Clinical potential of the acyclic nucleoside phosphonates cidofovir, adefovir, and tenofovir in treatment of DNA virus and retrovirus infections

Dual infection with polyomavirus BK and acyclovir-resistant herpes simplex virus successfully treated with cidofovir in a bone marrow transplant recipient

A hematopoietic stem cell transplant recipient developed a mucosal herpes simplex virus-1 (HSV-1) infection while under acyclovir (ACV) treatment (HSV was later shown to be resistant to ACV). Concomitantly, the patient presented a hemorrhagic cystitis (HC) due to polyomavirus BK, for which intravenous cidofovir (CDV) was prescribed. The patient benefited from the broad-spectrum anti-DNA virus activity of CDV, and not only the HC resolved without signs of nephrotoxicity but also the HSV-1 lesions disappeared. This is the first report describing the effect of CDV on 2 simultaneous and unrelated DNA viral infections in an immunosuppressed transplant recipient. In addition, we describe here that this HSV-1 isolate possesses a unique phenotype and genotype.

Tenofovir disoproxil fumarate for prevention of HIV infection in women: a phase 2, double-blind, randomized, placebo-controlled trial

OBJECTIVES

The objective of this trial was to investigate the safety and preliminary effectiveness of a daily dose of 300 mg of tenofovir disoproxil fumarate (TDF) versus placebo in preventing HIV infection in women.

DESIGN

This was a phase 2, randomized, double-blind, placebo-controlled trial.

SETTING

The study was conducted between June 2004 and March 2006 in Tema, Ghana; Douala, Cameroon; and Ibadan, Nigeria.

PARTICIPANTS

We enrolled 936 HIV-negative women at high risk of HIV infection into this study.

INTERVENTION

Participants were randomized 1:1 to once daily use of 300 mg of TDF or placebo.

OUTCOME MEASURES

The primary safety endpoints were grade 2 or higher serum creatinine elevations (>2.0 mg/dl) for renal function, grade 3 or 4 aspartate aminotransferase or alanine aminotransferase elevations (>170 U/l) for hepatic function, and grade 3 or 4 phosphorus abnormalities (<1.5 mg/dl). The effectiveness endpoint was infection with HIV-1 or HIV-2.

RESULTS

Study participants contributed 428 person-years of laboratory testing to the primary safety analysis. No significant differences emerged between treatment groups in clinical or laboratory safety outcomes. Study participants contributed 476 person-years of HIV testing to the primary effectiveness analysis, during which time eight seroconversions occurred. Two were diagnosed in participants randomized to TDF (0.86 per 100 person-years) and six in participants receiving placebo (2.48 per 100 person-years), yielding a rate ratio of 0.35 (95% confidence interval = 0.03-1.93), which did not achieve statistical significance. Owing to premature closures of the Cameroon and Nigeria study sites, the planned person-years of follow-up and study power could not be achieved.

CONCLUSION

Daily oral use of TDF in HIV-uninfected women was not associated with increased clinical or laboratory adverse events. Effectiveness could not be conclusively evaluated because of the small number of HIV infections observed during the study.

Selective inhibition of porcine endogenous retrovirus replication in human cells by acyclic nucleoside phosphonates

Several anti-human immunodeficiency virus type 1 reverse transcriptase inhibitors were evaluated for their antiviral activities against porcine endogenous retrovirus in human cells. Among the test compounds, zidovudine was found to be the most active. The order of potency was zidovudine > phosphonylmethoxyethoxydiaminopyrimidine = phosphonylmethoxypropyldiaminopurine > tenofovir > or = adefovir > stavudine.

Identification of 1-isopropylsulfonyl-2-amine benzimidazoles as a new class of inhibitors of hepatitis B virus

A series of 1-isopropylsulfonyl-2-amine benzimidazole derivatives were synthesized and evaluated for their anti-hepatitis B virus (HBV) activity and cytotoxicity in the HepG2.2.15 cell line. In general, these derivatives are potent HBV inhibitors (IC(50)<4 microM) with high selectivity indices (SIs>40). Compounds 5b-e, g, j, and 9a were among the most prominent compounds, with IC(50)s of 0.70-2.0 microM and SIs of 41-274. The potent anti-HBV activity and safety profiles of the most promising compounds 5d and j (IC(50)s=0.70 microM, SIs>120) demonstrate the potential of this series of benzimidazoles for the development of new anti-HBV drugs.

Real-time quantitative PCR for assessment of antiviral drug effects against Epstein-Barr virus replication and EBV late mRNA expression

This study assesses the ability of quantitative real-time PCR to measure the effects of virus DNA polymerase inhibitors on EBV DNA and late mRNAs syntheses in EBV-producing cell lines. In-house real-time quantitative PCRs were used to measure EBV DNA (thymidine kinase) and mRNAs (BLLF1 gene/gp350/220, BVRF2 gene/protease) in P3HR-1 and B95-8 cells induced for EBV production by PMA and exposed to ganciclovir, cidofovir and foscarnet. The calculated 50% effective concentrations (EC(50)) for viral DNA replication inhibition in P3HR-1 cells after 7 days of drug exposure were 0.28+/-0.06, 0.29+/-0.01 and 13.6+/-0.17 microg/mL for ganciclovir, cidofovir and foscarnet, respectively. The EC(50) for B95-8 cells were 0.44+/-0.02, 0.70+/-0.06 and 46.8+/-0.5 microg/mL, respectively. The quantitation of the late viral mRNAs showed a decrease of 79-89% in the mRNA amount after 4 days of antiviral treatment. Nevertheless, a substantial amount of mRNA still remained detectable after drug exposure. The real-time PCR is an improvement in the attempt to simplify EBV DNA-quantitation for antiviral assays. The quantitation of late mRNA does not appear as more informative than DNA quantitation for the assessment of the DNA polymerase inhibitor activity, but it may be useful to assess the antiviral activity of drugs acting by another mechanism.

Antiviral activity of triazine analogues of 1-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine (cidofovir) and related compounds

Treatment of 5-azacytosine sodium salt with diisopropyl [(2-chloroethoxy)methyl]phosphonate followed by removal of ester groups with BrSi(CH3)3 afforded 1-[2-(phosphonomethoxy)ethyl]-5-azacytosine (3). Reaction of 5-azacytosine with [(trityloxy)methyl]-(2S)-oxirane followed by etherification with diisopropyl (bromomethyl)phosphonate and removal of ester groups gave 1-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]-5-azacytosine (1). The synthesis of 6-azacytosine congener 2 was analogous using N4-benzoylated intermediates. Compound 1 was shown to exert strong activity against a broad spectrum of DNA viruses including adenoviruses, poxviruses, and herpesviruses (i.e., herpes simplex viruses, varicella zoster virus, and human cytomegalovirus). Decomposition of 1 in alkaline solutions resulted in products 17 and 18. While the N-formylguanidine derivative 17 proved active, the carbamyolguanidine derivative 18 was devoid of antiviral activity.

Synthesis, in vitro antiviral evaluation, and stability studies of novel alpha-borano-nucleotide analogues of 9-[2-(phosphonomethoxy)ethyl]adenine and (R)-9-[2-(phosphonomethoxy)propyl]adenine

We describe here the synthesis of 9-[2-(boranophosphonomethoxy)ethyl]adenine (6a) and (R)-9-[2-(boranophosphonomethoxy)propyl]adenine (6b), the first alpha-boranophosphonate nucleosides in which a borane (BH3) group substitutes one nonbridging oxygen atom of the alpha-phosphonate moiety. H-phosphinates 5a and 5b and alpha-boranophosphonates 6a and 6b were evaluated for their in vitro activity against human immunodeficiency virus (HIV) infected cells and against a panel of DNA or RNA viruses. Compounds 5a, 5b, 6a, and 6b exhibited no significant antiviral activity in vitro and cytotoxicity. To measure the chemical and enzymatic stabilities of the target compounds 6a and 6b, kinetic data of decomposition for derivatives 5a, 5b, 6a, 6b, and standard compounds were studied at 37 degrees C in several media. The alpha-boranophosphonates 6a and 6b were metabolized in culture medium into H-phosphinates 5a and 5b, with half-live values of 5.3 h for 6a and 1.3 h for 6b.

Bifunctional Acyclic Nucleoside Phosphonates: 2. Symmetrical 2-{[Bis(phosphono)methoxy]methyl}ethyl Derivatives of Purines and Pyrimidines

Novel bisphosphonate alkylating agent, tetraisopropyl {2-[(mesyloxy)methyl]propane-1,3-diyl}bis(oxymethylene)bisphosphonate 19, was synthesized from diethyl 2,2-bis(hydroxymethyl)malonate. Decarbethoxylation of the diethyl 2,2-dimethyl-1,3-dioxane-5,5-dicarboxylate was followed by chloromethylation of 2-[(benzyloxy)methyl]propane-1,3-diol and Arbuzov reaction with triisopropyl phosphite. Bisphosphonate building block 19 was used in the alkylation of various nucleobases (2-amino-6-chloropurine, adenine, 2-amino-6-(cyclopropyl)aminopurine, cytosine, uracil and 4-methoxy-5-methylpyrimidin-2(1H)-one). N9-Substituted purines and N1-substituted pyrimidines were converted to appropriate free bisphosphonic acids. No antiviral or cytostatic activity was detected.

Status Presens of Antiviral Drugs And Strategies: Part I: DNA Viruses and Retroviruses

More than 40 compounds have been formally licensed for clinical use as antiviral drugs, and half of these are used for the treatment of HIV infections. The others have been approved for the therapy of herpesvirus (HSV, VZV, CMV), hepadnavirus (HBV), hepacivirus (HCV) and myxovirus (influenza, RSV) infections. New compounds are in clinical development or under preclinical evaluation, and, again, half of these are targeting HIV infections. Yet, quite a number of important viral pathogens (i.e. HPV, HCV, hemorrhagic fever viruses) remain in need of effective and/or improved antiviral therapies.

Viruses and Viral Diseases

More than 40 compounds have been formally licensed for clinical use as antiviral drugs, and half of these are used for the treatment of human immunodeficiency virus (HIV) infections. The others have been approved for the therapy of herpesvirus (herpes simplex virus (HSV), varicella-zoster virus (VZV), cytomegalovirus (CMV)), hepadnavirus (hepatitis B virus (HBV)), hepacivirus (hepatitis C virus (HCV)), and myxovirus (influenza, respiratory synctural virus (RSV)) infections. New compounds are in clinical development or under preclinical evaluation, and, again, half of these target HIV infections. Yet, quite a number of important viral pathogens (i.e., human papilloma virus (HPV), HCV, hemorrhagic fever viruses) remain in need of effective and/or improved antiviral therapies.

Antiviral prodrugs - the development of successful prodrug strategies for antiviral chemotherapy

Following the discovery of the first effective antiviral compound (idoxuridine) in 1959, nucleoside analogues, especially acyclovir (ACV) for the treatment of herpesvirus infections, have dominated antiviral therapy for several decades. However, ACV and similar acyclic nucleosides suffer from low aqueous solubility and low bioavailability following oral administration. Derivatives of acyclic nucleosides, typically esters, were developed to overcome this problem and valaciclovir, the valine ester of ACV, was among the first of a new series of compounds that were readily metabolized upon oral administration to produce the antiviral nucleoside in vivo, thus increasing the bioavailility by several fold. Concurrently, famciclovir was developed as an oral formulation of penciclovir. These antiviral 'prodrugs' thus established a principle that has led to many successful drugs including both nucleoside and nucleotide analogues for the control of several virus infections, notably those caused by herpes-, retro- and hepatitisviruses. This review will chart the origins and development of the most important of the antiviral prodrugs to date.

Cidofovir administered with radiation displays an antiangiogenic effect mediated by E6 inhibition and subsequent TP53-dependent VEGF repression in HPV18+ cell lines

Therapeutic administration of the antiviral agent cidofovir with radiation markedly enhanced the antitumor effect of ionizing radiation in cells of two HPV18+ human cervical carcinoma cell lines. Although this potent radiosensitizing effect was associated with repression of the viral oncoproteins E6/ E7 and restoration of TP53 as shown previously, additional mechanisms may be involved. In the present study, we investigated the antiangiogenic effect of the combination of cidofovir and radiation in cells of two HPV18+ cervical cancer cell lines, HeLa and ME180, and assessed the molecular mechanisms associated with the antiangiogenic effect observed. Cells were exposed to cidofovir (10 microg/ml) and irradiated (1-9 Gy). The angiogenic response was studied in vitro by a matrigel invasion assay. Modulations of E6, TP53 and VEGF mRNA and protein levels were studied by real-time RT-PCR, Western blot analysis and ELISA, respectively. Then a double RNA interference approach was used to analyze the connection between E6/TP53 and VEGF. The combination of cidofovir and radiation had a potent antiangiogenic effect. It induced E6 inhibition, restoration of TP53, and reduction of the proangiogenic phenotype of HPV18+ cells associated with VEGF inhibition. A siRNA strategy showed an anti-VEGF action of the combination mediated directly by E6 inhibition and TP53 restoration, since E6 siRNA inhibited VEGF whereas co-transfection with E6 and TP53 siRNA abrogated the anti-VEGF effect. This study showed that the combination of cidofovir with ionizing radiation has an antiangiogenic effect associated with VEGF inhibition subsequent to E6 inhibition and TP53 restoration.

Functional involvement of multidrug resistance-associated protein 4 (MRP4/ABCC4) in the renal elimination of the antiviral drugs adefovir and tenofovir

Acyclic nucleotide phosphonates (adefovir, cidofovir, and tenofovir) are eliminated predominantly into the urine, and renal failure is their dose-limiting toxicity, particularly for adefovir and cidofovir. In this study, we examined the involvement of multidrug resistance-associated protein (MRP)4 (ABCC4) in their luminal efflux in the kidney. ATP-dependent uptake of adefovir and tenofovir but not cidofovir was observed only in the membrane vesicles expressing MRP4. The ATP-dependent uptake of adefovir and tenofovir by MRP4 was not saturated at 1 mM. The ATP-dependent uptake of adefovir by membrane vesicles expressing MRP4 was osmotic-sensitive. No ATP-dependent uptake of either agent was observed in the membrane vesicles expressing human MRP2 or breast cancer resistance protein. These nucleotide analogs were given to mice by constant intravenous infusion, and the plasma, urine, and tissue concentrations were determined. The kidney accumulation of adefovir and tenofovir was significantly greater in Mrp4 knockout mice (130 versus 66 and 191 versus 87 pmol/g tissue, respectively); thus, the renal luminal efflux clearance was estimated to be 37 and 46%, respectively, of the control. There was no difference in the fraction of mono- and diphosphorylated forms of adefovir in the kidney between wild-type and Mrp4 knockout mice. In mice, cidofovir was also eliminated via the urine by tubular secretion as well as glomerular filtration. There was no change in the kinetic parameters of cidofovir in Mrp4 knockout mice. Our results suggest that MRP4 is involved in the luminal efflux of both adefovir and tenofovir, but it makes only a limited contribution to the urinary excretion of cidofovir.

Mechanism of activation of beta-D-2'-deoxy-2'-fluoro-2'-c-methylcytidine and inhibition of hepatitis C virus NS5B RNA polymerase

Beta-D-2'-deoxy-2'-fluoro-2'-C-methylcytidine (PSI-6130) is a potent specific inhibitor of hepatitis C virus (HCV) RNA synthesis in Huh-7 replicon cells. To inhibit the HCV NS5B RNA polymerase, PSI-6130 must be phosphorylated to the 5'-triphosphate form. The phosphorylation of PSI-6130 and inhibition of HCV NS5B were investigated. The phosphorylation of PSI-6130 by recombinant human 2'-deoxycytidine kinase (dCK) and uridine-cytidine kinase 1 (UCK-1) was measured by using a coupled spectrophotometric reaction. PSI-6130 was shown to be a substrate for purified dCK, with a Km of 81 microM and a kcat of 0.007 s-1, but was not a substrate for UCK-1. PSI-6130 monophosphate (PSI-6130-MP) was efficiently phosphorylated to the diphosphate and subsequently to the triphosphate by recombinant human UMP-CMP kinase and nucleoside diphosphate kinase, respectively. The inhibition of wild-type and mutated (S282T) HCV NS5B RNA polymerases was studied. The steady-state inhibition constant (Ki) for PSI-6130 triphosphate (PSI-6130-TP) with the wild-type enzyme was 4.3 microM. Similar results were obtained with 2'-C-methyladenosine triphosphate (Ki=1.5 microM) and 2'-C-methylcytidine triphosphate (Ki=1.6 microM). NS5B with the S282T mutation, which is known to confer resistance to 2'-C-methyladenosine, was inhibited by PSI-6130-TP as efficiently as the wild type. Incorporation of PSI-6130-MP into RNA catalyzed by purified NS5B RNA polymerase resulted in chain termination.

Cidofovir resistance in vaccinia virus is linked to diminished virulence in mice

Cidofovir [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC)] is recognized as a promising drug for the treatment of poxvirus infections, but drug resistance can arise by a mechanism that is poorly understood. We show here that in vitro selection for high levels of resistance to HPMPC produces viruses encoding two substitution mutations in the virus DNA polymerase (E9L) gene. These mutations are located within the regions of the gene encoding the 3'-5' exonuclease (A314T) and polymerase (A684V) catalytic domains. These mutant viruses exhibited cross-resistance to other nucleoside phosphonate drugs, while they remained sensitive to other unrelated DNA polymerase inhibitors. Marker rescue experiments were used to transfer A314T and/or A684V alleles into a vaccinia virus Western Reserve strain. Either mutation alone could confer a drug resistance phenotype, although the degree of resistance was significantly lower than when virus encoded both mutations. The A684V substitution, but not the A314T change, also conferred a spontaneous mutator phenotype. All of the HPMPC-resistant recombinant viruses exhibited reduced virulence in mice, demonstrating that these E9L mutations are inextricably linked to reduced fitness in vivo. HPMPC, at a dose of 50 mg/kg of body weight/day for 5 days, still protected mice against intranasal challenge with the drug-resistant virus with A314T and A684V mutations. Our studies show that proposed drug therapies offer a reasonable likelihood of controlling orthopoxvirus infections, even if the viruses encode drug resistance markers.

Antiviral activity of HPMPC (cidofovir) against orf virus infected lambs

(S)-1-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine [corrected] (HPMPC, cidofovir, CDV, Vistide) is an acyclic nucleoside analogue with a potent and selective activity against a broad spectrum of DNA viruses including the poxviruses. In this study we present the results of different treatment regimens in lambs experimentally infected with orf virus with different cidofovir formulations prepared in Beeler basis and Unguentum M. Our results show that choice of excipient, concentration of codofovir [corrected] and treatment regimen were all important to the clinical outcome of the therapy. Whilst one particular regimen appeared to exacerbate the lesion, treatment with 1% (w/v) cidofovir cream, prepared in Beeler basis, for 4 consecutive days did result in milder lesions that resolved in milder lesions that resolved [corrected] more quickly than untreated lesions. Furthermore the scabs of the treated animals contained significantly lower amounts of viable virus meaning there should be less contamination of the environment with virus than would normally occur.

Indolopyridones inhibit human immunodeficiency virus reverse transcriptase with a novel mechanism of action

We have discovered a novel class of human immunodeficiency virus (HIV) reverse transcriptase (RT) inhibitors that block the polymerization reaction in a mode distinct from those of the nucleoside or nucleotide RT inhibitors (NRTIs) and nonnucleoside RT inhibitors (NNRTIs). For this class of indolopyridone compounds, steady-state kinetics revealed competitive inhibition with respect to the nucleotide substrate. Despite substantial structural differences with classical chain terminators or natural nucleotides, these data suggest that the nucleotide binding site of HIV RT may accommodate this novel class of RT inhibitors. To test this hypothesis, we have studied the mechanism of action of the prototype compound indolopyridone-1 (INDOPY-1) using a variety of complementary biochemical tools. Time course experiments with heteropolymeric templates showed "hot spots" for inhibition following the incorporation of pyrimidines (T>C). Moreover, binding studies and site-specific footprinting experiments revealed that INDOPY-1 traps the complex in the posttranslocational state, preventing binding and incorporation of the next complementary nucleotide. The novel mode of action translates into a unique resistance profile. While INDOPY-1 susceptibility is unaffected by mutations associated with NNRTI or multidrug NRTI resistance, mutations M184V and Y115F are associated with decreased susceptibility, and mutation K65R confers hypersusceptibility to INDOPY-1. This resistance profile provides additional evidence for active site binding. In conclusion, this class of indolopyridones can occupy the nucleotide binding site of HIV RT by forming a stable ternary complex whose stability is mainly dependent on the nature of the primer 3' end.

Where does adefovir stand amongst newly developed antivirals: from pharmacology to virology

Adefovir, an acyclic nucleotide analog of adenosine monophosphate, has demonstrated potent activities against several viruses in vitro. Since 2002, the diester prodrug of this molecule, adefovir dipivoxil, has been approved as a well-tolerated and efficacious treatment for chronic hepatitis B. It is the first nucleotide analog to be approved for this indication and it is now challenged by several other molecules that also inhibit hepatitis B virus replication. In this article, we analyze the strengths and limitations of adefovir in the context of hepatitis B treatment and consider the other alternatives in the treatment of this difficult-to-treat chronic disease. Adefovir dipivoxil has offered a real opportunity for patients who developed lamivudine resistance and were facing a therapeutic deadlock; the next challenge for clinicians will be to offer the best therapeutic strategy to limit the inexorable selection of resistant strains.

Papillomavirus and treatment

Human papillomaviruses (HPVs) are small DNA viruses responsible for a broad range of clinical presentations, characterized histologically by the proliferation of epithelial cells. HPVs are responsible for benign as well as malignant lesions, the most frequent of the latter being cervical carcinoma. A better knowledge of the immunobiology of these lesions allowed the development of prophylactic vaccines (for the most frequent genital types) that are presently under evaluation. The present paper describes different approaches for the treatment of HPV lesions, still mostly based on surgery, and underlines the importance of developing adjuvant therapies.

Hepatitis B: the pathway to recovery through treatment

Hepatitis B is a major public health problem in the world today. Since 1985, the number of reported cases has declined as a direct result of universal immunization of neonates, vaccination of at-risk populations, lifestyle or behavioral changes in high-risk groups, refinements in the screening of blood donors, and the use of virally inactivated or genetically engineered products in patients with bleeding disorders. New and potent antiviral agents being developed and evaluated provide hope and optimism for those who are chronically infected with hepatitis B virus. Prevention remains the most effective strategy in the global management of hepatitis B virus. Universal immunization programs prevent hepatitis B virus transmission and circumvent acute and chronic infection.

Antiviral therapy for adenovirus infections

The treatment of severe adenovirus keratoconjunctivitis and life-threatening adenovirus infections in immunocompromised patients is still unsatisfactory. We here review the mode of action and antiviral data for cidofovir and ribavirin, obtained in cell culture, animal models or patients. Several nucleoside or nucleotide analogues have been described that target the adenovirus polymerase, whereas other antiviral targets have been poorly investigated. Furthermore, optimal therapeutic response may be achieved by combining antiviral therapy with immunotherapeutic approaches, as currently being explored.

Detection of Molluscum contagiosum Virus (MCV) Subtype I as a Single Dominant Virus Subtype in Molluscum Lesions from a Turkish Population

BACKGROUND

Molluscum contagiosum has a worldwide occurrence and its primary mode of transmission is via direct human contact including sexual means. The aim of the study was to implement a polymerase chain reaction-based assay for detection and subtyping of Molluscum contagiosum virus (MCV) in skin lesions diagnosed with molluscum contagiosum in a large regional teaching hospital in Turkey.

METHODS

For this purpose, a total of 61 patients were included in the study. Randomly selected single lesion from each patient was used to extract DNA material and a specific PCR reaction amplifying 393-bp- and 575-bp-long regions from MCV genome was used in the detection. Subtyping was carried out by digestion of the amplified 575-bp product with restriction endonuclease enzyme BamHI. Both amplified and restriction enzyme digested products visualized on agarose gel electrophoresis.

RESULTS

All 61 molluscum cases (100%) included in the study contained MCV genetic material as demonstrated by the presence of 393- and 575-bp-long PCR amplified products. Restriction enzyme BamHI digestion of the 575-bp-long amplicon indicated that the infecting subtype in all the cases (100%) was MCV subtype I.

CONCLUSIONS

Results of this study demonstrate that subtype I is the only infecting strain dominant in our region. Because the only consecutive molluscum patients admitted to our hospital were included in the study, our data do not rule out the possibility that other genotypes might be present in the Turkish population. However, it is not unreasonable to conclude that similar trends exist in the rest of the country. Results also show that a molecular-based diagnostic assay would be feasible in cases where diagnosis was deemed necessary.

Activities of acyclic nucleoside phosphonates against Orf virus in human and ovine cell monolayers and organotypic ovine raft cultures

Orf virus, a member of the Parapoxvirus genus, causes a contagious pustular dermatitis in sheep, goats, and humans. Previous studies have demonstrated the activity of (S)-1-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine (HPMPC; cidofovir; Vistide) against orf virus in cell culture and humans. We have evaluated a broad range of acyclic nucleoside phosphonates (ANPs) against several orf virus strains in primary lamb keratinocytes (PLKs) and human embryonic lung (HEL) monolayers. HPMPC, (S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]-2,6- diaminopurine (HPMPDAP), and (R)-9-[3-hydroxy-2-(phosphonomethoxy)propoxy]-2,4-diaminopyrimidine (HPMPO-DAPy) were three of the most active compounds that were subsequently tested in a virus yield assay with PLK and HEL cells by virus titration and DNA quantification. HPMPC, HPMPDAP, and HPMPO-DAPy were evaluated for their activities against orf virus replication in organotypic epithelial raft cultures from differentiated PLK cells. At the highest concentrations (50 and 20 microg/ml), full protection was provided by the three drugs, while at 5 microg/ml, only HPMPDAP and HPMPC offered partial protection. The activities of the three compounds in the raft culture system were confirmed by quantification of infectious virus and viral DNA. These findings provide a rationale for the use of HPMPC and other ANPs in the treatment of orf (contagious ecthyma) in humans and animals.

Risk factors for the development of bronchiolitis obliterans in children with bronchiolitis

BACKGROUND

Bronchiolitis obliterans (BO) is an uncommon and severe form of chronic obstructive lung disease in children that results from an insult to the lower respiratory tract.

METHODS

A case-control study of children under the age of 3 years was performed in 109 cases and 99 controls to determine risk factors for the development of BO. Participants were evaluated by immunofluorescence viral tests, pulmonary function tests, and questions to assess tobacco and other exposures.

RESULTS

Bronchiolitis due to adenovirus (odds ratio (OR) 49, 95% confidence interval (CI) 12 to 199) and the need for mechanical ventilation (OR 11, 95% CI 2.6 to 45) were strongly and independently associated with an increased risk for BO. Factors not associated with post-infectious BO included age of the child, sex, and environmental tobacco exposure (either in utero or during infancy).

CONCLUSIONS

Adenovirus infection and need for mechanical ventilation are significant risk factors for developing BO in children. Further research is needed to determine why these risk factors are so strong and how they may contribute to the development of the disease.

A survey of antiviral drugs for bioweapons

Smallpox (variola major), and the haemorrhagic fever viruses (filoviruses and arenaviruses) are classified as Category A biowarfare agents by the Centers for Disease Control. Category A agents pose a significant risk to public health and national security because they can be easily disseminated by aerosol, although with the exception of variola, they are not easily transmitted from person to person. An attack with these viruses would result in high morbidity and mortality and cause widespread panic. With the exception of smallpox and Argentine haemorrhagic fever virus, there are no vaccines or approved treatments to protect against these diseases. In this review we focus on promising prophylactic, therapeutic and disease modulating drugs (see Figure 1 for select chemical structures).

Organotypic epithelial raft cultures as a model for evaluating compounds against alphaherpesviruses

The course of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) and varicella-zoster virus (VZV) infections in squamous epithelial cells cultured in a three-dimensional organotypic raft culture was tested. In these raft cultures, normal human keratinocytes isolated from neonatal foreskins grown at the air-liquid interface stratified and differentiated, reproducing a fully differentiated epithelium. Typical cytopathic changes identical to those found in the squamous epithelium in vivo, including ballooning and reticular degeneration with the formation of multinucleate cells, were observed throughout the raft following infection with HSV and VZV at different times after lifting the cultures to the air-liquid interface. For VZV, the aspects of the lesions depended on the stage of differentiation of the organotypic cultures. The activity of reference antiviral agents, acyclovir (ACV), penciclovir (PCV), brivudin (BVDU), foscarnet (PFA), and cidofovir (CDV), was evaluated against wild-type and thymidine kinase (TK) mutants of HSV and VZV in the raft cultures. ACV, PCV, and BVDU protected the epithelium against cytopathic effect induced by wild-type viruses in a concentration-dependent manner, while treatment with CDV and PFA proved protective against the cytodestructive effects induced by both TK+ and TK- strains. The quantification of the antiviral effects in the rafts were accomplished by measuring viral titers by plaque assay for HSV and by measuring viral DNA load by real-time PCR for VZV. A correlation between the degree of protection as determined by histological examination and viral quantification could be demonstrated The three-dimensional epithelial raft culture represents a novel model for the study of antiviral agents active against HSV and VZV. Since no animal model is available for the evaluation of antiviral agents against VZV, the organotypic cultures may be considered a model to evaluate the efficacy of new anti-VZV antivirals before clinical trials.

Synthesis and antiviral activity of 7-deazaneplanocin A against orthopoxviruses (vaccinia and cowpox virus)

An efficient method for the synthesis of 7-deazaneplanocin A (2) has been accomplished by the condensation of cyclopentenol 3 with 6-chloro-7-deazapurine followed by subsequent functional group manipulations. The synthesized 7-deazaneplanocin A (2) exhibited potent antiviral activity against cowpox and vaccinia viruses without cytotoxicity in HFF cells.

Recent highlights in the development of new antiviral drugs

Twenty antiviral drugs, that is about half of those that are currently approved, are formally licensed for clinical use in the treatment of human immunodeficiency virus infections (acquired immune deficiency syndrome). The others are used in the treatment of herpesvirus (e.g. herpes simplex virus, varicella zoster virus and cytomegalo virus), hepatitis B virus, hepatitis C virus or influenza virus infections. Recent endeavours have focussed on the development of improved antiviral therapies for virus infections that have already proved amenable to antiviral drug treatment, as well as for virus infections for which, at present, no antiviral drugs have been formally approved (i.e. human papilloma viruses, adenoviruses, human herpesvirus type 6, poxviruses, severe acute respiratory syndrome coronavirus and hemorrhagic fever viruses).

[Fatal outcome of varicella zoster sepsis in a 22-year old patient]

Infection with Varicella zoster virus (VZV) usually occurs in children up to 15 years with mild symptoms. We present a case of a 22-year old man with a fatal varicella zoster infection. He developed fulminant hepatitis with acute liver failure and an acute respiratory distress syndrom (ARDS). In this article the general aspects of VZV infection are discussed. Treatment options and previous publications are reviewed.

A guided tour through the antiviral drug field

Approximately 40 compounds have been formally licensed for clinical use as antiviral drugs, with half of these in use for the treatment of HIV infections. The remaining have been approved for use in the therapy of herpes virus (herpes simplex virus, varicella zoster virus and cytomegalovirus), hepadnavirus, hepacivirus and myxovirus (influenza and respiratory syncytial virus) infections. New compounds are in clinical development or under preclinical evaluation, and again, half of these are intended to target HIV infections. However, quite a number of important viral pathogens (i.e., human papillomavirus, hepatitis C virus and hemorrhagic fever viruses) remain in need of effective and/or improved antiviral therapies.

New N4-Hydroxycytidine Derivatives: Synthesis and Antiviral Activity

Two series of N4-hydroxycytidine derivatives were synthesized and evaluated as potential antipox virus agents. Acylation of N4-hydroxycytidine (1) with an excess of acyl chloride or imidazolide yielded the corresponding N4-(acyloxy) derivatives. 5'-Phosphonates of 1 were prepared by the reaction of cytidine 5'-phosphonates with aqueous hydroxylamine hydrochloride (pH 6.0). Nucleoside 1 and its N4-(acyloxy) derivatives inhibited replication of pox viruses in cell cultures, N4-(pivaloyloxy)- and N4-(benzoyloxy)cytidines being the most potent. The synthesized 5'-phosphonates were more cytotoxic than the parent nucleoside.

Antiviral potential of a new generation of acyclic nucleoside phosphonates, the 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidines

Three acyclic nucleoside phosphonates (ANPs) have been formally approved for clinical use in the treatment of 1) cytomegalovirus retinitis in AIDS patients (cidofovir, by the intravenous route), 2) chronic hepatitis B virus (HBV) infections (adefovir dipivoxil, by the oral route), and 3) human immunodeficiency virus (HIV) infections (tenofovir disoproxil fumarate, by the oral route). The activity spectrum of cidofovir {(S)- 1-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine [(S)-HPMPC)]}, like that of (S)-HPMPA [(S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]adenine) and (S)-HPMPDAP [(S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]-2, 6-diaminopurine), encompasses a broad spectrum of DNA viruses, including polyoma-, papilloma-, adeno-, herpes-, and poxviruses. Adefovir {9-[2-(phosphonomethoxy)ethyl]adenine (PMEA)} and tenofovir [(R)-9-[2-(phosphonomethoxy) propyl]adenine [(R)-PMPA)]} are particularly active against retroviruses (ie., HIV) and hepadnaviruses (ie., HBV); additionally, PMEA also shows activity against herpes- and poxviruses. We have recently identified a new class of ANPs, namely 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidines, named, in analogy with their alkylpurine counterparts, HPMPO-DAPy, PMEO-DAPy, and (R)-PMPO-DAPy. These compounds exhibit an antiviral activity spectrum and potency that is similar to that of (S)-HPMPDAP, PMEA, and (R)-PMPA, respectively. Thus, PMEO-DAPy and (R)-PMPO-DAPy, akin to PMEA and (R)-PMPA, proved particularly active against HIV- 1, HIV-2, and the murine retrovirus Moloney sarcoma virus (MSV). PMEO-DAPy and (R)-PMPO-DAPy also showed potent activity against both wild-type and lamivudine-resistant strains of HBV. HPMPO-DAPy was found to inhibit different poxviruses (ie., vaccinia, cowpox, and orf) at a similar potency as cidofovir. HPMPO-DAPy also proved active against adenoviruses. In vivo, HPMPO-DAPy proved equipotent to cidofovir in suppressing vaccinia virus infection (tail lesion formation) in immunocompetent mice and promoting healing of disseminated vaccinia lesions in athymic-nude mice. The 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidines offer substantial potential for the treatment of a broad range of retro-, hepadna-, herpes-, adeno-, and poxvirus infections.

Acyclic nucleoside phosphonates: a key class of antiviral drugs

Almost 20 years after the broad antiviral activity spectrum of the first acyclic nucleoside phosphonates was described, several of these compounds have become important therapies for DNA virus and retrovirus infections. Here, we review the discovery and development of acyclic nucleoside phosphonates, focusing on cidofovir and its potential in the treatment of various herpes-, papilloma-, polyoma-, adeno- and pox-virus infections, adefovir for the treatment of hepatitis B and tenofovir for the treatment of AIDS and the prevention of HIV infections.

Protective effect of the acyclic nucleoside phosphonate tenofovir toward human T-cell leukemia/lymphotropic virus type 1 infection of human peripheral blood mononuclear cells in vitro

9-(R)-[(2-Phosphonomethoxy)propyls]adenine (tenofovir), is an acyclic nucleoside phosphonate known to inhibit HIV replication in vitro and to reduce viremia in HIV-infected patients. Here we have investigated whether tenofovir is able to protect peripheral blood mononuclear cells (PBMCs) from healthy donors against human T-cell leukemia/lymphotropic virus type 1 (HTLV-1) infection in vitro. PBMCs were pre-treated with tenofovir and infected by exposure to an irradiated cell line chronically harbouring HTLV-1. Measurements of viral DNA, as well as viral gene and protein expression, at 4 weeks after infection, revealed that tenofovir at concentrations of 1 microM and higher completely protected PBMCs against HTLV-1; lower concentrations did not fully prevent HTLV-1 infection of the cultures. Nevertheless, in the long term, cell growth of infected PBMCs was inhibited in vitro even by 0.1 microM tenofovir. In addition, tenofovir directly inhibited HTLV-1 reverse transcriptase activity, in a cell-free assay that utilizes a crude preparation from HTLV-1 viral particles as a source of the enzyme. The selectivity index of tenofovir for HTLV-1, was about four times higher than that of azidothymidine. Taken together our results strongly encourage further studies to investigate the real impact of tenofovir towards HTLV-1 infection.

Antiviral drug discovery and development: Where chemistry meets with biomedicine

The successful development of antiviral drugs is highly dependent on a close interaction and collaboration between the chemist and the biologist (biomedic). This is illustrated by a number of representative examples: S-adenosylhomocysteine (SAH) hydrolase inhibitors which display broad-spectrum antiviral activity, bromovinyldeoxyuridine (BVDU) and derivatives thereof, that are highly selective inhibitors of varicella-zoster virus (VZV), (dideoxy)nucleoside reverse transcriptase inhibitors (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs) which are now widely used in the treatment of HIV infections (AIDS), the bicyclams (i.e. AMD3100) which were originally discovered as anti-HIV agents, then found to be potent CXCR4 antagonists and now being pursued for a number of indications such as stem cell mobilization, and the acyclic nucleoside phosphonates which have heralded a new strategy for the treatment of various DNA virus (herpes-, adeno-, pox-, papillomavirus) infections (cidofovir), hepatitis B (adefovir) and AIDS (tenofovir).

Cellular export of drugs and signaling molecules by the ATP-binding cassette transporters MRP4 (ABCC4) and MRP5 (ABCC5)

Like other members of the multidrug resistance protein (MRP)/ABCC subfamily of ATP-binding cassette transporters, MRP4 (ABCC4) and MRP5 (ABCC5) are organic anion transporters. They have, however, the outstanding ability to transport nucleotides and nucleotide analogs. In vitro experiments using drug-selected or -transfected cells indicated that these transport proteins, when overexpressed, can lower the intracellular concentration of nucleoside/nucleotide analogs, such as the antiviral compounds PMEA (9-(2-phosphonylmethoxyethyl)adenine) or ganciclovir, and of anticancer nucleobase analogs, such as 6-mercaptopurine, after their conversion into the respective nucleotides. This may lead to an impaired ability of these compounds to inhibit virus replication or cell proliferation. It remains to be tested whether antiviral or anticancer chemotherapy based on nucleobase, nucleoside, or nucleotide precursors can be modulated by inhibition of MRP4 and MRP5. MRP4 also seems to be able to mediate the transport of conjugated steroids, prostaglandins, and glutathione. Furthermore, cyclic nucleotides (cyclic adenosine monophosphate and cyclic guanine monophosphate) are exported from cells by MRP4 and MRP5. This may modulate the intracellular concentration of these important mediators, besides the action of phosphodiesterases, as well as provide extracellular nucleotides for a possible paracrine action. In this line, tissue distribution and subcellular localization of MRP4 and MRP5 specifically in smooth muscle cells (MRP5), platelet-dense granules (MRP4), and nervous cells (MRP4 and MRP5), besides the capillary endothelium, point not only to a possible function of these transporters as exporters in cellular defense, but also to a physiological function in signaling processes.

Stampidine: a selective oculo-genital microbicide

Adenoviruses (ADVs) are causative agents of severe and extremely contagious ocular and genital infections associated with conjunctivitis, genital ulcers and urethritis. Yet, no functional antiviral compounds are currently available against adenoviral infections. We discovered halogen-substituted phenyl phosphoramidate derivatives of stavudine (STV/d4T) as a new class of dual-function anti-human immunodeficiency virus (HIV) agents with potent and selective anti-ADV activity. The lead compound, stampidine [5'-(4-bromophenyl methoxyalaninylphosphate)-2',3'-didehydro-3'-deoxythymidine], was the most potent non-toxic dual-function antiviral agent. Stampidine displayed remarkable in vitro and in vivo anti-HIV activity against drug-sensitive and drug-resistant HIV strains. Stampidine was non-cytotoxic and nonirritating to mucosal epithelial cells. Several preclinical studies conducted thus far, suggest that stampidine has clinical potential as a dual-function topical agent for the prevention and/or effective treatment of oculo-genital ADV/HIV infections.

Epidemiology, pathogenesis and prevention of congenital cytomegalovirus infection

Cytomegalovirus is the most common cause of congenital infection. Congenital cytomegalovirus infection can follow both primary and recurrent maternal infections. It is associated with a significant burden of disease and death. The determinants of mother-to-child transmission and the pathogenesis of symptomatic fetal infection remain poorly understood. For a long time, congenital cytomegalovirus infection has been a neglected disease. Recently, the Institute of Medicine has recognized that the development of a vaccine against congenital cytomegalovirus infection is a public health priority, which should stimulate research in this area. The development of antiviral therapies to prevent symptoms in infected newborns also represents an important area of research.

Comparison of the antiviral activities of alkoxyalkyl and alkyl esters of cidofovir against human and murine cytomegalovirus replication in vitro

Alkoxyalkyl esters of cidofovir (CDV) have substantially greater antiviral activity and selectivity than unmodified CDV against herpesviruses and orthopoxviruses in vitro. Enhancement of antiviral activity was also noted when cyclic CDV was esterified with alkoxyalkanols. In vitro antiviral activity of the most active analogs against human cytomegalovirus (HCMV) and orthopoxviruses was increased relative to CDV up to 1,000- or 200-fold, respectively. Alkyl chain length and linker structure are important potential modifiers of antiviral activity and selectivity. In this study, we synthesized a series of alkoxyalkyl esters of CDV or cyclic CDV with alkyl chains from 8 to 24 atoms and having linker moieties of glycerol, propanediol, and ethanediol. We also synthesized alkyl esters of CDV which lack the linker to determine if the alkoxyalkyl linker moiety is required for activity. The new compounds were evaluated in vitro against HCMV and murine CMV (MCMV). CDV or cyclic CDV analogs both with and without linker moieties were highly active against HCMV and MCMV, and their activities were strongly dependent on chain length. The most active compounds had 20 atoms esterified to the phosphonate of CDV. Both alkoxypropyl and alkyl esters of CDV provided enhanced antiviral activities against CMV in vitro. Thus, the oxypropyl linker moiety is not required for enhanced activity. CDV analogs having alkyl ethers linked to glycerol or ethanediol linker groups also demonstrated increased activity against CMV.

High prevalence of respiratory viral infections in patients hospitalized in an intensive care unit for acute respiratory infections as detected by nucleic acid-based assays

Forty-seven bronchoalveolar lavages (BAL) were obtained from 41 patients with acute pneumonia attending an intensive care unit. By molecular diagnosis, 30% of total BAL and 63% of bacteria-negative BAL were positive for respiratory viruses. Molecular detection allows for high-rate detection of respiratory viral infections in adult patients suffering from severe pneumonia.

Emerging therapies for herpes viral infections (types 1 – 8)

There are eight members of the herpesviridae family: herpes simplex virus-1 (HSV-1), HSV-2, varicella-zoster virus, Epstein-Barr virus, cytomegalovirus, human herpes virus-6, human herpes virus-7 and human herpes virus-8. The diseases caused by viruses of the herpesviridae family are treated with and managed by systemic and topical antiviral therapies and immunomodulating drugs. Because these viruses establish a latent state in hosts, antiherpetic agents, such as nucleoside analogues, only control symptoms of disease or prevent outbreaks, and cannot cure the infections. There is a need for treatments that require less frequent dosing, can be taken even when lesions are more advanced than the first signs or symptoms, and can treat resistant strains of the viruses without the toxicities of existing therapies. Immunomodulating agents, such as resiquimod, can act on the viruses indirectly by inducing host production of cytokines, and can thereby reduce recurrences of herpes. The new helicase primase inhibitors, which are the first non-nucleoside antiviral compounds, are being investigated for treatment of HSV disease, including infections resistant to existing therapy.

Delivery of antiviral agents in liposomes

The intracellular activity of certain antiviral agents, including antisense oligonucleotides, acyclic nucleoside phosphonates, and protease inhibitors, is enhanced when they are delivered in liposome-encapsulated form. In this chapter we describe the preparation of pH-sensitive liposomes encapsulating antisense oligonucleotides, ribozymes, and acyclic nucleoside phosphonate analogues and their effects on HIV replication in macrophages. We outline the use of liposomal HIV protease inhibitors in infected macrophages. We present two methods for the covalent coupling of soluble CD4 to liposomes and show the association of these liposomes with HIV-infected cells. We also describe the synthesis of a novel antiviral agent based on cyclodextrin and its incorporation into liposomes.

Intravesical Instillation of Cidofovir in the Treatment of Hemorrhagic Cystitis Caused by Adenovirus Type 11 in a Bone Marrow Transplant Recipient

Hemorrhagic cystitis that occurs late after bone marrow transplantation (BMT) in BMT recipients is often associated with adenovirus or polyomavirus BK infections. Intravesical instillation of cidofovir in a BMT recipient with intractable hemorrhagic cystitis resulted in clinical improvement. Local cidofovir therapy for viral hemorrhagic cystitis could be an alternative to intravenous administration of cidofovir.

Update on human herpesvirus 6 biology, clinical features, and therapy

Human herpesvirus 6 (HHV-6) is a betaherpesvirus that is closely related to human cytomegalovirus. It was discovered in 1986, and HHV-6 literature has expanded considerably in the past 10 years. We here present an up-to-date and complete overview of the recent developments concerning HHV-6 biological features, clinical associations, and therapeutic approaches. HHV-6 gene expression regulation and gene products have been systematically characterized, and the multiple interactions between HHV-6 and the host immune system have been explored. Moreover, the discovery of the cellular receptor for HHV-6, CD46, has shed a new light on HHV-6 cell tropism. Furthermore, the in vitro interactions between HHV-6 and other viruses, particularly human immunodeficiency virus, and their relevance for the in vivo situation are discussed, as well as the transactivating capacities of several HHV-6 proteins. The insight into the clinical spectrum of HHV-6 is still evolving and, apart from being recognized as a major pathogen in transplant recipients (as exemplified by the rising number of prospective clinical studies), its role in central nervous system disease has become increasingly apparent. Finally, we present an overview of therapeutic options for HHV-6 therapy (including modes of action and resistance mechanisms).

Antivirals and antiviral strategies

In this article, the usefulness, or potential usefulness, of the currently licensed antiviral drugs and those in clinical or preclinical development is evaluated. The main conclusions are:

For the treatment of polyomavirus, papillomavirus, adenovirus and poxvirus infections, the acyclic nucleoside phosphonates such as cidofovir have the greatest potential.

For the treatment of HSV and VZV infections, (val)acyclovir, famciclovir and brivudin are important.

For the treatment of CMV infections, (val)ganciclovir, cidofovir and foscarnet are the most promising.

Ribavirin is proposed for the treatment of (−)RNA virus (such as arenavirus and bunyavirus) infections, whereas IFN and IFN inducers are envisaged for the treatment of (+)RNA virus infections, particularly picornavirus (for example, coxsackie B) and togavirus (for example, Western, Eastern and Venezuelan equine encephalitis virus) infections.

For the treatment of HCV infections, pegylated IFN, in combination with ribavirin, is currently recommended, although compounds targeted at the HCV protease and RNA-dependent RNA polymerase have also been developed.

For the therapy and prophylaxis of influenza virus infections, the neuraminidase inhibitors zanamivir and oseltamivir are the current drugs of choice.

Among the paramyxoviruses, human metapneumovirus (hMPV) and respiratory syncytial virus (RSV) are the viruses for which antiviral therapy is most required. Although ribavirin is available for the treatment of RSV infections, it is not ideal, and therefore, new compounds are required for the treatment of hMPV and RSV infections.

A plethora of 'old' and 'new' compounds are available or are being developed for the treatment of HIV infections. Multiple drug regimens might be beneficial for HIV treatment.

For other virus infections —rotavirus, and Ebola, Marburg and other haemorrhagic virus infections — the choice of potential antiviral agents is rather limited, however, SAH hydrolase inhibitors such as 3-deazaneplanocin A are currently the most promising.

In recent years, the demand for new antiviral strategies has increased markedly. There are many contributing factors to this increased demand, including the ever-increasing prevalence of chronic viral infections such as HIV and hepatitis B and C, and the emergence of new viruses such as the SARS coronavirus. The potential danger of haemorrhagic fever viruses and eradicated viruses such as variola virus being used as bioterrorist weapons has also increased the profile of antiviral drug discovery. Here, the virus infections for which antiviral therapy is needed and the compounds that are available, or are being developed, for the treatment of these infections are described.

Antiviral therapy for treatment-naïve hepatitis B virus patients

Hepatitis B virus infection is a major public health problem worldwide,responsible for considerable morbidity and mortality from chronic liver disease. It is estimated that there are 350 million hepatitis B virus carriers globally. The prevalence of chronic hepatitis B infection varies greatly in different regions of the world. In the United States, approximately 1.5 million people are infected and 50,000 to 100,000 new cases are reported annually despite the availability of effective vaccines. This article reviews various antiviral therapies for treatment naïve hepatitis B virus patients.