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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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