Current prodrug strategies for improving oral absorption of nucleoside analogues

Nucleoside analogues are first line chemotherapy in various severe diseases:AIDS(acquired immunodeficiency disease syndrome),cytomegalovirus infections,cancer,etc.However,many nucleoside analogues exhibit poor oral bioavailability because of their high polarity and low intestinal permeability.In order to get around this drawback,prodrugs have been utilized to improve lipophilicity by chemical modification of the parent drug.Alternatively,prodrugs targeting transporters present in the intestine have been applied to promote the transport of the nucleoside analogues.Valacyclovir and valganciclovir are two classic valine ester prodrugs transported by oligopeptide transporter 1.The ideal prodrug achieves delivery of a parent drug by attaching a non-toxic moiety that is stable during transport,but is readily degraded to the parent drug once at the target.This article presents advances of prodrug approaches for enhancing oral absorption of nucleoside analogues.

Effects of two novel nucleoside analogues on different hepatitis B virus promoters

AIM： To explore the effects of the nucleoside analogues β-L-D4A and β-LPA on hepatitis B virus （HBV） promoters. METHODS： Four HBV promoters were amplified by polymerase chain reaction （PCR） and subcloned into the expression vector pEGFP-1. The four recombinants controlled by HBV promoters were confirmed by restriction analysis and sequencing. Human hepatoma HepG2 cells transfected with the recombinant plasmids were treated with various concentrations of β-L-D4A and β-LPA. Then, enhanced green fluorescent protein （EGFP）-positive cells were detected by fluorescence microscopy and using a fluorescence activated cell sorter RESULTS： Four HBV promoters were separately obtained and successfully cloned into pEGFP-1, Expression of EGFP under the control of the surface promoter （Sp） and the X promoter （Xp） was inhibited by β-L-D4A in a dosedependent manner, while expression of EGFP under the control of the core promoter （Cp） and Xp was inhibited by β-LPA in a dose-dependent manner. CONCLUSION： The two novel nucleoside analogues investigated here can inhibit the activities of HBV promoters in a dose-dependent manner. These findings may explain the mechanisms of action by which these two novel compounds inhibit HBV DNA replication.

Clinical efficacy and safety of TCM prescriptions combined with nucleoside(acid)analogues in treating chronic hepatitis B:a meta-analysis

Objective There are many clinical reports on traditional Chinese medicine(TCM)combined with nucleoside(acid)analogues(NAs)for the treatment of chronic hepatitis B(CHB),but its efficacy and safety are not completely clear.This meta-analysis aims to evaluate the clinical efficacy and safety thus providing evidence for clinical applications.Methods We searched Chinese databases the China National Knowledge Infrastructure(CNKI),Wanfang Data,and China Science and Technology Journal Database(VIP),as well as English databases Pub Med and Cochrane Library,from time of establishment to April 14,2021.Literature quality was evaluated according to the bias risk assessment criteria of Cochrane Collaboration network.Rev Man 5.3 and Stata 12.0 software were used to perform this research.Results A total of 23 articles,3282 patients,and 25 TCM prescriptions were included in this study.NAs plus TCM remarkably improved the clinical total effective rate[Odds ratio(OR)=3.92,P<0.00001],TCM syndrome score(Mean difference=-3.73,P<0.00001),hepatitis B virus(HBV)DNA negative conversion rate(OR=1.49,P=0.0001),hepatitis Be antigen(HBe Ag)negative conversion rate(OR=2.03,P<0.00001),alanine aminotransferase levels[Std mean difference(SMD)=-0.95,P<0.00001],and aspartate aminotransferase levels(SMD=-0.70,P=0.0004).Adverse reaction rates did not increase in the combined treatment group(OR=0.97,P=0.84).A comprehensive analysis of the 25 TCM prescriptions suggested that the combination of spleen-strengthening prescriptions with NAs showed better effects than other prescriptions.Conclusion TCM in combination with NAs,demonstrated better clinical efficacy against CHB than NAs alone.In addition,the combination of spleen-strengthening prescriptions and NAs was identified as the best therapeutic strategy.However,more randomized controlled trials of high quality are needed to provide more reliable clinical basis for the application of TCM.

Clinical outcomes of cessation of nucleoside/nucleotide analogues in Chinese patients with HBeAg-negative chronic hepatitis B

Background and aims:Cessation of nucleoside/nucleotide analogue(Nuc)therapy in patients with HBeAg-negative chronic hepatitis B(CHB)remains controversial.Methods:In this prospective,single-center cohort study,we recruited 45 patients with HBeAg-negative CHB from The Fifth Medical Center of Chinese People's Liberation Army General Hospital in China's Mainland.Patients were classified into a Nuc cessation group(n?27)and Nuc continuation group(n?18)and followed-up for 36 months.Nuc were stopped after being inactive for at least 4 years(normal alanine aminotransferase(ALT),undetectable hepatitis B virus(HBV)DNA),with liver fibrosisStage1(S1)and inflammationGrade(G1).Results:Within 3 years of follow-up,51.9%patients with Nuc cessation had virological relapse and 14.8%had ALT elevation,while all patients with Nuc continuation had undetectable HBV DNA and normal ALT.The rate of HBsAg loss after Nuc cessation was 22.2%compared with no seroconversion in patients with Nuc continuation.The hepatitis flare rate was 11.1%and there were no cases of hepatic decompensation after Nuc cessation.End of treatment(EOT)HBsAg,HBV RNA,and decline in HBV core-related antigen(HBcrAg)rate were predictive markers for HBsAg seroconversion at 6 months post-Nuc cessation.Conclusion:This study showed favorable HBsAg loss and low hepatitis flare rates after Nuc cessation.EOT HBsAg,HBV RNA,and decline in HBcrAg rate were predictive markers for HBsAg seroconversion at 6 months post-Nuc cessation.

Risk of hepatitis B virus reactivation in oncological patients treated with tyrosine kinase inhibitors:A case report and literature analysis

Hepatitis B virus(HBV)reactivation(HBVr)represents a severe and potentially life-threatening condition,and preventive measures are available through blood test screening or prophylactic therapy administration.The assessment of HBVr traditionally considers factors such as HBV profile,including hepatitis B surface antigen(HBsAg)and antibody to hepatitis B core antigen,along with type of medication(chemotherapy;immunomodulants).Nevertheless,consideration of possible patient’s underlying tumor and the specific malignancy type(solid or hematologic)plays a crucial role and needs to be assessed for decision-making process.

Viral infection parameters not nucleoside analogue itself correlates with host immunity in nucleoside analogue therapy for chronic hepatitis B

AIM: To determine the relationship between host immunity and the characteristics of viral infection or nucleoside analogues (NAs) themselves in patients with chronic hepatitis B (CHB) receiving NA therapy.

Microwave-assisted Green and Efficient Synthesis of N^6-(2-Hydroxyethyl)adenosine and its Analogues

An efficient protocol for the synthesis of N^6-（2-Hydroxyethyl）adenosine and its analogues through nucleophilic substitution was developed. All the reactions were completed in 10 rain under microwave irradiation. Using water as solvent makes our method eco-friendly and easy to handle with.

Risk of hepatitis B virus reactivation in cancer patients undergoing treatment with tyrosine kinase-inhibitors

This editorial commented on an article in the World Journal of Gastroenterology titled“Risks of Reactivation of Hepatitis B Virus in Oncological Patients Using Tyrosine Kinase-Inhibitors:Case Report and Literature Analysis”by Colapietro et al.In this editorial,we focused on providing a more comprehensive exploration of hepatitis B virus reactivation(HBVr)associated with the usage of tyrosine kinase inhibitors(TKIs).It includes insights into the mechanisms underlying HBV reactivation,the temporal relationship between TKIs and HBV reactivation,and preventive measures.The aim is to understand the need for nucleos(t)ide analogs(NAT)and serial blood tests for early recognition of reactivation and acute liver injury,along with management strategies.TKIs are considered to be an intermediate(1%-10%)of HBVr.Current guidelines stipulate that patients receiving therapy with high or moderate risks of reactivation or recent cancer diagnosis must have at least tested hepatitis B surface antigen,anti-hepatitis B core antigen(HBc),and anti-hepatitis B surface antibody.Anti-HBc screening in highly endemic areas means people with negative tests should be vaccinated against HBV.Nucleoside or nucleotide analogs(NAs)like entecavir(ETV),tenofovir disoproxil fumarate(TDF),and tenofovir alafenamide(TAF)form the basis of HBV reactivation prophylaxis and treatment during immunosuppression.Conversely,lamivudine,telbivudine,and adefovir are generally discouraged due to their reduced antiviral efficacy and higher risk of fostering drug-resistant viral strains.However,these less effective NAs may still be utilized in cases where ETV,TDF,and TAF are not feasible treatment options.

Future prospectives for the management of chronic hepatitis B

Chronic hepatitis B virus infection affects about 400 million people around the globe and causes approximately a million deaths a year. Since the discovery of interferon-α as a therapeutic option the treatment of hepatitis B has evolved fast and management has become increasingly complicated. The amount of viral replication reflected in the viral load （HBV-DNA） plays an important role in the development of cirrhosis and hepatocellular carcinoma. The current treatment modalities for chronic hepatitis B are immunomodulatory （interferons） and antiviral suppressants （nucleoside and nucleotide analogues） all with their own advantages and limitations. An overview of the treatment efficacy for both immunomodulatory as antiviral compounds is provided in order to provide the clinician insight into the factors influencing treatment outcome. With nucleoside or nucleotide analogues suppression of viral replication by 5-7 log10 is feasible, but not all patients respond to therapy. Known factors influencing treatment outcome are viral load, ALT levels and compliance. Many other factors which might influence treatment are scarcely investigated. Identifying the factors associated with response might result in stopping rules, so treatment could be adapted in an early stage to provide adequate treatment and avoid the development of resistance. The efficacy of compounds for the treatment of mutant virus and the cross-resistance is largely unknown. However, genotypic and phenotypic testing as well as small clinical trials provided some data on efficacy in this population. Discontinuation of nucleoside or nucleotide analogues frequently results in viral relapse; however, some patients have a sustained response. Data on the risk factors for relapse are necessary in order to determine when treatment can be discontinued safely. In conclusion： chronic hepatitis B has become a treatable disease; however, much research is needed to tailor therapy to an individual patient, to predict the sustainability of response and determine the best treatment for those failing treatment.

Then and now: The progress in hepatitis B treatment over the past 20 years

The ultimate goals of treating chronic hepatitis B(CHB)is prevention of hepatocellular carcinoma(HCC)and hepatic decompensation.Since the advent of effective antiviral drugs that appeared during the past two decades,considerable advances have been made not only in controlling hepatitis B virus(HBV)infection,but also in preventing and reducing the incidence of liver cirrhosis and HCC.Furthermore,several recent studies have suggested the possibility of reducing the incidence of recurrent or new HCC in patients even after they have developed HCC.Currently,six medications are available for HBV treatment including,interferon and five nucleoside/nucleotide analogues.In this review,we will examine the antiviral drugs and the progresses that have been made with antiviral treatments in the field of CHB.

New strategies against drug resistance to herpes simplex virus

Herpes simplex virus （HSV）, a member of the Herpesviridae family, is a significant human pathogen that results in mucocutaneous lesions in the oral cavity or genital infections. Acyclovir （ACV） and related nucleoside analogues can successfully treat HSV infections, but the emergence of drug resistance to ACV has created a barrier for the treatment of HSV infections, especially in immunocompromised patients. There is an urgent need to explore new and effective tactics to circumvent drug resistance to HSV. This review summarises the current strategies in the development of new targets （the DNA helicase/primase （H/P） complex）, new types of molecules （nature products） and new antiviral mechanisms （lethal mutagenesis of Janus-type nucleosides） to fight the drug resistance of HSV.

Subclinical proximal tubulopathy in hepatitis B:The roles of nucleot(s)ide analogue treatment and the hepatitis B virus

BACKGROUND The recommended monitoring tools for evaluating nucleot(s)ide analogue renal toxicity,such as estimated glomerular filtration rate(eGFR)and phosphatemia,are late markers of proximal tubulopathy.Multiple early markers are available,but no consensus exists on their use.AIM To determine the 24 mo prevalence of subclinical proximal tubulopathy(SPT),as defined with early biomarkers,in treated vs untreated hepatitis B virus(HBV)-monoinfected patients.METHODS A prospective,non-randomized,multicenter study of HBV-monoinfected patients with a low number of renal comorbidities was conducted.The patients were separated into three groups:Naïve,starting entecavir(ETV)treatment,or starting tenofovir disoproxil(TDF)treatment.Data on the early markers of SPT,the eGFR and phosphatemia,were collected quarterly.SPT was defined as a maximal tubular reabsorption of phosphate/eGFR below 0.8 mmoL/L and/or uric acid fractional excretion above 10%.The prevalence and cumulative incidence of SPT at month 24(M24)were calculated.Quantitative data were analyzed using analyses of variance or Kruskal-Wallis tests,whereas chi-squared or Fisher’s exact tests were used to analyze qualitative data.Multivariate analyses were used to adjust for any potential confounding factors.RESULTS Of the 196 patients analyzed,138(84 naïve,28 starting ETV,and 26 starting TDF)had no SPT at inclusion.At M24,the prevalence of SPT was not statistically different between naïve and either treated group(21.1%vs 30.7%,P<0.42 and 50.0%vs 30.7%,P=0.32 for ETV and TDF,respectively);no patient had an eGFR lower than 50 mL/min/1.73 m²or phosphatemia less than 0.48 mmoL/L.In the multivariate analysis,no explanatory variables were identified after adjustment.The cumulative incidence of SPT over 24 mo(25.5%,13.3%,and 52.9%in the naïve,ETV,and TDF groups,respectively)tended to be higher in the TDF group vs the naïve group(hazard ratio:2.283,P=0.05).SPT-free survival at M24 was 57.6%,68.8%,and 23.5%for the naïve,ETV,and TDF groups,respectively.The median survival time without SPT,evaluated only in the TDF group,was 5.9 mo.CONCLUSION The prevalence and incidence of SPT was higher in TDF-treated patients compared to naïve patients.SPT in the naïve population suggests that HBV can induce renal tubular toxicity.

Hepatitis B in renal transplant patients

Hepatitis B virus(HBV) poses a significant challenge for both dialysis patients and kidney transplant recipients despite its decreasing rates, especially in developed countries. The best preventive method is vaccination. Patients with chronic renal disease should ideally be vaccinated prior to dialysis, otherwise, reinforced vaccination practices and close antibody titer monitoring should be applied while on dialysis. HBV infected dialysis patients who are renal transplant candidates must be thoroughly examined by HBV-DNA, and liver enzyme testing and by liver biopsy. When needed, one must consider treating patients with tenofovir or entecavir rather than lamivudine. Depending on the cirrhosis stage, dialysis patients are eligible transplant recipients for either a combined kidney-liver procedure in the case of decompensated cirrhosis or a lone kidney transplantation since even compensated cirrhosis after sustained viral responders is no longer considered an absolute contraindication. Nucleoside analogues have led to improved transplantation outcomes with both long-term patient and graft survival rates nearing those of HBs Ag(-) recipients. Moreover, in the cases of immunized HBs Ag(-) potential recipients with concurrent prophylaxis, we are enabled today to safely use renal grafts from both HBs Ag(+) and HBs Ag(-)/antiHBc(+) donors. In so doing, we avoid unnecessary organ discarding. Universal prophylaxis with entecavir is recommended in HBV kidney recipients and should start perioperatively. One of the most important issues in HBV(+) kidney transplantation is the duration of antiviral prophylaxis. In the absence of robust data, it seems that prophylactic treatment may be discontinued in selected stable, low-risk recipients during maintenance immunosuppression and should be reintroduced when the immune status is altered. All immunosuppressive agents in kidney transplantation can be used in HBV(+) recipients. Immunosuppression is intimately associated with increased viral replication; thus it is important to minimize the total immunosuppression burden long term.

Telbivudine:A new treatment for chronic hepatitis B

Three hundred and fifty million people worldwide are estimated to be chronically infected with hepatitis B virus. 15%-40% of these subjects will develop cirrhosis, liver failure or hepatocellular carcinoma during their life. The treatment of chronic hepatitis B has improved dramatically over the last decade merits to the advent of nucleoside/nucleotide analogues and the use of pegylated interferons. Approved drugs for chronic hepatitis B treatment include： standard interferon- alpha 2b, pegylated interferon-alpha 2a, lamivudine, adefovir dipivoxil, and entecavir. Unfortunately, these agents are not effective in all patients and are associated with distinct side effects. Interferons have numerous side effects and nucleoside or nucleotide analogues, which are well tolerated, need to be used for prolonged periods, even indefinitely. However, prolonged treatment with nucleoside or nucleotide analogues is associated with a high rate of resistance. Telbivudine is a novel, orally administered nucleoside analogue for use in the treatment of chronic hepatitis B. In contrast to other nucleoside analogues, Telbivudine has not been associated with inhibition of mammalian DNA polymerase with mitochondrial toxicity. Telbivudine has demonstrated potent activity against hepatitis B with a significantly higher rate of response and superior viral suppression compared with lamivudine, the standard treatment. Telbivudine has been generally well tolerated, with a low adverse effect profile, and at its effective dose, no dose- limiting toxicity has been observed. Telbivudine is one of the most potent antiviral agents for chronic hepatitis B virus and was approved by the FDA in late 2006.

Clinical features of adverse reactions associated with telbivudine

AIM: To analyze the clinical features and risk factors of adverse reactions associated with telbivudine. METHODS: Clinical data were collected from cases that presented with serious adverse reactions to telbivudine. We analyzed general information and medicine status, clinical features, results of examination, and misdiagnosis. RESULTS: Out of 105 patients who were treated with telbivudine for hepatitis B in an outpatient department from January, 2007 to January, 2008, five presented with serious adverse drug reactions. Most of these five patients had used other nucleoside analogues in the past. Four were treated with a combination of telbivudine and interferon or another nucleoside analogue, while the other received an increased dose of telbivudine. The main adverse reactions were myalgia and general weakness. This was accompanied by cardiac arrhythmia in one patient, and nervous symptoms in three. Serum creatine kinase was elevated. The rate of misdiagnosis was high. CONCLUSION: The adverse reactions were related to telbivudine, but the biological mechanism of the reactions is not yet clear. Combination therapy with interferon or another nucleoside analogue and a high dose may increase the risk of adverse reactions.

Potent antiviral therapy improves survival in acute on chronic liver failure due to hepatitis B virus reactivation

Acute on chronic liver failure(ACLF)is a disease entity with a high mortality rate.The acute event arises from drugs and toxins,viral infections,bacterial sepsis,interventions(both surgical and non-surgical)and vascular events on top of a known or occult chronic liver disease.ACLF secondary to reactivation of chronic hepatitis B virus is a distinct condition;the high mortality of which can be managed in the wake of new potent antiviral therapy.For example,lamivudine and entecavir use has shown definite short-term survival benefits,even though drug resistance is a concern in the former.The renoprotective effects of telbivudine have been shown in a few studies to be useful in the presence of renal dysfunction.Monotherapy with newer agents such as tenofovir and a combination of nucleos(t)ides is promising for improving survival in this special group of liver disease patients.This review describes the current status of potent antiviral therapy in patient with acute on chronic liver failure due to reactivation of chronic hepatitis B,thereby providing an algorithm in management of such patients.

Adverse effects of oral antiviral therapy in chronic hepatitis B

Oral nucleoside/nucleotide analogues(NAs) are currently the backbone of chronic hepatitis B(CHB) infection treatment. They are generally well-tolerated by patients and safe to use. To date, a significant number of patients have been treated with NAs. Safety data has accumulated over the years. The aim of this article is to review and update the adverse effects of oral NAs. NAs can cause class adverse effects(i.e., myopathy, neuropathy, lactic acidosis) and dissimilar adverse effects. All NAs carry a "Black Box" warning because of the potential risk for mitochondrial dysfunction. However, these adverse effects are rarely reported. The majority of cases are associated with lamivudine and telbivudine. Adefovir can lead to dose- and time-dependent nephrotoxicity, even at low doses. Tenofovir has significant renal and bone toxicity in patients with human immunodeficiency virus(HIV) infection. However, bone and renal toxicity in patients with CHB are not as prominent as in HIV infection. Entecavir and lamivudine are not generally associated with renal adverse events. Entecavir has been claimed to increase the risk of lactic acidosis in decompensated liver disease and high Model for End-Stage Liver Disease scores. However, current studies reported that entecavir could be safely used in decompensated cirrhosis. An increase in fetal adverse events has not been reported with lamivudine, telbivudine and tenofovir use in pregnant women, while there is no adequate data regarding entecavir and adefovir. Further long-term experience is required to highlight the adverse effects of NAs, especially in special patient populations, including pregnant women, elderly and patients with renal impairment.

Emerging antivirals for the treatment of hepatitis B

Chronic infection with hepatitis B virus(HBV)constitutes a major global public health threat,causing substantial disease burdens such as liver cirrhosis and hepatocellular carcinoma,thus representing high unmet medical needs.Currently available therapies are safe,well tolerated,and highly effective in decreasing viremia and improving measured clinical outcomes with low rates of antiviral resistance.However,long-term management remains a clinical challenge,mainly due to the slow kinetics of HBV surface antigen clearance.In this article,we review emerging antivirals directed at novel targets derived from mechanisms of viral cellular entry,viral replication,viral assembly,and the host immune response,leading to preclinical and clinical trials for possible future therapeutic intervention.The recent therapeutic advances in the development of all categories of HBV inhibitors may pave the way for regimens of finite duration that result in long-lasting control of chronic hepatitis B infection.

Synthesis of 5-Substituted-3-[(2’R,4’R)-4’-Hydroxy-2’-hydroxymethyltetrahydrofuran-4’-yl]-1,2,4-oxadiazoles and Their Epimers

The syntheses of 5-substituted-3-[( 2’ R, 4’ R)-4 ’ -hydroxy-2 ’ -hydroxymethyltetra-hydrofuran-4’ -yl]D-1 ,2, 4-oxadiazoles and their epimers were accomplished with the aid of th construction of 1,2, 4-oxadiazoles by condensation of O-acylated cyanohydrins with hydroxylamine via intramolecular transacylation and subsequent cyclization.

Selectively T cell phosphorylation activation of azvudine in the thymus tissue with immune protection effect

Thymus is the important immune organ,responsible for T cell development and differentiation.The lower circulating T counts have been observed in patients who died from COVID-19 compared with survivors.Azvudine,also known as FNC,is a thymus-homing anti-SARS-CoV-2 drug in treating COVID-19 patients.In this study,single-cell transcriptome,proteomics,and parallel reaction monitoring(PRM)were applied to insight into the activation process of FNC in rat and SARS-CoV-2 rhesus monkey thymus.The results indicated that thymic immune cells possess a robust metabolic capacity for cytidine-analogue drugs such as FNC.Key enzymes involved in the FNC phosphorylation process,such as Dck,Cmpk1,and Nme2,were highly expressed in CD4+ T cells,CD8+ T cells,and DP(CD4+ CD8+)cells.Additionally,FNC could upregulate multiple phosphorylated kinases in various cell types while downregulating the phosphatases,phosphoribosyl transferases,and deaminases,respectively.The robust phosphorylation capacity of the thymus for cytidine analogue drug FNC,and the activation effect of FNC on the NAs metabolism system potentially contribute to its enrichment in the thymus and immune protection effect.This suggests that it is crucial to consider the expression level of phosphorylation kinases when evaluating NA drug properties,as an important factor during antiviral drug design.