhibitor and preferentially inhibits HBV second strand (DNA-dependent) compared with first strand (RNA-dependent) DNA synthesis. More telbivudine than lamivudine recipients with hepatitis B e antigen (HBeAg)-positive chronic hepatitis B and similar proportions of telbivudine or lamivudine recipients with HBeAg-negative disease achieved a therapeutic response at 52 weeks in the large 2-year GLOBE trial. In a phase III trial in Chinese patients, greater reductions in serum HBV DNA occurred with telbivudine than lamivudine at 52 weeks. Reductions in serum HBV DNA at 24 weeks were greater with telbivudine than adefovir in the 1-year switching trial. A lower residual viral load at 52 weeks was seen in patients who received telbivudine or who switched from adefovir to telbivudine at 24 weeks than in patients receiving adefovir. In the 1-year lamivudine switching trial in patients with serum HBV DNA levels >3 log10 copies/mL despite having received prior treatment with lamivudine for a mean of [almost equal or equal to]7 months, those randomised to telbivudine therapy achieved greater reductions in serum HBV DNA levels at 24 weeks than patients randomised to continue lamivudine therapy. Telbivudine was generally well tolerated and most adverse events were of mild or moderate severity. The incidence of severe ALT flares with telbivudine was half that seen with lamivudine at both 52 and 104 weeks in the GLOBE trial.

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

BACKGROUND

Strong suppression of viral replication and normalization of alanine aminotransferase is feasible with nucleos(t)ide analogues. It is estimated viral replication and liver inflammation can be controlled in 90% of patients with chronic hepatitis B with the current available treatments.

AIM

To review the studies currently available on the management of chronic hepatitis B with nucleos(t)ide analogues.

RESULTS

Although very potent, nucleos(t)ide analogues are not effective in every patient. Some factors are known to influence treatment outcome, but many host and viral factors are still unknown. Stopping rules have to be defined to assess treatment efficacy in an early stage and change the regimen. Discontinuation of nucleos(t)ide analogues is often followed by reactivation of HBV. Data on the risk factors for relapse are necessary in order to decide if treatment can be safely discontinued. Another major drawback of nucleos(t)ide analogues is the emergence of resistance. The efficacy of compounds for the treatment of mutant virus and the impact of cross-resistance is largely unknown. The use of combination therapy to prevent resistance looks promising, but has to be proven.

CONCLUSIONS

HBV has become a treatable disease, however much research is needed to optimize treatment for individual patients and treatment failures.

Epsilon-poly-L-lysine and nisin A act synergistically against Gram-positive food-borne pathogens Bacillus cereus and Listeria monocytogenes

AIMS

To test epsilon-poly-L-lysine and nisin A for possible synergistic activity against selected food-borne pathogens and food spoilage organisms.

METHODS AND RESULTS

Synergistic activity was observed against Gram-positive Listeria monocytogenes and Bacillus cereus cells and spores of B. cereus in 96 well plate assays. However, nisin A had no effect alone or in combination with epsilon-poly-L-lysine against Gram-negative Escherichia coli cells. In addition, when tested against yeast Zygosaccharomyces bailii, nisin A and partially inhibitory concentrations of epsilon-poly-L-lysine antagonized each other.

CONCLUSIONS

Nisin A and epsilon-poly-L-lysine showed synergistic activity against B. cereus and L. monocytogenes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The application of nisin A and epsilon-poly-L-lysine is a promising all-natural method of controlling Gram-positive food-borne pathogens, spores and spoilage organisms.

Future prospectives for the management of chronic hepatitis B

Chronic hepatitis B virus infection affects about 400 million people around the globe and causes approximately one million deaths a year. Since the discovery of interferon-α as a therapeutic option the treatment of hepatitis B has evolved fast and management has become increasingly complicated. The amount of viral replication reflected in the viral load (HBV-DNA) plays an important role in the development of cirrhosis and hepatocellular carcinoma. The current treatment modalities for chronic hepatitis B are immunomodulatory (interferons) and antiviral suppressants (nucleoside and nucleotide analogues) all with their own advantages and limitations. An overview of the treatment efficacy for both immunomodulatory as antiviral compounds is provided in order to provide the clinician insight into the factors influencing treatment outcome. With nucleoside or nucleotide analogues suppression of viral replication by 5-7 log₁₀ is feasible, but not all patients respond to therapy. Known factors influencing treatment outcome are viral load, ALT levels and compliance. Many other factors which might influence treatment are scarcely investigated. Identifying the factors associated with response might result in stopping rules, so treatment could be adapted in an early stage to provide adequate treatment and avoid the development of resistance. The efficacy of compounds for the treatment of mutant virus and the cross-resistance is largely unknown. However, genotypic and phenotypic testing as well as small clinical trials provided some data on efficacy in this population. Discontinuation of nucleoside or nucleotide analogues frequently results in viral relapse; however, some patients have a sustained response. Data on the risk factors for relapse are necessary in order to determine when treatment can be discontinued safely. In conclusion: chronic hepatitis B has become a treatable disease; however, much research is needed to tailor therapy to an individual patient, to predict the sustainability of response and determine the best treatment for those failing treatment.

Telbivudine

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Treatment of chronic hepatitis B: efficacy of current drugs and prospects for the future

Chronic hepatitis B is an important clinical problem often leading to severe complications. In this review, the results obtained in the last few years with the use of current drugs, such as interferon and nucleo(t)side analogues, are summarized and the problems of obtaining a sustained remission, which is only achieved in a small number of patients, are discussed. The new approaches, such as the use of combinations of drugs, to optimize long-term tolerable treatment are also considered.

Where does adefovir stand amongst newly developed antivirals: from pharmacology to virology

Adefovir, an acyclic nucleotide analog of adenosine monophosphate, has demonstrated potent activities against several viruses in vitro. Since 2002, the diester prodrug of this molecule, adefovir dipivoxil, has been approved as a well-tolerated and efficacious treatment for chronic hepatitis B. It is the first nucleotide analog to be approved for this indication and it is now challenged by several other molecules that also inhibit hepatitis B virus replication. In this article, we analyze the strengths and limitations of adefovir in the context of hepatitis B treatment and consider the other alternatives in the treatment of this difficult-to-treat chronic disease. Adefovir dipivoxil has offered a real opportunity for patients who developed lamivudine resistance and were facing a therapeutic deadlock; the next challenge for clinicians will be to offer the best therapeutic strategy to limit the inexorable selection of resistant strains.

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

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

Entecavir for the treatment of chronic hepatitis B virus infection

OBJECTIVE

This article reviews the pharmacology/pharmacokinetics and therapeutic efficacy of entecavir, which was approved on March 29, 2005, for the management of adult patients with chronic hepatitis B virus (HBV) infection who have active viral replication and/or elevations in liver transaminases or signs of active liver disease on histologic examination. Potential drug interactions and adverse events associated with the use of entecavir are also reviewed.

METHODS

Relevant literature was identified through searches of MEDLINE (1996-July 2005) and BIOSIS (1993-July 2005). Search terms included, but were not limited to, entecavir, BMS-200475, hepatitis B, pharmacology, pharmacokinetics, adverse events, and therapeutic use. Further publications were identified from the reference lists of the identified articles and through correspondence with the manufacturer of entecavir.

RESULTS

Entecavir is highly selective for the HBV and inhibits all 3 steps of viral replication. Results of early studies indicated a 6% resistance potential after 48 weeks of therapy, although the potential may be higher in patients who harbor lamivudine-resistant mutants. The approved dosage in treatment-naive patients is 0.5 mg/d p.o., administered on an empty stomach; in patients who have failed lamivudine therapy or are known to harbor lamivudine-resistant mutants, the approved dosage is 1.0 mg/d p.o.. The oral tablet and solution can be used interchangeably. Entecavir is well absorbed orally, achieving a dose-related Cmax between 0.6 and 1.5 hours after administration. It is metabolized to a small extent and is not a substrate for the cytochrome P450 enzyme system. The mean elimination t(1/2) ranges from 77 to 149 hours in patients with normal kidney function. Entecavir is eliminated primarily in the urine via glomerular filtration and tubular secretion (62%-73%). No dose adjustment appears to be necessary in patients with moderate to severe liver disease alone. The potential for drug interactions with entecavir appears to be minimal, although medications that inhibit tubular secretion of drugs (eg, probenecid) may be expected to prolong serum concentrations of entecavir. One of the Phase III studies of entecavir found statistically significant benefits compared with lamivudine in terms of improvements in liver histology after 48 weeks of therapy (72% vs 62%, respectively; P<0.009), the proportions of patients with undetectable HBV DNA titers on branched DNA signal amplification assay after 48 weeks of therapy (91% vs 65%; P<0.001), and the proportion with undetectable HBV DNA on polymerase chain reaction (PCR) assay after 48 weeks of therapy (69% vs 38%; P<0.001). In another Phase III study, patients who had failed to respond to lamivudine therapy responded to entecavir: after 48 weeks of therapy, significant differences between entecavir and lamivudine were seen in histologic improvement (55% vs 28%; P<0.001) and the proportion of patients with undetectable HBV DNA on PCR assay (21% vs 1%; P<0.001). Adverse events associated with entecavir therapy were similar in character, severity, and incidence to those associated with placebo or lamivudine therapy. The most common adverse events in clinical trials of entecavir were headache (17%-23% of patients), upper respiratory tract infection (18%-20%), cough (12%-15%), nasopharyngitis (9%-14%), fatigue (10%-13%), dizziness (9%), upper abdominal pain (9%-10%), and nausea (6%-8%).

CONCLUSIONS

Entecavir is a new antiviral agent for the management of chronic HBV infection. Questions concerning the ideal length of therapy, long-term efficacy, and resistance rates over time await the results of ongoing clinical trials.