Lessons from HIV therapy applied to viral hepatitis therapy: summary of a workshop

Antiviral Evaluation of Dispirotripiperazines against Hepatitis B Virus

Hepatitis B virus (HBV) is a hepatotropic DNA virus that replicates by reverse transcription. It chronically infects >296 million people worldwide, including ∼850,000 in the USA, and kills 820,000 annually worldwide. Current nucleos(t)ide analogue (NA) or pegylated interferon α therapies do not eradicate the virus and would benefit from a complementary antiviral drug. We performed a preliminary screen of 28 dispirotripiperazines against HBV, identifying 9 hits with EC50 of 0.7-25 μM. Compound 11826096 displays the most potent activity and represents a promising lead for future optimization. While the mechanism of action is unknown, preliminary assays limit possible targets to activities involved in RNA accumulation, translation, capsid assembly, and/or capsid stability. In addition, we built machine learning models to determine if they were able to predict the activity of this series of compounds. The novelty of these molecules indicated they were outside of the applicability domain of these models.

Hepatitis B Virus Epsilon (ε) RNA Element: Dynamic Regulator of Viral Replication and Attractive Therapeutic Target

Hepatitis B virus (HBV) chronically infects millions of people worldwide, which underscores the importance of discovering and designing novel anti-HBV therapeutics to complement current treatment strategies. An underexploited but attractive therapeutic target is ε, a cis-acting regulatory stem-loop RNA situated within the HBV pregenomic RNA (pgRNA). The binding of ε to the viral polymerase protein (P) is pivotal, as it triggers the packaging of pgRNA and P, as well as the reverse transcription of the viral genome. Consequently, small molecules capable of disrupting this interaction hold the potential to inhibit the early stages of HBV replication. The rational design of such ligands necessitates high-resolution structural information for the ε-P complex or its individual components. While these data are currently unavailable for P, our recent structural elucidation of ε through solution nuclear magnetic resonance spectroscopy marks a significant advancement in this area. In this review, we provide a brief overview of HBV replication and some of the therapeutic strategies to combat chronic HBV infection. These descriptions are intended to contextualize our recent experimental efforts to characterize ε and identify ε-targeting ligands, with the ultimate goal of developing novel anti-HBV therapeutics.

Molecular Mechanisms during Hepatitis B Infection and the Effects of the Virus Variability

The immunopathogenesis and molecular mechanisms involved during a hepatitis B virus (HBV) infection have made the approaches for research complex, especially concerning the patients’ responses in the course of the early acute stage. The study of molecular bases involved in the viral clearance or persistence of the infection is complicated due to the difficulty to detect patients at the most adequate points of the disease, especially in the time lapse between the onset of the infection and the viral emergence. Despite this, there is valuable data obtained from animal and in vitro models, which have helped to clarify some aspects of the early immune response against HBV infection. The diversity of the HBV (genotypes and variants) has been proven to be associated not only with the development and outcome of the disease but also with the response to treatments. That is why factors involved in the virus evolution need to be considered while studying hepatitis B infection. This review brings together some of the published data to try to explain the immunological and molecular mechanisms involved in the different stages of the infection, clinical outcomes, viral persistence, and the impact of the variants of HBV in these processes.

HBV replication inhibitors

Chronic Hepatitis B Virus infections afflict >250 million people and kill nearly 1 million annually. Current non-curative therapies are dominated by nucleos(t)ide analogs (NAs) that profoundly but incompletely suppress DNA synthesis by the viral reverse transcriptase. Residual HBV replication during NA therapy contributes to maintenance of the critical nuclear reservoir of the HBV genome, the covalently-closed circular DNA, and to ongoing infection of naive cells. Identification of next-generation NAs with improved efficacy and safety profiles, often through novel prodrug approaches, is the primary thrust of ongoing efforts to improve HBV replication inhibitors. Inhibitors of the HBV ribonuclease H, the other viral enzymatic activity essential for viral genomic replication, are in preclinical development. The complexity of HBV's reverse transcription pathway offers many other potential targets. HBV's protein-priming of reverse transcription has been briefly explored as a potential target, as have the host chaperones necessary for function of the HBV reverse transcriptase. Improved inhibitors of HBV reverse transcription would reduce HBV's replication-dependent persistence mechanisms and are therefore expected to become a backbone of future curative combination anti-HBV therapies.

A meta-analysis on genetic variability of RT/HBsAg overlapping region of hepatitis B virus (HBV) isolates of Bangladesh

Background and aim

Hepatitis B caused by HBV is a serious public health hazard prevalent worldwide including Bangladesh. Few scattered molecular studies of HBV have been reported in Bangladesh. This study aimed to analyze the genetic variability of RT/HBsAg overlapping region of HBV isolates of Bangladesh and determination of correlation among the genotype/serotype and HBsAg escape and/or drug-resistant mutations.

Methods

A total of 97 complete HBsAg sequences of Bangladeshi HBV isolates from 2005 to 2017 from NCBI GenBank were extracted and analyzed using several HBV bioinformatics tools such as Geno2pheno-HBV, HBV Serotyper, HIV-Grade:HBV-Tool, and CLC sequence viewer.

Results

The prevalence of genotypes A, C, and D are 18, 46 and 35% which correspond to serotype adw, adr, and ayw, respectively. The prevalence of HBsAg escape mutations is 51% and most of which (62%) are found in the genotype D followed by 32% in genotype C and 6% in genotype A. Interestingly most (24/36) of the sequences of HBsAg escape mutations contained 128 V mutant which all belongs to only serotype ayw3 (Genotype D). Prevalence of drug-resistant mutations is ~ 11%, most of which are from genotype C (63.64%) and D (36.36%). Lamivudine resistant mutations were found in ~ 11% of sequences followed by Telbivudine 10% and Adefovir 3% where Tenofovir showed susceptibility to all 97 sequences. Moreover, 7 among of 97 sequences showed both HBsAg and drugs resistant mutations and none of them are found due to the same nucleotide substitutions.

Conclusion

There is a strong correlation among the genotype/serotype and HBsAg escape and/or drug-resistant mutations. This meta-analytical review will be helpful for genotype-serotype prediction by PCR-based diagnosis and development of vaccine and/or diagnostic kits, and the treatment against HBV infection in the future.

Cost-effectiveness of strategy-based approach to treatment of genotype 1 chronic hepatitis C

BACKGROUND AND AIM

The high cost of chronic hepatitis C (HCV) direct-acting antivirals (DAAs) poses significant financial challenges for health payers, especially in Asia. A personalized treatment strategy based on individualized probability of virological response using oral DAAs as second-line therapy would seem practical but has not been studied.

METHODS

We performed a Markov model to project health outcomes and costs for patients with genotype 1 HCV through 10 treatment strategies over a lifetime period. The implication of retreatment was also incorporated to reflect real-life situation.

RESULTS

Using boceprevir and peginterferon/ribavirin (BOC/PR, the least costly treatment) as a base case, the all-oral therapies such as ombitasvir/paritaprevir/ritonavir-dasabuvir are cost-effective with an incremental cost-effective ratio of $US50 828. However, the all-oral DAAs would no longer be cost-effective compared with conventional therapies if retreatment were taken into account. A road map strategy using rapid virological response to guide use of BOC/PR and sofosbuvir/PR had the most favorable incremental cost-effective ratio ($US27 782) relative to BOC/PR. Nevertheless, the trade-off with the cost-effectiveness of the road map strategy is an increased number of liver-related deaths compared with all-oral DAAs (52 vs 10-20 per 10 000 patients) by incorporating retreatment.

CONCLUSIONS

The 12-week all-oral DAAs were cost-effective options using conventional drug-to-drug comparison. However, they cease to be cost-effective when treatment strategies incorporating DAA retreatment for interferon failures are incorporated. HCV management can be optimized by adopting individualized treatment algorithm providing a practical solution to health payers to make oral DAAs accessible to those who need them most.

The hepatitis B virus ribonuclease H as a drug target

Chronic hepatitis B virus (HBV) infection is a leading cause of hepatitis, liver failure, and hepatocellular carcinoma. An outstanding vaccine is available; however, the number of infections remains high. Current anti-HBV treatments with interferon α and nucleos(t)ide analogs clear the infection in only a small minority of patients, and either induce serious side-effects or are of very long duration. HBV is a small, enveloped DNA virus that replicates by reverse transcription via an RNA intermediate. The HBV ribonuclease H (RNaseH) is essential for viral replication, but it has not been exploited as a drug target. Recent low-throughput screening of compound classes with anti-Human Immunodeficiency Virus RNaseH activity led to identification of HBV RNaseH inhibitors in three different chemical families that block HBV replication. These inhibitors are promising candidates for development into new anti-HBV drugs. The RNaseH inhibitors may help improve treatment efficacy enough to clear the virus from the liver when used in combination with existing anti-HBV drugs and/or with other novel inhibitors under development. This article forms part of a symposium in Antiviral Research on "An unfinished story: from the discovery of the Australia antigen to the development of new curative therapies for hepatitis B."

A pilot study examining the safety and tolerability of valacyclovir in veterans with hepatitis C virus/herpes simplex virus type 2 coinfection

INTRODUCTION

We performed a pilot study examining the safety and tolerability of valacyclovir in veterans with herpes simplex virus type 2 and hepatitis C virus (HCV) coinfection.

METHODS

We performed a randomized double-blind, placebo-controlled, crossover clinical trial in U.S. veterans with genotype 1 HCV/herpes simplex virus type 2 coinfection. Patients were randomized 1:1 in blocks of 10 to receive either 1 g twice-daily valacyclovir or matching placebo for 8 weeks followed by a 2-week washout phase with daily placebo. The alternate therapy (valacyclovir or placebo) was given for an additional 8-week period. Safety assessments were performed every 2 weeks. Changes in HCV RNA and alanine aminotransferase (ALT) were estimated using linear mixed models (SAS Proc Mixed).

RESULTS

Thirty patients were enrolled. Valacyclovir was not associated with toxicity or adverse events. ALT levels declined 6% to 10%; mean HCV RNA levels were reduced 24% (1.3 million IU/mL [0.21 log10 IU/mL]) during the valacyclovir phase (P = 0.08) with no carryover effect observed (P = 0.21).

CONCLUSIONS

Valacyclovir 1 g twice daily showed no evidence of hepatotoxicity in U.S. veterans with hepatitis C. A modest reduction in serum levels of ALT and plasma levels of HCV RNA was observed.

Inhibition of hepatitis C virus infection by DNA aptamer against NS2 protein

NS2 protein is essential for hepatitis C virus (HCV) replication. NS2 protein was expressed and purified. Aptamers against NS2 protein were raised and antiviral effects of the aptamers were examined. The molecular mechanism through which the aptamers exert their anti-HCV activity was investigated. The data showed that aptamer NS2-3 inhibited HCV RNA replication in replicon cell line and infectious HCV cell culture system. NS2-3 and another aptamer NS2-2 were demonstrated to inhibit infectious virus production without cytotoxicity in vitro. They did not affect hepatitis B virus replication. Interferon beta (IFN-β) and interferon-stimulated genes (ISGs) were not induced by the aptamers in HCV-infected hepatocytes. Furthermore, our study showed that N-terminal region of NS2 protein is involved in the inhibition of HCV infection by NS2-2. I861T within NS2 is the major resistance mutation identified. Aptamer NS2-2 disrupts the interaction of NS2 with NS5A protein. The data suggest that NS2-2 aptamer against NS2 protein exerts its antiviral effects through binding to the N-terminal of NS2 and disrupting the interaction of NS2 with NS5A protein. NS2-specific aptamer is the first NS2 inhibitor and can be used to understand the mechanisms of virus replication and assembly. It may be served as attractive candidates for inclusion in the future HCV direct-acting antiviral combination therapies.

Current management of hepatitis C virus infection in patients with HIV co-infection

As a result of shared routes of transmission, coinfection with hepatitis C virus (HCV) is common in human immunodeficiency virus (HIV)-infected patients. The prevalence of HIV/HCV coinfection is particularly high among persons who have used injection drugs; however, more recently, sexual transmission of HCV has been recognized among HIV-infected men who have sex with men (MSM). Over the past decade, the effectiveness of HIV treatment improved substantially, leading to a substantial reduction in HIV/AIDS-related deaths; in this context, liver disease due to HCV infection has emerged as major concern for co-infected patients. Over the same period, treatment of HCV remained stagnant, with pegylated interferon alfa (PegIFN) plus ribavirin (RBV; PegIFN/RBV) entrenched as the standard treatment for HCV infection for co-infected patients, who have the greatest risk for liver disease. However, the effectiveness of HCV treatment in this population has been disappointing because of low rates of treatment initiation and success. In 2011, novel HCV NS3/4A PIs (PIs), telaprevir and boceprevir, were approved for use in combination with PegIFN/RBV for the treatment of HCV genotype 1 infection; at the time of approval, important questions regarding the efficacy, safety, and potential for drug interactions with telaprevir and boceprevir had not been answered. More recently, data from drug-interaction studies and 2 small, phase II clinical trials indicate that these HCV treatment regimens may lead to higher rates of HCV eradication in HIV/HCV-coinfected patients, with manageable toxicity and pharmacologic interactions with antiretroviral drugs. As such, these HCV PI-based regimens have emerged as the standard for the treatment of HCV genotype 1 infection in carefully selected HIV-infected patients.

Differential cognitive impairment in HCV coinfected men with controlled HIV compared to HCV monoinfection

BACKGROUND

Individuals infected with both HIV and hepatitis C virus (HCV) have shown impaired performance on different neuropsychological (NP) tests; however, whether coinfected individuals with controlled HIV and minimal liver damage in the era of antiretroviral therapy have impairment is understudied.

METHODS

Nineteen HCV monoinfected, 17 HIV/HCV coinfected, and 17 control male participants were evaluated for depression, attention, executive function, information processing, fine motor speed, and verbal/visual learning/memory. Eleven controls and 14 HIV monoinfected participants with controlled viral load from a previous study were also included for comparison. At time of testing, participants were not using drugs or alcohol and did not have cirrhosis. A global deficit score (GDS) was calculated from 7 domains of NP tests and alterations in specific domains were determined.

RESULTS

HIV/HCV subjects had a higher depression score (11.1 ± 7.5) than controls (5.4 ± 4.1, P = 0.010) and a higher GDS score (0.77 ± 0.47) than HCV (0.46 ± 0.34, P = 0.036), HIV (0.45 ± 0.36, P = 0.008), and controls (0.30 ± 0.29, P = 0.001). Coinfection was associated with worse scores in attention working memory (P =0.007), executive function (P = 0.01), fine motor function (P = 0.011), verbal learning/memory (P < 0.001), and visual learning/memory (P < 0.001) compared to controls. Within the HCV group, viral load was associated with lower attention, executive function, and information processing speed and positively with GDS.

CONCLUSIONS

Coinfection significantly increased the risk of cognitive impairment in subjects with controlled HIV viral loads. In HCV monoinfected but not coinfected subjects, HCV viral load correlated with worsening GDS, suggesting different pathways for NP impairment.

The hepatitis B virus ribonuclease H is sensitive to inhibitors of the human immunodeficiency virus ribonuclease H and integrase enzymes

Nucleos(t)ide analog therapy blocks DNA synthesis by the hepatitis B virus (HBV) reverse transcriptase and can control the infection, but treatment is life-long and has high costs and unpredictable long-term side effects. The profound suppression of HBV by the nucleos(t)ide analogs and their ability to cure some patients indicates that they can push HBV to the brink of extinction. Consequently, more patients could be cured by suppressing HBV replication further using a new drug in combination with the nucleos(t)ide analogs. The HBV ribonuclease H (RNAseH) is a logical drug target because it is the second of only two viral enzymes that are essential for viral replication, but it has not been exploited, primarily because it is very difficult to produce active enzyme. To address this difficulty, we expressed HBV genotype D and H RNAseHs in E. coli and enriched the enzymes by nickel-affinity chromatography. HBV RNAseH activity in the enriched lysates was characterized in preparation for drug screening. Twenty-one candidate HBV RNAseH inhibitors were identified using chemical structure-activity analyses based on inhibitors of the HIV RNAseH and integrase. Twelve anti-RNAseH and anti-integrase compounds inhibited the HBV RNAseH at 10 µM, the best compounds had low micromolar IC₅₀ values against the RNAseH, and one compound inhibited HBV replication in tissue culture at 10 µM. Recombinant HBV genotype D RNAseH was more sensitive to inhibition than genotype H. This study demonstrates that recombinant HBV RNAseH suitable for low-throughput antiviral drug screening has been produced. The high percentage of compounds developed against the HIV RNAseH and integrase that were active against the HBV RNAseH indicates that the extensive drug design efforts against these HIV enzymes can guide anti-HBV RNAseH drug discovery. Finally, differential inhibition of HBV genotype D and H RNAseHs indicates that viral genetic variability will be a factor during drug development.

Current therapy for HBV blocks DNA synthesis by the viral reverse transcriptase and can control the infection indefinitely, but treatment rarely cures patients. More patients could be cured by suppressing HBV replication further using a new drug in combination with the existing ones. The HBV RNAseH is a logical drug target because it is the second of only two viral enzymes that are essential for viral replication, but it has not been exploited, primarily because it is very difficult to produce active enzyme. We expressed active recombinant HBV RNAseHs and demonstrated that it was suitable for antiviral drug screening. Twenty-one candidate HBV RNAseH inhibitors were identified based on antagonists of the HIV RNAseH and integrase enzymes. Twelve of these compounds inhibited the HBV RNAseH in enzymatic assays, and one inhibited HBV replication in cell-based assays. The high percentage of compounds developed against the HIV RNAseH and integrase that were also active against the HBV RNAseH indicates that the extensive drug design efforts against these HIV enzymes can be used to guide anti-HBV RNAseH drug discovery.

Hepatitis C virus-human immunodeficiency virus coinfection

As a result of shared modes of transmission, chronic hepatitis C infection is common in HIV-infected patients, particularly among those who have used injection drugs as well as men who have sex with men (MSMs). In the era of effective antiretroviral therapy, HCV infection has emerged as a major cause of morbidity and mortality worldwide. Over the last decade, treatment with peginterferon (PEG-IFN) plus ribavirin (RBV) has been recommended for coinfected patients who are at the greatest risk for liver disease; however, the effectiveness of HCV treatment in this population has been disappointing. Challenges to the use of HCV NS3/4A protease inhibitors, telaprevir and boceprevir, patients with HIV/HCV coinfection include the potential for interactions between different drugs, addition of drug toxicities, and the need for therapy with PEG-IFN. Despite these challenges, limited data indicate that telaprevir and boceprevir given in combination with PEG-IFN/RBV increase the rate of viral suppression in coinfected patients with manageable toxicity and drug-drug interaction profile. Accordingly, these agents may be recommended for HCV treatment in carefully selected HIV-infected persons.

Triple combination antiviral drug (TCAD) composed of amantadine, oseltamivir, and ribavirin impedes the selection of drug-resistant influenza A virus

Widespread resistance among circulating influenza A strains to at least one of the anti-influenza drugs is a major public health concern. A triple combination antiviral drug (TCAD) regimen comprised of amantadine, oseltamivir, and ribavirin has been shown to have synergistic and broad spectrum activity against influenza A strains, including drug resistant strains. Here, we used mathematical modeling along with three different experimental approaches to understand the effects of single agents, double combinations, and the TCAD regimen on resistance in influenza in vitro, including: 1) serial passage at constant drug concentrations, 2) serial passage at escalating drug concentrations, and 3) evaluation of the contribution of each component of the TCAD regimen to the suppression of resistance. Consistent with the modeling which demonstrated that three drugs were required to suppress the emergence of resistance in influenza A, treatment with the TCAD regimen resulted in the sustained suppression of drug resistant viruses, whereas treatment with amantadine alone or the amantadine-oseltamivir double combination led to the rapid selection of resistant variants which comprised ∼100% of the population. Furthermore, the TCAD regimen imposed a high genetic barrier to resistance, requiring multiple mutations in order to escape the effects of all the drugs in the regimen. Finally, we demonstrate that each drug in the TCAD regimen made a significant contribution to the suppression of virus breakthrough and resistance at clinically achievable concentrations. Taken together, these data demonstrate that the TCAD regimen was superior to double combinations and single agents at suppressing resistance, and that three drugs at a minimum were required to impede the selection of drug resistant variants in influenza A virus. The use of mathematical modeling with multiple experimental designs and molecular readouts to evaluate and optimize combination drug regimens for the suppression of resistance may be broadly applicable to other infectious diseases.

Emerging therapies in hepatitis C: dawn of the era of the direct-acting antivirals

The HCV viral life cycle provides targets for drug development at virtually every step, and many new drugs aimed at these targets are currently being developed. Clinical practice takes a major step forward this year with the arrival of telaprevir and boceprevir, which will be added to the current standard of care of pegIFNα/RBV. Patients will need to be monitored closely and counseled extensively, and clinicians will need to learn the new response-guided therapy algorithms with these therapies. Although there remains work to be done in the field of HCV, these therapies will allow many more patients the opportunity to eradicate HCV infection.

Combination Therapy for Chronic Hepatitis B: Current Indications

Hepatitis B infection remains a major public health problem globally and in the United States, with significant use of healthcare resources. Several therapeutic agents active against viral and host targets are currently available for its treatment. The success of combination therapy in HIV infection, which has similarities to hepatitis B in both therapeutic targets and treatment options, stimulated studies on the efficacy and safety of various combinations of available drugs in the treatment of hepatitis B infection. In this review, we analyze the current role of combination therapy in chronic hepatitis B infection.

A new standard of care for the treatment of chronic HCV infection

The introduction of direct acting antiviral agents (DAAs) will markedly change treatment options for individuals who have a chronic HCV infection. Within the next few months, licensing of two HCV protease inhibitors (boceprevir and telaprevir) for the treatment of patients with chronic hepatitis C as part of a triple therapy with PEG-IFN-α and ribavirin is anticipated in the USA, Europe and many other countries. Final results of pivotal phase III clinical trials in previously untreated and treatment-experienced patients with HCV genotype 1 infection were presented at the Annual Meeting of the American Association for the Study of the Liver 2010 held in Boston, MA, USA, and at the Annual Conference of the Asian Pacific Association for the Study of the Liver 2011, held in Bangkok, Thailand. This article summarizes the results of these phase III trials in consideration of accumulating data on important baseline and on-treatment predictive factors for treatment response, such as the host IL28B genotype and the rapid virologic response; the introduction of these new therapies into clinical practice is also covered. Furthermore, preliminary data on the combination of different classes of DAAs, such as HCV protease inhibitors and HCV polymerase inhibitors, without interferon α are discussed.

Forthcoming challenges in the management of direct-acting antiviral agents (DAAs) for hepatitis C

Agents that specifically target the replication cycle of the virus direct-acting antiviral agents (DAAs) by directly inhibiting the NS3/4A serine protease, the NS5B polymerase and NS5A are currently in clinical development. The need to achieve serum drug concentrations able to suppress viral replication is a key factor for a successful antiviral therapy and the prevention of resistance. Thus pharmacokinetics parameters became important issues for drugs used in the therapy of hepatitis C. The ratio of C(min)/IC(50) (inhibitory quotient or IQ) can provide a surrogate measure of a drug's ability to suppress HCV replication, by taking into account the relationship between plasma drug levels and viral susceptibility to the drug. Ritonavir boosting may be a useful strategy to improve pharmacokinetic parameters. Characterising resistance to DAAs in clinical trials is essential for the management of a drug regimen to reduce the development of resistance and thereby maximise SVR rate. The lesson of HIV therapy, provide a compelling case for the exploration of combinations of direct-acting antiviral agents.

Extended treatment duration for treatment naïve chronic hepatitis C genotype 1 late viral responders: a meta-analysis comparing 48 weeks vs 72 weeks of pegylated interferon and ribavirin

Patients with genotype I chronic hepatitis C virus (HCV) infection with late virological response to therapy have low sustained viral response (SVR) with standard 48 weeks of therapy and may benefit from extended therapy. We performed a systematic review and meta-analysis of five studies to compare the outcome of 48 weeks vs 72 weeks treatment in treatment naïve chronic hepatitis C genotype I patients with late virological response. The end of treatment response with extended 72 weeks of treatment compared to standard 48 weeks of treatment was similar 48% and 56%, respectively, with pooled odds ratio (OR) (0.85; 95% CI 0.52-1.37). However, the SVR rates were higher with 72 weeks of treatment compared to 48 weeks treatment 32%vs 25% with pooled OR of 1.67 in favour of extended duration therapy (95% CI 1.16-2.40). This was because of lower relapse rates with extended duration therapy (35%vs 55%) with OR of 0.39 in favour of 72 weeks therapy (95% CI 0.25-0.61). There was no heterogeneity. No publication bias was noted as assessed by Egger's test. Extending the treatment duration from 48 to 72 weeks in genotype 1 infected patients with late virological response improves SVR. Thus, therapy extension in genotype 1 late viral responders (LVR) may be a consideration to improve treatment response; however, the proportion of patients with LVR that might benefit from 72-week therapy appears to be small.

Mutant spectra in virus behavior

RNA viruses replicate as complex mutant spectra, also termed ‘mutant clouds’, known as viral quasispecies. While this is a widely observed viral population structure, it is less known that a number of biologically relevant features of this important group of viral pathogens depend on (or are strongly influenced by) the complexity and composition of mutant spectra. Among them, fitness increase or decrease depending on intrapopulation complementation or interference, selection triggered by memory genomes, pathogenic potential of viruses, disease evolution and the response to antiviral treatments. Quasispecies represent the recognition of complex behavior in viruses, and it is an oversimplification to equate such a population structure with the classic polymorphism of population biology. Darwinian principles acting on genome collectivities that replicate with high error rates provide a unique population structure prone to flexible and largely unpredictable behavior.

The Hepatitis C Virus Nonstructural Protein 2 (NS2): An Up-and-Coming Antiviral Drug Target

Infection with Hepatitis C Virus (HCV) continues to be a major global health problem. To overcome the limitations of current therapies using interferon-α in combination with ribavirin, there is a need to develop drugs that specifically block viral proteins. Highly efficient protease and polymerase inhibitors are currently undergoing clinical testing and will become available in the next few years. However, with resistance mutations emerging quickly, additional enzymatic activities or functions of HCV have to be targeted by novel compounds. One candidate molecule is the nonstructural protein 2 (NS2), which contains a proteolytic activity that is essential for viral RNA replication. In addition, NS2 is crucial for the assembly of progeny virions and modulates various cellular processes that interfere with viral replication. This review describes the functions of NS2 in the life cycle of HCV and highlights potential antiviral strategies involving NS2.