Download Is Hepatitis Virus Resistance to Antiviral Drugs a Threat?

GASTROENTEROLOGY 2012;142:1369 –1372
Is Hepatitis Virus Resistance to Antiviral Drugs a Threat?
*National Reference Center for Viral Hepatitis B, C and D, Department of Virology, Hôpital Henri Mondor, Université Paris-Est, Créteil, France; and ‡INSERM U955,
Créteil, France
T
he onset of the acquired immune deficiency syndrome epidemic in the early 1980s led to successful
antiviral drug discovery programs, which brought to the
market a large number of antiretroviral drugs with different targets and mechanisms of action. However, it soon
became apparent that human immunodeficiency virus
(HIV) resistance to these drugs would be a problem in
long-term antiretroviral therapy.1 A combination of drugs
with different viral targets and no cross-resistance (highly
active antiretroviral therapy [HAART]) was shown to be a
valuable option to prevent HIV resistance in the longterm. Nevertheless, multidrug-resistant viruses emerge in
some patients on HAART therapy, generally those who
have been on treatment for many years and have received
a number of different drugs during their life. These viruses escape the antiviral effect of all available drugs and
their outgrowth is responsible for treatment failure, disease progression, and death.1
Based on this experience, hepatitis B virus (HBV) and
hepatitis C virus (HCV) resistance to direct-acting antiviral (DAA) drugs often is seen as a dreadful threat. The
reality is, however, different.
Hepatitis B Virus Resistance to
Nucleoside/Nucleotide Analogues
Lamivudine, a drug widely used in HAART therapy, was the first nucleoside analogue available for HBV
treatment. Its broad use in monotherapy was associated
with a high incidence of virologic breakthrough owing to
the selection and outgrowth of lamivudine-resistant HBV
variants.2 Similar observations were reported after a few
years of monotherapy with adefovir, a nucleotide analogue developed for HIV and the second inhibitor approved for HBV therapy.3 Because these 2 drugs select
different resistance-associated amino acid substitutions,
they were combined to prevent resistance emergence. This
strategy proved to be efficient, with very few breakthroughs on de novo or add-on lamivudine–adefovir combination therapy,4,5 and it still is appropriate in resourceconstrained settings. However, viruses bearing an
rtA181V/T substitution, which confers cross-resistance to
the 2 drugs, occasionally were selected in patients receiving the combination of lamivudine and adefovir.6
Bearing this in mind, some investigators, including
myself, were convinced that, similar for HIV, de novo
combinations of drugs without cross-resistance were the
only valid therapeutic option for chronic hepatitis B treatment with nucleoside/nucleotide analogues, and that
even this option probably would not prevent outgrowth
of multidrug-resistant viruses after several years of combined therapy. In the meantime, 2 new drugs, entecavir
and tenofovir, had been approved for HBV therapy. Surprisingly, long-term follow-up studies of HBV resistance
with these drugs showed incredibly low cumulative resistance rates in treatment-naive patients: 1.2% with entecavir at 6 years and 0% with tenofovir at 5 years.7,8 These
results subsequently were confirmed in the real-life setting, in which treatment failures caused by resistance were
extremely rare in adherent treatment-naive patients receiving entecavir or tenofovir monotherapy. This led to the
conclusion that, unlike HIV, HBV infection can be treated
for years with either first-line entecavir or tenofovir monotherapy without a major risk of viral breakthrough owing
to resistance selection.9,10
This favorable situation can be explained by the characteristics of HBV and of the drugs used to block its
replication. Indeed, strong conservatory constraints exist
on the amino acid sequence of HBV proteins because of
the overlapping reading frames that encode different viral
proteins that cannot tolerate extensive variations. As a
result, the number of possible viable viruses with amino
acid substitutions in the reverse transcriptase that confer
primary resistance to HBV nucleoside/nucleotide analogues is limited. In addition, although rtM204V/I confers
Abbreviations used in this paper: DAA, direct-acting antiviral; HAART,
highly active antiretroviral therapy; HBV, hepatitis B virus; HCV, hepatitis C virus; HIV, human immunodeficiency virus; IFN, interferon.
© 2012 by the AGA Institute
0016-5085/$36.00
doi:10.1053/j.gastro.2011.12.060
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Jean-Michel Pawlotskyⴱ,‡
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reduced susceptibility to entecavir and rtN236T and
rtA181V/T confer reduced susceptibility to tenofovir in
vitro,11 the drug concentrations achieved in vivo are high
enough to control the replication of HBV variants bearing
these substitutions in the long term in treatment-naive
patients, preventing the accumulation of additional substitutions that could improve their fitness. Finally, triple
mutants that are fully resistant to entecavir do not appear
to pre-exist frequently at baseline in patients who have
not been exposed previously to lamivudine. Therefore,
their selection by first-line entecavir is unlikely, and the
antiviral potency of the drug prevents them from being
generated on treatment.7
In treated patients, adherence to therapy is a key factor
of maintained antiviral efficacy without virologic breakthroughs. Whether viral resistance could emerge after
many years in patients likely to receive life-long treatment
with these drugs remains unknown. Long-term follow-up
studies therefore are needed. For this reason, some experts
recommend de novo combination of tenofovir and one of
the nucleoside analogues, or tenofovir and emtricitabine
in one tablet, in patients with advanced HBV-related liver
disease, because resistance emergence would be life-threatening in these individuals.
In patients already exposed to a nucleoside/nucleotide
analogue who developed HBV resistance to this drug, the
“add-on” strategy was shown to be superior to the
“switch” strategy in preventing selection of viral variants
that are resistant to lamivudine and adefovir.4 However,
the superiority of the add-on vs switch strategy has not
been shown with entecavir or tenofovir, which are more
potent and have a higher barrier to resistance. Given the
number of patients and length of follow-up evaluation
needed to answer this question, it is likely that this information will never be available. In this context, it is reasonable to recommend that patients who developed resistance to one of the available HBV drugs be treated with a
combination of tenofovir plus 1 of the 3 nucleoside analogues (lamivudine, telbivudine, or entecavir), or with the
combination of tenofovir plus emtricitabine in one tablet,
because this strategy is the only one that can delay the
emergence of multidrug resistance. In this respect, the
best combination by far is tenofovir plus entecavir, but
long-term tolerance data are lacking and cost may be an
issue in certain areas of the world. This approach is
particularly important in the absence of any alternative
therapy active on viruses that would escape both nucleoside and nucleotide analogues, especially in patients with
advanced liver disease.
HCV Resistance to DAA Drugs
The virologic characteristics of HCV suggested
that HCV resistance would be an issue when DAA drugs
become available. Indeed, HCV is a highly variable positive-strand RNA virus, with large populations and a very
short half-life of free virions in peripheral blood.12,13
Mathematic modeling predicted that, in every infected
GASTROENTEROLOGY Vol. 142, No. 6
patient, all possible single, double, and possibly triple
mutants are generated each day and can be selected by
DAA administration.14 The pre-existence of viral variants
bearing amino acid substitutions that confer resistance to
the different classes of drugs in treatment-naive patients
has been shown by means of ultra-sensitive, pyrosequencing-based methods.15 In vitro, all DAAs currently in development select resistant, generally fit variants after multiple passages.16 Monotherapy studies with DAAs with a
low barrier to resistance, including NS3/4A protease inhibitors and non-nucleoside inhibitors of HCV RNA–
dependent RNA polymerase and NS5A inhibitors, have
shown early virologic breakthroughs owing to the selection and outgrowth of fit-resistant viral populations.
Other classes of drugs appear to have better resistance
profiles, such as, for instance, the nucleoside/nucleotide
analogue inhibitors of HCV RNA-dependent RNA polymerase, which select resistant variants that are poorly fit
and grow slowly in the presence of the drug, or the
cyclophylin inhibitors, which target a host protein involved in HCV replication, not a viral structure.16
To prevent resistance emergence, a DAA must be combined with one or several other, non– cross-resistant antiviral molecules. Three options currently are being explored: triple combinations with a DAA, pegylated
interferon (IFN)-alfa, and ribavirin; quadruple combinations with 2 non– cross-resistant DAAs, pegylated IFNalfa, and ribavirin; and all-oral, IFN-free drug regimens.
Clinical trials with these strategies have been reassuring
thus far. Indeed, in contrast to HIV and HBV, HCV infection is curable, and cure is easily achievable provided that
virus production is profoundly inhibited in a sustained
manner, to ensure progressive cure of infected cells, most
likely through the action of intracellular responses linked
to innate immunity, which are no longer suppressed by
viral protein expression. Therefore, the use of combinations of drugs that prevent the emergence of drug-resistant HCV variants over weeks to months is probably
sufficient to eradicate all viruses from a patient’s liver. The
choice of the drugs administered and of treatment duration are thus of the utmost importance.
What was learned from phase II and III triple combination trials is that, not surprisingly, cure of HCV infection is achieved easily in patients who respond to pegylated IFN-alfa and ribavirin; in contrast, treatment
failures are seen in poor IFN responders.17–19 In all patients who fail on this therapy, the population of viral
variants resistant to the protease inhibitor grows relative
to the wild-type virus that efficiently is inhibited. Indeed,
in phase II and III trials, resistant viruses were the dominant population at the time of failure (virologic breakthrough or relapse) in approximately 50%–70% of cases, as
detected by population sequencing. When treatment is
stopped, the wild-type, protease inhibitor–sensitive viral
population was shown to grow back and become dominant again in all patients within a few months, for up to
2 years, as assessed by population sequencing.20 It is
possible that protease inhibitor–resistant variants have
May 2012
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aggressive to the patient’s liver than wild-type viruses and
probably will be replaced by the latter within a few
months after treatment failure and discontinuation.
Given the current routes of transmission of HCV, such
resistant viruses also are unlikely to spread in newly infected individuals.
Conclusions
A good story never happens twice, and those who
thought that the HIV resistance adventure would start
again with hepatitis viruses may be disappointed. Most, if
not all, situations in HBV-infected patients now can be
controlled with entecavir and/or tenofovir. In resourceconstrained areas, tenofovir generally is accessible
through HIV programs at a reasonable cost and thus can
be used as first-line therapy or in combination with lamivudine in treatment-exposed patients. If tenofovir is
not available, the combination of lamivudine and adefovir
(often available as a generic drug in these countries) was
shown to be efficient in the long term, with a modest
risk of selection of resistance owing to rtA181V/T substitutions. Thus, HBV resistance no longer appears as a
major threat, at least in the short term to midterm, provided that patients are adherent to therapy. On the other
hand, the failure of DAA-containing therapies to cure
HCV infection is associated with selection of DAA-resistant viral populations. However, outgrowth of resistant
variants is not harmful, and the wild-type virus generally
grows back as the dominant species within a few months
after therapy. HCV remains curable in these patients, who
will have access to better combinations in the midterm
future. A pan-genotype, highly efficient, all-oral, IFN-free
treatment regimen most likely will be available within a
few years. As a result, the rising tide of HIV resistance
specialists moving to the hepatitis field might end up as
an ebb tide.
References
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3. Hadziyannis SJ, Tassopoulos NC, Heathcote EJ, et al. Long-term
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THERAPEUTIC
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DEVELOPMENTS
acquired additional substitutions that further improve
their fitness in the presence of a protease inhibitor. Nevertheless, 2 years after a triple combination treatment
failure, a situation close to the pretherapeutic one has
been restored, with a dominant wild-type viral population
and the presence of minor variants bearing amino acid
substitutions conferring resistance to protease inhibitors.
Selection of resistant HCV variants in these patients does
not appear to be harmful, and a new treatment with a
first-generation protease inhibitor sharing cross-resistance
with telaprevir and boceprevir is not contraindicated, provided that this drug is combined with another drug or
several drugs that potently inhibit HCV replication while
sharing no cross-resistance with protease inhibitors (thus,
excluding re-treatment in combination with pegylated
IFN-alfa and ribavirin only).
A recent study, based on a small number of null responders to a first course of pegylated IFN-alfa and ribavirin, has shown viral eradication in all cases with a
quadruple combination of pegylated IFN-alfa, ribavirin,
and 2 DAAs with no cross-resistance, including an
NS3/4A protease inhibitor and an NS5A inhibitor.21 Because the frequency of viral breakthroughs caused by
multidrug-resistant viruses was high with these 2 DAAs in
the absence of pegylated IFN-alfa and ribavirin for subtype 1a, this result indirectly suggests that sustaining
HCV inhibition and preventing early re-increase of viral
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Based on these data, there is no reason to think that an
IFN-free regimen would not be able to eradicate HCV in
virtually all cases if no resistant HCV variants are selected
during treatment. Such a DAA combination must have a
high barrier to resistance, and treatment must be administered for long enough to ensure that every infected cell
is cured. In a recent proof-of-concept study, 9 of 10 prior
null responders to pegylated IFN-alfa and ribavirin infected with HCV subtype 1b achieved viral eradication
after 24 weeks of treatment with an NS3/4A protease
inhibitor and an NS5A inhibitor, a DAA combination
with a high barrier to resistance in this subtype. No
patient broke through owing to selection of resistant
HCV variants.22 In another study, 10 of 10 treatmentnaive patients infected with HCV genotype 2 or 3 achieved
an SVR after 12 weeks of a combination of a nucleotide
analogue and ribavirin.23
The challenge now will be to identify the optimal IFNfree, all-oral DAA combination that can become the universal first-line therapy for chronic hepatitis C. This combination ideally must have pan-genotype coverage and a
high enough barrier to resistance to yield very high cure
rates within a reasonable time frame. Given the properties
of the drugs currently in development, such a combination could be available within the next 5–7 years. In the
meantime, treating physicians should be cautious when
using nonoptimal IFN-free combinations because some of
them will yield frequent selection of multidrug-resistant
viruses. However, these viruses are unlikely to be more
HEPATITIS VIRUS RESISTANCE
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DEVELOPMENTS
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17. Bacon BR, Gordon SC, Lawitz E, et al. HCV RESPOND-2 final
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20. Zeuzem S, Sulkowski MS, 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):436A.
21. Lok AS, Gardiner D, Lawitz E, et al. Quadruple therapy with BMS790052, 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.
22. Chayama K, Takahashi S, Kawakami Y, et al. Dual oral combination therapy with the NS5A inhibitor BMS-790052 and the NS3
protease inhibitor BMS-650032 achieved 90% sustained virologic
response (SVR12) in HCV genotype 1b-infected null responders.
Hepatology 2011;54(Suppl):1428A.
23. Gane EJ, Stedman CA, Hyland RH, et al. Once daily PSI-7977 plus
RBV: pegylated interferon-alfa not required for complete rapid viral
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Received October 28, 2011. Accepted December 2, 2011.
Reprint requests
Address requests for reprints to: Professor Jean-Michel Pawlotsky,
MD, PhD, Department of Virology, Hôpital Henri Mondor, 51 Avenue
du Maréchal de Lattre de Tassigny, 94010 Créteil, France. e-mail:
[email protected]; fax: (33) 1-4981-4831.
Conflicts of Interest
The author discloses the following: The author has served as an
advisor for Abbott, Achillion, Anadys, Biotica, Boehringer-Ingelheim,
Bristol-Myers Squibb, DebioPharm, Gen-Probe, Gilead, GlaxoSmithKline, Idenix, Inhibitex, Janssen-Cilag, Madaus-Rottapharm,
Sanofi-Aventis, Schering-Plough/Merck, Novartis, Pfizer, Roche,
Vertex, and Virco.
Funding
The author has received research grants from Gilead and Roche.