Inhibition of hepatitis B virus cccDNA by siRNA in transgenic mice

Current Status and Challenges in Anti-Hepatitis B Virus Agents Based on Inactivation/Inhibition or Elimination of Hepatitis B Virus Covalently Closed Circular DNA

There has been over half a century since the discovery of hepatitis B virus (HBV) to now, but approximately 300 million patients with chronic hepatitis B (CHB) still live in the world, resulting in about one million deaths every year. Although currently approved antivirals (e.g., nucleoside analogues) are effective at reducing HBV replication, they have almost no impact on the existing HBV covalently closed circular DNA (cccDNA) reservoir. HBV cccDNA is a critical obstacle to the complete elimination of the virus via antiviral therapy. The true cure of HBV infection requires the eradication of viral cccDNA from HBV-infected cells; thus, the development of new agents directly or indirectly targeting HBV cccDNA is urgently needed due to the limitations of current available drugs against HBV infection. In this regard, it is the major focus of current anti-HBV research worldwide via different mechanisms to either inactivate/inhibit (functional cure) or eliminate (complete cure) HBV cccDNA. Therefore, this review discussed and summarized recent advances and challenges in efforts to inactivate/silence or eliminate viral cccDNA using anti-HBV agents from different sources, such as small molecules (including epigenetic drugs) and polypeptides/proteins, and siRNA or gene-editing approaches targeting/attenuating HBV cccDNA via different mechanisms, as well as future directions that may be considered in efforts to truly cure chronic HBV infection. In conclusion, no breakthrough has been made yet in attenuating HBV cccDNA, although a number of candidates have advanced into the phase of clinical trials. Furthermore, the overwhelming majority of the candidates function to indirectly target HBV cccDNA. No outstanding candidate directly targets HBV cccDNA. Relatively speaking, CCC_R08 and nitazoxanide may be some of the most promising agents to clear HBV infection in small molecule compounds. Additionally, CRISPR-Cas9 systems can directly target HBV cccDNA for decay and demonstrate significant anti-HBV activity. Consequently, gene-editing approaches targeting HBV cccDNA may be one of the most promising means to achieve the core goal of anti-HBV therapeutic strategies. In short, more basic studies on HBV infection need to be carried out to overcome these challenges.

Emerging role of RNA interference in immune cells engineering and its therapeutic synergism in immunotherapy

RNAi effectors (e.g. siRNA, shRNA and miRNA) can trigger the silencing of specific genes causing alteration of genomic functions becoming a new therapeutic area for the treatment of infectious diseases, neurodegenerative disorders and cancer. In cancer treatment, RNAi effectors showed potential immunomodulatory actions by down-regulating immuno-suppressive proteins, such as PD-1 and CTLA-4, which restrict immune cell function and present challenges in cancer immunotherapy. Therefore, compared with extracellular targeting by antibodies, RNAi-mediated cell-intrinsic disruption of inhibitory pathways in immune cells could promote an increased anti-tumour immune response. Along with non-viral vectors, DNA-based RNAi strategies might be a more promising method for immunomodulation to silence multiple inhibitory pathways in T cells than immune checkpoint blockade antibodies. Thus, in this review, we discuss diverse RNAi implementation strategies, with recent viral and non-viral mediated RNAi synergism to immunotherapy that augments the anti-tumour immunity. Finally, we provide the current progress of RNAi in clinical pipeline.

Moving Fast Toward Hepatitis B Virus Elimination

Currently, there are two safe and effective therapeutic strategies for chronic hepatitis B treatment, namely, nucleoside analogs and interferon alpha (pegylated or non-pegylated). These treatments can control viral replication and improve survival; however, they do not eliminate the virus and therefore require long-term continued therapy. In addition, there are significant concerns about virus rebound on discontinuation of therapy and the development of fibrosis and hepatocellular carcinoma despite therapy. Therefore, the search for new, more effective, and safer antiviral agents that can cure hepatitis B virus (HBV) continues. Anti-HBV drug discovery and development is fundamentally impacted by our current understanding of HBV replication, disease physiopathology, and persistence of HBV covalently closed circular DNA (cccDNA). Several HBV replication targets are the basis for novel anti-HBV drug development strategies. Many of them are already in clinical trial phase 1 or 2, while others with promising results are still in preclinical stages. As research intensifies, potential HBV curative therapies and modalities in the pipeline are now on the horizon.

Potential Drug Targets Against Hepatitis B Virus Based on Both Virus and Host Factors

BACKGROUND

Hepatitis B is a very harmful and epidemic disease caused by hepatitis B virus (HBV). Although an effective anti-HBV vaccine is available, chronic infection poses still a huge health burden in the whole world. The present anti-HBV drugs including nucleoside analogues and interferonalpha have their limitations without exception. There is no effective drug and therapeutic method that can really and truly cure hepatitis B so far. The variability of HBV genome results in that a significant number of patients develop drug resistance during the long-term use of anti-HBV drugs. Hence, it is urgently needed to discover novel targets and develop new drugs against hepatitis B.

OBJECTIVE

The review aims to provide the theory support for designing of the anti-HBV innovative drugs by offering a summary of the current situation of antiviral potential targets.

RESULTS AND CONCLUSION

Since HBV is obligate intracellular parasite, and as such it depends on host cellular components and functions to replicate itself. The targeting both virus and host might be a novel therapeutic option for hepatitis B. Accordingly, we analyse the advances in the study of the potential drug targets for anti-HBV infection, focusing on targeting virus genome, on targeting host cellular functions and on targeting virus-host proteins interactions, respectively. Meanwhile, the immune targets against chronic hepatitis B are also emphasized. In short, the review provides a summary of antiviral therapeutic strategies to target virus factors, host factors and immune factors for future designing of the innovative drug against HBV infection.

Genome editing for the treatment of tumorigenic viral infections and virus-related carcinomas

Viral infections cause at least 10%-15% of all human carcinomas. Over the last century, the elucidation of viral oncogenic roles in many cancer types has provided fundamental knowledge on carcinogenetic mechanisms and established a basis for the early intervention of virus-related cancers. Meanwhile, rapidly evolving genome-editing techniques targeting viral DNA/RNA have emerged as novel therapeutic strategies for treating virus-related carcinogenesis and have begun showing promising results. This review discusses the recent advances of genome-editing tools for treating tumorigenic viruses and their corresponding cancers, the challenges that must be overcome before clinically applying such genome-editing technologies, and more importantly, the potential solutions to these challenges.

Pharmacokinetics and biodistribution of recently-developed siRNA nanomedicines

Small interfering RNA (siRNA) is a promising drug candidate, expected to have broad therapeutic potentials toward various diseases including viral infections and cancer. With recent advances in bioconjugate chemistry and carrier technology, several siRNA-based drugs have advanced to clinical trials. However, most cases address local applications or diseases in the filtering organs, reflecting remaining challenges in systemic delivery of siRNA. The difficulty in siRNA delivery is in large part due to poor circulation stability and unfavorable pharmacokinetics and biodistribution profiles of siRNA. This review describes the pharmacokinetics and biodistribution of siRNA nanomedicines, focusing on those reported in the past 5years, and their pharmacological effects in selected disease models such as hepatocellular carcinoma, liver infections, and respiratory diseases. The examples discussed here will provide an insight into the current status of the art and unmet needs in siRNA delivery.

Hepatitis B: Working Towards a Cure

First-line oral therapies for hepatitis B are effective at viral suppression, and treatment can lead to biochemical improvement and histologic regression. Unfortunately, recommended endpoints of treatment such as HBeAg loss and seroconversion may not be durable, with high rates of seroreversion, requiring monitoring, and unfortunately, low rates of  HBsAg loss/seroconversion. Additionally, meeting these endpoints requires years or even indefinite administration, leading to concerns regarding cost, side effects, and high rates of nonadherence. This article will review defined endpoints of therapy and their durability, the risks of long-term therapy, and the evolving new therapies aimed at a viral cure.

Recent advance of the hepatitis B virus inhibitors: a medicinal chemistry overview

Hepatitis B Virus (HBV) is one of the most prevalent viral infections of human worldwide. The therapies are limited in the clinical context because of negative side effects of interferons and the development of viral resistance to the nucleoside/nucleotide inhibitors. In this review, we summarize the recent advances in design and development of potent anti-HBV inhibitors from natural sources and synthetic compounds, targeting different steps in the life cycle of HBV. We attempt to emphasize the major structural modifications, mechanisms of action and computer-aided docking analysis of novel potent inhibitors that need to be addressed in the future to design potent anti-HBV molecules.

Impact of antiviral agents on levels of hepatitis B virus covalently closed circular DNA

Chronic hepatitis caused by hepatitis B virus (HBV) infection remains an incurable disease at present, which is mainly because the approved antiviral agents, such as interferon-alpha and nucleos(t)ide analogues, cannot effectively eradicate intrahepatic hepatitis B virus covalently closed circular DNA (cccDNA). And thus a suboptimal efficacy of antiviral agents and relapse after therapy occur very commonly. Therefore, novel drugs and treatment strategies remain to be developed on the basis of further theoretical and clinical research of HBV infection to achieve the ultimate goal of eradication of HBV cccDNA in the future. In this paper, we discuss multiple agents and therapeutic regimens influencing cccDNA levels, in order to help clinicians comprehensively understand the present situation in the research of the clearance of HBV cccDNA.

Progress and Prospects of Anti-HBV Gene Therapy Development

Despite the availability of an effective vaccine against hepatitis B virus (HBV), chronic infection with the virus remains a major global health concern. Current drugs against HBV infection are limited by emergence of resistance and rarely achieve complete viral clearance. This has prompted vigorous research on developing better drugs against chronic HBV infection. Advances in understanding the life cycle of HBV and improvements in gene-disabling technologies have been impressive. This has led to development of better HBV infection models and discovery of new drug candidates. Ideally, a regimen against chronic HBV infection should completely eliminate all viral replicative intermediates, especially covalently closed circular DNA (cccDNA). For the past few decades, nucleic acid-based therapy has emerged as an attractive alternative that may result in complete clearance of HBV in infected patients. Several genetic anti-HBV strategies have been developed. The most studied approaches include the use of antisense oligonucleotides, ribozymes, RNA interference effectors and gene editing tools. This review will summarize recent developments and progress made in the use of gene therapy against HBV.

Targeting the Achilles heel of the hepatitis B virus: a review of current treatments against covalently closed circular DNA

Chronic infection with hepatitis B virus (HBV) often leads to the development of liver cancer and cirrhosis, creating immense sociological, clinical and economic burdens worldwide. Although current anti-HBV medications manage to control the disease progression and help restore normal liver functions, they often fail to eliminate the virus completely. A major reason for this failure is the presence of a stable viral genome in the hepatocyte nucleus: the covalently closed circular DNA (cccDNA). Targeting HBV cccDNA is a promising approach that could lead to a complete cure. Here, we review various research approaches that are directed toward eliminating HBV cccDNA. This is a brief, yet comprehensive, summary of current state-of-the-art developments in this emerging area of interest.