Summary
Chronic hepatitis B (CHB) infection affects over 250 millon people worldwide and 800000 are expected to die yearly due to the development of hepatocellular carcinoma (HCC). Current antiviral ...therapies include nucleoside analogs (NAs) that target the viral retrotranscriptase inhibiting de novo viral production. Pegylated interferon (Peg‐IFN) is also effective in reducing the viral DNA load in serum. However, both treatments remain limited to control the infection, aiming for viral suppression and improving the quality of life of the infected patients. Complete cure is not possible due to the presence of the stable DNA intermediate covalently closed circular DNA (cccDNA). Attempts to achieve a functional cure are thus ongoing and novel targets and molecules, together with different combination therapies are currently in the pipeline for early clinical trials. In this review we discuss novel treatments both targeting directly and indirectly cccDNA. As we gain knowledge in the Hepatitis B virus (HBV) transcriptional control, and newer technologies emerge that could potentially allow the destruction of cccDNA, exciting new possibilities for curative therapies are discussed.
HBV has evolved a unique life cycle that results in the production of enormous viral loads during active replication without actually killing the infected cells directly. Two of the key events in the ...viral life cycle of HBV involve firstly the generation of a covalently closed circular (ccc)DNA transcriptional template, either from input genomic DNA or newly replicated capsid-associated DNA, and secondly, reverse transcription of the viral pregenomic (pg)RNA to form progeny HBV DNA genomes. New data are emerging regarding the epigenetic control of cccDNA, which might represent another key factor involved in the pathogenesis and natural history of the disease. Because HBV uses reverse transcription to copy its genome, mutant viral genomes emerge frequently. Particular selection pressures, both endogenous (host immune clearance) and exogenous (vaccines and antiviral drugs), readily select out these escape mutants. The particular viral mutations or combination of mutations that directly affect the clinical outcome of infection are not known; however, four major 'pathways' of antiviral drug resistance-associated substitutions have now been identified. Further studies are clearly needed to identify the pathogenetic basis and clinical sequelae arising from the selection of these particular mutants. In the clinical context of antiviral drug resistance, treating physicians need to adopt therapeutic strategies that effectively control viral replication. Finally, the role of host genetics in influencing the outcome of HBV disease in the context of natural history and therapy is beginning to aid understanding in pathogenesis and, when this knowledge is linked to pathogen-specific databases, this should translate into more individualized patient care.
Chronic hepatitis B virus (HBV) infection is a major factor in hepatocellular carcinoma (HCC) pathogenesis by a mechanism not yet understood. Elucidating mechanisms of HBV‐mediated ...hepatocarcinogenesis is needed to gain insights into classification and treatment of HCC. In HBV replicating cells, including virus‐associated HCCs, suppressor of zeste 12 homolog (SUZ12), a core subunit of Polycomb repressive complex2 (PRC2), undergoes proteasomal degradation. This process requires the long noncoding RNA, Hox transcript antisense intergenic RNA (HOTAIR). Intriguingly, HOTAIR interacts with PRC2 and also binds RNA‐binding E3 ligases, serving as a ubiquitination scaffold. Herein, we identified the RNA helicase, DEAD box protein 5 (DDX5), as a regulator of SUZ12 stability and PRC2‐mediated gene repression, acting by regulating RNA‐protein complexes formed with HOTAIR. Specifically, knockdown of DDX5 and/or HOTAIR enabled reexpression of PRC2‐repressed genes epithelial cell adhesion molecule (EpCAM) and pluripotency genes. Also, knockdown of DDX5 enhanced transcription from the HBV minichromosome. The helicase activity of DDX5 stabilized SUZ12‐ and PRC2‐mediated gene silencing, by displacing the RNA‐binding E3 ligase, Mex‐3 RNA‐binding family member B (Mex3b), from HOTAIR. Conversely, ectopic expression of Mex3b ubiquitinated SUZ12, displaced DDX5 from HOTAIR, and induced SUZ12 down‐regulation. In G2 phase of cells expressing the HBV X protein (HBx), SUZ12 preferentially associated with Mex3b, but not DDX5, resulting in de‐repression of PRC2 targets, including EpCAM and pluripotency genes. Significantly, liver tumors from HBx/c‐myc bitransgenic mice and chronically HBV‐infected patients exhibited a strong negative correlation between DDX5 messenger RNA levels, pluripotency gene expression, and liver tumor differentiation. Notably, chronically infected HBV patients with HCC expressing reduced DDX5 exhibited poor prognosis after tumor resection, identifying DDX5 as an important player in poor prognosis HCC. Conclusion: The RNA helicase DDX5, and E3 ligase Mex3b, are important cellular targets for the design of novel, epigenetic therapies to combat HBV infection and poor prognosis HBV‐associated liver cancer. (Hepatology 2016;64:1033‐1048)
Heparan sulfate proteoglycans (HSPGs) are a major constituent of the extracellular matrix (ECM) and are found to be implicated in viral infections, where they play a role in both cell entry and ...release for many viruses. The enzyme heparanase-1 is the only known endo-beta-D-glucuronidase capable of degrading heparan sulphate (HS) chains of HSPGs and is thus important for regulating ECM homeostasis. Heparanase-1 expression is tightly regulated as the uncontrolled cleavage of HS may result in abnormal cell activation and significant tissue damage. The overexpression of heparanase-1 correlates with pathological scenarios and is observed in different human malignancies, such as lymphoma, breast, colon, lung, and hepatocellular carcinomas. Interestingly, heparanase-1 has also been documented to be involved in numerous viral infections, e.g., HSV-1, HPV, DENV. Moreover, very recent reports have demonstrated a role of heparanase-1 in HCV and SARS-CoV-2 infections. Due to the undenied pro-carcinogenic role of heparanase-1, multiple inhibitors have been developed, some reaching phase II and III in clinical studies. However, the use of heparanase inhibitors as antivirals has not yet been proposed. If it can be assumed that heparanase-1 is implicated in numerous viral life cycles, its inhibition by specific heparanase-acting compounds should result in a blockage of viral infection. This review addresses the perspectives of using heparanase inhibitors, not only for cancer treatment, but also as antivirals. Eventually, the development of a novel class antivirals targeting a cellular protein could help to alleviate the resistance problems seen with some current antiretroviral therapies.
Hepatocellular carcinoma (HCC) ranks number three among the most frequent causes of death from solid tumors worldwide. With obesity and fatty liver diseases as risk factors on the rise, HCC ...represents an ever increasing challenge. While there is still no curative treatment for most patients numerous novel drugs have been proposed, but most ultimately failed in phase III trials. This manuscript targets therapeutic advances and most burning issues. Expert key point summaries and urgent research agenda are provided regarding risk factors, including microbiota, need for prognostic and predictive biomarkers and the equivocal role of liver biopsy. Therapeutic topics highlighted are locoregional techniques, combination therapies and the potential of immunotherapy. Finally the manuscript provides a critical evaluation of novel targets and strategies for personalized treatment of HCC.
Hepatitis B virus (HBV) covalently closed circular (ccc)DNA is the key genomic form responsible for viral persistence and virological relapse after treatment withdrawal. The assessment of residual ...intrahepatic cccDNA levels and activity after long-term nucleos(t)ide analogues therapy still represents a technical challenge. Quantitative (q)PCR, rolling circle amplification (RCA) and droplet digital (dd)PCR assays were used to quantify residual intrahepatic cccDNA in liver biopsies from 56 chronically HBV infected patients after 3 to 5 years of telbivudine treatment. Activity of residual cccDNA was evaluated by quantifying 3.5 kB HBV RNA (preC/pgRNA) and by assessing cccDNA-associated histone tails post-transcriptional modifications (PTMs) by micro-chromatin immunoprecipitation. Long-term telbivudine treatment resulted in serum HBV DNA suppression, with most of the patients reaching undetectable levels. Despite 38 out of 56 patients had undetectable cccDNA when assessed by qPCR, RCA and ddPCR assays detected cccDNA in all-but-one negative samples. Low preC/pgRNA level in telbivudine-treated samples was associated with enrichment for cccDNA histone PTMs related to repressed transcription. No difference in cccDNA levels was found according to serum viral markers evolution. This panel of cccDNA evaluation techniques should provide an added value for the new proof-of-concept clinical trials aiming at a functional cure of chronic hepatitis B.
Background & Aims The outcome of hepatitis B virus (HBV) infection may be influenced by early interactions between the virus and hepatocyte innate immune responses. To date, the study of such ...interactions during the very early step of infection has not been adequately investigated. Methods We used the HepaRG cell line, as well as primary human hepatocytes to analyze, within 24 h of exposure to HBV, either delivered by a physiologic route or baculovirus vector (Bac-HBV), the early modulation of the expression of selected antiviral/pro-inflammatory cytokines and interferon stimulated genes. Experiments were also performed in the presence or absence of innate receptor agonists to investigate early HBV-induced blockade of innate responses. Results We show that hepatocytes themselves could detect HBV, and express innate genes when exposed to either HBV virions or Bac-HBV. Whereas Bac-HBV triggered a strong antiviral cytokine secretion followed by the clearance of replicative intermediates, a physiologic HBV exposure led to an abortive response. The early inhibition of innate response by HBV was mainly evidenced on Toll-like receptor 3 and RIG-I/MDA5 signaling pathways upon engagement with exogenous agonist, leading to a decreased expression of several pro-inflammatory and antiviral cytokine genes. Finally, we demonstrate that this early inhibition of dsRNA-mediated response is due to factor(s) present in the HBV inoculum, but not being HBsAg or HBeAg themselves, and does not require de novo viral protein synthesis and replication. Conclusions Our data provide strong evidence that HBV viral particles themselves can readily inhibit host innate immune responses upon virion/cell interactions, and may explain, at least partially, the “stealthy” character of HBV.
HBV infection is a major cause of liver cirrhosis and hepatocellular carcinoma. Although HBV infection can be efficiently prevented by vaccination, and treatments are available, to date there is no ...reliable cure for the >240 million individuals that are chronically infected worldwide. Current treatments can only achieve viral suppression, and lifelong therapy is needed in the majority of infected persons. In the framework of the French National Agency for Research on AIDS and Viral Hepatitis 'HBV Cure' programme, a scientific workshop was held in Paris in June 2014 to define the state-of-the-art and unanswered questions regarding HBV pathobiology, and to develop a concerted strategy towards an HBV cure. This review summarises our current understanding of HBV host-interactions leading to viral persistence, as well as the roadblocks to be overcome to ultimately address unmet medical needs in the treatment of chronic HBV infection.
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