Introduction

The hepatitis C virus (HCV) is a leading cause of chronic liver disease worldwide infecting an estimated 130–170 million people, or 2.2–3.0 % of the global population [1, 2]. In Japan, hepatocellular carcinoma (HCC) is one of the most common causes of cancer mortality (incidence of 7 % in Japan, compared with 1–4 % in Europe and the USA [3]) and 79 % of HCC cases are due to HCV infection [4, 5]. An estimated 2 million Japanese people are infected, 70 % with HCV genotype 1b, 20 % with genotype 2a, and the remainder with genotype 2b or other genotypes [6].

Until recently, the standard of care for the treatment of chronic genotype 1 HCV infection was a combination of peginterferon (PegIFNα-2a) and ribavirin (RBV) for 48 weeks or longer [2, 7–9]. However, the long treatment duration is a substantial physical and mental burden for patients, and rates of treatment discontinuation and dose reduction due to adverse events (AEs) are high [10, 11]. Furthermore, sustained virologic response (SVR, defined as undetectable HCV RNA at a given time point after the end of treatment) is achieved in only 42–52 % of patients [10–12]. Novel, direct-acting antiviral agents (DAAs) are therefore under development. Two first-generation HCV NS3/4A protease inhibitors (PIs), boceprevir [13, 14] and telaprevir [15, 16], have recently been approved for the treatment of genotype 1-infected patients in the USA and Europe, and telaprevir is also approved in Japan [17, 18]. The inclusion of these agents in HCV treatment regimens has led to large improvements in SVR rates, though these agents require dosing three times daily (every 7-9 h) and their use is associated with increased incidence and, in some cases, severity of AEs such as anemia and rash [13, 16, 18–21].

Simeprevir (TMC435) is an investigational, once-daily (QD) oral NS3/4A protease inhibitor currently under clinical development globally. International Phase IIb trials of simeprevir in combination with PegIFNα-2a/RBV for treatment-naïve and -experienced patients infected with HCV genotype 1 demonstrated that simeprevir was generally well tolerated, had a pharmacokinetic profile that supports QD dosing and resulted in high virologic response rates [22–25].

In a Phase I study in 30 healthy Japanese adult male volunteers living in the USA (TMC435-C109; NCT00752544), simeprevir was generally well tolerated. Simeprevir plasma exposures were higher in Japanese healthy volunteers compared with Caucasian volunteers in the TMC435-C101 study (NCT00938899) [26].

The Dose and duration Ranging study of Antiviral agent TMC435 in Genotype One HCV treatment-Naïve patients (DRAGON; TMC435-C215) was a Phase II study conducted across Japan to evaluate the efficacy, safety and pharmacokinetics of simeprevir and PegIFNα-2a/RBV in treatment-naïve, HCV-infected patients. Based on the higher exposure of simeprevir in Japanese versus Caucasian healthy volunteers demonstrated in the Phase I study, simeprevir doses of 50 and 100 mg QD were selected for evaluation in this dose-ranging, Japanese Phase II study.

Methods

Patients

Patients recruited to the DRAGON study were treatment-naïve, chronically infected with genotype 1 HCV, aged 20–70 years and had plasma levels of HCV RNA ≥5.0 log10 IU/mL at screening.

Key exclusion criteria included: (1) presence of liver cirrhosis or hepatic failure, or other liver disease, (2) infection/co-infection with HIV-1, HIV-2, hepatitis B or nongenotype 1 HCV, (3) malignant tumor within 5 years prior to study, (4) HCC, (5) meeting conditions that required caution with PegIFNα-2a or RBV treatment, (6) any clinically significant disease, (7) organ transplant, and (8) defined laboratory abnormalities during screening.

Study design

The DRAGON study was a multicenter, randomized, open-label, parallel group comparison study performed to evaluate the efficacy, safety and pharmacokinetics of simeprevir in combination with PegIFNα-2a/RBV in treatment-naïve patients with chronic genotype 1 HCV infection. The study was performed from July 6, 2009, to April 1, 2011, in accordance with the Declaration of Helsinki, and was consistent with Good Clinical Practice guidelines and applicable regulatory requirements. The study protocol and amendments were reviewed by Institutional Review Boards and each patient provided written informed consent.

Eligible patients were randomized to one of five treatment groups (SMV12/PR24 50 mg, SMV24/PR24 50 mg, SMV12/PR24 100 mg, SMV24/PR24 100 mg and PR48) in a 2:1:2:1:1 ratio. In the SMV12/PR24 50 mg and SMV12/PR24 100 mg groups, patients received simeprevir (50 or 100 mg QD, respectively) combined with PegIFNα-2a/RBV for 12 weeks, followed by PegIFNα-2a/RBV for 12 weeks. In the SMV24/PR24 50 mg and SMV24/PR24 100 mg groups, patients received simeprevir (50 or 100 mg QD, respectively) combined with PegIFNα-2a/RBV for 24 weeks. In these four groups, at week 24, patients either stopped or continued treatment with PegIFNα-2a/RBV up to week 48, according to response-guided therapy (RGT) criteria (stop treatment if plasma HCV RNA <1.4 log10 IU/mL at week 4 and undetectable at weeks 12, 16 and 20, otherwise continuing PegIFNα-2a/RBV to week 48). In the PR48 group, criteria were not applied; patients received PegIFNα-2a/RBV for 48 weeks.

Major efficacy endpoints included the proportion of patients with undetectable plasma HCV RNA 24 weeks after the end of treatment (SVR24). Other efficacy endpoints included the proportion of patients with undetectable plasma HCV RNA at week 4 (rapid virologic response; RVR) or week 12 (complete early virologic response, cEVR) and change in plasma HCV RNA level from baseline to week 4 of treatment. Incidence of viral breakthrough (increase of >1 log10 IU/mL in plasma HCV RNA level from the lowest level reached, or plasma HCV RNA level of >2.0 log10 IU/mL in patients whose plasma HCV RNA level had previously been below 1.4 log10 IU/mL or undetectable), viral relapse (detectable plasma HCV RNA during the post-treatment follow-up period in patients who had undetectable plasma HCV RNA at the end of treatment) and the viral NS3 sequence were also assessed.

According to predefined virologic stopping rules, patients in the simeprevir groups discontinued simeprevir and continued PegIFNα-2a/RBV if viral breakthrough occurred during the first 24 weeks, and stopped all treatment if the decrease in plasma HCV RNA from baseline to week 12 was <2 log10 IU/mL, or plasma HCV RNA level at week 24 was ≥1.2 log10 IU/mL.

The population-based sequencing assay to determine HCV NS3/4A sequence based on the standard Sanger sequencing method was performed for patients with viral breakthrough and viral relapse. Sequencing data were reported as amino acid changes from Con1 (GenBank accession number AJ238799) or H77 (GenBank accession number AF009606) for genotype 1b and 1a/others, respectively.

Safety endpoints included the frequency and severity of AEs including serious AEs (SAEs), incidence of discontinuation of study drugs due to AEs, and changes in clinical laboratory test values.

Treatment administration

Simeprevir was administered orally at a dose of 50 or 100 mg as a single capsule QD. No simeprevir dose reduction was permitted. PegIFNα-2a (Pegasys®, Chugai) was administered as a subcutaneous injection (180 μg once weekly) and RBV (Copegus®, Chugai) as oral tablets (600–1000 mg total daily dose, depending on body weight) in accordance with the manufacturer’s prescribing information for both medications. Patients were hospitalized for a minimum of 1 week, starting on the first day that simeprevir and PegIFNα-2a/RBV were administered. Treatment of anemia with erythropoietin was not permitted in the study.

Measurements

Plasma HCV RNA was quantified upon screening, at baseline, at 4 and 8 h on day 1, on day 3, at weeks 1, 2, 3, 4, 6, 8, 12, 16, 20 and 24 (all patients), and weeks 28, 36 and 48 (patients stopping PegIFNα-2a/RBV at week 24) or weeks 28, 36, 42, 48, 52, 60 and 72 (patients receiving PegIFNα-2a/RBV until week 48), using the Roche COBAS® TaqMan® HCV Auto assay system (lower limit of quantification [LLOQ] 15 IU/mL, equivalent to 1.2 log10 IU/mL). Plasma HCV RNA below the LLOQ was either assigned as ‘HCV RNA <1.2 log10 IU/mL detectable’ if traces of HCV RNA were detected, or ‘undetectable HCV RNA’ if no HCV RNA was detected. Alanine aminotransferase (ALT) was quantified at baseline and weeks 1, 2, 4, 6, 8, 12, 16, 20 and 24 (all patients), and weeks 28 and 48 (patients stopping at week 24), or weeks 36, 42, 48, 52 and 72 (patients receiving PegIFNα-2a/RBV until week 48).

Laboratory test values, results of vital sign assessment and presence or absence of electrocardiogram abnormalities were recorded at screening and at regular intervals throughout treatment and the post-treatment follow-up period. AEs were recorded throughout the study period.

Statistical analysis

Efficacy analyses were performed on the full analysis set (FAS; all randomized patients with post-baseline efficacy assessment data). For virologic responses (RVR, cEVR and SVR24), rates were summarized for the combined simeprevir 50 mg (i.e. SMV12/PR24 50 mg and SMV24/PR24 50 mg groups pooled) and 100 mg (i.e. SMV12/PR24 100 mg and SMV24/PR24 100 mg groups pooled) groups, and compared with that of the PR48 group. In addition, for SVR24, rates were calculated for each of the five treatment groups. The change in HCV RNA from baseline to week 4 was assessed using analysis of covariance (ANCOVA), with the dose group as a factor and plasma HCV RNA at baseline as a covariate, to calculate the least-squares (LS) means and two-tailed corresponding 95 % confidence intervals (CIs). These were calculated for change from baseline for the combined simeprevir 50 mg or combined simeprevir 100 mg groups and the PR48 group, and the differences between groups. Fisher’s exact test was performed to compare RVR and cEVR between the combined simeprevir groups and the PR48 group.

A mutation was considered as emerging at a specific time point if the amino acid at a given position was absent at baseline and present at that time point. Incidence of emergent mutations at the time of viral breakthrough or relapse was summarized.

The proportion of patients displaying ALT within the normal limits was summarized for all patients in the combined simeprevir groups and for the PR48 group. Incidence of AEs and other safety endpoints were analyzed for all patients who received at least one dose of medication and were summarized per treatment group.

Results

Patient disposition and baseline characteristics

In total, 116 patients were screened and 93 were randomized to treatment groups, of whom 92 received at least one dose of a study drug (Supplementary Fig. 1). Ninety-one percent of the patients completed the study. The main reasons for study discontinuation were withdrawal of consent (5 %) and occurrence of AEs (2 %). Out of seven patients who discontinued from the study during the post-treatment follow-up period, five patients dropped out due to withdrawal of consent, and two (1 in SMV12/PR24 100 mg group, 1 in PR48 group) due to AEs.

In the simeprevir groups, nine patients permanently discontinued all treatment due to AEs (8/79, 10 %) or virologic stopping criteria (1/79, 1.3 %). In the PR48 group, three patients permanently discontinued all treatment due to AEs (n = 2) or another reason (n = 1).

There were no notable differences in baseline demographic characteristics between treatment groups (Table 1). Approximately half of the patients (39 to 62 %) were male, with a median age of 54 years (range 20–69 years) and median body weight of 58 kg (range 40–85 kg). All patients were infected with HCV genotype 1b and the median baseline HCV RNA was 6.3 log10 IU/mL (range 4.5–7.0 log10 IU/mL). A total of 7 % of patients displayed Metavir fibrosis stage 3; there were no patients with fibrosis stage 4.

Table 1 Patient demographics and baseline characteristics (safety population)
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Efficacy

On-treatment virologic response

During the first 3–7 days of simeprevir administration, an initial rapid reduction in plasma HCV RNA was evident in all simeprevir groups (Fig. 1). For analysis of the impact of simeprevir dose with regards to on-treatment virologic response, data were pooled by dose group (simeprevir 50 mg groups combined and 100 mg groups combined; Table 2).

Fig. 1
figure 1

Mean change from baseline in plasma HCV RNA through week 24. HCV hepatitis C virus, PR peginterferon + ribavirin, SD standard deviation, SMV simeprevir

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Table 2 On-treatment and post-treatment virologic response (full analysis set)
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The mean HCV RNA change from baseline to week 4 was significantly greater in the simeprevir combined 50 and 100 mg groups than in the PR48 group; LS mean differences from the PR48 group were 2.4 for both simeprevir 50 mg combined and 100 mg combined [both of the least-squares mean difference values (95 % confidence interval) were below zero].

The majority of patients in the simeprevir 50 mg combined and 100 mg combined groups achieved RVR and cEVR (83–90 and 92–98 %, respectively), compared with rates of 8 and 54 %, respectively, in the PR48 group.

Sustained virologic response

The SVR24 rate was higher in the simeprevir groups than in the PR48 group, with rates of 78, 77, 77, 92 and 46 in the SMV12/PR24 50 mg, SMV24/PR24 50 mg, SMV12/PR24 100 mg, SMV24/PR24 100 mg and PR48 groups, respectively (Table 2; Fig. 2).

Fig. 2
figure 2

Sustained virologic response rates (SVR24). PR peginterferon + ribavirin, SMV simeprevir

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All patients in the simeprevir groups, except for one patient in the SMV12/PR24 100 mg group, successfully completed treatment at week 24, as they met the RGT criteria. Among these patients, SVR24 rates ranged from 83 to 90 %.

All seven patients who discontinued the study during the follow-up period were classified as non-SVR, although four out of the seven patients had undetectable HCV RNA at the last visit before withdrawal.

Viral breakthrough, viral relapse or treatment failure

One patient in the SMV12/PR24 50 mg group experienced viral breakthrough at week 20 after the HCV RNA level became undetectable from weeks 3 to 16. This patient had viral breakthrough during treatment with PegIFNα-2a/RBV, after the completion of triple therapy. No viral breakthrough was reported in the other simeprevir groups or the PR48 group.

Compared to the PR48 group (36 %), viral relapse rates were apparently lower in the simeprevir groups regardless of dose or duration (15, 17, 15 and 8 % in the SMV12/PR24 50 mg, SMV24/PR24 50 mg, SMV12/PR24 100 mg, and SMV24/PR24 100 mg group, respectively) (Table 2).

Among the patients in the simeprevir treatment groups, 20 % (16/79) did not achieve SVR24. The reasons for this were detectable HCV RNA at the end of treatment (two patients), viral relapse (11 patients), or missing HCV RNA results for patients at 24 weeks after they had achieved undetectable levels at the end of treatment (three patients).

Viral population sequencing

No emerging mutations were observed in the selected HCV NS3 protease domain in the patient with viral breakthrough. Paired HCV NS3 sequence information (at baseline and time of relapse) was available for 10/11 simeprevir-treated relapsers, and emerging mutations in the NS3 protease domain (Q80R, R155Q, D169A, C, E, H and/or V, alone or in combination) were detected in six of these ten patients.

Alanine aminotransferase

The proportion of simeprevir-treated patients who had ALT levels within the normal limit had increased from 57 % at baseline to 92 % at the end of treatment (per protocol analysis).

Safety

The rates of simeprevir and PegIFNα-2a/RBV discontinuation and PegIFNα-2a/RBV dose modification due to AEs were similar between the simeprevir groups and the PR48 group.

There was one death reported due to cerebral infarction in the SMV12/PR24 100 mg group. The patient was a 64-year-old female with hypertension but no other notable medical history. The death occurred approximately 3 weeks after the end of treatment and was therefore considered to be unrelated to simeprevir and PegIFNα-2a/RBV.

A summary of AEs is shown in Table 3. There were no clinically relevant differences in the incidence of AEs across the groups and the majority of AEs were of grade 1 or 2 in severity according to the WHO toxicity grading predefined in the study protocol. Rash and arthralgia, which were slightly higher (>15 % numerical difference) in the simeprevir groups than in the PR48 group, were also grade 1 or 2 in severity.

Table 3 Summary of adverse events and changes in hemoglobin and total bilirubin levels across all treatment groups (safety population)
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For protocol-predefined rash/cutaneous reactions (except for pruritus without visible skin findings) considered by the investigator to be caused by any medication, the incidence rate was similar between the simeprevir groups and the PR48 group, with no notable differences across the simeprevir groups and with no grade 3 or 4 events, such as Stevens-Johnson syndrome or toxic epidermal necrosis, reported (Table 3). As for pruritus, which was reported in 19 % of the simeprevir-treated patients (compared to none in the PR group), all events were grade 1 or 2 in severity.

Incidences of anemia and decreased hemoglobin were similar in the simeprevir groups and the PR48 group, as were the rates of discontinuation and RBV dose reduction due to these two AEs. All were grade 1 or 2 and no notable differences were reported across the simeprevir groups. Of note, treatment with erythropoietin was not permitted in the study. Changes in hemoglobin levels from baseline were also similar across the groups and none of the patients had values <8 g/dL (Fig. 3a).

Fig. 3
figure 3

Mean hemoglobin and total bilirubin in patient plasma through week 48. Total bilirubin ULN = 17.1 μmol/L. Scr screening visit, BL baseline visit, PR peginterferon + ribavirin, SD standard deviation, SMV simeprevir, ULN upper limit of normal

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Mild and transient increases in bilirubin levels (direct and indirect) were observed in the simeprevir groups during the first 2 weeks. Mean bilirubin values stabilized or decreased during continued treatment and returned to baseline values after week 12 in the SMV12/PR24 groups and week 24 in the SMV24/PR24 groups (Fig. 3b). These changes were not associated with increases in the laboratory parameters for ALT or aspartate aminotransferase. Four simeprevir-treated patients experienced grade 3 (2.6–5.0 mg/dL) or 4 (>5.0 mg/dL) total bilirubin elevations during weeks 1 to 2 of treatment (the ratio direct/total bilirubin at the time point of the highest bilirubin value in these four patients were 26.5, 31.6, 60.7 and 17.5 %, respectively) and discontinued simeprevir in accordance with the treatment discontinuation criteria, which were predefined in the study protocol. All of these bilirubin elevations began to decrease before or immediately after the end of simeprevir treatment and returned to baseline after the end of simeprevir treatment. No particular changes (elevations) in other hepatic parameters or any clinically relevant symptoms were reported in these patients. No other clinically significant differences in laboratory parameters between the simeprevir groups and the PR48 group were observed.

Discussion

This study was the first in treatment-naïve Asian patients chronically infected with HCV genotype 1 and with high viral load, to investigate the efficacy, safety and pharmacokinetics of simeprevir as part of a treatment regimen including PegIFNα-2a and RBV. In this study, all patients were infected with HCV genotype 1b, reflecting the high prevalence of this subtype in Japan.

Results of the study indicated that once-daily simeprevir (50 and 100 mg) in combination with PegIFNα-2a/RBV significantly improved the SVR24 rate compared with PegIFNα-2a/RBV alone in this patient population.

In this study, an RGT strategy was employed to allow individualized shortening of PegIFNα/RBV treatment duration to 24 weeks, based on early viral kinetics. According to the RGT criteria, the majority of simeprevir patients were eligible to stop all treatment at week 24. Furthermore, these patients had high SVR24 rates (83–90 %). This indicates that an RGT approach is also beneficial for patients in Japan. Shorter overall treatment duration is highly desirable as it reduces the length of exposure to PegIFNα-2a/RBV, thereby potentially reducing the duration of AEs experienced by the patient, and is also a cost-effective alternative to standard-duration PegIFNα/RBV therapy [27].

During the first 3 days of dosing, both 50 and 100 mg doses of simeprevir demonstrated an initial rapid reduction in HCV RNA. Subsequent reduction in HCV RNA was less pronounced, and by week 4, the LS mean HCV RNA decline from baseline was −5.2 log10 IU/mL in both the simeprevir 50 mg combined and 100 mg combined groups, compared with −2.9 log10 IU/mL in the PR48 group. This biphasic reduction in HCV RNA was consistent with viral kinetics observed in a previous proof-of-concept simeprevir study (OPERA-1) [23] and other potent DAAs. In all simeprevir groups, RVR was highly predictive of SVR. Following high RVR rates (83–90 %, compared with 8 % in the PR48 group), simeprevir-treated patients achieved high SVR24 rates (77–92 %, compared with 46 % in the PR48 group), accompanied by low rates of viral relapse (8–17 %, compared with 36 % in the PR48 group). The response rates in the PR48 group are consistent with previous reports [18, 22, 28].

No viral breakthrough was reported in the simeprevir 100 mg groups during the treatment period. In addition, the on-treatment virologic response rate in the early treatment phase (weeks 2 to 4) was slightly higher in the simeprevir combined 100 mg group compared with the combined 50 mg group (e.g., 44 % of the patients in the simeprevir 100 mg group had undetectable HCV RNA, versus 28 % in the simeprevir 50 mg group at week 2). The on-treatment response was not affected by the duration of simeprevir treatment across dose group (RVR rate of 85, 77, 89 and 92 %; cEVR rate of 100, 92, 89 and 100 %, in the SMV12/PR24 50 mg, SMV24/PR24 50 mg, SMV12/PR24 100 mg and SMV24/PR24 100 mg groups, respectively), and no clear relationship between relapse rate and duration of simeprevir treatment was observed. Therefore, the simeprevir 100 mg dose with a 12-week duration as triple therapy has been selected to be taken forward into Phase III trials.

In addition to the notable virologic response, the study demonstrated greater increases from baseline to the end of treatment in the proportion of simeprevir-treated patients (per protocol population) with normal ALT levels.

Overall, these results are consistent with previous simeprevir trials which investigated HCV genotype 1-infected, treatment-naïve patients, conducted mainly in the USA and Europe [23].

In simeprevir-treated patients with viral relapse for whom sequence information was available, emerging mutations in the NS3 protease domain (Q80R, R155Q, D168A/C/E/H and V, alone or in combination) were detected around the time of viral relapse in 6/10 patients. Mutations at these positions have been previously identified in vitro [29]. Considering the dominance of the HCV genotype 1b in Japan, further evaluation of emerging mutations is required.

There were no notable differences in incidence of AEs or discontinuations due to AEs between groups receiving triple therapy of simeprevir with PegIFNα-2a/RBV and those receiving PegIFNα-2a/RBV alone. In contrast to the first-generation PIs [13, 16, 19–21], no severe anemia or severe rash/cutaneous reactions (including, though not limited to, Stevens-Johnson syndrome or toxic epidermal necrosis) were reported in this study. Except for bilirubin levels, there were no significant changes in laboratory values including hemoglobin, neutrophil count and platelet count. Mild, transient increases in bilirubin (direct, indirect and total) levels were observed in simeprevir-treated patients, though these were not clinically significant or accompanied by increases in other hepatic function parameters. These bilirubin level elevations were grade 3 (2.6–5.0 mg/dL) or 4 (>5.0 mg/dL) in four simeprevir-treated patients, which led to the discontinuation of simeprevir in these individuals. The bilirubin levels began to decrease before the end of simeprevir treatment and returned to baseline after the end of simeprevir treatment. In vitro studies indicated that this may be due to the inhibition of OATP1B1 and MRP2 transporters by simeprevir, as both have a role in bilirubin clearance [30]. However, it is not anticipated that inhibition of these transporters will affect dosing, efficacy or safety in ongoing studies.

In conclusion, in Japanese treatment-naïve patients infected with HCV genotype 1b with high viral load, treatment with oral, once-daily simeprevir in combination with PegIFNα-2a and RBV, regardless of simeprevir dose regimen (50 or 100 mg QD, for 12 or 24 weeks), demonstrated potent antiviral activity and high SVR rates, and shortened the overall treatment duration in the majority of patients. Simeprevir was well tolerated, with no additional side effects or incremental adverse events. The mild and reversible bilirubin elevation was asymptomatic and not accompanied by elevation of other hepatic parameters.

Novel DAAs are expected to continue the improvement of HCV treatment (i.e., further improved safety profile, more convenient dosing regimens, and reduced resistance), started by the addition of the first generation of protease inhibitors to PegIFN/RBV combination therapy. Based on the data provided by this Phase II DRAGON study, the Phase III CONCERTO trials will shed further light on the treatment of chronic HCV genotype-1 infection in treatment-naïve and -experienced patients in Japan.