The anti-hepatitis C agent nitazoxanide induces phosphorylation of eukaryotic initiation factor 2alpha via protein kinase activated by double-stranded RNA activation

Nitazoxanide plus pegylated interferon and ribavirin in the treatment of genotype 4 chronic hepatitis C, a randomized controlled trial

BACKGROUND & AIMS

Nitazoxanide has been proposed as a novel therapeutic agent for chronic hepatitis C virus (HCV) potentiating the effect of interferon and improving sustained virological response rates to up to 80% in genotype 4. This is an independent randomized trial to confirm the efficacy of nitazoxanide in the treatment of chronic hepatitis C genotype 4.

METHODS

This was an open-label trial. Treatment-naive genotype 4 HCV patients were recruited: Group 1 received weekly subcutaneous pegylated interferon 160 μg in addition to weight-based ribavirin (1200 mg if ≥ 75 kg and 1000 mg if <75 kg) for 48 weeks, Group 2 received 4 weeks lead-in therapy by nitazoxanide alone (500 mg bid) followed by triple therapy including nitazoxanide, pegylated interferon and ribavirin for a further 48 weeks.

RESULTS

Fifty patients were recruited in each group. Baseline characteristics were similar except for a higher BMI in group 1 (28.5 vs. 26.5, P = 0.01). SVR rates were similar (24/50 (48%) vs. 25/50 (50%) in groups 1 and 2 respectively, P: 0.84). RVR, cEVR and ETR rates were also similar (61% vs. 53% - P:0.4, 70% vs. 72% - P:0.8 and 62% vs. 58% - P:0.6 in groups 1 and 2 respectively). Biochemical response at week 12 was also similar (57% vs. 46% in groups 1 and 2 respectively, P:0.26). Complications were similar except for a higher rate of dyspepsia in the group receiving nitazoxanide (32% vs. 14%, P:0.03).

CONCLUSION

The addition of nitazoxanide to pegylated interferon and ribavirin does not improve the virological or biochemical response rates in chronic HCV genotype 4.

Addition of nitazoxanide to PEG-IFN and ribavirin to improve HCV treatment response in HIV-1 and HCV genotype 1 coinfected persons naïve to HCV therapy: results of the ACTG A5269 trial

BACKGROUND

We hypothesized that nitazoxanide (NTZ) added to pegylated interferon alfa-2a (PEG-IFN) and weight-based ribavirin (WBR) would improve hepatitis C virus (HCV) virologic responses in HCV treatment-naïve HIV-1/HCV genotype 1 coinfected persons.

METHODS

Prospective, single-arm study in which subjects received 4-week lead-in (NTZ 500 mg twice daily) followed by 48 weeks of NTZ, PEG-IFN, and WBR. We compared the HCV virologic responses of these subjects to historical controls from the completed ACTG study A5178 who received PEG-IFN and WBR and had similar subject characteristics. Primary endpoints were early virologic response and complete early virologic response (EVR and cEVR).

RESULTS

Among 67 subjects (78% male; 48% Black; median age, 50 years), EVR was achieved in 65.7% (90% CI, 55.0%-75.3%), cEVR in 38.8% (28.8%-49.6%). and SVR in 32.8% (23.4%-43.5%). EVR was higher with NTZ (51.4% in A5178; P = .03), but the sustained virologic response (SVR) proportion was similar (27.3% in A5178; P = .24). In contrast to A5178, SVR was similar across IL28B genotypes. Overall, NTZ was safe and well-tolerated.

CONCLUSION

Whereas EVR proportion improved significantly in this pilot study, the addition of NTZ to PEG-IFN/WBR did not significantly improve SVR compared to historical controls. NTZ may be associated with an attenuation of the effect of IL28B on HCV treatment response.

Thiazolides, a new class of antiviral agents effective against rotavirus infection, target viral morphogenesis, inhibiting viroplasm formation

Rotaviruses, nonenveloped viruses presenting a distinctive triple-layered particle architecture enclosing a segmented double-stranded RNA genome, exhibit a unique morphogenetic pathway requiring the formation of cytoplasmic inclusion bodies called viroplasms in a process involving the nonstructural viral proteins NSP5 and NSP2. In these structures the concerted packaging and replication of the 11 positive-polarity single-stranded RNAs take place to generate the viral double-stranded RNA (dsRNA) genomic segments. Rotavirus infection is a leading cause of gastroenteritis-associated severe morbidity and mortality in young children, but no effective antiviral therapy exists. Herein we investigate the antirotaviral activity of the thiazolide anti-infective nitazoxanide and reveal a novel mechanism by which thiazolides act against rotaviruses. Nitazoxanide and its active circulating metabolite, tizoxanide, inhibit simian A/SA11-G3P[2] and human Wa-G1P[8] rotavirus replication in different types of cells with 50% effective concentrations (EC50s) ranging from 0.3 to 2 μg/ml and 50% cytotoxic concentrations (CC50s) higher than 50 μg/ml. Thiazolides do not affect virus infectivity, binding, or entry into target cells and do not cause a general inhibition of viral protein expression, whereas they reduce the size and alter the architecture of viroplasms, decreasing rotavirus dsRNA formation. As revealed by protein/protein interaction analysis, confocal immunofluorescence microscopy, and viroplasm-like structure formation analysis, thiazolides act by hindering the interaction between the nonstructural proteins NSP5 and NSP2. Altogether the results indicate that thiazolides inhibit rotavirus replication by interfering with viral morphogenesis and may represent a novel class of antiviral drugs effective against rotavirus gastroenteritis.

Research perspective: potential role of nitazoxanide in ovarian cancer treatment. Old drug, new purpose?

Among gynecological malignancies epithelial ovarian cancer (EOC) is the leading cause of death. Despite improvements in conventional chemotherapy combinations, the overall cure rate has remained mostly stable over the years, and only 10%–15% of patients maintain a complete response following first-line therapy. To improve the efficacy of ovarian cancer chemotherapy it is essential to develop drugs with new mechanisms of action. Compared to normal tissues, protein disulfide isomerase (PDI) is overexpressed in ovarian tumors. PDI is a cellular enzyme in the lumen of the endoplasmic reticulum (ER) of eukaryotes or the periplasmic region of prokaryotes. This protein catalyzes the formation and breakage of disulphide bonds between cysteine residues in proteins, which affects protein folding. Selective inhibition of PDI activity has been exhibited both in vitro and in vivo anticancer activity in human ovarian cancer models. PDI inhibition caused accumulation of unfolded or misfolded proteins, which led to ER stress and the unfolded protein response (UPR), and in turn resulted in cell death. Nitazoxanide [NTZ: 2-acetyloxy-N-(5-nitro-2-thiazolyl)benzamide] is a thiazolide antiparasitic agent with excellent activity against a wide variety of protozoa and helminths. In this article, we propose that NTZ, acting as PDI inhibitor, may be a new and potent addition to the chemotherapeutic strategy against ovarian cancer.

A c-Myc activation sensor-based high-throughput drug screening identifies an antineoplastic effect of nitazoxanide

Deregulation of c-Myc plays a central role in the tumorigenesis of many human cancers. Yet, the development of drugs regulating c-Myc activity has been challenging. To facilitate the identification of c-Myc inhibitors, we developed a molecular imaging sensor-based high-throughput screening (HTS) system. This system uses a cell-based assay to detect c-Myc activation in a HTS format, which is established from a pure clone of a stable breast cancer cell line that constitutively expresses a c-Myc activation sensor. Optimization of the assay performance in the HTS format resulted in uniform and robust signals at the baseline. Using this system, we conducted a quantitative HTS against approximately 5,000 existing bioactive compounds from five different libraries. Thirty-nine potential hits were identified, including currently known c-Myc inhibitors. There are a few among the top potent hits that are not known for anti-c-Myc activity. One of these hits is nitazoxanide, a thiazolide for treating human protozoal infections. Validation of nitazoxanide in different cancer cell lines revealed a high potency for c-Myc inhibition with IC50 ranging between 10 and 500 nmol/L. Oral administration of nitazoxanide in breast cancer xenograft mouse models significantly suppressed tumor growth by inhibition of c-Myc and induction of apoptosis. These findings suggest a potential of nitazoxanide to be repurposed as a new antitumor agent for inhibition of c-Myc-associated neoplasia. Our work also demonstrated the unique advantage of molecular imaging in accelerating discovery of drugs for c-Myc-targeted cancer therapy.

Effects of triple-drug therapy with nitazoxanide, high-dose ribavirin and peginterferon-α-2a in patients with chronic hepatitis C

AIM

The historical standard of care for patients with chronic hepatitis C virus (HCV) was peginterferon (PEG IFN) and ribavirin combination therapy, yielding sustained virological response (SVR) rates of 38-52% in HCV genotype 1 patients. This study evaluated a novel three-drug regimen of nitazoxanide and high-dose ribavirin as lead-in therapy, followed by PEG IFN-α-2a in triple therapy.

METHODS

A prospective, open-label pilot study was conducted in treatment-naive patients with HCV genotype 1. Patients received nitazoxanide 500 mg twice a day for 2 weeks, then nitazoxanide plus ribavirin 1400 mg/day for 2 weeks, then nitazoxanide plus ribavirin plus PEG IFN-α-2a 180 μg weekly for 12 weeks, followed by ribavirin plus PEG IFN-α-2a for 12 weeks (48 weeks if HCV RNA negative after week 24). Primary outcome was SVR. Other outcomes included very rapid virological response (VRVR), rapid virological response (RVR), early virological response (EVR), end-of-treatment response (ETR), and safety and tolerability.

RESULTS

Thirty-three patients with a mean age of 46 years, detectable HCV RNA (64% with <600 000 IU/mL), and METAVIR fibrosis scores (F1:F2:F3) of 15%:49%:36% were enrolled. Outcomes were as follows: SVR, 67% (22/33); VRVR, 39% (13/33); RVR, 48% (16/33); EVR, 70% (23/33); and ETR, 67% (22/33). Most patients required at least one growth factor. Two patients discontinued because of adverse events.

CONCLUSION

This three-drug regimen was effective in achieving SVR in patients with HCV genotype 1. No patients relapsed, and the toxicity profile was favorable. Further studies on the role of nitazoxanide in the treatment of chronic HCV are warranted.

Curing a viral infection by targeting the host: the example of cyclophilin inhibitors

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Viruses exploit multiple host cell mechanisms for their own replication.

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These mechanisms may serve as targets for antiviral therapy.

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Host-targeted therapies may have a high barrier to resistance.

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Cyclophilin inhibitors have shown promise in curing chronic hepatitis C.

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Cyclophilin inhibitors may potentially be used to treat other viral infections.

Every step of the viral life cycle is dependent on the host, which potentially can be explored for antiviral targets. Historically, however, drug discovery has focused mainly on viral targets, because of their perceived specificity. Efforts to pursue host targets have been largely hampered by concern over potential on-target toxicity, the lack of predictive cell culture and animal models, and the complexity of host–virus interactions. On the other hand, there are distinct advantages of targeting the host, such as creating a high barrier to resistance, providing broad coverage of different genotypes/serotypes and possibly even multiple viruses, and expanding the list of potential targets, when druggable viral targets are limited. Taking hepatitis C virus (HCV) as the example, there are more than 20 inhibitors of the viral protease, polymerase and NS5A protein currently in advanced clinical testing. However, resistance has become a main challenge with these direct-acting antivirals, because HCV, an RNA virus, is notoriously prone to mutation, and a single mutation in the viral target may prevent the binding of an inhibitor, and rendering it ineffective. Host cyclophilin inhibitors have shown promising effects both in vitro and in patients to prevent the emergence of resistance and to cure HCV infection, either alone or in combination with other agents. They are also capable of blocking the replication of a number of other viral pathogens. While the road to developing host-targeting antivirals has been less traveled, and significant challenges remain, delivering the most effective antiviral regimen, which may comprise inhibitors of both host and viral targets, should be well worth the effort.

Efficacy of nitazoxanide against clinical isolates of Mycobacterium tuberculosis

Nitazoxanide (NTZ) has bactericidal activity against the H37Rv laboratory strain of Mycobacterium tuberculosis with a MIC of 16 μg/ml. However, its efficacy against clinical isolates of M. tuberculosis has not been determined. We found that NTZ's MIC against 50 clinical isolates ranged from 12 to 28 μg/ml with a median of 16 μg/ml and was unaffected by resistance to first- or second-line antituberculosis drugs or a diversity of spoligotypes.

Niclosamide is a proton carrier and targets acidic endosomes with broad antiviral effects

Viruses use a limited set of host pathways for infection. These pathways represent bona fide antiviral targets with low likelihood of viral resistance. We identified the salicylanilide niclosamide as a broad range antiviral agent targeting acidified endosomes. Niclosamide is approved for human use against helminthic infections, and has anti-neoplastic and antiviral effects. Its mode of action is unknown. Here, we show that niclosamide, which is a weak lipophilic acid inhibited infection with pH-dependent human rhinoviruses (HRV) and influenza virus. Structure-activity studies showed that antiviral efficacy and endolysosomal pH neutralization co-tracked, and acidification of the extracellular medium bypassed the virus entry block. Niclosamide did not affect the vacuolar H(+)-ATPase, but neutralized coated vesicles or synthetic liposomes, indicating a proton carrier mode-of-action independent of any protein target. This report demonstrates that physico-chemical interference with host pathways has broad range antiviral effects, and provides a proof of concept for the development of host-directed antivirals.

The future for the treatment of genotype 4 chronic hepatitis C

Hepatitis C virus genotype 4 (HCV-4) is the most common type of hepatitis C virus (HCV) in the Middle East and Africa, in particular Egypt. Since the development of new protease inhibitors, the response of HCV-4 to the standard regimen of treatment (pegylated interferon/ribavirin) lags behind other genotypes and has become the most resistant type to treat. The development of therapeutic strategies for all patients with HCV-4 whether they are naïve, have experienced a virological breakthrough, are relapsers or non-responders is still a considerable challenge. New types of interferon (Consensus Interferon, Y-shaped, Albinterferon...) and new direct action antiviral drugs (Nitazoxanide, Vit.D, other) may improve the treatment of patients with HCV-4. The IL28B CC polymorphism may be associated with sustained virological response.

Treatment of non-genotype 1 hepatitis C virus patients

The HCV genotype will remain an important, independent pre-treatment predictor of virological response. While direct acting antivirals (DAA) will improve in the coming months the rates of virological response in patients with HCV-1, the development of DAAs effective against other HCV genotypes is at an earlier stage. Therefore, Peg-Interferon and Ribavirin will continue to be used in the near future as standard treatment in these patients. In this manuscript, we will discuss highly debated aspects related to non-1 HCV genotypes. First of all, the predictive role of IL28B genetic variation, secondarily specific aspects related to HCV-4. In the final part, we will highlight potential differences between HCV-2 and HCV-3. Indeed, despite the fact that HCV-2 and HCV-3 have been evaluated together in the majority of studies, HCV-3 patients achieve lower rates of virological response as compared to HCV-2. Whether a genotype individualized treatment may increase virologic response is the object of current investigations.

Nitazoxanide for the empiric treatment of pediatric infectious diarrhea

We conducted a double-blind, placebo-controlled clinical trial to demonstrate the efficacy of nitazoxanide suspension for the treatment of presumed infectious diarrhea in children. Eligible patients must have had diarrheal illness lasting 3-29 days. Patients were randomized to receive either nitazoxanide or placebo twice daily for three days. The primary endpoint was time from first dose to resolution of symptoms. One hundred children mean age 3.3 years were enrolled. The median time to resolution of symptoms for nitazoxanide treated patients was 23 hours (IQR 4-48 hours) vs 103.5 hours (IQR 63->168 hours) for placebo (p<0.001). An analysis by disease subset indicated nitazoxanide treated patients had statistically shorter durations of diarrheal illness associated with Giardia lamblia (n=32, p<0.001) and those with no identified enteropathogen (n=38, p=0.008), when compared to placebo. The study medication was well tolerated. Overall, nitazoxanide was effective at reducing the duration of diarrheal illness associated with multiple etiologies, including patients with no identified enteropathogen. These results suggest nitazoxanide may be a viable therapeutic option for the empiric treatment of diarrheal illness in children where the etiology is unknown or presumed to be of infectious origin. Clinical trial registry number NCT01326338.

Thiazolides as novel antiviral agents. 2. Inhibition of hepatitis C virus replication

We report the activities of a number of thiazolides [2-hydroxyaroyl-N-(thiazol-2-yl)amides] against hepatitis C virus (HCV) genotypes IA and IB, using replicon assays. The structure-activity relationships (SARs) of thiazolides against HCV are less predictable than against hepatitis B virus (HBV), though an electron-withdrawing group at C(5') generally correlates with potency. Among the related salicyloylanilides, the m-fluorophenyl analogue was most promising; niclosamide and close analogues suffered from very low solubility and bioavailability. Nitazoxanide (NTZ) 1 has performed well in clinical trials against HCV. We show here that the 5'-Cl analogue 4 has closely comparable in vitro activity and a good cell safety index. By use of support vector analysis, a quantitative structure-activity relationship (QSAR) model was obtained, showing good predictive models for cell safety. We conclude by updating the mode of action of the thiazolides and explain the candidate selection that has led to compound 4 entering preclinical development.

Heparin activates PKR by inducing dimerization

Protein kinase R (PKR) is an interferon-induced kinase that plays a pivotal role in the innate immunity pathway. PKR is activated to undergo autophosphorylation upon binding to double-stranded RNAs or RNAs that contain duplex regions. Activated PKR phosphorylates the α subunit of eukaryotic initiation factor 2, thereby inhibiting protein synthesis. PKR is also activated by heparin, a highly sulfated glycosaminoglycan. We have used biophysical methods to define the mechanism of PKR activation by heparin. Heparins as short as hexasaccharide bind strongly to PKR and activate autophosphorylation. In contrast to double-stranded RNA, heparin activates PKR by binding to the kinase domain. Analytical ultracentrifugation measurements support a thermodynamic linkage model where heparin binding allosterically enhances PKR dimerization, thereby activating the kinase. These results indicate that PKR can be activated by small molecules and represents a viable target for the development of novel antiviral agents.

Hepatitis C therapy: other players in the game

Therapies in addition to the direct-acting antiviral agents (DAA) under evaluation for chronic hepatitis C include host targets such as cyclophilin inhibitors and immunomodulators. Both passive and therapeutic vaccines hold promise for the future. Although the numbers of drug categories and individual agents are increasing, only a handful of the non-DAAs seem to be ready to move on to phase III trials. New interferon agents are in development, and ribavirin variants are still under consideration. The role of the other players in the overall armamentarium against hepatitis C virus is still evolving.

Maximizing bactericidal activity with combinations of bioreduced drugs

Certain antimicrobial and anticancer drugs are only active following bioactivation within the target cell. Nitroimidazoles, nitrofurans and quinoxaline-di-N-oxides represent three chemical classes that are active as anti-tubercular drugs following intracellular bioreduction to reactive intermediates. Two nitroimidazoles are in clinical trials as new anti-tubercular drugs with significant bactericidal activity as well as activity on nonreplicating bacteria. Nitrofurans and quinoxaline-di-N-oxides, which are in preclinical development, also exhibit bactericidal activity and activity on nonreplicating bacteria. Current data indicate these drugs are bioreduced via distinct pathways that yield reactive free radical species. Since flux though each system would become saturated due to enzyme kinetics, cellular uptake or maximum drug concentration attainable in the host, one may propose that using three distinct systems simultaneously could produce a larger burst of free radicals to rapidly and efficiently kill bacteria and shorten the time to cure for tuberculosis. Arguments for the possible development of a novel combination therapy with maximized bacterial cell killing and the possibility of shortening the time to cure will be presented.

Mutations in HCV non-structural genes do not contribute to resistance to nitazoxanide in replicon-containing cells

Nitazoxanide (NTZ) exhibits potent antiviral activity against hepatitis C virus (HCV) in cell culture. Previously, HCV replicon-containing cell lines resistant to NTZ were selected, but transfer the HCV NTZ-resistance phenotype was not observed following transfection of whole cell RNA. To further explore the nature of the resistance of HCV to NTZ, full length HCV replicon sequences were obtained from two NTZ-resistant (NTZ-11, TIZ-9), and the parental (RP7) cell lines. Numerous nucleotide changes were observed in individual HCV genomes relative to the RP7 HCV consensus sequence, but no common mutations in the HCV non-structural genes or 3'-UTR were detected. A cluster of single nucleotide mutations was found within a 5-base portion of the 5'-UTR in 20/21 HCV replicon sequences from both resistant cell lines. Three mutations (5'-UTR G17A, G18A, C20U) were individually inserted into CON1 ('wild-type') HCV replicons, showed reduced replication (5 to 50-fold), but none conferred resistance to NTZ. RP7, NTZ-11, and TIZ-9 were cured of HCV genomes by serial passage under interferon. Transfection of cured NTZ-11 and TIZ-9 with either whole cell RNAs from RP7, NTZ-11, or TIZ-9, 'wild-type' or the 5'-UTR mutation-containing replicon RNAs exhibited an NTZ-resistance phenotype. TIZ (the active metabolite of NTZ) was found to be inactive against the activity of HCV polymerase, protease, and helicase in enzymatic assays. These data confirm previous speculations that HCV resistance to NTZ is not due to mutations in the virus, and demonstrate that HCV resistance and most likely the antiviral activity of TIZ are due to interactions with cellular target(s).

Management of hepatitis C virus genotype 4: recommendations of an international expert panel

HCV has been classified into no fewer than six major genotypes and a series of subtypes. Each HCV genotype is unique with respect to its nucleotide sequence, geographic distribution, and response to therapy. Genotypes 1, 2, and 3 are common throughout North America and Europe. HCV genotype 4 (HCV-4) is common in the Middle East and in Africa, where it is responsible for more than 80% of HCV infections. It has recently spread to several European countries. HCV-4 is considered a major cause of chronic hepatitis, cirrhosis, hepatocellular carcinoma, and liver transplantation in these regions. Although HCV-4 is the cause of approximately 20% of the 170 million cases of chronic hepatitis C in the world, it has not been the subject of widespread research. Therefore, this document, drafted by a panel of international experts, aimed to review current knowledge on the epidemiology, natural history, clinical, histological features, and treatment of HCV-4 infections.

Thiazolides as novel antiviral agents. 1. Inhibition of hepatitis B virus replication

We report the syntheses and activities of a wide range of thiazolides [viz., 2-hydroxyaroyl-N-(thiazol-2-yl)amides] against hepatitis B virus replication, with QSAR analysis of our results. The prototypical thiazolide, nitazoxanide [2-hydroxybenzoyl-N-(5-nitrothiazol-2-yl)amide, NTZ] 1 is a broad spectrum antiinfective agent effective against anaerobic bacteria, viruses, and parasites. By contrast, 2-hydroxybenzoyl-N-(5-chlorothiazol-2-yl)amide 3 is a novel, potent, and selective inhibitor of hepatitis B replication (EC(50) = 0.33 μm) but is inactive against anaerobes. Several 4'- and 5'-substituted thiazolides show good activity against HBV; by contrast, some related salicyloylanilides show a narrower spectrum of activity. The ADME properties of 3 are similar to 1; viz., the O-acetate is an effective prodrug, and the O-aryl glucuronide is a major metabolite. The QSAR study shows a good correlation of observed EC(90) for intracellular virions with thiazolide structural parameters. Finally we discuss the mechanism of action of thiazolides in relation to the present results.

HBV life cycle and novel drug targets

With up to 400 million affected people worldwide, chronic hepatitis B virus (HBV) infection is still a major health care problem. During the last decade, several novel therapeutic approaches have been developed and evaluated. In most regions of the world, interferon-α, and nucleos(t)ide analogues (NUCs) are currently approved. Despite major improvements, none of the existing therapies is optimal since viral clearance is rarely achieved. Recently, a better understanding of the HBV life cycle and the development of novel model systems of HBV infection have led to the development of novel antiviral strategies and drug targets. This review will focus on current and potential future drug targets in the HBV life cycle and strategies to modulate the virus-host interaction.

Mixing the right hepatitis C inhibitor cocktail

Therapy for hepatitis C virus (HCV) infection is on the cusp of a new era. Until now, standard-of-care therapy has involved interferon (IFN) and ribavirin. With the first successful Phase III trials of specific targeted antiviral therapy for HCV (STAT-C) compounds, as well as three trials in progress giving the first glimpse of IFN-free combinations of STAT-C agents, this review looks ahead to the new classes of anti-HCV agents currently in clinical development. Successful pharmacologic control of HIV and TB frames the discussion, as well as consideration of the mutation frequency of HCV replication. Maximizing synergy between agents and minimizing cumulative toxicity will be critical to the design of future IFN-free STAT-C regimens.

[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.

New frontiers of HCV therapy in HIV/HCV co-infection

Hepatitis C virus (HCV) leads to disproportionate morbidity and mortality in the HIV-positive population. A new era of anti-HCV therapeutics is emerging, with many direct antiviral agents and immunomodulating drugs in clinical development. This review discusses HCV treatments in development, with special attention to four agents being studied actively among HIV/HCV-co-infected persons.

Potential treatment options and future research to increase hepatitis C virus treatment response rate

Hepatitis C virus (HCV) is a liver-tropic blood-borne pathogen that affects more than 170 million people worldwide. Although acute infections are usually asymptomatic, up to 90% of HCV infections persist with the possibility of long-term consequences such as liver fibrosis, cirrhosis, steatosis, insulin resistance, or hepatocellular carcinoma. As such, HCV-associated liver disease is a major public health concern. Although the currently available standard of care therapy of pegylated interferon α plus ribavirin successfully treats infection in a subset of patients, the development of more effective, less toxic HCV antivirals is a health care imperative. This review not only discusses the limitations of the current HCV standard of care but also evaluates upcoming HCV treatment options and how current research elucidating the viral life cycle is facilitating the development of HCV-specific therapeutics that promise to greatly improve treatment response rates both before and after liver transplantation.

New antiviral therapies for chronic hepatitis C

Chronic hepatitis C is an important health issue worldwide. The current standard therapy is based on a combination of pegylated-interferon (pegIFN) and ribavirin (RBV), but this treatment leads to only ~50% sustained virological response (SVR) in patients with HCV genotype 1 and high viral loads, who were mostly null-responders or relapsers. Among HCV genotypes other than HCV genotype 1, especially HCV genotype 4 patients show only 40-70% SVR by this treatment. Although new drugs also depend on the combination of pegIFN and RBV, it appears that these drugs improve not only rapid virological response (RVR) but also early virological response, leading to SVR in these patients. In the near future, we predict higher SVR rates in chronic hepatitis C patients treated with these new drugs.

Treatment of chronic hepatitis C using a 4-week lead-in with nitazoxanide before peginterferon plus nitazoxanide

GOALS

The primary aim of this study was to further evaluate the efficacy of peginterferon plus nitazoxanide without ribavirin using a 4-week lead-in.

BACKGROUND

The initial treatment of chronic hepatitis C with nitazoxanide used 12 weeks of nitazoxanide monotherapy before combination therapy with peginterferon with or without ribavirin.

STUDY

This open-label pilot study enrolled 44 treatment-naive patients with chronic hepatitis C (40 with genotype 4; 3 with genotype 1; and 1 with genotype 2). The patients received oral nitazoxanide 500 mg twice daily for 4 weeks followed by nitazoxanide plus peginterferon alfa-2a 180 mug weekly for 36 weeks and were then followed for 24 weeks. The results of this study were compared with those from an overlapping historical trial using 12 weeks of nitazoxanide lead-in.

RESULTS

A sustained virologic response (SVR) was achieved in 80% of patients, which was similar to the SVR rates in the historical trial, that is, 79% and 61% in patients treated with and without ribavirin, respectively. A rapid virologic response occurred in 59% of patients, which was also similar to the rapid virologic response rates in the historical trial (64% and 54% in patients treated with and without ribavirin, respectively). All 4 patients with genotypes 1 and 2 had an SVR.

CONCLUSIONS

The nitazoxanide lead-in phase before combination therapy with peginterferon can likely be reduced from 12 weeks to 4 weeks without compromising virologic response rates. In addition, treatment of chronic hepatitis C with peginterferon plus nitazoxanide without ribavirin is promising and requires further study.

Development of novel antiviral therapies for hepatitis C virus

Over 170 million people worldwide are infected with hepatitis C virus (HCV), a major cause of liver diseases. Current interferon-based therapy is of limited efficacy and has significant side effects and more effective and better tolerated therapies are urgently needed. HCV is a positive, single-stranded RNA virus with a 9.6 kb genome that encodes ten viral proteins. Among them, the NS3 protease and the NS5B polymerase are essential for viral replication and have been the main focus of drug discovery efforts. Aided by structure-based drug design, potent and specific inhibitors of NS3 and NS5B have been identified, some of which are in late stage clinical trials and may significantly improve current HCV treatment. Inhibitors of other viral targets such as NS5A are also being pursued. However, HCV is an RNA virus characterized by high replication and mutation rates and consequently, resistance emerges quickly in patients treated with specific antivirals as monotherapy. A complementary approach is to target host factors such as cyclophilins that are also essential for viral replication and may present a higher genetic barrier to resistance. Combinations of these inhibitors of different mechanism are likely to become the essential components of future HCV therapies in order to maximize antiviral efficacy and prevent the emergence of resistance.

Role of ribavirin in HCV treatment response: now and in the future

IMPORTANCE OF THE FIELD

Ribavirin is a broad spectrum antiviral agent that is used with pegylated IFN (Peg-IFN) for HCV treatment. Ribavirin does not significantly reduce HCV viral load when used alone but increases rates of sustained virologic response (SVR) when combined with Peg-IFN. HCV genotype 1 infected patients require higher doses of ribavirin administered for a longer duration of time versus HCV genotypes 2 and 3 patients who respond effectively to Peg-IFN with lower doses of ribavirin and shorter duration of therapy. Higher serum concentrations of ribavirin are associated with higher response rates but also higher rates of hemolytic anemia which is a dose limiting side effect. Alternatives to current therapy are under clinical evaluation.

AREAS COVERED IN THIS REVIEW

Systematic literature review of ribavirin use in HCV patients from 1995 to 2009 was conducted.

WHAT THE READER WILL GAIN

To review the efficacy and safety of ribavirin in current HCV treatment and in new therapies in Phase III clinical trials.

TAKE HOME MESSAGE

Ribavirin is a drug which is essential to produce higher SVR rates both with Peg-IFN and HCV protease inhibitors currently in Phase III clinical trials. Thus, ribavirin is and will remain an important drug to achieving higher SVR rates in HCV infected persons.

New strategies for the treatment of hepatitis C virus infection and implications of resistance to new direct-acting antiviral agents

Persistent hepatitis C virus (HCV) infection is a leading cause of chronic hepatitis, cirrhosis, and hepatocellular carcinoma and the major indication for liver transplantation in adults. Current standard of care treatment (SOC) with pegylated-interferon-α 2 and ribavirin (RBV) has a limited efficacy and is associated with significant side effects frequently associated with poor compliance or treatment discontinuation, requiring specialized and frequent monitoring. To overcome the limited efficacy of SOC, more than 50 direct-acting antiviral agents (DAA) designed to target viral-encoded proteins essential in the HCV life cycle are currently under development. The rapid selection of resistant mutants associated with the quasispecies nature of HCV with high mutation and replication rates is one of the main challenges for the new HCV therapies. Predictive host and viral factors together with combination of DAAs with or without IFN and/or RBV need to be accurately evaluated to design the most effective individualized treatment strategy within the shortest time interval and with minimum side effects.