A screening assay for the identification of host cell requirements and antiviral targets for hepatitis D virus infection

Repurposing of CDK Inhibitors as Host Targeting Antivirals: A Mini- Review

Most of the antiviral drugs in the market are designed to target viral proteins directly. They are generally considered safe for human use. However, they also suffer from several inherent limitations, in particular, narrow-spectrum antiviral profiles and liability to drug resistance. The other strategy for antiviral drug development is targeting host factors, which are highly involved at different stages in the viral life cycle. In contrast to direct-acting antiviral agents, host-targeting antiviral ones normally exhibit broad-spectrum antiviral properties along with a much higher genetic barrier to drug resistance. Cyclin-dependent kinases (CDKs) represent one such host factor. In this review, we summarized a number of CDK inhibitors (CDKIs) of varied chemical scaffolds with demonstrated antiviral activity. Challenges and issues associated with the repurposing of CDKIs as antiviral agents were also discussed.

Hepatitis D virus infection, innate immune response and antiviral treatments in stem cell-derived hepatocytes

BACKGROUND

Human pluripotent stem cell (hPSC)-derived hepatocyte-like cells (HLCs) are a valuable model to investigate host-pathogen interactions of hepatitis viruses in a mature and authentic environment. Here, we investigate the susceptibility of HLCs to the hepatitis delta virus (HDV).

METHODS

We differentiated hPSC into HLCs, and inoculated them with infectious HDV produced in Huh7NTCP . HDV infection and cellular response was monitored by RTqPCR and immunostaining.

RESULTS

Cells undergoing hepatic differentiation become susceptible to HDV after acquiring expression of the viral receptor Na+ -taurocholate co-transporting polypeptide (NTCP) during hepatic specification. Inoculation of HLCs with HDV leads to detection of intracellular HDV RNA and accumulation of the HDV antigen in the cells. Upon infection, the HLCs mounted an innate immune response based on induction of the interferons IFNB and L, and upregulation of interferon-stimulated genes. The intensity of this immune response positively correlated with the level of viral replication and was dependant on both the JAK/STAT and NFκB pathway activation. Importantly, this innate immune response did not inhibit HDV replication. However, pre-treatment of the HLCs with IFNα2b reduced viral infection, suggesting that ISGs may limit early stages of infection. Myrcludex efficiently abrogated infection and blocked innate immune activation. Lonafarnib treatment of HDV mono infected HLCs on the other hand led to exacerbated viral replication and innate immune response.

CONCLUSION

The HDV in vitro mono-infection model represents a new tool to study HDV replication, its host-pathogen interactions and evaluate new antiviral drugs in cells displaying mature hepatic functions.

Hepatitis-D Virus Infection Is Not Impaired by Innate Immunity but Increases Cytotoxic T-Cell Activity

Approximately 70 million humans worldwide are affected by chronic hepatitis D, which rapidly leads to liver cirrhosis and hepatocellular carcinoma due to chronic inflammation. The triggers and consequences of this chronic inflammation, induced by co-infection with the hepatitis D virus (HDV) and the hepatitis B virus (HBV), are poorly understood. Using CRISPR technology, we characterized the recognition of HDV mono- and co-infection by intracellular innate immunity and determined its influence on the viral life cycle and effector T-cell responses using different HBV and HDV permissive hepatoma cell lines. We showed that HDV infection is detected by MDA5 and -after a lag phase -induces a profound type I interferon response in the infected cells. The type I interferon response, however, was not able to suppress HDV replication or spread, thus providing a persistent trigger. Using engineered T-cells directed against the envelope proteins commonly used by HBV and HDV, we found that HDV immune recognition enhanced T-cell cytotoxicity. Interestingly, the T-cell effector function was enhanced independently of antigen presentation. These findings help to explain immune mediated tissue damage in chronic hepatitis D patients and indicate that combining innate triggers with T-cell activating therapies might allow for a curative approach.

Cell Culture Models for the Study of Hepatitis D Virus Entry and Infection

Chronic hepatitis D is one of the most severe and aggressive forms of chronic viral hepatitis with a high risk of developing hepatocellular carcinoma (HCC). It results from the co-infection of the liver with the hepatitis B virus (HBV) and its satellite, the hepatitis D virus (HDV). Although current therapies can control HBV infection, no treatment that efficiently eliminates HDV is available and novel therapeutic strategies are needed. Although the HDV cycle is well described, the lack of simple experimental models has restricted the study of host–virus interactions, even if they represent relevant therapeutic targets. In the last few years, the discovery of the sodium taurocholate co-transporting polypeptide (NTCP) as a key cellular entry factor for HBV and HDV has allowed the development of new cell culture models susceptible to HBV and HDV infection. In this review, we summarize the main in vitro model systems used for the study of HDV entry and infection, discuss their benefits and limitations and highlight perspectives for future developments.

Evaluation of the results of MOTAKK hepatitis C virus RNA genotyping and hepatitis delta virus external quality assessment programs during 2015-2016

BACKGROUND/AIMS

To evaluate the HCV RNA genotyping and HDV RNA tests that are performed in molecular microbiology laboratories in Turkey as part of a national external quality assessment programme, MOTAKK (Moleküler Tanıda Kalite Kontrol) (English translation: Quality control in molecular diagnostics).

MATERIALS AND METHODS

Plasmas having different HCV RNA genotypes were used to prepare HCV genotype control sera. The HDV RNA main stock was prepared from patients with chronic delta hepatitis who had a significant amount of viral load detected, as per the WHO reference materials on viral load studies that were compiled for the purpose of developing HDV RNA control sera. Samples with different viral loads were prepared from this main stock by dilution. The prepared controls were delivered to the registered laboratories. The laboratories carried out the relevant tests and entered their results via the MOTAKK web page. External quality assessment (EQA) reports of the participants were uploaded to the website as well.

RESULTS

In total, there were 23 participating laboratories, out of which 20 exclusively performed HCV genotyping, and 15 and 16 only performed HDV RNA in 2015 and 2016, respectively. The success rate of the results of the HCV genotype was 56-96% in 2015 and 30-95% in 2016. The tube with a 30% success rate had a recombinant type of HCV, therefore, it could not be detected in most of the laboratories. The HDV RNA results were evaluated qualitatively. Accordingly, HDV RNA detection rates of participant laboratories were 71-100% in 2015 and 50-100% in 2016.

CONCLUSION

This study was the first national external quality control program in Turkey regarding HCV RNA genotyping and HDV RNA in the field of molecular microbiology, and it was implemented successfully.

Targeting the Host for New Therapeutic Perspectives in Hepatitis D

Hepatitis D virus (HDV) is a small satellite virus of hepatitis B virus (HBV) requiring HBV infection to complete its life cycle. It has been recently estimated that 13% of chronic HBV infected patients (60 million) are co-infected with HDV. Chronic hepatitis D is the most severe form of viral hepatitis with the highest risk to develop cirrhosis and liver cancer. Current treatment is based on pegylated-interferon-alpha which rarely controls HDV infection and is complicated by serious side effects. The development of novel antiviral strategies based on host targeting agents has shown promising results in phase I/II clinical trials. This review summarizes HDV molecular virology and physiopathology as well as new therapeutic approaches targeting HDV host factors.

Recapitulation of HDV infection in a fully permissive hepatoma cell line allows efficient drug evaluation

Hepatitis delta virus (HDV) depends on the helper function of hepatitis B virus (HBV), which provides the envelope proteins for progeny virus secretion. Current infection-competent cell culture models do not support assembly and secretion of HDV. By stably transducing HepG2 cells with genes encoding the NTCP-receptor and the HBV envelope proteins we produce a cell line (HepNB2.7) that allows continuous secretion of infectious progeny HDV following primary infection. Evaluation of antiviral drugs shows that the entry inhibitor Myrcludex B (IC₅₀: 1.4 nM) and interferon-α (IC₅₀: 28 IU/ml, but max. 60–80% inhibition) interfere with primary infection. Lonafarnib inhibits virus secretion (IC₅₀: 36 nM) but leads to a substantial intracellular accumulation of large hepatitis delta antigen and replicative intermediates, accompanied by the induction of innate immune responses. This work provides a cell line that supports the complete HDV replication cycle and presents a convenient tool for antiviral drug evaluation.

Hepatitis delta virus (HDV) depends on the envelope proteins of hepatitis B virus (HBV) for virion production. Here, Lempp et al. produce a cell line expressing HBV envelope proteins and their receptor, which allows continuous secretion of infectious progeny HDV and testing of antiviral drugs.

HDV evolution-will viral resistance be an issue in HDV infection?

Hepatitis D virus (HDV) is a hepatotropic subviral infectious agent, obligate satellite of the Hepatitis B virus (HBV) and is highly related to viroids. HDV affects around 5% of the 257 million chronic HBV-carriers worldwide, leading to the most severe form of chronic viral hepatitis. Interferon alpha is the only approved treatment for chronic hepatitis D, albeit with low response rates (around 20%-30%). New antiviral strategies are currently under study. Due to the high viral evolution rates (10-3 to 10-4 substitutions/site/year) HDV forms an extremely complex viral population (quasispecies) that can be studied by Next-Generation Sequencing. Therefore, although specific viral resistance in HDV infection has not been reported, it cannot be completely discarded.

Methods and approaches to disease mechanisms using systems kinomics

All cellular functions, ranging from regular cell maintenance and homeostasis, specialized functions specific to cellular types, or generating responses due to external stimulus, are mediated by proteins within the cell. Regulation of these proteins allows the cell to alter its behavior under different circumstances. A major mechanism of protein regulation is utilizing protein kinases and phosphatases; enzymes that catalyze the transfer of phosphates between substrates [1]. Proteins involved in phosphate signaling are well studied and include kinases and phosphatases that catalyze opposing reactions regulating both structure and function of the cell. Kinomics is the study of kinases, phosphatases and their targets, and has been used to study the functional changes in numerous diseases and infectious diseases with aims to delineate the cellular functions affected. Identifying the phosphate signaling pathways changed by certain diseases or infections can lead to novel therapeutic targets. However, a daunting 518 putative protein kinase genes have been identified [2], indicating that this protein family is very large and complex. Identifying which enzymes are specific to a particular disease can be a laborious task. In this review, we will provide information on large-scale systems biology methodologies that allow global screening of the kinome to more efficiently identify which kinase pathways are pertinent for further study.

Investigational drugs in development for Hepatitis D

INTRODUCTION

Treatment of chronic hepatitis D still relies on Interferon. To improve efficacy, new therapeutic strategies are in development which aim to deprive the Hepatitis D Virus (HDV) of functions of the Hepatitis B Virus and of the host required for its life-cycle. Areas covered: The therapeutic options are; 1) The inhibition of the farnesylation of the large HD-protein permissive of virion assembly with Lonafarnib, 2) The blocking of HBsAg entry into cells with Myrcludex B via the inhibition of the Sodium Taurocholate Cotransporting Receptor, to prevent the spreading of HDV to uninfected hepatocytes, 3) The reduction of subviral HBsAg particles by REP 2139, leading to diminished virion morphogenesis . Expert opinion: Lonafarnib and Myrcludex reduced serum HVD-RNA; neither diminished serum HBsAg. NAP REP-2139 diminished both HDV-RNA and HBsAg in serum; a full report is awaited. In combination with Peg-Interferon, these new drugs may provide additional efficacy.