Download 590 KB - International Medical Press

Antiviral Therapy 2012; 17:411–423 (doi: 10.3851/IMP2088)
Review
Resistance to mericitabine, a nucleoside analogue
inhibitor of HCV RNA-dependent RNA polymerase
Jean-Michel Pawlotsky1,2*, Isabel Najera3, Ira Jacobson4
National Reference Center for Viral Hepatitis B, C and D, Department of Virology, Hôpital Henri Mondor, Université Paris-Est, Créteil, France
INSERM U955, Créteil, France
3
Roche, Nutley, NJ, USA
4
Weill Cornell Medical College, New York-Presbyterian Hospital, New York, NY, USA
1
2
*Corresponding author e-mail: [email protected]
Mericitabine (RG7128), an orally administered prodrug
of PSI-6130, is the most clinically advanced nucleoside
analogue inhibitor of the RNA-dependent RNA polymerase (RdRp) of HCV. This review describes what has
been learnt so far about the resistance profile of mericitabine. A serine to threonine substitution at position 282
(S282T) of the RdRp that reduces its replication capacity
to approximately 15% of wild-type is the only variant
that has been consistently generated in serial in vitro
passage experiments. To date, no evidence of genotypic
resistance to mericitabine has been detected by population or clonal sequence analysis in any baseline or ontreatment samples collected from >600 patients enrolled
in Phase I/II trials of mericitabine administered as monotherapy, in combination with pegylated interferon/
ribavirin, or in combination with the protease inhibitor,
danoprevir, for 14 days in the proof-of-concept study of
interferon-free therapy.
Introduction
The approval of boceprevir and telaprevir [1,2], the first
inhibitors of the non-structural (NS) 3/4A (NS3/4A)
serine protease of HCV, for use in combination with
pegylated interferon-a and ribavirin (triple therapy),
has ushered in a new era of direct acting antiviral
agents (DAAs) for the treatment of chronic hepatitis
C. Triple therapy significantly increases viral eradication rates in both treatment-naive and previous nonsustained virological responders to interferon-based
therapy while also decreasing the required duration of
treatment for many patients [3–10]. These advances
do, however, have limitations: the side-effect burden is increased and the available protease inhibitors
(boceprevir and telaprevir) are only approved for treatment of HCV genotype 1 infection. In addition, these
first-generation protease inhibitors have a low barrier
to antiviral resistance. As a result, resistance to protease inhibitors develops rapidly in most patients when
these agents are administered alone [11–13]. Resistance
to DAAs appears to be characterized by outgrowth
of pre-existing minor viral populations with amino
acid substitutions that confer reduced susceptibility
to the drug [14,15]. In combination with pegylated
interferon‑a and ribavirin, protease-inhibitor-resistant
©2012 International Medical Press 1359-6535 (print) 2040-2058 (online)
AVT-11-RV-2317_Pawlotsky.indd 411
HCV variants are selected and grow when the interferon response is inadequate [3,4,6]. Among patients
who did not achieve a sustained virological response
(SVR) during clinical development trials of triple
therapy, 53% of patients treated with boceprevir and
62% of patients treated with telaprevir had proteaseinhibitor-resistant viral variants detected by population sequencing (or direct sequencing) as the dominant
population at the time of treatment failure [16,17].
Long-term follow-up studies have shown that the wildtype viral population becomes dominant within 1–2
years in the majority of patients [18,19]. However, the
resistant variants may not have cleared completely and
could continue to replicate at low levels.
Mericitabine (RG7128) is an orally administered
prodrug of PSI-6130 (b-d-2′-deoxy-2′-fluoro-2′-Cmethylcytidine), a potent and selective nucleoside
analogue inhibitor of the NS5B protein-encoded
RNA-dependent RNA polymerase (RdRp) of HCV
(Figure 1). The objective of this review is to describe
what has been learnt so far about the resistance profile of mericitabine, the nucleoside analogue RdRp
inhibitor that is furthest advanced in terms of clinical
phase development.
411
10/04/2012 11:22:04
J-M Pawlotsky et al.
HCV lifecycle and DAA targets
particles in the circulation of infected patients. The
lifecycle of HCV is shown in Figure 2. The virus gains
entry into hepatocytes through a complex interaction between HCV envelope glycoproteins E1 and
HCV is an enveloped, single-stranded positive RNA
hepatotropic virus that associates with lipoprotein
Figure 1. Structures of mericitabinea and its active metabolites, PSI-6130 and RO2433
O
NH2
O
O
N
O
O
O
HO
HO
N
F
O
PSI-6130
(nucleoside analogue
inhibitor of HCV NS5B)
Mericitabine (RG7128;
orally administered prodrug)
a
N
O
F
O
NH2
N
O
HO
HO
N
F
NH
O
RO2433
(deaminated form
of PSI-6130)
RG7128.
Figure 2. Lifecycle of HCV and potential drug targets
7. Transport and release
1. Receptor binding
and endocytosis
Entry inhibitors
6. Viral assembly
2. Fusion and
uncoating
RNA
3. Translation of
RNA into polyprotein
5. RNA replication
by polymerase
Inhibitors of NS3
and NS3/4A
Inhibitors of
NS5A, NS5B
and cyclophilin
4. Polyprotein cleaved into
mature viral proteins by
host cell and viral proteases
Reprinted by permission from MacMillan Publishers Ltd: Nature [62], 2011.
412 AVT-11-RV-2317_Pawlotsky.indd 412
©2012 International Medical Press
10/04/2012 11:22:08
Mericitabine resistance profile
E2 and several essential host cell surface components
(glycosaminoglycans, the tetraspanin CD81, the scavenger receptor class B type-I and the tight junction
proteins claudin-1 and occludin). Entry is followed by
clathrin-mediated endocytosis [20].
Viral protein synthesis and replication are cytoplasmic processes [21]. Membrane-associated HCV
replication complexes generate new HCV RNA molecules while translation of RNA genomes produces a
polyprotein comprising approximately 3,000 amino
acids that is subsequently cleaved by host and viral
proteases into 10 structural and NS proteins. Capsid
proteins and genomic RNA are assembled into nucleocapsids that bud into the lumen of the endoplasmic
reticulum. Newly formed virions mature in the Golgi
apparatus before exiting the cell through the secretory pathway [21].
The lifecycle of HCV presents a number of potential targets against which many DAA drugs are currently being developed [15,22]. The most advanced
drug development programmes to date have targeted
polyprotein processing (by inhibiting the NS3/4A serine protease) and HCV replication (through different
mechanisms). Two NS3/4A serine protease inhibitors
(boceprevir and telaprevir) that target polyprotein
processing and, as a result, HCV production have
now been approved for the treatment of HCV infection in both the USA and Europe. In addition, at least
10 other molecules in this class have been and/or are
being investigated in humans and at least 4 other
classes of drugs that inhibit HCV replication are
currently in clinical trials. These include nucleoside/
nucleotide analogue inhibitors and non-nucleoside
inhibitors of RdRp, inhibitors of NS5A, a viral protein involved in the regulation of HCV replication,
and inhibitors of cyclophilin A, a host cell protein
required for HCV replication [15,22].
HCV resistance to DAAs
DAAs provide not only an opportunity to improve
cure rates for patients with chronic hepatitis C, but
also a challenge because HCV is prone to the rapid
selection of resistant variants when exposed to these
drugs [15]. The large viral population and rapid replication rate of HCV, combined with the fact that the
viral RdRp makes errors during replication that are
not corrected in the absence of proofreading activity,
implies that HCV exists as a quasispecies in any given
patient, that is, a mixture of genetically distinct but
closely related viral populations [15]. Resistance to
DAAs emerges when minority variants in a patient’s
quasispecies are selected during treatment because
they carry amino acid substitutions that modify the
drug binding site and confer a survival advantage in
Antiviral Therapy 17.3
AVT-11-RV-2317_Pawlotsky.indd 413
the presence of the drug. Sustained antiviral pressure
on the majority wild-type virus creates vacant replication space for the resistant variant, which can subsequently grow and fill in this space [15].
Resistance profiles vary greatly between classes of
DAAs but less so between drugs in the same class.
The binding site of a particular DAA is important in
determining the potential for cross-resistance. Two
different drugs that bind to different ‘pockets’ on the
same molecule or to two entirely different proteins
(‘targets’) are unlikely to show cross-resistance. By
contrast, two different compounds that bind to the
same pocket on the same target are likely to exhibit
cross-resistance.
Viral replication is suppressed when the serum drug
concentration remains above a threshold. Thus, drug
exposure, which reflects the amount of drug absorbed
into the blood and the concentration that is sustained
during the dosing interval, is an important factor in
the prevention of resistance to a DAA.
The frequency and speed at which resistance develops when a given patient is treated with a DAA
depends on the genetic barrier to resistance (number of amino acid substitutions required to generate
resistance to the drug), the fitness of resistant variants, the level of resistance the mutant(s) confers and
exposure to the drug. Altogether, these parameters
account for the so-called ‘barrier to resistance’ of
the drug [15,23,24]. When resistance does develop,
it generally manifests as a virological breakthrough,
that is, a re-increase in the HCV RNA level. Several
different breakthrough patterns associated with antiviral resistance have been characterized. For example,
if a high degree of resistance is conferred by an amino
acid substitution and the fitness of the virus is only
modestly affected, then the escape pattern will be
characterized by a rapid increase in HCV RNA level
despite ongoing DAA administration. Conversely, if
the degree of resistance is lower and/or the fitness of
the resistant virus is impaired, the slope of the HCV
RNA level rebound will be less steep [15,23,24].
If a drug is highly efficacious against wild-type
virus, resistance can emerge relatively early in treatment. However, the selection and emergence of resistance-associated mutations can be much slower when
treated with a DAA that is less active against wildtype virus.
Among the drug classes that are currently in human
clinical trials, the NS3/4A protease inhibitors, the nonnucleoside inhibitors of HCV RdRp and the NS5A
inhibitors have been reported to have a low barrier to
resistance [15,23]. When telaprevir is given as monotherapy, a virological breakthrough can be observed
in HCV RNA levels within days, and resistant variants are detected as the dominant viral population at
413
10/04/2012 11:22:08
J-M Pawlotsky et al.
the time of breakthrough [11,25]. Patients infected
with HCV subtype 1a develop telaprevir, boceprevir
and danoprevir resistance more often and more rapidly than those infected with subtype 1b [16,17,26].
This is due, at least in part, to the fact that only one
nucleotide change is required in subtype 1a, but two
in subtype 1b, to generate the key amino acid change
at position 155 of the NS3/4A protease that confers
resistance to the drugs [27]. HCV that is resistant to
telaprevir is extensively cross-­resistant to boceprevir
and to all of the other first-generation NS3/4A protease inhibitors in development, but not to drugs from
other classes [15,23,28].
Non-nucleoside inhibitors of RdRp have been
developed that bind to one of four allosteric sites of
the viral polymerase [15]. Available data suggest that
drugs in this class have a low barrier to resistance,
with extensive cross-resistance among drugs targeting the same site. Cross-resistance may also occur
between drugs targeting different allosteric sites, albeit
not frequently; however, there is no cross-resistance
with drugs from other classes [15]. When the nonnucleoside inhibitor of RdRp filibuvir was given as
monotherapy for 8–10 days, breakthrough occurred
in approximately 50% of patients [29]. Mutations at
NS5B position 423 were consistently associated with
breakthrough [29].
NS5A inhibitors also have a low genetic barrier to
resistance. They are able to select resistant variants
with substitutions in the NS5A region, with no cross-­
resistance with drugs from other classes [15].
The combination of two drugs with a low barrier to
resistance did not appear to substantially increase the
overall barrier to resistance in recent trials. For example, during a study of daclatasvir (BMS-790052), an
NS5A inhibitor, and asunaprevir (BMS-650032), an
NS3/4A protease inhibitor, 4 of 11 patients experienced SVR, an important proof of concept, but variants resistant to both drugs were detected in all six
patients who experienced breakthrough [30]. Variants in the NS5A domain included Q30E/R, L31M/V
and Y93C/N, and those in the NS3 domain included
R155K and D168A/E/T/V/Y [30]. Similarly, breakthrough during treatment with a non-nucleoside polymerase inhibitor (GS-9190) and a protease inhibitor
(GS-9256) was associated with emergence of resistance mutations in both the polymerase (Y448H) and
NS3 (R155K and/or D168V/E/N) domains [31].
The remaining two classes of drugs, namely cyclophilin inhibitors and nucleoside/nucleotide analogues,
have been associated with more favourable resistance
profiles when given as monotherapy. Cyclophilin
inhibitors target a host protein that plays a key role
in viral replication by interacting with viral proteins
in the replication complex, although the molecular
414 AVT-11-RV-2317_Pawlotsky.indd 414
mechanisms are still unknown. Low-level in vitro
resistance to the most advanced cyclophilin inhibitor,
alisporivir, is conferred by amino acid substitutions
in the NS2 and, more commonly, in the NS5A coding
regions. Little is known of the potential for clinically
meaningful resistance in patients with chronic hepatitis C receiving this drug; however, in vivo the variants
appear to be poorly fit and they are rarely selected
[15,32,33].
Several nucleoside/nucleotide analogue inhibitors
of HCV RdRp have been evaluated in clinical trials. Drugs in this class generally have a high barrier
to resistance due to poor in vivo fitness of selected
variants. Cross-resistance is possible between agents
with a common binding site or mechanism of action.
For example, 2′-methyl substituted nucleosides such
as PSI-6130, the active derivative of mericitabine,
and PSI-7977 select for substitutions at amino acid
position 282. By contrast, R1479 (4′-azidocytidine;
the active drug released by hydrolysis of the prodrug
balapiravir, which is no longer in development) selects
for amino acid substitutions at amino acid position
96 and 96+142 and there is no cross-resistance in
vitro between this drug and the 2′-methyl substituted nucleosides [34]. Similarly, significant resistance
to PSI-938 requires the presence of three mutations
(S15G, C223H and V321I) [35]; however, this purine
analogue inhibitor of RdRp is active against S282T
variants [36].
Mode of action and in vitro potency of
mericitabine
The target for mericitabine is the catalytic site of the
HCV RdRp. Several steps are necessary to activate
its derivative PSI-6130. After oral administration,
mericitabine (the prodrug) is hydrolysed to PSI-6130.
Next, after being taken up by hepatocytes, PSI-6130
is converted to two pharmacologically active triphosphate metabolites [37–39]. The 5′-monophosphate
derivative (PSI-6130-MP) undergoes conversion to
diphosphate and triphosphate metabolites by cellular kinases. PSI-6130-MP also undergoes deamination to form a uridine metabolite (RO2433) that is
subsequently phosphorylated (Figure 1) [39]. In vitro
experiments in primary human hepatocytes have
shown that PSI-6130-TP and RO2433-TP are the predominant intracellular metabolites, and that steadystate levels are reached within 48 h of exposure to the
parent compound in this model [37].
The triphosphorylated moieties serve as ­alternative
substrates that compete with natural cytidine-­
triphosphate at the active site of the RdRp for incorporation into the nascent viral RNA. This results in
chain termination, which is thought to occur through
©2012 International Medical Press
10/04/2012 11:22:08
Mericitabine resistance profile
steric hindrance between the bulky 2′C-methyl groups
of PSI-6130-TP and RO2433-TP and the ribose moiety
on the next incoming nucleotide (Figure 3) [37–39].
Mericitabine is active against all HCV genotypes
(1–6) [40], but has been most extensively studied
against HCV genotype 1. PSI-6130-TP and RO2433TP have similar potency for inhibition of RNA synthesis, with 50% inhibitory concentration (IC50) values of 0.34 and 1.19 mM, respectively, for the native
HCV replicase complex isolated from replicon cell
lines, and 0.13 and 0.52 mM, respectively, for the
recombinant RdRp in a cell-free enzyme assay [37].
PSI-6130-TP has equal inhibitory potency in both
subtype 1a and 1b. In vitro in a transient replicon
system, PSI-6130 was equipotent against genotype
1a and 1b, with 50% effective concentration (EC50)
values ranging from 0.6 to 1.41 mM for different subtype 1b clinical isolates (0.51 mM for the reference
strain Con1), and from 0.20 to 0.43 mM for different
subtype 1a isolates (0.30 mM for the reference strain
H77) [41].
experiments, the initial concentration of PSI-6130
was 2.5 mM (approximately 5× the EC50) and was ultimately increased to a concentration of 100 mM at passage 53. As cells were passaged with increasing concentrations of the drug, increasing numbers of amino
acid substitutions were detected. However, the S282T
substitution was the only one that emerged during all
three sets of experiments, and it emerged only after 20
or more cell passages and exposure to a PSI-6130 concentration of at least 30 mM in each experiment [41].
Of the other amino acid substitutions that emerged
with S282T during these experiments, none appeared
consistently in all three experiments.
The presence of the S282T substitution reduces
the susceptibility of the HCV RdRp to different
2′-C-methyl-containing analogues [42]; however,
the extent of the reduction varies with the particular compound. For example, S282T decreases the
Figure 3. Crystal structure of RdRp active site with PSI-6130
modelled
Mechanisms of resistance to mericitabine
and preclinical data
Several nucleoside analogue inhibitors of HCV
RdRp that have 2′-C-methyl substituents including
2′-C-methyladenosine, 2′-C-methylcytidine (NM107;
a derivative of valopicitabine, which was discontinued
due to toxicity) and 2′-C-methyl-7′-deaza-adenosine
(MK-0608; another discontinued compound), select
for a common amino acid substitution, a change from
serine to threonine at position 282 (S282T), in the
HCV replicon system [42–44]. This substitution is
located in the active site of HCV RdRp and results in
an 11-fold reduction in the catalytic efficiency of the
enzyme compared with wild-type [42]. In the genotype 1b replicon system, the replication capacity of
S282T-containing RdRp was approximately 15% of
the wild-type enzyme [41].
Selection of replicons resistant to PSI-6130 required
approximately 6 months of sequential passages in cell
culture with exposure to increasing concentrations
of the drug [41]. Throughout the three independent
Thumb
S282
Fingers
Palm
Residue S282T is depicted.
Table 1. In vitro resistance conferred by the S282T substitution
Compound
Metabolite
Active metabolites of mericitabine
Active metabolite of valopicitabine
PSI-6130-TP
0.13
0.70
5.4
RO2433-TP0.52 11.0 20.2
NM107-TP
0.09
10.0
111.1
Wild-type, µM
Mean EC50
S282T, µM
Fold change
Comparative in vitro efficacy of the active metabolites of mericitabine and valopicitabine in wild-type versus S282T-containing recombinant HCV RNA-dependent RNA
polymerase in a cell-free enzyme assay [41]. EC50, 50% effective concentration.
Antiviral Therapy 17.3
AVT-11-RV-2317_Pawlotsky.indd 415
415
10/04/2012 11:22:12
J-M Pawlotsky et al.
Table 2. Definitions of virological responses used in clinical trials of mericitabine
Virological response
Definition
Decrease in HCV RNA level of ≤0.5 log10 IU/ml from baseline.
Non-response
Partial responseInitial decrease in HCV RNA level of ≥0.5 log10 IU/ml from baseline followed by plateau
(HCV RNA within ±0.5 log10 IU/ml from nadir for three time points)
OR
HCV RNA level of ≥1,000 IU/ml at end of treatment.
Virological breakthrough (Phase I studies)Initial decrease in HCV RNA level of ≥0.5 log10 IU/ml from baseline followed by a sustained
increase of ≥0.5 IU/ml from nadir.
Virological breakthrough (Phase II studies)Initial decrease in HCV RNA level of ≥0.5 log10 IU/ml from baseline followed by a sustained
increase of ≥1 log10 IU/ml from nadir.
susceptibility of RdRp to PSI-6130-TP by approximately 5-fold and to NM107-TP by approximately
111-fold in vitro (Table 1) [41]. The lesser effect of
the S282T substitution on PSI-6130 than NM107 and
other 2′-C-substituted nucleoside analogues may be
due to the presence of the fluorine substituent, which
may increase the structural flexibility of the molecule
in the active site of RdRp and reduce the extent of
steric hindrance [41]. By contrast, PSI-938 and PSI661, prodrugs of b-d-2′-deoxy-2′-a-fluoro-2′-b-Cmethylguanosine-5′-monophosphate show no loss of
activity against replicons with the S282T substitution,
although they also possess a 2′-C-methyl moiety.
The experimental introduction of the S282T amino
acid substitution into a wild-type RdRp resulted in
a 3.5–8-fold decrease in mericitabine susceptibility
in the replicon system (using a laboratory reference
strain and genetically different clinical isolates as
backbones) and in an RdRp enzyme assay (using a
laboratory reference enzyme) [41].
Other amino acid substitutions that emerged
and persisted after exposure to PSI-6130 in in vitro
experiments include K81R, K72M, I239V, I239L,
L320F, A396G, A421V, C575S and Y586C. Similar
to the S282T variant, these substitutions generally
reduced the replication capacity of a genotype 1b
replicon compared with wild-type [41]. Moreover,
the reduction in replication capacity was magnified
when these mutations were combined with S282T.
When present alone, none of these mutations altered
the susceptibility of the replicon to PSI-6130, mericitabine or NM107. However, the combination of
S282T plus C575S and S282T plus L320F produced
further reductions in the susceptibility of replicons
to PSI-6130 beyond that seen with S282T alone. By
contrast, the introduction of I239L, A396G or A421V
to a replicon containing S282T appeared to partially
compensate for the loss of susceptibility conferred by
S282T [41].
Collectively, these observations from in vitro
studies demonstrate that resistance to the active
416 AVT-11-RV-2317_Pawlotsky.indd 416
metabolite of mericitabine results from the selection
of HCV variants bearing one particular amino acid
substitution (S282T). However, this variant is difficult to select in vitro and S282T significantly impairs
the replication capacity of the resulting HCV strain.
Moreover, S282T-containing variants have slightly
higher susceptibility to PSI-6130-TP than to NM107TP, the active metabolite of valopicitabine. Only
when S282T is accompanied by accessory mutations,
such as C575S or L320F, is a further reduction in susceptibility to mericitabine observed. Cross-resistance
between mericitabine and members of other DAA
classes has not yet been observed [41,44].
Resistance to mericitabine in clinical trials
Mericitabine is currently in Phase II clinical trials.
To date, efficacy and safety data are available from
studies in treatment-naive and treatment-experienced
patients, including individuals infected with HCV genotypes 1, 2, 3 and 4. Mericitabine has been evaluated
as monotherapy [45], in combination with pegylated
interferon plus ribavirin up to 24 weeks [46–49] and
in combination with the HCV protease inhibitor danoprevir in the proof-of-concept study of a dual oral
interferon-free DAA regimen for 2 weeks [50].
Collectively these trials have enrolled >600 patients.
All patients enrolled in the trials have been monitored
for the development of resistance to mericitabine.
Consistent definitions of clinical responses were used
to identify patients for resistance monitoring during
these trials and population and clonal sequence analysis techniques were used to analyse samples in resistance studies (Table 2). There was one case of breakthrough during combination therapy with pegylated
interferon and ribavirin and five patients had an HCV
RNA level >1,000 IU/ml after 4 weeks of therapy
with pegylated interferon and ribavirin [51]. Only one
patient experienced a breakthrough during dual combination therapy with danoprevir in the INFORM-I
trial [50]. Analyses of samples from these patients has
©2012 International Medical Press
10/04/2012 11:22:12
Mericitabine resistance profile
not detected any evidence of selection of HCV variants resistant to mericitabine thus far. Importantly,
S282T has not been detected in any clinical samples
by population or clonal sequence analysis, or by ultradeep sequencing to date [50,52–54]. Similar findings
demonstrating that resistance mutations at residue
S282 are uncommon at baseline have been reported
in several other studies of large multinational cohorts
of treatment-naive patients with either genotype 1/3
HCV monoinfection or HCV–HIV coinfection [55–
57]. By contrast, variants resistant to other DAAs
(protease inhibitors and non-nucleoside polymerase
inhibitors) have been detected in some baseline samples from patients in trials evaluating mericitabine.
Resistance to mericitabine from a long-term, Phase
II trial of interferon-free treatment with mericitabine
and danoprevir (INFORM-SVR) are awaited.
Short-term Phase I trials of mericitabine alone or
in combination with pegylated interferon-a2a plus
ribavirin
Mericitabine was first evaluated as monotherapy in
a Phase I 14-day multiple ascending-dose trial in 32
patients infected with HCV genotype 1 who had not
responded to previous interferon-based treatment. At
dosages ranging from 750 to 3,000 mg/day, mericitabine produced dose-dependent reductions in HCV
RNA levels. The greatest mean reduction in HCV
RNA (2.7 log10 IU/ml, range 1.2–4.1 log10 IU/ml) was
achieved at day 15 with the highest dosage level (1,500
mg twice daily), although even at lower doses mean
changes from baseline at day 15 were 0.9 log10 IU/ml
(750 mg once daily, range 0.67–1.10 log10 IU/ml) and
1.48 log10 IU/ml (1,500 mg once daily, range 0.9–2.5
log10 IU/ml) [45]. HCV RNA levels were unchanged
after 14 days in eight patients who received oral placebo in this study.
Next the drug was evaluated in short-term (4-week)
randomized placebo-controlled trials in combination
with pegylated interferon-a2a (40 KD) and ribavirin.
The first trial enrolled treatment-naive patients with
HCV genotype 1 infection who were randomized to
mericitabine-based triple therapy (n=65) or pegylated
interferon-a2a plus ribavirin (n=16) [47]. A rapid
virological response (RVR), defined as an HCV RNA
level <15 IU/ml at week 4, was achieved in 88% and
85% patients, respectively, who received oral mericitabine at a dosage of 1,000 mg twice daily or 1,500
mg twice daily in combination with pegylated interferon-a2a plus ribavirin [47]. By contrast, the RVR
rate was 19% in patients randomized to the pegylated
interferon-a2a/ribavirin control group. Factors significantly associated with the change in HCV RNA level
at week 4 in this trial included treatment with mericitabine, baseline HCV RNA level and race/ethnicity.
Antiviral Therapy 17.3
AVT-11-RV-2317_Pawlotsky.indd 417
By contrast, patient weight, gender and HCV subtype
were not significantly associated with the decrease in
HCV RNA level in patients randomized to mericitabine [47].
The second trial included patients infected with genotypes 2 or 3 who had experienced non-response or
relapse to a previous course of interferon-based therapy. A total of 20 patients were randomized to mericitabine-based triple therapy and five to a pegylated
interferon-a2a/ribavirin control group [47]. Of them,
90% achieved an RVR when re-treated with mericitabine 1,500 mg twice daily in combination with
pegylated interferon-a2a plus ribavirin [46].
Resistance in Phase I monotherapy and
combination therapy trials
The collective results of resistance studies conducted
in patients enrolled in the Phase I monotherapy and
combination studies were recently reported [53].
The S282T variant was not detected by population sequence analysis in baseline samples collected
from any of the 145 patients enrolled in these trials.
Of 117 patients who received mericitabine in these
studies, a total of 13 individuals met the criteria for
resistance monitoring, including 5 who experienced
a viral breakthrough (defined as an increase of 0.5
log in HCV RNA from nadir) and 8 who had a partial response (Figure 4 and Table 3). None met the
criteria for non-response. The S282T variant was not
detected in any on-treatment samples from these 13
patients. It was also not detected by clonal sequence
analysis of 1,165 molecular clones from baseline isolates and 1,250 molecular clones from on-treatment
isolates from the patients who met the criteria for
resistance monitoring (approximately 90 clones/sample were sequenced) [53].
A number of amino acid substitutions were identified when on-treatment samples were compared
with baseline samples for individual patients. However, only one of them was detected in more than
one patient (F162F/Y at day 4 in one patient and F/
Y162F at day 29 in another patient; Table 3) [53].
Amino acid substitutions S282R and S282G were
identified at low frequencies (approximately 1%) in
the quasispecies of five individuals at baseline; however, samples containing these variants remained fully
susceptible to mericitabine and both of these substitutions were replication-incompetent when tested as
individual variants in the replicon system [53].
Phase II studies of mericitabine plus pegylated
interferon-a2a plus ribavirin
In longer-term Phase II trials, mericitabine was administered to patients infected with HCV genotypes 1 or
4 at a dosage of 500 mg twice daily or 1,000 mg twice
417
10/04/2012 11:22:12
J-M Pawlotsky et al.
Figure 4. Viral load profile of patients selected for viral resistance monitoring
0.00
Days
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
-0.50
-1.00
-1.50
-2.00
-2.50
Pt A – 750 mg once daily
Pt B – 1,500 mg once daily
Pt C – 1,500 mg twice daily
Pt D – 1,500 mg twice daily
Pt E – 1,500 mg twice daily
+ Mericitabine/P/R
HCV viral load change from baseline, log10 IU/ml
HCV viral load change from baseline, log10 IU/ml
+ Mericitabine
0.00
-0.50
0
3
6
9
12
Days
15 18 21 24 27 30
-1.00
-1.50
-2.00
-2.50
-3.00
-3.50
-4.00
-4.50
-5.00
Pt F – 500 mg twice daily + P/R
Pt G – 1,500 mg twice daily + P/R
Pt H – 1,500 mg twice daily + P/R
Pt I – 500 mg twice daily + P/R
Pt J – 500 mg twice daily + P/R
Pt K – 500 mg twice daily + P/R
Pt L – 500 mg twice daily + P/R
Pt M – 500 mg twice daily + P/R
Viral load profile of patients (Pt) selected for viral resistance monitoring in Phase I trials of (A) mericitabine (RG7128) monotherapy or (B) combination therapy with
pegylated interferon-a2a (40 KD; P) and ribavirin (R; standard of care). Profiles drawn in solid lines display the breakthrough pattern; those drawn in dotted lines show
the viral load stabilization pattern. Patient identifications correspond to those shown in Table 3.
daily for 8 or 12 weeks (PROPEL; n=408) or at a dosage of 1,000 mg twice daily for 24 weeks (JUMP-C;
n=166) in combination with pegylated interferon-a2a
plus ribavirin.
The results of a planned week 12 interim analysis
of PROPEL showed that the complete early virological response rate (cEVR; HCV RNA level <15 IU/ml
at week 12) ranged from 80% to 88% among patients
randomized to receive mericitabine-based triple therapy for 12 weeks (n=324). The cEVR rate was 68%
in patients who had received 8 weeks of mericitabinebased therapy and 49% in those in the control group
(pegylated interferon-a2a plus ribavirin; n=84) [48].
Non-response (defined as <0.5 log decrease in HCV
RNA level from baseline after 2 weeks of treatment)
or virological breakthrough (defined as ≥1 log increase
in HCV RNA level above the nadir) was not observed
in any patient during treatment with mericitabine for
up to 12 weeks in PROPEL. Moreover, no evidence of
S282T was detected by population or clonal sequencing (approximately 90 clones/sample) of selected
baseline or on-treatment samples [58]. A total of 11
patients were classified as partial responders because
418 AVT-11-RV-2317_Pawlotsky.indd 418
they had an HCV RNA level >1,000 IU/ml at end of
mericitabine treatment. Amino acid changes observed
in on-treatment samples collected from the 11
patients with a partial response were not consistent
between patients enrolled in the trial or with changes
observed in other trials of mericitabine. Phenotypic
drug susceptibility data showed that the samples were
equally susceptible before and at the end of mericitabine treatment, suggesting that these variants do not
play a role in the partial responses observed in these
individuals [58].
The randomized, double-blind, placebo-controlled
JUMP-C study is evaluating response-guided therapy
with a mericitabine-based triple therapy regimen in
patients infected with HCV genotypes 1 or 4 [49].
For mericitabine recipients who remained HCVRNA-negative between weeks 4 and 22 (extended
RVR [eRVR]), all treatment was stopped at week 24,
whereas those individuals who did not achieve an
eRVR stopped mericitabine at week 24 but continued pegylated interferon-a2a plus ribavirin to complete 48 weeks of treatment. The control group comprises patients randomized to 48 weeks of pegylated
©2012 International Medical Press
10/04/2012 11:22:13
Mericitabine resistance profile
Table 3. Patients selected for viral resistance monitoring in mericitabine studies
Patient (HCV genotype)
Mericitabine dose
Reason for resistance
monitoring
Sample day
Amino acid changes detected in RdRp compared
with baseline sequences from the same patient
Mericitabine monotherapy (n=32)
A (1a)
750 mg Breakthrough
14
None
once daily
B (1a)
1,500 mg Breakthrough
14
M423I
once daily
C (1a)
1,500 mg Breakthrough
14
None
once daily
D (1b)
1,500 mg Partial response
14
F162F/Y, S218A/S, K254K/R, T267I/T, A/V400A,
twice daily
A442A/T, I585I/V
1,500 mg Partial response
14
K/M426M, H/Y452Y
E (1b)
twice daily
Mericitabine plus pegylated
interferon-a2a (40 KD) plus
ribavirin combination therapy (n=85)
F (1a)
1,500 mg Breakthrough
28–29
I/V11V, A/S15A, A73A/V, C/S110S, K/Q206Q,
twice daily
Q/R300R, D444A
G (3a)
1,500 mg Breakthrough
19
I432V
twice daily
H (3a)
1,500 mg Breakthrough
21
A/V67V, V147M, A/V150A, I/T184I, S376N
twice daily
I (1a)
500 twice Partial response
29
A16T, T235M, Q/R309R, A/V327V, S/T389T,
daily
I/V405V, A/T552T, F/S/Y588Y
500 twice Partial response
29
N/S130S, F/Y162F, S180G, S189N/S, N/S231S,
J (1a)
daily
K/R270R, A/V421A
500 twice Partial response
29
K510R, F/L572L
K (1a)
daily
L (1a)
500 twice Partial response
29
E/K77K, C/S110S, A/V178V, S556G
daily
M (1a)
500 twice Partial response
29
S470G/S, K523K/R, S543G/S, A553A/T
daily
Amino acid changes relative to baseline identified by population sequencing in patients selected for resistance monitoring in clinical studies of mericitabine monotherapy
and triple mericitabine plus pegylated interferon-a2a plus ribavirin combination therapy [53]. Breakthrough, increase in HCV RNA level ≥0.5 log10 IU/ml above nadir
before the end of therapy; partial response, initial reduction in HCV RNA level after initiation of therapy followed by plateau; RdRp, RNA-dependent RNA polymerase.
Table 4. Patients selected for resistance monitoring on the JUMP-C trial
Patients
Patient group
S282T variants detected
Baseline sequence analysis (all patients)
Genotype 1a (n=119)None
Genotype 1b (n=41)None
Genotype 4 (n= 3)
None
Virological response (HCV RNA<15 IU/ml; n=80)
–
No samples tested
(no breakthrough)
None
Partial response (HCV RNA≈2,000 IU/ml; n=1)–
Patients with an eRVR
SVR-12 (n=37)
No samples tested
Relapse (n=10)None
Failure to return (n=2)
No samples tested
Patients selected for resistance monitoring and results of testing for mericitabine-resistant variants in the JUMP-C study [49]. eRVR, extended rapid virological response
defined as HCV RNA<15 IU/ml at every time point between weeks 4 and 22.
interferon-a2a plus ribavirin (n=85). A planned
interim analysis at week 36 showed that 60% (49/81)
of patients randomized to mericitabine-based triple
therapy achieved an eRVR; of these, 76% (37/49)
Antiviral Therapy 17.3
AVT-11-RV-2317_Pawlotsky.indd 419
achieved an SVR-12 (HCV RNA<15 IU/ml) at week
12 of untreated follow-up [49]. The SVR rates in
patients with an eRVR were similar irrespective of
IL28B genotype.
419
10/04/2012 11:22:13
J-M Pawlotsky et al.
A summary of the resistance analysis from JUMPC is shown in Table 4. Among mericitabine-treated
patients, all but one individual had undetectable HCV
RNA levels (<15 IU/ml) by week 24 and none experienced viral breakthrough. The patient with the partial
response had an HCV RNA level of approximately
2,000 IU/ml at the end of triple therapy (week 24) and
no amino acid substitutions associated with resistance have been identified to date in any sample collected from this individual. Among patients included
in the interim analysis who have completed treatment
and follow-up, 10 (24%) individuals experienced a
virological relapse, none of whom had detectable variants with substitutions associated with mericitabine
resistance.
Presently, neither the final SVR rates nor the
results of on-treatment resistance analyses have been
reported for patients assigned to 48 weeks of treatment in JUMP-C.
Mericitabine plus danoprevir dual oral interferonfree combination regimen
Two weeks of treatment with various dosage regimens of mericitabine and the NS3/4A protease
inhibitor danoprevir produced median reductions in
serum HCV RNA levels of 3.7–5.2 log10 IU/ml from
baseline in the proof-of-concept study of a dual oral
interferon-free regimen in patients with chronic hepatitis C genotype 1 (INFORM-1) [50]. Only 1 of 73
patients dosed in this study experienced viral breakthrough; however, no evidence of the S282T variant
nor of resistance variants typically associated with
protease inhibitor treatment were detected by population or clonal sequencing (80 to >100 clones assessed
per sample) in this patient.
A danoprevir-resistant variant (D168E) was
detected in the baseline sample collected from one
patient assigned to mericitabine 1,000 mg twice daily
and danoprevir 200 mg every 8 h. When this sample was tested in vitro, susceptibility to danoprevir
was shown to be reduced by approximately 37-fold,
but susceptibility to mericitabine remained unaltered
compared with wild-type. The patient experienced a
continuous decline in serum HCV RNA of 2.7 log10
IU/ml during dual treatment [50].
The combination of mericitabine and danoprevir
is currently being evaluated in two ongoing trials.
In the INFORM-SVR trial, interferon-naive patients
with HCV genotype 1 infection are receiving mericitabine (1,000 mg twice daily) and ritonavir-boosted
danoprevir (100/100 mg twice daily) with or without
ribavirin [59]. The duration of treatment in the trial
is based on the time to become HCV-RNA-negative.
The MATTERHORN trial is evaluating mericitabine (1,000 mg twice daily) in combination with
420 AVT-11-RV-2317_Pawlotsky.indd 420
ritonavir-boosted danoprevir (100/100 mg twice
daily) in HCV genotype 1 patients with a previous
partial response or null response to pegylated interferon plus ribavirin [60]. MATTERHORN will determine the efficacy of a triple oral combination regimen
(mericitabine, danoprevir/ritonavir and ribavirin), a
protease-inhibitor-based triple therapy combination
regimen (danoprevir/ritonavir, pegylated interferona2a and ribavirin) and a quadruple therapy regimen
(mericitabine, danoprevir/ritonavir, pegylated interferon-a2a and ribavirin). All regimens are administered for 24 weeks in the study, with the exception of
one treatment group of previous non-responders who
are receiving 24 weeks of quadruple therapy followed
by 24 weeks of pegylated interferon-a2a plus ribavirin (total duration of 48 weeks). Formal analyses
of resistance to mericitabine and danoprevir will be
reported in this trial.
Conclusions
The approval of the first DAAs for treatment of
chronic hepatitis C will stimulate further research to
identify combination regimens that maximize viral
eradication rates, shorten the duration of treatment
and reduce the side-effect burden. Highly potent
agents with a broader spectrum of activity and different resistance profiles will be required in the near
future. Drugs with a high barrier to resistance like
nucleoside/nucleotide analogues may be particularly
useful in this context.
Mericitabine is a prodrug of the potent nucleoside analogue inhibitor of RdRp PSI-6130 that has a
demonstrated high barrier to resistance both in vitro
and in patients with chronic hepatitis C. To date,
there has been no evidence of the in-vitro-identified
mericitabine-­resistant variant S282T at baseline and
up to 24 weeks of triple therapy with mericitabine,
pegylated interferon-a2a and ribavirin in clinical
trials. This variant has not been selected when mericitabine was used for 2 weeks in combination with
danoprevir, an HCV protease inhibitor, in an interferon-free regimen [48,50]. Although restricted to
short-term administration, the absence of resistance
to either drug after 2 weeks of combination therapy
with mericitabine plus the protease inhibitor danoprevir suggests that mericitabine has a protective
effect against resistance to danoprevir (that is typically observed after 7 days of monotherapy) [61].
Random variants with other amino acid substitutions have been observed to arise sporadically during and after treatment with mericitabine; however,
these variants have not been associated with diminished susceptibility to the drug. Pending the results
from ongoing clinical trials with mericitabine in
©2012 International Medical Press
10/04/2012 11:22:13
Mericitabine resistance profile
interferon-free regimens [59,60], it can be concluded
that mericitabine has a high barrier to resistance in
combination with pegylated interferon and ribavirin and that the selection of resistant variants was
not observed. The findings thus far underscore the
potential for mericitabine and other nucleoside or
nucleotide analogues to help avoid the emergence of
resistance seen in trials with drugs that have a lower
barrier to resistance. Reinforcement of the emerging
impression that mericitabine has a high barrier to
resistance will require monitoring for resistant variants in ongoing and future clinical trials including
those investigating interferon-free regimens.
3.
McHutchison JG, Everson GT, Gordon SC, et al.
Telaprevir with peginterferon and ribavirin for chronic
HCV genotype 1 infection. N Engl J Med 2009;
360:1827–1838.
4.
Hézode C, Forestier N, Dusheiko G, et al. Telaprevir and
peginterferon with or without ribavirin for chronic HCV
infection. N Engl J Med 2009; 360:1839–1850.
5.
Kwo PY, Lawitz EJ, McCone J, et al. 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 2010; 376:705–716.
6.
McHutchison JG, Manns MP, Muir AJ, et al. Telaprevir
for previously treated chronic HCV infection. N Engl J
Med 2010; 362:1292–1303.
7.
Bacon BR, Gordon SC, Lawitz E, et al. Boceprevir for
previously treated chronic HCV genotype 1 infection.
N Engl J Med 2011; 364:1207–1217.
Acknowledgements
8.
Poordad F, McCone J, Jr., Bacon BR, et al. Boceprevir for
untreated chronic HCV genotype 1 infection. N Engl J
Med 2011; 364:1195–1206.
9.
Jacobson IM, McHutchison JG, Dusheiko G, et al.
Telaprevir for previously untreated chronic hepatitis C
virus infection. N Engl J Med 2011; 364:2405–2416.
All authors have contributed to the work and w
­ riting
of the manuscript and they have all read and approved
the paper. They take full responsibility for its scientific
content. Support for third-party writing assistance
for a preliminary draft of this manuscript, furnished
by Blair Jarvis, was provided by F Hoffmann–­
La
Roche Ltd.
Disclosure statement
J-MP has received research grants from Gilead and
Roche. He has served as an advisor for Abbott Laboratories, Anadys, Biotica, Boehringer–Ingelheim,
Bristol–­Myers Squibb, DebioPharm, Gilead, GlaxoSmithKline, Idenix, Janssen–Cilag, Madaus–Rottapharm, Schering–Plough/Merck, Novartis, Pfizer, Pharmasset, Roche, Vertex and Virco. IN is an employee of
Hoffmann–La Roche (Nutley, NJ, USA). IJ has acted
as a consultant to Abbott Laboratories, Achillion,
Biolex, Boehringer, Roche/Genentech, Tibotec, Bristol–Myers Squibb, Novartis, Gilead, Pfizer, Vertex,
Schering Plough/Merck, Boehringer–Ingelheim, Pharmasset; has received research support from Schering
Plough/Merck, Gilead, Vertex, Novartis, Boehringer–
Ingelheim, Pharmasset, Roche/Genentech, Tibotec/
Janssen, Anadys, GlobeImmune; and acted as a
speaker for Schering–Plough/Merck, Gilead, Bristol–
Myers Squibb, Genentech and Vertex.
References
1. US Food and Drug Administration. Approval of Incivek
(telaprevir), a direct acting antiviral drug (DAA) to treat
hepatitis C (HCV). (Updated 25 May 2011. Accessed
15 February 2012.) Available from http://www.fda.
gov/ForConsumers/ByAudience/ForPatientAdvocates/
ucm256328.htm
2. US Food and Drug Administration. Approval of Victrelis
(boceprevir) a direct acting antiviral drug (DAA) to
treat hepatitis C virus (HCV). (Updated 25 May 2011.
Accessed 15 February 2012.) Available from http://www.
fda.gov/ForConsumers/ByAudience/ForPatientAdvocates/
ucm255413.htm
Antiviral Therapy 17.3
AVT-11-RV-2317_Pawlotsky.indd 421
10. Zeuzem S, Andreone P, Pol S, et al. Telaprevir for
retreatment of HCV infection. N Engl J Med 2011;
364:2417–2428.
11. Sarrazin C, Kieffer TL, Bartels D, et al. Dynamic
hepatitis C virus genotypic and phenotypic changes in
patients treated with the protease inhibitor telaprevir.
Gastroenterology 2007; 132:1767–1777.
12. Sarrazin C, Rouzier R, Wagner F, et al. SCH 503034, a
novel hepatitis C virus protease inhibitor, plus pegylated
interferon alpha-2b for genotype 1 nonresponders.
Gastroenterology 2007; 132:1270–1278.
13. Kieffer TL, Sarrazin C, Miller JS, et al. Telaprevir and
pegylated interferon-alpha-2a inhibit wild-type and
resistant genotype 1 hepatitis C virus replication in
patients. Hepatology 2007; 46:631–639.
14. Chevaliez S, Rodriguez A, Soulier A, Ahmed-Belkacem A,
Hézode C, Pawlotsky J-M. Molecular characterization
of HCV resistance to telaprevir by means of ultra-deep
pyrosequencing: preexisting resistant variants and dynamics
of resistant populations. J Hepatol 2011; 54 Suppl 1:S30.
15. Pawlotsky JM. Treatment failure and resistance with
direct-acting antiviral drugs against hepatitis C virus.
Hepatology 2011; 53:1742–1751.
16. Incivek (telaprevir). Package insert 2011. Vertex
Pharmaceuticals, Inc., Cambridge, MA, USA.
17. Victrelis (Boceprevir). Package insert 2011. Schering
Corporation, a subsidiary of Merck and Co., Whitehouse
Station, NJ, USA.
18. Zeuzem S, Sulkowski M, Zoulim F, et al. Long-term
follow-up of patients with chronic hepatitis C treated
with telaprevir in combination with peginterferon alfa-2a
and ribavirin: interim analysis of the EXTEND study.
Hepatology 2010; 52 Suppl 1:436A.
19. Sullivan J, De Meyer S, Bartels D, et al. Evolution of
treatment-emergent resistant variants in telaprevir phase 3
clinical trials. J Hepatol 2011; 54 Suppl 1:S4.
20. Zeisel MB, Fofana I, Fafi-Kremer S, Baumert TF. Hepatitis
C virus entry into hepatocytes: molecular mechanisms and
targets for antiviral therapies. J Hepatol 2011; 54:566–576.
21. Ashfaq UA, Javed T, Rehman S, Nawaz Z, Riazuddin S.
An overview of HCV molecular biology, replication and
immune responses. Virol J 2011; 8:161.
22. Pawlotsky JM, Chevaliez S, McHutchison JG. The
hepatitis C virus life cycle as a target for new antiviral
therapies. Gastroenterology 2007; 132:1979–1998.
23. Halfon P, Locarnini S. Hepatitis C virus resistance to
protease inhibitors. J Hepatol 2011; 55:192–206.
421
10/04/2012 11:22:13
J-M Pawlotsky et al.
24. Vermehren J, Sarrazin C. New HCV therapies on the
horizon. Clin Microbiol Infect 2011; 17:122–134.
25. Reesink HW, Zeuzem S, Weegink CJ, et al. Rapid decline
of viral RNA in hepatitis C patients treated with VX-950:
a phase Ib, placebo-controlled, randomized study.
Gastroenterology 2006; 131:997–1002.
26. Le Pogam S, Yan J, Chhabra M, et al. Low prevalence
of danoprevir resistance identified in genotype 1b HCV
patients with prior null response treated with danoprevir
plus low-dose ritonavir plus peginterferon alfa-2a (40KD)/
ribavirin for 12 weeks. J Hepatol 2011; 54 Suppl 1:S485.
27. McCown MF, Rajyaguru S, Kular S, Cammack N, Najera I.
GT-1a or GT-1b subtype-specific resistance profiles for
hepatitis C virus inhibitors telaprevir and HCV-796.
Antimicrob Agents Chemother 2009; 53:2129–2132.
28. Sarrazin C, Zeuzem S. Resistance to direct antiviral
agents in patients with hepatitis C virus infection.
Gastroenterology 2010; 138:447–462.
29. Wagner F, Thompson R, Kantaridis C, et al. Antiviral
activity of the hepatitis C virus polymerase inhibitor
filibuvir in genotype 1-infected patients. Hepatology
2011; 54:50–59.
30. Lok A, Gardiner D, Lawitz E, et al. Quadruple therapy
with BMS-790052, BMS-650032 and PEG-IFN/RBV for
24 weeks results in 100% SVR12 in HCV genotype 1 null
responders. J Hepatol 2011; 54 Suppl 1:S536.
31. Zeuzem S, Buggisch P, Agarwal K, et al. Dual, triple, and
quadruple combination treatment with a protease inhibitor
(GS-9256) and a polymerase inhibitor (GS-9190) alone
and in combination with ribavirin (RBV) or PEGIFN/
RBV for up to 28 days in treatment naive genotype 1 HCV
subjects. Hepatology 2010; 52 Suppl 1:400A.
32. Coelmont L, Hanoulle X, Chatterji U, et al. DEB025
(Alisporivir) inhibits hepatitis C virus replication by
preventing a cyclophilin A induced cis-trans isomerisation
in domain II of NS5A. PLoS ONE 2010; 5:e13687.
33. Puyang X, Poulin DL, Mathy JE, et al. Mechanism of
resistance of hepatitis C virus replicons to structurally
distinct cyclophilin inhibitors. Antimicrob Agents
Chemother 2010; 54:1981–1987.
34. McCown MF, Rajyaguru S, Le Pogam S, et al. The
hepatitis C virus replicon presents a higher barrier to
resistance to nucleoside analogs than to nonnucleoside
polymerase or protease inhibitors. Antimicrob Agents
Chemother 2008; 52:1604–1612.
35. Lam AM, Espiritu C, Bansal S, et al. Hepatitis C virus
nucleotide inhibitors PSI-352938 and PSI-353661 exhibit a
novel mechanism of resistance requiring multiple mutations
with replicon RNA. J Virol 2011; 85:12334–12342.
36. Lawitz E, Rodriguez-Torres M, Denning J, et al. Once
daily dual-nucleotide combination of PSI-938 and
PSI-7977 provides 94% HCV RNA < LOD at day 14:
first purine/pyrimidine clinical combination data (the
NUCLEAR study). J Hepatol 2011; 54 Suppl 1:S543.
37. Ma H, Jiang WR, Robledo N, et al. Characterization of the
metabolic activation of hepatitis C virus nucleoside inhibitor
beta-d-2’-Deoxy-2’-fluoro-2’-C-methylcytidine (PSI-6130)
and identification of a novel active 5’-triphosphate species.
J Biol Chem 2007; 282:29812–29820.
38. Murakami E, Bao H, Ramesh M, et al. Mechanism of
activation of beta- d-2’-deoxy-2’-fluoro-2’-c-methylcytidine
and inhibition of hepatitis C virus NS5B RNA polymerase.
Antimicrob Agents Chemother 2007; 51:503–509.
39. Murakami E, Niu C, Bao H, et al. The mechanism of
action of beta- d-2′-deoxy-2′-fluoro-2′-C-methylcytidine
involves a second metabolic pathway leading to betad-2′-deoxy-2′-fluoro-2′-C-methyluridine 5′-triphosphate,
a potent inhibitor of the hepatitis C virus RNA-dependent
RNA polymerase. Antimicrob Agents Chemother 2008;
52:458–464.
40. Leveque V, Fung A, Le Pogam S, et al. Nucleoside analog
R7128, a prodrug of PSI-6130, shows inhibition potency
across HCV genotypes 1–6 in vitro. 16th International
Symposium on Hepatitis C Virus and Related Viruses. 3–7
October 2009, Nice, France. Poster P-215.
422 AVT-11-RV-2317_Pawlotsky.indd 422
41. Ali S, Leveque V, Le Pogam S, et al. Selected replicon
variants with low-level in vitro resistance to the hepatitis
C virus NS5B polymerase inhibitor PSI-6130 lack crossresistance with R1479. Antimicrob Agents Chemother
2008; 52:4356–4369.
42. Migliaccio G, Tomassini JE, Carroll SS, et al. Characterization
of resistance to non-obligate chain-terminating ribonucleoside
analogs that inhibit hepatitis C virus replication in vitro. J
Biol Chem 2003; 278:49164–49170.
43. Olsen DB, Eldrup AB, Bartholomew L, et al. A
7-deaza-adenosine analog is a potent and selective
inhibitor of hepatitis C virus replication with excellent
pharmacokinetic properties. Antimicrob Agents
Chemother 2004; 48:3944–3953.
44. Le Pogam S, Jiang WR, Leveque V, et al. In vitro selected
Con1 subgenomic replicons resistant to 2’-C-methylcytidine or to R1479 show lack of cross resistance.
Virology 2006; 351:349–359.
45. Reddy R, Rodriguez-Torres M, Gane E, et al. Antiviral
activity, pharmacokinetics, safety, and tolerability of
R7128, a novel nucleoside HCV RNA polymerase
inhibitor, following multiple, ascending, oral doses in
patients with HCV genotype 1 infection who have failed
prior interferon therapy. Hepatology 2007; 46 Suppl
1:862A–863A.
46. Gane E, Rodriguez-Torres M, Nelson D, et al. Antiviral
activity of the HCV nucleoside polymerase inhibitor R7128
in HCV genotype 2 and 3 prior non-responders: interim
results of R7128 1500mg BID with PEG-IFN and ribavirin
for 28 days. Hepatology 2008; 48 Suppl 1:1024A.
47. Rodriguez-Torres M, Lalezari J, Gane E, et al. Potent
antiviral response to the HCV nucleoside polymerase
inhibitor R7128 for 28 days with PEG-IFN and ribavirin:
subanalysis by race/ethnicity, weight and HCV genotype.
Hepatology 2008; 48 Suppl 1:1160A.
48. Jensen D, Wedemeyer H, Herring R, et al. High rates of
early viral response, promising safety profile and lack of
resistance-related breakthrough in HCV GT 1/4 patients
treated with RG7128 plus PegIFN alfa-2a (40KD)/RBV:
planned week 12 interim analysis from the PROPEL
study. Hepatology 2010; 52 Suppl 1:360A.
49. Pockros P, Jensen D, Tsai N, et al. First SVR data with the
nucleoside analogue polymerase inhibitor mericitabine
(RG7128) combined with peginterferon/ribavirin in
treatment-naive HCV G1/4 patients: interim analysis from
the JUMP-C trial. J Hepatol 2011; 54 Suppl 1:S538.
50. Gane EJ, Roberts SK, Stedman CA, et al. Oral
combination therapy with a nucleoside polymerase
inhibitor (RG7128) and danoprevir for chronic hepatitis
C genotype 1 infection (INFORM-1): a randomised,
double-blind, placebo-controlled, dose-escalation trial.
Lancet 2010; 376:1467–1475.
51. Le Pogam S, Chhabra M, Yan J-M, et al. Low rate of viral
load rebound observed among treatment-naive genotype 1
patients with chronic hepatitis C treated with danoprevir
(RG7227) plus PEG-IFN alfa-2a (40KD) (PEGASYS)
plus ribavirin: interim analysis. Hepatology 2010; 52
Suppl 1:703A–704A.
52. Le Pogam S, Seshaaddri A, Kosaka A, et al. No evidence
of drug resistance after up to 4 weeks treatment of GT 1,
2 and 3 hepatitis C virus infected individuals. J Hepatol
2009; 50 Suppl 1:S348.
53. Le Pogam S, Seshaadri A, Ewing A, et al. RG7128 alone
or in combination with pegylated interferon-alpha2a and
ribavirin prevents hepatitis C virus (HCV) replication and
selection of resistant variants in HCV-infected patients.
J Infect Dis 2010; 202:1510–1519.
54. Margeridon S, Le Pogam S, Liu T, et al. Ultra-deep
sequencing of the NS3 and NS5B regions detects preexisting resistant variants to direct acting antivirals (DAA)
in HCV genotype 1 treatment-naive infected patients.
Hepatology 2010; 52 Suppl 1:714A.
55. Kuntzen T, Timm J, Berical A, et al. Naturally occurring
dominant resistance mutations to hepatitis C virus
protease and polymerase inhibitors in treatment-naive
patients. Hepatology 2008; 48:1769–1778.
©2012 International Medical Press
10/04/2012 11:22:14
Mericitabine resistance profile
56. Gaudieri S, Rauch A, Pfafferott K, et al. Hepatitis C virus
drug resistance and immune-driven adaptations: relevance
to new antiviral therapy. Hepatology 2009; 49:1069–1082.
57. Treviño A, de Mendoza C, Parra P, et al. Natural
polymorphisms associated with resistance to new antivirals
against HCV in newly diagnosed HIV-HCV-coinfected
patients. Antivir Ther 2011; 16:413–416.
58. Le Pogam S, Yan J-M, Kosaka A, et al. No evidence of drug
resistance or baseline S282T resistance mutation among GT1
and GT4 HCV-infected patients on nucleoside polymerase
inhibitor RG7128 and PEG-IFN/RBV combination treatment
for up to 12 weeks: interim analysis from the PROPEL study.
Hepatology 2010; 52 Suppl 1:701A–702A.
59. Clinicaltrials.gov. A study on the combination of
RO5024048 and ritonavir-boosted danoprevir with and
without Copegus (ribavirin) in interferon-naive patients
with chronic hepatitis C genotype 1 (INFORM-SVR).
Clinicaltrials.gov NCT01278134. (Accessed 27 July 2011.)
Available from http://clinicaltrials.gov/ct2/show/NCT01278
134?term=danoprevir&rank=3
60. Clinicaltrials.gov. A study of danoprevir/ritonavir
and Copegus with RO5024048 and/or Pegasys in
patients with chronic hepatitis C. Clinicaltrials.gov
NCT01331850. (Accessed 31 July 2011.) Available from
http://clinicaltrials.gov/ct2/show/NCT01331850?term=R
O5024048&rank=2
61. Sarrazin C, Lim S, Qi X, et al. Kinetic analysis of viral
rebound and drug-resistant viral variant dynamics in
patients treated with ITMN-191 (RG7227) monotherapy
suggests a high barrier to viral escape. Hepatology 2009;
50 Suppl 1:953A.
62. Schlütter J. Therapeutics: new drugs hit the target. Nature
2011; 474:S5–7.
Accepted 10 October 2011; published online 8 March 2012
Antiviral Therapy 17.3
AVT-11-RV-2317_Pawlotsky.indd 423
423
10/04/2012 11:22:14