Adefovir dipivoxil in the treatment of chronic hepatitis B virus infection

Treatment of hepatitis B virus infection in children and adolescents

Hepatitis B virus (HBV) infection is one of the main causes of morbidity and mortality worldwide. Most children acquire the infection perinatally or during early childhood and develop a chronic hepatitis characterized by a high viral replication and a low-inflammation phase of infection, with normal or only slightly raised aminotransferases. Although a conservative approach in children is usually recommended, different therapies exist and different therapeutic approaches are possible. The main goals of antiviral treatment for children with chronic HBV infection are to suppress viral replication and to warn the disease progression to cirrhosis and hepatocellular carcinoma, although these complications are rare in children. Both United States Food and Drug Administration (US-FDA) and European Medicines Agency (EMA) have approved interferon alfa-2b for children aged 1 year and older, pegylated interferon alfa-2a and lamivudine for children aged 3 years and older, entecavir for use in children aged 2 years and older, and adefovir for use in those 12 years of age and older. Tenofovir disoproxil fumarate is approved by EMA for children aged 2 years and older and by US-FDA for treatment in children aged 12 years and older. Finally, EMA has approved the use of tenofovir alafenamide for treatment of children aged 12 years and older or for children weighing more than 35 kg independent of age. This narrative review will provide the framework for summarizing indications to antiviral therapy in the management of chronic HBV infection in children and adolescents.

Clinical Implications of Hepatitis B Virus RNA and Covalently Closed Circular DNA in Monitoring Patients with Chronic Hepatitis B Today with a Gaze into the Future: The Field Is Unprepared for a Sterilizing Cure

. Chronic hepatitis B virus (HBV) infection has long remained a critical global health issue. Covalently closed circular DNA (cccDNA) is a persistent form of the HBV genome that maintains HBV chronicity. Decades of extensive research resulted in the two therapeutic options currently available: nucleot(s)ide analogs and interferon (IFN) therapy. A plethora of reliable markers to monitor HBV patients has been established, including the recently discovered encapsidated pregenomic RNA in serum, which can be used to determine treatment end-points and to predict the susceptibility of patients to IFN. Additionally, HBV RNA splice variants and cccDNA and its epigenetic modifications are associated with the clinical course and risks of hepatocellular carcinoma (HCC) and liver fibrosis. However, new antivirals, including CRISPR/Cas9, APOBEC-mediated degradation of cccDNA, and T-cell therapies aim at completely eliminating HBV, and it is clear that the diagnostic arsenal for defining the long-awaited sterilizing cure is missing. In this review, we discuss the currently available tools for detecting and measuring HBV RNAs and cccDNA, as well as the state-of-the-art in clinical implications of these markers, and debate needs and goals within the context of the sterilizing cure that is soon to come.

Drug Delivery Strategies for Antivirals against Hepatitis B Virus

Chronic hepatitis B virus (HBV) infection poses a significant health challenge due to associated morbidity and mortality from cirrhosis and hepatocellular cancer that eventually results in the breakdown of liver functionality. Nanotechnology has the potential to play a pivotal role in reducing viral load levels and drug-resistant HBV through drug targeting, thus reducing the rate of evolution of the disease. Apart from tissue targeting, intracellular delivery of a wide range of drugs is necessary to exert a therapeutic action in the affected organelles. This review encompasses the strategies and techniques that have been utilized to target the HBV-infected nuclei in liver hepatocytes, with a significant look at the new insights and most recent advances in drug carriers and their role in anti-HBV therapy.

Liquid oral suspension adefovir dipivoxil (GS-02-526): an update on treatments for hepatitis B infection

Though the global epidemiology of hepatitis B virus infection has declined due to effective immunization, chronic hepatitis B (CHB) remains a serious public health problem and there is still a need for more treatment options that are efficient, safe and simple for different kinds of CHB patients. Adefovir dipivoxil (ADV) liquid suspension (GS-02-526), as a new form of oral ADV, not only has competent antiviral efficacy, but is also more convenient for patients with swallowing difficulties or patients with impaired renal function requiring dosage adjustment. The clinical data evaluating the safety, tolerability and antiviral activity of liquid suspension of ADV as well as its tablet are summarized in this article. The availability of liquid oral suspension of ADV would allow more patients to receive timely and reasonable antiviral treatments.

Review article: nucleos(t)ide analogues in patients with chronic hepatitis B virus infection and chronic kidney disease

BACKGROUND

The treatment of chronic hepatitis B (CHB) in patients with chronic kidney disease (CKD) is based on nucleoside (lamivudine, telbivudine, entecavir) or nucleotide (adefovir, tenofovir) analogues (NAs), but it may be complex and the information is scarce. Entecavir and tenofovir represent the currently recommended first-line NAs for NA-naive CHB patients, while tenofovir is the NA of choice for CHB patients with resistance to nucleosides.

AIM

To review the efficacy and safety of NAs in adult CHB patients with CKD and to provide reasonable recommendations for their optimal management.

METHODS

Literature search in PubMed/Medline and manual search of relevant articles, reviews and book chapters.

RESULTS

NAs are cleared by kidneys and their dosage should be adjusted in patients with creatinine clearance <50 mL/min. There are concerns about nephrotoxic potential of the nucleotides, particularly adefovir, while improvements of creatinine clearance have been reported under telbivudine. Most existing data in CHB patients with CKD are for lamivudine and, less frequently, for other NAs, mostly entecavir. Besides CHB, NA should be used in case of immunosuppressive therapy in any HBsAg-positive patient with CKD including renal transplant (RT) recipients and in anti-HBs-positive recipients of kidney grafts from HBsAg-positive donors.

CONCLUSIONS

Chronic hepatitis B patients with chronic kidney disease receiving nucleoside analogues should be followed carefully for treatment efficacy and renal safety. Despite the absence of strong data, entecavir and telbivudine seem to be the preferred options for nucleoside analogue-naive CHB patients with chronic kidney disease, depending on viraemia and severity of renal dysfunction. More studies are certainly needed in this setting.

Review of the pharmacological management of hepatitis B viral infection before and after liver transplantation

The progress in treatment against hepatitis B virus (HBV) with the development of effective and well tolerated nucleotide analogues (NAs) has improved the outcome of patients with HBV decompensated cirrhosis and has prevented post-transplant HBV recurrence. This review summarizes updated issues related to the management of patients with HBV infection before and after liver transplantation (LT). A literature search using the PubMed/Medline databases and consensus documents was performed. Pre-transplant therapy has been initially based on lamivudine, but entecavir and tenofovir represent the currently recommended first-line NAs for the treatment of patients with HBV decompensated cirrhosis. After LT, the combination of HBV immunoglobulin (HBIG) and NA is considered as the standard of care for prophylaxis against HBV recurrence. The combination of HBIG and lamivudine is related to higher rates of HBV recurrence, compared to the HBIG and entecavir or tenofovir combination. In HBIG-free prophylactic regimens, entecavir and tenofovir should be the first-line options. The choice of treatment for HBV recurrence depends on prior prophylactic therapy, but entecavir and tenofovir seem to be the most attractive options. Finally, liver grafts from hepatitis B core antibody (anti-HBc) positive donors can be safely used in hepatitis B surface antigen negative, preferentially anti-HBc/anti-hepatitis B surface antibody positive recipients.

Evolution of an amino acid based prodrug approach: stay tuned

Certain acyclic nucleoside phosphonates (ANPs) such as (S)-HPMPC (cidofovir, Vistide) and (S)-HPMPA have been shown to be active against a broad spectrum of DNA and retroviruses. However, their poor absorption as well as their toxicity limit the utilization of these therapeutics in the clinic. Nucleoside phosphonates are poorly absorbed primarily due to the presence of the phosphonic acid group, which ionizes at physiological pH. When dosed intravenously they display dose-limiting nephrotoxicity due to their accumulation in the kidney. To overcome these limitations, nucleoside phosphonate prodrug strategies have taken center stage in the development pathway and a number of different approaches are at various stages of development. Our efforts have focused on the development of ANP prodrugs in which a benign amino acid promoiety masks a phosphonate P-OH via a hydroxyl side chain. The design of these prodrugs incorporates multiple chemical groups (the P-X-C linkage, the amino acid stereochemistry, the C-terminal and N-terminal functional groups) that can be tuned to modify absorption, pharmacokinetic and efficacy properties with the goal of improving overall prodrug performance.

Current treatment indications and strategies in chronic hepatitis B virus infection

The optimal approach to the management of several marginal cases with chronic hepatitis B virus (HBV) infection is controversial. Serum HBV DNA and aminotransferase levels, and the degree of necroinflammation and fibrosis determine the therapeutic decisions. All patients with elevated aminotransferase (> twice the upper limit of normal) and serum HBV DNA above 20 000 IU/mL should be treated. Liver biopsy is important for therapeutic decisions in cases with mild aminotransferase elevations and serum HBV DNA below 20 000 IU/mL. Chronic HBV patients who do not receive treatment should be followed for life. There are seven agents licensed for chronic hepatitis B: standard and pegylated interferon-alpha, lamivudine, adefovir, entecavir, telbivudine and tenofovir. One-year courses with pegylated interferon-alpha induce sustained off-therapy remission in 30%-32% of patients with HBeAg-positive chronic hepatitis B and in a smaller proportion of patients with HBeAg-negative chronic hepatitis B. Oral antivirals achieve initial on-therapy responses in the majority of patients, but are intended as long-term therapies. Viral suppression has favourable effects on patients’ outcome and modifies the natural course of the disease. Viral resistance, however, is the major drawback of long-term oral antiviral therapy. Lamivudine monotherapy is associated with the highest and entecavir monotherapy with the lowest resistance rate so far. There has been no resistance to tenofovir, but after only 18 mo of treatment to date. The optimal first-line anti-HBV therapy with the best long-term cost/benefit ratio remains unclear. If oral antiviral agents are used, compliance should always be ascertained and HBV DNA levels should be regularly tested.

The Molecular Diagnosis of Hepatitis B Virus-Associated Hepatocellular Carcinoma

Hepatitis B virus (HBV) infection is the major cause of hepatocellular carcinoma (HCC) worldwide. The pathogenesis of HBV-associated HCC has been studied extensively, and molecular changes during malignant transformation have been identified. It has been proposed that the insertion of HBV DNA into the human genome results in chromosomal instability and inactivation of tumor suppressor genes. Transactivation of oncogenes, inactivation of tumor suppressor genes, and alteration of the cell cycle by HBV proteins are also involved in the progression of hepatocellular carcinogenesis. Traditional clinical examinations of HCC, such as biopsy, computer tomography, ultrasonic imaging, and detection of such biomarkers as a-fetoprotein, are currently the "gold standard" in diagnosis. These tests diagnose HCC only in the late stages of disease. This limitation has greatly reduced the chance of survival of HCC patients. To resolve this problem, new biomarkers that can diagnose HCC in earlier stages are necessary. Based on recent molecular studies of the effects of HBV on cellular transformation, differentially expressed biomarkers of HBV infection have been elucidated. With the analyses of the HBV replication profile, the viral load (HBV DNA levels) of patients, and the viral protein expression, the severity of hepatitis in the preneoplastic stages can be assessed. In the future, with the molecular profiles identified by genomic and proteomic approaches, stage-specific biomarkers should be identified to monitor the progression and prognosis of HCC.

Therapeutic effect of adeforvir dipivoxil for HBeAg-positive patients with chronic hepatitis B

AIM: To verify the efficacy and safety of adeforvir dipivoxil in the treatment of HbeAg-positive chronic hepatitis B (CHB).

METHODS: A total of 40 HbeAg-positive patients with CHB were divided into group A (n = 26) and B (n = 14). The patients in group A and B were treated with adeforvir dipivoxil (10 mg/d) and placebo, respectively, for 12 wk, and then all the patients were treated with adeforvir dipivoxil (10 mg/d). The responses were observed 12, 24, and 48 wk after treatment, and the hepatitis B virus markers (HBVMs), and HBV DNA, liver function, kidney function, blood routine and urine routine were also measured.

RESULTS: After 12 wk of treatment, the viral response rates were significantly different between group A and B (80.77% vs 7.14%, P < 0.01); the ALT/AST normalization rates had no marked difference between the two groups. After 48 wk of treatment, the viral response rates in both groups were 78.38%, and the ALT/AST normalization rates were 59.46%; the levels of ALT, AST and TBiL level reduced significantly (t = 5.19, 4.48, 2.47, P < 0.01) compared with those before treatment, and the HbeAg-negative rates were 18.92%. No severe adverse reactions were found in both groups.

CONCLUSION: Adeforvir dipivoxil has obvious effect on viral and biochemical responses in CHB patients, and it is effective and safe in the treatment of CHB.

Therapeutic strategies in the management of patients with chronic hepatitis B virus infection

Currently available options for the treatment of chronic hepatitis B virus (HBV) infection include standard and pegylated interferon alfa and four oral antiviral agents (lamivudine, adefovir, entecavir, and telbivudine). These treatment strategies are either therapies of finite duration that aim to achieve sustained off-therapy responses, or long-term treatments that aim to maintain on-therapy remission. Pegylated interferon alfa may offer higher sustained off-therapy responses after 1 year, but most patients do not respond. Oral antivirals are the only candidates for long-term treatment of patients with chronic HBV infection. Viral suppression has favourable effects on patients' outcome and modifies the natural history of the disease. Viral resistance is the main drawback of long-term antiviral therapy. Lamivudine monotherapy is associated with higher resistance (year 1, 10-27%; year 2, 37-48%; year 4, 60-65%) than adefovir (year 1, 0%; year 2, 3%; year 5, 29%) or telbivudine (year 1, 3-4%; year 2, 9-22%). Entecavir resistance is rare in naive individuals (year 4, <1%), but increases over time in lamivudine-resistant patients (year 4, 43%). The best strategy for long-term therapy in chronic HBV infection has yet to be established.

In vivo effects of antiviral acyclic nucleoside phosphonate 9-[2-(phosphonomethoxy)ethyl]adenine (adefovir) on cytochrome P450 system of rat liver microsomes

Interference of antiviral agent adefovir, i.e. 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA) with microsomal drug metabolizing system was investigated in rats. The content of total liver cytochrome P450 (CYP) was lowered while that of its denaturated form, P420, was elevated in animals intraperitoneally treated with PMEA (25 mg/kg). Similar effect was observed after treatment with a prodrug of adevofir, adefovir dipivoxil (bisPOM-PMEA). The CYP2E1-dependent formation of 4-nitrocatechol from p-nitrophenol was diminished, though the specific activity of p-nitrophenol hydroxylase remained unchanged. PMEA had no influence on expression of CYP2E1 protein and mRNA and mRNAs of other P450 isoenzymes (1A1, 1A2, 2C11, 3A1, 3A2, and 4A1). It may be concluded that repeated systemic administration of higher doses of PMEA results in a partial degradation of rat CYP protein to inactive P420.

Strategies to improve oral drug bioavailability

Efforts to improve oral drug bioavailability have grown in parallel with the pharmaceutical industry. As the number and chemical diversity of drugs has increased, new strategies have been required to develop orally active therapeutics. The past two decades have been characterised by an increased understanding of the causes of low bioavailability and a great deal of innovation in oral drug delivery technologies, marked by an unprecedented growth of the drug delivery industry. The advent of biotechnology and consequent proliferation of biopharmaceuticals have brought new challenges to the drug delivery field. In spite of the difficulties associated with developing oral forms of this type of therapeutics, significant progress has been made in the past few years, with some oral proteins, peptides and other macromolecules currently advancing through clinical trials. This article reviews the approaches that have been successfully applied to improve oral drug bioavailability, primarily, prodrug strategies, lead optimisation through medicinal chemistry and formulation design. Specific strategies to improve the oral bioavailability of biopharmaceuticals are also discussed.

Emerging treatments in chronic hepatitis B

Although the management of chronic hepatitis B has improved over the last decade, none of the available therapeutic agents, IFN-alpha, lamivudine and adefovir dipivoxil, can achieve sustained off-therapy responses in most cases. Therefore, several newer, mainly antiviral and immunomodulatory agents, are being evaluated. Pegylated IFN-alpha(2a) has been shown to be more effective than lamivudine or standard IFN-alpha monotherapy in achieving post-therapy biochemical and virological responses, and is expected to be licensed soon for the treatment of chronic hepatitis B. Newer antiviral agents, such as entecavir and telbivudine, appear to be quite effective initially, but their sustained off-therapy response rates remain unknown. The preliminary data of monotherapies with immunomodulatory agents, or of combination therapies, have been rather disappointing. Long-term maintenance treatment with antiviral agent(s) with good safety and tolerability profiles and low resistance rates appears to be the most realistic future therapeutic option for most chronic hepatitis B patients.