Long-term follow-up of chronic hepatitis B after the emergence of mutations in the hepatitis B virus polymerase region

The impact of the hepatitis B virus polymerase rtA181T mutation on replication and drug resistance is potentially affected by overlapping changes in surface gene

The emergence of drug-resistant hepatitis B virus (HBV) is a major problem for antiviral treatment in chronic hepatitis B infection. In this study, we analyzed the evolution of drug-resistant mutations and characterized the effects of the rtA181T and rtI233V mutations on viral replication and drug resistance. We performed a clonal analysis of the HBV polymerase gene from serum samples during viral breakthrough treated with antiviral agents. A series of mutant clones containing rtA181T and/or rtI233V mutations were constructed and determined the effect of these mutations on the replication ability and drug resistance. An in vitro study revealed that the effect of the rtA181T mutation on viral replication and drug resistance is dependent on the mutations in the overlapping surface gene. Compared to the rtA181T surface missense mutation (rtA181T/sW172S), the introduction of rtA181T surface nonsense mutation (rtA181T/sW172*) resulted in decreased viral replication and increased drug resistance. Complementation assay revealed that the truncated PreS1 is responsible for reduced replication of rtA181T/sW172* mutant. Moreover, the rtA181T/sW172* mutant exhibited a defect in viral particle secretion. The rtI233V mutation that emerged during adefovir therapy reduced viral replication and conferred resistance to adefovir. Our data suggest that the impact of the rtA181T mutation on replication and drug resistance differs based on the mutation status of the corresponding surface gene. The rtI233V mutation also affects replication ability and drug resistance. This observation suggests the need for genotypic analysis of overlapping surface genes to manage antiviral drug resistance if clinical isolates harbor the rtA181T mutation.

IMPORTANCE

The emergence of drug-resistant HBV that are no longer susceptible to nucleos(t)ide analogues is a major problem for antiviral treatment in chronic hepatitis B infection. Among drug-resistant mutations, the single rtA181T mutation is known to confer cross-resistance to antiviral drugs. This mutation causes intermediate or reduced susceptibility to tenofovir. Moreover, the clinical occurrence of the rtA181T mutation during antiviral therapy is also high. Our study revealed that the effect of the rtA181T mutation on viral replication and drug resistance is dependent on the mutations in the overlapping surface gene. This observation suggests the need for genotypic analysis of overlapping surface genes to manage antiviral drug resistance if clinical isolates harbor the rtA181T mutation. We believe that our study will not only extend the understanding of the drug resistance mechanism, but it will also ultimately provide new treatment options for patients with multidrug resistant HBV.

Should lamivudine monotherapy be stopped or continued in patients infected with hepatitis B with favorable responses after more than 5 years of treatment?

Regarding the limited evidence for determining the optimal duration of antiviral treatment for hepatitis B, the long-term outcome of patients with favorable responses to over 5 years of lamivudine monotherapy was investigated. Two hundred seventy-one patients who had received lamivudine for at least 5 years were enrolled. Ultimately, 72 patients without YMDD mutations and showing hepatitis B virus (HBV) DNA levels <2.5 pg/ml after 5 years of treatment were analyzed. Mean treatment duration with lamivudine was 9.1 ± 2.6 years. During the treatment, HBeAg and HBsAg loss/seroconversion rates were 95 and 6.9%, respectively. Decompensation and hepatocellular carcinoma (HCC) developed in 2.8 and 6.9% of patients, respectively. Old age and cirrhosis were risk factors for HCC development. Finally, 11.1% of patients developed YMDD mutations after 8.3 ± 2.4 years of treatment. There was no hepatic decompensation among the patients who developed delayed YMDD mutations. Sixteen patients who achieved a complete response stopped lamivudine and four patients showed relapses 10.3 ± 8.5 months after stopping lamivudine. Relapsed patients had more cirrhotic livers and higher rates of HBeAg positivity at 5 years than patients who maintained complete response. The present study suggests that patients who do not develop YMDD mutations over 5 years of treatment with lamivudine may continue lamivudine monotherapy until the loss of HBsAg. However, even for the patients showing favorable response over 5 years of treatment, those in older ages, with cirrhosis or who show poor HBeAg responses should be on careful monitoring to detect the development of viral mutations, relapse and even HCC.

Sensitive assay for quantification of hepatitis B virus mutants by use of a minor groove binder probe and peptide nucleic acids

Lamivudine is the first nucleoside analogue that was shown to have a potent effect on hepatitis B virus (HBV). However, the emergence of mutants resistant or cross-resistant to nucleoside/nucleotide analogues remains a serious problem. Several assays for the detection and quantification of antiviral-resistant mutants have been reported, but it has been difficult to measure the amounts of mutants accurately, especially when the target strain is a minor component of the mixed population. It has been shown that accurate measurement of a minor strain is difficult as long as a matching reaction with a single probe is included in the assay. We developed a new method for the quantification of lamivudine-resistant strains in a mixed-virus population by real-time PCR using minor groove binder probes and peptide nucleic acids, and we achieved a wide and measurable range, from 3 to 10 log10 copies/ml, and high sensitivity, with a discriminative limit of 0.01% of the predominant strain. The clinical significance of measuring substitutions not only of M204 but also of L180 residues of HBV polymerase was demonstrated by this method. This assay increases the versatility of a sensitive method for the quantification of a single-nucleotide mutation in a heterogeneous population.

Evolution of hepatitis B virus quasispecies during sequential therapy in patients with lamivudine-resistant hepatitis B virus infection

AIM: To investigate the evolution characteristics of hepatitis B virus (HBV) quasispecies during sequential therapy in patients with lamivudine-resistant HBV infection.

METHODS: Serum samples were collected from seven patients with lamivudine-resistant HBV infection during sequential therapy. The reverse-transcriptase (RT) region of the HBV polymerase gene was amplified, cloned and sequenced. Sequence mutations were analyzed to characterize the evolution of HBV quasispecies.

RESULTS: Lamivudine-resistant strains were persistently present in the serum of patients 1, 4 and 5. The main mutation patterns were M204I+L80I, M204I+L80I+L180M, M204V+L180M+G173L, and M204V+L180M. The proportion of these mutant strains changed constantly. The wild-type strain was detected in patients 2 and 3. However, lamivudine-resistant strains were detected in patient 2 during following therapy. Double-resistant mutant strains M204V+L180M+G173L+T184A and M204V+L180M+G173L+N236D were detected in patient 6, who underwent combination therapy with adefovir dipivoxil and lamivudine, and in patient 7, who underwent adefovir dipivoxil monotherapy.

CONCLUSION: Lamivudine-resistant mutant strains in the serum of patients with HBV infection do not easily disappear during sequential therapy. Cross-resistant or multi-resistant strains of HBV quasispecies are often present during sequential therapy and affect the response to the therapy, thereby resulting in therapeutic failure.

Current prophylactic strategies against hepatitis B virus recurrence after liver transplantation

Prophylactic strategies against hepatitis B virus (HBV) recurrence after liver transplantation (LT) are essential for patients with HBV-related disease. Before LT, lamivudine (LAM) was proposed to be down-graded from first- to second-line therapy. In contrast, adefovir dipivoxil (ADV) has been approved not only as first-line therapy but also as rescue therapy for patients with LAM resistance. Furthermore, combination of ADV and LAM may result in lower risk of ADV resistance than ADV monotherapy. Other new drugs such as entecavir, telbivudine and tenofovir, are probably candidates for the treatment of hepatitis-B-surface-antigen-positive patients awaiting LT. After LT, low-dose intramuscular hepatitis B immunoglobulin (HBIG), in combination with LAM, has been regarded as the most cost-effective regimen for the prevention of post-transplant HBV recurrence in recipients without pretransplant LAM resistance and rapidly accepted in many transplant centers. With the introduction of new antiviral drugs, new hepatitis B vaccine and its new adjuvants, post-transplant HBIG-free therapeutic regimens with new oral antiviral drug combinations or active HBV vaccination combined with adjuvants will be promising, particularly in those patients with low risk of HBV recurrence.

Pharmacotherapy of chronic viral hepatitis and hepatocellular carcinoma

BACKGROUND

Hepatitis B virus (HBV) is a major etiologic agent of chronic liver disease (CLD) and hepatocellular carcinoma. Drugs have been developed and shown to be effective against HBV replication. These treatments are often associated with the resolution of CLD. However, they are too expensive, not well tolerated, and result in the development of resistance when given as mono or salvage therapies. In addition, most of these drugs target only the virus polymerase.

OBJECTIVE

To revitalize the field, drugs with other targets and combination therapies need to be developed.

METHODS

Major advances in HBV and liver cancer drug development over the past decade, focusing on Phase III trials and FDA-approved compounds, are presented.

RESULTS/DISCUSSION

A number of potent nucleoside/nucleotide analogs are now available for treatment, but for the long-term management of CLD, the development of combination therapies will probably be required. Development of compounds with new virus targets will enhance the utility of combination therapies. Development of compounds to host targets altered prior to or after the development of liver cancer, as demonstrated by sorafenib, need to be developed. The goal is to devise drug cocktails that will yield sustained virus responses and halt disease progression and tumor development.

Potential and limitations of lamivudine monotherapy in chronic hepatitis B: evidence from genotyping

BACKGROUND

Current oral therapy for hepatitis B virus (HBV) is limited by the presence of resistance leading to resumption of higher levels of HBV replication. Therefore, there is a need for a better definition of the potential role and limitations of lamivudine or similar therapies, used alone.

AIMS

To examine the viability of lamivudine and similar monotherapies as a treatment strategy in chronic HBV in the face of the worldwide burden of disease.

METHODS

We have reviewed the role of lamivudine monotherapy in the treatment of chronic HBV in a single tertiary referral liver centre over a 9-year period. We analysed the outcome in 90 patients where lamivudine has apparently conferred long-term viral suppression and investigated the development of genotypic resistance in the absence of ostensible phenotypic resistance. Patients were subdivided into hepatitis B e antigen (HBeAg)-positive and anti-HBe-positive groups.

RESULTS

Virtually all HBeAg-positive patients who failed to seroconvert have progressed to combination antiviral therapy. Only 19%(7/36) of HBeAg-negative patients have continued suppression without detectable genotypic change after 4 years of therapy.

CONCLUSIONS

These data demonstrate that despite a relatively low level of viraemia in HBeAg-negative patients, we could detect resistance mutations by direct sequencing in all patients with amplifiable HBV DNA. Our results suggest that for patients with ongoing replication at 'amplifiable' levels of HBV DNA, but <10(5) copies/ml, genotypic selection is readily detectable. Lamivudine monotherapy has not sufficed for the overwhelming majority of patients.

Quantification of lamivudine-resistant hepatitis B virus mutants by type-specific TaqMan minor groove binder probe assay in patients with chronic hepatitis B

BACKGROUND

Lamivudine (LAM)-resistant hepatitis B virus (HBV) with mutations in the polymerase region frequently appears after long-term use of LAM. Several methods allowing detection of mutant strains (YIDD, YVDD) have been reported, but they have no quantitative characteristics. In this study, we explored a unique approach for quantification of each mutant strain.

METHODS

A method for detection and quantification of wild and mutant strains was developed using realtime polymerase chain reaction and type-specific minor groove binder (MGB) probes, and tested in patients with chronic hepatitis B before and after additive treatment with adefovir dipivoxil (ADV).

RESULTS

A good correlation was confirmed in HBV DNA quantity obtained between the YMDD-specific MBG probe assay and Amplicor HBV Monitor assay results (P < 0.001), linear between 3 and 9 log copies/mL serum. Of 109 samples from patients with chronic hepatitis B tested by both these assays and conventional direct sequencing, 90 (88.2%) showed identical results. The assays successfully detected and quantified a single type of mutant in three of four patients with additive ADV treatment, and also two coexisting mutant types (YIDD and YVDD) in the remaining patient.

CONCLUSIONS

Our specific and sensitive method for detection and quantification of HBV DNA with the wild-type YMDD motif and its two mutant forms (YIDD and YVDD) appears to be clinically useful, especially in patients with multiple mutant HBV infections.

The emergence of YMDD mutants precedes biochemical flare by 19 weeks in lamivudine-treated chronic hepatitis B patients: an opportunity for therapy reevaluation

Given the loss of therapeutic efficacy associated with the development of resistance to lamivudine (LMV) and the availability of new alternative treatments for chronic hepatitis B patients, early detection of viral genotypic resistance could allow the clinician to consider therapy modification before viral breakthrough and biochemical relapse occur. To this end, 28 LMV-treated patients (44 +/- 12 years; 24 men), on their first therapy schedule, were monitored monthly at four Brazilian centers for the emergence of drug resistance using the reverse hybridization-based INNO-LiPA HBV DR assay and occasionally sequencing (two cases). Positive viral responses (HBV DNA clearance) after 6, 12, and 18 months of therapy were achieved by 57, 68, and 53% of patients, while biochemical responses (serum alanine aminotransferase normalization) were observed in 82, 82, and 53% of cases. All viral breakthrough cases (N = 8) were related to the emergence of YMDD variants observed in 7, 21, and 35% of patients at 6, 12, and 18 months, respectively. The emergence of these variants was not associated with viral genotype, HBeAg expression status, or pretreatment serum alanine aminotransferase levels. The detection of resistance-associated mutations was observed before the corresponding biochemical flare (41 +/- 14 and 60 +/- 15 weeks) in the same individuals. Then, if highly sensitive LMV drug resistance testing is carried out at frequent and regular intervals, the relatively long period (19 +/- 2 weeks) between the emergence of viral resistance and the onset of biochemical relapse can provide clinicians with ample time to re-evaluate drug therapy.

Prolonged persistence of lamivudine-resistant mutant and emergence of new lamivudine-resistant mutants two years after lamivudine withdrawal in HBsAg-positive chronic hepatitis patient: a case report

Lamivudine can select resistant hepatitis B virus (HBV) tyrosine-methionine-aspartate-aspartate aminoacid motif (YMDD) mutants, which usually disappear in few months after lamivudine withdrawal. We report an unusual case of a male adult patient who showed a prolonged persistence of the M204I mutation up to 24 months after lamivudine withdrawal followed by the emergence of new distinct YMDD mutants (namely M204V, V207L). Only 42 months after lamivudine withdrawal wild-type YMDD motif became dominant over the YMDD mutants. To our knowledge, a so prolonged persistence of a YMDD mutant and also the emergence of new YMDD mutants many months after drug withdrawal are unusual.

Major Causes of Antiviral drug Resistance and Implications for Treatment of Hepatitis B virus Monoinfection and Coinfection with HIV

The two key events in the life-cycle of the hepatitis B virus (HBV) involve (1) the generation from viral genomic DNA of the covalently closed circular DNA transcriptional template, and (2) the reverse transcription of the viral pregenomic RNA to form the HBV DNA genome. Diversity in the HBV genome is ensured by the low fidelity of the viral reverse transcriptase (rt). Particular selection pressures such as antiviral therapy readily select out escape mutants from this pre-existing quasispecies pool. Antiviral drug resistance in chronic hepatitis B can be caused by many factors, including the viral mutation frequency, the intrinsic mutability of the antiviral target site, the selective pressure exerted by the drug, the magnitude and rate of virus replication, the overall replication fitness of the mutant, the genetic barrier of the >compound and the availability of replication space. In the setting of HIV coinfection, the rate of replication is increased by one to two orders of magnitude, accelerating the emergence of drug resistance in this setting. The HBV genome is arranged into frame-shifted and overlapping reading frames in such a manner that antiviral drug-resistance-associated changes in the rt can result in changes in the viral envelope protein. These HBV isolates with altered surface antigens exhibit reduced binding of specific and neutralizing antibody and so have diagnostic and public health implications, especially in the setting of HIV coinfection where the risk of transmission is increased. Thus, prevention of resistance requires the adoption of strategies that effectively control virus replication, including the use of combination chemotherapy.

Low risk of hepatitis B virus recurrence after withdrawal of long-term hepatitis B immunoglobulin in patients receiving maintenance nucleos(t)ide analogue therapy

Hepatitis B virus (HBV) recurrence rates of 0-16% had been reported in patients maintained on nucleoside analogues (NA) after hepatitis B immunoglobulin (HBIG) discontinuation after orthotopic liver transplantation (OLT). However, follow-up in most studies was short. We aimed to determine the long-term risk of HBV recurrence using this strategy. All HBV patients who received > or =7 doses of intravenous HBIG after OLT, with no HBV recurrence while receiving HBIG, and who eventually discontinued HBIG and were maintained on NA, were included. HBV recurrence was defined as HBsAg-positive or HBV DNA > or =5 log copies/mL on 2 consecutive occasions. Twenty-one patients met the inclusion criteria. Immediate post-OLT prophylaxis was combination HBIG and NA in 15 patients, whereas 6 patients received HBIG monotherapy for 62-109 months before NA was added. HBIG was discontinued a median of 26 (range, 0.2-121) months after OLT. Median follow-up post-HBIG discontinuation was 40 (range, 5-51) months. Only 1 patient, who had 12 months of HBIG and was noncompliant to NA therapy, had HBV recurrence, 34 months after HBIG discontinuation. One patient had HBV DNA of 3.3 log copies/mL 47 and 48 months after HBIG discontinuation but remained HBsAg-negative. Lamivudine-resistant mutations were detected in both patients. Probability of HBV recurrence was 0% and 9% at 2 and 4 years after HBIG discontinuation. Three patients had 1-2 episodes of transiently detectable HBV DNA. All were HBV DNA and HBsAg negative on repeated tests over a period of 2-36 months. Maintenance therapy with NA after discontinuation of long-term HBIG therapy is associated with a low risk of HBV recurrence after OLT in compliant HBV patients.

Fatal liver failure caused by reactivation of lamivudine-resistant hepatitis B virus: A case report

We present a case of fetal liver failure caused by the activation of lamivudine-resistant hepatitis B virus (HBV) nine months after lamivudine treatment. A 57-year old man visited our hospital for the treatment of decompensated chronic hepatitis B. Lamivudine was started in December 2001. Subsequently, serum HBV was negative for HBV DNA with seroconversion from HBeAg to anti-HBe and improvement of liver function. However, HBV DNA and HBeAg were again detected in September 2002. He was complicated by breakthrough hepatitis and admitted to our hospital in November for severely impaired liver function. Vidarabine treatment was started and serum HBV DNA and alanine aminotransferase (ALT) decreased transiently. However, after the start of α-interferon treatment, HBV DNA level increased and liver function deteriorated. He died 1 mo after admission. An analysis of amino acid sequences in the polymerase region revealed that rtM204I/V with rtL80I/V occurred at the time of viral breakthrough. After the start of antiviral treatment, rtL180M was detected in addition to rtM204I/V and rtL80I/V, and became predominant in the terminal stage of the disease. HBV clone with a high replication capacity may be produced by antiviral treatment leading to the worsening of liver function. Antiviral therapy for patients with breakthrough hepatitis in advanced liver disease should be carefully performed.

Evolution of multi-drug resistant hepatitis B virus during sequential therapy

Multi-drug resistant hepatitis B virus (HBV) has been reported in hepatitis B patients who received sequential antiviral therapy. In vitro studies showed that HBV constructs with mutations resistant to lamivudine and adefovir have marked reduction in sensitivity to combination of lamivudine and adefovir, whereas constructs with mutations resistant to either drug remain sensitive to the other drug. We conducted this study to determine whether mutations conferring resistance to multiple antiviral agents co-locate on the same HBV genome in vivo and to describe the evolution of these mutations. Sera from six patients who had been found to have multi-drug resistant HBV mutations to lamivudine+adefovir, lamivudine+hepatitis B immunoglobulin (HBIG), or lamivudine+entecavir on direct sequencing were cloned after nested polymerase chain reaction (PCR). Analysis of 215 clones from 11 samples with multi-drug resistant mutations on direct sequencing showed that 183 (85%) clones had mutations to both therapies on the same genome; 31 clones had lamivudine-resistant mutants only. Clonal analysis of serial samples from three patients showed progressive evolution from all clones with lamivudine-resistant HBV mutations only to mixtures of clones that have multi-drug resistant mutations and clones that have lamivudine-resistant HBV mutations only, and ultimately all clones having multi-drug resistant HBV mutations. In conclusion, mutations conferring resistance to multiple antiviral agents co-locate on the same viral genome, suggesting that combination therapy directed against mutants resistant to each treatment may not be adequate in suppressing multi-drug resistant HBV. De novo combination therapy may prevent the emergence of multi-drug resistant mutants.

The Clinical Impact of Early Detection of the Ymdd Mutant on the Outcomes of Long-Term Lamivudine Therapy in Patients with Chronic Hepatitis B

The early emergence of lamivudine (3TC)-resistant tyro-sine–methionine–aspartate–aspartate (YMDD) mutants has been reported during 3TC therapy in patients with chronic hepatitis B (CHB) in hepatitis B virus (HBV)-endemic areas; however, its clinical impact during long-term 3TC therapy is unknown. This study was performed to investigate the impact of the early emergence of YMDD mutants 3 months after the initiation of treatment on the outcomes of long-term 3TC therapy in HBV e antigen (HBeAg)-positive CHB. We analysed YMDD genotypes in consecutive samples from 30 patients with HBeAg positive CHB throughout 3TC treatment using both restriction fragment length polymorphism and mass spectrometric assays. Long-term outcome was compared between patients who had YMDD mutations detected at 3 months and those who had no mutations. YMDD mutation was detected in 16 (53.3%) out of 30 patients at 3 months and only the rtM204I mutation was found. Cumulative HBeAg loss rates at 3 years was 12.5% and 57.4% in patients who had the rtM204I mutant and wild-type virus at 3 months, respectively ( P=0.010). Cumulative viral breakthrough rates at 3 years was 75.0% and 14.3% in patients who had the rtM204I mutant and wild-type virus at 3 months, respectively ( P=0.002). Logistic regression revealed that YMDD mutation at 3 months was significantly related to viral breakthrough within 24 months ( P=0.003). In conclusion, early detection for HBV YMDD mutation at 3 months may be useful to predict the long-term outcomes of 3TC therapy in patients with HBeAg-positive CHB in HBV-endemic areas.

Personal view: the management of chronic hepatitis B infection

There are two new nucleoside analogues available for the management of chronic hepatitis B, adefovir and entecavir, and several more in development. In addition, pegylated interferon has become available. Large-scale population studies have re-emphasized the significance of viral load in predicting a poor outcome over the longer term. These new developments have prompted a reassessment of the indications and objectives of therapy for chronic hepatitis B. Hepatitis B virus deoxyribonucleic acid, rather than alanine aminotransferase should be the prime indication for therapy. Hepatitis B e antigen seroconversion can be achieved in 30-40% of treated patients whatever agent is used. However, it takes longer for nucleoside analogues to achieve the same seroconversion rates as interferon. In anti-HBe-positive disease long-term therapy is required for most patients because the relapse rate after withdrawal of therapy is very high, irrespective of the agent used. Viral resistance limits the use of lamivudine, and to a lesser extent adefovir. Resistance to entecavir has so far only been described in pre-existing lamivudine resistance. Although therapy with combinations of nucleoside analogues has not been investigated to any extent, this is the only way to reduce the emergence or resistance, and studies are urgently needed.

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