In vivo antiviral efficacy of prenylation inhibitors against hepatitis delta virus

Hepatitis delta virus: A fascinating and neglected pathogen

Hepatitis delta virus (HDV) is the etiologic agent of the most severe form of virus hepatitis in humans. Sharing some structural and functional properties with plant viroids, the HDV RNA contains a single open reading frame coding for the only virus protein, the Delta antigen. A number of unique features, including ribozyme activity, RNA editing, rolling-circle RNA replication, and redirection for a RNA template of host DNA-dependent RNA polymerase II, make this small pathogen an excellent model to study virus-cell interactions and RNA biology. Treatment options for chronic hepatitis Delta are scarce and ineffective. The disease burden is perhaps largely underestimated making the search for new, specific drugs, targets, and treatment strategies an important public health challenge. In this review we address the main features of virus structure, replication, and interaction with the host. Virus pathogenicity and current treatment options are discussed in the light of recent developments.

Hepatitis delta virus: Making the point from virus isolation up to 2014

Chronic infection with hepatitis delta virus (HDV) has lately regained clinical importance because of the recent evidence of increasing prevalence in several European countries, due to immigration from highly endemic areas. HDV requires the mandatory presence of hepatitis B virus (HBV) for propagation to hepatocytes. It is transmitted by the same routes of HBV and it can be acquired either by co-infection (simultaneous transmission of the two viruses) or super-infection (acquisition of HDV by an already chronic carrier of HBV). As a consequence, every HBV carrier is potentially at risk for HDV superinfection. Since the clinical course of super-infection can be severe, early diagnosis of HDV infection is necessary.

Hepatitis delta virus: a peculiar virus

The hepatitis delta virus (HDV) is distributed worldwide and related to the most severe form of viral hepatitis. HDV is a satellite RNA virus dependent on hepatitis B surface antigens to assemble its envelope and thus form new virions and propagate infection. HDV has a small 1.7 Kb genome making it the smallest known human virus. This deceivingly simple virus has unique biological features and many aspects of its life cycle remain elusive. The present review endeavors to gather the available information on HDV epidemiology and clinical features as well as HDV biology.

Direct acting antivirals for the treatment of chronic viral hepatitis

The development and evaluation of antiviral agents through carefully designed clinical trials over the last 25 years have heralded a new dawn in the treatment of patients chronically infected with the hepatitis B and C viruses, but not so for the D virus (HBV, HCV, and HDV). The introduction of direct acting antivirals (DDAs) for the treatment of HBV carriers has permitted the long-term use of these compounds for the continuous suppression of viral replication, whilst in the case of HCV in combination with the standard of care [SOC, pegylated interferon (PegIFN), and ribavirin] sustained virological responses (SVRs) have been achieved with increasing frequency. Progress in the case of HDV has been slow and lacking in significant breakthroughs.This paper aims to summarise the current state of play in treatment approaches for chonic viral hepatitis patients and future perspectives.

Treatment of chronic hepatitis D

Despite recent advances in the treatment of chronic viral hepatitis, therapy of chronic hepatitis D is not yet satisfactory. The only option currently available is interferon-alpha (IFN), whose efficacy is related to the dose and duration of treatment. However, the rate of sustained hepatitis D virus (HDV) clearance after a 1-year course with high doses of standard IFN is low. Better results have recently been reported with pegylated IFN both in IFN-naïve and in previous nonresponders to standard IFN, suggesting the use of pegylated IFN as a first-line therapy in chronic hepatitis D. Nucleoside analogues that inhibit hepatitis B virus (HBV) are ineffective against HDV and combination therapy with lamivudine or ribavirin has not shown significant advantages over monotherapy with either standard or pegylated IFN. Because the ultimate goal of treatment is eradication of both HDV and HBV, in responders IFN therapy should be continued as long as possible until the loss of hepatitis B surface antigen, adjusting the dose to patient tolerance. However, because side-effects are common, continuous monitoring is mandatory. Although the first results obtained with pegylated IFN have been encouraging, the rate of sustained virological response is still low and the rate of relapse high, emphasizing the need for developing novel classes of antivirals specifically interfering with the life cycle of this unique virus.

Host cell targets for antiviral therapy: an update

The discovery of antiviral therpeutic targets has traditionally focussed on conserved viral gene products. Since viruses are obligate molecular parasites requiring and manipulating host cell functions, the identification of host proteins essential to viruses but not cellular survival represent attractive and underutilized targets for antiviral therapies. Numerous studies have identified host cell functions, pathways and proteins that are essential for viral propagation, from entry to replication, assembly and egress. Importantly, several studies demonstrate virus inhibition through nonlethal impairment of host cell function both in vitro and in vivo. In addition, high-throughput experimental platforms allowing global or near-global surveillance of host gene products in the context of virus replication are now being used to systematically identify host cell targets. Recent breakthrough studies that have employed such methods successfully to identify host proteins and pathways crucial for virus growth are discussed in this review.

Lamivudine therapy in chronic delta hepatitis: a multicentre randomized-controlled pilot study

BACKGROUND

Delta virus (HDV)-related chronic hepatitis is difficult to treat.

AIMS

To evaluate the efficacy of lamivudine 100 mg daily on serum HDV-RNA, hepatitis D virus antibodies and alanine aminotransferase levels, liver histology, and on hepatitis B surface antigen seroconversion.

METHODS

Thirty-one hepatitis B surface antigen-positive, HDV-RNA-positive patients with ALT > or = 1.5 upper normal level and compensated liver disease were randomized (1:2 ratio) to placebo (group A, n = 11) or lamivudine (group B, n = 20) for 52 weeks; thereafter, all patients were given lamivudine for 52 weeks and followed up for 16 weeks.

RESULTS

Twenty-five patients (81%) completed the study. No patient was HDV-RNA-negative at week 52; three patients (11%) were negative at week 104. Two of them remained HDV-RNA-negative at week 120, and one lost the hepatitis B surface antigen without seroconversion. Paired pre-treatment and week 104 liver biopsies were available from 19 patients: of which three of seven (43%) from group A and two of 12 patients (17%) from group B had a > or =2 point decrease in the Ishak necroinflammatory score.

CONCLUSION

A sustained complete response was achieved in 8% of hepatitis D virus-infected patients treated with lamivudine and a partial histological response in 26% of them. Hepatitis D virus viraemia was unaffected, even in patients when hepatitis B virus replication was lowered by lamivudine therapy.

Treatment of hepatitis D

Delta virus related chronic hepatitis is difficult to treat. The response to alpha-interferon (IFN), which still represents the only therapy for chronic hepatitis D, varies widely and occurs at different times from the beginning of treatment. The rate of response is proportional to the dose of IFN, with 9 million units (MU) three times a week being more effective than 3 MU thrice weekly. Sustained responses are unusual and are accompanied by the clearance of serum hepatitis B virus surface antigen (HBsAg), seroconversion to anti-HBs and improvement of liver histology. Although disease of a short-standing may respond better to therapy, clear predictors of response are still unidentified. Besides IFN, other therapeutic approaches such as immunosuppressive drugs, acyclovir, ribavirin and thymosin, have been unhelpful. Available evidence does not support the use of deoxynucleotide analogues. Famciclovir has no effect on disease activity and hepatitis D virus (HDV)-RNA levels. Twelve- or 24-month lamivudine treatment does not significantly affect biochemical, virological or histological parameters. Pegylated-IFN could represent a reasonable therapeutic option in the long-term treatment required for chronic hepatitis D. Antisense oligonucleotides and prenylation inhibitors hold promise as therapeutic agents of the future. Liver transplantation provides a valid option for end-stage HDV liver disease; the risk of re-infection is lower for HDV than for HBV under long-term administration of hyperimmune serum against HBsAg. Molecularly tailored drugs capable of interfering with crucial viral replicative processes of HDV appear to be the best prospect in the treatment of hepatitis D.