Ganciclovir treatment of active hepatitis B virus infection in a heart transplant patient

Drug discovery and development of antiviral agents for the treatment of chronic hepatitis B virus infection

A safe and effective vaccine for hepatitis B virus (HBV) has been available for nearly twenty years and currently campaigns to provide universal vaccination in developing countries are underway. Nevertheless, chronic HBV infection remains a leading cause of chronic hepatitis worldwide and there is a strong need for safe and effective antiviral therapies. Attempts to identify and develop antiviral agents to treat chronic HBV infection remains focused on nucleoside analogs such as 3TC (lamivudine), adefovir dipivoxil, (bis-POMPMEA), and others. However, advances in our understanding of the molecular biology of HBV and the development of new assays for HBV polymerase activity, such as the reconstitution of active HBV polymerase in vitro, should facilitate large screening efforts for non-nucleoside reverse transcriptase inhibitors. Recent advances have furthered our understanding of clinical resistance to lamivudine, have provided new approaches to treatment, and have offered new perspectives on the major challenges to the identification and development of antiviral agents for chronic HBV infection. Here, in an update to our previous review article that appeared in this series [59a], we focus on recent advances that have occurred in the areas of virus structure and replication, in vitro viral polymerase assays, cell culture systems, and animal models.

Hepatitis B in transplantation

Hepatitis B has been a major challenge within the field of transplantation over the past few decades. Due to aggressive recurrence post-transplant, patients with hepatitis B have been excluded from the benefits of both solid organ and bone marrow transplants. Progress has been made, however, through an improved understanding of the biology of hepatitis B and the development of new antiviral strategies that can reliably suppress the virus. Patients with hepatitis B are now candidates for transplantation in an increasing number of circumstances. Careful pre-transplant evaluation is mandatory, together with a tailored antiviral regimen depending on the replicative status of the virus and the organ being transplanted. Minimizing steroid dose following transplantation is an important part of the strategy to reduce the risk of viral reactivation. Lamivudine has been an important development and it has assumed an increasing role in the management of these patients. As additional antivirals are developed, increasingly effective drug combinations will prevent viral recurrence as well as the emergence of drug-resistant mutants, which plagues the use of single agents. It is a rapidly evolving field and there is every reason for continued optimism.

Development of resistance and perspectives for future therapies against hepatitis B infections: lessons to be learned from HIV

Several first-generation nucleoside analogues have been tested against chronic hepatitis B virus (HBV) infection, but trials were unsuccessful or accompanied by toxicity. Recently, oral second-generation nucleoside analogues have been developed that have potent activity against HBV. The best-studied compound so far is lamivudine ((-)2'-deoxy-3'-thiacytidine; 3TC). Lamivudine is an inhibitor of reverse transcriptase (RT) activity and is in clinical use in human immunodeficiency virus (HIV)-infected individuals. As several studies on the use of lamivudine for hepatitis B show, the development of resistance in the viral polymerase under lamivudine treatment, however, causes a significant clinical problem. All other drugs in advanced clinical development for HBV are nucleosides; cross-resistance is therefore expected in most cases. The history of HIV treatment demonstrates that new classes of drugs, the protease inhibitors and non-nucleosidic inhibitors of RT, allowed for a longer-term clinical benefit when used in combination with nucleoside analogues. The development of non-nucleosidic compounds with different modes of action therefore appears very important for the treatment of chronic hepatitis B as well.

Recurrence of hepatitis B after single lung transplantation

This study describes a patient who developed decompensated liver disease secondary to reactivation of hepatitis B infection 20 months after single lung transplantation following augmentation of immunosuppression to treat allograft rejection. Discussion focuses on the virologic and management issues of this case and reviews the approach taken when considering patients with chronic hepatitis B infection for lung transplantation.

Oral ganciclovir treatment in chronic hepatitis B virus infection: a pilot study

BACKGROUND/AIMS

Ganciclovir is a nucleoside analogue with an excellent safety record; it is effective against cytomegalovirus infection in both its intravenous and its oral form. Intravenous administration of ganciclovir is active against hepatitis B virus but the efficacy of oral ganciclovir is unknown. The aim of this study was to evaluate the tolerability and primary efficacy in reducing HBV DNA levels and liver enzymes of 2 dosing schedules of oral ganciclovir in HBeAg-positive and -negative patients with chronic hepatitis B.

METHODS

Oral ganciclovir was administered to 15 consecutive patients with active chronic hepatitis B (age 43+/-12 years; 73% males; seven HBeAg-positive and eight negative; no cirrhosis) in a pilot, phase I, open-label study. Before treatment, all patients were screened for 8 weeks to ascertain the persistence of biochemical and virological activity, and then randomized to receive 3 g (eight patients), or 6 g (seven patients) of oral ganciclovir daily for 8 weeks; following therapy, they were closely observed for 8 more weeks.

RESULTS

Baseline HBV DNA declined by 99% or 2 log10 at the end of treatment (405.0 vs 3.9 MEq/ml, respectively) and in four patients serum HBV DNA became undetectable by the Monitor assay. Oral ganciclovir suppressed HBV equally well in HBeAg-positive and -negative patients, and the 3- and 6-g daily dose regimens were equally effective. The pre-treatment viral load, however, was a determinant of response, with patients in the lowest quartile of baseline HBV DNA levels responding significantly better than those in the upper quartile (3.0 vs 0.6 log10 respectively, p=0.002). Serum alanine aminotransferase levels became normal or declined in most patients. Oral ganciclovir was very well tolerated. Within 8 weeks after stopping medication, a relapse in serum HBV DNA levels occurred in nine of the 15 patients (60%).

CONCLUSIONS

These findings suggest that ganciclovir administered orally at a dose of 3 g can achieve sufficient suppression of HBV replication. This dose, and even higher doses, are well tolerated and could be used as an alternative or in combination with other antivirals for the treatment of chronic hepatitis B.

The identification and development of antiviral agents for the treatment of chronic hepatitis B virus infection

Hepatitis B virus (HBV) is the leading cause of chronic hepatitis throughout the world. Notwithstanding the availability of a safe and effective vaccine, the world prevalence of HBV has not declined significantly, thus resulting in the need for a selective antiviral agent. HBV is a small, partially double-stranded DNA virus which replicates through an RNA intermediate. Most efforts to develop anti-HBV agents have been targeted to the viral DNA polymerase which possesses reverse transcriptase activity. Currently, the most promising anti-HBV agents are nucleoside analogs which interfere with viral DNA replication. Although earlier nucleoside analogs such as vidarabine (ara-A) and fialuridine (FIAU) have displayed unacceptable toxicities, newer analogs such as lamivudine (3TC), bis-POM PMEA (GS-840), lobucavir, and BMS-200,475 have demonstrated clinical utility. In particular, the use of lamivudine has generated considerable interest in the development of other L-enantiomeric nucleoside analogs for use against HBV. Here, we provide an overview of HBV structure and replication strategy and discuss the use of cell culture systems, in vitro viral polymerase systems, and animal models to identify and evaluate anti-HBV agents. We also discuss the various classes of nucleoside analogs in terms of structure, mechanism of action, status in clinical development, ability to select for resistant HBV variants, and use in combination therapies. Finally, we present a discussion of novel antiviral approaches, including antisense and gene therapy, and address the various challenges to successful anti-HBV chemotherapeutic intervention.