Effect of ribavirin on the frequency of RNase L cleavage sites within the hepatitis C viral genome

Summary. The mechanisms of synergy in antiviral activity of interferon‐α and ribavirin in treating chronic hepatitis C virus (HCV) infection are still unknown. Interferon‐α indirectly induces cleavage of viral RNA by RNase L at UU/UA dinucleotides. There is evidence that HCV genomes with a higher number of UU/UA dinucleotides are more sensitive to interferon‐α. As a guanosine analogue, ribavirin exerts a mutagenic effect promoting G‐to‐A and C‐to‐U transitions. This study investigates whether ribavirin‐induced mutagenesis causes a higher frequency of UU/UA dinucleotides in the viral progeny sequences. Increased mutational frequencies in favour of G‐to‐A and C‐to‐U transitions during ribavirin treatment was reported by Hofmann et al. (Gastroenterology 2007;132:921–930). Overall, 937 nucleotide sequences from that publication were reanalysed for RNase L cleavage sites. These included HCV NS3 quasispecies from three patients with ribavirin monotherapy and NS5B quasispecies from patients who received ribavirin alone (n = 7) or in combination with interferon‐α (n = 7) at baseline and during treatment; NS5B quasispecies from a subgenomic HCV replicon system after 24, 48 and 72 h of cultivation with or without ribavirin or with levovirin. For NS3 quasispecies during ribavirin monotherapy and NS5B quasispecies from patients who received ribavirin alone or in combination with interferon‐α, analysis of RNase L cleavage sites did not reveal changes during treatment or differences between treatment regimes. Similarly, RNaseL cleavage sites from NS5B quasispecies of the HCV replicon did not differ significantly between time points or treatments. In conclusion, Ribavirin‐induced mutagenesis did not increase RNase L cleavage sites (UU/UA dinucleotides) within the HCV NS3 or NS5B encoding regions.     

Mutagenic effects of ribavirin and response to interferon/ribavirin combination therapy in chronic hepatitis C

BACKGROUND/AIMS: To elucidate whether ribavirin acts as a mutagen in the clinical setting and to clarify the relationship between ribavirin-induced mutations and virological response to combined therapy. METHODS: Thirty-four patients with hepatitis C virus (HCV) genotype 1b received ribavirin monotherapy for 4 weeks, followed by a 24-week course of IFN/ribavirin therapy. HCV mutations during a non-treatment observation period and during subsequent ribavirin monotherapy were determined, and the relationship between mutations and response to subsequent IFN/ribavirin therapy was evaluated. RESULTS: Serum HCV significantly decreased from 6.90 to 6.56 log10copy/ml in response to ribavirin monotherapy (P < 0.0001). Nucleotide mutations in the NS5A and NS5B regions occurred during ribavirin monotherapy at a rate of 2.9 x 10(-2)/site/year and 1.3 x 10(-2)/site/year, respectively, a significantly higher rate than the mutation rates during the prior non-treatment observation period (0.60 x 10(-2)/site/year and 0.24 x 10(-2)/site/year, P = 0.02, respectively). Mutation rates in the NS5A region were significantly higher in sustained viral responders (SVRs, n = 10) than in non-responders (8.8 x 10(-2)/site/year vs. 0.38 x 10(-2)/site/year, P = 0.0005, respectively). In the NS5A region, non-synonymous mutations only occurred in SVRs. CONCLUSIONS: Ribavirin may act as a mutagen, and mutations occurring during ribavirin therapy correlate with the virological response to subsequent IFN/ribavirin combination therapy.     

In vivo interferon system assessed by 2′‐5′ oligoadenylate synthetase activity in chronic hepatitis C virus patients treated with pegylated interferon and ribavirin

Aim: 2′,5′ oligoadenylate synthetase (2‐5AS), an enzyme induced by interferon, is an accurate indicator of the antiviral effect of interferon. We measured it during pegylated interferon based therapies in patients with chronic hepatitis C virus (HCV) in order to determine the dynamics of antiviral status in vivo and the relationship between the response to exogenous interferon and the outcome of therapy. Methods: A total of 160 patients with chronic HCV were treated with pegylated interferon alfa 2a or 2b or non‐pegylated interferon, with or without ribavirin. Serum 2‐5AS activity was measured by radioimmunoassay assay kits every 2 weeks. Results: In 60 patients treated with pegylated interferon alfa 2a or 2b, 2‐5AS levels increased to 7–40 times (average 235 pmol/dL) above the pretreatment levels (30 pmol/dL), which were significantly higher than the levels during non‐pegylated interferon therapy. Ribavirin did not enhance 2‐5AS levels. 2‐5AS levels between sustained virological response (SVR) and non‐SVR, including null responders to pegylated interferon plus ribavirin therapy were not significantly different. Conclusion: 2‐5AS levels were significantly higher in patients treated with pegylated interferon than in those treated with non‐pegylated interferon, suggesting that pegylated interferon is more potent at inducing interferon response genes resulting in an improved antiviral effect. Ribavirin did not appear to be related to interferon response gene induction.     

Effect of ribavirin in genotype 1 patients with hepatitis C responding to pegylated interferon alfa-2a plus ribavirin

BACKGROUND & AIMS: Pegylated interferon alfa-ribavirin combination is the standard treatment for chronic hepatitis C, but the mechanisms by which ribavirin enhances the rate of sustained hepatitis C virus (HCV) eradication remain unknown. We aimed to investigate the role of ribavirin in HCV clearance during therapy and to evaluate the consequences of ribavirin discontinuation in patients infected with genotype 1 hepatitis C who cleared HCV RNA at week 24. METHODS: A total of 516 patients were treated with pegylated interferon alfa-2a, 180 microg/wk, plus ribavirin, 800 mg/day. Seventy percent were RNA negative at week 24. They were randomized to continue with the combination or receive pegylated interferon alone. RESULTS: Responders at week 24 who stopped ribavirin had a significantly higher rate of breakthroughs during, and relapses after, therapy (sustained virologic response, 52.8% vs 68.2%; P = .004), but their side-effect profile and quality of life tended to improve. Multiple logistic regression analysis in the pegylated interferon alfa monotherapy group allowed identification of responders at week 24 who could stop ribavirin without losing their chance of a sustained virologic response, based on baseline viral load and age. Forty-eight weeks of ribavirin may not be needed when HCV RNA is undetectable at week 2. CONCLUSIONS: We made 3 conclusions from this study. First, ribavirin primarily acts by sustaining the virologic response to pegylated interferon alfa; second, ribavirin must be administered for the full treatment duration in most genotype 1-infected patients who respond; third, baseline parameters may help identify patients who could discontinue ribavirin or reduce the dose without losing their chance of success.     

Identification of a ribavirin-resistant NS5B mutation of hepatitis C virus during ribavirin monotherapy

Ribavirin (RBV), a guanosine analogue, has been suggested to exert an antiviral action against hepatitis C virus (HCV) by causing lethal mutations and suppressing RNA polymerase in vitro, but the mechanism of its clinical therapeutic effects is currently unknown. To test the hypothesis that RBV could act both as an RNA mutagen and inhibit viral RNA synthesis in vivo, we studied the evolution of the nucleotide sequences of HCV RNA at the nonstructural (NS) 5B region in patients receiving RBV, placebo, or interferon alfa (IFN-alpha) monotherapy. The RBV group showed a slightly more accelerated evolution rate of HCV RNA quasispecies than either the IFN-alpha or placebo group. RBV caused preferentially A-to-G and U-to-A mutations. Interestingly, an NS5B amino acid 415 Phe-to-Tyr (F415Y) mutation emerged in all (5 of 5) patients infected with HCV genotype 1a during the RBV treatment. Subsequently, the parental 415F strain reemerged in some patients after the treatment was discontinued. The effect of the amino acid substitution at NS5B415 on HCV RNA replication was then investigated using an HCV subgenomic replicon in Huh7 cells. We showed that treatment of replicon cells with RBV reduced the HCV RNA level of NS5B415F replicon, but not NS5B415Y, in a dose-dependent manner. Thus, NS5B F415Y mutation represents an RBV-resistant variant. The 3-dimensional modeling and structure analysis of NS5B protein revealed that the 415th amino acid is located at the P helix region of the thumb subdomain, which may interact with the minor groove of the template-primer duplex in the putative RNA-binding cleft. In conclusion, RBV could work as a weak mutagen for HCV RNA in HCV-infected patients. Furthermore, the selection of an RBV-resistant variant with a single amino acid substitution in NS5B suggested that RBV may directly interact with HCV RNA polymerase, thus interfering with its enzymatic activity.     

Treatment for hepatitis C virus in human immunodeficiency virus-infected patients: clinical benefits and cost-effectiveness

BACKGROUND: Hepatitis C virus (HCV) is an important cause of liver disease in human immunodeficiency virus (HIV)-infected patients. OBJECTIVE: To assess the cost-effectiveness of alternative management strategies for chronic HCV in co-infected patients with moderate hepatitis. METHODS: A state-transition model was used to simulate a cohort of HIV-infected patients with a mean CD4 cell count of 350 cells/ micro L and moderate chronic hepatitis C stratified by genotype. Strategies included interferon alfa (48 weeks), pegylated interferon alfa (48 weeks), interferon alfa and ribavirin (24 and 48 weeks), pegylated interferon alfa and ribavirin (48 weeks), and no treatment. Outcomes included life expectancy, quality-adjusted life years (QALYs), and incremental cost-effectiveness ratios. RESULTS: Treatment for moderate chronic HCV with combination therapy using an interferon-based regimen reduced the incidence of cirrhosis and provided gains in quality-adjusted life expectancy ranging from 6.2 to 13.9 months, depending on genotype. Regardless of genotype, the cost-effectiveness of interferon alfa and ribavirin for patients with moderate hepatitis was lower than $50 000 per QALY vs the next best strategy. With genotype 1, pegylated interferon alfa (vs interferon alfa) and ribavirin therapy provided an additional 1.6 quality-adjusted life-months for $40 000 per QALY. Because treatment is more effective with non-1 genotypes, pegylated interferon (vs interferon alfa) and ribavirin provided only 3 additional quality-adjusted life-months for $105 300 per QALY. For patients who were intolerant of ribavirin, monotherapy with pegylated interferon was always the most cost-effective option. CONCLUSIONS: Combination therapy for moderate hepatitis in coinfected patients will increase quality-adjusted life expectancy and have a cost-effectiveness ratio comparable to that of other well-accepted clinical interventions.     

Changes in serum hepatitis C virus RNA in interferon nonresponders retreated with interferon plus ribavirin: a preliminary report.

Ribavirin, a nucleoside analogue, inhibits replication of RNA and DNA viruses and may control hepatitis C virus (HCV) infection through modulation of anti-inflammatory and antiviral actions. Ribavirin monotherapy has no effect on serum HCV RNA levels. In combination with interferon, this agent appears to enhance the efficacy of interferon. The aim of this study was to monitor serum HCV RNA levels early during therapy with interferon and ribavirin compared with that previously seen in the same patients during interferon monotherapy. Five patients who previously showed no response to therapy with interferon alfa 3 MU three times weekly for 6 months were retreated with the identical dose of interferon alfa 2b in combination with oral ribavirin 1,000 mg/day. Serum HCV RNA levels were monitored at baseline, week 4, week 8, and week 12 of therapy by a quantitative multicycle polymerase chain reaction assay. In the first 8 to 12 weeks, serum HCV RNA levels showed a greater decrease in all patients when retreated with combination therapy compared with interferon alone. Mean (+/- SEM) serum HCV RNA levels for interferon therapy alone were 3.3 +/- 0.95, 1.2 +/- 0.95, 1.6 +/- 1.2, and 2.3 +/- 1.2 x 10(6) copies/ml at week 0, 4, 8, and 12, respectively. This was compared with 3.3 +/- 0.83, 0.3 +/- 0.2, 0.03 +/- 0.02, and 0.15 +/- 0.14 x 10(6), respectively, for the interferon and ribavirin group (p < 0.07 at week 8). Two of five patients had undetectable serum HCV RNA during combination therapy. Combination therapy with interferon and ribavirin in prior interferon nonresponders reduces serum HCV RNA levels compared with interferon alone. This may suggest some additional antiviral effect of ribavirin when given with interferon.     

Mutation rate of the hepatitis C virus NS5B in patients undergoing treatment with ribavirin monotherapy

BACKGROUND & AIMS: Error catastrophe from an increase in mutation rate may be a possible mechanism of action of ribavirin in chronic hepatitis C (CHC). We sought to evaluate the mutagenic potential of ribavirin in vivo and to determine if conserved regions of hepatitis C virus (HCV) NS5B are mutated during ribavirin therapy. METHODS: Thirty-one patients with CHC genotype 1 who participated in a randomized, placebo-controlled trial of ribavirin for 48 weeks were studied. After 48 weeks, patients on placebo were crossed-over to open-label ribavirin for 48 weeks. Viral RNA was extracted from paired, stored sera at day 0 and week 24 during the randomized phase and weeks 48, 52, and 72 during the cross-over phase. The entire NS5B region was sequenced and the mutation rates were calculated. RESULTS: An increase in mutation rate was observed after 4 weeks (4.4 x 10(-2) vs 2.1 x 10(-3) per site/y, P = .02) but not after 24 weeks (4.0 x 10(-3) vs. 5.5 x 10(-3) per site/y, P = .1) in patients who crossed over to ribavirin. Similarly, during the randomized phase no increase in the number of mutations or the mutation rate was observed at week 24 between the ribavirin- and placebo-treated patients 6.6 vs 4.3 x 10(-3) per site/y, respectively (P = .4). No mutations were observed in conserved regions of NS5B. CONCLUSIONS: Ribavirin therapy is associated with an early, transient increase in the mutation rate of HCV. Lethal mutagenesis and error catastrophe is unlikely to be the sole mechanism of action of ribavirin during therapy for CHC.     

Past, present, and future hepatitis C treatments

Conventional interferon (IFN) alfa has been used for many years in the treatment of chronic hepatitis C. However, few patients achieve sustained virological responses with IFN. Combining IFN with ribavirin improves efficacy considerably, but at the expense of diminished tolerability attributable to ribavirin. Pegylated interferons have improved pharmacokinetic profiles, may be administered once weekly, and are more effective than IFN is alone or in combination with ribavirin. In addition to enhanced efficacy, pegylated interferon alfa-2a (40 kD) also improves health-related quality of life during therapy compared with IFN-based therapy. New adjuvant agents have the potential to further improve sustained response rates and tolerability; however, pegylated interferons will likely remain the backbone of therapy in the foreseeable future. Therapies under development and evaluation for patients with HCV infection include adjunctive use of the antiviral agent amantadine and the immunomodulatory agent thymalfasin. Novel small molecules include the ribavirin analogues, viramidine and levovirin, and BILN 2061, an inhibitor of HCV serine protease. Other therapeutic strategies that have reached the clinic include antisense oligonucleotides (ISIS 14803), nuclease-resistant ribozymes targeting HCV RNA (Heptazyme), human monoclonal antibodie, and human antibody fragments directed at HCV helicase.     

Ribavirin in the treatment of chronic hepatitis C

Background and Aim:  Current practice guidelines recommend that individuals chronically infected with the hepatitis C virus (HCV) be treated with pegylated interferon plus ribavirin. Ribavirin, however, is associated with serious adverse events (AE), especially anemia. We review its mechanism of action, its importance in treating chronic hepatitis C (CHC) patients, the AE associated with its use, and techniques used to lessen these AE.
Methods:  Medline searches were performed using the keywords ribavirin and hepatitis, together with the keywords mechanism, anemia, liver transplant, renal function, pharmacokinetics, and dose reduction. Searches of abstracts of recent Digestive Diseases Week, American Association for the Study of Liver Diseases, and European Association for the Study of Liver Diseases meetings were also performed.
Results:  Ribavirin may be effective in treating CHC by affecting the virus or the host; for example by inducing viral mutations, blocking cellular enzymes, or affecting the host immune response. Although the pegylated interferons are the primary drugs used to treat CHC, a combination with ribavirin is more effective than pegylated interferon alone. Ribavirin-associated AE may be lessened by ribavirin dose reductions and by maintenance of the hematocrit.
Conclusions:  Treatments of ribavirin toxicities, especially anemia, can allow patients to continue full-dose combination therapy with peginterferon and ribavirin, enhancing their probability of attaining a sustained virologic response (SVR). Treatment of CHC should be tailored to individual patients, especially those with renal dysfunction, and should include agents that treat the side-effects of CHC treatment. Monitoring of plasma ribavirin concentrations during treatment may help in the future.     

Hepatitis C in patients with chronic kidney disease: Course and management

The prevalence of chronic hepatitis C (CHC) is significantly higher in patients with end-stage renal disease undergoing hemodialysis than in the general population. CHC adversely affects survival in patients on hemodialysis and those who have undergone renal transplantation (RT); routine screening for hepatitis C virus infection is recommended for both groups. Treatment of CHC in post-RT patients and those undergoing hemodialysis remains challenging. Data on nonpegylated interferon alfa and pegylated interferon alfa monotherapies remain limited, and treatment-induced adverse effects are common. Ribavirin is contraindicated in these patients, but a combination of low-dose ribavirin with interferon is being assessed in clinical trials. Further studies are needed to clarify the pathogenesis and natural history of CHC in hemodialysis patients and post-RT patients and to develop effective treatment for hepatitis C virus infection in these patients.     

The Evolution of HCV Treatment in Taiwan

The treatment strategies used in Taiwan for patients with chronic hepatitis C (CHC) have evolved from conventional interferon monotherapy, consensus interferon therapy, conventional interferon/ribavirinand to pegylated interferon/ribavirin combination therapy. In the past two decades, the sustained virological response (SVR) rate in Taiwanese patients improved from 6 to 75-90 %. By following genotype-guided therapy, an SVR rate of 75-80 % and 85-95 % could be achieved in Taiwanese patients with HCV-1 and HCV-2 infections, respectively. The study of HCV viral kinetics has facilitated studies in Taiwan regarding response-guided therapy with tailored regimens. The majority of Taiwanese patients can be treated successfully with pegylated interferon/ribavirin. The application of IL-28B genetic tests and the insight provided by the viral kinetics might aid in selecting the best candidates for treatment with direct antivirals in the near future in Taiwan.     

Clinical significance of in vitro replication-enhancing mutations of the hepatitis C virus (HCV) replicon in patients with chronic HCV infection

BACKGROUND: Mutations in nonstructural (NS) hepatitis C virus (HCV) proteins enhance replication in HCV-1a/b replicons. The prevalence of such mutations and their clinical significance in vivo are unknown. METHODS: Parts of HCV NS3 and NS4B-NS5B genes that included 31 in vitro replication-enhancing sites were sequenced for 26 patients with chronic HCV genotype 1 infection. RESULTS: Five patients showed specific mutations within NS3 at sites enhancing replication in the replicon. Those mutations were associated with a slower decrease in HCV RNA concentration during interferon (IFN)- alpha -based therapy (P = .007). Neither specific nor other mutations within NS3 and NS4B-NS5B were associated with baseline HCV RNA concentrations. Within NS5A, fewer mutations in the major HCV strain (P = .001) and increased quasi-species complexity (P = .02) and diversity (P = .02) correlated with increasing baseline HCV RNA concentrations. In silico analyses of NS3 protein structures suggested that the majority of observed mutations did not lead to major conformational changes. CONCLUSIONS: Specific mutations leading to enhanced replication in the replicon system were detected in 5 of 26 patients in vivo and were not associated with baseline HCV RNA concentrations but were associated with a slower decrease in HCV RNA concentration during IFN- alpha -based therapy. Quasi-species heterogeneity of NS5A correlated with baseline HCV RNA concentrations.     

Effect of lactoferrin in patients with chronic hepatitis C: combination therapy with interferon and ribavirin

OBJECTIVES: Lactoferrin has been reported to inhibit hepatitis C virus (HCV) infection in cultured human hepatocytes and HCV viremia in patients with chronic hepatitis C (CHC). The aim of this study was to evaluate the effect of combined triple therapy of lactoferrin, interferon and ribavirin in patients with CHC. METHODS: A total of 111 Japanese patients with CHC were randomly assigned to a lactoferrin group (n = 50) and a control group (n = 61). The lactoferrin group was treated with lactoferrin for 8 weeks and then with lactoferrin, interferon and ribavirin for 24 weeks; the control group was treated with interferon and ribavirin for 24 weeks. Serum anti-lactoferrin antibody, clinical and laboratory measurement were determined. RESULTS: The mean HCV RNA titer significantly decreased at the end of lactoferrin monotherapy. Sustained virological response to therapy was significantly higher (P < 0.05) in the lactoferrin responder group (55%) than in the control group (18%). CONCLUSIONS: The results show that the decrease in HCV RNA titer by lactoferrin monotherapy contributes to the effectiveness of the combined therapy of interferon and ribavirin in patients with CHC. Lactoferrin is a potential useful adjunct treatment for patients with CHC.     

Hepatitis C viral dynamics during ribavirin priming differ according to prior treatment response and HCV type

The mode of action of ribavirin is not completely understood. Ribavirin monotherapy has a measurable antiviral effect, which shows great variability. It might lead to an earlier steady state of plasma concentration and therefore enhance the effect of following combination treatment. The aim of this study was to evaluate the antiviral effect of ribavirin priming and its influence on sustained virologic response after combination treatment in a group of patients with different hepatitis C virus (HCV) types with or without prior treatment experience. Retrospective analysis of 75 patients (37 treatment naïve, 20 prior relapse, 16 prior nonresponse, genotype 1 present in 60 patients) from five centres who received ribavirin priming as part of an individual strategy in order to improve treatment outcome. All patients received ribavirin monotherapy with a mean dose of 14.5 mg kg^?1 body weight for a mean of 28 days. After ribavirin priming, dual combination treatment with pegylated interferon alfa and ribavirin was started. The mean HCV RNA decline after ribavirin priming was 0.6 log₁₀ IU mL^?1 (P<.001). The initial viral decline depended on HCV type and previous treatment status being highest among prior relapsers (0.8 log₁₀ IU mL^?1; P=.002) and HCV type 2/3 (1.2 log₁₀ IU mL^?1; P=.05) and lowest among those with prior nonresponse (0.3 log₁₀ IU mL^?1, P=.01). IFNL4 (formerly IL28B) genotype for rs12979860 and IFNL3 genotype rs8099917 did not influence the initial viral decline. The study demonstrates a significant variability in the viral dynamics and antiviral efficacy of ribavirin monotherapy, which is mainly influenced by prior treatment status. The fact that the lowest response pattern was observed in prior nonresponder patients to pegylated interferon alfa plus ribavirin combination therapy can be taken as a hint that not only the individual interferon, but also the ribavirin sensitivity contributes significantly to the nonresponsive state.     

Ribavirin mode of action in chronic hepatitis C: from clinical use back to molecular mechanisms

Ribavirin is an old broad‐spectrum antiviral that is highly effective when used in combination with interferon‐α and also as part of triple therapies containing new inhibitors of the hepatitis C virus (HCV) non‐structural (NS)3/4 protease or HCV NS5B polymerase for the treatment of patients with chronic hepatitis C. However, the molecular mechanisms by which ribavirin enhances early and sustained virological response rates during interferon‐based antiviral HCV therapy are still unknown. Several mechanisms including (i) immunomodulatory properties, (ii) inhibition of the inosine monophosphate dehydrogenase, (iii) direct inhibition of the HCV‐encoded NS5B RNA polymerase, (iv) induction of lethal mutagenesis and (v) modulation of interferon‐stimulated gene expression are currently proposed. Here, we discuss recent advances from in vitro data and their importance for the situation in patients with chronic hepatitis C. Furthermore, theoretical aspects from mathematical modelling of ribavirin action in chronic hepatitis C are reviewed.     

Aktueller Stand der Hepatitis-C-Therapie

The approval of two NS3/4A protease inhibitors, boceprevir and telaprevir, as the first directly acting antiviral substances in combination with pegylated (PEG) interferon alfa and ribavirin, markedly changed the treatment of chronic hepatitis C genotype 1 infections. The pivotal studies showed significantly improved rates of sustained virologic response (SVR) of triple therapy combining a protease inhibitor with PEG interferon alfa and ribavirin in the range of 63–75 % in treatment-naïve patients and 59–65 % in treatment-experienced patients compared to 38–44 % and 17–21 %, respectively in the control groups without the protease inhibitor. The standard of care for all other HCV genotypes is still dual combination therapy with PEG interferon and ribavirin. Besides this considerable progress, HCV genotype 1 infected patients with previous null response and with liver cirrhosis showed limited response rates. In addition management of triple therapy is complicated by complex treatment schedules, drug-drug interactions and supplemental side effects, such as aggravation of anemia or a rash. The second generation of direct acting antiviral substances is currently in advanced stages of clinical development and will lead to a shortening and simplification of HCV therapy in addition to further improvement of efficiency including all HCV genotypes and interferon-free therapy.     

Moving beyond interferon alfa: investigational drugs for hepatitis C virus infection

Numerous direct-acting drugs to treat hepatitis C virus (HCV) infection are in development, offering the potential for substantial improvement over current interferon alfa-based therapy and the possibility of effective interferon alfa-sparing regimens in achieving cure of HCV infection. Drugs furthest along in clinical development include HCV nonstructural protein 3 (NS3) protease inhibitors (eg, telaprevir, boceprevir), which have potent anti-HCV activity but low barriers to resistance and considerable likelihood of cross-resistance. Nucleoside analogue nonstructural protein 5B (NS5B) polymerase inhibitors exhibit a high barrier to resistance and cross-HCV genotype and subtype activity. Nonnucleoside analogue polymerase inhibitors have a low barrier to resistance and are characterized by a substantial frequency of preexisting resistance mutations. The initial use of direct-acting drugs will be as add-on treatment to interferon alfa and ribavirin regimens. The success of interferon alfa-sparing regimens will depend on presenting a sufficiently high barrier to resistance with direct-acting drugs and whether the immunomodulatory effects of interferon alfa are needed for cure of HCV infection.     

Antiviral therapy: inhibition of Hepatitis C Virus expression by RNA interference directed against the NS5B region of the viral genome

Background: Hepatitis C virus (HCV) is a major public health problem with 170 million chronically infected people throughout the world. Currently, the only treatment available consists of a combination of pegylated interferon (INF-a) and ribavirin, but only half of the patients treated show a sufficient antiviral response. Thus there is a great need for the development of new treatments for HCV infections. RNA interference (RNAi) represents a new promising approach to develop effective antiviral drugs and has been extremely effective against HCV gene expression in short-term cell culture. Our aim was to determine the effect of RNAi directed against the NS5B-HCV region on HCV expression in a human hepatoma cell line that expresses HCV-subgenomic replicon (Huh7 HCV replicon cells). Methods: We transfected Huh7 HCV replicon cells with different concentrations of RNAi (100-200 nM) targeting the NS5B region of the viral genome. 2-6 days post-transfection HCV-RNA was quantified by semiquantitative and real-time RT-PCR, and HCV NS5B protein levels were assayed by western blot. Cell viability was also quantified by MTT assay. Results: Our results indicate that the NS5B-siRNAs used in this study can specifically inhibit HCV-RNA replication and protein expression (more than 90%) compared to control cells. Conclusions: Synthetic siRNA against NS5B-HCV inhibited HCV replication and viral proteins levels and thereby becomes a powerful strategy to combat hepatitis C virus.