The Era of Direct-acting Antivirals Has Begun: The Beginning of the End for HCV?

From Seminars in Liver Disease

Marie-Louise Vachon, M.D., M.Sc.; Douglas T. Dieterich, M.D.

Posted: 02/15/2012; Semin Liver Dis. 2011;31(4):399-409. © 2011 Thieme Medical Publishers

Abstract and Introduction

Abstract

The year 2011 marks the dawn of the new era of direct-acting antivirals for hepatitis C. For the first time since 1998, the U.S. Food and Drug Administration approved two new antiviral drugs for the treatment of chronic hepatitis C virus genotype 1. Dual therapy with pegylated interferon and ribavirin is no longer the standard of care for genotype 1. The new treatment paradigm includes one direct-acting antiviral, a protease inhibitor, in combination with pegylated interferon and ribavirin. This combination nearly doubles the chances of response to treatment, but at the cost of increased toxicity. Many agents with different mechanisms of action and improved safety profiles are in clinical development. The holy grail of HCV treatment is an all oral, interferon-free treatment. The ideal regimen will be potent, well tolerated, with minimal drug-drug interactions and once daily. This article covers new concepts of treatment of hepatitis C with DAAs and gives an overview of the recent highlights in direct-acting antiviral development.

Introduction

In May 2011, telaprevir and boceprevir were approved by the U.S. Food and Drug Administration (FDA) for treatment of chronic hepatitis C virus (HCV) genotype 1. Dual therapy with pegylated interferon (pegIFN) and ribavirin (RBV) is no longer the standard of care for genotype 1 HCV. The new treatment paradigm includes one direct-acting antiviral (DAA), a protease inhibitor (PI), in combination with pegIFN and RBV. The addition of a DAA to pegIFN/RBV nearly doubles the chances of response to treatment at the cost of increased toxicity. This is only the first wave of DAA use since many agents with different mechanisms of action and improved safety profiles are in phase I, II, and III of clinical development (Table 1 and Table 2). The use of three agents to treat HCV mirrors human immunodeficiency virus (HIV) triple combination treatment in many ways. Combination treatment seems inevitable to prevent emergence of resistance in HCV. Clinical trials are ongoing to identify the ideal regimen which would be potent, well tolerated, with minimal drug-drug interactions, once daily, all oral, and for as short a duration as possible (Table 3). Two major differences between HIV and the treatment of HCV are that treatment of HCV is for a definite duration and that HCV is curable. In this article, we examine new concepts of treatment of HCV with DAAs in general and review investigational compounds that have entered phase II of clinical development.

New Concepts of DAA Use

Several new concepts arose with the development of DAAs to treat hepatitis C. Because DAAs are true antivirals that target critical steps of HCV replication, similar to antiretrovirals inhibiting HIV, selection of resistant mutants is inevitable with monotherapy.^[1] The HCV replication cycle and the different sites at which DAAs can interfere with HCV replication are thoroughly reviewed elsewhere.^[2,3] RNA viruses like HCV inherently possess an error-prone RNA-dependent RNA polymerase that lacks the proofreading function. As a result, and with the rapid HCV viral turnover (up to 10¹² virions produced each day), it is estimated that one mutation is contained in every single genome copied.^[4] There are thus many variant populations coexisting in a given individual, the patient's quasispecies. Most of these variant populations are susceptible to DAAs because wild-type viruses usually have the advantage of fitness, but some of these preexisting variants are drug-resistant at baseline.^[5,6] When selection pressure is applied with the use of a DAA in monotherapy, these preexistent variants are rapidly selected and can become the predominant circulating population, potentially leading to treatment failure.^[7–9] Resistance profiles differ between drug classes. Some drugs have different resistance mutations within the same class. A new concept that emerged as part of PI development is the difference in resistance profile between genotype 1a and genotype 1b. For example, the R155K substitution typically emerges when HCV genotype 1a is exposed to telaprevir.^[8] Only one nucleotide change is required for the 1a subtype to develop resistance whereas two nucleotide changes must occur in genotype 1b.^[10] This is not specific to PI use and has been described with other drug classes, for example, nonnucleoside polymerase inhibitors.^[10] As a result, antiviral responses can vary between HCV genotype 1 subtypes during treatment with DAAs, while response was similar when treated with pegIFN and RBV dual therapy.

Response-guided therapy (RGT) refers to the use of on-treatment virologic response to tailor the duration of therapy for an individual patient.^[11] This concept was used with pegIFN/RBV treatment but really emerged in the era of DAAs. Both telaprevir and boceprevir can be used for a shorter treatment duration in patients who achieve HCV RNA undetectability early on in treatment.^[12,13] This is RGT. In the telaprevir studies, extended rapid virologic response (eRVR) was used to determine if RGT could be used.^[12,14] The definition of eRVR was HCV RNA <10 IU/mL at week 4 and 12. In the boceprevir studies, RGT was used when HCV RNA was less than 9.3 IU/mL at week 8 through week 24.^[13] Most phase II and III clinical trials of DAAs are exploring this possibility of shortening treatment duration in patients who achieve eRVR.

The concept of lead-in is also widely discussed in the DAA literature. Lead-in is the use of pegIFN and RBV for a short duration preceding the initiation of DAA. Lead-in was initially introduced in an attempt to lower HCV RNA levels before PI exposure to minimize the emergence of resistance. Also, by achieving proper pegIFN and RBV drug levels before the initiation of the DAA, it would avoid functional monotherapy. Studies of boceprevir used a 4-week lead-in of pegIFN and RBV. It turns out the lead-in was most useful in the assessment of interferon responsiveness. In the SPRINT-2 study evaluating boceprevir in combination with pegIFN/RBV in previously untreated patients with chronic HCV genotype 1, a decrease in the HCV RNA level by ≥1 log₁₀ IU/mL after the 4-week lead-in increased the chances of sustained virologic response (SVR; undetectable HCV RNA 24 weeks after the end of treatment) ninefold (adjusted odds ratio [AOR], 9.0; 95% confidence interval [CI], 6.3–12.8; P <.001).^[13] There was no advantage to lead-in when used with other DAAs, for example, with telaprevir and BI 201335.^[14,15]

Lower Limit of Detection (LLOD) Versus Lower Limit of Quantification (LLOQ)

The LLOD is the HCV RNA concentration at which less than 5% of the samples that contain a known amount of an RNA standard yield a signal that can be detected. The LLOQ refers to the lowest HCV RNA concentration that is within the validated quantitative range of an assay. An undetectable result indicates that HCV RNA was not detected in the sample. The limit of detection and the limit of quantification vary according to the assay used. Both the boceprevir and telaprevir phase III studies used the COBAS TaqMan HCV RNA assay, version 2.0 (Roche), with a LLOD of 10 IU/mL and a LLOQ of 25 IU/mL. Eligibility for RGT was based on the lower limit of detection (<10 IU/mL) of the assay. There is thus a range in which HCV RNA can be detectable, but falls below the level of quantification. This situation is not uncommon during HCV treatment and is associated with lower SVR rates. In the SPRINT-2 trial, 53% of the 1071 patients enrolled had at least one on-treatment result showing detectable HCV RNA, but below the level of quantification.^[13] For example, in the patients who received boceprevir and who had detectable HCV RNA at week 6 (any level), detectable HCV RNA at week 8 but below level of quantification, and undetectable HCV RNA at week 10, the SVR rate was 74%. In the patients who received boceprevir and who had detectable HCV RNA at week 6 (any level) but undetectable HCV RNA at weeks 8 and 10, the SVR rate was 86%. When assessing eligibility to response-guided therapy with DAAs, an undetectable HCV RNA (<LLOD) is not equivalent to a detectable HCV RNA that is below the limit of quantification of the assay (detectable but <LLOQ). The package inserts of telaprevir and boceprevir reflect this fact.

NS3/4A PIs

HCV NS3/4A PIs are often divided in two classes. The first generation PIs include the linear α-ketoamide derivatives, boceprevir and telaprevir. They bind the catalytic site of the enzyme covalently in a reversible reaction. Boceprevir and telaprevir are considered the first wave of the first-generation PIs. These two PIs are the first DAAs to have completed phase III clinical trials for treatment of HCV genotype 1 and to have received FDA approval. Second-wave PIs are mostly linear and macrocyclic noncovalent inhibitors of the NS3/4A enzyme. Both waves are highly potent inhibitors of the NS3/4A enzyme. The advantages of second wave PIs over first wave PIs are their convenience and improved side effect profile. Unfortunately, they share the same basic resistance mutations that are generated by the first wave of PIs. The truly second-generation PIs are the two drugs MK-5172 and the ACH-2684. They do not share the same resistance mutations and are pangenotypic. There are currently two first-generation, second-wave PIs that recently initiated phase III of clinical development: TMC435 and BI-201335.

TMC435

In phase I studies, TMC435 was generally safe and well tolerated. It showed potent anti-HCV activity. After 5 days of TMC-435 at a dose of 200 mg once daily, HCV RNA decreased by a median of 3.9 log₁₀ IU/mL in HCV genotype 1-infected patients who failed prior interferon-based therapy.^[16] The phase IIb PILLAR study is ongoing and week 24 results have recently been presented.^[17] PILLAR is investigating the use of once-daily TMC435 at two different dosages (75 mg vs 150 mg) for 12 versus 24 weeks in combination with pegIFN/RBV for 24 vs 48 weeks (vs placebo/pegIFN/RBV for 48 weeks), in 386 patients with HCV genotype 1 naïve to HCV treatment. Patients with HCV RNA less than 25 IU/mL from week 4 to week 20 were eligible for RGT and stopped treatment at week 24. Of the patients receiving TMC435, 83% achieved eRVR and 94 to 97% achieved undetectable HCV RNA at week 24 of treatment compared with a high 82% in the pegIFN/RBV control group. Of the 83% of patients who achieved eRVR and stopped therapy at week 24, 88 to 97% achieved SVR12 (undetectable HCV RNA 12 weeks after the end of treatment). Discontinuation of TMC435 or placebo occurred in 7.1% of patients receiving TMC435/pegIFN/RBV versus 7.8% of patients receiving placebo/pegIFN/RBV. The most common adverse events occurred in a similar proportion of patients receiving or not receiving TMC435. TMC435 at the 150 mg once-daily dose was associated with mild and reversible increases in direct and indirect bilirubin. Elevation in bilirubin is thought to occur through inhibition of the two transporters: organic anion transporting polypeptide 1B1 (OATP1B1) and multidrug resistance-associated protein 2 (MRP2). OATP1B1 is responsible for bilirubin uptake into hepatocytes (influx) and MRP2 is responsible for efflux into bile. No inhibition of bilirubin conjugation has been observed.^[18]

The ASPIRE study is the ongoing phase IIb study in prior partial responders (≥2 log₁₀ drop in HCV RNA at week 12 but detectable HCV RNA at week 24), prior null responders (<2 log₁₀ drop in HCV RNA at week 12 of treatment) and prior relapsers (undetectable HCV RNA at the end of treatment, but detectable HCV RNA within 24 weeks of end of treatment) to interferon-based therapy. Patients received TMC435 at doses of 100 mg versus 150 mg once daily in combination with pegIFN/RBV for 12, 24, or 48 weeks. In all seven arms of the trial, patients received pegIFN/RBV to complete 48 weeks of treatment. There was no RGT. The week 24 interim analysis showed that 92 to 96% of prior relapsers who received TMC435 had undetectable HCV RNA at week 24 compared with 83% of patients in the control group. Of the prior partial responders receiving TMC435, 83 to 89% had undetectable HCV RNA at week 24 versus 20% of the control group. Of the prior null responders, 70 to 87% had undetectable HCV RNA at week 24 versus 45% of the control group (higher than expected). The prior null responders typically have the lowest response rates to retreatment. The end of treatment and SVR data are eagerly awaited.

In summary, TMC435 is a highly potent once-daily dosing PI. Duration of treatment can be shortened to 24 weeks for the majority of patients; viral breakthroughs are low when used in combination with pegIFN and RBV. The 150 mg once-daily dose is being used in phase III trials in both patients who are naïve to HCV treatment and patients who previously relapsed to an interferon-based therapy. Patients will receive once-daily 150 mg of TMC435 during 12 weeks in combination with pegIFN/RBV for a 24 versus 48 weeks. A trial for HIV-infected patients has started enrollment in the second half of 2011.

BI 201335

BI201335 is a HCV NS3 PI given once daily currently in phase III. The phase IIb SILEN-C1 trial was conducted in patients with HCV genotype 1 naïve to HCV treatment to evaluate safety and efficacy of BI 201335 given once daily at a dose of 120 mg or 240 mg for 24 weeks in combination with pegIFN and RBV for 24 vs 48 weeks.^[14] A lead-in of pegIFN and RBV for 3 days was also evaluated in 2 of the 4 arms (with 120 mg and 240 mg once daily). In the two arms using BI 201335 at a dose of 240 mg (with and without a lead-in), patients achieving eRVR were rerandomized to either stop treatment at week 24 or continue with pegIFN/RBV for a total of 48 weeks. Patients receiving 240 mg once daily without a lead-in achieved the highest eRVR rate of 87% and were thus eligible for shortened treatment duration. As expected with this high eRVR rate, this arm also had the highest SVR rate of 83% versus 73% of patients receiving 240 mg with a lead-in and 56% of patients in the pegIFN/RBV control group. Prolonging treatment to 48 weeks in those patients achieving eRVR did not result in higher SVR rates. Of those who completed 24 weeks, 93% achieved SVR versus 90% of those who completed 48 weeks. Viral breakthroughs occurred in 2.8 to 5.8% of patients receiving BI 201335 with the highest rate in those of the 120 mg daily with lead-in arm.

The phase IIb SILEN-C2 trial evaluated BI 201335 for 24 weeks in combination with pegIFN/RBV for 24 versus 48 weeks, with or without a 3-day lead-in of pegIFN/RBV in previous partial and null responders infected with HCV genotype 1.^[19] The 240 mg once-daily dose (with and without a lead-in) was compared with 240 mg twice daily with a lead-in. Patients of the 240 mg once-daily group with lead-in achieving eRVR were rerandomized to stopping therapy or continuing 48 weeks with pegIFN/RBV. Similar to the SILEN-C1 trial, the lead-in did not appear to be useful. The 240 mg once-daily dosing without a lead-in led to the highest SVR rates. Overall, eRVR was achieved by 45% of patients and SVR was achieved by 27 to 41% of patients. The lowest SVR rate was observed in the 240 mg once daily with the lead-in arm, the one group that used RGT for those achieving eRVR. In comparison to the good results observed with 24 weeks of treatment in the naïve patients achieving eRVR in the SILEN-C1 trial,^[14] prior partial and null responders achieving eRVR in SILEN-C2 achieved lower SVR rates when stopped at week 24. Only 40% of patients achieved SVR when stopped at week 24 compared with 72% of those who completed 48 weeks of treatment. The additional 24 weeks of peg/RBV greatly impacted the relapse rate. Sixty percent of those who stopped at week 24 relapsed compared with 21% of those who completed 48 weeks of treatment. Viral breakthroughs occurred predominantly on BI 201335 compared with peg/RBV (17–28% vs 5–7%). Several adverse events were reported in a higher proportion of patients receiving BI 201335 compared with those on placebo and were dose-dependent. Jaundice, skin manifestations including rash, photosensitivity reactions, pruritus and dry skin, and gastrointestinal side effects, mostly nausea, vomiting, and diarrhea were reported in the BI 201335 arms in a proportion exceeding 10% of the placebo/peg/RBV group. Jaundice was secondary to predominantly indirect or unconjugated hyperbilirubinemia. This was dose-dependent, rapidly reversible in all cases at cessation of BI 201335, and not associated with liver injury. The mechanism of action is inhibition of hepatic uptake of uridine diphosphate glucuronosyltransferase 1 family polypeptide A1 (UGT1A1).^[20]

ACH-0141625 (ACH-1625)

ACH-1625 is an inhibitor of the HCV NS3 protease. ACH-1625 exhibits rapid and selective distribution to the liver and has high liver/plasma ratios. In phase Ib, 5 days of ACH-1625 monotherapy at doses ranging from 200 to 600 mg twice daily or 400 to 600 mg once daily led to mean maximal reductions in HCV RNA ranging from 3.1 log₁₀ to 4.25 log₁₀.^[21]

This PI is currently in phase IIa of clinical development to evaluate its safety, tolerability, and antiviral activity in combination with pegIFN and RBV in patients with HCV genotype 1 naïve to treatment. This study has two segments. Segment 1 compares three different dosages of ACH-1625, 200 mg, 400 mg, and 800 mg once daily with placebo in combination with pegIFN/RBV for 28 days followed by pegIFN/RBV for a total duration of 48 weeks in 64 patients with HCV genotype 1. Segment 2 compares the same three dosing regimens to placebo for 12 weeks followed by 36 weeks of pegIFN/RBV. Week 4 results of Segment 1 showed achievement of rapid virologic response (RVR) in 74 to 81% of patients compared with 20% of patients receiving placebo/pegIFN/RBV. Reductions in HCV RNA on ACH-1625 ranged from 4.63 log₁₀ to 4.96 log₁₀ IU/mL after 4 weeks of triple therapy compared with 2.25 log₁₀ IU/mL with placebo/pegIFN/RBV. It is worth noting that the majority of the patients enrolled were carriers of the unfavorable IL28B CT or TT genotypes and infected with HCV genotype 1a. The safety profile was comparable between all groups. No viral breakthroughs were observed during the first 4 weeks.

Danoprevir (RG7227/ITMN-191)

Danoprevir is a potent macrocyclic inhibitor of the HCV NS3/4A serine protease. In phase 1b studies in treatment naïve patients with HCV genotype 1, administration of danoprevir for 14 days was associated with a maximal median reduction of HCV RNA of 3.8 log₁₀ in monotherapy and 5.7 log₁₀ IU/mL in combination therapy with pegIFN and RBV.^[22] In subsequent studies, danoprevir was boosted by ritonavir, a strong inhibitor of the CYP3A4 enzyme. A phase 1b study evaluated multiple ascending doses of ritonavir-boosted danoprevir in combination with pegIFN/RBV in 30 patients with HCV genotype 1 naïve to treatment.^[23] More patients using boosted danoprevir (72%, 18/25 and 100%, 8/8 in the group receiving danoprevir 200 mg/ritonavir 100 mg twice daily) achieved undetectable HCV RNA (<15 IU/mL) at day 15 compared with patients who had previously received high-dose unboosted danoprevir (14%, 1/7) or placebo (20%, 1/5). This boosting allowed the use of a significantly lower dose of danoprevir, resulting in lower area under the curve (AUC) and maximum concentration (Cmax) of danoprevir. This reduced systemic exposure can improve the safety profile and reduce the probability of grade 4 ALT elevations, which had been seen with unboosted danoprevir at a dose of 900 mg twice daily.^[24] Danoprevir/ritonavir is now being evaluated in several phase II clinical trials. A randomized, open-label study is evaluating SVR of danoprevir/ritonavir in combination with pegIFN/RBV in treatment of naïve patients with HCV genotype 1. Week 12 results of a substudy of 24 prior null responders treated with open-label danoprevir/ritonavir 100 mg/100 mg twice daily with pegIFN and RBV were recently presented.^[25] Patients received 12 weeks of triple therapy after which they continued on pegIFN/RBV for a total of 48 weeks. At week 12, results showed a significant disparity between patients with HCV genotype 1a versus 1b. Fifty percent (50%) of patients with HCV genotype 1a achieved EVR versus 88% of those with HCV genotype 1b. Four of the eight patients with HCV genotype 1a experienced viral breakthrough with selection of the R155K mutation compared with 6% of patients with HCV genotype 1b.

A randomized open-label phase II study is evaluating SVR with danoprevir/ritonavir and RBV in combination with mericitabine (RG7128), a polymerase inhibitor, and/or pegIFN in patients with HCV genotype 1 who failed previous standard therapies. In this study, the six study arms contain RBV, but two of the six study arms are pegIFN-free.

A second phase II study, INFORM-SVR, is recruiting patients to evaluate the combination of danoprevir/ritonavir plus mericitabine with and without RBV in patients with HCV genotype 1. This is a pegIFN-free trial. In two arms, interferon-naïve patients will receive danoprevir 100 mg/ritonavir 100 mg twice daily with mericitabine 1000 mg twice daily with or without RBV for 12 weeks or 24 weeks. The third arm will enroll interferon-unable/intolerant patients who will receive an open-label combination of danoprevir/ritonavir/mericitabine plus RBV for 24 weeks. The combination of danoprevir/ritonavir with mericitabine looks promising and results of these phase II trials are awaited.

BMS-650032

One of the most important results, if not the most important, in the study of DAAs in the year 2011 was the result of the phase IIa study evaluating quadruple therapy with the PI BMS-650032 (600 mg twice daily) and BMS-790052 (an HCV NS5A replication complex inhibitor; 60 mg once daily) with and without pegIFN/RBV for 24 weeks in patients with HCV genotype 1 who were prior null responders to IFN-based therapy.^[26] Prior null responders are typically the most difficult-to-retreat patient population. In this study four (36%) of the 11 null responders who received BMS-650032 and BMS-790052 alone for 24 weeks achieved SVR. This result is proof of the concept that HCV can be cured without pegIFN/RBV. Of the 11 patients in this arm, six had a viral breakthrough and resistant variants to both drugs were detected.^[27] In four of these six, HCV RNA became undetectable when pegIFN/RBV was added at the time of viral breakthrough. All 10 patients who received the quadruple therapy were cured. There was 100% SVR12 and 90% SVR24 (one patient had SVR12, detectable HCV RNA 6 months posttreatment and undetectable HCV RNA when retested later on). These two DAAs are currently being evaluated in a phase IIb study in combination with pegIFN lambda (BMS-914143) with and without ribavirin for 24 weeks in patients with chronic HCV genotype 1 naïve to treatment. This study also compares the use of a single DAA (either BMS-650032 or BMS-790052) with RBV and either pegIFN-lambda or pegIFN-alfa. It will be very interesting to learn the role of RBV when these two DAAs are combined with pegIFN.

GS-9451 and GS-9256

GS-9451 is a potent macrocyclic HCV NS3 PI that achieved a median maximal change in HCV RNA of 3.6 log₁₀ IU/mL (range, -4.7 log₁₀ to -3.1 log₁₀ IU/mL) following 3-day monotherapy in treatment-naïve patients with HCV genotype 1 infection during phase I.^[28] It is currently being evaluated in phase II studies in combination with other DAAs. A phase IIb study with RGT will evaluate the efficacy and safety of 16 and 24 weeks of a four-drug regimen with GS-9451 and tegobuvir (a nonnucleoside HCV polymerase inhibitor) and 24 weeks of a three-drug regimen of GS-9451 without tegobuvir, all with pegIFN and RBV. Other phase II studies evaluating different DAA combinations that include the NS5A inhibitor GS-5885 are ongoing.

GS-9451 has additive to synergistic antiviral activity when combined with pegIFN, RBV, NS5A inhibitors, or polymerase inhibitors. Although a PI, GS-9451 retains activity against V36M and T54S, two NS3 mutations. However, R155K, A156T, and D168V are cross-resistant to GS-9451. The NS3 resistance mutations selected during treatment with GS-9451 are fully susceptible to other HCV inhibitor classes.^[29] This supports its use in combination with other DAAs of the company's pipeline. A new study evaluating a four all-oral drug regimen is currently recruiting patients. In this study, GS-9451 is administered with GS-5885 (a NS5A inhibitor given at two different dosages), tegobuvir, and RBV for 12 or 24 weeks in patients with chronic HCV genotype 1 infection. This type of combination could completely revolutionize HCV treatment if found potent and well tolerated.

GS-9256 is also a potent PI that was being evaluated until recently. Preliminary results of the phase II study evaluating GS-9256 in combination with tegobuvir ± RBV and ± pegIFN for 28 days have been presented.^[28] With the three oral drugs, 38% achieved RVR, 100% then achieved complete early virologic response (cEVR; undetectable HCV RNA at week 12) and maintained undetectability at week 24. With four drugs, 100% achieved RVR and were still undetectable at week 24. Without RBV and pegIFN, GS-9256 and tegobuvir led to RVR in only 7% of patients (1/15). Of these 15 patients, 12 achieved cEVR following the addition of pegIFN/RBV. All combinations were well tolerated. It was decided that GS-9256 would not be further developed, in part due to its higher potential to inhibit the transport and metabolism of bilirubin compared with GS-9451.^[30]

Nucleoside and Nucleotide NS5B Polymerase Inhibitors

The nucleoside and nucleotide analog inhibitors of the HCV polymerase target the catalytic site of the enzyme. When they incorporate in the RNA chain in lieu of the natural substrate, they cause RNA chain termination. Nucleoside analogs must be phosphorylated three times by cellular kinases to become active as the triphosphate form. Nucleotide analogs are already in the active form. Because the NS5B target is highly conserved between HCV genotypes, polymerase inhibitors usually have pangenotypic activity (Fig. 1).

Figure 1. Characteristics of the five classes of direct-acting antivirals (DAAs). *Varies with the generation. **Palm II are effective against multiple genotypes. (DAA, direct acting antiviral; NS3/4A, nonstructural 3/4A protein; PI, protease inhibitor; NS5A, nonstructural 5A protein; NS5B, nonstructural 5B protein; Nuc, nucleoside.)

PSI-352938 (PSI-938)

PSI-938 is a purine (guanosine) nucleotide analog polymerase inhibitor of HCV. In earlier phases of development, PSI-938 was shown to have pangenotypic coverage, high liver to plasma ratios, residual activity against S282T variants (substitution selected by and associated with resistance to the 2'-methyl nucleosides), and low risk of drug-drug interactions. The 14-day results of a phase II study, the NUCLEAR study, were recently presented.^[31] The NUCLEAR study compared different combinations of once daily PSI-938 plus PSI-7977 (a second polymerase inhibitor) to PSI-938 monotherapy for 14 days in treatment naïve patients with HCV genotype 1. It is the first to evaluate the combination of two nucleotide analogs for the treatment of HCV infection. Of the 24 patients who received combination treatment, 22 (92%) achieved HCV RNA <15 IU after 14 days of treatment. The two drugs are known to have complementary resistant profiles and not surprisingly, no viral breakthroughs were observed. Treatment was well tolerated. An interferon-free combination trial of PSI-938 and PSI-7977, the QUANTUM trial, has been initiated. PSI-938 was granted the fast track designation by the FDA for treatment of chronic HCV infection in August 2011.

PSI-7977

PSI-7977 is a pyrimidine (uridine) nucleotide analog active against all HCV genotypes. The dramatic results of the phase 2b study PROTON assessing safety and efficacy of PSI-7977 in combination with pegIFN/RBV against HCV genotypes 2 and 3 were presented earlier in 2011.^[32] PROTON enrolled 25 treatment-naïve patients. One patient was lost to follow-up early in the study. Among the 24 patients who completed 12 weeks of triple therapy, 24 (100%) achieved SVR. These results suggest that therapy can be significantly shortened in patients infected with HCV genotypes 2 and 3 without compromising the chances of response. A phase II study in patients with HCV genotype 2 and 3 is ongoing to explore the use of PSI-7977 in monotherapy for 12 weeks versus PSI-7977 in combination with peg/RBV for 8 weeks.

Nonnucleoside NS5B Polymerase Inhibitors

Whereas the nucleoside inhibitors bind to the polymerase's active site, the nonnucleoside inhibitors bind to allosteric sites of the enzyme. This induces conformational changes that downregulate the polymerase's activity. Different binding sites disposed in a right hand motif with the thumb (thumb 1 and thumb 2), finger and palm (palm 1 and palm 2) domains are potential targets of nonnucleoside inhibitors. As a result of different target sites, mechanism of inhibition, and potency differences, nonnucleoside inhibitors have a low genetic barrier to resistance compared with nucleoside/nucleotide analogs (Fig. 1).^[33]

SETROBUVIR (ANA598)

Setrobuvir (ANA598) is a potent nonnucleoside inhibitor and the most advanced in development. In a phase II combination study with pegIFN and RBV, 72% of patients achieved undetectable HCV RNA at week 8.^[34] It is currently in a phase IIb study for the treatment of chronic HCV infection. In this ongoing study, 133 patients naïve to HCV treatment and 141 previously treated patients (n = 133) have been enrolled to receive setrobuvir 200 mg twice daily in combination with pegIFN/RBV. Patients naïve to HCV treatment with undetectable HCV RNA at week 8 and at subsequent visits will complete treatment at week 28 (RGT). Previously treated patients will receive 48 weeks of treatment. Future trials combining ANA598 with DAAs of different classes will likely offer the best SVR results.

Nonstructural Protein 5A (NS5A) Replication Complex Inhibitors

Inhibitors of NS5A block viral production at an early stage of assembly. The exact mechanism of action of the NS5A protein is unknown.^[35] Without having an enzymatic function, this multifunctional protein is essential for replication and assembly of HCV and has no human homologs.^[36,37]

DACLATASVIR (BMS-790052)

BMS-790052 is the first NS5A inhibitor with proof-of-concept in the clinic. The results of the first placebo-controlled, multiple ascending-dose clinical study evaluate its antiviral activity, resistance profile, pharmacokinetics, safety, and tolerability in 30 patients with chronic HCV infection infected with HCV genotype 1 were recently published.^[38] Its pharmacokinetic profile supports once-daily dosing and the drug was well tolerated. Patients received BMS-790052 for 14 days. The mean maximum decline from baseline in HCV RNA ranged from 2.8 to 4.1 log₁₀ IU/mL. Most patients experienced viral rebound during the first 7 days of BMS-790052 monotherapy. Viral breakthroughs were associated with mutations that had been previously found in the NS5A at baseline and at the time of resistance development.^[39,40]

Cyclophilin Inhibitors

Cyclophilin inhibitors are derived from cyclosporine A, but lack calcineurin-binding properties and thus do not exhibit immunosuppressive effects.^[41,42] Alisporivir (Debio 025) is the first-in-class cyclophilin inhibitor that recently initiated a phase III trial. It binds to cyclophilin A, an essential cofactor for HCV replication and shows additive antiviral effect with pegIFN in patients with genotype 1 and 4 HCV.^[41] Cyclophilin inhibitors are sometimes referred to as host-targeted agents, but can also be part of the DAAs because they are known to interact with the NS5A protein.

In a phase II study of patients with HCV genotype 1, 2, 3, and 4 naïve to HCV treatment, alisporivir doses of 200, 600, and 1,000 mg/day in combination with pegIFN for 4 weeks were compared with monotherapy with alisporivir 1,000 mg/day or pegIFN.^[42] In patients with genotypes 1 and 4, the 600- and 1,000-mg combination treatments reduced HCV RNA by up to 4.61 ( ± 1.88) log₁₀ IU/ml and 4.75 (±2.19) log₁₀ IU/mL at week 4, respectively. In patients with genotypes 2 and 3, HCV RNA levels were reduced by -5.91 (±1.11) log₁₀ IU/mL and -5.89 (±0.43) log₁₀ IU/mL at week 4, respectively, with the same treatment regimens. Alisporivir 1000 mg/day was associated with a higher incidence of isolated hyperbilirubinemia. SVR results of the phase II ESSENTIAL study were recently presented.^[43] Alisporivir (600 mg twice daily during one week followed by once-daily dosing) with pegIFN/RBV led to SVR in 76% of patients taking the triple therapy for 48 weeks compared with 55% of the control group (P = .008). Triple therapy with alisporivir for 24 weeks was as effective as pegIFN/RBV dual therapy for 48 weeks with 53% SVR compared with 55%, respectively. In the RGT arm in which patients could stop triple therapy at week 24 if they achieved RVR, the SVR rate was 69%. Alisporivir demonstrates a high barrier to resistance and interestingly, the resistance mutation identified with its use (D320E) is mainly located in the NS5A domain II. Recent findings indicate that alisporivir inhibits hepatitis C virus replication by preventing a cyclophilin A induced cis-trans isomerization in domain II of NS5A.^[44] Metabolism is through cytochrome P450 3A4, which can compromise its ability to be given concomitantly with substrates, inhibitors, or inducers of this cytochrome. Cyclophilin inhibitors could be part of a potent DAA combination in patients not taking concomitant P450 3A4 medications.

Conclusion

After many years of little or no progress in the development of HCV DAAs, 2011 was a watershed year for several reasons. The most clinically significant development was the approval of boceprevir and telaprevir for the treatment of HCV genotype 1. That will revolutionize the treatment of HCV in the clinic and change the landscape of HCV treatment forever because of the dramatically increased SVR demonstrated by both drugs. The Berlin EASL meeting in March of 2011 showcased some equally dramatic and positive results of drugs in development. Among many huge advances in the field, we saw the first 100% SVR for pegIFN/RBV plus PSI-7977 for HCV genotypes 2 and 3, with a shortened course of treatment. The most revolutionary results were revealed by the combination of the PI BMS-650032 and the NS5A inhibitor BMS-790052. In previous null responders to interferon treated with quadruple therapy consisting of a PI, a NS5A inhibitor, pegIFN and RBV, 100% SVR was achieved. This alone would merit a special mention, but the truly groundbreaking results were in the other arm of the study, which combined only the PI and the NS5A compound without pegIFN/RBV. In that arm, an SVR of 36% was achieved demonstrating for first time ever, an interferon-free, RBV-free cure of HCV.

Not only did we have the first FDA, European Medicines Agency (EMEA), and Canadian approvals for the PIs telaprevir and boceprevir in 2011, but we saw the proof of principle that the Holy Grail of HCV therapy is achievable; SVR without interferon. There are dozens of new drugs in clinical development now and many will fall by the wayside, but there are clearly enough that will be approved to reassure us that the future is very bright indeed for DAA treatment of HCV.

References

1. Kieffer TL, Kwong AD, Picchio GR. Viral resistance to specifically targeted antiviral therapies for hepatitis C (STAT-Cs). J Antimicrob Chemother 2010;65(2):202–212
2. Moradpour D, Penin F, Rice CM. Replication of hepatitis C virus. Nat Rev Microbiol 2007;5(6):453–463
3. Pawlotsky JM, Chevaliez S, McHutchison JG. The hepatitis C virus life cycle as a target for new antiviral therapies. Gastroenterology 2007;132(5):1979–1998
4. Ogata N, Alter HJ, Miller RH, Purcell RH. Nucleotide sequence and mutation rate of the H strain of hepatitis C virus. Proc Natl Acad Sci U S A 1991;88(8):3392–3396
5. Bartels DJ, Zhou Y, Zhang EZ, et al. Natural prevalence of hepatitis C virus variants with decreased sensitivity to NS3.4A protease inhibitors in treatment-naive subjects. J Infect Dis 2008;198(6):800–807
6. Pawlotsky JM. Hepatitis C virus genetic variability: pathogenic and clinical implications. Clin Liver Dis 2003;7(1):45–66
7. Susser S, Welsch C, Wang Y, et al. Characterization of resistance to the protease inhibitor boceprevir in hepatitis C virus-infected patients. Hepatology 2009;50(6):1709–1718
8. Sarrazin C, Kieffer TL, Bartels D, et al. Dynamic hepatitis C virus genotypic and phenotypic changes in patients treated with the protease inhibitor telaprevir. Gastroenterology 2007;132(5):1767–1777
9. Wagner F, Thompson R, Kantaridis C, et al. Antiviral activity of the hepatitis C virus polymerase inhibitor filibuvir in genotype 1-infected patients. Hepatology 2011;54(1):50–59
10. McCown MF, Rajyaguru S, Kular S, Cammack N, Nájera I. GT-1a or GT-1b subtype-specific resistance profiles for hepatitis C virus inhibitors telaprevir and HCV-796. Antimicrob Agents Chemother 2009;53(5):2129–2132
11. Lee SS, Ferenci P. Optimizing outcomes in patients with hepatitis C virus genotype 1 or 4. Antivir Ther 2008;13(Suppl 1):9–16
12. Jacobson IM, McHutchison JG, Dusheiko G, et al; ADVANCE Study Team. Telaprevir for previously untreated chronic hepatitis C virus infection. N Engl J Med 2011;364(25):2405–2416
13. Poordad F, McCone JJr, ,Bacon BR, et al; SPRINT-2 Investigators. Boceprevir for untreated chronic HCV genotype 1 infection. N Engl J Med 2011;364(13):1195–1206
14. Sulkowski MS, Ceasu E, Asselah T, et al. SILEN-C1: sustained virologic response (SVR) and safety of BI 201335 combined with peginterferon alfa-2a and ribavirin (P/R) in treatment-naive patients with chronic genotype 1 HCV. J Hepatol 2011;54(Suppl 1):S27
15. Zeuzem S, Andreone P, Pol S, et al; REALIZE Study Team. Telaprevir for retreatment of HCV infection. N Engl J Med 2011;364(25):2417–2428
16. Lin TI, Lenz O, Fanning G, et al. In vitro activity and preclinical profile of TMC435350, a potent hepatitis C virus protease inhibitor. Antimicrob Agents Chemother 2009;53(4):1377–1385
17. Fried MW, Buti M, Dore GJ, et al. Efficacy and safety of TMC435 in combination with peginterferon alfa-2a and ribavirin in treatment-naive genotype 1 HCV patients: 24 week interim results from the PILLAR study. Hepatology 2010;52(Suppl 1):107A
18. Huisman MT, Snoeys J, Monbaliu J, et al. In vitro studies investigating the mechanisms of interaction between TMC435 and hepatic transporters. Hepatology 2010;52(Suppl 1):461A
19. Sulkowski MS, Bourliere M, Bronowicki JP, et al. SILEN-C2: sustained virologic response (SVR) and safety of BI201335 combined with peginterferon alfa-2a and ribavirin (P/R) in chronic HCV genotype-1 patients with non-response to P/R. J Hepatol 2011;24(Suppl 1):S30
20. Sane R, Podila L, Mathur A, et al. Mechanisms of isolated unconjugated hyperbilirubinemia induced by the HCV NS3/4A protease inhibitor BI201335. J Hepatol 2011;54(Suppl 1):S488
21. Detishin V, Haazen R, Hooijmaijers R, et al. Final results of the pharmacokinetics, efficacy, safety/tolerability of 400 and 600 mg once-daily dosing of ACH-1625 (HCV NS3 protease inhibitor) in HCV genotype 1. J Hepatol 2011;54(Suppl 1):S186–S187
22. Forestier N, Larrey D, Marcellin P, et al. Antiviral activity of danoprevir (ITMN-191/RG7227) in combination with pegylated interferon α-2a and ribavirin in patients with hepatitis C. J Infect Dis 2011;204(4):601–608
23. Gane EJ, Rouzier R, Stedman C, et al. Antiviral activity, safety, and pharmacokinetics of danoprevir/ritonavir plus PEG-IFN a-2a/RBV in hepatitis C patients. J Hepatol 2011;55(5):972–979
24. Terrault N, Cooper C, Balart LA, et al. Phase II randomized, partially blind, parallel-group study of oral danoprevir (RG7227) with PegIFN alfa-2a (PEGASYS) plus ribavirin (COPEGUS) in treatment-naive genotype 1 patients with CHC: results of planned week 12 interim analysis of the ATLAS study. Hepatology 2010;52(Suppl 1):73A
25. Rouzier R, Larrey D, Gane EJ, et al. Danoprevir plus low-dose ritonavir (DNV/R) in combination with peginterferon alfa-2a (40KD) plus ribavirin (PEGIFN-2a/RBV) in previous null responders. J Hepatol 2011;54(Suppl 1):S28
26. Lok AS, Gardiner D, Lawitz E, et al. Quadruple therapy with BMS-790052, BMS-650032 and Peg-IFN/RBV for 24 weeks results in 100% SVR12 in HCV genotype 1 null responders. J Hepatol 2011;54(Suppl 1):S536
27. Mcphee F, Hernandez D, Yu F, et al. Charcterization of virologic escape in HCV genotype 1 null responders receiving a combination of the NS3 protease inhibitor BMS-650032 and NS5A inhibitor BMS-790052. J Hepatol 2011;54(Suppl 1):S28–S29
28. Foster GR, Buggisch P, Marcellin P, et al. Four-week treatment with GS-9256 and tegobuvir (GS-9190) ± RBV ± PEG, results in enhanced viral suppression of follow-up PEG/RBV therapy, in genotype 1a/1b HCV patients. J Hepatol 2011;54(Suppl 1):S172
29. Wong KA, Bae A, Ku K, et al. Genotypic and phenotypic characterization of HCV resistance from a multiple dose clinical trial of GS-9451, a novel NS3 protease inhibitor. J Hepatol 2011;54(Suppl 1):S493
30. Tong L, Mwangi J, Roy A, et al. In vitro studies on the potential for the hepatitis C virus protease inhibitors GS-9256 and GS-9451 to affect bilirubin elimination. J Hepatol 2011;54(Suppl 1):S487
31. Lawitz E, Rodriguez-Torres M, Denning J, et al. Once daily dual-nucleotide combination of PSI-938 and PSI-7977 provides 94% HCV RNA <LOD at day 14: first purine/pyrimidine clinical combination cata (The NUCLEAR Study). J Hepatol 2011;54(Suppl 1):S543
32. Lalezari J, Lawitz E, Rodriguez-Torres M, et al. Once daily PSI-7977 plus PEGIFN/RBV in a phase 2b trial: rapid virologic suppression in treatment-naïve patients with GT2/GT3. J Hepatol 2011;54(Suppl 1):S28
33. McCown MF, Rajyaguru S, Le Pogam S, et al. The hepatitis C virus replicon presents a higher barrier to resistance to nucleoside analogs than to nonnucleoside polymerase or protease inhibitors. Antimicrob Agents Chemother 2008;52(5):1604–1612
34. Lawitz E, Rodriquez-Torres M, Rustgi VK, et al. Safety and antiviral activity of ANA598 in combination with pegylated interferon α2A plus ribavirin in treatment-naïve genotype 1 chronic HCV patients. J Hepatol 2010;52(Suppl 1):S467
35. Gao M, Nettles RE, Belema M, et al. Chemical genetics strategy identifies an HCV NS5A inhibitor with a potent clinical effect. Nature 2010;465(7294):96–100
36. Tellinghuisen TL, Foss KL, Treadaway J. Regulation of hepatitis C virion production via phosphorylation of the NS5A protein. PLoS Pathog 2008;4(3):e1000032
37. Qiu D, Lemm JA, O'Boyle DR II, , et al. The effects of NS5A inhibitors on NS5A phosphorylation, polyprotein processing and localization. J Gen Virol 2011;92(Pt 11):2502–2511
38. Nettles RE, Gao M, Bifano M, et al. Multiple ascending dose study of BMS-790052, an NS5Areplication complex inhibitor, in patients infected with hepatitis C virus genotype 1. Hepatology 2011Epub ahead of print
39. Fridell RA, Wang C, Sun JH, et al. Genotypic and phenotypic analysis of variants resistant to HCV NS5A replication complex inhibitor BMS-790052: in vitro and in vivo correlations. Hepatology 2011Epub ahead of print
40. Fridell RA, Qiu D, Wang C, Valera L, Gao M. Resistance analysis of the hepatitis C virus NS5A inhibitor BMS-790052 in an in vitro replicon system. Antimicrob Agents Chemother 2010;54(9):3641–3650
41. Crabbé R, Vuagniaux G, Dumont JM, Nicolas-Métral V, Marfurt J, Novaroli L. An evaluation of the cyclophilin inhibitor Debio 025 and its potential as a treatment for chronic hepatitis C. Expert Opin Investig Drugs 2009;18(2):211–220
42. Flisiak R, Feinman SV, Jablkowski M, et al. The cyclophilin inhibitor Debio 025 combined with PEG IFNalpha2a significantly reduces viral load in treatment-naïve hepatitis C patients. Hepatology 2009;49(5):1460–1468
43. Flisiak R, Pawlotsky J, Crabbé R, et al. Once daily alisporivir (Deb025) plus PEGIFNalfa2a/ribavirin results in superior sustained virologic response (SVR24) in chronic hepatitis C genotype 1 treatment naïve patients. J Hepatol 2011;54(Suppl 1):S2–S2
44. Coelmont L, Hanoulle X, Chatterji U, et al. DEB025 (Alisporivir) inhibits hepatitis C virus replication by preventing a cyclophilin A induced cis-trans isomerisation in domain II of NS5A. PLoS ONE 2010;5(10):e13687

Source

The protease inhibitor GS-9256 and non-nucleoside polymerase inhibitor tegobuvir alone, with RBV or peginterferon plus RBV in hepatitis C

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Hepatology Jan 2012
Accepted Article (Accepted, unedited articles published online for future issues)

Stefan Zeuzem,1 Peter Buggisch,2 Kosh Agarwal,3 Patrick Marcellin,4 Daniel Sereni,5 Hartwig Klinker,6 Christophe Moreno,7 Jean-Pierre Zarski,8 Yves Horsmans,9 Hongmei Mo,10 Sarah Arterburn,10 Steven Knox,10 David Oldach,10 John G. McHutchison,10 Michael P. Manns,11 and Graham R. Foster 12 From the 1University Hospital, JW Goethe University, Frankfurt, Germany; 2IFI Studien-und Projekte, Hamburg, Germany; 3King's College Hospital, London, United Kingdom; 4Hospital Beaujon, University of Paris, Clichy, France; 5Hospital Saint-Louis, Paris, France; 6Universitatsklinikum Wurzburg, Medizinische Klinik und Poliklinik II, Wurzburg, Germany; 7Erasme Hospital, Universite Libre de Bruxelles, Brussels, Belgium; 8CHU de Grenoble -Hopital Michallon La Tronche, France; 9Cliniques Universitaires Saint-Luc, Universite Catholique de Louvain, Bruxelles, Belgium; 10Gilead Sciences, Inc., Foster City, CA, USA;11Medical School of Hannover, Hannover, Germany; and 12The Liver Unit, Queen Mary University of London, London, United Kingdom

Abstract

Tegobuvir (GS-9190), a non-nucleoside NS5B polymerase inhibitor, and GS-9256, an NS3 serine protease inhibitor, individually have activity against hepatitis C virus (HCV) genotype 1. The antiviral activity of tegobuvir and GS-9256 as oral combination therapy, or together with ribavirin (RBV) or peginterferon alfa-2a (PEG-IFN) and RBV, was assessed in a phase 2, randomized, open-label trial. Treatment-naïve patients with genotype 1 HCV were assigned 28 days of tegobuvir 40 mg twice daily and GS-9256 75 mg twice daily (n=16), tegobuvir and GS-9256 plus RBV 1000-1200 mg daily (n=15), or tegobuvir and GS-9256 plus PEG-IFN alfa-2a (180 mcg qw)/RBV (n=15). The primary efficacy endpoint was rapid virologic response (RVR), HCV RNA <25 IU/mL at Day 28. After 28 days, all patients received PEG-IFN/RBV. All patients with viral rebound or nonresponse, defined as >0.5-log10 increase in HCV RNA from nadir or <2-log decrease at Day 5, initiated PEG-IFN/RBV immediately. Median maximal reductions in HCV RNA were -4.1 log10 IU/mL for tegobuvir/GS-9256, -5.1 log10 IU/mL for tegobuvir/GS-9256/RBV, and -5.7 log10 IU/mL for tegobuvir/9256/PEG-IFN/RBV. RVR was observed in 7% (1/15) of patients receiving tegobuvir/GS-9256, 38% (5/13) receiving tegobuvir/GS-9256/RBV, and 100% (14/14) receiving tegobuvir/9256/PEG-IFN/RBV. The addition of PEG-IFN/RBV at Day 28 or earlier resulted in HCV RNA <25 IU/mL at Week 24 in 67% (10/15), 100% (13/13) and 94% (13/14) of patients in the 3 treatment groups. Transient elevations in serum bilirubin occurred in all treatment groups. Conclusion: In genotype 1 HCV, adding RBV or RBV with PEG-IFN provides additive antiviral activity to combination therapy with tegobuvir and GS-9256. (HEPATOLOGY 2011.)

For the past decade, standard of care for patients with chronic infection with genotype 1 hepatitis C virus (HCV) has been 48 weeks of peginterferon alfa (PEG-IFN) and ribavirin (RBV). Observed rates of sustained virologic response with PEG-IFN and RBV therapy are 40-52% (1-4). However, the addition of the HCV NS3 serine protease inhibitors telaprevir or boceprevir results in higher rates of sustained virologic response (67-75%), leading to the recent approval of these two drugs in the United States and the European Union (5-10). Because triple therapy can result in higher rates of rapid virologic response (RVR, HCV RNA < lower limit of quantification at Week 4) in the range of 60% to 70% (5,6,9,10), shortened treatment duration from 48 to 24 weeks is possible in a significant proportion of patients.

Several novel inhibitors of viral replication, including those targeting the NS3 serine protease and NS5B RNA-dependent RNA polymerase, are in clinical development (11). Although many of these direct-acting antiviral agents (DAAs) can cause rapid and substantial reductions in viral load, their use as monotherapies has been limited by inadequate suppression of replication and/or the development of resistance (12,13). In the context of polymerase or protease inhibitor therapy, PEG-IFN and RBV have repeatedly demonstrated their importance in reducing viral load and suppressing viral breakthrough (14-16). In studies of regimens containing telaprevir or boceprevir, excluding RBV or using a reduced dose results in higher rates of viral breakthrough and relapse (5,7,17).

Several recent studies have explored combining two DAAs to enhance early antiviral activity and to theoretically minimize development of resistance. In a study of treatment-naïve patients with HCV genotype 1, 14 days of combination therapy with the nucleoside analog RG7128 and the NS3 protease inhibitor danoprevir resulted in 5-log10 IU/mL HCV RNA reductions from baseline (18). More recently, the combination of the non-nucleoside NS5B polymerase inhibitor VX-222 with telaprevir improved early antiviral response but was associated with high rates of viral breakthrough (19).

Tegobuvir (GS-9190) is a novel, non-nucleoside inhibitor of the NS5B polymerase. Studies to elucidate tegobuvir's mechanism of action are ongoing; however, current data indicate the inhibitory effect may be exerted via an interaction with the ß-hairpin in the NS5B thumb subdomain (20). Tegobuvir and the NS3 protease inhibitor GS-9256 each have demonstrated antiviral activity in HCV-infected patients (21-23). Tegobuvir demonstrated median reductions in HCV RNA of 1.5 log10 IU/mL for individual patients with 8 days of monotherapy (21) and enhanced rates of RVR (HCV RNA <25 IU/mL at Week 4) when combined with PEG-IFN and RBV (22). At 200 mg twice daily for 3 days, GS-9256 monotherapy demonstrated a median HCV RNA reduction of 2.7 log10 IU/mL (22). Both tegobuvir and GS-9256 were well-tolerated in these short-term monotherapy studies. We therefore evaluated the antiviral activity of tegobuvir and GS-9256 dual therapy, tegobuvir and GS-9256 plus RBV, and tegobuvir and GS-9256 plus PEG-IFN and RBV for 28 days. After 28 days of treatment, patients then continued treatment with PEG-IFN and RBV for 48 weeks.

RESULTS

Patient Population

Between February and October of 2010, a total of 46 patients were randomized and treated in 4 European countries (Belgium, France, Germany, United Kingdom). Among the treatment arms, patients were predominately male (73% to 88%) and white (80% to 93%), and mean age ranged from 45 to 54 years (Table 1). Of the 46 patients treated, 45 patients completed Week 6 of the study (Table 2), and 42 were still on PEG-IFN/RBV at Week 24. Treatment with PEG-IFN/RBV is ongoing at the time of this report. As evaluated at Baseline with the LiPA 2.0 assay, 15 (33%) patients were HCV genotype 1a, 30 (65%) were genotype 1b, and 1 (2%) was unable to be genotyped. Upon subsequent NS5B sequencing/phylogenetic analysis, 4 patients were identified as having HCV genotypes 1e, 1l, 1e/m, and 4r (refer to supplementary table for virologic outcomes). These patients were therefore excluded from the primary efficacy analysis.

The majority of patients were genotype CT (ranging from 53% to 63%) at the IL28B polymorphism rs12979860. A higher percentage of patients were IL28B genotype CC in the tegobuvir/GS-9256/RBV arm (40%) versus the tegobuvir/GS-9256 arm (12.5%) or tegobuvir/GS-9256/PEG-IFN/RBV arm (26.7%).

Efficacy Assessments

HCV RNA

Patients in all treatment arms had an initial sharp decline in plasma HCV RNA levels during the first 48 hours of therapy (Figure 1). In the tegobuvir/GS-9256 arm, this decrease was generally maintained through Day 7, after which HCV RNA levels began to rebound, associated with the emergence (detection) of resistance-associated variants. The addition of ribavirin to the treatment regimen increased the magnitude, extent, and duration of viral reduction; in the tegobuvir/GS-9256/RBV arm, reductions in HCV RNA levels were observed through Day 14 and were generally maintained through Day 28. The addition of PEG-IFN alfa-2a had a similar additive effect; in the tegobuvir/GS-9256/PEG-IFN/RBV arm, reductions in HCV RNA levels were observed through Day 28. The association of IL28B genotype and initial antiviral response was variable, with a trend towards a greater magnitude of HCV RNA reductions in IL28B-CC patients. No differences in mean maximal HCV RNA reduction by HCV subtype (1a or 1b) were observed. Virologic responses in the four patients infected with other HCV-1-subtypes are presented in the Supplementary table. In each case, HCV RNA reductions from Baseline during randomized therapy ranged from -0.75 to -2.84 log10 IU/mL. Following the switch to PEGIFN/ RBV, continued viral load reductions were observed ranging from -2.98 to -5.23 log10 IU/mL from Baseline by Week 6.

In the primary efficacy analysis, a greater percentage of patients achieved RVR after receiving tegobuvir/GS-9256 in combination with RBV (38%) compared with tegobuvir/GS-9256 alone (7%) (Table 3). All patients (14/14) receiving tegobuvir/GS-9256 in combination with PEGIFN/RBV achieved RVR.

Excluding datapoints following the early introduction of PEG-IFN/RBV, the median (Q1, Q3) maximal reduction in HCV RNA was highest for patients receiving tegobuvir/GS-9256/PEGIFN/RBV, -5.7 (-5.9, -5.5) log10 IU/mL, versus -5.1 (-5.3, -4.4) for tegobuvir/GS-9256/RBV, and -4.1 (-4.4, -2.9) for tegobuvir/GS-9256 alone.

Viral breakthrough was most common in the tegobuvir/GS-9256 arm, where the majority of patients (80%) started standard of care with PEG-IFN and RBV prior to Day 28. Although RBV decreased and delayed breakthrough, in the tegobuvir/GS-9256/RBV arm, 31% started standard of care early because of the observed increases in HCV RNA at or prior to Day 28. None of the patients receiving tegobuvir/GS-9256/PEG-IFN/RBV experienced viral plateau or rebound through Day 28. For patients in the tegobuvir/GS-9256 arm who had an increase in HCV RNA levels observed at Day 14 or Day 21, HCV RNA levels declined again by Day 28 after initiating PEG-IFN and RBV.

Among the patients who either did not experience early response or had viral rebound, several achieved RVR after starting either PEG-IFN or PEG-IFN and RBV early. Two patients in the tegobuvir/GS-9256 arm who started PEG-IFN and RBV early achieved RVR, as did 3 patients in the tegobuvir/GS-9256/RBV arm who started PEG-IFN early (Table 3).

Viral suppression continued through 24 weeks for many patients, especially those initially assigned to therapy with RBV (arm 2) or PEG-IFN/RBV (arm 3). All patients (13/13) receiving tegobuvir/GS-9256/RBV initially and continuing on PEG-IFN/RBV had HCV RNA <25 IU/mL at Week 24; 13 of 14 (94%) of patients assigned to tegobuvir/GS-9256/PEG-IFN/RBV and continuing on PEG-IFN/RBV maintained HCV RNA <25 IU/mL at Week 24.

Resistance Mutants

Population sequence analysis was performed in 15 rebound patients whose HCV RNA was ≥1000 IU/mL at the time of rebound. In 14/15 of these patients, mutations were detected in both the NS3 and NS5B genes (Table 4), and the mutations are known to cause lowered antiviral susceptibility to GS-9256 and tegobuvir in vitro. The remaining patient had only the NS3 R155K mutation detected. The dual therapy arm with tegobuvir/GS-9256 had the highest rate of detected mutations. In HCV genotype 1a patients, NS3 R155K and NS5B Y448H were the most common mutations selected; in HCV genotype 1b patients, NS3 D168E/V and NS5B Y448H were most common. In 4 of 5 patients with HCV genotype 1b with either NS5B C316N or C445F at Baseline, the viral rebound was associated with the emergence of NS3 D168E/V/H/L mutations without the selection of additional NS5B mutations.

Safety Assessments

Tegobuvir/GS-9256 was well tolerated, and most adverse events were mild to moderate in severity. Adverse events were more common in the tegobuvir/GS-9256/PEG-IFN/RBV treatment arm, with events consistent with those reported for IFNs (Table 5). Two serious adverse events were reported during the study: infective bursitis and vasovagal collapse. Both were considered by the investigator to be unrelated to study drug. One patient, in the tegobuvir/GS-9256 arm, discontinued tegobuvir and GS-9256 on Day 22 because of fatigue. This patient had initiated PEG-IFN and RBV on Day 19 but continued with PEG-IFN/RBV after discontinuing tegobuvir and GS-9256. The patient completed study participation to Week 6 but was later lost to followup.

No Grade 4 adverse events or lab abnormalities were observed. Reductions in hemoglobin and neutrophils were consistent with those associated with RBV and PEG-IFN alfa-2a administration. Transient bilirubin elevations, primarily Grades 1 and 2, occurred in all treatment groups but were generally indirect and not associated with elevations in ALT or AST. Overall, while taking assigned therapy, 9 patients experienced Grade 1 elevations in total bilirubin, 4 had Grade 2 elevations, and 2 had Grade 3 elevations (3.2 mg/dL maximum). The overall incidence of hyperbilirubinemia (Grade 1 and above) in treated patients was 4/16 (25%), 5/15 (33%) and 6/15 (40%) in the tegobuvir/GS-9256, tegobuvir/GS-9256/RBV, and tegobuvir/GS-9256/PEGIFN/ RBV arms, respectively.
No clinically significant impact on cardiac repolarization (prolongation of the QTcF interval >60 msec change from Baseline or increase to >500 msec) was observed for the tegobuvir/GS-9256 combination following multiple dosing.

DISCUSSION

This study of tegobuvir plus GS-9256 is the first to explore the additional contribution of RBV to a 2-drug oral DAA regimen during a limited 4-week dosing period. The two oral DAAs exhibited additive antiviral activity: tegobuvir 40 mg BID monotherapy induces median HCV RNA reductions of 1.5 log10 (21), whereas GS-9256 monotherapy induces median HCV RNA reductions of 2.7 log10 (22), and in this study, the combination of the two drugs resulted in median HCV RNA reductions of 4.1 log10. The additive antiviral effect we observed is consistent with the additive interaction of tegobuvir and GS-9256 in the replicon system (Gilead Sciences, unpublished data). Even with the additive antiviral activity of these 2 classes of HCV inhibitors, viral breakthrough was common, especially in patients with genotype 1a HCV infection. The addition of RBV enhanced antiviral activity, delayed the emergence/selection of resistance, and resulted in a greater proportion of patients achieving an RVR. Adding PEG-IFN plus RBV to the 2 antiviral agents further enhanced viral suppression, with 100% of patients reaching RVR. In the majority of patients, treatment with PEG-IFN plus RBV after 28 days maintained HCV RNA suppression to <25 IU/mL up to Week 24. Virologic response data beyond Week 24 is awaited. Four patients with non-1 HCV genotype were treated in the study. The virologic responses in these patients were sub-optimal. Three patients discontinued randomized treatment and initiated PEG-IFN/RBV. The fourth patient, assigned to tegobuvir/GS-9256/RBV/PEG-IFN, remained on assigned therapy for 28 days per protocol. The virologic response rates observed in these patients are consistent with the specificity of tegobuvir and GS-9256 for HCV genotypes 1a and 1b.

A small imbalance in the proportion of IL28B-CC patients was observed across groups (Figure 1). The small sample size limits interpretation; however, it is possible that the apparent impact of ribavirin in reducing viral load and suppressing resistance could be partially related to a relatively high proportion of IL28B-CC patients in the tegobuvir/GS-9256/RBV arm.

Most adverse events occurring in the tegobuvir/GS-9256 arm were mild to moderate in severity. Although the number of adverse events was highest in the tegobuvir/GS-9256/PEG-IFN/RBV treatment arm, these events were consistent with those associated with IFNs. Transient bilirubin elevations were also observed, consistent with the known class effects of NS3 serine protease inhibitors on bilirubin transporters, such as organic anion transporting polypeptide 1B1 (OATPB1), with resulting increase in unconjugated bilirubin (25,26).

The emergence of resistance-associated variants with non-nucleoside NS5B or NS3 inhibitors has been described in other studies and is consistent with the lower genetic barrier against resistance for non-nucleoside analogs and NS3 protease inhibitors (for review see [13]). The high rate of emergence of the protease resistant variant R155K in genotype 1a, but not in genotype 1b infected patients has also been described previously with this class of agents, and is reflective of single-nucleotide change that is required for the development of resistance in genotype 1a patients, but two-nucleotide changes in the majority of genotype 1b patients (27). It is of note that single-nucleotide change is required for both mutations at NS3 R155 and D168 in genotype 1a patients; however, a mutation at only R155, and not D168, was identified in genotype 1a patients by population sequencing. The R155 nucleotide sequence may be more susceptible to change than D168, or the R155K may be more fit than mutations at D168 in this genotype. Mutations at D168 were commonly selected in genotype 1b-infected patients, consistent with genotype 1b replicon data.

The Y448H mutation observed with tegobuvir has been observed frequently in monotherapy studies and is consistent with in vitro mutational data indicating the tegobuvir interaction likely involves the ß-hairpin in the thumb sub-domain of the NS5B polymerase (20). In the present study, 7/8 genotype 1a patients developed dual-class resistance: R155K against the NS3 protease inhibitor and Y448H for the NS5B polymerase inhibitor. However, with the addition of RBV, the incidence of resistance was significantly reduced, with none of genotype 1a patients (n=3) exhibiting drug resistant variants. While RBV has been shown to have modest antiviral activity (28), its ability to significantly reduce development of resistance highlights a distinct mechanism of action. This may indicate a broader mutational effect of RBV on viral fitness, which renders a proportion of virus non-infectious, regardless of oral antiviral resistance mutations. Although similar trials have been reported (29), the present study is the first report of an interferon-free NS5B polymerase/NS3 protease combination both with and without RBV, thus allowing for prospective evaluation of the contribution of RBV to the antiviral effect of the regimen. The emergence of various classes of DAAs for treating chronic HCV infection has enabled evaluation of multiple combination approaches either with or without PEG-IFN and RBV (19,30,31). Specifically, the strategy of quadruple therapy with a non-nucleoside analog, a protease inhibitor, and PEG-IFN and RBV has been supported by results from a recently reported study in which the non-nucleoside NS5B polymerase inhibitor VX-222, telaprevir, and PEG-IFN/RBV resulted in RVR in 51/59 (86%) of treatment-naïve patients (19), which is higher than those reported with telaprevir and PEG-IFN/RBV (6,9). In this study, 100% of patients receiving quadruple therapy achieved RVR at Week 4, and a high proportion of patients (71%) had HCV RNA below 25 IU/mL at Week 2. The rapidity of viral clearance in patients with quadruple therapy provides a basis for examining response-guided therapy in which total duration of treatment could be fewer than 24 weeks. To explore this possibility, phase 2 combination studies of tegobuvir plus GS-9256 with PEG-IFN and RBV are underway.

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The end of the beginning for hepatitis C treatment

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"The development of an oral regimen of DAA's that can produce SVR in a high proportion of patients is the grail that we seek. It will prolong life and prevent death from liver disease, just as the epidemic reaches crisis proportions. The two studies in this issue of Hepatology bring us much closer to providing the answer to the epidemic."

1. Douglas Dieterich Mt Sinai Hosp NYC
Hepatology Jan 2012

Accepted Article (Accepted, unedited articles published online for future issues)

THE END OF THE BEGINNING FOR HEPATITIS C TREATMENT

"Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning." Winston Churchill.

These are extraordinary times in the history of HCV drug development. We waited 13 years between the approval of ribavirin in 1998 and the approval of telaprevir and boceprevir in 2011. The trajectory of drug discovery and clinical trials has gone from exponential to warp speed since the EASL meeting in April 2011, and these two articles are perfect examples of what has changed the world of hepatitis C; interferon-free combination therapy and in one of the trials, leading to eradication of the virus. The first demonstration in man of IFN-free combination therapy with direct acting antivirals (DAA's) was the INFORM-1 trial presented first at EASL 2009 and published in 2010(1) It showed that a nucleoside analogue polymerase inhibitor (now known as mericitabine) and a protease inhibitor (now known as danoprevir (now boosted with ritonavir) together without PEG or RBV could reduce HCV viral load by 5·1 log10 IU/mL in 14 days with no sign of resistant virus. This was the proof of principle that two DAA's by themselves could render most patients undetectable without PEG or RBV. This combination hit a snag with some danoprevir toxicity issues, and development has slowed. Those issues were successfully resolved with ritonavir boosting and the follow up study to INFORM is now proceeding apace and data will be forthcoming from that trial in 2012 or 2013.

The Zeuzem study published in this journal (2) compared an all-oral combination of tegobuvir a nonnucleoside polymerase inhibitor given twice daily plus GS 9256 an NS3 serine protease inhibitor with and without ribavirin in two arms for 28 days, at which point they received peginterferon and ribavirin standard of care. The third arm used quadruple therapy with both DAA's plus peginterferon and ribavirin for 28 days and then peginterferon and ribavirin alone. All patients with viral rebound of >.5 log10 from nadir or non response defined as < 2.0 log10 decline at day 5 received peginterferon and ribavirin immediately. Median maximal reductions in HCV RNA were -4.1log10 IU/ml, -5,1 log10 IU/ml and -5.7 log10 IU/ml for tegobuvir plus GS 9256, tegobuvir , GS9256 plus ribavirin and the tegobuvir, GS9256, peg and ribavirin arms. The results were quite instructive. RVR for the two DAA's alone was 7%, for the two DAA's plus ribavirin 38% and for the quadruple therapy arm 100%. The importance of ribavirin in preventing resistance is very clear with this combination and reemphasizes the continuing value of using ribavirin in all oral regimens of DAA's. It also demonstrates the real, but weak antiviral activity of ribavirin (3). Why was this result so much different than that of INFORM where virtually all patients were undetectable at 14 days of dual therapy? The answer lies in the barrier to resistance (4). The nucleoside/nucleotide analogues in general have a very high barrier to resistance and the INFORM study used the nucleoside mericitabine. The barrier to resistance for protease inhibitors is relatively low, and lower still for genotype 1a as opposed to genotype 1b, since the 1a virus only requires one mutation to generate resistance to protease inhibitors, while the 1b virus requires two. Most nonnucleoside polymerase inhibitors have a relatively low barrier to resistance. When you combine two DAA's with relatively low barriers to resistance, it is easy for the virus to produce the double mutants that are resistant to both drugs. Ribavirin slows this down somewhat, but does not add enough antiviral activity to prevent resistance over 60% of the time with tegobuvir and GS 9256. There is one other factor involved in preventing resistance and that is the activity of the DAA. Extremely potent agents, which drop the viral load down to undetectable rapidly, also prevent resistance. A good example of this is the combination study of BI 201335 and BI 207127 (5). This study compared two groups: BI201727 400 mg or 600 mg given thrice daily plus BI 201335 and ribavirin 1000-1200 mg for 4 weeks. In the 400 mg group, the RVR was 73 %( with better response in genotype 1b than 1a, as one would expect with a protease inhibitor in the regimen). In the 600 mg group, the RVR was 100% and did not differ between genotype 1a and 1b. From this data one can infer that the potency of either the protease inhibitor or the nonnucleoside polymerase inhibitor was different, since the same two classes of drugs, plus ribavirin yielded a much higher RVR. To be fair, there was no arm without ribavirin in this study and, of course, it is hard to compare results between studies. The designs of both studies are elegant, simple and easy to understand and advance the field enormously. Gilead is now aggressively addressing the issue of potency by adding a third DAA to tegobuvir and GS 9256 with and without ribavirin. (6)

The other study in this issue of Hepatology (7) advances the field dramatically further. Not only does it move us from RVR without interferon to SVR, but it does it in null responders! This represents a giant step towards the "Holy Grail" of HCV therapy: once daily, oral interferon-free treatment. The world of HCV treatment changed forever in April of 2011 when the first interferon-free SVR's were presented using an NS5A inhibitor and a protease inhibitor, the same two drugs used in the Chayama paper. (8) The 100% SVR with quadruple therapy was overshadowed by the all-oral double DAA combination, without ribavirin that resulted in a 36% SVR. This was the long awaited proof of principle that HCV could be eradicated without interferon. Of note in the all-oral arm was that both of the genotype 1b patients achieved an SVR, but only 2/9 of the genotype 1a patients achieved an SVR demonstrating the differences in activity of protease inhibitors in genotypes 1a and 1b.

The Chayama study in this issue examined the combination of the NS5A BMS-790052 60 mg qd ( now called daclatasvir) and the protease inhibitor BMS-650032 600mg (now called asunaprevir) in null responders, but only in genotype 1b, the most common genotype in Japan. Ten patients received both drugs for 24 weeks. Of the nine patients who completed the study, all achieved an SVR. HCV RNA remained undetectable in the patient who discontinued treatment after two weeks. This is truly a remarkable achievement in the field of HCV treatment. It is only partially applicable to genotype 1a patients around the world, but nonetheless brings us closer to what we seek in HCV therapy: all oral highly effective treatment. This publication marks a turning point in the HCV drug development world. It demonstrates that a protease and an NS5A inhibitor together can achieve an extremely high SVR in null responders, at least in genotype 1b. It is the second trial to show that an SVR is possible without either interferon or ribavirin in null responders.

In the patois of HCV drug development, we often speak of an all-oral regimen as the "Holy Grail" we all seek. In history that term has had many meanings, particularly in Arthurian legends beginning in the late 12th century. The meaning that comes closest, though to what we really intend, is in Wolfram von Eschenbach's Parzival. In it he portrays the grail as a stone that prevents anyone who sees it from dying. The development of an oral regimen of DAA's that can produce SVR in a high proportion of patients is the grail that we seek. It will prolong life and prevent death from liver disease, just as the epidemic reaches crisis proportions. The two studies in this issue of Hepatology bring us much closer to providing the answer to the epidemic.

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Treatment of chronic hepatitis C – are interferons really necessary?

Liver International

Special Issue: Proceedings of the 5th Paris Hepatitis Conference. International Conference of the Management of Patients with Viral Hepatitis: Special Edition Hepatitis C

Volume 32, Issue Supplement s1, pages 108–112, February 2012

Review Article

Peter Ferenci

Article first published online: 29 DEC 2011

DOI: 10.1111/j.1478-3231.2011.02705.x

© 2012 John Wiley & Sons A/S

Abstract

Due to the side effect profile of pegylated interferons interferon treatment has become the holy grail of drug development for chronic hepatitis C. The precise role of interferon in treatment of hepatitis C is not fully understood, besides its antiviral effects interferon is an immune modulator. Nevertheless, recent proof of concept studies indicated, that cure of chronic hepatitis C can be achieved without interferon. Various compounds achieved this goal, like the polymerase inhibitor PSI 7977, the combination of NS5a inhibitor (daclatasvir) and a protease inhibitor (asunaprevir) and the cyclophillin antagonist alisporivir. Various other combinations are investigated currently. Providing that phase 3 studies will confirm these exciting data, direct acting antivirals or host targets will replace peginterferon/ribavirin combination therapy.

The current standard of care (SoC) for treatment of chronic hepatitis C is still a combination of a pegylated interferon-α2 (PEG-IFN) with ribavirin (RBV) [1]. Recently, the first two direct-acting antivirals (DAA) were licensed in the USA and the European Union. In combination with PEG-IFN/RBV, telaprevir and boceprevir significantly increases the rate of cure of chronic hepatitis C, genotype 1, both in naïve and treatment-experienced patients [2, 3, 4]. Nevertheless, treatment is still restricted to patients who can tolerate PEG-IFN and RBV. As many as 50% of patients, including those with the greatest need of effective treatment such as those with advanced liver disease, cannot receive the new triple therapy. Thus, an interferon-free treatment regimen is required .

Investigation of DAA combination regimens has exploded in the last 12 months. This is possible because of the diversity of antiviral mechanisms besides protease inhibitors that are now in Phase II of the drug development pipeline for hepatitis C [5]. Diverse mechanisms are important because they often have different resistance profiles, and antiviral combinations are being assembled with new compounds with non-overlapping profiles to provide a greater barrier to antiviral resistance. Other factors that are important when assembling optimal combinations include the safety and tolerability profile of each agent, compatible pharmacokinetic profiles and a low potential for unfavourable drug–drug interactions.

The role of interferon in the treatment of chronic hepatitis C

Although interferon (IFN) has been used to treat chronic hepatitis C for more than 25 years, its precise role in eradicating the hepatitis C virus (HCV) still remains unknown. Determining the mechanism(s) involved in an IFN-induced cure is mandatory if IFN-free treatment regimens are to be developed. IFNs play a pivotal role in the outcome of a viral infection. IFNs are a family of pleiotropic cytokines that typically exhibit antiviral, antiproliferative, antitumour and immunomodulatory properties. The first response of an organism to intruding pathogens is an inflammatory reaction that includes secretion of cytokines and chemokines. These signalling molecules activate or attract innate immune cells, such as neutrophils, macrophages, natural killer (NK) cells, and dendritic cells (DCs), to orchestrate an effective response at the site of infection. Induction of innate immune mechanisms is not pathogen-specific, but is dependent upon interactions between pathogenic factors and host-cell determinants. During viral infection, some of the most prominent cytokines produced are IFNs. The importance of IFNs goes beyond their antiviral activities and includes numerous immunoregulatory functions that affect both innate and adaptive immunity [6]. IFN-induced clearance of HCV is both cytolytic (clearance of HCV-infected hepatocytes) and non-cytolytic (intra-cytoplasmic destruction of HCV without cell injury).

Innate immunity can be principally affected by HCV at the level of both: (i) type I IFN production by infected hepatocytes and (ii) the signals provided by the relative receptors (IFNAR-1/2) once they are engaged by soluble type I IFNs (mainly produced by plasmacytoid dendritic cells). If these defects are combined with a low viral load or infection by HCV strains that are highly susceptible to the antiviral effects of IFN, the spread of the HCV virus is contained, and the functions of dendritic cells, NK, B and T cells would not be heavily affected. Induction of type I IFN production in HCV-infected cells (i.e. hepatocytes) either on contact with TLR3 in the endosomal compartments, or upon recognition of the polyuridine motif of the HCV 30 untranslated region (UTR) by the retinoid acid-inducible gene I (RIG-I) in the cytoplasm, may be affected by HCV [7, 8, 9]. Thus, the initial response to HCV infection might not be sufficient to induce effective primary or secondary CD8 T-cell responses [10]. In chronic HCV infection, two major pathways, T-cell exhaustion and viral escape, contribute to CD8⁺ T-cell failure. In vivo models of HCV infection demonstrate selective impairment of T cells infiltrating HCV-infected livers because of the high concentrations of viral proteins produced at the site of infection, which may play a role in HCV persistence by affecting local adaptive immune responses [9].

The immunomodulatory activity of PEG-IFN-α and RBV induced T-cell immune responses may be important to eliminate chronic HCV infection [11]. In a prospective study, the kinetics of T-cell responses to HCV antigens (NS3-4 and core) correlated with virological outcome in patients undergoing PEG-IFN-α2a/RBV therapy. NS3-4-directed T helper cell type 1 (Th1) responses were detected in 77% of patients with a significant decline in viremia at treatment week 4, but were not detected in those with a slower viral decline. HCV-specific T-cell reactivity was uncommon at baseline, but increased markedly during antiviral therapy, peaking at around treatment weeks 4–8. Resolution of hepatitis C viremia was significantly more likely in patients who developed HCV-specific T-cell proliferation with increased IFN-gamma production [12]. The detectability of NS3-4-directed Th1 responses was associated with faster viral clearance, was short-lived and was not associated with the final treatment outcome [13]. This may be explained because HCV abolishes the blockade of the adaptative immune response by inhibiting viral replication. T-cell activation was transient, but not always sufficient to clear infected hepatocytes. Thus, if rapid inhibition of HCV replication by DAA is sufficient to restore adaptative immunity, exogenous IFN administration may not be necessary.

The other important role of IFN is the inhibition of viral replication. In drugs with a low genetic barrier such as first generation protease inhibitors, IFN and RBV are required to block the emergence of DAA resistant viral strains [14, 15]. Potential strategies to overcome this problem are: (i) DAA combinations including polymerase inhibitors with a high barrier to resistance; (ii) triple DAA therapy; and (iii) combinations of two DAAs with a lower genetic barrier to resistance plus RBV. A mathematical model by Perelson et al. [16] suggests that IFN-free regimens will need to contain three or four distinct antiviral mechanisms to obtain a sustained viral response (SVR) before the development of resistance.

Proof-of-concept studies

The first published trial with an all-oral combination treatment with two experimental anti-HCV drugs [mericitabine, a nucleoside polymerase inhibitor (NI); and danoprevir, an NS3/4A protease inhibitor] in patients with chronic HCV infection was the INFORM-1 study [17]. Patients with chronic hepatitis C, genotype 1, received up to 13 days of oral combination treatment with mericitabine (500 or 1000 mg twice daily) and danoprevir (100 or 200 mg every 8 h or 600 or 900 mg twice daily) or placebo. Eligible patients were sequentially enrolled into one of seven treatment cohorts and were randomly assigned by interactive voice or a web response system to either active treatment or placebo. The primary outcome was a change in HCV RNA concentrations from baseline to day 14 in patients who received 13 days of combination treatment. Eighty-eight patients were randomly assigned to a drug treatment regimen (n = 74 over seven treatment groups; 73 received at least one dose of study drug) or to placebo (n = 14, all of whom received at least one dose). The median change in HCV RNA concentrations from baseline to day 14 ranged from −3.7 to −5.2 log₁₀ IU/mL in the cohorts that received 13 days of combination treatment. At the highest combination doses tested (1000 mg RG7128 and 900 mg danoprevir twice daily), the median change in HCV RNA concentrations from baseline to day 14 was −5.1 log₁₀ IU/mL in treatment-naive patients and −4.9 log₁₀ IU/mL in previous SoC non-responders. The combination of RG7128 and danoprevir was well tolerated with no severe treatment-related or adverse events, no grade 3 or 4 changes in laboratory parameters and no safety-related treatment discontinuations. Virological breakthrough, with the selection of resistant variants, has not yet been observed in short-term clinical studies of the NS3/4A protease inhibitor danoprevir plus the NI, mericitabine, suggesting that inclusion of an NI in DAA combination therapy may be an attractive strategy. However, additional efficacy (SVR) and safety data from longer term treatments are still required. A phase 2a study is ongoing (Matterhorn study).

In another study [18], the combination of the protease inhibitor BI 201335, the polymerase inhibitor BI 207127 and RBV was shown to have a rapid and strong activity against HCV genotype-1 with no severe adverse events. Thirty-two treatment-naïve patients with chronic HCV genotype-1 infection were randomly assigned to groups that were administered 400 or 600 mg BI 207127, three times a day (TID), plus 120 mg BI 201335, once a day and 1000–1200 mg RBV per day for 4 weeks. The primary efficacy endpoint was virological response (HCV RNA < 25 IU/mL at week 4). The virological response rates were 47, 67 and 73% at days 15, 22, and 29, respectively, in the group receiving BI 207127 400 mg TID; a higher response rate was observed in patients with genotype-1b compared with genotype-1a. The virological response rates were 82, 100 and 100%, respectively, in the group receiving BI 207127 600 mg TID, and did not differ among genotypes. One patient in the group receiving 400 mg TID had a virological breakthrough [≥1 log [10] rebound in HCV RNA] at day 22. The most frequent adverse events were mild gastrointestinal disorders, rash and photosensitivity. There were no severe or serious adverse events; none of the patients discontinued treatment early.

The results of a proof-of-concept study for SVR with a PEG-IFN-free treatment regimen in HCV patients was recently reported. Four of eleven genotype 1 patients, who were non-responders to PEG-IFN/RBV treatment, achieved a SVR after 24 weeks of treatment with the combination of an NS5A inhibitor and an NS3/4A protease inhibitor, with only one relapse in this cohort [19], especially in patients with genotype 1b [20]. This suggests that HCV can be eradicated in chronically infected patients with a PEG-IFN-free DAA combination regimen, and supports investigations of various DAA combinations to improve SVR rates without PEG-IFN.

These observations provide a proof-of-concept for an oral approach to the treatment of HCV, including a combination of DAA without PEG-IFN.

ZENITH is an ongoing Phase 2 study of multiple 12- and 24-week response-guided treatment regimens with VX-222 (400 or 100 mg), a polymerase inhibitor in development, in combination with telaprevir [21]. The all-oral treatment arms (VX-222 400 or 100 mg plus telaprevir 1125 mg BID) were discontinued because of a pre-defined stopping rule in relation to viral breakthrough. The two treatment arms including PEG-IF and RBV (quadruple therapy) could stop all treatments at week 12, if hepatitis C virus was undetectable at weeks 2 and 8. Twenty-six of fifty-nine (44%) patients qualified for 12 weeks of therapy, and 88.4% of these had a SVR. The remaining patients received an additional 12 weeks of PEG-IFN/RBV. SVR was achieved in 96%. The overall SVR rate was 86.4%.

Another approach is the combination of nucleoside polymerase inhibitors (PSI-7997 with PSI-938) [22] with promising initial data. The approach of combining three non-cross resistant DAAs with a lower genetic barrier to resistance, i.e. an NNI plus a NS3/4A protease inhibitor and an NS5A inhibitor, is well supported by mathematical analyses. Rong et al. demonstrated that resistant variants against the three drug classes are unlikely to pre-exist before treatment initiation, and emergence is unlikely to occur during therapy [23]. However, drug–drug interaction and overlapping safety profiles remain an issue.

A third highly attractive strategy is to combine two DAA with a lower genetic barrier to resistance, plus RBV. A trial evaluating GS-9256 plus tegobuvir, with or without RBV demonstrated the central role of RBV in the decrease in HCV RNA and the reduction of viral breakthroughs for DAA combinations with a low barrier to resistance. Unfortunately, this study was interrupted because of safety concerns (Table 1).

Finally, a new class of drugs called cyclophilin inhibitors may be used in an IFN-free approach. Alisporivir (DEB025) is the first in this class of drugs, and is currently under investigation. Unlike other compounds under development that target the virus directly, Alisporivir is a host targeting antiviral that targets host proteins essential for the replication of HCV. As these proteins play a key role in the replication of all types of HCV, alisporivir may offer an effective treatment option for a broad range of HCV forms and be effective against other common HCV genotypes. High SVR rates were obtained in combination with PEG-IFN/RBV [24]. INF-free regimens in patients with genotypes 2 and 3 were recently presented [25, 26]. Alisporivir as IFN-free therapy achieves early on-treatment viral response in up to half of G2/3 patients by treatment week 6 and in most patients who reached end of treatment [25]. In a phase 2a study PSI 7977 in combination with ribavirin reached a 100% cure rate in just 12 weeks [26].

Summary

As a result of the side effects of IFN, there is ongoing search for interferon-free antiviral approaches to cure chronic hepatitis C. The FDA, EMA as well as patient advocacy groups are strong proponents of investigating antiviral drug combinations prior to approval of individual components. Although proof-of-concept studies confirm that such approaches may be feasible, at present, only oral combinations together with PEG-IFN/RBV offer the best chances for cure even in non-responders to SoC treatment. The best drug combinations must prevent the emergence of drug resistant viral strains, have a high degree of safety and efficacy, an easy treatment algorithm and short treatment duration. The treatment should work for all genotypes. Although the ideal drug has not yet been found there is an urgent medical need because patients with advanced liver disease or organ transplant patients (excluding liver transplants) cannot tolerate IFN and are in great need of effective treatment.

Conflicts of interest

Dr Ferenci is a member of the global advisory board and of the speaker bureau of ROCHE. He also receives an unrestricted research grant from ROCHE Austria. He is also member of the global advisory boards of Vertex/Tibotec, Böhringer-Ingelheim, MSD and Rottapharm-Madaus, and serves as advisor to Pfizer, Novartis, Achilleon, GSK.

References

Source

Gilead's Hepatitis C Therapy Called Successful

CDC 3-14-11

Abstract

In early-stage study results reported recently to investors, Gilead Sciences Inc. said its four-drug combination eliminated hepatitis C virus in patients. The trial examined the use of Gilead GS-9256 and GS-9190 with the standard drugs ribavirin and peginterferon. The researchers plan to present their findings at the annual meeting of the European Association for the Study of the Liver, which begins March 30 in Berlin.

Source
http://www.sfgate.com/

Date of Publication
03/09/2011

Author
Kristen Hallam, Bloomberg News

Article Type
General media

Article Category
News Briefs

Source

Gilead Drug Combination Cut Hepatitis Virus in Study, RBC Says

By Kristen Hallam - Mar 8, 2011 7:27 AM ET

Gilead Sciences Inc. (GILD)’s four-drug combination eliminated hepatitis C virus in patients in an early-stage study, RBC Capital Markets LLC analysts said.

The findings support an ongoing mid-stage study of the combination, the analysts, led by Michael Yee in San Francisco, wrote yesterday in a note to investors, citing an abstract of the trial. The analysts said they expect data next year from a mid-stage study by the Foster City, California-based company.

The early-stage study examined a combination of Gilead’s GS-9256 and GS-9190 with two older drugs that are the standard of care, ribavirin and Peg-interferon, according to the note.

The data will be presented at the annual meeting of the European Association for the Study of the Liver starting March 30 in Berlin.

To contact the reporter on this story: Kristen Hallam in London at khallam@bloomberg.net
To contact the editor responsible for this story: Phil Serafino at pserafino@bloomberg.net

Source