Inhibition of hepatitis B virus by a novel L-nucleoside, 2'-fluoro-5-methyl-beta-L-arabinofuranosyl uracil

A randomized phase 1b trial of the active site polymerase inhibitor nucleotide ATI-2173 in patients with chronic hepatitis B virus infection

ATI-2173 is an active site polymerase inhibitor nucleotide in development as part of a potentially curative regimen for chronic hepatitis B virus (HBV) infection. This study evaluated the safety, tolerability, pharmacokinetics (PK) and antiviral activity of ATI-2173. This was a phase 1b, randomized, double-blind, placebo-controlled trial in treatment-naive adults with chronic HBV infection conducted in the Republic of Moldova and Ukraine (ClinicalTrials.gov: NCT04248426). Patients positive for hepatitis B surface antigen were randomized 6:2 to receive once-daily oral doses of ATI-2173 10, 25, or 50 mg (n = 6 per dose) or placebo (n = 7) for 28 days, with off-treatment monitoring for 24 weeks. Endpoints included PK parameters of ATI-2173 and its metabolite clevudine, maximum reduction from baseline in HBV DNA, and safety and tolerability. Treatment-emergent adverse events occurred in eight patients (47%) receiving ATI-2173 and five (71%) receiving placebo; headache was the most common (n = 4). ATI-2173 PK was generally dose proportional. Systemic clevudine exposure with ATI-2173 dosing was substantially reduced compared with historical values observed with clevudine administration. On Day 28, mean changes from baseline in HBV DNA were -2.72 to -2.78 log₁₀  IU/ml with ATI-2173 and +0.17 log₁₀  IU/ml with placebo. Off-treatment sustained viral suppression and decreases in covalently closed circular DNA biomarkers were observed in most patients; one maintained undetectable HBV DNA at 24 weeks off treatment. In this 28-day monotherapy study, ATI-2173 demonstrated safety and antiviral activity, with sustained off-treatment effects and substantially reduced systemic clevudine exposure. These results support evaluation of ATI-2173 with tenofovir disoproxil fumarate in phase 2 studies.

Synthesis of Novel Amide and Schiff’s Base Functionalized Novel Pyrido[ 1,2-a] Pyrimidin-4-One Derivatives and Their Anticancer Activity Studies

Abstract:

A series of novel amide and Schiffs base functionalized novel pyrido[1,2-a] pyrimidin- 4-one derivatives was prepared starting from 6-(thiophen-2-yl)/phenyl-4-(trifluoromethyl) pyridin- 2-amine 1a and 1b. These compounds on reacting with EMME afford compounds 2a and 2b, followed by cyclization to afford compounds 3a and 3b. Treatment of compounds 3a and 3b with hydrazine hydrate gave compounds 4a and 4b, which further reacted with different substituted aromatic aldehydes to give Schiff’s base derivatives 5a-j. In another way, compounds 3a, 3b by reacting with aliphatic amines give amide derivatives 6a-f. All the compounds, 5a-j and 6a-f, were screened against four human cancer cell lines (HeLa, COLO205, Hep G2, and MCF 7). Among all the derivatives, compounds 5c, 5e, 6a, and 6b showed promising anticancer activity.

Active site polymerase inhibitor nucleotides (ASPINs): Potential agents for chronic HBV cure regimens

Chronic hepatitis B virus (HBV) infection affects 240 to 300 million people worldwide. In the nucleus of infected hepatocytes, the HBV genome is converted to covalently closed circular DNA (cccDNA), which persists and serves as a transcriptional template for viral progeny. Therefore, a long-term cure for chronic HBV infection will require elimination of cccDNA. Although currently available nucleos(t)ide analogues (eg, tenofovir disoproxil fumarate, tenofovir alafenamide, entecavir) effectively control HBV replication, they are seldom curative (functional cure rate ∼10%) and require lifelong treatment for most patients. As such, antiviral agents with novel mechanisms of action are needed. Active site polymerase inhibitor nucleotides (ASPINs) noncompetitively distort the HBV polymerase active site to completely inhibit all polymerase functions, unlike traditional chain-terminating nucleos(t)ide analogues, which only target select polymerase functions and are consumed in the process. Clevudine, a first-generation ASPIN, demonstrated potent and prolonged HBV suppression in phase 2 and 3 clinical studies, but long-term treatment was associated with reversible myopathy in a small number of patients. ATI-2173, a novel next-generation ASPIN, is structurally similar to clevudine but targets the liver and demonstrates potent anti-HBV activity on and off treatment, and may ultimately demonstrate an improved pharmacokinetic and safety profile by significantly reducing systemic clevudine exposure. Thus, ATI-2173 is currently in clinical development as an agent for HBV cure. Here, we review the mechanism of action and preclinical and clinical profiles of clevudine and ATI-2173 to support the role of ASPINs as part of curative regimens for chronic HBV infection.

Protecting-group-free synthesis of clevudine (l-FMAU), a treatment of the hepatitis B virus

A new strategy for the synthesis of unnatural 2′-deoxy-2′-fluoro-l-nucleoside is described.

Clevudine attenuates bleomycin-induced early pulmonary fibrosis via regulating M2 macrophage polarization

Pulmonary fibrosis (IPF) is a chronic, progressive interstitial lung disease. It is a growing clinical problem which can result in breathlessness or respiratory failure and has an average life expectancy of 3 years from diagnosis. Predominantly accumulation of M2 macrophages accelerates fibrosis progression by secreting multiple cytokines that promote fibroblast to myofibroblast transition and aberrant wound healing of epithelial cells. Targeting activated macrophages to inhibit the pro-fibrotic phenotype is considered as an approach for the potential treatment of PF. Clevudine is s a purine nucleoside analogue which in an oral formulation is approved for treatment of patients with hepatitis B virus (HBV). Here, we found that clevudine is capable of suppressing pro-fibrotic phenotype (i.e., CD206, Arg1 and YM1) of M2 macrophages while enhancing anti-fibrotic phenotype (i.e., CD86, IL-6 and IL-10) by inhibiting PI3K/Akt signaling pathway. This effect further alleviates M2-induced myofibroblast activation and epithelial-to-mesenchymal transition (EMT), thus resulting in a decline of collagen deposition, pro-fibrotic cytokines secretion, with a concomitant recover ofpulmonary functions in vivo. Less infiltration of M2 macrophages between α-SMA + cells was also found in clevudine treated mice. Our findings indicate a potential anti-fibrotic effect of clevudine by regulating macrophage polarization and might be meaningful in clinical settings.

ATI-2173, a Novel Liver-Targeted Non-Chain-Terminating Nucleotide for Hepatitis B Virus Cure Regimens

ATI-2173 is a novel liver-targeted molecule designed to deliver the 5′-monophosphate of clevudine for the treatment of chronic hepatitis B infection. Unlike other nucleos(t)ides, the active clevudine-5′-triphosphate is a noncompetitive, non-chain-terminating inhibitor of hepatitis B virus (HBV) polymerase that delivers prolonged reduction of viremia in both a woodchuck HBV model and in humans for up to 6 months after cessation of treatment. However, long-term clevudine treatment was found to exhibit reversible skeletal myopathy in a small subset of patients and was subsequently discontinued from development.

ATI-2173 is a novel liver-targeted molecule designed to deliver the 5′-monophosphate of clevudine for the treatment of chronic hepatitis B infection. Unlike other nucleos(t)ides, the active clevudine-5′-triphosphate is a noncompetitive, non-chain-terminating inhibitor of hepatitis B virus (HBV) polymerase that delivers prolonged reduction of viremia in both a woodchuck HBV model and in humans for up to 6 months after cessation of treatment. However, long-term clevudine treatment was found to exhibit reversible skeletal myopathy in a small subset of patients and was subsequently discontinued from development. ATI-2173 was designed by modifying clevudine with a 5′-phosphoramidate to deliver the 5′-monophosphate to the liver. Bypassing the first phosphorylation step of clevudine, the 5′-monophosphate is converted to the active 5′-triphosphate in the liver. ATI-2173 is a selective inhibitor of HBV with an anti-HBV 50% effective concentration (EC₅₀) of 1.31 nM in primary human hepatocytes, with minimal to no toxicity in hepatocytes, skeletal muscle, liver, kidney, bone marrow, and cardiomyocytes. ATI-2173 activity was decreased by viral polymerase mutations associated with entecavir, lamivudine, and adefovir resistance, but not capsid inhibitor resistance mutations. A single oral dose of ATI-2173 demonstrated 82% hepatic extraction, no food effect, and greatly reduced peripheral exposure of clevudine compared with equimolar oral dosing of clevudine. Despite reduced plasma clevudine exposure, liver concentrations of the 5′-triphosphate were equivalent following ATI-2173 versus clevudine administration. By selectively delivering the 5′-monophosphate to the liver, while retaining the unique anti-HBV activity of the 5′-triphosphate, ATI-2173 may provide an improved pharmacokinetic profile for clinical use, reducing systemic exposure of clevudine and potentially eliminating skeletal myopathy.

Utility of 2-thioxo-pyrido[2,3-d]pyrimidinone in synthesis of pyridopyrimido[2,1-b][1,3,5]-thiadiazinones and pyridopyrimido[2,1-b][1,3]thiazinones as antimicrobial agents

Background

Pyridopyrimidines are of current interest because of their extensive variety of biological and pharmacological activities.

Results

A series of pyrido[2′,3′:4,5]pyrimido[2,1-b][1,3,5]thiadiazinones was obtained by aminomethylation of pyridopyrimidinethione with formaldehyde solution (37%) and different primary aromatic amines. Another series of pyrido[2′,3:4,5]pyrimido[2,1-b][1,3]thiazinones was prepared by Michael addition reaction of pyridopyrimidinethione to the activated double bond of a number of arylidene malononitrile and 2-(benzo[d][1,3]dioxol-5-ylmethylene)malononitrile. The mechanisms of formation of the synthesized compounds were discussed and the assigned structure was established via microanalysis and spectral data (IR, ¹H NMR, and Ms.). A comparative study of the biological activity of the synthesized compounds with chloramphenicol and trimethoprim/sulphamethoxazole is shown in Table 1. Generally, all synthesized compounds showed adequate inhibitory effects on the growth of Gram-positive and Gram-negative bacteria.

Conclusions

In this study, we use a simple (synthetic) strategy for the synthesis of pyrimidothiadiazines, based on their aminomethylation through the Mannich reaction; they have also been synthesized by the application of the Michael addition to activated nitriles. Mechanisms and structures of the newly synthesized compounds were examined: the antimicrobial activity of some selected compounds was evaluated, which demonstrated adequate inhibitory effects. Graphical abstract

In vitro antiviral activity of three enantiomeric sesquiterpene lactones from Senecio species against hepatitis B virus

Three enantiomeric sesquiterpene lactones were isolated under the bioguidance of the suppression of hepatitis B virus (HBV) surface antigen (HBsAg) from Senecio species, a widely distributed Chinese medicinal herb traditionally used for the treatment of hepatitis B, dermatosis and inflammation. The anti-HBV activity of the purified compounds was measured; all of them showed suppressive activity on the expression of HBsAg and HBV e antigen (HBeAg) in the HepG2.2.15 cell line. Realtime quantitative PCR analysis showed that the studied compounds decreased the number of infectious virions released, but did not inhibit the intracellular HBV DNA. The results suggest that enantiomeric sesquiterpene lactones may possess the potential to work synergistically with other antiviral compounds for the treatment of HBV infection.

Hepatitis B virus reverse transcriptase - Target of current antiviral therapy and future drug development

Hepatitis B virus (HBV) infections rely on the proper functioning of the viral polymerase enzyme, a specialized reverse transcriptase (RT) with multiple activities. All currently approved antiviral drugs for the treatment of chronic HBV infection, except for interferon, target the RT and belong to the same chemical class - they are all nucleoside analogs. Viral DNA synthesis is carried out by the RT enzyme in several different steps, each with distinct RT conformational requirements. In principle, each stage may be targeted by distinct antiviral drugs. In particular, the HBV RT has the unique ability to initiate viral DNA synthesis using itself as a protein primer in a novel protein priming reaction. In order to help identify RT inhibitors and study their mechanisms of action, a number of experimental systems have been developed, each varying in its ability to dissect the protein priming stage and subsequent stages of viral DNA synthesis at the molecular level. Two of the most effective drugs to date, entecavir and tenofovir, can inhibit both the protein priming and the subsequent DNA elongation stages of HBV DNA synthesis. Interestingly, clevudine, a thymidine analog, can inhibit both protein priming and DNA elongation in a non-competitive manner and without being incorporated into the viral DNA. Thus, a nucleoside RT inhibitor (NRTI) can functionally mimic a non-NRTI (NNRTI) in its inhibition of the HBV RT. Therefore, novel NRTIs as well as NNRTIs may be developed to inhibit the DNA synthesis activity of the HBV RT. Furthermore, additional activities of the RT that are also essential to HBV replication, including specific recognition of the viral RNA and its packaging into viral nucleocapsids, may be exploited for antiviral development. To achieve a more potent inhibition of viral replication and ultimately cure chronic HBV infection, the next generation of anti-HBV therapies will likely need to include NRTIs, NNRTIs, and other agents that target the viral RT as well as other viral and host factors in various combinations. This article forms part of a symposium in Antiviral Research on "An unfinished story: from the discovery of the Australia antigen to the development of new curative therapies for hepatitis B."

Antiviral Agents☆

Antiviral agents are drugs approved in the USA by the Food and Drug Administration (FDA) for the treatment or control of viral infections. Available antiviral agents mainly target stages in the viral life cycle. The target stages in the viral life cycle are; viral attachment to host cell, uncoating, synthesis of viral mRNA, translation of mRNA, replication of viral RNA and DNA, maturation of new viral proteins, budding, release of newly synthesized virus, and free virus in body fluids.

Two important factors that can limit the utility of antiviral drugs are toxicity and the development of resistance to the antiviral agent by the virus. In addition, host phenotypic behaviors toward antiviral drugs because of either genomic or epigenetic factors could limit the efficacy of an antiviral agent in an individual. This article summarizes the most relevant pharmacologic and clinical properties of current antiviral agents, and targets for novel antiviral agents.

Noncompetitive inhibition of hepatitis B virus reverse transcriptase protein priming and DNA synthesis by the nucleoside analog clevudine

All currently approved antiviral drugs for the treatment of chronic hepatitis B virus (HBV) infection are nucleos(t)ide reverse transcriptase inhibitors (NRTI), which inhibit the DNA synthesis activity of the HBV polymerase. The polymerase is a unique reverse transcriptase (RT) that has a novel protein priming activity in which HP initiates viral DNA synthesis using itself as a protein primer. We have determined the ability of NRTI-triphosphates (TP) to inhibit HBV protein priming and their mechanisms of action. While entecavir-TP (a dGTP analog) inhibited protein priming initiated specifically with dGTP, clevudine-TP (a TTP analog) was able to inhibit protein priming independently of the deoxynucleoside triphosphate (dNTP) substrate and without being incorporated into DNA. We next investigated the effect of NRTIs on the second stage of protein priming, wherein two dAMP nucleotides are added to the initial deoxyguanosine nucleotide. The obtained results indicated that clevudine-TP as well as tenofovir DF-DP strongly inhibited the second stage of protein priming. Tenofovir DF-DP was incorporated into the viral DNA primer, whereas clevudine-TP inhibited the second stage of priming without being incorporated. Finally, kinetic analyses using the HBV endogenous polymerase assay revealed that clevudine-TP inhibited DNA chain elongation by HP in a noncompetitive manner. Thus, clevudine-TP appears to have the unique ability to inhibit HBV RT via binding to and distorting the HP active site, sharing properties with both NRTIs and nonnucleoside RT inhibitors.

Long-term treatment outcomes of clevudine in antiviral-naive patients with chronic hepatitis B

AIM: To evaluate the treatment outcomes of clevudine compared with entecavir in antiviral-naive patients with chronic hepatitis B (CHB).

METHODS: We retrospectively analyzed the clinical data of CHB patients treated with clevudine 30 mg/d and compared their clinical outcomes with patients treated with entecavir 0.5 mg/d. The biochemical response, as assessed by serum alanine aminotransferase (ALT) activity, virologic response, as assessed by serum hepatitis B virus DNA (HBV DNA) titer, serologic response, as assessed by hepatitis B e antigen (HBeAg) status, and virologic breakthrough with genotypic mutations were assessed.

RESULTS: Two-hundred and fifty-four patients [clevudine (n = 118) vs entecavir (n = 136)] were enrolled. In clevudine-treated patients, the cumulative rates of serum ALT normalization were 83.9% at week 48 and 91.5% at week 96 (80.9% and 91.2% in the entecavir group, respectively), the mean titer changes in serum HBV DNA were -6.03 and -6.55 log₁₀ copies/mL (-6.35 and -6.86 log₁₀ copies/mL, respectively, in the entecavir group), and the cumulative non-detection rates of serum HBV DNA were 72.6% and 83.1% (74.4% and 83.8%, respectively, in the entecavir group). These results were similar to those of entecavir-treated patients. The cumulative rates of HBeAg seroconversion were 21.8% at week 48 and 25.0% at week 96 in patients treated with clevudine, which was similar to patients treated with entecavir (22.8% and 27.7%, respectively). The virologic breakthrough in the clevudine group occurred in 9 (7.6%) patients at weeks 48 and 15 (12.7%) patients at week 96, which primarily corresponded to genotypic mutations of rtM204I and/or rtL180M. There was no virologic breakthrough in the entecavir group.

CONCLUSION: In antiviral-naive CHB patients, long-term treatment outcomes of clevudine were not inferior to those of entecavir, except for virologic breakthrough.

Long-term treatment efficacy and safety of clevudine therapy in naïve patients with chronic hepatitis B

Background/Aims

Clevudine (CLV) has potent antiviral activity against chronic hepatitis B (CHB) virus infection. The long-term efficacy and safety of CLV therapy in naïve patients with CHB were investigated.

Methods

In this retrospective study, 152 naïve Korean patients with CHB who received 30 mg of CLV once daily for at least 12 months were investigated.

Results

The cumulative rates at months 12, 24, and 36, respectively, were 65.8%, 74.7%, and 74.7% for undetectable serum hepatitis B virus (HBV) DNA (<12 IU/mL); 77.6%, 86.2%, and 86.2% for normalization of serum alanine aminotransferase (<40 IU/L); 17.6%, 23.5%, and 23.5% for hepatitis B e antigen (HBeAg) loss or seroconversion; and 6.6%, 22.5%, and 30.0% for viral breakthrough. HBeAg positivity (p=0.010), baseline serum HBV DNA level ≥6 log₁₀ IU/mL (p=0.032) and detectable serum HBV DNA (≥12 IU/mL) at week 24 (p=0.023) were independently associated with the development of viral breakthrough. During follow-up, CLV-induced myopathy developed in 5.9% of patients.

Conclusions

The results of long-term CLV therapy for the treatment of naïve patients with CHB showed a high frequency of antiviral resistance and substantial associated myopathy. Therefore, we advise that CLV should not be used as a first-line treatment for naïve patients given the availability of other more potent, safer antiviral agents.

Evaluation of single and combination therapies with tenofovir disoproxil fumarate and emtricitabine in vitro and in a robust mouse model supporting high levels of hepatitis B virus replication

Next-generation therapies for chronic hepatitis B virus (HBV) infection will involve combinations of established and/or experimental drugs. The current study investigated the in vitro and in vivo efficacy of tenofovir disoproxil fumarate (TDF) and/or emtricitabine [(-)-FTC] alone and in combination therapy for HBV infection utilizing the HepAD38 system (human hepatoblastoma cells transfected with HBV). Cellular pharmacology studies demonstrated increased levels of (-)-FTC triphosphate with coincubation of increasing concentrations of TDF, while (-)-FTC had no effect on intracellular tenofovir (TFV) diphosphate levels. Quantification of extracellular HBV by real-time PCR from hepatocytes demonstrated the anti-HBV activity with TDF, (-)-FTC, and their combination. Combination of (-)-FTC with TDF or TFV (ratio, 1:1) had a weighted average combination index of 0.7 for both combination sets, indicating synergistic antiviral effects. No cytotoxic effects were observed with any regimens. Using an in vivo murine model which develops robust HBV viremia in nude mice subcutaneously injected with HepAD38 cells, TDF (33 to 300 mg/kg of body weight/day) suppressed virus replication for up to 10 days posttreatment. At 300 mg/kg/day, (-)-FTC strongly suppressed virus titers to up to 14 days posttreatment. Combination therapy (33 mg/kg/day each drug) sustained suppression of virus titer/ml serum (<1 log(10) unit from pretreatment levels) at 14 days posttreatment, while single-drug treatments yielded virus titers 1.5 to 2 log units above the initial virus titers. There was no difference in mean alanine aminotransferase values or mean wet tumor weights for any of the groups, suggesting a lack of drug toxicity. TDF-(-)-FTC combination therapy provides more effective HBV suppression than therapy with each drug alone.

High-dose clevudine impairs mitochondrial function and glucose-stimulated insulin secretion in INS-1E cells

Background

Clevudine is a nucleoside analog reverse transcriptase inhibitor that exhibits potent antiviral activity against hepatitis B virus (HBV) without serious side effects. However, mitochondrial myopathy has been observed in patients with chronic HBV infection taking clevudine. Moreover, the development of diabetes was recently reported in patients receiving long-term treatment with clevudine. In this study, we investigated the effects of clevudine on mitochondrial function and insulin release in a rat clonal β-cell line, INS-1E.

Methods

The mitochondrial DNA (mtDNA) copy number and the mRNA levels were measured by using quantitative PCR. MTT analysis, ATP/lactate measurements, and insulin assay were performed.

Results

Both INS-1E cells and HepG2 cells, which originated from human hepatoma, showed dose-dependent decreases in mtDNA copy number and cytochrome c oxidase-1 (Cox-1) mRNA level following culture with clevudine (10 μM-1 mM) for 4 weeks. INS-1E cells treated with clevudine had reduced total mitochondrial activities, lower cytosolic ATP contents, enhanced lactate production, and more lipid accumulation. Insulin release in response to glucose application was markedly decreased in clevudine-treated INS-1E cells, which might be a consequence of mitochondrial dysfunction.

Conclusions

Our data suggest that high-dose treatment with clevudine induces mitochondrial defects associated with mtDNA depletion and impairs glucose-stimulated insulin secretion in insulin-releasing cells. These findings partly explain the development of diabetes in patients receiving clevudine who might have a high susceptibility to mitochondrial toxicity.

Comparison of clevudine and entecavir for treatment-naive patients with chronic hepatitis B virus infection: two-year follow-up data

BACKGROUND/AIM

Clevudine and entecavir are highly potent antiviral agents being used in treatment of chronic hepatitis B. However, no data comparing clinical efficacy and safety of these 2 drugs over a long-term period is available. The aims of this study are to compare virologic, biochemical, and serologic response rates of clevudine and entecavir, as well as treatment failure rates up to 2 years.

METHODS

Data of patients who started clevudine (n = 86) or entecavir (n = 159) as a primary treatment for chronic hepatitis B at Korea University Ansan or Guro Hospital between January 2007 and June 2008 were analyzed.

RESULTS

Treatment responses were compared at 3-month intervals up to 24 months. Per protocol analysis showed no difference in virologic responses between the 2 groups at all time points, except at 18 months. When analyzed on intention-to-treat basis for virologic response at 24 months, the response rates were 45.3% in the clevudine group and 72.3% in the entecavir group, which are significantly different (P < 0.001). Rates of biochemical response and HBeAg seroconversion were not significantly different between the groups at all time points. Up to 24 months, antiviral resistance developed in 18 patients (24.4%) in the clevudine group. Clevudine was discontinued owing to muscle-related problems in 10 patients (11.6%).

CONCLUSIONS

Although both drugs showed potent antiviral activity, entecavir showed better virologic response at 24 months, primarily owing to treatment failures in the clevudine group that were associated with development of drug resistance and muscle-related problems.

Nucleoside/nucleotide analogues in the treatment of chronic hepatitis B

The current available agents for the treatment of chronic hepatitis B (CHB) include immunomodulatory agents, such as interferon-α and pegylated interferon-α, and oral nucleoside/nucleotide analogues (NAs), including lamivudine, adefovir, telbivudine, entecavir and tenofovir. The NAs work mainly by inhibiting hepatitis B virus (HBV) DNA polymerase activity and thus suppress HBV replication. Oral NAs have become the mainstay of CHB treatment, mainly due to their profound viral suppressive effects and also due in part to the ease of single daily dosing and lack of significant side effects. One major drawback of NA therapy is the development of drug resistance mutations with long-term treatment. Lamivudine, the first oral NA approved for CHB patients, is associated with high rates of drug resistance, with resultant virological relapse and biochemical flare. Fortunately, newer and more potent NAs, such as entecavir and tenofovir, have very low resistance rates, with potent and durable viral suppression. This review is aimed at the current developments in NAs for CHB treatment, detailing the mechanisms of antiviral activity of the different agents, the efficacy of viral suppression, the achievement of treatment endpoints, the development of drug resistance and the optimal strategies for using these drugs.

Current Nucleos(t)ide Analogue Therapy for Chronic Hepatitis B

Although the prevalence of chronic hepatitis B has decreased considerably in recent years due to widespread use of the hepatitis B virus (HBV) vaccine, its prevalence still remains high in adults, and this can place a significant burden on health care in areas with endemic HBV. Since the introduction of nucleos(t)ide analogues (NUCs), there has been marked improvement in the care of patients with chronic hepatitis B, resulting in increased survival. However, the emergence of drug resistance in patients treated with NUCs is a major concern. The number of multi-drug resistant patients is increasing, and many patients may not respond to the currently available drugs. In this review, we describe the current status of NUC therapy for antiviral-naïve and -resistant patients.

Synthesis of new 2'-deoxy-2'-fluoro-4'-azido nucleoside analogues as potent anti-HIV agents

We prepared 1-(4'-azido-2'-deoxy-2'-fluoro-β-D-arabinofuranosyl)cytosine (10) and its hydrochloride salt (11) as potential antiviral agents based on the favorable antiviral profiles of 4'-substituted nucleosides. Compounds 10 and 11 were synthesized from 1,3,5-O-tribenzoyl-2-deoxy-2-fluoro-D-arabinofuranoside in multiple steps, and their structures were unequivocally established by IR, (1)H NMR, (13)C NMR, and (19)F NMR spectroscopy, HRMS, and X-ray crystallography. Compounds 10 and 11 exhibited potent anti-HIV-1 activity (EC(50): 0.3 and 0.13 nM, respectively) without significant cytotoxicity in concentrations up to 100 μM. Compound 11 exhibited extremely potent anti-HIV activity against NL4-3 (wild-type), NL4-3 (K101E), and RTMDR viral strains, with EC(50) values of 0.086, 0.15, and 0.11 nM, respectively. Due to the high potency of 11, it was also screened against an NIH Reagent Program NRTI-resistant virus panel containing eleven mutated viral strains and for cytotoxicity against six different human cell lines. The results of this screening indicated that 11 is a novel NRTI that could be developed as an anti-AIDS clinical trial candidate to overcome drug-resistance issues.

A comparison of 48-week treatment efficacy between clevudine and entecavir in treatment-naïve patients with chronic hepatitis B

PURPOSE

Clevudine and entecavir are currently available in Korea as antiviral drugs against chronic hepatitis B (CHB). We aimed to compare the efficacy of clevudine and entecavir therapy.

METHODS

Treatment-naïve CHB patients who received 30 mg of clevudine or 0.5 mg of entecavir a day were analyzed. Mean reduction of hepatitis B virus (HBV) DNA levels, complete virological response (cVR, undetectable HBV DNA by real-time PCR), biochemical response (recovery to normal ALT level), and hepatitis B e antigen (HBeAg) seroconversion rate at the 48th week of treatment were assessed.

RESULTS

A number of 59 patients in clevudine group and 61 patients in entecavir group were included. Mean HBV DNA reductions from baseline were similar in the clevudine and entecavir groups, -6.4 versus -6.8 log(10) copies/mL in HBeAg-positive (p = 0.417) and -6.9 versus -7.0 log(10) copies/mL in HBeAg-negative patients (p = 0.640). The proportion of patients who achieved cVR was not different between the two groups, 53 versus 55% in HBeAg-positive (p = 1.000) and 100 versus 95% in HBeAg-negative patients (p = 0.452). Biochemical response rates and HBeAg seroconversion rates were also similar in both the groups. Two (3.4%) patients in clevudine group showed virologic breakthrough with rtM204I mutation using direct sequencing analysis. Clinical myopathy occurred in two (3.4%) patients in clevudine group.

CONCLUSION

Mean reduction of viral loads was similar between clevudine and entecavir groups during 48 weeks. However, virologic breakthrough and significant myopathy were noted only in clevudine-treated patients. Therefore, more attention should be paid to patients receiving clevudine.

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.

Clinical, biochemical, and pathological characteristics of clevudine-associated myopathy

BACKGROUND & AIMS

The aim of this study was to define the clinical, biochemical, and pathological characteristics of myopathy developed during clevudine therapy.

METHODS

We prospectively enrolled 36 consecutive myopathy patients who were receiving clevudine therapy for the treatment of chronic hepatitis B (CHB). We evaluated patients with a complete medical history, neurologic examination with a questionnaire on neuromuscular diseases, laboratory tests, electrophysiology studies, and muscle biopsies.

RESULTS

The median duration of clevudine therapy was 18.0 months (ranging from 9 to 24 months). The chief complaint was weakness of the lower extremities in 30 patients (83.3%) and asthenia in five patients (13.9%). One patient (2.8%) had only persistently elevated serum muscle enzyme without any symptoms. Weakness of the lower extremity mainly involved proximal muscle group of the lower extremity, characterized by difficulty in climbing stairs (83.3%), a decrease in exercise capacity (75.0%) and difficulty in walking (55.6%). All patients showed an elevation of more than two of serum creatine kinase, lactate dehydrogenase, and lactate levels. Muscle biopsies performed in 23 patients revealed myopathic features with abnormal mitochondria in 21 patients, and nonspecific myositis in two patients. Motor weakness gradually improved after discontinuation of clevudine.

CONCLUSIONS

Myopathy associated with clevudine is characterized by a weakness in proximal muscles of the lower extremities with elevated muscle enzymes and presumably caused by mitochondrial toxicities. Careful medical and serologic examinations are essential for the early detection and management of this potential adverse reaction in CHB patients under clevudine therapy.

A transient kinetic approach to investigate nucleoside inhibitors of mitochondrial DNA polymerase gamma

Nucleoside analogs play an essential role in treating human immunodeficiency virus (HIV) infection since the beginning of the AIDS epidemic and work by inhibition of HIV-1 reverse transcriptase (RT), a viral polymerase essential for DNA replication. Today, over 90% of all regimens for HIV treatment contain at least one nucleoside. Long-term use of nucleoside analogs has been associated with adverse effects including mitochondrial toxicity due to inhibition of the mitochondrial polymerase, DNA polymerase gamma (mtDNA pol gamma). In this review, we describe our efforts to delineate the molecular mechanism of nucleoside inhibition of HIV-1 RT and mtDNA pol gamma based upon a transient kinetic approach using rapid chemical quench methodology. Using transient kinetic methods, the maximum rate of polymerization (k(pol)), the dissociation constant for the ground state binding (K(d)), and the incorporation efficiency (k(pol)/K(d)) can be determined for the nucleoside analogs and their natural substrates. This analysis allowed us to develop an understanding of the structure activity relationships that allow correlation between the structural and stereochemical features of the nucleoside analog drugs with their mechanistic behavior toward the viral polymerase, RT, and the host cell polymerase, mtDNA pol gamma. An in-depth understanding of the mechanisms of inhibition of these enzymes is imperative in overcoming problems associated with toxicity.

Treatment outcomes of clevudine versus lamivudine at week 48 in naïve patients with HBeAg positive chronic hepatitis B

The authors assessed the efficacy and antiviral resistance of 48-week clevudine therapy versus lamivudine in treatment of naïve patients with HBeAg positive chronic hepatitis B. In this retrospective study, a total of 116 HBeAg positive patients, who received 30 mg of clevudine once daily (n=53) or 100 mg of lamivudine once daily (n=63) for 48 weeks, were included. At week 48, clevudine therapy produced a significantly greater mean reductions in serum HBV DNA levels from baseline than lamivudine therapy (-5.2 vs. -4.2 log(10)IU/mL; P=0.005). Furthermore, a significantly higher proportion of patients on clevudine achieved negative serum HBV DNA by PCR (<13 IU/mL) at week 48 (60.4% vs. 38.1%; P=0.025). The incidence of virologic breakthrough in the clevudine group was significantly lower than in the lamivudine group (9.4% vs. 25.4%; P=0.031). However, rates of alanine aminotransferase normalization and HBeAg loss or seroconversion were similar in the two groups (83.0% vs. 81.0%, 11.3% vs. 11.1%; P=0.813, 1.000, respectively). In conclusion, clevudine is more potent for viral suppression and lower for antiviral resistance at week 48 than lamivudine in treatment of naïve patients with HBeAg positive chronic hepatitis B.

Identification and characterization of clevudine-resistant mutants of hepatitis B virus isolated from chronic hepatitis B patients

Clevudine (CLV) is a nucleoside analog with potent antiviral activity against chronic hepatitis B virus (HBV) infection. Viral resistance to CLV in patients receiving CLV therapy has not been reported. The aim of this study was to characterize CLV-resistant HBV in patients with viral breakthrough (BT) during long-term CLV therapy. The gene encoding HBV reverse transcriptase (RT) was analyzed from chronic hepatitis B patients with viral BT during CLV therapy. Sera collected from the patients at baseline and at the time of viral BT were studied. To characterize the mutations of HBV isolated from the patients, we subjected the HBV mutants to in vitro drug susceptibility assays. Several conserved mutations were identified in the RT domain during viral BT, with M204I being the most common. In vitro phenotypic analysis showed that the mutation M204I was predominantly associated with CLV resistance, whereas L229V was a compensatory mutation for the impaired replication of the M204I mutant. A quadruple mutant (L129M, V173L, M204I, and H337N) was identified that conferred greater replicative ability and strong resistance to both CLV and lamivudine. All of the CLV-resistant clones were lamivudine resistant. They were susceptible to adefovir, entecavir, and tenofovir, except for one mutant clone. In conclusion, the mutation M204I in HBV RT plays a major role in CLV resistance and leads to viral BT during long-term CLV treatment. Several conserved mutations may have a compensatory role in replication. Drug susceptibility assays reveal that adefovir and tenofovir are the most effective compounds against CLV-resistant mutants. These data may provide additional therapeutic options for CLV-resistant patients.

A mechanistic view of human mitochondrial DNA polymerase gamma: providing insight into drug toxicity and mitochondrial disease

Mitochondrial DNA polymerase gamma (Pol gamma) is the sole polymerase responsible for replication of the mitochondrial genome. The study of human Pol gamma is of key importance to clinically relevant issues such as nucleoside analog toxicity and mitochondrial disorders such as progressive external ophthalmoplegia. The development of a recombinant form of the human Pol gamma holoenzyme provided an essential tool in understanding the mechanism of these clinically relevant phenomena using kinetic methodologies. This review will provide a brief history on the discovery and characterization of human mitochondrial DNA polymerase gamma, focusing on kinetic analyses of the polymerase and mechanistic data illustrating structure-function relationships to explain drug toxicity and mitochondrial disease.

[Long-term clevudine therapy in nucleos(t)ide-naïve and lamivudine-experienced patients with hepatitis B virus-related chronic liver diseases]

BACKGROUNDS/AIMS

Clevudine is an effective antiviral nucleoside analogue, but there are few data regarding its long-term effects, resistance, and safety. The aim of this study was to evaluate the long-term clinical efficacy of clevudine over a 1-year treatment period in nucleos(t)ide-naive and lamivudine-experienced chronic hepatitis B patients.

METHODS

Nucleos(t)ide-naive (group A, n=196) and lamivudine-experienced (serum hepatitis B virus, HBV DNA >2,000 copies/mL without resistant mutants at the start of clevudine therapy, group B, n=75) patients were included in this study. Basic clinical characteristics including age, sex, the presence of cirrhosis, laboratory data, and hepatitis B surface antigen (HBeAg) positivity were similar between the two groups. Pretreatment serum levels of HBV DNA were 7.4 and 6.6 log(10) copies/mL (P<0.001). The mean treatment duration was 8 months for both groups (range for group A: 3-21 months; range for group B: 3-20 months). Genotypic analysis for resistant mutations in the reverse transcriptase of HBV was performed after viral breakthrough.

RESULTS

After 1 year of therapy, 75.0% and 51.9% of groups A and B, respectively, had HBV DNA levels of <2,000 copies/mL (P=0.032), and HBeAg seroconversion rates were 16.9% and 16.7%, respectively. The rates of viral breakthrough at 1 year were 10.0% (8/80) and 44.4% (12/27), respectively (P<0.001). Proven sites of mutation of HBV DNA polymerase in naive patients were, for example, L80I, L180M, A181V/T, M204I and V207I. Ten patients complained of prominent fatigue and revealed elevated serum levels of aspartate aminotransferase (AST) and creatine phosphokinase (CPK). Two of these patients presented with severe myopathy from which they recovered completely after quitting clevudine.

CONCLUSIONS

Clevudine is one of the recommended first-line medicines for the treatment of chronic hepatitis B, but it is not free from resistance, particularly in patients with a history of previous lamivudine treatment, but also in naive patients. Clevudine should be avoided in previously lamivudine-exposed patients. In addition, reelevation of serum AST and CPK levels is not a rare occurrence, and close observation and follow-up tests are essential.

Clevudine myopathy in patients with chronic hepatitis B

Clevudine (L-FMAU) is a thymidine l-nucleoside analogue that was recently introduced for the treatment of chronic hepatitis B virus infection. Previous studies showed that clevudine has potent and sustained antiviral activity without causing viral resistance. No severe adverse event occurred during clinical trials. We describe two cases of drug-induced myopathy during long-term treatment of chronic hepatitis B with clevudine.

Mitochondrial myopathy caused by clevudine therapy in chronic hepatitis B patients

As a pyrimidine analog with potent and sustained antiviral activity against hepatitis B virus, clevudine has been known to have no effect on mitochondrial structure, DNA content, or function. There is little information on the side effects of clevudine, which has not been approved for the treatment of chronic hepatitis B outside of South Korea. We report here two cases of chronic hepatitis B patients who experienced mitochondrial myopathy after clevudine medication. These cases raise concerns about the safety profile of clevudine for the treatment of chronic hepatitis B.

Long-term therapy with clevudine for chronic hepatitis B can be associated with myopathy characterized by depletion of mitochondrial DNA

Clevudine (Revovir), a pyrimidine nucleoside analogue, is a recently introduced antiviral drug. Clinical trials have demonstrated potent, sustained antiviral activity against hepatitis B virus without specific adverse events. The lack of cytotoxicity and absence of an effect on mitochondrial function have been considered the reasons for the fewer adverse events. However, it came to our attention that several hepatitis B patients developed myopathy during clevudine therapy. Our study was aimed to analyze the clinical and pathological features of patients with clevudine-induced myopathy with some consideration of its pathogenetic mechanism. Seven hepatitis B patients who developed severe skeletal myopathy during clevudine therapy were examined in this study. The demographic data, clinical features, pathological findings, and molecular studies of these patients were analyzed with speculation about the underlying pathogenic mechanisms. All seven patients were treated with clevudine for more than 8 months (8-13 months). In all, the main symptom was slowly progressive proximal muscular weakness over several months. A markedly elevated creatine kinase level and myopathic patterns on electromyography were found. Muscle biopsies revealed severe myonecrosis associated with numerous ragged red fibers, cytochrome c oxidase-negative fibers, and predominant type II fiber atrophy. Molecular studies using quantitative polymerase chain reaction showed a depletion of the mitochondrial DNA in the patients' skeletal muscle.

CONCLUSION

To the best of our knowledge, this is the first report of myopathy associated with clevudine therapy. This study has clearly shown that long-term clevudine therapy can induce the depletion of mitochondrial DNA and lead to mitochondrial myopathy associated with myonecrosis. Careful clinical and laboratory attention should be paid to patients on long-term clevudine therapy for this skeletal muscle dysfunction.

Synthesis and antiviral evaluation of novel 2,3-dihydroxypropyl nucleosides from 2- and 4-thiouracils

Regioselective alkylation of 2-thiouracils 1a-c and 4-thiouracils 7a,b with 2,3-O-isopropylidene-2,3-dihydroxypropyl chloride (2) afforded 2-[[(2,2-Dimethyl-1,3-dioxolan-4-yl) methyl]thio]pyrimidin-4(1H)-ones 3a-c and 4-[[(2,2-Dimethyl-1,3-dioxolan-4-yl)methyl]thio] pyrimidin-2(1H)-ones 8a,b, respectively. Further alkylation with 2 and/or 2,3-O-isopropylidine-1-O-(4-toluenesulfonyl)-glycerol (4) gave the acyclo N-nucleosides 5a-c and 9a,b whose deprotection afforded 6a-c and 10a,b. 2-(Methylthio)pyrimidin-4(1H)-ones 11a-c and 4-(methylthio)pyrimidin-2(1H)-ones 14a,b were treated with 2 and/or 4 to give 12a-c and 15a,b which were deprotected to give 13a-c and 16a,b. Pyrimidine-2,4(1H,3H)-dithiones 17a-c were treated with two equivalents of 2 to give 2,4-bis[[(2,2-dimethyl-1,3-dioxolan-4-yl)methyl]thio] pyrimidines 18a-c. Deprotection of compounds 18a-c gave 2,4-bis[(2,3-dihydroxypropyl)thio]pyrimidines 19a-c. The activity of the deprotected nucleosides against Hepatitis B virus was evaluated and showed moderate inhibition activity against HBV with mild cytotoxicity.

Understanding the molecular basis of HBV drug resistance by molecular modeling

Despite the significant successes in the area of anti-HBV agents, resistance and cross-resistance against available therapeutics are the major hurdles in drug discovery. The present investigation is to understand the molecular basis of drug resistance conferred by the B and C domain mutations of HBV-polymerase on the binding affinity of five anti-HBV agents [lamivudine (3TC, 1), adefovir (ADV, 2), entecavir (ETV, 3), telbivudine (LdT, 4) and clevudine (l-FMAU, 5)]. In this regard, homology modeled structure of HBV-polymerase was used for minimization, conformational search and induced fit docking followed by binding energy calculation on wild-type as well as on mutant HBV-polymerases (L180M, M204V, M204I, L180M+M204V, L180M-M204I). Our studies suggest a significant correlation between the fold resistances and the binding affinity of anti-HBV nucleosides. The binding mode studies reveals that the domain C residue M204 is closely associated with sugar/pseudosugar ring positioning in the active site. The positioning of oxathiolane ring of 3TC (1) is plausible due the induced fit orientation of the M204 residue in wild-type, and further mutation of M204 to V204 or I204 reduces the final binding affinity which leads to the drug resistance. The domain B residue L180 is not directly close ( approximately 6A) to the nucleoside/nucleoside analogs, but indirectly associated with other active-site hydrophobic residues such as A87, F88, P177 and M204. These five hydrophobic residues can directly affect on the incoming nucleoside analogs in terms of its association and interaction that can alter the final binding affinity. There was no sugar ring shifting observed in the case of adefovir (2) and entecavir (3), and the position of sugar ring of 2 and 3 is found similar to the sugar position of natural substrate dATP and dGTP, respectively. The exocyclic double bond of entecavir (3) occupied in the backside hydrophobic pocket (made by residues A87, F88, P177, L180 and M204), which enhances the overall binding affinity. The active site binding of LdT (4) and l-FMAU (5) showed backward shifting along with upward movement without enforcing M204 residue and this significant different binding mode makes these molecules as polymerase inhibitors, without being incorporated into the growing HBV-DNA chain. Structural results conferred by these l- and d-nucleosides, explored the molecular basis of drug resistance which can be utilized for future anti-HBV drug discovery.

Mechanisms of substrate selectivity for Bacillus anthracis thymidylate kinase

Bacillus anthracis is well known in connection with biological warfare. The search for new drug targets and antibiotics is highly motivated because of upcoming multiresistant strains. Thymidylate kinase is an ideal target since this enzyme is at the junction of the de novo and salvage synthesis of dTTP, an essential precursor for DNA synthesis. Here the expression and characterization of thymidylate kinase from B. anthracis (Ba-TMPK) is presented. The enzyme phosphorylated deoxythymidine-5'-monophosphate (dTMP) efficiently with K (m) and V (max) values of 33 microM and 48 micromol mg(-1) min(-1), respectively. The efficiency of deoxyuridine-5'-monophosphate phosphorylation was approximately 10% of that of dTMP. Several dTMP analogs were tested, and D-FMAUMP (2'-fluoroarabinosyl-5-methyldeoxyuridine-5'-monophosphate) was selectively phosphorylated with an efficiency of 172% of that of D-dTMP, but L-FMAUMP was a poor substrate as were 5-fluorodeoxyuridine-5'-monophosphate (5FdUMP) and 2',3'-dideoxy-2',3'-didehydrothymidine-5'-monophosphate (d4TMP). No activity could be detected with 3'-azidothymidine-5'-monophosphate (AZTMP). The corresponding nucleosides known as efficient anticancer and antiviral compounds were also tested, and d-FMAU was a strong inhibitor with an IC(50) value of 10 microM, while other nucleosides--L-FMAU, dThd, 5-FdUrd, d4T, and AZT, and 2'-arabinosylthymidine--were poor inhibitors. A structure model was built for Ba-TMPK based on the Staphylococcus aureus TMPK structure. Docking with various substrates suggested mechanisms explaining the differences in substrate selectivity of the human and the bacterial TMPKs. These results may serve as a start point for development of new antibacterial agents.