Pharmacokinetics of LB80331 and LB80317 following oral administration of LB80380, a new antiviral agent for chronic hepatitis B (CHB), in healthy adult subjects, CHB patients, and mice

Besifovir dipivoxil maleate: a novel antiviral agent with low toxicity and high genetic barriers for chronic hepatitis B

INTRODUCTION

Chronic hepatitis B is an important public health concern. Introduction of oral nucleos(t)ide analogs (NAs), inhibitors of hepatitis B virus (HBV) polymerase, was a milestone that lowered the high viral loads associated with an increased risk of liver-related complications.

AREAS COVERED

Although the currently available NAs are effective in suppressing viral replication, anti-HBV treatment in principle requires lifelong drug administration, and some patients have limitations such as the incidence of liver cancer and the likelihood of toxicities following long-term treatment despite viral suppression. Besifovir dipivoxil maleate (BSV), an oral nucleotide analog, is a prodrug that is metabolized to its active form. It has consistent and well-characterized pharmacokinetics in animals and human. In clinical studies, BSV exhibits significant and potent viral suppression of HBV replication with maintenance of antiviral efficacy for over 192 weeks without resistance, or renal and bone toxicities. Herein, the authors discuss the data of BSV and provide the reader with their expert opinion.

EXPERT OPINION

BSV is a newly developed antiviral agent against HBV. This new agent has strong antiviral activity with low toxicity and a high barrier to resistance. Because there is concern that patients treated with a high dose of BSV require carnitine supplementation, BSV with carnitine supplementation is recommended during antiviral therapy.

Influence of renal function on the single-dose pharmacokinetics of besifovir, a novel antiviral agent for the treatment of hepatitis B virus infection

Per the well-known resistance of hepatitis B virus (HBV) to nucleos(t)ide analogs, alternative treatment options with higher resistance barriers have been approved for use in both treatment-naïve and lamivudine-resistant HBV infections. This phase I study was conducted in adults with normal and impaired renal function to evaluate the effect of renal impairment on the pharmacokinetics of besifovir, a prodrug of an acyclic nucleotide phosphonate, that is mainly cleared via renal excretion. An open-label, single-dose parallel-group clinical study was conducted in subjects with normal renal function and mild, moderate and severe renal impairment. Subjects received a single oral dose of besifovir dipivoxil 150 mg, and serial blood and urine samples were collected for up to 72 hours post-dose to assess the pharmacokinetic characteristics of besifovir. The extent of plasma exposure of besifovir, detected as its major and active metabolites, LB80331 and LB80317, respectively, increased with worsening renal function. Compared to the normal renal function subjects, the mean areas under the concentration-time curves of LB80331 increased by 1.5-, 2.5-, and 4.5-fold in subjects with mild, moderate and severe impairment, respectively. LB80317 showed a 1.8-, 3.2-, and 6.2-fold increase in mild, moderate and severe renal impairment subjects compared to those with normal function. The ratios of LB80331 renal clearance and the average estimated glomerular filtration rate of each renal impairment group with respect to the normal group were similar. The increase in plasma exposure and decrease in renal clearance suggest the need to adjust dosage regimens in patients with moderate-to-severe renal impairment. This article is protected by copyright. All rights reserved.

Overview of Biologically Active Nucleoside Phosphonates

The use of the phosphonate motif featuring a carbon-phosphorous bond as bioisosteric replacement of the labile P–O bond is widely recognized as an attractive structural concept in different areas of medicinal chemistry, since it addresses the very fundamental principles of enzymatic stability and minimized metabolic activation. This review discusses the most influential successes in drug design with special emphasis on nucleoside phosphonates and their prodrugs as antiviral and cancer treatment agents. A description of structurally related analogs able to interfere with the transmission of other infectious diseases caused by pathogens like bacteria and parasites will then follow. Finally, molecules acting as agonists/antagonists of P2X and P2Y receptors along with nucleotidase inhibitors will also be covered. This review aims to guide readers through the fundamentals of nucleoside phosphonate therapeutics in order to inspire the future design of molecules to target infections that are refractory to currently available therapeutic options.

Influence of Besifovir Dipivoxil Maleate Combined with L-Carnitine on Hepatic Steatosis in Patients with Chronic Hepatitis B

BACKGROUND

Besifovir dipivoxil maleate (BSV) with L-carnitine is the first-line antiviral agent for chronic hepatitis B (CHB) infection. We investigated whether BSV combined with L-carnitine improves hepatic steatosis (HS).

METHODS

Treatment-naïve patients with CHB who were initiated on antiviral therapy (AVT) were enrolled. The magnitude of HS was assessed using hepatic steatosis index (HSI), and HS improvement was defined as a ≥ 10% reduction in the HSI score from the baseline.

RESULTS

The mean age of the study patients was 56 years with a male predominance (n = 178, 64.7%). The mean body mass index (BMI), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and platelet count were 23.5 kg/m², 49.6 IU/L, 49.0 IU/L, and 191.3 × 10⁹/L, respectively. The mean HSI and fibrosis (FIB)-4 index were 32.6 and 0.5, respectively. After 6 months of AVT, platelet count (mean, 191.3→167.0 × 10⁹/L), fasting glucose (mean, 113.1→105.9 mg/dL), AST (mean, 49.6→28.0 IU/L), ALT (mean, 49.0→33.9 IU/L), and total cholesterol (mean, 170.0→162.1 mg/dL) levels significantly decreased (all P < 0.05). In the BSV group, AST (mean, 95.2→30.2 IU/L) and ALT (mean, 81.1→31.1 IU/L) levels significantly reduced (all P < 0.05), whereas HSI and FIB-4 index were maintained (all P > 0.05). In the univariate analysis, age, BMI, diabetes, cirrhosis, fasting glucose level, and ALT were significantly associated with HS improvement (all P < 0.05).

CONCLUSION

BSV with L-carnitine did not show any improvement of HS in patients with CHB. Further prospective randomized controlled studies are needed to validate the potential beneficial effects of BSV with L-carnitine in CHB infection.

Strategies for the treatment of HBV/HDV

An estimated 240 million people worldwide are chronically infected with the hepatitis B virus (HBV). Despite readily available vaccination, HBV infections remain highly prevalent. As established HBV infections constitute a strong risk factor for developing hepatocellular carcinoma their treatment is a major task for the health system. Unfortunately, HBV is not curable with today's medicine. Approximately 15 million HBV patients have developed a hepatitis delta (HDV) infection on top of their HBV infection. The patients superinfected with this satellite virus suffer from a more severe disease development. The knowledge of the viruses, their classifications, clinical implications, treatment options and efforts to increase the drug variety are compiled in this review. The current standard therapies include nucleosidic reverse transcriptase inhibitors and interferon. As the known treatments fail to cure HBV and HDV, targeted treatment is highly warranted. The focus of this review is set on the drugs currently under clinical investigation. Furthermore, strategies for the development of targeted treatment, and compounds with novel mode of action are described.

Pharmacokinetic evaluation of besifovir for the treatment of HBV infection

INTRODUCTION

Besifovir (LB80380) is a relatively new oral acyclic nucleotide phosphonate. We reviewed the pharmacokinetic characteristics of LB80380 and discussed its role in the treatment of chronic hepatitis B infection. Areas covered: LB80380 is a prodrug of LB80331 and LB80317. It is rapidly absorbed when taken orally. Escalating doses of besifovir produce linear increase of the plasma concentration. Doses above 60mg are effective for inhibiting HBV in human. Using 60mg as an example, the maximal concentration of LB80331 in plasma is 397 ng/mL. The time required to reach maximal concentration in plasma and elimination half-life are 2.0 and 3.0 h, respectively. Besifovir and its metabolites are mainly excreted via the kidneys. Its antiviral efficacy is non-inferior to ETV 0.5mg daily. It is generally safe in terms of renal and bone toxicity. The most common adverse event is carnitine depletion which affects almost all patients on besifovir requiring carnitine supplementation. Expert opinion: Besifovir demonstrated predictable pharmacokinetic characteristics in human subjects. Few clinical studies on besifovir have been conducted. More data are expected particularly for special populations. The adverse events upon long term exposure should be monitored. Large scale head-to-head trials comparing besifovir with existing NA, especially tenofovir alafenamide, should be conducted.

New directions in hepatitis B therapy research

Chronic hepatitis B treatment is available for a long period, allowing disease control and infection suppression, but it is rarely responsible for HBsAg clearance. None of the drugs available aim at cccDNA, the obstacle in HBV infection eradication. Complications related to CHB, such as liver insufficiency, cirrhosis, and hepatocellular carcinoma are reduced in conditions of good viremia suppression, but still exist even after HBsAg seroclearance, what makes a need for urgent forthcoming of new therapeutics. Recent years brought promising and interesting results of experimental approaches, which are directed against different phases of HBV life cycle, target ccc DNA, or boost, and restore host immune response. Unfortunately, encouraging results in vitro and on animal models are not always reflected in human. Nevertheless, the multiplicity of novel antivirals allows to expect that at least some of them will enter clinical practice and relieve patients from chronic hepatitis B, fatal and devastating disease.

Two-year treatment outcome of chronic hepatitis B infection treated with besifovir vs. entecavir: results from a multicentre study

BACKGROUND & AIMS

We aimed to compare the viral suppression, safety and rate of drug resistance between besifovir (a new acyclic nucleotide analogue) and entecavir.

METHODS

Treatment-naïve chronic hepatitis B patients receiving besifovir 90 mg (n=31), 150 mg (n=28) and entecavir 0.5 mg (n=30) were monitored for liver biochemistry, viral serology, HBV DNA levels, development of drug resistance mutations, and adverse events throughout 96 weeks of treatment.

RESULTS

The mean decline of HBV DNA levels from baseline to week 96 were 5.29, 5.15, and 5.67 logs IU/ml for patients receiving besifovir 90 mg, 150 mg and entecavir 0.5 mg, respectively (p>0.05). Undetectable HBV DNA (<20 IU/ml) were achieved in 80.7%, 78.6%, and 80%; ALT normalization in 90.3%, 78.6%, and 93.3%; and loss of HBeAg in 20%, 21.4%, and 22.2% of patients respectively (all p>0.05). One patient receiving besifovir 90 mg had a virological breakthrough due to drug non-compliance. No patient developed drug resistance mutations. Ten patients had serious adverse events, which were not related to the study medications. The most common side effect related to besifovir was carnitine depletion. Carnitine supplements were prescribed to 83.9% and 100% of patients, who had low carnitine level for any one time during follow-up, receiving besifovir 90 mg and 150 mg respectively. No patient had increased creatinine>0.5 mg/dl from baseline.

CONCLUSIONS

Besifovir had the same antiviral property as compared to entecavir over 96 weeks of treatment for chronic hepatitis B patients. Besifovir was well tolerated and also had a good clinical safety profile.

Nucleoside/nucleotide analog inhibitors of hepatitis B virus polymerase: mechanism of action and resistance

Hepatitis B virus (HBV) polymerase and human immunodeficiency virus (HIV) reverse transcriptase are structurally related. However, the HBV enzyme has a protein priming activity absent in the HIV enzyme. Approved nucleoside/nucleotide inhibitors of the HBV polymerase include lamivudine, adefovir, telbivudine, entecavir and tenofovir. Although most of them target DNA elongation, guanosine and adenosine analogs (e.g. entecavir and tenofovir, respectively) also impair protein priming. Major mutational patterns conferring nucleoside/nucleotide analog resistance include the combinations rtL180M/rtM204(I/V) (for lamivudine, entecavir, telbivudine and clevudine) and rtA181V/rtN236T (for adefovir and tenofovir). However, development of drug resistance is very slow for entecavir and tenofovir. Novel nucleoside/nucleotide analogs in advanced clinical trials include phosphonates similar to adefovir or tenofovir, and new tenofovir derivatives with improved pharmacological properties.

Unraveling the complexity of hepatitis B virus: from molecular understanding to therapeutic strategy in 50 years

Hepatitis B virus (HBV) is a well-known hepadnavirus with a double-stranded circular DNA genome. Although HBV was first described approximately 50 years ago, the precise mechanisms of HBV infection and effective therapeutic strategies remain unclear. Here, we focus on summarizing the complicated mechanisms of HBV replication and infection, as well as genomic factors and epigenetic regulation. Additionally, we discuss in vivo models of HBV, as well as diagnosis, prevention and therapeutic drugs for HBV. Together, the data in this 50-year review may provide new clues to elucidate molecular mechanisms of HBV pathogenesis and shed new light on the future HBV therapies.

HBV life cycle and novel drug targets

With up to 400 million affected people worldwide, chronic hepatitis B virus (HBV) infection is still a major health care problem. During the last decade, several novel therapeutic approaches have been developed and evaluated. In most regions of the world, interferon-α, and nucleos(t)ide analogues (NUCs) are currently approved. Despite major improvements, none of the existing therapies is optimal since viral clearance is rarely achieved. Recently, a better understanding of the HBV life cycle and the development of novel model systems of HBV infection have led to the development of novel antiviral strategies and drug targets. This review will focus on current and potential future drug targets in the HBV life cycle and strategies to modulate the virus-host interaction.

Discovery and development of anti-HBV agents and their resistance

Hepatitis B virus (HBV) infection is a prime cause of liver diseases such as hepatitis, cirrhosis and hepatocellular carcinoma. The current drugs clinically available are nucleot(s)ide analogues that inhibit viral reverse transcriptase activity. Most drugs of this class are reported to have viral resistance with breakthrough. Recent advances in methods for in silico virtual screening of chemical libraries, together with a better understanding of the resistance mechanisms of existing drugs have expedited the discovery and development of novel anti-viral drugs. This review summarizes the current status of knowledge about and viral resistance of HBV drugs, approaches for the development of novel drugs as well as new viral and host targets for future drugs.