Hepatic gene expression during treatment with peginterferon and ribavirin: Identifying molecular pathways for treatment response

Treatment failure in hepatitis C: mechanisms of non-response

Hepatitis C virus (HCV) has evolved remarkable mechanisms that favor viral persistence by interfering with host innate and adaptive immune responses. These same mechanisms are likely to contribute to resistance to exogenously administered interferon used for HCV treatment. We review the host innate and adaptive immune responses in the context of HCV infection as well as the strategies by which these responses are subverted by the virus. In addition, the contribution of host factors, such as race and insulin resistance, to interferon non-responsiveness is discussed. Our progress in understanding the molecular underpinnings of interferon treatment failure in HCV infection has resulted in several promising and novel treatment strategies for HCV treatment non-responders.

Retreatment of chronic hepatitis C: who and how?

All but about 10% of patients with chronic hepatitis C (CHC) (predominantly those infected with genotype 1) can respond to some degree to 'combination' therapy with interferon (IFN) and ribavirin. The slower the virological response to treatment, the less likely sustained viral clearance will take place. Many factors influence response to antiviral therapy; most cannot be reversed (e.g. sex, age, cirrhosis, genotype and viral load). A sustained viral clearance is considerably facilitated by compliance with full-dose therapy for the prescribed time. The potential cause(s) for non-response need(s) to be ascertained before attempting retreatment. The 10% of patients who are true 'null' responders may respond to the new specifically targeted antiviral therapies but whether the response can be sustained off-therapy is unclear. Adjunctive therapies may facilitate response to retreatment if intolerance to treatment leading to diminished or absent doses was problematic in the past. Retreatment with a long-acting IFN and an adequate ribavirin dose (15 mg/kg), but given for 72 weeks in prior relapsers following 48 weeks of treatment, will enhance sustained virological response (SVR) rates. No benefit is gained from changing one pegylated IFNalpha (PEG IFNalpha) to another unless the treatment duration is extended. Only alpha-interferons are effective. For those individuals who still fail to achieve SVR, recruitment to trials of new treatments should be encouraged particularly for those with advanced liver disease. Lifestyle modification may be appropriate in attempt to reduce the chance of complications of liver disease, namely hepatocellular carcinoma, by smoking cessation, eliminating obesity and increasing coffee consumption.

Management of hepatitis C virus genotype 2 or 3 infection: treatment optimization on the basis of virological response

Current guidelines recommend a full 24-week regimen for all patients undergoing treatment for genotype 2 or 3 hepatitis C virus (HCV) infection. Recent data from two large randomized studies, one with pegylated interferon-alpha2a plus ribavirin (RBV) and one with pegylated interferon-alpha2b plus RBV assessed treatment duration and on-treatment predictors, such as rapid virological response (RVR; HCV RNA <50 IU/ml at week 4) or sustained virological response rates. Overall, these studies have shown that abbreviated regimens are generally less effective than standard 24-week regimens in genotype 2 or 3 patients because of a higher rate of relapse. However, abbreviated treatment might be offered to selected patients with an RVR provided that they have a low baseline viral load and minimal hepatic fibrosis.

Outcomes of peginterferon alpha-2a and ribavirin hepatitis C therapy in Aboriginal Canadians

BACKGROUND

There is little published information on baseline characteristics and therapeutic outcomes in hepatitis C virus (HCV)-infected Aboriginal Canadians. It is unclear what proportion of HCV-infected Aboriginal people receive therapy relative to other populations.

METHODS

Adults with chronic HCV infection, quantifiable serum HCV-RNA levels and compensated liver disease were assigned, at the physician's discretion, to either 24 or 48 weeks of treatment with peginterferon alpha-2a 180 mug/week plus ribavirin at a dose of 800 mg/day, or 1000 mg/day or 1200 mg/day in an open-label, expanded access program. The primary outcome was sustained virological response, defined as undetectable HCV-RNA by qualitative polymerase chain reaction (less than 50 IU/mL) at the end of 24 weeks of untreated follow-up. Baseline characteristics and outcomes in Aboriginal and non-Aboriginal patients were compared.

RESULTS

A total of 2614 patients were eligible for the analysis; 44 individuals (1.7%) self-identified as being of Aboriginal heritage. The baseline characteristics of these two groups were similar. An overall sustained virological response was achieved in 47.7% and 46.5% of Aboriginal and non-Aboriginal patients, respectively. The overall frequencies of adverse events and laboratory abnormalities were similar between the two groups, although cytopenias occurred less frequently in Aboriginal patients.

INTERPRETATION

Aboriginal patients were greatly under-represented in the present 'community'-based treatment program, yet viral responses were similar to those of a non-Aboriginal cohort. To increase the uptake of HCV therapy in the Aboriginal population, clarification of the obstacles to treatment is warranted.

Interferon-alpha therapy does not modulate hepatic expression of classical type I interferon inducible genes

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease. Treatment with interferon-alpha(2) (IFN-alpha(2)) can induce viral clearance and marked biochemical and histological improvement. IFN-alpha(2) treatment has been shown to stimulate the expression of type I IFN regulated genes in peripheral blood mononuclear cells (PBMCs) of hepatitis C patients; however, whether it affects hepatic expression remains unknown. This study thus aimed at comparing hepatic gene expression with particular emphasis on type I IFN inducible genes in patients with chronic hepatitis C before and during an IFN-alpha(2) monotherapy. Responsiveness to IFN-alpha(2) therapy was monitored by determining serum and hepatic viral load. Differential gene expression analysis was performed by two different techniques, namely suppression subtractive hybridization (SSH) and differential display (DD). Expression of two prototype type I IFN regulated genes was quantified in further PBMC and liver samples. Among different genes found to be up-regulated during an effective, that is, virus clearing, IFN-alpha treatment, only a single one was identified which can be accounted to type I IFN responsive genes. Parallel quantitative real time PCR analyses demonstrated significant induction of the type I IFN regulated genes MxA and PKR in PBMC, but not in the liver. Taken together, while IFN-alpha treatment leads to the induction of type I IFN regulated genes in PBMC, such an induction appears not to occur in the liver of hepatitis C patients. The mechanism by which IFN-alpha treatment causes viral clearance might be independent of hepatic activation of type I IFN regulated genes.

A fresh look at interferon-alpha signaling and treatment outcomes in chronic hepatitis C

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease worldwide. The current standard therapy for chronic hepatitis C (CHC) consists of a combination of pegylated IFN alpha (pegIFNalpha) and ribavirin. It achieves a sustained viral clearance in only 50-60% of patients. To learn more about molecular mechanisms underlying treatment failure, we investigated IFN-induced signaling in paired liver biopsies collected from CHC patients before and after administration of pegIFNalpha. In patients with a rapid virological response to treatment, pegIFNalpha induced a strong up-regulation of IFN-stimulated genes (ISGs). As shown previously, nonresponders had high expression levels of ISGs before therapy. Analysis of posttreatment biopsies of these patients revealed that pegIFNalpha did not induce expression of ISGs above the pretreatment levels. In accordance with ISG expression data, phosphorylation, DNA binding, and nuclear localization of STAT1 indicated that the IFN signaling pathway in nonresponsive patients is preactivated and refractory to further stimulation. Some features characteristic of nonresponders were more accentuated in patients infected with HCV genotypes 1 and 4 compared with genotypes 2 and 3, providing a possible explanation for the poor response of the former group to therapy. Taken together with previous findings, our data support the concept that activation of the endogenous IFN system in CHC not only is ineffective in clearing the infection but also may impede the response to therapy, most likely by inducing a refractory state of the IFN signaling pathway.

Treatment predictors of a sustained virologic response in hepatitis B and C

Treatment predictors are important tools for the management of therapy in patients with chronic hepatitis B and C virus (HBV, HCV) infection. In chronic hepatitis B, several pretreatment parameters have been identified for prediction of virologic response to interferon alfa-based antiviral therapies or treatment with polymerase inhibitors. In interferon alfa and pegylated interferon alfa-treated patients, low baseline HBV DNA concentrations, HBV genotype A (B), and high baseline ALT levels are significantly associated with treatment response. In patients treated with nucleos(t)ide analogues, low baseline HBV DNA but not viral genotype is positively associated with virologic response. During treatment the best predictor of response is HBV DNA kinetics. Early viral suppression is associated with favourable virologic response and reduced risk for subsequent resistance mutations. For the current standard treatment with pegylated interferon alfa and ribavirin in patients with chronic hepatitis C, infection with HCV genotypes 2 and 3, baseline viral load below 400,000-800,000 IU/ml, Asian and Caucasian ethnicity, younger age, low GGT levels, absence of advanced fibrosis/cirrhosis, and absence of steatosis in the liver have been identified as independent pretreatment predictors of a sustained virologic response. After initiation of treatment, initial viral decline with undetectable HCV-RNA at week 4 of therapy (RVR) is the best predictor of sustained virologic response independent of HCV genotype.

Innate immune modulation by RNA viruses: emerging insights from functional genomics

By providing a global and integrated view of the host response to infection, functional genomic and systems-biology approaches are contributing to our understanding of RNA virus–host interactions. One area in which these approaches are being put to particularly good use is in shedding new light on the components of innate antiviral defence mechanisms and the viral strategies used to regulate or overcome them.

Genomic analyses have helped to reveal virus-specific differences in the way that viral recognition through pathogen-recognition receptors (PRRs) initiates intracellular signalling cascades. Whereas influenza virus appears to signal primarily through retinoic-acid-inducible gene I (RIG-I), West Nile virus signals through both RIG-I and melanoma differentiation-associated gene 5 (MDA5). Both viruses induce the expression of interferon (IFN)-regulatory factor 3 (IRF3) target genes and IFN-stimulated genes (ISGs).

Genomic analyses have provided a comprehensive view of the transcriptional programmes that are induced by Toll-like receptor (TLR) activation. One transcriptional profile is universally activated by all TLRs and a second profile is specific to TLR3 and TLR4. Nuclear factor-κB (NF-κB) is the key regulator of the universal response, which occurs early after TLR stimulation, and the IFN-stimulated response element (ISRE) is the key component of the TLR3/TLR4 response, which is induced after the NF-κB response.

Some highly virulent viruses, such as Ebola virus and rabies virus, are successful at inhibiting ISG expression, resulting in the marked suppression of genes in key innate antiviral pathways, including those mediated by IRF3. There seems to be a correlation between the antagonism of the IFN response and virulence.

Genomic analyses of the host response to the reconstructed 1918 pandemic influenza virus have revealed similarities and differences to contemporary influenza virus infection. Contemporary and 1918 influenza viruses each trigger an innate immune response that includes the expression of NF-κB and IRF3 target genes, and both viruses trigger a robust cytokine response that attracts immune-cell infiltration to infected tissues. Unlike contemporary virus strains, in which the early response to infection is resolved, the innate immune response triggered by the 1918 influenza virus is characterized by a strong and sustained induction that is associated with massive tissue damage and death.

Global gene-expression profiling has revealed that many effective, attenuated live-virus vaccines transiently induce a stronger type I IFN response than the cognate pathogen, and therefore implicates modulation of this response as an important strategy in rational vaccine design.

By providing a global view of the host response to infection, functional genomic approaches are proving useful in deciphering complex virus–host interactions. Here, the authors reveal how such approaches are being used to better understand viral triggering and regulation of host innate immune responses.

Although often encoding fewer than a dozen genes, RNA viruses can overcome host antiviral responses and wreak havoc on the cells they infect. Some manage to evade host antiviral defences, whereas others elicit an aberrant or disproportional immune response. Both scenarios can result in the disruption of intracellular signalling pathways and significant pathology in the host. Systems-biology approaches are increasingly being used to study the processes of viral triggering and regulation of host immune responses. By providing a global and integrated view of cellular events, these approaches are beginning to unravel some of the complexities of virus–host interactions and provide new insights into how RNA viruses cause disease.

Potential relevance of cytoplasmic viral sensors and related regulators involving innate immunity in antiviral response

BACKGROUND & AIMS

Clinical significance of molecules involving innate immunity in treatment response remains unclear. The aim is to elucidate the mechanisms underlying resistance to antiviral therapy and predictive usefulness of gene quantification in chronic hepatitis C (CH-C).

METHODS

We conducted a human study in 74 CH-C patients treated with pegylated interferon alpha-2b and ribavirin and 5 nonviral control patients. Expression of viral sensors, adaptor molecule, related ubiquitin E3-ligase, and modulators were quantified.

RESULTS

Hepatic RIG-I, MDA5, LGP2, ISG15, and USP18 in CH-C patients were up-regulated at 2- to 8-fold compared with nonhepatitis C virus patients with a relatively constitutive Cardif. Hepatic RIG-I, MDA5, and LGP2 were significantly up-regulated in nonvirologic responders (NVR) compared with transient (TR) or sustained virologic responders (SVR). Cardif and RNF125 were negatively correlated with RIG-I and significantly suppressed in NVR. Differences among clinical responses in RIG-I/Cardif and RIG-I/RNF125 ratios were conspicuous (NVR/TR/SVR = 1.3:0.6:0.4 and 2.3:1.3:0.8, respectively). Like viral sensors, ISG15 and USP18 were significantly up-regulated in NVR (4-fold and 2.3-fold, respectively). Multivariate and receiver operator characteristic analyses revealed higher RIG-I/Cardif ratio, ISG15, and USP18 predicted NVR. Lower Cardif in NVR was confirmed by its protein level in Western blot. Also, transcriptional responses in peripheral blood mononuclear cells to the therapy were rapid and strong except for Cardif in not only a positive (RIG-I, ISG15, and USP18) but also in a negative regulatory manner (RNF125).

CONCLUSIONS

NVR may have adopted a different equilibrium in their innate immune response. High RIG-I/Cardif and RIG-I/RNF125 ratios and ISG15 and USP18 are useful in identifying NVR.

Hepatic gene expression and prediction of therapy response in chronic hepatitis C patients

Chronic hepatitis C (HCV) infection remains a major health problem worldwide. The current standard of care is a combination of pegylated interferon-alpha and ribavirin. Considering the length of antiviral therapy, as well as its side effects and costs, accurate prediction of treatment response prior to initiation of treatment is critical. In addition to viral, demographic and environmental factors, host genetic diversity is believed to contribute to the spectrum of clinical outcomes of chronic HCV. The development of high-throughput technologies provides opportunities to define patterns of gene expression that are associated with certain disease outcomes and/or response to therapy. This article reviews genomics-based predictors of pre-treatment response to antiviral therapy.

Ribavirin exposure after the first dose is predictive of sustained virological response in chronic hepatitis C

The impact of ribavirin exposure on sustained virological response (SVR) in patients with chronic hepatitis C is unknown. Preliminary studies showed marked inter-individual variability of ribavirin concentrations despite dose adjustment for body weight (BW) and suggested there was a correlation between single time point concentrations and SVR. None of them evaluated the global exposure to ribavirin. This study was conducted to determine whether early ribavirin global exposure is related with SVR. An exploratory pharmacokinetic-pharmacodynamic (PK-PD) study was conducted in genotype 1 hepatitis C patients treated with peginterferon alfa-2a and ribavirin (dose-adjusted for BW) for 12 weeks, to which amantadine was added for the following 36 weeks. Full and abbreviated ribavirin area under the concentration time curves (AUC(0-12h), AUC(0-4h)) were derived from plasma concentration profiles at day 0 (D0), week 12 (W12), W12 + 1 day, and W24. Virological follow-up was performed at D0 (0, 12, and 24 hours), W2, W4, W6, and monthly until W72 (TaqMan polymerase chain reaction, cut-off 15 international units/mL). Twenty-eight patients were enrolled in the study and 24 completed it. Patients with a SVR had a significantly higher D0 AUC(0-12h) (3695 [1571-6916] versus 2937 [1266-4913] microg/hour/L, P = 0.03) and D0 AUC(0-4h) (2010 [615-3175] versus 1340 [622-2246] microg/hour/L, P = 0.03). Patients with D0 AUCs above the cut-off values defined by receiver operating characteristic curves (3014 microg/hour/L and 1755 microg/hour/L for AUC(0-12h) and AUC(0-4h), respectively) had a significantly better chance of achieving an SVR than patients with AUCs under the thresholds (odds ratio = 16.0, 95% confidence interval 1.54-166.6, P = 0.02 and odds ratio = 8.9, 95% confidence interval, 1.4-56.6; P = 0.02).

CONCLUSION

Ribavirin exposure at D0 is significantly related to SVR. To our knowledge, this is the first study to give an early pharmacokinetic predictor of SVR. We propose a minimum AUC(0-4h) threshold of 1755 microg/hour/L at D0 as a target for ribavirin dose adjustment.

Prediction of Sustained Virological Response by Ribavirin Plasma Concentration at Week 4 of Therapy in Hepatitis C virus Genotype 1 Patients

Background

Pegylated interferon/ribavirin combination is currently the standard treatment for chronic hepatitis C virus (HCV) infection. Body weight adjustment of ribavirin is crucial for response. However, previous studies found no relation between ingested dose and plasma concentration. The aim of this study was to define the ribavirin trough plasma concentration at week 4 (W4) associated with sustained virological response (SVR).

Methods

Thirty-one HCV genotype 1 patients (8 naive and 23 non-responders to a previous pegylated interferon/ribavirin therapy) were treated with pegylated interferon/ribavirin and assessed by HPLC for ribavirin plasma concentration at W4.

Results

Eleven patients (35%) achieved SVR, whereas 20 (65%) were non-responders. The median ribavirin plasma concentration at W4 (1.90 mg/l) varied from 1.62 mg/l in patients with subsequent non-response to 2.28 mg/l in sustained responders ( P=0.007). Receiver operating characteristic curve analysis indicated that the 2.01 mg/l threshold gave the best sensitivity and specificity (73% and 80%, respectively, area under the curve=0.80; P=0.007). Sixty-seven percent of patients with median ribavirin plasma concentration >2 mg/l achieved SVR versus only 16% below this level ( P=0.007). Multivariate regression analysis indicated that a ribavirin plasma concentration >2 mg/l at W4 was associated with SVR independent of gender, age, weight, baseline viral load and response to previous therapy.

Conclusion

These results, which remain to be confirmed in large clinical trials, highlight the potential relevance of ribavirin plasma level monitoring at an early stage of treatment. This monitoring could be of help in guiding antiviral therapy by offering dose adjustment in patients with ribavirin plasma level below the 2 mg/l threshold.

Ribavirin considerations in treatment optimization

Ribavirin is a guanosine analogue that has little antiviral activity when used alone, but considerably enhances the efficacy of conventional and pegylated interferon in the treatment of hepatitis C virus (HCV). The precise mode of action of ribavirin is not fully understood; however, it is crucial for the achievement of high sustained virological response (SVR) rates by enhancing virological response and reducing relapse rates. Data from several studies have confirmed that higher initial doses of ribavirin lead to higher SVR rates. Furthermore, intensified ribavirin dosing might also improve SVR rates in ‘difficult-to-cure’ patients. It is also important to minimize ribavirin dose reductions to promote high SVR rates and to maintain ribavirin levels throughout treatment to prevent viral breakthrough and relapse. The pharmacokinetic profile of ribavirin reveals a long elimination half-life due to accumulation in the blood, such that its side-effect profile includes haemolytic anaemia. Therefore, finding the optimal ribavirin dose requires a balance between efficacy and its associated side effects to ensure improved patient outcomes. Here, we discuss how optimizing the ribavirin component of combined therapy for HCV is an essential part of treatment optimization.