Structural biology of SARS-CoV-2: open the door for novel therapies.

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is the causative agent of the pandemic disease COVID-19, which is so far without efficacious treatment. The discovery of therapy reagents for treating COVID-19 are urgently needed, and the structures of the potential drug-target proteins in the viral life cycle are particularly important. SARS-CoV-2, a member of the Orthocoronavirinae subfamily containing the largest RNA genome, encodes 29 proteins including nonstructural, structural and accessory proteins which are involved in viral adsorption, entry and uncoating, nucleic acid replication and transcription, assembly and release, etc. These proteins individually act as a partner of the replication machinery or involved in forming the complexes with host cellular factors to participate in the essential physiological activities. This review summarizes the representative structures and typically potential therapy agents that target SARS-CoV-2 or some critical proteins for viral pathogenesis, providing insights into the mechanisms underlying viral infection, prevention of infection, and treatment. Indeed, these studies open the door for COVID therapies, leading to ways to prevent and treat COVID-19, especially, treatment of the disease caused by the viral variants are imperative.

Effectiveness of tenofovir alafenamide for chronic hepatitis B patients with a poor response to the previously used nucleos(t)ide analogs.

BACKGROUND: Few studies have demonstrated the potency of tenofovir alafenamide (TAF) in patients with poor response to other nucleos(t)ide analogs (NAs). METHODS: We conducted a retrospective study comprising consecutive 40 patients exhibiting a poor response to other NAs, who subsequently received TAF-containing regimens. The primary outcome was the prevalence of virological response (VR) at each time and maintained virological response (MVR) under TAF-containing regimens until week 96. RESULTS: In the entire cohort, the prevalence of MVR was 71.1% (27/38). Further, poor tenofovir disoproxil fumarate (TDF) response was significantly associated with a lower prevalence of MVR (p = 0.014). In TDF-naïve patients, the prevalence of MVR was 92.3% (12/13) and 62.5% (5/8) in patients with lamivudine resistance (LAM-r) and entecavir resistance (ETV-r), respectively. Further, viral load and HBeAg status at baseline were associated with a lower prevalence of MVR (p = 0.013). Among the seven patients with prior TDF exposure, 2 patients achieved MVR. Among them, one patient with development of viral breakthrough during TDF/LAM achieved MVR after switching to TAF/ETV. In contrast, one of the five patients with non-MVR had three substitutions (rtS106C, rtD134N/S, and rtL269I) of quadruple mutations in addition to ETV-r. Other patients with rtA181T + rtN236T also could not achieve MVR. CONCLUSION: TAF exhibited high antiviral potency in patients with LAM-r and ETV-r. However, TAF potency was associated with previous TDF response, viral load, and HBeAg status at baseline. Additionally, a quadruple mutation may impact tenofovir resistance; however, further studies are needed to verify this.

Nucleoside analogs assisted with Chinese compound prescription in treating hepatic fibrosis of chronic hepatitis B patients: A protocol of systematic review and meta-analysis.

BACKGROUND: Chronic hepatitis B is often complicated with different degrees of hepatic fibrosis, which affects the quality of life. Nucleoside analogs are recommended by almost all guidelines in the world for the treatment of chronic hepatitis B. At present, there is no specific and effective chemical and biological agents for hepatic fibrosis. In China, Chinese compound prescription combined with nucleoside analogs have been used to treat hepatic fibrosis of chronic hepatitis B patients in more and more cases, and good results have been achieved. Several Chinese compound prescriptions that have been made into proprietary Chinese medicine for the convenience of use. This article aims to systematically evaluate the efficacy and safety of Chinese medicine compounds assisting nucleoside analogs in the treatment of hepatic fibrosis in chronic hepatitis B patients. METHOD: The following databases will be searched from their inception to September 2019: PubMed, EMBASE, EBSCOhost, The Cochrane Library, China National Knowledge Infrastructure (CNKI), Chinese Biomedical literature Database (CBM), VIP Database, Wanfang Database. Languages are limited to Chinese and English. The study includes randomized controlled trials using Chinese compound prescription combined with entecavir and Chinese compound prescription combined with tenofovir disoproxil fumarate to treat hepatic fibrosis of chronic hepatitis B patients. The primary outcomes including effective rate and biochemical parameters (levels of hyaluronic acid, laminin, pre-type-III collagen and type IV collagen will be tested. Additional outcomes include liver function indexes (levels of alanine aminotransferase, aspartate aminotransferase, total bilirubin) and levels of hepatitis B virus DNA. Stata14.0 software will be used for meta-analysis. RESULT: The efficacy and safety of Chinese compound prescriptions assisting nucleoside analogs for hepatic fibrosis of chronic hepatitis B patients will be assessed from the effective rate, biochemical parameters, liver function indexes, and levels of hepatitis B virus DNA. CONCLUSION: The conclusion of this study will be used to evaluate the efficacy and safety of Chinese compound prescriptions assisting nucleoside analogs in the treatment of hepatic fibrosis of chronic hepatitis B patients, as well as the adjuvant effectiveness of Chinese compound prescriptions in combined therapy. PROSPERO REGISTRATION NUMBER: CRD42020156859.

Drug treatment options for the 2019-new coronavirus (2019-nCoV).

As of January 22, 2020, a total of 571 cases of the 2019-new coronavirus (2019-nCoV) have been reported in 25 provinces (districts and cities) in China. At present, there is no vaccine or antiviral treatment for human and animal coronavirus, so that identifying the drug treatment options as soon as possible is critical for the response to the 2019-nCoV outbreak. Three general methods, which include existing broad-spectrum antiviral drugs using standard assays, screening of a chemical library containing many existing compounds or databases, and the redevelopment of new specific drugs based on the genome and biophysical understanding of individual coronaviruses, are used to discover the potential antiviral treatment of human pathogen coronavirus. Lopinavir /Ritonavir, Nucleoside analogues, Neuraminidase inhibitors, Remdesivir, peptide (EK1), abidol, RNA synthesis inhibitors (such as TDF, 3TC), anti-inflammatory drugs (such as hormones and other molecules), Chinese traditional medicine, such ShuFengJieDu Capsules and Lianhuaqingwen Capsule, could be the drug treatment options for 2019-nCoV. However, the efficacy and safety of these drugs for 2019- nCoV still need to be further confirmed by clinical experiments.

Effects of 4-Pyridone-3-carboxamide-1ß-D-ribonucleoside on adenine nucleotide catabolism in the aortic wall; Implications for atherosclerosis in ApoE-/-LDLR-/- mice.

4-Pyridone-3-carboxamide-1-beta-D-ribonucleoside (4PYR) is an endogenously produced nucleoside that had been identified as a substrate for intracellular phosphorylation to form intracellular nucleotides. Previous studies demonstrated that 4PYR adversely affects metabolism of endothelial cells that is known risk factor for atherosclerosis. The purpose of this study was to evaluate effects of 4PYR on the progression of atherosclerosis and changes in extracellular nucleotides degradation on the surface of the vessel wall in the murine model. METHODS: Two month old ApoE-/-LDLR-/- mice were subcutaneously injected with 4PYR (4P) twice per day for one month or with saline in controls (C). Then, at the age of eight month hydrolysis rates of ATP, AMP and adenosine were evaluated in the intact aorta sections by HPLC based assays. Oil Red O (ORO) staining that indicates lipid deposition was quantified spectrophotometrically after extraction from the vessel. Serum amyloid A (SAA) content was analyzed with ELISA. RESULTS: Adenosine deamination rate (activity of eADA) increased from 8.7±1.4 nmol/min/cm2 in C to 16.0±2.6 nmol/min/cm2 in 4P (p<0.05). AMP dephosphorylation rate (activity of e5NT) and ATP hydrolysis rate (activity of eNTPD) were not different between C and 4P. ORO staining in the aorta of 4P mice increased by 75% as compared to C (p<0.01) while SAA content was similar in both groups. CONCLUSIONS: This data demonstrated that prolonged exposure to 4PYR of ApoE-/-LDLR-/- mice results in sustained elevation of vascular eADA activity and increased ORO staining indicating endothelial impairment and accelerated atherosclerosis.

Variability of apoptosis and response in N1-S1 rodent hepatomas to benzamide riboside and correlation to early changes in water apparent diffusion coefficient and sodium MR imaging.

PURPOSE: This pilot trial assesses variability of apoptosis and response 1 day after hepatic intraarterial (IA) benzamide riboside (BR) in rodent hepatomas and its correlation to water apparent diffusion coefficient (ADC) and single-quantum (SQ) and triple-quantum-filtered (TQF) sodium-23 ((23)Na) magnetic resonance (MR) imaging. MATERIALS AND METHODS: Sprague-Dawley rats (n = 8) were inoculated with 10(6) N1-S1 cells. IA BR (20 mg/kg) was infused after 14 days. Animals were killed 1 day (n = 4) or 21 days (n = 4) after therapy. Imaging was performed 1 day before and after treatment. Volume was assessed over 2 weeks. Percentage apoptosis was counted from terminal deoxynucleotidyl transferase dUTP nick-end labeling-stained slides at 400×magnification. Kruskal-Wallis tests were used to compare apoptosis, and Wilcoxon signed-rank tests were used to compare MR signal intensity (SI). RESULTS: Apoptosis was marginally greater in tumor than in nontumor (6.7% vs 1.3%; P = .08), varying from 2% to 10%. Before treatment, MR SI was greater in tumor than in nontumor (ADC, 1.18 vs 0.76 [P = .0078]; SQ, 1.20 vs 1.04 [P = .03]; TQF, 0.55 vs 0.34 [P = .03]). After treatment, tumors increased in volume (0.62 vs 0.33; P = .016) variably over 2 weeks. MR SI remained greater in tumor than in nontumor (ADC, 1.20 vs 0.77 [P = .0078]; SQ, 1.76 vs 1.15 [P = .016]; TQF, 0.84 vs 0.49 [P = .03]). SQ and TQF SI increased by 47% (P = .016) and 53% (P = .016) in tumors, whereas ADC did not change. CONCLUSIONS: Apoptosis was marginal and varied from 2% to 10%. Water ADC, SQ, and TQF MR imaging distinguished tumor from nontumor. Changes in water ADC and sodium MR imaging correlated to apoptosis and volume in select cases, but additional animals are needed to validate this trend against tumor growth.

[Influences of warming kidney prescription on antiviral therapeutic efficacy and creatine kinase in telbivudine-treated HBeAg-positive chronic hepatitis B patients].

To study the influences of warming kidney prescription on antiviral therapeutic efficacy and creatine kinase (CK) level in telbivudine-treated HBeAg-positive chronic hepatitis B patients with kidney yang deficiency syndrome. Ninety-six cases were enrolled and randomly divided into two groups (n=48 each): warming kidney prescription treatment or control. Both groups were treated for 52 weeks with telbivudine monotherapy, but the treatment group received additional treatment with the warming kidney prescription. Traditional Chinese medicine (TCM) syndrome score, biochemical response, virological response, serological response, CK level, and adverse reactions were recorded for each group in order to perform comparative analysis of the warming kidney prescription's effects. A total of 84 patients, including 43 cases in the treatment group, completed the study. The warming kidney prescription led to significantly improved total clinical syndrome efficacy, TCM syndrome score, biochemical response, virological response, and HBeAg serological responses, as evidenced by changes for each parameter observed in the treatment group versus the control group (respectively, 88.37% vs. 63.41%, 4.97+/-1.88 vs. 10.13+/-3.72, 95.35% vs. 75.61%, 81.40% vs. 56.10%, 48.84% vs. 26.83% (all, P less than 0.05)). No patient in either group experienced primary treatment failure. Seven cases, all from the control group, experienced virological breakthrough. Elevated CK was observed in both the treatment and control groups, but significantly more patients in the control group experienced this adverse reaction (respectively, 73.17% vs. 44.19%; P less than 0.01). The warming kidney prescription can increase telbivudine antiviral therapeutic efficacy and decrease the telbivudine-induced increase in creatine kinase in HbeAg-positive chronic hepatitis B patients with kidney yang deficiency syndrome.

Medicinal chemistry of nucleoside phosphonate prodrugs for antiviral therapy.

Considerable attention has been focused on the development of phosphonate-containing drugs for application in many therapeutic areas. However, phosphonate diacids are deprotonated at physiological pH and thus phosphonate-containing drugs are not ideal for oral administration, an extremely desirable requisite for the treatment of chronic diseases. To overcome this limitation several prodrug structures of biologically active phosphonate analogues have been developed. The rationale behind the design of such agents is to achieve temporary blockade of the free phosphonic functional group until their systemic absorption and delivery, allowing the release of the active drug only once at the target. In this paper, an overview of acyclic and cyclic nucleoside phosphonate prodrugs, designed as antiviral agents, is presented.

Validation of the INNO-LiPA HBV DR assay (version 2) in monitoring hepatitis B virus-infected patients receiving nucleoside analog treatment.

Hepatitis B virus (HBV) antiviral drug resistance mutations prevent successful outcome of treatment and lead to worsening of liver disease. Detection of its emergence permits opportune treatment with alternative drugs. Unfortunately, the use of newly approved antivirals, including adefovir dipivoxil, emtricitabine, and telbivudine, is also associated with the development of drug resistance, albeit to a lesser extent than the use of lamivudine. The objectives of this work were to assess the performance characteristics (sensitivity and accuracy) of an updated drug resistance test, the INNO-LiPA HBV DR v2, which includes detection of mutations associated with lamivudine, adefovir, emtricitabine, and telbivudine resistance, and to compare the results with consensus sequencing of serum samples from patients treated with HBV antivirals. Diagnostic sensitivity, defined as detection of a positive amplification line on the line probe assay (LiPA) strip, was 94.8% (95% confidence interval [CI], 89.7 to 97.9) after initial testing, increasing to 96.3% (95% CI, 91.6 to 98.8) after repeat test 1 and to 100% (95% CI, 97.3 to 100.0) after repeat test 2. In diagnostic accuracy determinations, full concordance was observed between sequencing and LiPA for 77.0% of the codons tested (620/805 codons [95% CI, 74.0 to 79.9]), whereas LiPA and sequencing were partially concordant 22% of the time (177/805 codons). In 167 out of 177 cases, LiPA detected a wild-type/mutant mixture whereas sequencing detected only one of the two results. Performance testing of the new LiPA test, the INNO-LiPA HBV DR v2, showed convincing diagnostic sensitivity and accuracy. The ability of the test to detect mixed infections and minority viral populations associated with resistance to the current generation of antivirals, including adefovir, emtricitabine, and telbivudine, makes it a useful tool for HBV therapy monitoring.

Efficacy of favipiravir (T-705) and T-1106 pyrazine derivatives in phlebovirus disease models.

Several studies have reported favipiravir (T-705) to be effective in treating a number of viral diseases modeled in rodent systems. Notably, the related pyrazine derivative, T-1106, was found to be more effective than T-705 in treating yellow fever virus infection in hamsters. Based on these findings, we hypothesized that T-1106 may be more effective in treating hepatotropic Punta Toro virus (PTV, Phlebovirus) infection in rodents. In cell culture, the inhibitory concentrations of the compounds against various phleboviruses ranged from 3 to 55microM for T-705 and from 76 to 743microM for T-1106. In PTV-challenged hamsters, a model that generally presents with high liver viral loads, T-1106 was more effective at reducing mortality. However, in mice infected with PTV, a model wherein systemic infection is more prominent, the greater efficacy exhibited by T-1106 in the hamster system was not apparent. In contrast, T-705 was superior in preventing mortality in hamsters challenged with Pichinde virus (PICV, Arenavirus), an infection characterized as diffuse and pantropic. Remarkably, T-1106 has proven more active in vivo than would have been expected from our cell culture results, and our in vivo findings suggest that it is more effective in infections characterized predominantly by high levels of hepatic viral burden.

Telbivudine in the treatment of chronic hepatitis B.

INTRODUCTION: The treatment of chronic hepatitis B virus (HBV) infection has been revolutionized in the past decade by the increased availability of effective antiviral agents. Telbivudine is an L-nucleoside that is structurally related to lamivudine and has recently been approved for use in patients with chronic HBV infection. Telbivudine is highly selective for HBV DNA and inhibits viral DNA synthesis with no effect on human DNA or other viruses. This article reviews the pharmacology, pharmacokinetics, therapeutic efficacy and safety of telbivudine, and discusses its place in the current armamentarium against HBV. METHODS: Relevant publications were identified from searches of Medline and PubMed between 2000 and 2008, using the search terms "hepatitis B/HBV," "telbivudine/LdT," "beta-L-thymidine," "pharmacokinetics," "safety," "adverse events," and "resistance." The reference lists of retrieved articles were searched for relevant studies. RESULTS: Phase 3 clinical studies demonstrate that telbivudine is superior to lamivudine over a 2-year period in hepatitis B e-antigen (HBeAg)-positive and HBeAg-negative patients. Telbivudine was associated with a statistically significantly greater reduction in HBV DNA, greater proportion of alanine aminotransferase normalization, and greater histological response than lamivudine. Furthermore, telbivudine use resulted in fewer cases of treatment failure and less virological resistance than lamivudine. However, after 2 years of therapy, telbivudine resistance was appreciable (25%) and considerably higher than that seen with other new antivirals such as tenofovir and entecavir. Overall, telbivudine was found to be safe, although grade 3 or 4 adverse events, including elevations in creatine kinase, were more commonly found in patients receiving telbivudine than lamivudine. Telbivudine is not active against lamivudine-resistant HBV. CONCLUSIONS: Telbivudine is a new antiviral agent joining the armamentarium against HBV. It is superior to lamivudine in terms of therapeutic response and resistance profile. However, concerns about resistance with long-term use, along with inferior cost-effective analyses, have relegated telbivudine to a second-line agent in the management of chronic HBV infection.

R-1626, a specific oral NS5B polymerase inhibitor of hepatitis C virus.

Roche Holding AG is developing R-1626, an oral nucleoside inhibitor of HCV RNA polymerase. R-1626 has been demonstrated to be well absorbed and rapidly converted to the active component R-1479. The compound has demonstrated a strong capacity to inhibit HCV replication in vitro and in vivo, without the rapid development of viral resistance. After 4 weeks of treatment with R-1626 in combination with PEG-IFN plus ribavirin in treatment-naïve patients with genotype 1 HCV infection, HCV RNA could no longer be detected in approximately 74% of patients, compared with 5% of patients treated with PEG-IFN plus ribavirin alone, indicating the high potency of R-1626 to induce HCV RNA viral load reductions. R-1626 was generally well tolerated, although severe side effects of neutropenia were observed at high doses. A phase IIb clinical trial was ongoing at the time of publication to test the efficacy of R-1626 in combination with a standard or lower dose of PEG-IFN and ribavirin in HCV genotype 1-infected patients. Given its potent antiviral effect with an apparent high genetic barrier, R-1626 represents an important advancement in improving the outcome of patients with chronic HCV infection.

A review of telbivudine for the management of chronic hepatitis B virus infection.

BACKGROUND: Chronic hepatitis B is a worldwide health problem. Research interests have focused on the development of potent and safe antiviral agents with low resistance rates. Telbivudine is a nucleoside analogue that has been approved for treatment of chronic hepatitis B. OBJECTIVE: This review article concentrates on the pharmacokinetics and therapeutic efficacy of telbivudine. The resistance and safety profiles are also addressed. METHODS: Relevant publications were identified from searches of MEDLINE (1996-June 2007), the Cochrane Library and BIOSIS (1993-June 2007). Search items included, but were not limited to, telbivudine, pharmacokinetics, hepatitis B, resistance and adverse events. CONCLUSIONS: Clinical trials demonstrated telbivudine to be a safe and potent antiviral agent for treatment of chronic hepatitis B. Telbivudine has superior efficacy compared to lamivudine and adefovir.

Cytotoxic nucleoside analogues: different strategies to improve their clinical efficacy.

Cytotoxic nucleoside analogues are clinically important anticancer drugs. These agents behave as antimetabolites, compete with physiologic nucleosides, and, consequently, interact with a large number of intracellular targets to induce cytotoxicity. Nucleoside analogues share some general common characteristics, namely in terms of requiring transport by specific membrane transporters and intracellular metabolism. However these compounds differ in regard to the preferential interaction with certain targets which may explain why some compounds are more effective against rapidly proliferating tumours and others on neoplasia with a more protracted evolution. Purine and pyrimidine analogues are widely used not only as antileukaemic agents, but also as cytotoxic agents to treat solid tumours. However, the clinical use of these compounds is limited by important side-effects and primary or acquired drug resistance. Thus, there is an unmet medical need for the development of new antimetabolites and for technologies allowing a more suitable and effective administration of nucleoside analogues for the treatment of cancer patients. Here, we will review literature data concerning the recent development of novel purine nucleoside analogues (clofarabine, nelarabine and forodesine) and pyrimidine nucleoside analogues (troxacitabine, sapacitabine, CP-4055, 3'-C-ethynylcytidine and 5-azapyrimidines) that are in evaluation at the clinical level.

Evaluation of the L-stereoisomeric nucleoside analog troxacitabine for the treatment of acute myeloid leukemia.

Troxacitabine (BCH-4556; [-]-2'-deoxy-3'-oxacytidine) is a synthetic dioxolane that represents the first nucleoside analog with an L-isomer configuration to have shown important cytotoxic activity. Troxacitabine was obtained by exchanging the sulfur endocyclic atom with oxygen in the structure of lamivudine (3TC). Its unnatural stereochemistry renders it insensitive to some mechanisms of resistance of tumor cells to D-nucleosides, such as deamination by deoxycytidine deaminase and decreased active uptake by nucleoside transporters. These characteristics make troxacitabine a suitable alternative for patients with acute myelogenous leukemia as a potential way for overcoming resistance to ara-C therapy, which is the mainstay of acute myelogenous leukemia therapy at present. Clinically significant activity has been reported in Phase I studies in patients with advanced hematologic malignancies and has prompted troxacitabine to enter a series of Phase II trials in patients with refractory and relapsed acute myelogenous leukemia.

Squalenoyl nanomedicines as potential therapeutics.

Nucleoside analogues display significant anticancer or antiviral activity by interfering with DNA synthesis. However, there are some serious restrictions to their use, including their rapid metabolism and the induction of resistance. We have discovered that the linkage of nucleoside analogues to squalene leads to amphiphilic molecules that self-organize in water as nanoassemblies of 100-300 nm, irrespective of the nucleoside analogue used. The squalenoyl gemcitabine exhibited superior anticancer activity in vitro in human cancer cells and gemcitabine-resistant murine leukemia cells, and in vivo in experimental leukemia both after intravenous and oral administration. The squalenoylation of other antiretroviral nucleosides also led to more potent drugs when tested in primary cultures of HIV-infected lymphocytes. Thus, the squalenoylation is an original technology platform for generating more potent anticancer and antiviral nanomedicines.

New directions in the treatment of mantle cell lymphoma: an overview.

Mantle cell lymphoma (MCL) is one of the most challenging lymphomas to treat. In the first-line setting, high-dose therapy (HDT) and autologous stem cell transplantation or hyperCVAD/rituximab suggest benefit, especially in patients aged < 60 years. Nucleoside analogue-based regimens represent an alternate option in patients ineligible for HDT. Fludarabine in combination with cyclophosphamide or mitoxantrone has shown activity, and the results were superior with the addition of rituximab. Other cytotoxic agents, such as cladribine, clofarabine, or bendamustin, showed promising activity as well. A variety of new monoclonal antibody (MoAb) agents, such as humanized anti-CD20, alemtuzumab, anti-HLA-DR, anti-CD22 (as an immunotoxin carrier), anti-CD40, as well as MoAb-targeting TRAIL-R1 and TRAIL-R2 are being tested. Radioimmunotherapy with Yttrium 90-ibritumomab tiuxetan and Iodine 131 tositumomab have been tested alone or in combination with chemotherapy, including as part of HDT and autologous stem cell transplantation, in which they showed the best results. New vaccine modalities are exploring the use of tumor cell-based vaccines or of agents that block or activate costimulatory pathways/molecules, such as CTLA-4-Ig. Allogenic transplantation represents a potential curative option for MCL, especially nonmyeloablative transplantation, more feasible in that population. A plethora of novel biologic agents have surfaced, such as bortezomib, temsirolimus, thalidomide, lenalidomide, MoAb anti-vascular endothelial growth factor or vascular endothelial growth factor-Trap, and flavopiridol. Other targets include gene transcription through histone regulation; nuclear factor-kB pathway; protein kinase C inhibitors; small-molecules targeting apoptosis, such as antisense Bcl-2, pan-Bcl-2 family member inhibitors; MoAb agonists of cell death receptors; caspases regulators (inhibitors of apoptosis proteins, survivin); and MDM2 antagonist regulators of p53. A molecular approach to define biomarkers might help identify subgroups of patients and help develop rational therapies.

Nucleoside analogs as anti-HBV agents.

Chronic hepatitis B virus (HBV) infection affects about 400 million people worldwide. The development of nucleoside analogs that inhibit HBV polymerase provides an important approach for treating HBV infection. The approval of lamivudine, adefovir and entecavir represents a cornerstone of hepatitis B therapy. However, the challenges from the resistance and the off-therapy viral rebound are still unmet, and there is a need of developing new therapeutic agents. This review will discuss the structure-activity relationship of the most significant anti-HBV nucleoside analogs and the latest development in the field.