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Long-term follow-up of patients receiving boceprevir for treatment of chronic hepatitis C
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Contents lists available at ScienceDirect
Antiviral Research journal homepage: www.elsevier.com/locate/antiviral 5 6
Long-term follow-up of patients receiving boceprevir for treatment of chronic hepatitis C
3 4 7
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8 9 10 11 12 13 1 2 5 7 16 17 18 19 20 21 22 23 24 25 26
Anita Y.M. Howe a,⇑, Jianmin Long a, David Nickle b,c, Richard Barnard a, Seth Thompson a, John Howe a, Katia Alves a,1, Janice Wahl a a
Q2
b c
Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA Department of Genetics, Merck Research Laboratories, Whitehouse Station, NJ, USA Department of Pharmacogenomics, Merck Research Laboratories, Whitehouse Station, NJ, USA
a r t i c l e
i n f o
Article history: Received 4 August 2014 Revised 3 October 2014 Accepted 16 October 2014 Available online xxxx Keywords: Boceprevir Hepatitis C Resistance Relapse
a b s t r a c t The durability of sustained virologic response (SVR) following boceprevir-based therapy in patients with hepatitis C virus (HCV) infection has not been reported. Furthermore, in patients receiving protease inhibitor-based therapies, development of resistance can contribute to treatment failure. The aim of the present study was to follow the clinical progression of patients treated with boceprevir after treatment in phase 2/3 clinical trials. This was a 3-year, long-term follow-up analysis of patients enrolled in boceprevir phase 2/3 studies. No treatment was administered during follow-up. Patients with SVR were assessed for durability of viral eradication. Non-SVR patients with on-treatment resistance-associated variants (RAVs) were assessed for longevity of RAVs. A total of 1148 patients (SVR, n = 696; virologic failure, n = 452) were enrolled in this follow-up analysis. The median duration of follow-up was approximately 3.4 years (range of 0.0–4.1 years). Overall, 3 of 696 patients with SVR had detectable HCV RNA during the follow-up period (relapse rate of 0.4% or 1.3 relapses/1000 person-years). The majority of patients who developed RAVs during the initial treatment study (228/314, 73%) reverted to wild-type (WT) within 3 years (RAVs persisted in 27% of patients). The median time for all RAVs to become undetectable was 1.11 years (95% confidence interval 1.05– 1.20 years). V36M, T54A, A156S, I/V170A, and V36M + R155K appeared to have a faster rate of return to WT (median times to return to WT of 60.9 years); whereas, T54S, R155K, V55A and T54S + R155K had a slower rate of return to WT (median times to return to WT of approximately 1.1 years). Return to WT appeared slightly faster in patients with G1b RAVs compared to those with G1a RAVs, and in patients with previous non-response or relapse versus breakthrough or incomplete virologic response. SVR was durable in most patients treated with boceprevir. Furthermore, most RAVs present at the time of virologic failure reverted to WT over time. Time to return to WT was associated with the phenotype of RAV, presumably a reflection of the fitness of the mutant virus, suggesting that HCV RAVs are not permanently archived, but are replaced in the viral population by WT virus. Ó 2014 Published by Elsevier B.V.
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1. Introduction Boceprevir is a hepatitis C virus (HCV) non-structural (NS) 3/4A protease inhibitor approved for treatment of patients with genotype (G) 1 chronic HCV infection. In phase 2 and 3 clinical ⇑ Corresponding author at: Merck Research Laboratory, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA. Tel.: +1 908 740 3050; fax: +1 908 740 4780. E-mail addresses: [email protected] (A.Y.M. Howe), Jianmin.long@merck. com (J. Long), [email protected] (D. Nickle), [email protected] (R. Barnard), [email protected] (S. Thompson), [email protected] (J. Howe), [email protected] (K. Alves), [email protected] (J. Wahl). 1 Former employee of Merck.
trials, treatment with boceprevir combined with peginterferon alfa-2b and ribavirin (PR) was associated with marked viral suppression, and a significant increase in rates of sustained virologic response (SVR) at week 24 of follow-up compared to patients receiving PR alone (Bacon et al., 2011; Kwo et al., 2010; Poordad et al., 2011). While SVR is known to be durable in the vast majority of patients following treatment with interferon or peginterferon and ribavirin, (Marcellin et al., 1997; Manns et al., 2013; Rutter et al., 2013; Swain et al., 2010) the long-term outcomes of patients achiev- Q3 ing SVR following boceprevir-based therapy have not been reported. In patients receiving protease inhibitor-based therapies, development of resistance can contribute to treatment failure. In vitro
http://dx.doi.org/10.1016/j.antiviral.2014.10.010 0166-3542/Ó 2014 Published by Elsevier B.V.
Please cite this article in press as: Howe, A.Y.M., et al. Long-term follow-up of patients receiving boceprevir for treatment of chronic hepatitis C. Antiviral Res. (2014), http://dx.doi.org/10.1016/j.antiviral.2014.10.010
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studies have confirmed that while wild-type (WT) HCV is sensitive to boceprevir, variants of the virus containing amino acid substitutions can confer resistance to the drug (Barnard et al., 2013; Ogert et al., 2013; Tong et al., 2006, 2008). In the presence of boceprevir, these resistance-associated variants (RAVs) have a selection advantage over the WT virus, and in some patients have been associated with virologic failure (Ogert et al., 2013). In the boceprevir phase 3 studies, 53% of patients failing to achieve SVR had RAVs detected post-baseline (Barnard et al., 2013). However, in vitro studies have also shown that many boceprevir RAVs replicate poorly and are outgrown by WT virus in the absence of continued antiviral suppression (Shimakami et al., 2011). This study’s goal was to follow the clinical progression of patients treated with boceprevir after completing treatment in phase 2 and phase 3 clinical trials. Patients achieving a SVR were followed for durability of SVR, and patients with virologic failure and RAVs emerging during boceprevir treatment were monitored for longevity of RAVs and rate of return to WT virus.
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2. Methods
91
2.1. Study design
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This was a 3-year-long-term follow-up analysis of patients enrolled in boceprevir phase 2 (SPRINT-1 and RESPOND-1) and phase 3 studies (SPRINT-2 and RESPOND-2) (Kwo et al., 2010; Poordad et al., 2011; Bacon et al., 2011). All studies were carried out in accordance with the Declaration of Helsinki, current guidelines on Good Clinical Practices, and local ethical and legal requirements. All patients provided voluntary written informed consent before trial entry. The detailed methodology and primary outcomes from these studies have been published previously (NCT00423670 [SPRINT-1, Protocol P03523], NCT00708500 [RESPOND-2, Protocol P05101]; NCT00705432 [SPRINT-2, Protocol P05216], NCT00160251 [RESPOND-1, Protocol P03659]) (Kwo et al., 2010; Poordad et al., 2011; Bacon et al., 2011; Schiff et al., 2008).
72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88
93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
2.1.1. Patients Patients with HCV G1 infection and compensated liver disease were enrolled in the initial treatment studies. Patients from SPRINT-1 and -2 (who were previously untreated) and patients from RESPOND-1 and -2 (who previously received PR dual therapy) were offered enrolment into this follow-up study. Patients with human immunodeficiency virus (HIV) or hepatitis B virus co-infection, liver disease due to a non-HCV etiology, pre-existing psychiatric disease or uncontrolled diabetes were excluded. 2.1.2. Initial therapy Treatment regimens from each study have been reported in detail previously (Kwo et al., 2010; Poordad et al., 2011; Bacon et al., 2011; Schiff et al., 2008). The SPRINT-1, SPRINT-2 and RESPOND-2 studies included a lead-in treatment period with peginterferon alfa-2b (1.5 lg/kg/wk) plus ribavirin (800–1400 mg/d) for 4 weeks prior to initiating boceprevir (800 mg three times daily) in combination with PR. In SPRINT-1, patients received leadin or no lead-in PR treatment followed by boceprevir plus PR for 24 or 44 weeks (Kwo et al., 2010). The SPRINT-2 and RESPOND-2 studies included a fixed duration treatment arm consisting of boceprevir plus PR therapy for a 44-week period; and a response-guided therapy arm with treatment duration tailored according to on-treatment response. The maximum treatment duration in all 3 studies was 48 weeks. All 3 studies also included a control arm in which patients received PR for a standard 48 weeks. In RESPOND-1, patients received peginterferon for 1 week then boceprevir (100–400 mg TID) plus peginterferon in combination
with ribavirin or placebo for an additional 24 or 48 weeks. After completion of these treatment regimens, an additional treatment arm was enrolled in which patients received peginterferon for 1 week, followed by boceprevir (800 mg/d TID) plus peginterferon for a further 24 weeks. Subsequent observations of resistance development in patients not receiving ribavirin, and poor anti-HCV activity at lower boceprevir doses led to all patients being switched to treatment with boceprevir (800 mg TID) + PR for 24 weeks. All patients were followed for 24 weeks after completion of therapy and in all studies the primary end point was SVR, defined as undetectable HCV RNA at the end of follow-up. In SPRINT-1, SPRINT-2 and RESPOND-2 studies, HCV RNA samples were assayed using COBAS Taqman 2.0 (Roche, LLQ = 25 IU/mL and LLD = 9.3 IU/ mL). In RESPOND-1, HCV RNA samples were tested using a quantitative PCR Taqman assay at Schering-Plough (LLQ, 29 IU/mL) and confirmed using Roche COBAS Taqman (Quest Laboratories, LLQ 50 IU/mL).
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2.1.3. Long-term follow-up protocol No treatment was administered during this follow-up study. Patients with SVR following initial treatment were assessed for durability of viral eradication. In patients with recurrence of viral infection, phylogenetic techniques determined whether patients were re-infected with a different virus or had late relapse with the same virus lineage. The HCV NS3 sequences were codonaligned using the software package Muscle (Edgar, 2004) and a maximum likelihood tree from the codon alignment of the sequence data was estimated using PhyML with a general timereversible nucleotide model of evolution (Guindon et al., 2010). During follow-up, HCV RNA assessments were made every 3 months for 6 months and then every 6 months thereafter with sustained response defined as HCV RNA levels below limit of detection (COBAS Taqman v2.0). Non-SVR patients with on-treatment RAVs (RAVs emerging during treatment and persisting for at least 12 weeks following completion of treatment) were assessed for longevity of RAVs. In these patients, plasma samples were collected at baseline in the long-term follow-up study, and then at months 3, 6, 12, 18, 24, 30 and 36 months after completion of the initial treatment protocol. The HCV NS3/4A region was amplified from the resulting plasma samples, using standard RT-PCR techniques and analyzed by population sequencing, capable of detecting variants at a frequency of >20% in the viral population.
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2.1.4. Statistics Patients who achieved SVR following treatment with boceprevir/PR, and patients not achieving SVR and with on-treatment RAVs were included in this follow-up analysis. Patients with RAVs during treatment that returned to WT before the end of treatment were excluded. The long-term durability of SVR was studied by the distribution of time to relapse for all patients who were sustained responders at 24 weeks post-treatment in the previous studies, using Kaplan– Meier method. The rate of re-emergence of WT sequence for each boceprevir resistant variant, V36M, T54A, T54S, V55A, R155K, A156S and I/V170A, was calculated. Variants R155K + T54S and R155K + V36M were also studied as these pairings have been observed frequently in patients failing boceprevir therapy. The rate of return to WT at individual resistance locus was determined, treating each mutation independently and including only those positions that were WT at baseline. The Kaplan–Meier curves were plotted using all available data at the time of database cutoff (December 31, 2012). Because the populations with these RAVs are not randomized and not necessarily independent, no formal comparisons were performed for the behaviors of these RAVs.
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Please cite this article in press as: Howe, A.Y.M., et al. Long-term follow-up of patients receiving boceprevir for treatment of chronic hepatitis C. Antiviral Res. (2014), http://dx.doi.org/10.1016/j.antiviral.2014.10.010
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A.Y.M. Howe et al. / Antiviral Research xxx (2014) xxx–xxx Table 1 Duration of follow-up in patients who received boceprevir during phase 2 and 3 clinical trials. Patients with non-SVRa
Patients with SVR
SPRINT-1 SPRINT-2b RESPOND-1 RESPOND-2c All
N
Duration of follow-up median (range)
N
Duration of follow-up median (range)
240 294 20 142 696
3.4 3.4 3.5 3.4 3.4
21 92 167 34 314d
3.3 1.0 3.5 3.2 3.3
(CI (CI (CI (CI (CI
0.5–4.1) 0.7–3.9) 2.5–4.0) 0.7–3.8) 0.5–4.1)
(CI (CI (CI (CI (CI
0.7–3.8) 0.0–3.9) 0.5–4.1) 0.1–4.1) 0.0–4.1)
CI, confidence interval; RAV, resistance-associated variant; SVR, sustained virologic response. a Includes only patients enrolled in long-term follow-up and with on-treatment RAVs. b Includes 135 patients that remain in active follow-up (8 non-SVR and 127 SVRs). c Includes 65 patients that remain in active follow-up (7 non-SVR and 58 SVRs). d Includes 68 patients who were followed for the end of their treatment period but did not enroll in this long-term follow-up protocol.
Table 2 List of patients with SVR and detectable HCV RNA during follow-up. Previous trial
Patient
Genotype at original study
End of treatment date
Last PCR negative date
First PCR positive date
Genotype at follow-up
Viral load (IU/mL) at PCR positive date
SPRINT-1 SPRINT-2 SPRINT-2 SPRINT-2
001 002 003 004
GT1a GT1b GT1b GT1a
11–19–2007 11–11–2009 10–16–2009 10–02–2009
05–27–2008 04–29–2010 04–07–2010 05–11–2011
06–23–2009 07–01–2010 11–19–2010 08–10–2011
GT1b GT1b GT1b GT1a
1,580,000 113,000 1,190,000 TD(u)
HCV, hepatitis C virus; PCR, polymerase chain reaction; RNA, ribonucleic acid; SVR, sustained virologic response; TD(u), HCV RNA target detected, unquantifiable (<25 IU/mL).
100%
Probability of Retaining a RAV
90% V36M T54A T54S R155K A156S R155K + T54S R155K + V36M I/V170A ALL
80% 70% 60% 50% 40% 30% 20% 10% 0% FU D1
4M
8M
1Y
152 45 150 189 37 85 125 25 314
112 23 131 175 30 72 91 14 284
91 14 111 150 25 62 62 11 247
53 9 84 104 14 46 30 3 173
V36M T54A T54S R155K A156S R155K + T54S R155K + V36M I/V170A ALL
1Y4M 1Y8M 2Y 2Y4M 2Y8M Time Since the End of Treatment
3Y
3Y4M
3Y8M
20
11
8
7
4
2
2
56 66 5 30 8 2 107
44 46 4 21 2 1 81
36 34 4 19
34 30 4 17
31 27 1 15
24 23 1 12
20 15 1 10
4 5 1 2
1 63
1 58
1 50
1 40
1 27
7
4Y
Fig. 1. Probability of retaining a resistance-associated variant. Patients with first RAVs detected during treatment + 12 weeks in follow-up were included. Patients with ontreatment RAVs returned to WT before FU day 1 were excluded. Phase 2 and phase 3 studies included. V55A excluded due to low patient numbers with this variant.
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3. Results
198
At the time of database cut-off, 1148 patients (SVR, n = 696; virologic failure, n = 452) who had received boceprevir during the original treatment study were enrolled in this follow-up analysis
199 200
(Table 1). In total, 314 of the 452 patients with virologic failure had sequence data available and are included in the analysis of RAV longevity. The median duration of follow-up was 3.4 years (range of 0.5–4.1 years) in patients with SVR and 3.3 years (range of 0.0–4.1 years) in patients without SVR.
Please cite this article in press as: Howe, A.Y.M., et al. Long-term follow-up of patients receiving boceprevir for treatment of chronic hepatitis C. Antiviral Res. (2014), http://dx.doi.org/10.1016/j.antiviral.2014.10.010
201 202 203 204 205
4
a
V36M
T54A
T54S
V55A
R155K
R155K + T54S
R155K + V36M
A156S
I/V170A
ALL
7/9 (77.8)
143/189 (75.7)
65/85 (76.5)
118/125 (94.4)
34/37 (91.9)
24/25 (96.0)
228/314 (72.6)
All patients WT within 3 years, n/N (%) Rate of return to WT per 100-PYs (95% CI), in 3 years Median time to return to WT, y (95% CI)
138/152 (90.8)
44/45 (97.8)
107/150 (71.3)
110.7 (93.7, 130.8)
203.1 (151.3, 272.6)
52.6 (43.5, 63.5) 56.1 (27.2, 115.8) 58.7 (49.8, 69.2) 59.6 (46.8, 76.0) 143.5 (119.9, 171.9)
96.2 (68.8, 134.4) 190.7 (128.2, 283.8)
55.6 (48.9, 63.3)
0.89 (0.74, 0.96)
0.46 (0.25, 0.49)
1.12 (1.01, 1.42) 1.09 (0.08)b
1.08 (1.02, 1.20) 1.07 (0.91, 1.33) 0.69 (0.49, 0.84)
0.90 (0.70, 1.05)
1.11 (1.05, 1.20)
Genotype 1a WT within 3 years, n/N (%) Rate of return to WT per 100-PYs (95% CI), in 3 years Median time to return to WT, y (95% CI)
136/149 (91.3) 110.4 (93.4, 130.6) 0.89 (0.74, 0.98)
12/13 (92.3) 334.8 (191.5, 585.2) 0.23 (0.08, 0.46)
61/88 (69.3) 0/1 (0) 50.9 (39.6, 65.4) 0.0 (0.0, 128.0)
140/185 (75.7) 62/81 (76.5) 117/124 (94.4) 58.8 (49.8, 69.4) 59.8 (46.7, 76.7) 143.8 (120.0, 172.3) 1.08 (1.02, 1.22) 1.05 (0.90, 1.33) 0.69 (0.49, 0.86)
10/11 (90.9) 0/0 91.4 (49.7, 168.3) n/a
Genotype 1b WT within 3 years, n/N (%) Rate of return to WT per 100-PYs (95% CI), in 3 years Median time to return to WT, y (95% CI)
2/3 (66.7) 134.8 (37.0, 491.6) 0.83 (0.11, 0.83)
32/32 (100) 177.0 (125.4, 249.8) 0.47 (0.26, 0.90)
46/62 (74.2) 7/8 (87.5) 3/4 (75.0) 55.0 (41.3, 73.4) 73.9 (35.8, 152.5) 55.2 (18.8, 162.2) 1.11 (0.90, 1.58) 1.08 (0.08, 2.58) 1.10 (0.23)b
RESPOND-1 WT within 3 years, n/N (%) Rate of return to WT per 100-PYs (95% CI), in 3 years Median time to return to WT, y (95% CI)
79/80 (98.8) 113.2 (90.8, 141.1) 0.77 (0.48, 1.02)
24/24 (100) 305.6 (205.4, 454.8) 0.26 (0.13, 0.44)
81/113 (71.7) 2/4 (50) 51.7 (41.6, 64.2) 23.1 (6.3, 84.2)
SPRINT-2 and RESPOND-2 WT within 3 years, n/N (%) 45/57 (78.9) 18/19 (94.7) Rate of return to WT per 100-PYs 97.4 (72.8, 130.3) 135.5 (85.7, 214.2) (95% CI), in 3 years Median time to return to 0.91 (0.87, 1.00) 0.90 (0.46, 1.04) WT, y (95% CI)
1.14 (0.92, 1.45) n/a
3/4 (75) 55.2 (18.8, 162.2) 1.10 (0.23)b
0.92 (0.32, 1.11)
0.46 (0.24, 0.75)
n/a
1/1 (100) 24/26 (92.3) 24/25 (96.0) 120.0 (21.2, 679.8) 98.3 (66.1, 146.3) 190.7 (128.2, 283.8) 0.83 0.89 (0.52, 1.05) 0.46 (0.24, 0.75)
1.18 (0.92, 1.52) (0.08)b
79/106 (74.5) 48/63 (76.2) 72/72 (100) 48.7 (39.1, 60.7) 57.3 (43.3, 76.0) 164.9 (130.9, 207.6) 1.40 (1.05, 1.55) 1.07 (0.80, 1.45) 0.47 (0.46, 0.51)
16/18 (88.9) 13/14 (92.9) 92.5 (57.0, 150.3) 256.8 (150.1, 439.4) 0.69 (0.26, 1.05) 0.25 (0.14, 0.50)
21/28 (75.0) 67.8 (44.3, 103.6) 0.95 (0.90, 1.12)
54/70 (77.1) 82.8 (63.5, 108.0) 0.96 (0.90, 1.02)
15/16 (93.8) 102.5 (62.1, 169.1) 0.92 (0.88, 1.09)
5 /5 (100) 131.0 (56.0, 306.7) 1.07 (0.08, 1.12)
PY, patient year; RAV, resistance-associated variants; WT, wild type. a ALL = RAV detected at boceprevir resistance-associated loci (positions V36, T54, V55, R155, A156, V170 or M175).
10/14 (71.4) 35/41 (85.4) 64.0 107.6 (77.3, 149.6) (34.7, 117.8) 0.91 (0.88, 1.12) 0.90 (0.86, 1.00)
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Boceprevir resistance-associated variants
162/230 (70.4) 52.4 (44.9, 61.1) 1.17 (1.07, 1.34) 66/84 (78.6) 65.6 (51.6, 83.5) 1.04 (0.89, 1.12) 119/167 (71.3) 44.7 (37.4, 53.5) 1.45 (1.22, 1.67)
9/9 (100) 94/126 (74.6) 136.2 (71.7, 258.9) 81.4 (66.6, 99.7) 0.88 (0.07, 0.90) 0.95 (0.90, 1.02)
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Q6
Table 3 Longevity of boceprevir resistance-associated variants according to baseline characteristics and treatment.
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(A)
1.4 1.2 1 0.8 0.6 n=314
n=150
n=9
All RAVs
T54S
V55A
0.4
n=189
n=85
n=37
n=152
R155K R155K+ A156S T54S
n=45
n=25
n=125
V36M R155K+ I/V170A V36M
T54A
(B)
1.6 1.4 1.2 1 0.8 0.6
-re
R
el
on
ap
de
R
r
se
n=27
on
ea
kt
sp
hr
ou
IV
gh
1b
n=60
N
R &
n=165
SP
R
IN
T2
Br
PO ES
ES R
n=62
n=84
G
N PO
n=230
1a
-2
D
nt ie at lP Al
n=126
-1
s
n=167
G
n=314
0.4
D
Median time to return to WT (y)
1.8
N
Median time to return to WT (y)
1.6
Fig. 2. Median time to return to WT virus for (A) individual variants in all patients and (B) for all variants in selected patient subgroups. G = genotype; IVR = incomplete virologic response; error bars indicate 95% confidence intervals.
206
3.1. Durability of SVR
207
In total, 4 of 696 (0.6%) patients who achieved SVR following the original clinical trial had detectable HCV RNA during the follow-up period (Table 2). One patient (#001) was infected with GT1a at entry into the original study but had G1b infection at the time of relapse in the follow-up analysis (about 19 months after completing initial treatment). Phylogenetic analysis indicated that the viruses detected prior to treatment and during long-term followup were phylogenetically distinct, suggesting that this patient may have acquired a new infection after SVR was achieved during the original study. A second patient had detectable but not quantifiable HCV RNA (<25 IU/mL) during long-term follow-up, approximately 2.5 years after completing treatment and attaining SVR (#004). Per protocol, this patient was categorized as having experienced viral relapse. The remaining 2 patients had ‘‘true’’ late relapse. Thus, of the 4 patients with detectable HCV RNA during follow-up, 1 patient possibly had HCV re-infection (#001) and the remaining 3 were considered to have late viral relapse (although in these latter 3 patients, re-infection with virus from the same lineage present at baseline cannot be excluded). These data translate into a relapse rate of 0.4% or 1.3 relapses/1000 person-years (total follow-up time was 2227.2 years). (A phylogenetic tree of the 4 patients with detectable HCV RNA during follow-up is shown in the Supplementary Appendix.)
208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232
3.1.1. Natural history of RAVs during long-term follow-up This analysis includes data from 314 boceprevir-treated patients who developed RAVs during the initial treatment study.
73.0
Non-response
68.1
Relapse
52.7
Incomplete virologic resonse
46.6
Breakthrough
0
10
20
30
40
50
60
70
80
Rate of return to WT per 100-Pys in 3 Years
Fig. 3. Rate of return to WT according to type of virologic failure.
Most patients had multiple different RAVs. The majority (n = 228, 73%) reverted to WT within 3 years post-therapy and no longer had RAVs detectable by population sequencing. The median time for all RAVs to become undetectable was 1.11 (95% confidence interval [CI] 1.05–1.20) years (Fig. 1 and Table 3). Eighty-six patients had RAVs detected at their last tested time point during follow-up. Forty patients with detectable RAVs at their last test had completed the 3-year follow-up and were confirmed with detectable RAVs at boceprevir resistance-associated loci; 16 patients had discontinued from the study prior to reaching 3 years of participation with detectable RAVs at their last visit; and
Please cite this article in press as: Howe, A.Y.M., et al. Long-term follow-up of patients receiving boceprevir for treatment of chronic hepatitis C. Antiviral Res. (2014), http://dx.doi.org/10.1016/j.antiviral.2014.10.010
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B. Genotype 1b
100%
100%
90%
90%
80%
80%
Probability of Retaining a RAV
Probability of Retaining a RAV
A. Genotype 1a
70% 60% 50% 40% 30%
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10%
10%
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8M
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1Y4M 1Y8M 2Y 2Y4M 2Y8M Time Since the End of Treatment
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80%
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90%
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50% 40% 30% 20% 10%
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1Y4M
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10%
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1Y
70%
20%
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8M
D. Phase 3 Studies
100%
0% FU D1
4M
Time Since the End of Treatment
C. Phase 2 Studies
Probability of Retaining a RAV
70%
20%
0% FU D1
V36M T54A T54S R155K A156S R155K + T54S R155K + V36M I/V170A ALL
1Y4M 1Y8M 2Y 2Y4M 2Y8M Time Since the End of Treatment
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0% FU D1
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Fig. 4. Probability of retaining a resistance-associated variant in selected patient subgroups according to genotype (A and B) or enrollment in phase 2 or phase 3 studies (C and D). Patients with first RAVs detected during treatment + 12 weeks in follow-up were included. Patients with on-treatment RAVs returned to WT before FU day 1 were excluded. Phase 2 and phase 3 studies included.
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the remaining 30 patients had detectable RAV at their last clinic visit but had not yet completed 3-years of follow-up (ie, monitoring was ongoing). 3.1.2. All patients The rate of return to WT varied across different RAVs (Figs. 1 and 2A) allowing RAVs to be broadly grouped into two categories according to median time to return to WT. Variants V36M, T54A, A156S, I/V170A, and V36M + R155K appeared to have a faster rate of return to WT, with median times to return to WT of 60.9 years. In contrast, variants T54S, R155K, V55A and T54S + R155K had a slower rate of return to WT, with median times to return to WT of approximately 1.1 years (Fig. 2A). Overall, 98% of T54A, 96% of I/V170A, 94% of R155K + V36M, 92% of A156S, 91% of V36M, 76% of T54S + R155K, 76% of R155K and 71% of T54S variants were undetectable by population sequencing after 3 years of follow-up (Table 3). 3.1.3. HCV genotype 1 subtype Return to WT appeared slightly faster in patients with G1b RAVs compared to those with G1a RAVs (Table 3), with median time to return to WT of 1.04 years (95% CI 0.89–1.12) and 1.17 years (95% CI 1.07–1.34), respectively. Among patients with G1a infection, the most common RAVs were V36M (n = 149), R155K (n = 185), and T54S (n = 88); also commonly occurring in pairs as R155K + V36M (n = 124) and R155K + T54S (n = 81). T54A and
V36M were associated with the fastest time to return to WT (T54A 0.23 years [95% CI 0.08–0.46], V36M 0.89 years [95% CI 0.74–0.98], R155K + V36M, 0.69 years [95% CI 0.49–0.86]) (Table 3; Fig. 4). In contrast, the most common RAVs in patients with G1b infection were T54S (n = 62), T54A (n = 32), A156S (n = 26), and I/V170A (n = 25). Among RAVs detected in patients with G1b infection, T54A and I/V170A were associated with the fastest median time to revert to WT (0.47 [95% CI 0.26–0.90] and 0.46 years [95% CI 0.24–0.75], respectively) (Table 3). Overall, at 3 years post-therapy, 70% of patients with G1a and 79% of those with G1b had undetectable RAVs by population sequencing.
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3.1.4. Virologic failure Profile of virologic failure during initial therapy was also associated with varying rates of return to WT (Fig. 2B). Patients with breakthrough or incomplete virologic response tended to have a slower return to WT (median times to return to WT were 1.22 years [95% CI 0.1.02–1.70], 1.17 years [95% CI 1.06–1.35], respectively); whereas, patients with non-response2 or relapse showed a faster return to WT; (medians of 0.95 years [95% CI 0.89–1.11] and 0.58 years [95% CI 0.45–1.55], respectively). Rate of return to WT per 100 patient years within 3 years was 68% among patients with relapse, 73% in those with non-response, 53% in those
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2 Non-responder population includes patients who discontinued because of adverse event, and who may have had largely WT virus.
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Breakthrough (N = 62), n (%) Incomplete viral response (N = 165), n (%) Relapse (N = 27), n (%) Non-responder (N = 60), n (%)
V36M
T54A
T54S
V55A
R155K
R155K + T54S
R155K + V36M
A156S
I/V170A
ALLa
35 (56%) 77 (47%)
4 (6%) 28 (17%)
30 (48%) 95 (58%)
4 (6%) 5 (3%)
39 (63%) 108 (65%)
19 (31%) 53 (32%)
28 (45%) 72 (44%)
8 (13%) 22 (13%)
2 (3%) 18 (11%)
62 (100%) 165 (100%)
6 (22%) 34 (57%)
7 (26%) 6 (10%)
10 (37%) 15 (25%)
0 (0%) 0 (0%)
7 (26%) 35 (58%)
4 (15%) 9 (15%)
3 (11%) 22 (37%)
2 (7%) 5 (8%)
3 (11%) 2 (3%)
27 (100%) 60 (100%)
Breakthrough: detectable HCV RNA after previous undetectable HCV RNA; Incomplete virologic response: >1.5 log decline from baseline but failure to attain undetectable HCV RNA; Relapse: undetectable HCV RNA at end of treatment followed by subsequent detectable HCV RNA during follow-up; Nonresponder: <1.5 log decline in HCV RNA from baseline. a ALL = RAV detected at boceprevir resistance-associated loci (positions V36, T54, V55, R155, A156, V170 or M175).
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with incomplete virologic response, and 47% in those with breakthrough (Fig. 3). The distribution of T54S, R155K and R155K + T54S was more prevalent in patients who had breakthrough and incomplete virologic response than those who experienced relapse and non-response. Because T54S, R155K and T54S + R155K are slow to return to WT, in patients who had breakthrough or incomplete virologic response, this might account for the slower re-emergence of WT virus in these groups (Table 4).
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3.1.5. Phase 2 versus phase 3 studies Patients in the phase 3 SPRINT-2 and RESPOND-2 studies exhibited a faster return to WT compared to patients treated in the RESPOND-1 study, most of whom received doses of boceprevir lower than the currently approved dose (doses of boceprevir in RESPOND-1 were 100–800 mg/d TID) (Table 3, Fig. 4). The rate of return to WT per 100-person years was 44.7 in the RESPOND-1 trial compared to 81.4 in the phase 3 studies. The large distribution of T54S (113/167, 68%) in RESPOND-1 might have contributed to the slower overall reversion rate of RAVs in the RESPOND-1 trial.
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4. Discussion
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SVR is universally accepted as the gold standard end point for evaluation of treatments for HCV infection. Data from the present study confirm that SVR is durable in the vast majority of patients treated with boceprevir, and can be considered a surrogate for viral eradication. Re-emergence of virus in patients who attained SVR occurred at a rate of 1.3 relapses/1000 person-years. Furthermore, one patient in the present study had detectable but unquantifiable HCV RNA during follow-up and was classified as having relapse, per protocol; however, it is unclear whether this result represents bona fide late viral relapse, versus a false positive assay reading. According to the United States Food and Drug Administration (FDA), transient detectable but unquantifiable HCV RNA during follow-up most likely represents a false-positive HCV RNA reading, and under FDA criteria, this patient would be considered to have enduring SVR (Harrington et al., 2012). RAVs that arise during therapy with HCV protease inhibitors have the potential to precipitate virologic failure (Ogert et al., 2013). However, RAVs also have impaired replicative fitness compared to WT virus (Tong et al., 2006; Susser et al., 2009) and thus when pharmacologic pressure is relieved, a gradual resurgence in WT virus is typically paralleled by a decline in the RAV population. The rate of return to WT was independent of baseline viral load or lead-in response in the primary studies (data not shown). In the boceprevir phase 3 studies, the rate of return to WT virus was 0.95 years compared to 1.1 years in the combined phase 2 and phase 3 study populations. With regard to genotype subtype, clinically SVR rates are generally higher in patients with G1b infection compared to those with G1a infection (Poordad et al., 2012).
Time to return to WT for each RAV in the present study is generally consistent with data from patients receiving telaprevir (Sullivan et al., 2013). Median times to return to WT in boceprevir-treated patients from SPRINT-2 and RESPOND-2 were broadly similar to those reported in follow-up studies from the phase 3 telaprevir clinical trials (V36M, 11.9 vs 9.3 months; T54S, 11.4 vs 11.5 months; R155K, 11.5 vs 9.8 months; A156S, 11.0 vs 6.7 months) (Sullivan et al., 2013). Median times to return to WT in patients with G1a and G1b infection were 14 months and 12.5 months with boceprevir and 10.6 months and 0.9 months with telaprevir (Sullivan et al., 2013). In addition to causing drug resistance, departure from the WT genotype can impact viral replicative fitness. Variants that display relatively unaffected replicative fitness in vitro may be expected to endure longer within the HCV population; whereas, variants with poor replicative fitness may exhibit a more rapid return to WT. This theory implies a correlation between in vitro replicative fitness and rate of return to WT; however, establishing consistent correlations in this regard has proved challenging. For example, in vitro studies indicate the V36M and I170A variants retain >90% relative fitness compared with WT (Shimakami et al., 2011), yet our data indicate these variants have a relatively rapid return to WT, consistent with poor replicative fitness relative to WT. Conversely, R155K has approximately 50% replicative fitness compared with WT in vitro (Shimakami et al., 2011); however, in our studies R155K had a slow return to WT. Other examples however, support a correlation between in vitro replicative fitness and rate of return to WT: A156S shows >50% impaired replication in vitro (Lenz et al., 2010) and demonstrated a rapid return to WT in the present study. Further study is required to identify additional factors that may affect the frequency of selection and clinical durability of resistant variants, and the relevance of in vitro replicative fitness. There are some limitations to the present analysis. The population sequencing techniques used in the present study are capable of detecting RAVs at a frequency of >20% in the circulating viral population but do not permit analysis of RAVs at lower levels. The clinical implications of RAVs enduring at levels <20% of the total viral population are therefore unclear. In addition, there are limited numbers of patients with certain RAVs (e.g., V55A, n = 9), or within particular patient subgroups (e.g., relapse, n = 27) restricting the interpretation of data from these groups.
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5. Conclusions
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SVR was durable in most patients treated with boceprevir plus PR, with only rare instances of late relapse. Furthermore, most RAVs present at the time of virologic failure reverted to WT over time, with a median time to WT of approximately 1.1 years. Time to return to WT was associated with the phenotype of RAV, presumably a reflection of the fitness of the mutant virus.
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Conflict of interest
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All of the authors are employees of Merck & Co., Inc. or of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., except for Dr. Alves, who is a former employee of Merck Sharp & Dohme Corp., and remains a stockholder in that company. Additionally, Drs. Wahl, Barnard and Thompson are stockholders of Merck & Co., Inc. The authors have no other conflicts to disclose.
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Acknowledgments
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Q4 The studies described in this analysis were funded by Merck & Q5 Co., Inc., Whitehouse Station, NJ, USA, and all authors were employees of Merck at the time when the research was conducted. The authors were involved in study design; data collection, analysis and interpretation; and in the writing of this report. Medical writing and editorial assistance was provided by Tim Ibbotson, PhD of ApotheCom (Yardley, PA, USA). This assistance was funded by Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Whitehouse Station, NJ, USA.
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Appendix A. Supplementary data
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Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.antiviral.2014.10. 010.
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References
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Bacon, B., Gordon, S.C., Lawitz, E., et al., 2011. Boceprevir for previously treated chronic HCV genotype 1 infection. N. Engl. J. Med. 364, 1207–1217. Barnard, R.J., Howe, J.A., Ogert, R.A., et al., 2013. Analysis of boceprevir resistance associated amino acid variants (RAVs) in two phase 3 boceprevir clinical studies. Virology 444, 329–336. Edgar, R.C., 2004. MUSCLE: a multiple sequence alignment method with reduced time and space complexity. BMC Bioinformatics 5, 113. Guindon, S., Dufayard, J.F., Lefort, V., Anisimova, M., Hordijk, W., Gascuel, O., 2010. New algorithms and methods to estimate maximum-likelihood phylogenies: assessing the performance of PhyML 3.0. Syst. Biol. 59, 307–321.
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Harrington, P.R., Zeng, W., Naeger, L.K., 2012. Clinical relevance of detectable but not quantifiable hepatitis C virus RNA during boceprevir or telaprevir treatment. Hepatology 55, 1048–1057. Kwo, P.Y., Lawitz, E.J., McCone, J., et al., 2010. Efficacy of boceprevir, an NS3 protease inhibitor, in combination with peginterferon alfa-2b and ribavirin in treatmentnaive patients with genotype 1 hepatitis C infection (SPRINT-1): an open-label, randomised, multicentre phase 2 trial. Lancet 376, 705–716. Lenz, O., Verbinnen, T., Lin, T.I., et al., 2010. In vitro resistance profile of the hepatitis C virus NS3/4A protease inhibitor TMC435. Antimicrob. Agents Chemother. 54, 1878–1887. Manns, M.P., Pockros, P.J., Norkrans, G., et al., 2013. Long-term clearance of hepatitis C virus following interferon alpha-2b or peginterferon alpha-2b, alone or in combination with ribavirin. J. Viral Hepat. 20, 524–529. Marcellin, P., Boyer, N., Gervais, A., et al., 1997. Long-term histologic improvement and loss of detectable intrahepatic HCV RNA in patients with chronic hepatitis C and sustained response to interferon-alpha therapy. Ann. Intern. Med. 127, 875–881. Ogert, R.A., Howe, J.A., Vierling, J.M., et al., 2013. Resistance-associated amino acid variants associated with boceprevir plus pegylated interferon-alpha2b and ribavirin in patients with chronic hepatitis C in the SPRINT-1 trial. Antiviral Ther. 18, 387–397. Poordad, F., Bronowicki, J.P., Gordon, S.C., et al., 2012. Factors that predict response of patients with HCV Infection to boceprevir. Gastroenterology 143, 608–618. Poordad, F., McCone, J., Bacon, B.R., et al., 2011. Boceprevir for untreated chronic HCV genotype 1 infection. N. Engl. J. Med. 364, 1195–1206. Rutter, K., Hofer, H., Beinhardt, S., et al., 2013. Durability of SVR in chronic hepatitis C patients treated with peginterferon-a2a/ribavirin in combination with a direct-acting antiviral. Aliment. Pharmacol. Ther. 38, 118–123. Schiff, E., Poordad, F., Jacobson, I., et al., 2008. Boceprevir (b) combination therapy in null responders (NR): response dependent on interferon responsiveness. J. Hepatol. 48 (Suppl. 2), S46. Shimakami, T., Welsch, C., Yamane, D., et al., 2011. Protease inhibitor-resistant hepatitis C virus mutants with reduced fitness from impaired production of infectious virus. Gastroenterology 140, 667–675. Sullivan, J.C., De Meyer, S., Bartels, D.J., et al., 2013. Evolution of treatment-emergent resistant variants in telaprevir phase 3 clinical trials. Clin. Infect. Dis. 57, 221– 229. Susser, S., Welsch, C., Wang, Y., et al., 2009. Characterization of resistance to the protease inhibitor boceprevir in hepatitis C virus-infected patients. Hepatology 50, 1709–1718. Swain, M.G., Lai, M.Y., Shiffman, M.L., et al., 2010. A sustained virologic response is durable in patients with chronic hepatitis C treated with peginterferon alfa-2a and ribavirin. Gastroenterology 139, 1593–1601. Tong, X., Bogen, S., Chase, R., et al., 2008. Characterization of resistance mutations against HCV ketoamide protease inhibitors. Antiviral Res. 77, 177–185. Tong, X., Chase, R., Skelton, A., Chen, T., Wright-Minogue, J., Malcolm, B.A., 2006. Identification and analysis of fitness of resistance mutations against the HCV protease inhibitor SCH 503034. Antiviral Res. 70, 28–38.
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Contents lists available at ScienceDirect
Antiviral Research journal homepage: www.elsevier.com/locate/antiviral 5 6
Long-term follow-up of patients receiving boceprevir for treatment of chronic hepatitis C
3 4 7
Q1
8 9 10 11 12 13 1 2 5 7 16 17 18 19 20 21 22 23 24 25 26
Anita Y.M. Howe a,⇑, Jianmin Long a, David Nickle b,c, Richard Barnard a, Seth Thompson a, John Howe a, Katia Alves a,1, Janice Wahl a a
Q2
b c
Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA Department of Genetics, Merck Research Laboratories, Whitehouse Station, NJ, USA Department of Pharmacogenomics, Merck Research Laboratories, Whitehouse Station, NJ, USA
a r t i c l e
i n f o
Article history: Received 4 August 2014 Revised 3 October 2014 Accepted 16 October 2014 Available online xxxx Keywords: Boceprevir Hepatitis C Resistance Relapse
a b s t r a c t The durability of sustained virologic response (SVR) following boceprevir-based therapy in patients with hepatitis C virus (HCV) infection has not been reported. Furthermore, in patients receiving protease inhibitor-based therapies, development of resistance can contribute to treatment failure. The aim of the present study was to follow the clinical progression of patients treated with boceprevir after treatment in phase 2/3 clinical trials. This was a 3-year, long-term follow-up analysis of patients enrolled in boceprevir phase 2/3 studies. No treatment was administered during follow-up. Patients with SVR were assessed for durability of viral eradication. Non-SVR patients with on-treatment resistance-associated variants (RAVs) were assessed for longevity of RAVs. A total of 1148 patients (SVR, n = 696; virologic failure, n = 452) were enrolled in this follow-up analysis. The median duration of follow-up was approximately 3.4 years (range of 0.0–4.1 years). Overall, 3 of 696 patients with SVR had detectable HCV RNA during the follow-up period (relapse rate of 0.4% or 1.3 relapses/1000 person-years). The majority of patients who developed RAVs during the initial treatment study (228/314, 73%) reverted to wild-type (WT) within 3 years (RAVs persisted in 27% of patients). The median time for all RAVs to become undetectable was 1.11 years (95% confidence interval 1.05– 1.20 years). V36M, T54A, A156S, I/V170A, and V36M + R155K appeared to have a faster rate of return to WT (median times to return to WT of 60.9 years); whereas, T54S, R155K, V55A and T54S + R155K had a slower rate of return to WT (median times to return to WT of approximately 1.1 years). Return to WT appeared slightly faster in patients with G1b RAVs compared to those with G1a RAVs, and in patients with previous non-response or relapse versus breakthrough or incomplete virologic response. SVR was durable in most patients treated with boceprevir. Furthermore, most RAVs present at the time of virologic failure reverted to WT over time. Time to return to WT was associated with the phenotype of RAV, presumably a reflection of the fitness of the mutant virus, suggesting that HCV RAVs are not permanently archived, but are replaced in the viral population by WT virus. Ó 2014 Published by Elsevier B.V.
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1. Introduction Boceprevir is a hepatitis C virus (HCV) non-structural (NS) 3/4A protease inhibitor approved for treatment of patients with genotype (G) 1 chronic HCV infection. In phase 2 and 3 clinical ⇑ Corresponding author at: Merck Research Laboratory, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA. Tel.: +1 908 740 3050; fax: +1 908 740 4780. E-mail addresses: [email protected] (A.Y.M. Howe), Jianmin.long@merck. com (J. Long), [email protected] (D. Nickle), [email protected] (R. Barnard), [email protected] (S. Thompson), [email protected] (J. Howe), [email protected] (K. Alves), [email protected] (J. Wahl). 1 Former employee of Merck.
trials, treatment with boceprevir combined with peginterferon alfa-2b and ribavirin (PR) was associated with marked viral suppression, and a significant increase in rates of sustained virologic response (SVR) at week 24 of follow-up compared to patients receiving PR alone (Bacon et al., 2011; Kwo et al., 2010; Poordad et al., 2011). While SVR is known to be durable in the vast majority of patients following treatment with interferon or peginterferon and ribavirin, (Marcellin et al., 1997; Manns et al., 2013; Rutter et al., 2013; Swain et al., 2010) the long-term outcomes of patients achiev- Q3 ing SVR following boceprevir-based therapy have not been reported. In patients receiving protease inhibitor-based therapies, development of resistance can contribute to treatment failure. In vitro
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studies have confirmed that while wild-type (WT) HCV is sensitive to boceprevir, variants of the virus containing amino acid substitutions can confer resistance to the drug (Barnard et al., 2013; Ogert et al., 2013; Tong et al., 2006, 2008). In the presence of boceprevir, these resistance-associated variants (RAVs) have a selection advantage over the WT virus, and in some patients have been associated with virologic failure (Ogert et al., 2013). In the boceprevir phase 3 studies, 53% of patients failing to achieve SVR had RAVs detected post-baseline (Barnard et al., 2013). However, in vitro studies have also shown that many boceprevir RAVs replicate poorly and are outgrown by WT virus in the absence of continued antiviral suppression (Shimakami et al., 2011). This study’s goal was to follow the clinical progression of patients treated with boceprevir after completing treatment in phase 2 and phase 3 clinical trials. Patients achieving a SVR were followed for durability of SVR, and patients with virologic failure and RAVs emerging during boceprevir treatment were monitored for longevity of RAVs and rate of return to WT virus.
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2. Methods
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2.1. Study design
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This was a 3-year-long-term follow-up analysis of patients enrolled in boceprevir phase 2 (SPRINT-1 and RESPOND-1) and phase 3 studies (SPRINT-2 and RESPOND-2) (Kwo et al., 2010; Poordad et al., 2011; Bacon et al., 2011). All studies were carried out in accordance with the Declaration of Helsinki, current guidelines on Good Clinical Practices, and local ethical and legal requirements. All patients provided voluntary written informed consent before trial entry. The detailed methodology and primary outcomes from these studies have been published previously (NCT00423670 [SPRINT-1, Protocol P03523], NCT00708500 [RESPOND-2, Protocol P05101]; NCT00705432 [SPRINT-2, Protocol P05216], NCT00160251 [RESPOND-1, Protocol P03659]) (Kwo et al., 2010; Poordad et al., 2011; Bacon et al., 2011; Schiff et al., 2008).
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2.1.1. Patients Patients with HCV G1 infection and compensated liver disease were enrolled in the initial treatment studies. Patients from SPRINT-1 and -2 (who were previously untreated) and patients from RESPOND-1 and -2 (who previously received PR dual therapy) were offered enrolment into this follow-up study. Patients with human immunodeficiency virus (HIV) or hepatitis B virus co-infection, liver disease due to a non-HCV etiology, pre-existing psychiatric disease or uncontrolled diabetes were excluded. 2.1.2. Initial therapy Treatment regimens from each study have been reported in detail previously (Kwo et al., 2010; Poordad et al., 2011; Bacon et al., 2011; Schiff et al., 2008). The SPRINT-1, SPRINT-2 and RESPOND-2 studies included a lead-in treatment period with peginterferon alfa-2b (1.5 lg/kg/wk) plus ribavirin (800–1400 mg/d) for 4 weeks prior to initiating boceprevir (800 mg three times daily) in combination with PR. In SPRINT-1, patients received leadin or no lead-in PR treatment followed by boceprevir plus PR for 24 or 44 weeks (Kwo et al., 2010). The SPRINT-2 and RESPOND-2 studies included a fixed duration treatment arm consisting of boceprevir plus PR therapy for a 44-week period; and a response-guided therapy arm with treatment duration tailored according to on-treatment response. The maximum treatment duration in all 3 studies was 48 weeks. All 3 studies also included a control arm in which patients received PR for a standard 48 weeks. In RESPOND-1, patients received peginterferon for 1 week then boceprevir (100–400 mg TID) plus peginterferon in combination
with ribavirin or placebo for an additional 24 or 48 weeks. After completion of these treatment regimens, an additional treatment arm was enrolled in which patients received peginterferon for 1 week, followed by boceprevir (800 mg/d TID) plus peginterferon for a further 24 weeks. Subsequent observations of resistance development in patients not receiving ribavirin, and poor anti-HCV activity at lower boceprevir doses led to all patients being switched to treatment with boceprevir (800 mg TID) + PR for 24 weeks. All patients were followed for 24 weeks after completion of therapy and in all studies the primary end point was SVR, defined as undetectable HCV RNA at the end of follow-up. In SPRINT-1, SPRINT-2 and RESPOND-2 studies, HCV RNA samples were assayed using COBAS Taqman 2.0 (Roche, LLQ = 25 IU/mL and LLD = 9.3 IU/ mL). In RESPOND-1, HCV RNA samples were tested using a quantitative PCR Taqman assay at Schering-Plough (LLQ, 29 IU/mL) and confirmed using Roche COBAS Taqman (Quest Laboratories, LLQ 50 IU/mL).
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2.1.3. Long-term follow-up protocol No treatment was administered during this follow-up study. Patients with SVR following initial treatment were assessed for durability of viral eradication. In patients with recurrence of viral infection, phylogenetic techniques determined whether patients were re-infected with a different virus or had late relapse with the same virus lineage. The HCV NS3 sequences were codonaligned using the software package Muscle (Edgar, 2004) and a maximum likelihood tree from the codon alignment of the sequence data was estimated using PhyML with a general timereversible nucleotide model of evolution (Guindon et al., 2010). During follow-up, HCV RNA assessments were made every 3 months for 6 months and then every 6 months thereafter with sustained response defined as HCV RNA levels below limit of detection (COBAS Taqman v2.0). Non-SVR patients with on-treatment RAVs (RAVs emerging during treatment and persisting for at least 12 weeks following completion of treatment) were assessed for longevity of RAVs. In these patients, plasma samples were collected at baseline in the long-term follow-up study, and then at months 3, 6, 12, 18, 24, 30 and 36 months after completion of the initial treatment protocol. The HCV NS3/4A region was amplified from the resulting plasma samples, using standard RT-PCR techniques and analyzed by population sequencing, capable of detecting variants at a frequency of >20% in the viral population.
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2.1.4. Statistics Patients who achieved SVR following treatment with boceprevir/PR, and patients not achieving SVR and with on-treatment RAVs were included in this follow-up analysis. Patients with RAVs during treatment that returned to WT before the end of treatment were excluded. The long-term durability of SVR was studied by the distribution of time to relapse for all patients who were sustained responders at 24 weeks post-treatment in the previous studies, using Kaplan– Meier method. The rate of re-emergence of WT sequence for each boceprevir resistant variant, V36M, T54A, T54S, V55A, R155K, A156S and I/V170A, was calculated. Variants R155K + T54S and R155K + V36M were also studied as these pairings have been observed frequently in patients failing boceprevir therapy. The rate of return to WT at individual resistance locus was determined, treating each mutation independently and including only those positions that were WT at baseline. The Kaplan–Meier curves were plotted using all available data at the time of database cutoff (December 31, 2012). Because the populations with these RAVs are not randomized and not necessarily independent, no formal comparisons were performed for the behaviors of these RAVs.
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A.Y.M. Howe et al. / Antiviral Research xxx (2014) xxx–xxx Table 1 Duration of follow-up in patients who received boceprevir during phase 2 and 3 clinical trials. Patients with non-SVRa
Patients with SVR
SPRINT-1 SPRINT-2b RESPOND-1 RESPOND-2c All
N
Duration of follow-up median (range)
N
Duration of follow-up median (range)
240 294 20 142 696
3.4 3.4 3.5 3.4 3.4
21 92 167 34 314d
3.3 1.0 3.5 3.2 3.3
(CI (CI (CI (CI (CI
0.5–4.1) 0.7–3.9) 2.5–4.0) 0.7–3.8) 0.5–4.1)
(CI (CI (CI (CI (CI
0.7–3.8) 0.0–3.9) 0.5–4.1) 0.1–4.1) 0.0–4.1)
CI, confidence interval; RAV, resistance-associated variant; SVR, sustained virologic response. a Includes only patients enrolled in long-term follow-up and with on-treatment RAVs. b Includes 135 patients that remain in active follow-up (8 non-SVR and 127 SVRs). c Includes 65 patients that remain in active follow-up (7 non-SVR and 58 SVRs). d Includes 68 patients who were followed for the end of their treatment period but did not enroll in this long-term follow-up protocol.
Table 2 List of patients with SVR and detectable HCV RNA during follow-up. Previous trial
Patient
Genotype at original study
End of treatment date
Last PCR negative date
First PCR positive date
Genotype at follow-up
Viral load (IU/mL) at PCR positive date
SPRINT-1 SPRINT-2 SPRINT-2 SPRINT-2
001 002 003 004
GT1a GT1b GT1b GT1a
11–19–2007 11–11–2009 10–16–2009 10–02–2009
05–27–2008 04–29–2010 04–07–2010 05–11–2011
06–23–2009 07–01–2010 11–19–2010 08–10–2011
GT1b GT1b GT1b GT1a
1,580,000 113,000 1,190,000 TD(u)
HCV, hepatitis C virus; PCR, polymerase chain reaction; RNA, ribonucleic acid; SVR, sustained virologic response; TD(u), HCV RNA target detected, unquantifiable (<25 IU/mL).
100%
Probability of Retaining a RAV
90% V36M T54A T54S R155K A156S R155K + T54S R155K + V36M I/V170A ALL
80% 70% 60% 50% 40% 30% 20% 10% 0% FU D1
4M
8M
1Y
152 45 150 189 37 85 125 25 314
112 23 131 175 30 72 91 14 284
91 14 111 150 25 62 62 11 247
53 9 84 104 14 46 30 3 173
V36M T54A T54S R155K A156S R155K + T54S R155K + V36M I/V170A ALL
1Y4M 1Y8M 2Y 2Y4M 2Y8M Time Since the End of Treatment
3Y
3Y4M
3Y8M
20
11
8
7
4
2
2
56 66 5 30 8 2 107
44 46 4 21 2 1 81
36 34 4 19
34 30 4 17
31 27 1 15
24 23 1 12
20 15 1 10
4 5 1 2
1 63
1 58
1 50
1 40
1 27
7
4Y
Fig. 1. Probability of retaining a resistance-associated variant. Patients with first RAVs detected during treatment + 12 weeks in follow-up were included. Patients with ontreatment RAVs returned to WT before FU day 1 were excluded. Phase 2 and phase 3 studies included. V55A excluded due to low patient numbers with this variant.
197
3. Results
198
At the time of database cut-off, 1148 patients (SVR, n = 696; virologic failure, n = 452) who had received boceprevir during the original treatment study were enrolled in this follow-up analysis
199 200
(Table 1). In total, 314 of the 452 patients with virologic failure had sequence data available and are included in the analysis of RAV longevity. The median duration of follow-up was 3.4 years (range of 0.5–4.1 years) in patients with SVR and 3.3 years (range of 0.0–4.1 years) in patients without SVR.
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4
a
V36M
T54A
T54S
V55A
R155K
R155K + T54S
R155K + V36M
A156S
I/V170A
ALL
7/9 (77.8)
143/189 (75.7)
65/85 (76.5)
118/125 (94.4)
34/37 (91.9)
24/25 (96.0)
228/314 (72.6)
All patients WT within 3 years, n/N (%) Rate of return to WT per 100-PYs (95% CI), in 3 years Median time to return to WT, y (95% CI)
138/152 (90.8)
44/45 (97.8)
107/150 (71.3)
110.7 (93.7, 130.8)
203.1 (151.3, 272.6)
52.6 (43.5, 63.5) 56.1 (27.2, 115.8) 58.7 (49.8, 69.2) 59.6 (46.8, 76.0) 143.5 (119.9, 171.9)
96.2 (68.8, 134.4) 190.7 (128.2, 283.8)
55.6 (48.9, 63.3)
0.89 (0.74, 0.96)
0.46 (0.25, 0.49)
1.12 (1.01, 1.42) 1.09 (0.08)b
1.08 (1.02, 1.20) 1.07 (0.91, 1.33) 0.69 (0.49, 0.84)
0.90 (0.70, 1.05)
1.11 (1.05, 1.20)
Genotype 1a WT within 3 years, n/N (%) Rate of return to WT per 100-PYs (95% CI), in 3 years Median time to return to WT, y (95% CI)
136/149 (91.3) 110.4 (93.4, 130.6) 0.89 (0.74, 0.98)
12/13 (92.3) 334.8 (191.5, 585.2) 0.23 (0.08, 0.46)
61/88 (69.3) 0/1 (0) 50.9 (39.6, 65.4) 0.0 (0.0, 128.0)
140/185 (75.7) 62/81 (76.5) 117/124 (94.4) 58.8 (49.8, 69.4) 59.8 (46.7, 76.7) 143.8 (120.0, 172.3) 1.08 (1.02, 1.22) 1.05 (0.90, 1.33) 0.69 (0.49, 0.86)
10/11 (90.9) 0/0 91.4 (49.7, 168.3) n/a
Genotype 1b WT within 3 years, n/N (%) Rate of return to WT per 100-PYs (95% CI), in 3 years Median time to return to WT, y (95% CI)
2/3 (66.7) 134.8 (37.0, 491.6) 0.83 (0.11, 0.83)
32/32 (100) 177.0 (125.4, 249.8) 0.47 (0.26, 0.90)
46/62 (74.2) 7/8 (87.5) 3/4 (75.0) 55.0 (41.3, 73.4) 73.9 (35.8, 152.5) 55.2 (18.8, 162.2) 1.11 (0.90, 1.58) 1.08 (0.08, 2.58) 1.10 (0.23)b
RESPOND-1 WT within 3 years, n/N (%) Rate of return to WT per 100-PYs (95% CI), in 3 years Median time to return to WT, y (95% CI)
79/80 (98.8) 113.2 (90.8, 141.1) 0.77 (0.48, 1.02)
24/24 (100) 305.6 (205.4, 454.8) 0.26 (0.13, 0.44)
81/113 (71.7) 2/4 (50) 51.7 (41.6, 64.2) 23.1 (6.3, 84.2)
SPRINT-2 and RESPOND-2 WT within 3 years, n/N (%) 45/57 (78.9) 18/19 (94.7) Rate of return to WT per 100-PYs 97.4 (72.8, 130.3) 135.5 (85.7, 214.2) (95% CI), in 3 years Median time to return to 0.91 (0.87, 1.00) 0.90 (0.46, 1.04) WT, y (95% CI)
1.14 (0.92, 1.45) n/a
3/4 (75) 55.2 (18.8, 162.2) 1.10 (0.23)b
0.92 (0.32, 1.11)
0.46 (0.24, 0.75)
n/a
1/1 (100) 24/26 (92.3) 24/25 (96.0) 120.0 (21.2, 679.8) 98.3 (66.1, 146.3) 190.7 (128.2, 283.8) 0.83 0.89 (0.52, 1.05) 0.46 (0.24, 0.75)
1.18 (0.92, 1.52) (0.08)b
79/106 (74.5) 48/63 (76.2) 72/72 (100) 48.7 (39.1, 60.7) 57.3 (43.3, 76.0) 164.9 (130.9, 207.6) 1.40 (1.05, 1.55) 1.07 (0.80, 1.45) 0.47 (0.46, 0.51)
16/18 (88.9) 13/14 (92.9) 92.5 (57.0, 150.3) 256.8 (150.1, 439.4) 0.69 (0.26, 1.05) 0.25 (0.14, 0.50)
21/28 (75.0) 67.8 (44.3, 103.6) 0.95 (0.90, 1.12)
54/70 (77.1) 82.8 (63.5, 108.0) 0.96 (0.90, 1.02)
15/16 (93.8) 102.5 (62.1, 169.1) 0.92 (0.88, 1.09)
5 /5 (100) 131.0 (56.0, 306.7) 1.07 (0.08, 1.12)
PY, patient year; RAV, resistance-associated variants; WT, wild type. a ALL = RAV detected at boceprevir resistance-associated loci (positions V36, T54, V55, R155, A156, V170 or M175).
10/14 (71.4) 35/41 (85.4) 64.0 107.6 (77.3, 149.6) (34.7, 117.8) 0.91 (0.88, 1.12) 0.90 (0.86, 1.00)
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162/230 (70.4) 52.4 (44.9, 61.1) 1.17 (1.07, 1.34) 66/84 (78.6) 65.6 (51.6, 83.5) 1.04 (0.89, 1.12) 119/167 (71.3) 44.7 (37.4, 53.5) 1.45 (1.22, 1.67)
9/9 (100) 94/126 (74.6) 136.2 (71.7, 258.9) 81.4 (66.6, 99.7) 0.88 (0.07, 0.90) 0.95 (0.90, 1.02)
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Q6
Table 3 Longevity of boceprevir resistance-associated variants according to baseline characteristics and treatment.
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(A)
1.4 1.2 1 0.8 0.6 n=314
n=150
n=9
All RAVs
T54S
V55A
0.4
n=189
n=85
n=37
n=152
R155K R155K+ A156S T54S
n=45
n=25
n=125
V36M R155K+ I/V170A V36M
T54A
(B)
1.6 1.4 1.2 1 0.8 0.6
-re
R
el
on
ap
de
R
r
se
n=27
on
ea
kt
sp
hr
ou
IV
gh
1b
n=60
N
R &
n=165
SP
R
IN
T2
Br
PO ES
ES R
n=62
n=84
G
N PO
n=230
1a
-2
D
nt ie at lP Al
n=126
-1
s
n=167
G
n=314
0.4
D
Median time to return to WT (y)
1.8
N
Median time to return to WT (y)
1.6
Fig. 2. Median time to return to WT virus for (A) individual variants in all patients and (B) for all variants in selected patient subgroups. G = genotype; IVR = incomplete virologic response; error bars indicate 95% confidence intervals.
206
3.1. Durability of SVR
207
In total, 4 of 696 (0.6%) patients who achieved SVR following the original clinical trial had detectable HCV RNA during the follow-up period (Table 2). One patient (#001) was infected with GT1a at entry into the original study but had G1b infection at the time of relapse in the follow-up analysis (about 19 months after completing initial treatment). Phylogenetic analysis indicated that the viruses detected prior to treatment and during long-term followup were phylogenetically distinct, suggesting that this patient may have acquired a new infection after SVR was achieved during the original study. A second patient had detectable but not quantifiable HCV RNA (<25 IU/mL) during long-term follow-up, approximately 2.5 years after completing treatment and attaining SVR (#004). Per protocol, this patient was categorized as having experienced viral relapse. The remaining 2 patients had ‘‘true’’ late relapse. Thus, of the 4 patients with detectable HCV RNA during follow-up, 1 patient possibly had HCV re-infection (#001) and the remaining 3 were considered to have late viral relapse (although in these latter 3 patients, re-infection with virus from the same lineage present at baseline cannot be excluded). These data translate into a relapse rate of 0.4% or 1.3 relapses/1000 person-years (total follow-up time was 2227.2 years). (A phylogenetic tree of the 4 patients with detectable HCV RNA during follow-up is shown in the Supplementary Appendix.)
208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232
3.1.1. Natural history of RAVs during long-term follow-up This analysis includes data from 314 boceprevir-treated patients who developed RAVs during the initial treatment study.
73.0
Non-response
68.1
Relapse
52.7
Incomplete virologic resonse
46.6
Breakthrough
0
10
20
30
40
50
60
70
80
Rate of return to WT per 100-Pys in 3 Years
Fig. 3. Rate of return to WT according to type of virologic failure.
Most patients had multiple different RAVs. The majority (n = 228, 73%) reverted to WT within 3 years post-therapy and no longer had RAVs detectable by population sequencing. The median time for all RAVs to become undetectable was 1.11 (95% confidence interval [CI] 1.05–1.20) years (Fig. 1 and Table 3). Eighty-six patients had RAVs detected at their last tested time point during follow-up. Forty patients with detectable RAVs at their last test had completed the 3-year follow-up and were confirmed with detectable RAVs at boceprevir resistance-associated loci; 16 patients had discontinued from the study prior to reaching 3 years of participation with detectable RAVs at their last visit; and
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B. Genotype 1b
100%
100%
90%
90%
80%
80%
Probability of Retaining a RAV
Probability of Retaining a RAV
A. Genotype 1a
70% 60% 50% 40% 30%
60% 50% 40% 30% 20%
10%
10%
4M
8M
1Y
1Y4M 1Y8M 2Y 2Y4M 2Y8M Time Since the End of Treatment
3Y
3Y4M
3Y8M
0% FU D1
4Y
90%
80%
80%
Probability of Retaining a RAV
100%
90%
70% 60% 50% 40% 30%
1Y8M
2Y
2Y4M
2Y8M
3Y
3Y4M
3Y8M
4Y
50% 40% 30% 20% 10%
1Y
1Y4M
60%
10%
8M
1Y
70%
20%
4M
8M
D. Phase 3 Studies
100%
0% FU D1
4M
Time Since the End of Treatment
C. Phase 2 Studies
Probability of Retaining a RAV
70%
20%
0% FU D1
V36M T54A T54S R155K A156S R155K + T54S R155K + V36M I/V170A ALL
1Y4M 1Y8M 2Y 2Y4M 2Y8M Time Since the End of Treatment
3Y
3Y4M
3Y8M
4Y
0% FU D1
4M
8M
1Y
1Y4M
1Y8M
2Y
2Y4M
2Y8M
3Y
3Y4M
3Y8M
4Y
Time Since the End of Treatment
Fig. 4. Probability of retaining a resistance-associated variant in selected patient subgroups according to genotype (A and B) or enrollment in phase 2 or phase 3 studies (C and D). Patients with first RAVs detected during treatment + 12 weeks in follow-up were included. Patients with on-treatment RAVs returned to WT before FU day 1 were excluded. Phase 2 and phase 3 studies included.
244 245 246
247 248 249 250 251 252 253 254 255 256 257 258 259
260 261 262 263 264 265 266 267
the remaining 30 patients had detectable RAV at their last clinic visit but had not yet completed 3-years of follow-up (ie, monitoring was ongoing). 3.1.2. All patients The rate of return to WT varied across different RAVs (Figs. 1 and 2A) allowing RAVs to be broadly grouped into two categories according to median time to return to WT. Variants V36M, T54A, A156S, I/V170A, and V36M + R155K appeared to have a faster rate of return to WT, with median times to return to WT of 60.9 years. In contrast, variants T54S, R155K, V55A and T54S + R155K had a slower rate of return to WT, with median times to return to WT of approximately 1.1 years (Fig. 2A). Overall, 98% of T54A, 96% of I/V170A, 94% of R155K + V36M, 92% of A156S, 91% of V36M, 76% of T54S + R155K, 76% of R155K and 71% of T54S variants were undetectable by population sequencing after 3 years of follow-up (Table 3). 3.1.3. HCV genotype 1 subtype Return to WT appeared slightly faster in patients with G1b RAVs compared to those with G1a RAVs (Table 3), with median time to return to WT of 1.04 years (95% CI 0.89–1.12) and 1.17 years (95% CI 1.07–1.34), respectively. Among patients with G1a infection, the most common RAVs were V36M (n = 149), R155K (n = 185), and T54S (n = 88); also commonly occurring in pairs as R155K + V36M (n = 124) and R155K + T54S (n = 81). T54A and
V36M were associated with the fastest time to return to WT (T54A 0.23 years [95% CI 0.08–0.46], V36M 0.89 years [95% CI 0.74–0.98], R155K + V36M, 0.69 years [95% CI 0.49–0.86]) (Table 3; Fig. 4). In contrast, the most common RAVs in patients with G1b infection were T54S (n = 62), T54A (n = 32), A156S (n = 26), and I/V170A (n = 25). Among RAVs detected in patients with G1b infection, T54A and I/V170A were associated with the fastest median time to revert to WT (0.47 [95% CI 0.26–0.90] and 0.46 years [95% CI 0.24–0.75], respectively) (Table 3). Overall, at 3 years post-therapy, 70% of patients with G1a and 79% of those with G1b had undetectable RAVs by population sequencing.
268
3.1.4. Virologic failure Profile of virologic failure during initial therapy was also associated with varying rates of return to WT (Fig. 2B). Patients with breakthrough or incomplete virologic response tended to have a slower return to WT (median times to return to WT were 1.22 years [95% CI 0.1.02–1.70], 1.17 years [95% CI 1.06–1.35], respectively); whereas, patients with non-response2 or relapse showed a faster return to WT; (medians of 0.95 years [95% CI 0.89–1.11] and 0.58 years [95% CI 0.45–1.55], respectively). Rate of return to WT per 100 patient years within 3 years was 68% among patients with relapse, 73% in those with non-response, 53% in those
279
2 Non-responder population includes patients who discontinued because of adverse event, and who may have had largely WT virus.
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A.Y.M. Howe et al. / Antiviral Research xxx (2014) xxx–xxx Table 4 Number of patients with on-treatment resistance-associated variants (RAVs) according to virologic failure group. Boceprevir resistance-associated variants
Breakthrough (N = 62), n (%) Incomplete viral response (N = 165), n (%) Relapse (N = 27), n (%) Non-responder (N = 60), n (%)
V36M
T54A
T54S
V55A
R155K
R155K + T54S
R155K + V36M
A156S
I/V170A
ALLa
35 (56%) 77 (47%)
4 (6%) 28 (17%)
30 (48%) 95 (58%)
4 (6%) 5 (3%)
39 (63%) 108 (65%)
19 (31%) 53 (32%)
28 (45%) 72 (44%)
8 (13%) 22 (13%)
2 (3%) 18 (11%)
62 (100%) 165 (100%)
6 (22%) 34 (57%)
7 (26%) 6 (10%)
10 (37%) 15 (25%)
0 (0%) 0 (0%)
7 (26%) 35 (58%)
4 (15%) 9 (15%)
3 (11%) 22 (37%)
2 (7%) 5 (8%)
3 (11%) 2 (3%)
27 (100%) 60 (100%)
Breakthrough: detectable HCV RNA after previous undetectable HCV RNA; Incomplete virologic response: >1.5 log decline from baseline but failure to attain undetectable HCV RNA; Relapse: undetectable HCV RNA at end of treatment followed by subsequent detectable HCV RNA during follow-up; Nonresponder: <1.5 log decline in HCV RNA from baseline. a ALL = RAV detected at boceprevir resistance-associated loci (positions V36, T54, V55, R155, A156, V170 or M175).
290 291 292 293 294 295 296 297
with incomplete virologic response, and 47% in those with breakthrough (Fig. 3). The distribution of T54S, R155K and R155K + T54S was more prevalent in patients who had breakthrough and incomplete virologic response than those who experienced relapse and non-response. Because T54S, R155K and T54S + R155K are slow to return to WT, in patients who had breakthrough or incomplete virologic response, this might account for the slower re-emergence of WT virus in these groups (Table 4).
307
3.1.5. Phase 2 versus phase 3 studies Patients in the phase 3 SPRINT-2 and RESPOND-2 studies exhibited a faster return to WT compared to patients treated in the RESPOND-1 study, most of whom received doses of boceprevir lower than the currently approved dose (doses of boceprevir in RESPOND-1 were 100–800 mg/d TID) (Table 3, Fig. 4). The rate of return to WT per 100-person years was 44.7 in the RESPOND-1 trial compared to 81.4 in the phase 3 studies. The large distribution of T54S (113/167, 68%) in RESPOND-1 might have contributed to the slower overall reversion rate of RAVs in the RESPOND-1 trial.
308
4. Discussion
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SVR is universally accepted as the gold standard end point for evaluation of treatments for HCV infection. Data from the present study confirm that SVR is durable in the vast majority of patients treated with boceprevir, and can be considered a surrogate for viral eradication. Re-emergence of virus in patients who attained SVR occurred at a rate of 1.3 relapses/1000 person-years. Furthermore, one patient in the present study had detectable but unquantifiable HCV RNA during follow-up and was classified as having relapse, per protocol; however, it is unclear whether this result represents bona fide late viral relapse, versus a false positive assay reading. According to the United States Food and Drug Administration (FDA), transient detectable but unquantifiable HCV RNA during follow-up most likely represents a false-positive HCV RNA reading, and under FDA criteria, this patient would be considered to have enduring SVR (Harrington et al., 2012). RAVs that arise during therapy with HCV protease inhibitors have the potential to precipitate virologic failure (Ogert et al., 2013). However, RAVs also have impaired replicative fitness compared to WT virus (Tong et al., 2006; Susser et al., 2009) and thus when pharmacologic pressure is relieved, a gradual resurgence in WT virus is typically paralleled by a decline in the RAV population. The rate of return to WT was independent of baseline viral load or lead-in response in the primary studies (data not shown). In the boceprevir phase 3 studies, the rate of return to WT virus was 0.95 years compared to 1.1 years in the combined phase 2 and phase 3 study populations. With regard to genotype subtype, clinically SVR rates are generally higher in patients with G1b infection compared to those with G1a infection (Poordad et al., 2012).
Time to return to WT for each RAV in the present study is generally consistent with data from patients receiving telaprevir (Sullivan et al., 2013). Median times to return to WT in boceprevir-treated patients from SPRINT-2 and RESPOND-2 were broadly similar to those reported in follow-up studies from the phase 3 telaprevir clinical trials (V36M, 11.9 vs 9.3 months; T54S, 11.4 vs 11.5 months; R155K, 11.5 vs 9.8 months; A156S, 11.0 vs 6.7 months) (Sullivan et al., 2013). Median times to return to WT in patients with G1a and G1b infection were 14 months and 12.5 months with boceprevir and 10.6 months and 0.9 months with telaprevir (Sullivan et al., 2013). In addition to causing drug resistance, departure from the WT genotype can impact viral replicative fitness. Variants that display relatively unaffected replicative fitness in vitro may be expected to endure longer within the HCV population; whereas, variants with poor replicative fitness may exhibit a more rapid return to WT. This theory implies a correlation between in vitro replicative fitness and rate of return to WT; however, establishing consistent correlations in this regard has proved challenging. For example, in vitro studies indicate the V36M and I170A variants retain >90% relative fitness compared with WT (Shimakami et al., 2011), yet our data indicate these variants have a relatively rapid return to WT, consistent with poor replicative fitness relative to WT. Conversely, R155K has approximately 50% replicative fitness compared with WT in vitro (Shimakami et al., 2011); however, in our studies R155K had a slow return to WT. Other examples however, support a correlation between in vitro replicative fitness and rate of return to WT: A156S shows >50% impaired replication in vitro (Lenz et al., 2010) and demonstrated a rapid return to WT in the present study. Further study is required to identify additional factors that may affect the frequency of selection and clinical durability of resistant variants, and the relevance of in vitro replicative fitness. There are some limitations to the present analysis. The population sequencing techniques used in the present study are capable of detecting RAVs at a frequency of >20% in the circulating viral population but do not permit analysis of RAVs at lower levels. The clinical implications of RAVs enduring at levels <20% of the total viral population are therefore unclear. In addition, there are limited numbers of patients with certain RAVs (e.g., V55A, n = 9), or within particular patient subgroups (e.g., relapse, n = 27) restricting the interpretation of data from these groups.
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SVR was durable in most patients treated with boceprevir plus PR, with only rare instances of late relapse. Furthermore, most RAVs present at the time of virologic failure reverted to WT over time, with a median time to WT of approximately 1.1 years. Time to return to WT was associated with the phenotype of RAV, presumably a reflection of the fitness of the mutant virus.
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Conflict of interest
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All of the authors are employees of Merck & Co., Inc. or of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., except for Dr. Alves, who is a former employee of Merck Sharp & Dohme Corp., and remains a stockholder in that company. Additionally, Drs. Wahl, Barnard and Thompson are stockholders of Merck & Co., Inc. The authors have no other conflicts to disclose.
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Acknowledgments
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Q4 The studies described in this analysis were funded by Merck & Q5 Co., Inc., Whitehouse Station, NJ, USA, and all authors were employees of Merck at the time when the research was conducted. The authors were involved in study design; data collection, analysis and interpretation; and in the writing of this report. Medical writing and editorial assistance was provided by Tim Ibbotson, PhD of ApotheCom (Yardley, PA, USA). This assistance was funded by Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Whitehouse Station, NJ, USA.
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Appendix A. Supplementary data
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Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.antiviral.2014.10. 010.
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Please cite this article in press as: Howe, A.Y.M., et al. Long-term follow-up of patients receiving boceprevir for treatment of chronic hepatitis C. Antiviral Res. (2014), http://dx.doi.org/10.1016/j.antiviral.2014.10.010