In vitro and in vivo anti-hepatitis B virus activities of a plant extract from Geranium carolinianum L

Natural products provide a large reservoir of potentially active agents with anti-hepatitis B virus (HBV) activity. We examined the effect of the polyphenolic extract from Geranium carolinianum L. (PPGC) on HBV replication both in vitro and in vivo. In the human HBV-transfected liver cell line HepG(2) 2.2.15, PPGC effectively suppressed the secretion of the HBV antigens in a dose-dependent manner with IC(50) values of 46.85 microg/ml for HBsAg and 65.60 microg/ml for HBeAg at day 9. Consistent with the HBV antigen reduction, PPGC (100 microg/ml) also reduced HBV DNA level by 35.9%. In the duck hepatitis B virus (DHBV) infected ducks, after PPGC was dosed intragastricly (i.g.) once a day for 10 days, the plasma DHBV DNA level was reduced, with an ED(50) value of 47.54 mg/kg. In addition, Southern blot analysis confirmed the in vivo anti-HBV effect of PPGC in ducks and PPGC also reduced the plasma and the liver DHBV DNA level in a dose-dependent manner. Furthermore, significant improvement of the liver was observed after PPGC treatment, as evaluated by the histopathological analysis.     

Protocatechuic aldehyde inhibits hepatitis B virus replication both in vitro and in vivo

Natural compounds provide a large reservoir of potentially active anti-hepatitis B virus (HBV) agents. We examined the direct effects of protocatechuic aldehyde (PA; derived from the Chinese herb, Salvia miltiorrhiza) on HBV replication in HepG2 2.2.15 cell line and duck hepatitis B virus (DHBV) replication in ducklings in vivo. The extracellular HBV DNA, hepatitis B e antigen (HBeAg) and hepatitis B surface antigen (HBsAg) concentrations in cell culture medium were determined by quantitative real-time PCR and ELISA, respectively. DHBV in duck serum was analyzed by dot blot. PA appeared to downregulate the secretion of HBsAg and HBeAg as well as the release of HBV DNA from HepG2 2.2.15 in a dose- and time-dependent manner at concentrations between 24 and 48 microg/mL. PA (25, 50, or 100 mg/kg, intraperitoneally, twice daily) also reduced viremia in DHBV-infected ducks. We provide the first evidence that PA, a novel anti-HBV substance derived from traditional Chinese herb S. miltiorrhiza, can efficiently inhibits HBV replication in HepG2 2.2.15 cell line in vitro and inhibit DHBV replication in ducks in vivo. PA therefore warrants further investigation as a potential therapeutic agent for HBV infections.     

In vitro antiviral activity of 1,2,3,4,6-penta-O-galloyl-beta-D-glucose against hepatitis B virus

This study examined the antiviral activity of the root of Paeonia lactiflora PALL. Among the solvent fractions of the crude drug, the ethyl acetate fraction showed anti-hepatitis B virus (HBV) activity (IC50, 8.1 microg/ml) in an HBV-producing HepG2.2.15 cell culture system. The active anti-HBV principle was isolated and identified as 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (PGG) from the crude drug by activity-guided fractionation. PGG isolated from P. lactiflora was examined for the inhibition of HBV multiplication by measurement of HBV DNA and hepatitis B surface antigen (HBsAg) levels in the extracellular medium of HepG2.2.15 cells after 8-d treatment. PGG decreased the level of extracellular HBV (IC50, 1.0 microg/ml) in a dose-dependent manner. PGG also reduced the HBsAg level by 25% at a concentration of 4 microg/ml. The gallate structure of PGG may play a critical role in the inhibition of anti-HBV activity. These results suggest that PGG could be a candidate for developing an anti-HBV agent.     

Characterization of antiviral activity of entecavir in transgenic mice expressing hepatitis B virus

Entecavir (ETV), a cyclopentyl guanosine nucleoside analog, was evaluated in transgenic mice expressing hepatitis B virus (HBV). ETV administered orally once daily for 10 days at a dosage of 3.2mg/kg significantly (P相似文献   

血根碱、白屈菜红碱衍生物的合成与体外抗HBV活性研究

目的合成季铵类苯并菲啶生物碱血根碱(1)和白屈菜红碱(2)的衍生物,评价其体外抗HBV活性,初步探讨抗HBV活性。方法以血根碱和白屈菜红碱为原料,通过结构修饰获得衍生物,采用Hep G2.2.15细胞模型评价衍生物对HBsAg和HBeAg分泌抑制活性和HBV DNA复制的抑制活性。结果血根碱和白屈菜红碱对HBsAg、HBeAg和HBV DNA复制具有较高的抑制活性,但细胞毒性较高。氧化白屈菜红碱(6)对HBV DNA的复制具有一定的抑制作用(IC50=0.75 mmol·L-1),细胞毒性较白屈菜红碱明显降低(CC50>3.0 mmol·L-1)。6-乙氧基二氢血根碱(7)和6-乙氧基二氢白屈菜红碱(8)对HBsAg和HBeAg和HBV DNA复制具有一定的抑制活性。结论季铵类苯并菲啶生物碱具有显著的体外抗HBV活性,烯胺正离子结构单元对化合物的抗HBV活性产生重要的影响。     

Antiviral effects of three novel derivatives of adefovir on the replication of hepatitis B virus

Nucleoside/tide analogs are now widely used for treatment of chronic hepatitis B (CHB). However, available nucleoside/tide analogs for treatment of CHB usually have limited therapeutic effect and potential adverse effects on CHB patients. We evaluated the anti-HBV effects of three novel derivatives (compounds 1, 4, and 8) of adefovir on the replication of hepatitis B virus (HBV) and determined their cytotoxicity. The effects of those compounds on the replication of human HBV in the HepG2 2.2.15 cell line and duck HBV in infected ducks were characterized by measuring the extracellular and intracellular HBV DNA using the quantitative real-time PCR and Southern blot assays. Their cytotoxicities against HepG2 cells were evaluated by MTT and measuring the contents of mitochondrial DNA using the dot blot assay. We found that all of the compounds inhibited the production of HBV in a dose-dependent manner, similar to that of adefovir dipivoxil. Furthermore, treatment with any of the compounds reduced significantly the replication of DHBV in ducks, accompanied by a significant reduction of inflammation in the livers, and the compound 1 appeared to be a fast-acting and long-lasting anti-DHBV reagent. Importantly, all of the compounds showed little cytotoxicity against HepG2 cells, even at a concentration of 1?mM. Collectively, those novel derivatives of adefovir had potent anti-HBV activity with little adverse effect and may be therapeutic candidates for potential clinical studies.     

抗HBV治疗性疫苗联合拉米夫定治疗慢性HBV感染者的临床实验研究

目的进一步验证抗HBV治疗性疫苗联合拉米夫定治疗慢性HBV感染者的临床疗效。方法确诊为慢性HBV感染者520例患者随机分为实验组260例,用抗HBV治疗性疫苗,1次/月,皮下注射,同时联合口服拉米夫定100mg/d,疗程为12个月;对照组260例,单纯口服拉米夫定100mg/d,疗程为12个月。检测血清HBsAg、HBeAg、HBVDNA、抗-HBe、抗-HBs及ALT。结果实验组HBsAg、HBeAg、HBVDNA阴转率及抗-HBe、抗-HBs阳转率分别为25.4%、45.0%、53.5%、30.4%、14.6%;对照组分别为11.9%、22.3%、28.1%、9.6%、2.7%,两组相比差异有统计学意义(P<0.05)。结论抗HBV治疗性疫苗联合拉米夫定对慢性HBV感染者有较好的临床疗效。     

A flavonoid from medicinal plants blocks hepatitis B virus-e antigen secretion in HBV-infected hepatocytes

A flavonoid molecule that showed a unique anti-HBV function was isolated from Phyllanthus urinaria. The molecular formula was determined as C14H6O8 based on FAM-MS analysis and the structure was determined by NMR. The identified flavonoid molecule, ellagic acid, showed unique anti-HBV functions. Ellagic acid did not inhibit either HBV polymerase activity, HBV replication or block HBsAg secretion. Rather, ellagic acid blocks effectively HBeAg secretion in HepG2 2.2.15 cells (IC50=0.07 microg/ml). Since HBeAg is involved in immune tolerance during HBV infection, ellagic acid, a newly identified functional anti-HBV compound, may be a new candidate therapeutic against immune tolerance in HBV-infected individuals.     

Antiviral activity of methyl helicterate isolated from Helicteres angustifolia (Sterculiaceae) against hepatitis B virus

The anti-HBV effect of methyl helicterate (MH), a triterpenoid isolated from the Chinese herb Helicteres angustifolia, was explored both in vitro and in vivo. In the HBV-transfected cell line HepG2.2.15, the secretion of HBsAg/HBeAg, the levels of HBV DNA and cccDNA, and the amount of viral RNA were significantly decreased after treatment with MH for 144 h. In addition, MH had no inhibitory effect on the mitochondrial DNA content. In DHBV-infected ducklings, MH significantly reduced the serum DHBV DNA, liver total viral DNA, and cccDNA levels. Furthermore, analysis of the liver pathological changes confirmed the hepatoprotective effect of MH. These results indicate that MH efficiently inhibits HBV replication both in vitro and in vivo and that MH may be a major bioactive ingredient in H. angustifolia.     

In vivo and in vitro antiviral activity of hyperoside extracted from Abelmoschus manihot （L） medik

AIM: To assess the anti-hepatitis B virus (HBV) effect of hyperoside extracted from Abelmoschus manihot (L) medik. METHODS: The human hepatoma Hep G2.2.15 cell culture system and duck hepatitis B virus (DHBV) infection model were used as in vivo and in vitro models to evaluate the anti-HBV effects. RESULTS: In the cell model, the 50% toxic concentration of hyperoside was 0.115 g/L; the maximum nontoxic concentration was 0.05 g/L. On the maximum nontoxic concentrations, the inhibition rates of hyperoside on HBeAg and HBsAg in the 2.2.15 cells were 86.41% and 82.27% on d 8, respectively. In the DHBV infection model, the DHBV-DNA levels decreased significantly in the treatment of 0.05 g x kg(-1 ) x d(-1 ) and 0.10 g x kg(-1) x d(-1) dosage groups of hyperoside (P<0.01). The inhibition of the peak of viremia was at the maximum at the dose of 0.10 g x kg(-1 ) x d(-1) and reached 60.79% on d 10 and 69.78% on d 13, respectively. CONCLUSION: These results suggested that hyperoside is a strong inhibitor of HBsAg and HBeAg secretion in 2.2.15 cells and DHBV-DNA levels in the HBV-infected duck model.     

Effect of various pyrimidines possessing the 1-[(2-hydroxy-1-(hydroxymethyl)ethoxy)methyl] moiety, able to mimic natural 2'-deoxyribose, on wild-type and mutant hepatitis B virus replication

Hepatitis B virus (HBV) is the most common cause of chronic liver disease worldwide. Development of drug resistance against clinical anti-HBV drug lamivudine due to long-term use and rebound of viral DNA after cessation of treatment has been a major setback of the current therapy. We have synthesized a series of pyrimidine nucleosides possessing a variety of substituents at the C-5 position, and a 1-[(2-hydroxy-1-(hydroxymethyl)ethoxy)methyl] flexible acyclic glycosyl moiety at the N-1 position, that have the ability to mimic the natural 2'-deoxyribosyl moiety. Some of these potential antiviral compounds included variations at both C-5 and C-6 positions of the uracil base. Other variations of the uracil derivatives were the 6-aza congeners. 4-Amino and 4-methoxy pyrimidine derivatives were also made. Compounds in which the base moiety was substituted by 5-chloro- (25), 5-(2-bromovinyl)- (32), or 5-bromo-6-methyl- (37) groups possess significant activity against duck-HBV, wild-type human HBV (2.2.15 cells), and lamivudine-resistant HBV containing single and double mutations. No cytotoxicity was seen in host HepG2 and Vero cells, up to the highest concentration tested. The anti-HBV activity exhibited by compounds 25, 32, and 37 was superior for human HBV and comparable for DHBV to that of the corresponding purine nucleoside, ganciclovir. Further, they were only 10-15-fold less inhibitory against human HBV in 2.2.15 cells than the reference drug, lamivudine. Other compounds in the series were moderately inhibitory against DHBV and wild-type human HBV. The size of the halogen and the electronegativity of the substituents at the 5- and 6-positions are important for antiviral activity toward HBV. These compounds were also evaluated for their antiviral activity for West Nile virus, respiratory syncytial virus, SARS-coronavirus, and hepatitis C virus. They were generally inactive in these antiviral assay systems (at concentrations up to 100 microg/mL). 1-[(2-Hydroxy-1-(hydroxymethyl) ethoxy)methyl]-5-fluorocytosine (34) showed some inhibitory activity against hepatitis C virus. Taken together, these data support our previous observations that the 5-substituted pyrimidine nucleosides containing acyclic glycosyl moieties have potential to serve as a new generation of potent, selective, and nontoxic anti-HBV agents for wild-type and lamivudine-resistant mutant HBV.     

肝细胞癌及相关慢性肝病肝组织中乙型肝炎病毒的研究

目的：初步探讨HBV感染与肝细胞癌之间的关系。方法：应用免疫组化和原位杂交分别在检测慢性肝炎、肝硬化、肝细胞癌及癌旁肝组织中HBsAg和HBVDNA的基础上，选择HBsAg和HBVDNA均为阳性的标本进行免疫组化与原位杂交双标记。结果：癌组织中HBsAg及HBVDNA阳性率低，信号少，且HBVDNA多在核内；而慢性肝炎、肝硬化和癌旁肝组织中HBsAg及HBVDNA阳性率高，信号多而强，HBVDNA可在胞浆或胞核。HBVDNA与HBsAg可共存于同一细胞或分布于不同肝小叶或同一肝小叶的不同部位。结论：大多数肝细胞癌的发生与HBV感染所致的慢性肝炎和肝硬化密切相关；双标记法有利于分析2种不同病毒标志物之间的关系。     

岩黄连提取物体内抗乙型肝炎病毒作用研究

目的观察岩黄连提取物的体内抗鸭乙型肝炎病毒（DHBV）作用。方法采用1日龄广西麻鸭感染DHBV,7d后用聚合酶链反应（PCR）法筛选出DHBV强阳性鸭,随机分成岩黄连高、中、低剂量组[剂量分别为8,4,2mg／（kg·d）],模型对照组（生理盐水）和阿昔洛韦阳性对照组[0．1mg／（kg·d）]5组,每组10只,各组雏鸭均灌胃给药14d。于用药前（T0）、用药第7天（T4）、用药第14天（T14）及停药后第3天（P3）分别采血,以荧光定量聚合酶链反应（FQ-PCR）法检测血清DHBV-DNA的含量,以改良赖氏法检测血清丙氨酸氨基转移酶（AIJT）和天门冬酸氨基转移酶（AST）活性,取肝组织作常规HE染色观察病理改变。结果岩黄连各剂量组用药后血清DHBV-DNA水平显著降低（P〈0．05）,P3时中、低剂量组血清有明显回升现象,而高剂量组回升现象不明显;用药前后血清A1月和AST变化与DHBV-DNA水平改变相似;鸭肝脏病理学检查显示岩黄连提取物对DHBV所致肝损伤有显著的保护作用。结论岩黄连提取物在体内有显著的抗DHBV作用。     

Inhibition of hepatitis B virus by D-fraction from Grifola frondosa: synergistic effect of combination with interferon-alpha in HepG2 2.2.15

In this study, D-fraction extracted from Grifola frondosa (GF-D) and its combination with human interferon alpha-2b (IFN) were investigated for the inhibitory effect on hepatitis B virus (HBV) in HepG2 2.2.15 cells (2.2.15 cells). HBV DNA and viral antigens were analyzed by a quantitative real-time polymerase chain reaction and end-point titration in radioimmunoassays, respectively. The results showed that GF-D or IFN alone could inhibit HBV DNA in 2.2.15 cells with the 50% inhibitory concentration (IC50) of 0.59 mg/ml and 1399 IU/ml, respectively. We further investigated the combination of GF-D and IFN for anti-HBV activity and found that they synergistically inhibited HBV replication in 2.2.15 cells. In combination with 0.45 mg/ml GF-D, the apparent IC50 value for IFN was 154 IU/ml. This 9-fold increase in antiviral activity of IFN suggested that GF-D could synergize with IFN. These results indicate that GF-D, in combination with IFN, might provide a potentially effective therapy against chronic HBV infections.     

Anti-hepatitis B virus activities of Geranium carolinianum L. extracts and identification of the active components

The ethanol extract of Geranium carolinianum L., a domestic plant grown in China, was subjected to sequential extractions with different organic solvents. The extracts were assayed for anti-hepatitis B virus (HBV) activities. The ethyl acetate fraction was found to contain the highest level of anti-HBV activity. In order to identify the active ingredients, the ethyl acetate fraction was further fractionated by column chromatography. Seven compounds were identified including ellagic acid, geraniin, quercitrin, hyperin, hirsutrin, quercetin, and kaempferol, whose structures were determined by NMR. The presence of the anti-HBV compounds geraniin, ellagic acid and hyperin in G. carolinianum L. may account for the effectiveness of this folk medicine in the treatment of HBV infections. Geraniin inhibited hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) secretion by more than 85.8% and 63.7%, respectively, at the non-cytotoxic concentration of 200 microg/ml. The inhibitions of HBsAg and HBeAg secretion by geraniin were higher than the inhibition by the positive control Lamivudine, 33.5% and 32.2% respectively, at the same concentration. Since HBeAg is involved in immune tolerance during HBV infection, the newly identified anti-HBV compound geraniin might be a candidate agent to overcome the immune tolerance in HBV-infected individuals. This is the first report of the anti-HBV effects of geraniin and hyperin, the active substances derived from G. carolinianum L.     

Antiviral therapeutic efficacy of foscarnet in hepatitis B virus infection

Foscarnet (PFA), a viral DNA polymerase inhibitor, is a clinical agent for herpes viruses. The goal of the study was to evaluate the therapeutic efficacy of PFA in hepatitis B virus (HBV) infection. Intravenous infusion of PFA (1 g/day) for 4 weeks significantly reduced serum HBeAg (p<0.01) and HBV DNA copies (p<0.05) in 31 patients who were diagnosed with active chronic HBV infection (CHB) and had not received antiviral treatment previously. Alanine aminotransaminase (ALT), aspartate aminotransaminase (AST) and gamma glutamyl transpeptidase (gamma-GT) of the patients declined (p<0.001, 0.001 and 0.01, respectively). Kidney function (blood creatinine and urea nitrogen) remained unchanged. Another 21 lamivudine-resistant CHB patients with mutations at the tyrosine-methionine-aspartate-aspartate motif (YMDD) displayed a response to PFA similar to that mentioned above, with reductions in HBeAg (p<0.05), HBV DNA (p<0.01) and liver enzymes (ALT and AST, p<0.001; gamma-GT, p<0.05). Moreover, PFA reduced serum HBeAg (p<0.01), HBV DNA (P<0.05), AST (p<0.05) and ALT (p<0.02) in a cohort of 13 severe CHB patients with advanced liver damage. PFA was also evaluated in vitro and in vivo. PFA inhibited HBV DNA replication in HBV-transfected human HepG2 cells (2.2.15 cells) with reduced amount of HBV RC-DNA and DS-DNA. In the duck HBV-infected ducklings, PFA reduced viral DNA and duck HBsAg in the serum (p<0.01 for both).     

Isothiafludine,a novel non-nucleoside compound,inhibits hepatitis B virus replication through blocking pregenomic RNA encapsidation

Aim： To investigate the action of isothiafludine （NZ-4）, a derivative of bis-heterocycle tandem pairs from the natural product leucamide A, on the replication cycle of hepatitis B virus （HBV） in vitro and in vivo. Methods： HBV replication cycle was monitored in HepG2.2.15 cells using qPCR, qRT-PCR, and Southern and Northern blotting. HBV protein expression and capsid assembly were detected using Western blotting and native agarose gel electrophoresis analysis. The interaction of pregenomic RNA （pgRNA） and the core protein was investigated by RNA immunoprecipitation. To evaluate the anti-HBV effect of NZ-4 in vivo, DHBV-infected ducks were orally administered NZ-4 （25, 50 or 100 mg.k~l{1-1） for 15 d. Results： NZ-4 suppressed intracellular HBV replication in HepG2.2.15 cells with an IC~o value of 1.33 pmol/L, whereas the compound inhibited the cell viability with an IC5o value of 50.4 pmol/L. Furthermore, NZ-4 was active against the replication of various drug- resistant HBV mutants, including 3TC/ETV-dual-resistant and ADV-resistant HBV mutants. NZ-4 （5, 10, and 20 pmol/L） concentration- dependently reduced the encapsidated HBV pgRNA, resulting in the assembly of replication-deficient capsids in HepG2.2.15 cells. Oral administration of NZ-4 dose-dependently inhibited DHBV DNA replication in the DHBV-infected ducks. Conclusion： NZ-4 inhibits HBV replication by interfering with the interaction between pgRNA and HBcAg in the capsid assembly process thus increasing the replication-deficient HBV capsids. Such mechanism of action might provide a new therapeutic strategy to combat H BV infection.     

脱氧野尻霉素衍生物抗乙型肝炎病毒的体外试验研究

目的:观察脱氧野尻霉素(DNJ)衍生物N—苄基—1—脱氧野尻霉素(P-DNJ)与N—壬基—1—脱氧野尻霉素(NN-DNJ)的体外抗乙型肝炎病毒(HBV)作用。方法:以HBVDNA转染的人肝癌细胞株HepG22,2,15细胞为靶细胞,以不同浓度的试验药物培养细胞,在第6天、第10天时应用时间分辨免疫荧光分析法和荧光实时定量聚合酶链反应法检测培养基上清液中HBsAg、HBeAg和HBVDNA,同时应用MTT法检测药物对细胞的毒性。结果:P-DNJ、NN-DNJ在试验浓度(5~125μg.mL-1)内未见细胞毒性作用,在浓度为125μg.mL-1时能显著减少细胞培养基上清液中HBsAg、HBeAg、HBVDNA的分泌。结论:P-DNJ、NN-DNJ在体外细胞培养试验中发现有抗HBV作用。     

Comparative evaluation of L-Fd4C and related nucleoside analogs as promising antiviral agents

As documented in the recent literature, there are more than 50 million people infected with HIV worldwide to date since the emergence of HIV and AIDS in the Western world in 1981. More importantly, about 7000 people die of AIDS daily with 2.5 and 2.6 millions total deaths in 1998 and 1999, respectively. On the other hand, human hepatitis B virus (HBV) is the leading cause of chronic hepatitis in the world. According to WHO executive summary, over 350 millions (approximately 5% of the world s population) people are chronically infected with HBV. There are about 1 million chronic HBV carriers in the United States. Although safe and effective vaccination for HBV is available for developing countries, there is still no effective treatment for the millions of chronically infected individuals. Consequently, long term infection with chronic HBV could lead to cirrhosis, and hepatocellular carcinoma. In light of these facts, it is evident that the discovery and development of novel antiviral agents for the treatment of HIV and HBV is an extremely important undertaking.The interest in L-nucleosides was spurred in recent years by the findings that L-nucleosides are generally endowed with lower host toxicity while maintaining good antiviral activity in comparison to their respective D-nucleosides. The recent FDA approval of Lamivudine [L-BCH 189 (3TC)] for the treatment of HIV and HBV further supports these notions. Since the discovery of Lamivudine, a large number of 2 ,3 -dideoxy (dd)- and 2 ,3 -didehydro-2 ,3 -dideoxy (D4)-L-nucleoside analogs have been synthesized and evaluated in hopes of identifying even better antiviral agents. As a result, 2 ,3 -Dideoxy-2 ,3 -didehydro-beta-L-fluorocytidine (beta-L-Fd4C) was found to be a promising new lead. The first synthesis and antiviral activity assessment of L-Fd4C were reported by Lin and Cheng et al. in 1996. Recent disclosures from several laboratories clearly demonstrated that L-Fd4C was the most potent anti-HBV agent reported to date (vs. 3TC, L-FddC, L-FMAU, etc.). In fact, L-Fd4C proved to be at least 10 times more potent than Lamivudine on HBV DNA synthesis in the hepatoma cell line HepG2 2.2.15. Compared with L-Fd4C, D-Fd4C showed similar anti-HIV activity yet reduced anti-HBV activity. 2 F-L-Fd4C exhibited excellent acid stability but reduced antiviral activity and cytotoxicity. Although L-Fd4C is converted intracellularly by cytoplasmic deoxycytidine kinase to its mono-, di- and triphosphate metabolites,43 the newly prepared bis(SATE)-L-Fd4CMP proved to be more potent against HBV yet less cytotoxic than L-Fd4C itself. The chemically synthesized L-Fd4CTP was found to be a poor substrate for human polymerase gamma. A recent report from Zhu and Cheng et al. indicated that L-Fd4C had no inhibitory effect on mitochondrial DNA synthesis at concentrations up to 10 microM. An in vivo study involving HBV-infected ducks showed that longer administration of L-Fd4C induced a sustained suppression of viremia (>95%) and of viral DNA synthesis in the liver. The same study also demonstrated that L-Fd4C is more potent than 3TC in vivo. In summary, on the basis of the data presented in this chapter, it is evident that L-Fd4C is endowed with exceptional anti-HBV activity (both in vitro and in vivo) as well as an acceptable toxicity profile, thus rendering it a very promising development candidate.