Treatment failure and resistance with direct-acting antiviral drugs against hepatitis C virus

Current treatment of chronic hepatitis C virus (HCV) infection is based on the combination of pegylated interferon-α and ribavirin. The recent development of direct-acting antiviral (DAA) molecules that are active on HCV, together with in vitro and in vivo studies showing that these drugs may lead to the selection of resistant viruses if administered alone, has raised concerns that resistance may undermine therapy based on DAAs. A new standard-of-care treatment will soon be available for both treatment-naive and treatment-experienced patients infected with HCV genotype 1, based on a triple combination of pegylated interferon-α, ribavirin, and a protease inhibitor (either telaprevir or boceprevir). With this therapy, most failures to eradicate infection in treatment-adherent patients are due to an inadequate response to pegylated interferon-α and ribavirin, in the context of a low genetic barrier to resistance of first-generation protease inhibitors. This article reviews patterns of resistance to HCV DAA drugs in development, the mechanisms underlying treatment failure when these drugs are combined with pegylated interferon-α and ribavirin, the consequences of treatment failure, and possible means of optimizing future therapies that use DAAs.     

Targeting HCV entry for development of therapeutics

Recent progress in defining the molecular mechanisms of Hepatitis C Virus (HCV) entry affords the opportunity to exploit new viral and host targets for therapeutic intervention. Entry inhibitors would limit the expansion of the infected cell reservoir, and would complement the many replication inhibitors now under development. The current model for the pathway of entry involves the initial docking of the virus onto the cell surface through interactions of virion envelope and associated low density lipoproteins (LDL) with cell surface glycosaminoglycans and lipoprotein receptors, followed by more specific utilization with other hepatocyte membrane proteins: Scavenger Receptor Class B type 1 (SR-BI), CD81, Claudin 1 (CLDN1) and Occludin (OCLN). The use of blockers of these interactions, e.g. specific antibodies, suggests that inhibition of any one step in the entry pathway can inhibit infection. Despite this knowledge base, the tools for compound screening, HCV pseudoparticles (HCVpp) and cell culture virus (HCVcc), and the ability to adapt them to industrial use are only recently available and as a result drug discovery initiatives are in their infancy. Several therapies aiming at modulating the virus envelope to prevent host cell binding are in early clinical testing. The first test case for blocking a cellular co-receptor is an SR-BI modulator. ITX 5061, an orally active small molecule, targets SR-BI and has shown potent antiviral activity against HCVpp and HCVcc. ITX 5061 has exhibited good safety in previous clinical studies, and is being evaluated in the clinic in chronic HCV patients and patients undergoing liver transplantation. Entry inhibitors promise to be valuable players in the future development of curative therapy against HCV.     

Treatment of chronic hepatitis C: Anticipated impact of resistance in patients treated with protease inhibitors

A main target of specifically targeted antiviral therapy for hepatitis C (STAT-C) is the NS3-protease, which has key functions in the hepatitis C virus (HCV) replication cycle. HCV/NS3-protease inhibitors have shown high antiviral activity in vitro and in patients with chronic hepatitis C. Protease-resistant HCV variants occurred rapidly in patients receiving protease-inhibitor monotherapy. The development of resistance can be best explained by selection of preexisting resistant variants, which grow out under selective pressure. Numerous mutations associated with resistance were identified. Clinical trials showed that protease-resistant strains are sensitive to interferon and that a triple combination of protease inhibitors, peginterferon, and ribavirin may improve the sustained virologic response rate compared with standard peginterferon/ribavirin combination therapy. Overall, it can be anticipated that successful treatment with protease inhibitors will require either combination therapy with peginterferon/ribavirin or a combination of STAT-C compounds with distinct modes of action and resistance patterns.     

New direct-acting antiviral agents for the treatment of hepatitis C virus infection and perspectives

Until recently, the standard of care (SOC) for patients with chronic hepatitis C virus (HCV) infection has consisted of a combination of pegylated interferon-α [corrected] plus ribavirin, administered for 24- to 48-weeks depending on the HCV genotype. The sustained virologic response rate for this SOC has been only about 50% in patients infected with genotype 1 HCV, the most prevalent genotype in Europe and North America. HCV therapy has been revolutionised recently by the approval of two direct-acting antiviral agents (DAA) against the NS3/4A serine protease for use in genotype 1 HCV, the ketoamide inhibitors boceprevir and telaprevir. The novel SOC marks the beginning of an extraordinary new era in HCV therapy. We review this new SOC with an emphasis on practical issues related to protease inhibitors, e.g. prescribing guidelines, futility rules and management of adverse events. We also give a perspective on what to expect in the coming years. Newer DAA with simplified dosing regimens and/or minimal toxicity which, when used in combination, will lead to viral eradication in most if not all CHC patients who undergo treatment. The novel agents in clinical development are paving the way for future interferon-sparing regimens.     

Antiviral activity of narlaprevir combined with ritonavir and pegylated interferon in chronic hepatitis C patients

Narlaprevir (SCH 900518) is a potent inhibitor of the hepatitis C virus (HCV) nonstructural protein 3 serine protease that is primarily metabolized by the cytochrome P450-3A4 system. In order to explore the use of ritonavir-based pharmacokinetic enhancement of an HCV protease inhibitor, this study investigated the safety, tolerability, pharmacokinetics, and antiviral activity of narlaprevir (with or without ritonavir) administered as monotherapy and as combination therapy with pegylated interferon-α-2b (PEG-IFN-α-2b) to HCV genotype 1-infected patients. This was a randomized, placebo-controlled, two-period, blinded study in 40 HCV genotype 1-infected patients (na?ve and treatment-experienced). In period 1, narlaprevir was administered for 7 days as 800 mg three times daily without ritonavir or 400 mg twice daily with 200 mg ritonavir twice daily. In period 2, after a 4-week washout, the same dose and regimen of narlaprevir was administered in combination with PEG-IFN-α-2b for 14 days. Upon completion of period 2, all patients initiated PEG-IFN-α-2b and ribavirin treatment. A rapid and persistent decline in plasma HCV-RNA was observed in both treatment-experienced and treatment-na?ve patients during period 1, with a mean viral load decline of at least 4 log?? in all treatment groups. A high percentage of both treatment-experienced (50%) and treatment-na?ve (≥ 60%) patients had undetectable HCV-RNA (< 25 IU/mL) after period 2. Standard of care resulted in sustained virological response (SVR) rates of 38% and 81% in treatment-experienced and treatment-na?ve patients, respectively. Narlaprevir (with or without ritonavir) alone or in combination with PEG-IFN-α-2b was safe and well tolerated. CONCLUSION: Narlaprevir administration resulted in a robust HCV-RNA decline and high SVR rates when followed by standard of care in both treatment-experienced and treatment-na?ve HCV genotype 1-infected patients.     

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.     

Second Generation Protease Inhibitors and Nucleotide Inhibitors

The hepatitis C virus (HCV) protease and polymerase inhibitors are in rapid phases of development. Following closely behind the approval of the inhibitors of the HCV RNA NS3/4A protease, boceprevir and telaprevir, include both a) more potent protease inhibitors and b) the development of the viral NS5B RNA-dependent RNA polymerase inhibitors. Protease inhibitors generally have a low barrier to resistance and extensive cross-resistance between agents. NS5B polymerase inhibitors are generally considered to have a high barrier to resistance and the potential for use across all genotypes. However, in the absence of ribavirin or of other direct-acting antivirals these agents may predispose to the selection of resistant variants or for viral relapse following treatment completion. Optimal combination of agents and therapy durations remain major challenges in clinical research.     

San-Huang-Xie-Xin-Tang extract suppresses hepatitis C virus replication and virus-induced cyclooxygenase-2 expression

Chronic hepatitis C virus (HCV) infection is associated with chronic inflammation of liver, which leads to the development of cirrhosis and hepatocellular carcinoma (HCC). Because of severe side effects and only a 50-70% cure rate in genotype 1 HCV-infected patients upon current standard treatment with pegylated interferon-α plus ribavirin, new therapeutic regimens are still needed. San-Huang-Xie-Xin-Tang (SHXT) is a transitional Chinese herbal formula, composed of Rhei rhizoma, Scutellaria radix and Coptidis rhizome, and possesses anti-inflammatory effect. Here, we describe a (+)-catechin-containing fraction extracted from SHXT, referred as SHXT-frC, exhibited effective inhibition of HCV replication, with selectivity index value (SI; CC50 /EC50) of 84, and displayed synergistic anti-HCV effects when combined with interferon-α, HCV protease inhibitor telaprevir or polymerase inhibitor 2'-C-methylcytidine. The activation of factor-κB (NF-κB) and cyclooxygenase-2 (COX-2) signalling pathway has particular relevance to HCV-associated HCC. SHXT-frC treatment also caused a concentration-dependent decrease in the induction of COX-2 and NF-κB expression caused by either HCV replication or HCV NS5A protein. Collectively, SHXT-frC could be an adjuvant treatment for patients with HCV-induced liver diseases.     

Hepatitis C virus genotype 5: epidemiological characteristics and sensitivity to combination therapy with interferon-alpha plus ribavirin

Twenty-six patients living in the Midi-Pyrenees region of France who were infected with hepatitis C virus (HCV) genotype 5 were investigated. Most of these patients were of advanced age and had been infected nosocomially or by blood transfusion. Our case-control study, in which we treated patients with interferon- alpha plus ribavirin, indicated that, 24 weeks after the beginning of treatment, the virus response in patients infected with HCV genotype 5 was better than that in patients infected with HCV genotype 1 (100% of patients negative for detectable HCV RNA vs. 36.3%, respectively; P < .01); furthermore, 48 weeks after the end of treatment, the virus response in patients infected with HCV genotype 5 was better than that in patients infected with HCV genotype 1 (63.6% vs. 22.7%, respectively; P < .05) and was similar to that in patients infected with HCV genotype 2 or 3 (66.6%). These results show that HCV genotype 5 might have good intrinsic sensitivity to combination therapy with interferon- alpha plus ribavirin.     

Antiviral effects of amantadine and iminosugar derivatives against hepatitis C virus

Current therapy of chronic hepatitis C is based on the combination of pegylated interferon-alpha and ribavirin. In spite of 50% sustained virological response, therapy is still limited by unsatisfying success rates with genotype 1 infections and adverse side effects. One attempt to increase success rates is triple combination therapy of interferon and ribavirin with amantadine, a drug assumed to interfere with HCV p7 ion channel function. However, results from clinical trials indicate limited efficacy and the antiviral activity is unclear. In contrast, NS3 protease inhibitors have shown potent antiviral effects in clinical trials but rapid selection for drug resistance may limit their benefit. Targeting cellular factors required for HCV is therefore an attractive alternative. In this study, employing a system for production of infectious HCV particles in cell culture, we determined the antiviral effects of amantadine and iminosugar derivatives; the second of which primarily target host cell glucosidases required for folding and maturation of HCV envelope glycoproteins. We found that across a spectrum of HCV isolates and genotypes, amantadine affected neither RNA replication nor the release or infectivity of HCV particles. In agreement, p7 ion channel activity was not affected by amantadine, demonstrating that amantadine is not an HCV-selective antiviral. In contrast, a dose-dependent reduction of virus titers was achieved with iminosugars. Furthermore, HCV was rapidly eliminated from cell culture upon passage in the presence of a long alkyl chain deoxynojirimycin (DNJ). CONCLUSION: Iminosugar derivatives are potential drugs for treatment of HCV infections.     

Effect of Combined Interferon-α Induction Therapy and Ribavirin on Chronic Hepatitis C Virus Infection: a Randomized Multicentre Study

Background: The efficacy of interferon- α (IFN) induction in combination with ribavirin for chronic hepatitis C virus (HCV) infection is not known. Methods: A total of 256 treatment-naive HCV RNA-positive patients with biopsy-confirmed chronic hepatitis were enrolled in a randomized multicentre study. The patients received either standard combination therapy with 3 MIU interferon- α 2b thrice weekly for 26 weeks or 6 MIU interferon- α 2b daily for 4 weeks and 3 MIU 3/7 days for 22 weeks. All patients received ribavirin 1000 mg or 1200 mg (weight dependent) daily during the 26-week treatment period. Patients were monitored for HCV RNA during and following treatment. Results: The sustained virological response rates (26 weeks after end of treatment) were 54% and 47% for patients receiving IFN induction/ribavirin and standard IFN/ribavirin, respectively ( P = 0.35). Among patients infected with genotype 1a/1b, the sustained response rates were 32% and 35%. In patients infected with genotype 2b/3a IFN induction/ribavirin led to a sustained response rate of 80% as compared to 65% in the standard combination therapy group ( P = 0.073). Steatosis was more frequently seen in liver biopsies from patients infected with genotype 3a as compared to genotypes 1a/1b. Among genotype 1a/1b infected patients, steatosis was a highly significant predictor of failure to achieve sustained virological response. Logistic regression analysis (multivariate analysis) showed that independent predictors of sustained virological response were low age, female gender, genotype 2b/3a and HCV RNA negativity at 2 weeks. Conclusions: IFN induction in combination with ribavirin does not increase the sustained virological response rate among patients infected with HCV. Absence of steatosis is an independent predictor of sustained virological response in patients infected with genotypes 1a/1b.     

High-dose interferon-α2b induction therapy in combination with ribavirin for treatment of chronic hepatitis C in patients with non-response or relapse after interferon-α monotherapy

AIM: To evaluate the daily high-dose induction therapy with interferon-α2b (IFN-α2b) in combination with ribavirin for the treatment of patients who failed with interferon monotherapy and had a relapse, based on the assumption that the viral burden would decline faster, thus increasing the likelihood of higher response rates in this diffficult-to-treat patient group.METHODS: Seventy patients were enrolled in this study.Treatment was started with 10 MU IFN-α2b daily for 3 wk,followed by IFN-α2b 5 MU/TIW in combination with ribavirin (1 000-1 200 mg/d) for 21 wk. In case of a negative HCV RNA PCR, treatment was continued until wk 48 (IFN-α2b 3 MU/TIW+1 000-1 200 mg ribavirin/daily).RESULTS: The dose of IFN-α2b or ribavirin was reduced in 16% of patients because of hematologic side effects,and treatment was discontinued in 7% of patients. An early viral response (EVR) was achieved in 60% of patients. Fifty percent of all patients achieved an end-of-treatment response (EOT) and 40% obtained a sustained viral response (SVR). Patients with no response had a significantly lower response rate than those with a former relapse (SVR 30% vs 53%; P = 0.049). Furthermore,lower response rates were observed in patients infected with genotype 1a/b than in patients with non-1-genotype (SVR 28% vs74%; P= 0.001). As a significant predictive factor for a sustained response, a rapid initial decline of HCV RNA could be identified. No patient achieving a negative HCV-RNA PCR at wk 18 or later eventually eliminated the virus.CONCLUSION: Daily high-dose induction therapy with interferon-α2b is well tolerated and effective for the treatment of non-responders and relapsers, when interferon monotherapy fails. A fast decline of viral load during the first 12 wk is strongly associated with a sustained viral response.     

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.     

Emerging strategies for pegylated interferon combination therapy

Several advances afford promise for improving the management of hepatitis C virus (HCV) infection. Current therapies primarily target the immune system; the now proven ability to culture the entire virus in vitro could ultimately facilitate the identification of therapies directly targeting viral replication. Several therapies are presently in development. Taribavirin hydrochloride (Viramidine, Valeant Pharmaceutical International, Singapore), a ribavirin prodrug, has shown promise, although the rate of sustained virologic response with this agent has been disappointing. The next generation of antivirals will consist of protease and polymerase inhibitors, a number of which are undergoing investigation, initially as monotherapy and subsequently in combination with pegylated interferon and ribavirin. Challenges include the prevention of recurrent HCV infection in liver-transplant recipients and development of a safe and effective HCV vaccine.     

Nonstructural protein 3-4A: the Swiss army knife of hepatitis C virus

Hepatitis C virus (HCV) nonstructural protein 3-4A (NS3-4A) is a complex composed of NS3 and its cofactor NS4A. It harbours serine protease as well as NTPase/RNA helicase activities and is essential for viral polyprotein processing, RNA replication and virion formation. Specific inhibitors of the NS3-4A protease significantly improve sustained virological response rates in patients with chronic hepatitis C when combined with pegylated interferon-α and ribavirin. The NS3-4A protease can also target selected cellular proteins, thereby blocking innate immune pathways and modulating growth factor signalling. Hence, NS3-4A is not only an essential component of the viral replication complex and prime target for antiviral intervention but also a key player in the persistence and pathogenesis of HCV. This review provides a concise update on the biochemical and structural aspects of NS3-4A, its role in the pathogenesis of chronic hepatitis C and the clinical development of NS3-4A protease inhibitors.     

Antiviral strategies in hepatitis C virus infection

Resolution of the three-dimensional structures of several hepatitis C virus (HCV) proteins, together with the development of replicative cell culture systems, has led to the identification of a number of potential targets for direct-acting antiviral (DAA) agents. Numerous families of drugs that potently inhibit the HCV lifecycle in vitro have been identified, and some of these molecules have reached early to late clinical development. Two NS3/4A protease inhibitors, telaprevir and boceprevir, were approved in Europe and the United States in 2011 in combination with pegylated interferon (IFN)-α and ribavirin for the treatment of chronic hepatitis C related to HCV genotype 1, in both treatment-na?ve and treatment-experienced patients. Sustained virological response rates in the range of 6675% and 5966% (2988% if the response to the first course of therapy is taken into account) have been achieved in these two patient populations, respectively, with treatment durations of 24 to 48 weeks. A number of other DAAs are at the clinical developmental stage in combination with pegylated IFN-α and ribavirin or with other DAAs in IFN-free regimens, with or without ribavirin. They include second-wave, first-generation, and second-generation NS3/4A protease inhibitors, nucleoside/nucleotide analogue inhibitors and non-nucleoside inhibitorsof HCVRNA-dependent RNA polymerase, inhibitors of nonstructural protein 5A (NS5A) and host-targeted compounds, such as cyclophilin inhibitors and silibinin. The proof of concept that IFN-free regimens may lead to HCV eradication has recently been brought. However, new drugs may be associated with troublesome side effects and drugdrug interactions, and the ideal IFN-free DAA combination remains to be found.     

Hepatitis C virus protease inhibitor-resistance mutations: Our experience and review

Direct-acting antiviral agents(DAAs)for hepatitis C virus(HCV)infection are one of the major advances in its medical treatment.The HCV protease inhibitors boceprevir and telaprevir were the first approved DAAs in the United States,Europe,and Japan.When combined with peginterferon plus ribavirin,these agents increase sustained virologic response rates to70%-80%in treatment-na?ve patients and previoustreatment relapsers with chronic HCV genotype 1 infection.Without peginterferon plus ribavirin,DAA monotherapies increased DAA-resistance mutations.Several new DAAs for HCV are now in clinical development and are likely to be approved in the near future.However,it has been reported that the use of these drugs also led to the emergence of DAA-resistance mutations in certain cases.Furthermore,these mutations exhibit cross-resistance to multiple drugs.The prevalence of DAA-resistance mutations in HCV-infected patients who were not treated with DAAs is unknown,and it is as yet uncertain whether such variants are sensitive to DAAs.We performed a population sequence analysis to assess the frequency of such variants in the sera of HCV genotype 1-infected patients not treated with HCV protease inhibitors.Here,we reviewed the literature on resistance variants of HCV protease inhibitors in treatment na?ve patients with chronic HCV genotype 1,as well as our experience.     

Current and future treatment options for HCV

Aim of antiviral therapy of patients with chronic hepatitis C is the sustained elimination of the hepatitis C virus (HCV). The standard of care (SOC) is peginterferon alfa-2a/-2b with ribavirin for 48 weeks or 24 weeks in patients infected with HCV genotype 1 or 2/3, respectively. Overall, approximately half of the patients can be cured by SOC. Based on baseline viral load and the speed of virologic response during treatment, individualization of treatment duration is possible. However, this approach is not sufficient to substantially improve the sustained virologic response (SVR) rates. This goal can be achieved with new HCV specific inhibitors against the NS3/4A polymerase and the NS5B polymerase. Recent trials reported SVR rates in the order of 67-69% and 67-75% for the combination of SOC with the protease inhibitors telaprevir and boceprevir, respectively, in patients with HCV genotype 1 infection. Several new HCV specific inhibitors such as protease inhibitors, nucleoside and non-nucleoside polymerase inhibitors as well as non HCV specific compounds with anti-HCV activity such as cyclophilin inhibitors, silibinin, and nitazoxanide are currently in clinical evaluation. The review describes recent developments and discusses limitations posed by resistance development and drug toxicity.     

Therapie der Hepatitis C

The standard treatment for patients with chronic hepatitis C (HCV) is a combination therapy with pegylated interferon and ribavirin. Patients infected with HCV genotype 1 are treated for 48 weeks, and patients infected with HCV genotype 2 or 3 for 24 weeks. Using the HCV genotype together with a baseline viremia and the initial virologic response to therapy enables further individualization of treatment duration. Viramidine could become an alternative to ribavirin with a reduction of ribavirin induced anemia. Many new drugs are currently under investigation in preclinical and clinical studies. The first results of phase I/II studies with specific HCV protease and polymerase inhibitors are promising.