Rapid and strong antiviral activity of the non-nucleosidic NS5B polymerase inhibitor BI 207127 in combination with peginterferon alfa 2a and ribavirin

Direct-acting antivirals for chronic hepatitis C

BACKGROUND

Millions of people worldwide suffer from hepatitis C, which can lead to severe liver disease, liver cancer, and death. Direct-acting antivirals (DAAs), e.g. sofosbuvir, are relatively new and expensive interventions for chronic hepatitis C, and preliminary results suggest that DAAs may eradicate hepatitis C virus (HCV) from the blood (sustained virological response). Sustained virological response (SVR) is used by investigators and regulatory agencies as a surrogate outcome for morbidity and mortality, based solely on observational evidence. However, there have been no randomised trials that have validated that usage.

OBJECTIVES

To assess the benefits and harms of DAAs in people with chronic HCV.

SEARCH METHODS

We searched for all published and unpublished trials in The Cochrane Hepato-Biliary Group Controlled Trials Register, CENTRAL, MEDLINE, Embase, Science Citation Index Expanded, LILACS, and BIOSIS; the Chinese Biomedical Literature Database (CBM), China Network Knowledge Information (CNKI), the Chinese Science Journal Database (VIP), Google Scholar, The Turning Research into Practice (TRIP) Database, ClinicalTrials.gov, European Medicines Agency (EMA) (www.ema.europa.eu/ema/), WHO International Clinical Trials Registry Platform (www.who.int/ictrp), the Food and Drug Administration (FDA) (www.fda.gov), and pharmaceutical company sources for ongoing or unpublished trials. Searches were last run in October 2016.

SELECTION CRITERIA

Randomised clinical trials comparing DAAs versus no intervention or placebo, alone or with co-interventions, in adults with chronic HCV. We included trials irrespective of publication type, publication status, and language.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Our primary outcomes were hepatitis C-related morbidity, serious adverse events, and health-related quality of life. Our secondary outcomes were all-cause mortality, ascites, variceal bleeding, hepato-renal syndrome, hepatic encephalopathy, hepatocellular carcinoma, non-serious adverse events (each reported separately), and SVR. We systematically assessed risks of bias, performed Trial Sequential Analysis, and followed an eight-step procedure to assess thresholds for statistical and clinical significance. We evaluated the overall quality of the evidence, using GRADE.

MAIN RESULTS

We included a total of 138 trials randomising a total of 25,232 participants. The trials were generally short-term trials and designed primarily to assess the effect of treatment on SVR. The trials evaluated 51 different DAAs. Of these, 128 trials employed matching placebo in the control group. All included trials were at high risk of bias. Eighty-four trials involved DAAs on the market or under development (13,466 participants). Fifty-seven trials administered DAAs that were discontinued or withdrawn from the market. Study populations were treatment-naive in 95 trials, had been exposed to treatment in 17 trials, and comprised both treatment-naive and treatment-experienced individuals in 24 trials. The HCV genotypes were genotype 1 (119 trials), genotype 2 (eight trials), genotype 3 (six trials), genotype 4 (nine trials), and genotype 6 (one trial). We identified two ongoing trials.We could not reliably determine the effect of DAAs on the market or under development on our primary outcome of hepatitis C-related morbidity or all-cause mortality. There were no data on hepatitis C-related morbidity and only limited data on mortality from 11 trials (DAA 15/2377 (0.63%) versus control 1/617 (0.16%); OR 3.72, 95% CI 0.53 to 26.18, very low-quality evidence). We did not perform Trial Sequential Analysis on this outcome.There is very low quality evidence that DAAs on the market or under development do not influence serious adverse events (DAA 5.2% versus control 5.6%; OR 0.93, 95% CI 0.75 to 1.15 , 15,817 participants, 43 trials). The Trial Sequential Analysis showed that there was sufficient information to rule out that DAAs reduce the relative risk of a serious adverse event by 20% when compared with placebo. The only DAA that showed a lower risk of serious adverse events when meta-analysed separately was simeprevir (OR 0.62, 95% CI 0.45 to 0.86). However, Trial Sequential Analysis showed that there was not enough information to confirm or reject a relative risk reduction of 20%, and when one trial with an extreme result was excluded, the meta-analysis result showed no evidence of a difference.DAAs on the market or under development may reduce the risk of no SVR from 54.1% in untreated people to 23.8% in people treated with DAA (RR 0.44, 95% CI 0.37 to 0.52, 6886 participants, 32 trials, low quality evidence). Trial Sequential Analysis confirmed this meta-analysis result.Only 1/84 trials on the market or under development assessed the effects of DAAs on health-related quality of life (SF-36 mental score and SF-36 physical score).There was insufficient evidence from trials on withdrawn or discontinued DAAs to determine their effect on hepatitis C-related morbidity and all-cause mortality (OR 0.64, 95% CI 0.23 to 1.79; 5 trials, very low-quality evidence). However, these DAAs seemed to increase the risk of serious adverse events (OR 1.45, 95% CI 1.22 to 1.73; 29 trials, very low-quality evidence). Trial Sequential Analysis confirmed this meta-analysis result.None of the 138 trials provided useful data to assess the effects of DAAs on the remaining secondary outcomes (ascites, variceal bleeding, hepato-renal syndrome, hepatic encephalopathy, and hepatocellular carcinoma).

AUTHORS' CONCLUSIONS

The evidence for our main outcomes of interest come from short-term trials, and we are unable to determine the effect of long-term treatment with DAAs. The rates of hepatitis C morbidity and mortality observed in the trials are relatively low and we are uncertain as to how DAAs affect this outcome. Overall, there is very low quality evidence that DAAs on the market or under development do not influence serious adverse events. There is insufficient evidence to judge if DAAs have beneficial or harmful effects on other clinical outcomes for chronic HCV. Simeprevir may have beneficial effects on risk of serious adverse event. In all remaining analyses, we could neither confirm nor reject that DAAs had any clinical effects. DAAs may reduce the number of people with detectable virus in their blood, but we do not have sufficient evidence from randomised trials that enables us to understand how SVR affects long-term clinical outcomes. SVR is still an outcome that needs proper validation in randomised clinical trials.

Direct-acting antivirals for chronic hepatitis C

BACKGROUND

Millions of people worldwide suffer from hepatitis C, which can lead to severe liver disease, liver cancer, and death. Direct-acting antivirals (DAAs), e.g. sofosbuvir, are relatively new and expensive interventions for chronic hepatitis C, and preliminary results suggest that DAAs may eradicate hepatitis C virus (HCV) from the blood (sustained virological response). Sustained virological response (SVR) is used by investigators and regulatory agencies as a surrogate outcome for morbidity and mortality, based solely on observational evidence. However, there have been no randomised trials that have validated that usage.

OBJECTIVES

To assess the benefits and harms of DAAs in people with chronic HCV.

SEARCH METHODS

We searched for all published and unpublished trials in The Cochrane Hepato-Biliary Group Controlled Trials Register, CENTRAL, MEDLINE, Embase, Science Citation Index Expanded, LILACS, and BIOSIS; the Chinese Biomedical Literature Database (CBM), China Network Knowledge Information (CNKI), the Chinese Science Journal Database (VIP), Google Scholar, The Turning Research into Practice (TRIP) Database, ClinicalTrials.gov, European Medicines Agency (EMA) (www.ema.europa.eu/ema/), WHO International Clinical Trials Registry Platform (www.who.int/ictrp), the Food and Drug Administration (FDA) (www.fda.gov), and pharmaceutical company sources for ongoing or unpublished trials. Searches were last run in October 2016.

SELECTION CRITERIA

Randomised clinical trials comparing DAAs versus no intervention or placebo, alone or with co-interventions, in adults with chronic HCV. We included trials irrespective of publication type, publication status, and language.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Our primary outcomes were hepatitis C-related morbidity, serious adverse events, and health-related quality of life. Our secondary outcomes were all-cause mortality, ascites, variceal bleeding, hepato-renal syndrome, hepatic encephalopathy, hepatocellular carcinoma, non-serious adverse events (each reported separately), and SVR. We systematically assessed risks of bias, performed Trial Sequential Analysis, and followed an eight-step procedure to assess thresholds for statistical and clinical significance. We evaluated the overall quality of the evidence, using GRADE.

MAIN RESULTS

We included a total of 138 trials randomising a total of 25,232 participants. The trials were generally short-term trials and designed primarily to assess the effect of treatment on SVR. The trials evaluated 51 different DAAs. Of these, 128 trials employed matching placebo in the control group. All included trials were at high risk of bias. Eighty-four trials involved DAAs on the market or under development (13,466 participants). Fifty-seven trials administered DAAs that were discontinued or withdrawn from the market. Study populations were treatment-naive in 95 trials, had been exposed to treatment in 17 trials, and comprised both treatment-naive and treatment-experienced individuals in 24 trials. The HCV genotypes were genotype 1 (119 trials), genotype 2 (eight trials), genotype 3 (six trials), genotype 4 (nine trials), and genotype 6 (one trial). We identified two ongoing trials.We could not reliably determine the effect of DAAs on the market or under development on our primary outcome of hepatitis C-related morbidity or all-cause mortality. There were no data on hepatitis C-related morbidity and only limited data on mortality from 11 trials (DAA 15/2377 (0.63%) versus control 1/617 (0.16%); OR 3.72, 95% CI 0.53 to 26.18, very low-quality evidence). We did not perform Trial Sequential Analysis on this outcome.There is very low quality evidence that DAAs on the market or under development do not influence serious adverse events (DAA 5.2% versus control 5.6%; OR 0.93, 95% CI 0.75 to 1.15 , 15,817 participants, 43 trials). The Trial Sequential Analysis showed that there was sufficient information to rule out that DAAs reduce the relative risk of a serious adverse event by 20% when compared with placebo. The only DAA that showed a lower risk of serious adverse events when meta-analysed separately was simeprevir (OR 0.62, 95% CI 0.45 to 0.86). However, Trial Sequential Analysis showed that there was not enough information to confirm or reject a relative risk reduction of 20%, and when one trial with an extreme result was excluded, the meta-analysis result showed no evidence of a difference.DAAs on the market or under development may reduce the risk of no SVR from 54.1% in untreated people to 23.8% in people treated with DAA (RR 0.44, 95% CI 0.37 to 0.52, 6886 participants, 32 trials, low quality evidence). Trial Sequential Analysis confirmed this meta-analysis result.Only 1/84 trials on the market or under development assessed the effects of DAAs on health-related quality of life (SF-36 mental score and SF-36 physical score).There was insufficient evidence from trials on withdrawn or discontinued DAAs to determine their effect on hepatitis C-related morbidity and all-cause mortality (OR 0.64, 95% CI 0.23 to 1.79; 5 trials, very low-quality evidence). However, these DAAs seemed to increase the risk of serious adverse events (OR 1.45, 95% CI 1.22 to 1.73; 29 trials, very low-quality evidence). Trial Sequential Analysis confirmed this meta-analysis result.None of the 138 trials provided useful data to assess the effects of DAAs on the remaining secondary outcomes (ascites, variceal bleeding, hepato-renal syndrome, hepatic encephalopathy, and hepatocellular carcinoma).

AUTHORS' CONCLUSIONS

The evidence for our main outcomes of interest come from short-term trials, and we are unable to determine the effect of long-term treatment with DAAs. The rates of hepatitis C morbidity and mortality observed in the trials are relatively low and we are uncertain as to how DAAs affect this outcome. Overall, there is very low quality evidence that DAAs on the market or under development do not influence serious adverse events. There is insufficient evidence to judge if DAAs have beneficial or harmful effects on other clinical outcomes for chronic HCV. Simeprevir may have beneficial effects on risk of serious adverse event. In all remaining analyses, we could neither confirm nor reject that DAAs had any clinical effects. DAAs may reduce the number of people with detectable virus in their blood, but we do not have sufficient evidence from randomised trials that enables us to understand how SVR affects long-term clinical outcomes. SVR is still an outcome that needs proper validation in randomised clinical trials.

Allosteric mechanism of cyclopropylindolobenzazepine inhibitors for HCV NS5B RdRp via dynamic correlation network analysis

HCV RNA dependent RNA polymerase (RdRp) nonstructural protein 5B (NS5B) is a major target against hepatitis C virus (HCV) for antiviral therapy. Recently discovered cyclopropylindolobenzazepine derivatives have been considered as the most potent for their ability to bind the thumb site 1 domain and allosterically inhibit HCV NS5B RdRp activity. However, the allosteric mechanism for these derivatives has not been clarified at the molecular level. In this study, fluctuation correlation networks were constructed based on all-atom molecular dynamics simulations to elucidate the allosteric mechanism. The fluctuation correlation networks between free and M2 bound NS5B are significantly different. Information can better transfer from the allosteric site to the catalytic site for bound NS5B than for free NS5B. Thus, the hypothesis of "binding induced allosteric regulation" is proposed to link the enzyme activation and inhibitor binding and then confirmed by the mutant network. Finally, one possible allosteric pathway was identified with the shortest path and evaluated by the perturbation of the network. These methods will be helpful to identify the allosteric pathway of other proteins and to design new drugs targeting the pathway.

The Role of Direct-acting Antivirals in the Treatment of Children with Chronic Hepatitis C

In the United States, chronic infection with the hepatitis C virus (HCV) affects an estimated 0.1-2% of the pediatric population, who are consequently at risk for major complications, including cirrhosis, hepatocellular carcinoma, and death. The current standard of treatment for chronic hepatitis C (CHC) in children is pegylated-interferon-alpha (PEG-IFN) in combination with ribavirin. PEG-IFN/ribavirin therapy is approved for children ages 3 and older; however, it is often held from use until adulthood because of its extensive list of potential side effects and high likelihood of causing adverse symptoms. While CHC is usually indolent in children and adolescents, immediately treating and curbing the spread of HCV before adulthood is important, as there can be transmission to other individuals via sexual activity and infected females can later vertically transmit the infection during pregnancy, the latter representing the most common means of transmission for children in the United States. The recent development of direct-acting antivirals has shown promising results in clinical trials for use in children and has dramatically increased the rates of sustained virological response in adults while improving side effect profiles as compared to interferon-based treatments. Given the usually indolent course of CHC in children, significant side effects of the currently-approved PEG-IFN/ribavirin therapy, and likely availability of all-oral interferon-free regimens for children within a few years, deferring treatment in clinically-stable children with CHC in anticipation of upcoming superior treatment modalities may be justified.

HCVerso1 and 2: faldaprevir with deleobuvir (BI 207127) and ribavirin for treatment-naïve patients with chronic hepatitis C virus genotype-1b infection

The interferon-free combination of once-daily faldaprevir 120 mg, twice-daily deleobuvir 600 mg, and weight-based ribavirin was evaluated in two Phase III studies (HCVerso1, HCVerso2) in hepatitis C virus genotype-1b-infected, treatment-naïve patients, including those ineligible for peginterferon (HCVerso2). Patients without cirrhosis were randomized to 16 weeks (Arm 1; n=208 HCVerso1, n=213 HCVerso2) or 24 weeks (Arm 2; n=211 in both studies) of faldaprevir + deleobuvir + ribavirin. Patients with compensated cirrhosis received open-label faldaprevir + deleobuvir + ribavirin for 24 weeks (Arm 3; n=51, n=72). Primary endpoints were comparisons of adjusted sustained virologic response (SVR) rates with historical rates: 71% (HCVerso1) and 68% (HCVerso2). Adjusted SVR12 rates were significantly greater than historical controls for Arms 1 and 2 in HCVerso2 (76%, 95% confidence interval [CI] 71-81, P=0.002; 81%, 95% CI 76-86, P<0.0001) and Arm 2 in HCVerso1 (81%, 95% CI 77-86, P<0.0001), but not for Arm 1 of HCVerso1 (72%, 95% CI 66-77, P=0.3989). Unadjusted SVR12 rates in Arms 1, 2, and 3 were 71.6%, 82.5%, and 72.5%, respectively, in HCVerso1 and 75.6%, 82.0%, and 73.6%, respectively, in HCVerso2. Virologic breakthrough and relapse occurred in 24-week arms in 8%-9% and 1% of patients, respectively, and in 16-week arms in 7%-8% and 9%-11% of patients, respectively. The most common adverse events were nausea (46%-61%) and vomiting (29%-35%). Adverse events resulted in discontinuation of all medications in 6%-8% of patients. In treatment-naïve patients with hepatitis C virus genotype-1b infection, with or without cirrhosis, faldaprevir + deleobuvir + ribavirin treatment for 24 weeks resulted in adjusted SVR12 rates significantly higher than historical controls. Both studies were registered in ClinicalTrials.gov (NCT01732796, NCT01728324).

Resistance Analyses of HCV NS3/4A Protease and NS5B Polymerase from Clinical Studies of Deleobuvir and Faldaprevir

Background & Aim

The resistance profile of anti-hepatitis C virus (HCV) agents used in combination is important to guide optimal treatment regimens. We evaluated baseline and treatment-emergent NS3/4A and NS5B amino-acid variants among HCV genotype (GT)-1a and -1b-infected patients treated with faldaprevir (HCV protease inhibitor), deleobuvir (HCV polymerase non-nucleoside inhibitor), and ribavirin in multiple clinical studies.

Methods

HCV NS3/4A and NS5B population sequencing (Sanger method) was performed on all baseline plasma samples (n = 1425 NS3; n = 1556 NS5B) and on post-baseline plasma samples from patients with virologic failure (n = 113 GT-1a; n = 221 GT-1b). Persistence and time to loss of resistance-associated variants (RAVs) was estimated using Kaplan–Meier analysis.

Results

Faldaprevir RAVs (NS3 R155 and D168) and deleobuvir RAVs (NS5B 495 and 496) were rare (<1%) at baseline. Virologic response to faldaprevir/deleobuvir/ribavirin was not compromised by common baseline NS3 polymorphisms (e.g. Q80K in 17.5% of GT-1a) or by NS5B A421V, present in 20% of GT-1a. In GT-1b, alanine at NS5B codon 499 (present in 15% of baseline sequences) was associated with reduced response. Treatment-emergent RAVs consolidated previous findings: NS3 R155 and D168 were key faldaprevir RAVs; NS5B A421 and P495 were key deleobuvir RAVs. Among on-treatment virologic breakthroughs, RAVs emerged in both NS3 and NS5B (>90%). Virologic relapse was associated with RAVs in both NS3 and NS5B (53% GT-1b; 52% GT-1b); some virologic relapses had NS3 RAVs only (47% GT-1a; 17% GT-1b). Median time to loss of GT-1b NS5B P495 RAVs post-treatment (5 months) was less than that of GT-1b NS3 D168 (8.5 months) and GT-1a R155 RAVs (11.5 months).

Conclusion

Faldaprevir and deleobuvir RAVs are more prevalent among virologic failures than at baseline. Treatment response was not compromised by common NS3 polymorphisms; however, alanine at NS5B amino acid 499 at baseline (wild-type in GT-1a, polymorphism in GT-1b) may reduce response to this deleobuvir-based regimen.

Treatment of HCV in Patients who Failed First-Generation PI Therapy: a Review of Current Literature

The addition of the first direct-acting antiviral agents, the NS3 protease inhibitors boceprevir or telaprevir, to peg interferon and ribavirin was a major advance in the treatment of genotype 1 hepatitis C individuals with sustained virological response (SVR) rates of 63-75 %. Those who did not achieve SVR had high rates of resistance-associated variants against NS3 protease domain. Retreatment options for those who have failed first-generation protease inhibitors generally are guided by retreatment with direct-acting antiviral agents from other classes. Phase 2 and phase 3 data have demonstrated that retreatment with 12-24 weeks of a NS5B inhibitor (sofosbuvir) in combination with a NS5a inhibitor (daclatasvir or ledipasvir) with or without ribavirin can achieve SVR at high rates comparable to treatment-naive individuals.

New hepatitis C virus therapies: drug classes and metabolism, drug interactions relevant in the transplant settings, drug options in decompensated cirrhosis, and drug options in end-stage renal disease

PURPOSE OF REVIEW

This article will review the new direct acting antiviral agent (DAA) drug classes for the treatment of hepatitis C, how they are combined and the relevant drug-drug interactions in the postliver transplant setting. Treatment options for chronic hepatitis C in patients with decompensated cirrhosis and end-stage renal disease will also be discussed.

RECENT FINDINGS

The availability of new drug classes has increased the treatment options in patients with hepatitis C in the post-transplant settings. Clinical trials have concluded that sofosbuvir (SOF) with ledipasvir (LDV) may be safely administered with calcineurin inhibitors (tacrolimus, cyclosporine) and rapamycin inhibitors (sirolimus, everolimus). Similarly, paritaprevir/ritonavir, ombitasvir, and dasabuvir may be administered with tacrolimus and cyclosporine though appropriate dose adjustments must be made to the calcineurin inhibitors. In those with decompensated Childs B/C cirrhosis, SOF, SOF and LDV, as well as daclatasvir may be given without dose adjustment. In renal impairment, all DAAs may be used safely down to a glomerular filteration rate (GFR) of 30 ml/min. Simeprevir, paritaprevir, ombitasvir, and dasabuvir may be given for those down to GFR of 15 ml/min. Finally, daclatasvir may be given without dose administration change.

SUMMARY

In summary, DAAs have better tolerability and greater efficacy than interferon-based therapy post-transplant. Drug-drug interactions must be carefully assessed when these newer agents are used for therapy in the postliver transplant settings. Thus far, dose adjustments for DAAs have not been required in chronic kidney disease though data are incomplete in those with severe chronic kidney disease (CKD) or on dialysis. Hepatitis C treatment in those with decompensated cirrhosis results in impaired hepatic metabolism that may affect DAA levels, and clinicians should carefully choose treatment options for Childs B and C cirrhotic patients.

Using the Hepatitis C Virus RNA-Dependent RNA Polymerase as a Model to Understand Viral Polymerase Structure, Function and Dynamics

Viral polymerases replicate and transcribe the genomes of several viruses of global health concern such as Hepatitis C virus (HCV), human immunodeficiency virus (HIV) and Ebola virus. For this reason they are key targets for therapies to treat viral infections. Although there is little sequence similarity across the different types of viral polymerases, all of them present a right-hand shape and certain structural motifs that are highly conserved. These features allow their functional properties to be compared, with the goal of broadly applying the knowledge acquired from studying specific viral polymerases to other viral polymerases about which less is known. Here we review the structural and functional properties of the HCV RNA-dependent RNA polymerase (NS5B) in order to understand the fundamental processes underlying the replication of viral genomes. We discuss recent insights into the process by which RNA replication occurs in NS5B as well as the role that conformational changes play in this process.

Synthesis of deleobuvir, a potent hepatitis C virus polymerase inhibitor, and its major metabolites labeled with carbon-13 and carbon-14

Deleobuvir, (2E)-3-(2-{1-[2-(5-bromopyrimidin-2-yl)-3-cyclopentyl-1-methyl-1H-indole-6-carboxamido]cyclobutyl}-1-methyl-1H-benzimidazol-6-yl)prop-2-enoic acid (1), is a non-nucleoside, potent, and selective inhibitor of hepatitis C virus NS5B polymerase. Herein, we describe the detailed synthesis of this compound labeled with carbon-13 and carbon-14. The synthesis of its three major metabolites, namely, the reduced double bond metabolite (2) and the acyl glucuronide derivatives of (1) and (2), is also reported. Aniline-(13) C6 was the starting material to prepare butyl (E)-3-(3-methylamino-4-nitrophenyl-(13) C6 )acrylate [(13) C6 ]-(11) in six steps. This intermediate was then used to obtain [(13) C6 ]-(1) and [(13) C6 ]-(2) in five and four more steps, respectively. For the radioactive synthesis, potassium cyanide-(14) C was used to prepare 1-cylobutylaminoacid [(14) C]-(23) via Buchrer-Bergs reaction. The carbonyl chloride of this acid was then used to access both [(14) C]-(1) and [(14) C]-(2) in four steps. The acyl glucuronide derivatives [(13) C6 ]-(3), [(13) C6 ]-(4) and [(14) C]-(3) were synthesized in three steps from the acids [(13) C6 ]-(1), [(13) C6 ]-(2) and [(14) C]-(1) using known procedures.

Two Distinct Hepatitis C Virus Genotype 1a Clades Have Different Geographical Distribution and Association With Natural Resistance to NS3 Protease Inhibitors

Background.  Hepatitis C virus (HCV) genotype 1 is the most prevalent worldwide. Subtype 1a, compared with 1b, shows lower response rates and higher propensity to select for drug resistance to NS3 and selected NS5A and nonnucleoside NS5B inhibitors. Two distinct clades of subtype 1a have been described. Methods.  Using Bayesian methodology, we performed a time-scaled phylogeny reconstruction of clade separation and characterized the geographic distribution, phylodynamics, and association with natural resistance variants of NS3 sequences from 362 patients carrying subtype 1a HCV. Results.  All sequences segregated in 2 clearly distinct clades. Clade I showed an earlier origin from the common ancestor compared with clade II. Clade I virus was more prevalent in non-European countries, represented mostly by United States, compared with European (75.7% vs 49.3%; P < .001). The prevalence of the natural NS3 variant Q80K, associated with resistance to the macrocyclic protease inhibitor simeprevir, was detected in 51.6% of clade I and 0% of clade II (P < .001); clade I showed a lower genetic barrier for Q80K, whereas no sign of selective pressure at any protease inhibitor resistance-associated codon was detected. Conclusions.  Hepatitis C virus subtype 1a clades have a clearly different distribution in Europe and the United States, and the natural resistance mutation Q80K is exclusively associated with clade I.

New treatments for chronic hepatitis C: an overview for paediatricians

Pegylated interferon (IFN) α-2a or 2b in combination with ribavirin for children aged 3 years and older is the standard treatment for paediatric chronic hepatitis C. This treatment regimen was developed firstly in adults. In recent years, a number of direct-acting antiviral agents (DAAs) are under development for treatment of chronic hepatitis C virus (HCV) infection. These agents block viral replication inhibiting directly one of the several steps of HCV lifecycle. DAAs are classified into several categories based on their molecular target: HCV NS3/4A protease inhibitors, HCV NS5B polymerase inhibitors and HCV NS5A inhibitors. Other promising compounds are cyclophilin A inhibitors, mi-RNA122 and IFN-λ. Several new drugs associations will be developed in the near future starting from the actual standard of care. IFN-based and IFN-free regimens are being studied in adults. In this constantly evolving scenario new drug regimens targeted and suitable for children would be possible in the next future. Especially for children, it is crucial to identify the right combination of drugs with the highest potency, barrier to resistance and the best safety profile.

Hepatitis C virus infection treatment: An era of game changer direct acting antivirals and novel treatment strategies

Chronic hepatitis C virus infection and associated liver diseases represent a major health care burden all over the world. The current standard of care, i.e. peginterferon-alfa (PEG-IFNα) plus ribavirin (RBV) are associated with frequent and sometimes serious adverse effects and contraindications, which further limit their therapeutic efficacy. The approval of first and second generation HCV protease inhibitors represents a major breakthrough in the development of novel direct acting antivirals (DAAs) against different HCV genotypes and establishes a new standard of care for chronically infected HCV genotypes 1 patients. Similarly, next generation protease inhibitors and HCV RNA polymerase inhibitors have shown better pharmacokinetics and pharmacodynamics in terms of broader HCV genotypes coverage, better safety profile, fewer drug interactions and possible once daily administration than first generation direct acting antivirals. The testing of adenovirus-based vector vaccines, which escalates the innate and acquired immune responses against the most conserved regions of the HCV genome in chimpanzees and humans, may be a promising therapeutic approach against HCV infection in coming future. This review article presents up-to-date knowledge and recent developments in HCV therapeutics, insights the shortcomings of current HCV therapies and key lessons from the therapeutic potential of improved anti-HCV treatment strategies.

Mechanism of inhibition for BMS-791325, a novel non-nucleoside inhibitor of hepatitis C virus NS5B polymerase

HCV infection is an urgent global health problem that has triggered a drive to discover therapies that specifically target the virus. BMS-791325 is a novel direct antiviral agent specifically targeting HCV NS5B, an RNA-dependent RNA polymerase. Robust viral clearance of HCV was observed in infected patients treated with BMS-791325 in combination with other anti-HCV agents in Phase 2 clinical studies. Biochemical and biophysical studies revealed that BMS-791325 is a time-dependent, non-competitive inhibitor of the polymerase. Binding studies with NS5B genetic variants (WT, L30S, and P495L) exposed a two-step, slow binding mechanism, but details of the binding mechanism differed for each of the polymerase variants. For the clinically relevant resistance variant (P495L), the rate of initial complex formation and dissociation is similar to WT, but the kinetics of the second step is significantly faster, showing that this variant impacts the final tight complex. The resulting shortened residence time translates into the observed decrease in inhibitor potency. The L30S variant has a significantly different profile. The rate of initial complex formation and dissociation is 7-10 times faster for the L30S variant compared with WT; however, the forward and reverse rates to form the final complex are not significantly different. The impact of the L30S variant on the inhibition profile and binding kinetics of BMS-791325 provides experimental evidence for the dynamic interaction of fingers and thumb domains in an environment that supports the formation of active replication complexes and the initiation of RNA synthesis.

Telaprevir or boceprevir triple therapy in patients with chronic hepatitis C and varying severity of cirrhosis

BACKGROUND

Risks and benefits of protease inhibitor (PI) (telaprevir or boceprevir) triple therapy in hepatitis C virus (HCV)-infected patients with mildly decompensated cirrhosis, including those wait-listed for liver transplantation (LT), are incompletely known.

AIM

To assess virological responses and safety of PI triple therapy in patients with mildly decompensated Child-Pugh (CP) CP ≥6 vs. compensated (CP = 5) cirrhosis.

METHODS

Multicentre cohort of 160 adults with cirrhosis treated with peginterferon/ribavirin (peg-IFN/RBV) plus telaprevir (69%) or boceprevir (31%), comparing outcomes between those with CP = 5 and CP ≥6.

RESULTS

Patients, 47% with CP ≥6 cirrhosis (CP range 6-10), received PI triple therapy for a targeted duration of 48 weeks. The cohort was median age 59 years, 32% female, 59% genotype 1a, 35% previous null/partial responders. Sustained virological response at 12 weeks (SVR12) was achieved by 35% of patients with CP ≥6 vs. 54% of those with CP = 5 (P = 0.02). CP = 5, achievement of rapid virological response and genotype 1b/other, independently predicted SVR12. Compared to those with CP = 5, patients with CP ≥6 had more peg-IFN dose reductions, eltrombopag use, transfusions and hospitalisations to manage adverse events (all P < 0.05). Overall, 67 (42%) discontinued treatment early. Nine wait-listed patients were treated for a median of 97 days (IQR 60-160) prior to liver transplantation and five achieved post-LT SVR.

CONCLUSIONS

In the presence of mild decompensation (Child-Pugh ≥6), SVR12 rates with protease inhibitor triple therapy are significantly reduced and adverse events increased. Thus, treatment with protease inhibitor triple therapy, if judged as necessary, should be undertaken with close monitoring and awareness of the significant risks.

Randomized, placebo-controlled, single-ascending-dose study of BMS-791325, a hepatitis C virus (HCV) NS5B polymerase inhibitor, in HCV genotype 1 infection

BMS-791325 is a nonnucleoside inhibitor of hepatitis C virus (HCV) NS5B polymerase with low-nanomolar potency against genotypes 1a (50% effective concentration [EC50], 3 nM) and 1b (EC50, 7 nM) in vitro. BMS-791325 safety, pharmacokinetics, and antiviral activity were evaluated in a double-blind, placebo-controlled, single-ascending-dose study in 24 patients (interferon naive and experienced) with chronic HCV genotype 1 infection, randomized (5:1) to receive a single dose of BMS-791325 (100, 300, 600, or 900 mg) or placebo. The prevalence and phenotype of HCV variants at baseline and specific posttreatment time points were assessed. Antiviral activity was observed in all cohorts, with a mean HCV RNA decline of ≈2.5 log10 copies/ml observed 24 h after a single 300-mg dose. Mean plasma half-life among cohorts was 7 to 9 h; individual 24-hour levels exceeded the protein-adjusted EC90 for genotype 1 at all doses. BMS-791325 was generally well tolerated, with no serious adverse events or discontinuations. Enrichment for resistance variants was not observed at 100 to 600 mg. At 900 mg, variants (P495L/S) associated with BMS-791325 resistance in vitro were transiently observed in one patient, concurrent with an observed HCV RNA decline of 3.4 log10 IU/ml, but were replaced with wild type by 48 h. Single doses of BMS-791325 were well tolerated; demonstrated rapid, substantial, and exposure-related antiviral activity; displayed dose-related increases in exposure; and showed viral kinetic and pharmacokinetic profiles supportive of once- or twice-daily dosing. These results support its further development in combination with other direct-acting antivirals for HCV genotype 1 infection. (This trial has been registered at ClinicalTrials.gov under registration no. NCT00664625.).

Preclinical characterization of BMS-791325, an allosteric inhibitor of hepatitis C Virus NS5B polymerase

BMS-791325 is an allosteric inhibitor that binds to thumb site 1 of the hepatitis C virus (HCV) NS5B RNA-dependent RNA polymerase. BMS-791325 inhibits recombinant NS5B proteins from HCV genotypes 1, 3, 4, and 5 at 50% inhibitory concentrations (IC50) below 28 nM. In cell culture, BMS-791325 inhibited replication of HCV subgenomic replicons representing genotypes 1a and 1b at 50% effective concentrations (EC50s) of 3 nM and 6 nM, respectively, with similar (3 to 18 nM) values for genotypes 3a, 4a, and 5a. Potency against genotype 6a showed more variability (9 to 125 nM), and activity was weaker against genotype 2 (EC50, 87 to 925 nM). Specificity was demonstrated by the absence of activity (EC50s of >4 μM) against a panel of mammalian viruses, and cytotoxic concentrations (50%) were >3,000-fold above the HCV EC50. Resistance substitutions selected by BMS-791325 in genotype 1 replicons mostly mapped to a single site, NS5B amino acid 495 (P495A/S/L/T). Additive or synergistic activity was observed in combination studies using BMS-791325 with alfa interferon plus ribavirin, inhibitors of NS3 protease or NS5A, and other classes of NS5B inhibitor (palm site 2-binding or nucleoside analogs). Plasma and liver exposures in vivo in several animal species indicated that BMS-791325 has a hepatotropic disposition (liver-to-plasma ratios ranging from 1.6- to 60-fold across species). Twenty-four hours postdose, liver exposures across all species tested were ≥ 10-fold above the inhibitor EC50s observed with HCV genotype 1 replicons. These findings support the evaluation of BMS-791325 in combination regimens for the treatment of HCV. Phase 3 studies are ongoing.

Importance of HCV genotype 1 subtypes for drug resistance and response to therapy

The treatment for patients infected with hepatitis C virus (HCV) genotype 1 has undergone major changes with the availability of direct-acting antivirals. Triple therapy, containing telaprevir or boceprevir, first-wave NS3 protease inhibitors, in combination with peginterferon and ribavirin, improved rates of sustained virologic response compared with peginterferon and ribavirin alone in patients with HCV genotype 1. However, the development of drug-resistant variants is a concern. In patients treated with telaprevir or boceprevir, different patterns of resistance are observed for the two major HCV genotype 1 subtypes, 1a and 1b. Genotype 1b is associated with a lower rate of resistant variant selection and better response to triple therapy compared with genotype 1a. Similar subtype-specific patterns have been observed for investigational direct-acting antivirals, including second-wave NS3 protease inhibitors, NS5A inhibitors and non-nucleoside NS5B inhibitors. This review explores resistance to approved and investigational direct-acting antivirals for the treatment of HCV, focusing on the differences between genotype 1a and genotype 1b. Finally, given the importance of HCV genotype 1 subtype on resistance and treatment outcomes, clinicians must also be aware of the tests currently available for genotype subtyping and their limitations.

Hepatitis C virus genetic variability and the presence of NS5B resistance-associated mutations as natural polymorphisms in selected genotypes could affect the response to NS5B inhibitors

Because of the extreme genetic variability of hepatitis C virus (HCV), we analyzed the NS5B polymerase genetic variability in circulating HCV genotypes/subtypes and its impact on the genetic barrier for the development of resistance to clinically relevant nucleoside inhibitors (NIs)/nonnucleoside inhibitors (NNIs). The study included 1,145 NS5B polymerase sequences retrieved from the Los Alamos HCV database and GenBank. The genetic barrier was calculated for drug resistance emergence. Prevalence and genetic barrier were calculated for 1 major NI and 32 NNI resistance variants (13 major and 19 minor) at 21 total NS5B positions. Docking calculations were used to analyze sofosbuvir affinity toward the diverse HCV genotypes. Overall, NS5B polymerase was moderately conserved among all HCV genotypes, with 313/591 amino acid residues (53.0%) showing ≤1% variability and 83/591 residues (14.0%) showing high variability (≥25.1%). Nine NNI resistance variants (2 major variants, 414L and 423I; 7 minor variants, 316N, 421V, 445F, 482L, 494A, 499A, and 556G) were found as natural polymorphisms in selected genotypes. In particular, 414L and 423I were found in HCV genotype 4 (HCV-4) (n = 14/38, 36.8%) and in all HCV-5 sequences (n = 17, 100%), respectively. Regardless of HCV genotype, the 282T major NI resistance variant and 10 major NNI resistance variants (316Y, 414L, 423I/T/V, 448H, 486V, 495L, 554D, and 559G) always required a single nucleotide substitution to be generated. Conversely, the other 3 major NNI resistance variants (414T, 419S, and 422K) were associated with a different genetic barrier score development among the six HCV genotypes. Sofosbuvir docking analysis highlighted a better ligand affinity toward HCV-2 than toward HCV-3, in agreement with the experimental observations. The genetic variability among HCV genotypes, particularly with the presence of polymorphisms at NNI resistance positions, could affect their responsiveness to NS5B inhibitors. A pretherapy HCV NS5B sequencing could help to provide patients with the full efficacy of NNI-containing regimens.

Chronic hepatitis C: future treatment

The launch of first-generation protease inhibitors (PIs) is a major step forward in HCV treatment. However, the major advance is up to now restricted to genotype 1 (GT-1) patients. The development of second-wave and second-generation PIs yields higher antiviral potency through plurigenotypic activity, more convenient daily administration, fewer side effects and, for the second-generation PIs, potential activity against resistance-associated variants. NS5B inhibitors include nucleoside/nucleotide inhibitors (NIs) and non-nucleotide inhibitors (NNIs). NIs have high efficacy across all genotypes. Sofosbuvir has highly potent antiviral activity across all genotypes in association with pegylated interferon and ribavirin (PR), thus allowing shortened treatment duration. NS5A inhibitors (NS5A.I) have highly potent antiviral activity. It has recently been shown for the first time that NS5A.I in combination with protease inhibitors can cure GT-1b null responders in an interferon-free regimen. Besides, several studies demonstrate that interferon (IFN)-free regimens with direct-acting antiviral agent combinations are able to cure a large number of either naïve or treatment-experienced GT-1 patients. Moreover, quadruple regimen with PR is able to cure almost all GT-1 null responders. The development of pan-genotypic direct-acting antiviral agents (NIs or NS5A.I) allows new combinations with or without PR that increase the rate of sustained virological response for all patients, even for those with cirrhosis and independently of the genotype. Therefore, the near future of HCV treatment looks promising. The purpose of this article is to provide an overview of the clinical results recently reported for HCV treatment.

Antiviral treatment of hepatitis C virus infection and factors affecting efficacy

Hepatitis C virus (HCV) infection is the leading cause of chronic liver-related diseases, including cirrhosis, liver failure, and hepatocellular carcinoma. Currently, no effective vaccine is available for HCV infection. Polyethylene glycol interferon-α (PegIFN-α) in combination with ribavirin (RBV) is the standard of care (SOC) for chronic hepatitis C. However, the efficacy of PegIFN-α and RBV combination therapy is less than 50% for genotype 1 HCV, which is the dominant virus in humans. In addition, IFN and RBV have several severe side effects. Therefore, strategies to improve sustained virological response (SVR) rates have been an important focus for clinical physicians. The serine protease inhibitors telaprevir and boceprevir were approved by the United States Food and Drug Administration in 2011. The addition of HCV protease inhibitors to the SOC has significantly improved the efficacy of treatments for HCV infection. Several direct-acting antiviral drugs currently in late-stage clinical trials, both with and without peg-IFN and RBV, have several advantages over the previous SOC, including higher specificity and efficacy, fewer side effects, and the ability to be administered orally, and might be optimal regimens in the future. Factors affecting the efficacy of anti-HCV treatments based on IFN-α include the HCV genotype, baseline viral load, virological response during treatment, host IL28B gene polymorphisms and hepatic steatosis. However, determining the effect of the above factors on DAA therapy is necessary. In this review, we summarize the development of anti-HCV agents and assess the main factors affecting the efficacy of antiviral treatments.

An update on the treatment of genotype-1 chronic hepatitis C infection: lessons from recent clinical trials

The launch of first-generation protease inhibitors (PIs) was a major step forward in hepatitis C virus (HCV) treatment. However, this major advance is, up to now, restricted to genotype-1 (GT-1) patients. However, the ongoing development of new direct-acting antiviral agents (DAAs) allows new hope for the future. The development of second-wave and second-generation PIs yields higher antiviral potency through plurigenotypic activity, more convenient daily administration, fewer side effects and, for the second-generation PIs, potential activity against resistance-associated variants. NS5B inhibitors (NS5B.I) include nucleoside/nucleotide inhibitors (NIs) and nonnucleotide inhibitors (NNIs). NIs have high efficacy across all genotypes. Sofosbuvir has highly potent antiviral activity across all genotypes in association with pegylated interferon (IFN) and ribavirin (PR), thus allowing shortened treatment duration. NS5A inhibitors (NS5A.I) have highly potent antiviral activity. It has recently been shown for the first time that NS5A.I in combination with PI can cure GT-1b null-responder patients in an IFN-free regimen. In addition, several studies demonstrate that IFN-free regimens with DAA combinations are able to cure a large number of either naïve or treatment-experienced GT-1 patients. Moreover, a quadruple regimen with PR is able to cure almost all GT-1 null-responders. The development of pan-genotypic DAAs (NIs or NS5A.I) allows new combinations with or without PR that increase the rate of sustained virological response (SVR) for all patients, even for those with cirrhosis and independently of the genotype. Therefore, the near future of HCV treatment looks promising. The purpose of this article is to provide an overview of the clinical results recently reported for HCV treatment in GT-1 patients.

Novel therapeutic approaches for hepatitis C

Chronic hepatitis C virus (HCV) infection afflicts a reported 170 million people worldwide and is often complicated by cirrhosis and hepatocellular carcinoma. Morbidity and mortality are decreased with the successful treatment of chronic HCV infection. The current standard of care in the treatment for genotype 1 chronic HCV is pegylated interferon (IFN)-alfa, termed PEG, and ribavirin (RBV) in conjunction with a protease inhibitor, either telaprevir or boceprevir, which results in 67-75% sustained viral response rates. Increased understanding of the HCV has allowed further development of new direct-acting antiviral (DAA) agents against the HCV and has also allowed the development of IFN-free oral treatment regimens. We anticipate the approval in late 2013 of the first nucleotide polymerase inhibitor regimen with RBV alone for genotypes 2/3 and in combination with a 12-week regimen of PEG+RBV for genotypes 1, 4, 5, and 6. Most of the promising new DAA regimens are discussed herein.

New horizons in hepatitis C antiviral therapy with direct-acting antivirals

Most direct-acting antivirals (DAAs) that are being developed as therapy against hepatitis C virus target the NS3/4A protease, the NS5A protein, and the NS5B polymerase. The latter enzyme offers different target sites: the catalytic domain for nucleos(t)ide analogues as well as a number of allosteric sites for nonnucleos(t)ide inhibitors. Two NS3/4A protease inhibitors have been approved recently, and more than 40 new NS3/4A, NS5A, or NS5B inhibitors are in development. These agents can achieve very high cure rates when combined with pegylated interferon-β and ribavirin and show promising clinical results when administered in all-oral combinations. In addition to the more canonical drug targets, new alternative viral targets for small-molecule drug development are emerging, such as p7 or NS4B and viral entry. Future research will need to define well-tolerated and cost-effective DAA combinations that provide the highest rates of viral eradication in all patients (including those with advanced liver disease), the broadest spectrum of action on viral genotypes showing minimal or no clinical resistance, and the shortest treatment duration.

Design and Development of NS5B Polymerase Non‐nucleoside Inhibitors for the Treatment of Hepatitis C Virus Infection

The hepatitis C virus (HCV) infects an estimated 130–170 million people worldwide and is associated with life‐threatening liver diseases. The recent introduction of the first two HCV direct‐acting antivirals (DAAs) as a complement to the interferon/ribavirin standard of care has provided patients with improved outcomes. Still, 25–30% of subjects infected with genotype 1 HCV do not respond adequately to treatment owing to the emergence of resistant virus and many suffer from severe side effects. A paradigm shift towards the development of interferon‐free combinations of DAAs with complementary modes of action is currently taking place. Virally encoded proteins and enzymes have become the target of HCV drug discovery efforts and several promising new agents are currently being evaluated in the clinic for treatment of chronic HCV infection. The NS5B RNA‐dependent RNA polymerase is responsible for replication of viral RNA and plays a pivotal role in the virus life cycle. NS5B is undoubtedly the most druggable HCV target and is susceptible to several classes of allosteric inhibitors that bind to four distinct sites on the enzyme. This chapter describes successful strategies that have led to the discovery of HCV NS5B antivirals. It is divided according to allosteric sites and describes how each of the known families of inhibitors was discovered, characterized and optimized to provide clinical candidates. When available, the strategies adopted by medicinal chemists to optimize initial leads and address challenges and liabilities encountered on the path to candidate selection are described, along with reported clinical outcomes.

Structure-based design of novel HCV NS5B thumb pocket 2 allosteric inhibitors with submicromolar gt1 replicon potency: discovery of a quinazolinone chemotype

We describe the structure-based design of a novel lead chemotype that binds to thumb pocket 2 of HCV NS5B polymerase and inhibits cell-based gt1 subgenomic reporter replicons at sub-micromolar concentrations (EC50<200nM). This new class of potent thumb pocket 2 inhibitors features a 1H-quinazolin-4-one scaffold derived from hybridization of a previously reported, low affinity thiazolone chemotype with our recently described anthranilic acid series. Guided by X-ray structural information, a key NS5B-ligand interaction involving the carboxylate group of anthranilic acid based inhibitors was replaced by a neutral two-point hydrogen bonding interaction between the quinazolinone scaffold and the protein backbone. The in vitro ADME and in vivo rat PK profile of representative analogs are also presented and provide areas for future optimization of this new class of HCV polymerase inhibitors.

Synthetic anti-lipopolysaccharide peptides and hepatitis C virus infection

INTRODUCTION

Hepatitis C virus (HCV) infection is a leading cause of cirrhosis and hepatocellular carcinoma. Although antiviral therapy has been markedly improved by the licensing of direct-acting antivirals, safety, resistance, high costs and difficult-to-treat patients remain important challenges.

AREAS COVERED

This article focuses and comments on the recent development of synthetic anti-lipopolysaccharide peptides (SALPs) which bind to highly sulfated glycosaminoglycan/heparan sulfate (HS) on cell surface. HS serves as a primary docking site for several viruses to their respective host cells before the viruses interact with their cell surface receptor(s). In vitro studies have shown that SALPs inhibit entry of HCV without cell toxicity.

EXPERT OPINION

SALPs prevent viral infection in cell culture model systems. Treatment studies of established HCV infection in cell culture models as well as proof-of-concept and safety studies in animal models are needed to evaluate their potential for drug development. The mechanism of action of SALPs as entry inhibitors suggests a potential application for HCV-infected patients to prevent reinfection of the liver graft in liver transplantation. Potential limitations may include high doses to obtain an antiviral effect and a target which is widely expressed and has a key function in cell physiology.

Faldaprevir (BI 201335), deleobuvir (BI 207127) and ribavirin oral therapy for treatment-naive HCV genotype 1: SOUND-C1 final results

BACKGROUND

Faldaprevir (BI 201335) and deleobuvir (BI 207127) are direct-acting antiviral agents under development for the treatment of chronic HCV infection. This article describes the final results of the Phase Ib SOUND-C1 study that evaluated the interferon-free oral combination of faldaprevir, deleobuvir and ribavirin in 32 treatment-naive patients infected with HCV genotype 1.

METHODS

Patients were randomized to receive deleobuvir 400 mg (n=15) or 600 mg (n=17) three times daily plus faldaprevir 120 mg once daily and weight-based ribavirin for 4 weeks. Interferon-free therapy was followed by response-guided faldaprevir plus pegylated interferon-α2a/ribavirin to week 24 or 48.

RESULTS

At week 4, 73% (11/15) and 100% (17/17) of patients in the deleobuvir 400 mg and 600 mg groups achieved HCV RNA<25 IU/ml, respectively. During interferon-free treatment, virological breakthrough was reported in one patient and re-increase of HCV RNA in one patient. Both patients were successfully treated with interferon-containing therapy. The rate of sustained virological response 24 weeks after completion of treatment was 73% (11/15) in the deleobuvir 400 mg group and 94% (16/17) in the 600 mg group. During faldaprevir plus pegylated interferon-α2a/ribavirin treatment, the most common adverse events were pruritus (38% of patients), rash (31%) and asthenia (31%); these were severe in approximately 3% of patients.

CONCLUSIONS

Potent antiviral activity and favourable safety of the treatment regimen were demonstrated. Furthermore, the results suggest that patients with breakthrough at week 4 may be rescued with an interferon-containing regimen. Clinical trials.gov number NCT01132313.

Perspectives and challenges of interferon-free therapy for chronic hepatitis C

Recent data have clearly shown that a sustained virologic response can be achieved in different HCV infected patient populations with various interferon-free treatment regimens. Despite the successful implementation of telaprevir- and boceprevir-based triple therapies, all-oral regimens will certainly become a first choice for a number of HCV-infected patients in the very near future, as triple therapy approaches are burdened with significant side-effects and limited success in patients with advanced liver fibrosis and prior null-response to pegylated interferon-α (pegIFN-α)/ribavirin therapy. However, available data from phase I and II clinical trials evaluating interferon-free regimens have not yet revealed a clearly outstanding all-oral combination, and numerous challenges remain to be addressed by intensive ongoing and future research. In particular, thus far evaluated all-oral regimens did not cure a satisfactory percentage of patients with unfavorable baseline characteristics, namely patients infected with HCV genotype 1a, previous null-response to pegIFN-α/ribavirin, or liver cirrhosis. In this review, we summarize available data of interferon-free regimens for the treatment of chronic hepatitis C and assess implications for perspectives and challenges in the further development of all-oral therapies.

RNA dependent RNA polymerase of HCV: a potential target for the development of antiviral drugs

Hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma, cirrhosis and end stage liver disease. More than 200million people are living with HCV worldwide with high morbidity and mortality. There is no vaccine available for this virus; the approved treatment option for the majority of HCV genotypes is the combination of pegylated (Peg) interferon and ribavirin. The therapy has a different response rate on different HCV genotypes and has a number of side effects. Recently, as well as Peg interferon and ribavirin, two protease inhibitors have been introduced to treat patients with HCV genotype 1 infection. The protease inhibitors have rapid onset of resistance and are not approved for use for infections with other HCV genotypes. The HCV NS5B gene encodes RNA dependent RNA polymerase (RdRp), which is the key player in viral replication and is a promising target for the development of antiviral drugs. HCV NS5B has been studied in various biochemical assays, cell based assays and animal model systems. So far, a number of nucleoside and non-nucleoside inhibitors have been screened for effects on viral replication. This review presents a deep insight into the structure and function of HCV polymerase and the effect of various nucleoside and non-nucleoside inhibitors on viral replication.

Hepatitis C viral kinetics: the past, present, and future

Mathematical modeling of hepatitis C viral kinetics has been an important tool in understanding hepatitis C virus (HCV) infection dynamics and in estimating crucial in vivo parameters characterizing the effectiveness of HCV therapy. Because of the introduction of direct-acting antiviral agents, there is a need to extend previous models so as to understand, characterize, and compare various new HCV treatment regimens. Here we review recent modeling efforts in this direction.

New Antiviral Therapies in the Management of HCV Infection

Improved knowledge of the HCV life cycle and of structural features of HCV proteins have led to the discovery of numerous potential targets for antiviral therapy. Viral replication and polyprotein processing have been tagged as promising viral targets. Clathrin-mediated endocytosis, fusion of HCV with cellular membranes, translation of viral RNA, virus production and release as well as several host cell factors may provide alternative targets for future anti-HCV therapies. Several compounds are currently under investigation in clinical trials and showed high antiviral activity in patients with chronic hepatitis C. Recently, Phase III studies for two protease inhibitors, telaprevir and boceprevir, each given in combination with pegylated interferon (standard of care [SOC]), were completed. In HCV-genotype-1-infected patients, the addition of telaprevir or boceprevir to SOC increased sustained virological response rates from <50% to >70%. Nucleoside/nucleotide inhibitors of the HCV NS5B polymerase have shown antiviral activity against different HCV genotypes, and have a higher barrier to resistance than protease inhibitors. In addition, several allosteric binding sites have been identified for non-nucleoside inhibitors of the NS5B polymerase. Inhibitors of NS5A are potentially active against all HCV genotypes. Among the different host cell-targeting compounds, cyclophilin inhibitors have shown promising results. Future hope lies in the combination of direct-acting antiviral agents with the possibility of interferon-free treatment regimens.

Inhibitors of the Hepatitis C Virus RNA-Dependent RNA Polymerase NS5B

More than 20 years after the identification of the hepatitis C virus (HCV) as a novel human pathogen, the only approved treatment remains a combination of pegylated interferon-α and ribavirin. This rather non-specific therapy is associated with severe side effects and by far not everyone benefits from treatment. Recently, progress has been made in the development of specifically targeted antiviral therapy for HCV (STAT-C). A major target for such direct acting antivirals (DAAs) is the HCV RNA-dependent RNA polymerase or non-structural protein 5B (NS5B), which is essential for viral replication. This review will examine the current state of development of inhibitors targeting the polymerase and issues such as the emergence of antiviral resistance during treatment, as well as strategies to address this problem.