Novel hepatitis C drugs in current trials

Targeting the non-structural proteins of hepatitis C virus: beyond hepatitis C virus protease and polymerase

BACKGROUND

Chronic hepatitis C virus (HCV) infection is a main cause of cirrhosis of the liver and hepatocellular carcinoma. The standard of care is a combination of pegylated interferon with ribavirin, a regimen that has undesirable side effects and is frequently ineffective. Compounds targeting HCV protease and polymerase are in late-stage clinical trials and have been extensively reviewed elsewhere.

OBJECTIVE

To review and evaluate the progress towards finding novel HCV antivirals targeting HCV proteins beyond the already precedented NS3 protease and NS5B polymerase.

METHODS

Searches of CAplus and Medline databases were combined with information from key conferences. This review focuses on NS2/3 serine protease, NS3 helicase activity and the non-structural proteins 4A, 4B and 5A.

CONCLUSIONS

Use of the replicon model of HCV replication and biochemical assays of specific targets has allowed screening of vast libraries of compounds, but resulted in clinical candidates from only NS4A and NS5A. The field is hindered by a lack of good chemical matter that inhibits the remaining enzymes from HCV, and a lack of understanding of the functions of non-structural proteins 4A, 4B and 5A in the replication of HCV.

Comparison of current US risk strategy to screen for hepatitis C virus with a hypothetical targeted birth cohort strategy

OBJECTIVES

We compared the theoretical performance of a 1-time, birth cohort strategy with the currently recommended risk strategy for screening for hepatitis C virus (HCV) infection, which is undetected in an estimated 75% of 4 million affected people in the United States.

METHODS

We applied current American Association for the Study of Liver Disease risk screening guidelines and a targeted birth cohort strategy to National Health and Nutrition Examination Survey data from 2003 to 2006 to estimate their performance in identifying HCV cases.

RESULTS

Risk guidelines would recommend testing 25% of the US population aged 20 years or older and, if fully implemented, identify 82% of the projected HCV-exposed population. A targeted birth cohort (1946-1964) strategy would test 45% of the same population and identify 76% of the projected HCV population.

CONCLUSIONS

In this ideal-world simulation, birth year and risk screening had similar theoretical performances for predicting HCV infection. However, actual implementation of risk screening has not achieved its theoretical performance, and birth cohort screening might increase HCV testing rates.

Treating hepatitis C: current standard of care and emerging direct-acting antiviral agents

Summary.  During the late 1990s and early 2000s, major advances were made in the treatment of patients with chronic hepatitis C virus (HCV) infection. Interferon, combination interferon plus ribavirin (RBV) and pegylated interferon plus RBV increased sustained virologic response (SVR) rates from ~5% to ~40-80%, depending on the genotype of HCV infection. Advances in molecular biology have allowed investigators to begin to understand the mechanisms of HCV infection and replication. Advances in understanding of viral kinetics have provided tools to identify patients who are most likely to attain SVR. With the advances in the science of HCV infection, the first part of the 21st century has seen the development and early introduction of a number of direct-acting antiviral (DAA) drugs. These novel medications interfere with critical steps in HCV replication and have the potential to significantly increase SVR rates. This article will review the key elements of HCV replication and evaluate the various classes of new and investigational DAA that have the potential to create a revolution in the management of patients with chronic hepatitis C.

Hepatitis C viral protein translation: mechanisms and implications in developing antivirals

Hepatitis C viral protein translation occurs in a cap-independent manner through the use of an internal ribosomal entry site (IRES) present within the viral 5'-untranslated region. The IRES is composed of highly conserved structural domains that directly recruit the 40S ribosomal subunit to the viral genomic RNA. This frees the virus from relying on a large number of translation initiation factors that are required for cap-dependent translation, conferring a selective advantage to the virus especially in times when the availability of such factors is low. Although the mechanism of translation initiation on the Hepatitis C virus (HCV) IRES is well established, modulation of the HCV IRES activity by both cellular and viral factors is not well understood. As the IRES is essential in the HCV life cycle and as such remains well conserved in an otherwise highly heterogenic virus, the process of HCV protein translation represents an attractive target in the development of novel antivirals. This review will focus on the mechanisms of HCV protein translation and how this process is postulated to be modulated by cis-acting viral factors, as well as trans-acting viral and cellular factors. Numerous therapeutic approaches investigated in targeting HCV protein translation for the development of novel antivirals will also be discussed.

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.

A novel class of geldanamycin derivatives as HCV replication inhibitors targeting on Hsp90: synthesis, structure-activity relationships and anti-HCV activity in GS4.3 replicon cells

A novel class of geldanamycin (GA) derivatives as hepatitis C virus (HCV) replication inhibitors has been synthesized and their anti-HCV activities were evaluated in GS4.3 HCV replicon cells. Most of the synthesized compounds demonstrated potential activities against HCV in vitro. Substitution with an aliphatic cyclic group (2b) and polar phosphate group (2f) at the 17 position of GA resulted in more potent inhibitory activity. The configurations of the tetrahydrofurfurylamino (THFM) substituents obviously affected their antiviral activities. The 2b with a 2'-(R)-THFM group at the 17 position showed much potent activity and higher selectivity than its 2'-(S) and 2'-(R, S) epimers. In the tested GA derivatives, 2b and 2f show the most potential leading compounds for development of novel anti-HCV agents.

[New possibilities on the horizon for the treatment of hepatitis C virus infection: direct-acting antiviral therapy]

Current treatment for chronic hepatitis C virus (HCV) infection results 40-45% sustained virological response (SVR) rates in patients with HCV genotype 1, which is the most prevalent genotype in Europe and in Hungary. This therapy requires long duration, high costs and is associated with side effects. For these reasons, progress needs to develop more effective treatment regimes. In the past 5 years, advances have been made in better knowledge of HCV viral life cycle, and in the researches of HCV-specific directly acting antivirals. Recent data suggest that protease and polymerase inhibitors, in triple combinations with interferon plus ribavirin-based treatment are able to shorten treatment duration and improve SVR rates even in "hard to cure" HCV genotype 1 patients. The aim of this review is to summarize results obtained with novel anti-HCV compounds.

Gene therapeutic approach for inhibiting hepatitis C virus replication using a recombinant protein that controls interferon expression

The hepatitis C virus (HCV) is a continuing threat to public health. The systemic administration of interferon alpha with ribavirin is the only currently approved treatment. However, this treatment is associated with a wide spectrum of systemic side effects that limits its effectiveness; thus, there is an urgent need for new treatment modalities. In this study, we describe a novel anti-HCV strategy employing a recombinant transcription factor that we have engineered in such a way that NS3/4a viral protease controls its intracellular localization, thereby restoring interferon secretion specifically in cells infected with HCV. Proof-of-concept experiments validated the strategy, showing that the recombinant transcription factor was triggered to stimulate interferon promoter by NS3/4A and remained inactive in cells without NS3/4a. Using an adenovirus-associated viral vector delivery system, we found that the recombinant transcription factor inhibited HCV replication effectively in vitro in cultured cells.

Viral response to specifically targeted antiviral therapy for hepatitis C and the implications for treatment success

Currently, hepatitis C virus (HCV) antiviral therapy is characterized by long duration, a multitude of side effects, difficult administration and suboptimal success; clearly, alternatives are needed. Collectively, specifically targeted antiviral therapy for HCV (STAT-C) molecules achieve rapid viral suppression and very high rapid virological response rates, and improve sustained virological response rates. The attrition rate of agents within this class has been high due to various toxicities. Regardless, several STAT-C molecules are poised to become the standard of care for HCV treatment in the foreseeable future. Optimism must be tempered with concerns related to the rapid development of drug resistance with resulting HCV rebound. Strategies including induction dosing with interferon and ribavirin, use of combination high-potency STAT-C molecules and an intensive emphasis on adherence to HCV antiviral therapy will be critical to the success of this promising advance in HCV therapy.

[Hepatitis C virus infection--after 20 years]

The paper is devoted to the two decades of hepatitis C virus related basic researches and clinical experiences, from the discovery of the virus to the newest therapeutic options. Virology, epidemiology, pathology-pathogenesis, the virus-induced immunological and metabolic changes, the diagnosis and advances in antiviral treatment are discussed.

Mechanism of hepatitis C virus RNA polymerase inhibition with dihydroxypyrimidines

We studied the biochemical mechanisms associated with inhibition and resistance to a 4,5-dihydroxypyrimidine carboxylate that inhibits the hepatitis C virus (HCV) RNA-dependent RNA polymerase NS5B. On the basis of the structure of the pharmacophore, it has been suggested that these compounds may act as pyrophosphate (PP(i)) mimics. We monitored nucleotide incorporation events during the elongation phase and showed that the polymerase activity of wild-type NS5B was inhibited by the dihydroxypyrimidine at a 50% inhibitory concentration (IC(50)) of 0.73 muM. Enzymes with the G152E or P156L mutation, either of which confers resistance to this compound, showed four- to fivefold increases in IC(50)s. The inhibitor was competitive with respect to nucleotide incorporation. It was likewise effective at preventing the PP(i)-mediated excision of an incorporated chain terminator in a competitive fashion. In the absence of the dihydroxypyrimidine, the reaction was not significantly affected by the G152E or P156L mutation. These data suggest that the resistance associated with these two mutations is unlikely due to an altered interaction with the pyrophosphate-mimicking domain of the compound but, rather, is due to altered interactions with its specificity domain at a region distant from the active site. Together, our findings provide strong experimental evidence that supports the notion that the members of this class of compounds can act as PP(i) mimics that have the potential to mechanistically complement established nucleoside and nonnucleoside analogue inhibitors.

Antiviral therapy of chronic hepatitis C in patients with advanced liver disease and after liver transplantation

Chronic infection with the hepatitis C virus (HCV) represents one of the major causes for end-stage liver disease worldwide. Although liver transplantation offers an effective treatment, HCV reinfection of the transplanted graft is a critical and almost inevitable complication with major influence on graft- and patient survival. Pre-transplant antiviral therapy in advanced liver disease is limited by poor tolerance and only applicable to mildly decompensated patients but was able to show promising results in patients reaching negative viral load when undergoing transplantation. Prophylactic therapy with HCV antibodies during the anhepatic phase has not been shown to be effective in studies to date. Antiviral therapy after transplantation but before evidence of reinfection, so called pre-emptive treatment, is limited by frequent complications and a high rate of side effects. The mainstay of management represents directed antiviral therapy after evidence of recurrence of chronic Hepatitis C. With a combination therapy of pegylated interferon and ribavirin, sustained virologic response rates of 25-45% are achieved. However, tolerability is often poor, and the need of dose reduction is frequent. To date, there is no general consensus on modality, timing and dosing of antiviral treatment of HCV in patients with advanced liver disease and after liver transplantation. More randomised, controlled trials are needed. Moreover, upcoming new treatment approaches, e.g. specifically targeted antiviral therapy for hepatitis C (STAT-C) with HCV-specific polymerase and protease inhibitors, may represent a therapeutic alternative.

Hepatitis C virus infection and immunomodulatory therapies

Hepatitis C virus (HCV) infection remains a large-scale and significant health concern. The combination of subcutaneously administered pegylated interferon and oral ribavirin is the FDA-approved regimen for the treatment of chronic HCV infection. Combination therapy may result in a sustained virologic response leading to HCV eradication, with a reduction in risk for cirrhosis, hepatic decompensation, and hepatocellular carcinoma. However, the combination of PEG-IFN and ribavirin does not universally result in cure in all patients who undergo treatment. In this article, the authors discuss immunomodulatory therapies and clinical trials in the treatment of HCV infection.

Review article: adherence to medication for chronic hepatitis C - building on the model of human immunodeficiency virus antiretroviral adherence research

BACKGROUND

Treatment of hepatitis C virus (HCV) infection with pegylated interferon/ribavirin achieves sustained virological response in up to 56% of HCV mono-infected patients and 40% of HCV/human immunodeficiency virus (HIV)-co-infected patients. The relationship of patient adherence to outcome warrants study.

AIM

To review comprehensively research on patient-missed doses to HCV treatment and discuss applicable research from adherence to HIV antiretroviral therapy.

METHODS

Publications were identified by PubMed searches using the keywords: adherence, compliance, hepatitis C virus, interferon and ribavirin.

RESULTS

The term 'non-adherence' differs in how it is used in the HCV from the HIV literature. In HCV, 'non-adherence' refers primarily to dose reductions by the clinician and early treatment discontinuation. In contrast, in HIV, 'non-adherence' refers primarily to patient-missed doses. Few data have been published on the rates of missed dose adherence to pegylated interferon/ribavirin and its relationship to virological response.

CONCLUSIONS

As HCV treatment becomes more complex with new classes of agents, adherence will be increasingly important to treatment success as resistance mutations may develop with suboptimal dosing of HCV enzyme inhibitors. HIV adherence research can be applied to that on HCV to establish accurate methods to assess adherence, investigate determinants of non-adherence and develop strategies to optimize adherence.

Helicase inhibitors as specifically targeted antiviral therapy for hepatitis C

The hepatitis C virus (HCV) leads to chronic liver disease and affects more than 2% of the world's population. Complications of the disease include fibrosis, cirrhosis and hepatocellular carcinoma. Current therapy for chronic HCV infection, a combination of ribavirin and pegylated IFN-alpha, is expensive, causes profound side effects and is only moderately effective against several common HCV strains. Specifically targeted antiviral therapy for hepatitis C (STAT-C) will probably supplement or replace present therapies. Leading compounds for STAT-C target the HCV nonstructural (NS)5B polymerase and NS3 protease, however, owing to the constant threat of viral resistance, other targets must be continually developed. One such underdeveloped target is the helicase domain of the HCV NS3 protein. The HCV helicase uses energy derived from ATP hydrolysis to separate based-paired RNA or DNA. This article discusses unique features of the HCV helicase, recently discovered compounds that inhibit HCV helicase catalyzed reactions and HCV cellular replication, and new methods to monitor helicase action in a high-throughput format.

Treatment of chronic hepatitis C in Asia: when East meets West

The issue of best treatment for chronic hepatitis C virus (HCV) infection is in constant flux, not only in Western countries but also in Asia. Currently, pegylated-interferon plus ribavirin is the standard of care. Studies from Asia provide evidence to support the same broad treatment strategies for Asian patients as recommended in Western countries. Nevertheless, there is increasing evidence that Asians have a higher likelihood of achieving a sustained virological response (SVR) than their Caucasians counterparts when treated with the corresponding regimen. With the recommended 'standard dose and duration treatment regimens', SVR is achieved in Asia for around 70% of HCV genotype 1 (HCV-1) infected cases, approximately 90% of HCV-2/3, approximately 65% of HCV-4, and approximately 80% of HCV-6 patients. Difference of body weight in race might contribute the superior response in Asian patients. HCV genotype distribution in Asia also differs from North-America/Europe. HCV-6 and its variants, previously mistyped as HCV-1, needs accurate genotyping. Increasing data support the proposal that HCV genotype, baseline viral load and on-treatment virological response provide information for decision-making so that treatment can be individualized. Beyond the older recommendations, an abbreviated 24-week regimen could be suggested for HCV-1/4 patients with baseline viral loads < 400 000 IU/mL and a rapid virological response (RVR, HCV RNA undetectable at week 4), and an abbreviated 12-16 weeks of pegylated-interferon with weight-based doses of ribavirin could be suggested for HCV-2/3 patients with a RVR. Such tailored treatment regimens can reduce the costs of treatment and incidence of adverse events without compromising efficacy. Hepatitis C virus (HCV) infection is one of the most important causes of cirrhosis worldwide, and particularly in some countries of Asia (notably Japan) where it is now more prevalent than chronic hepatitis B virus infection. Hepatitis C virus infection can also lead to hepatocellular carcinoma (HCC). It is estimated that there are more than 170 million people chronically infected with HCV, and 3 to 4 million persons are newly infected each year. The risk for developing cirrhosis 20 years after initial HCV infection among those chronically infected varies between studies, but is estimated at around 10%-15% for men and 1-5% for women. Once cirrhosis is established, the rate of developing HCC is at 1%-4% per year. Approximately 280 000 deaths per year are related to HCV infection. Hepatitis C virus-related end-stage liver disease and HCC have become the leading cause for liver transplantation worldwide. In the Asia-Pacific area, the estimated prevalence of antibodies to HCV (anti-HCV) range from 0.3% in New Zealand to 5.6% in Thailand. In Japan, Middle East, Vietnam and Taiwan, several HCV hyper-endemic areas have been reported with an anti-HCV prevalence rate of 12% to as high as 58%. In addition to the well-known endemic status of HBV infection in most countries of the Asia-Pacific region, HCV infection presents another critical scenario of public health issue in this region, as outlined in Guidelines by the Asia-Pacific Association for Study of the Liver (APASL). Given the lack of an effective vaccine, optimal treatment of chronic HCV infection is now perceived as a 'must' in terms of public health strategies, as well as of the clinical setting for individual patients.