Comparative efficacy and selectivity of some nucleoside analogs against Epstein-Barr virus

Selected nucleos(t)ide-based prescribed drugs and their multi-target activity

Nucleos(t)ide analogues play pivotal roles as antiviral, cytotoxic or immunosuppressive agents. Here, we review recent reports of nucleoside analogues that exhibit broad-spectrum activity towards multiple life-threatening RNA and DNA viruses. We also present a discussion about nucleoside antimetabolites-approved antineoplastic agents-that have recently been shown to have antiviral and/or antibacterial activity. The approved drugs and drug combinations, as well as recently identified candidates for investigation and/or experimentation, are discussed. Several examples of repurposed drugs that have already been approved for use are presented. This strategy can be crucial for the first-line treatment of acute infections or coinfections and for the management of drug-resistant strains.

Antiviral agents for infectious mononucleosis (glandular fever)

BACKGROUND

Infectious mononucleosis (IM) is a clinical syndrome, usually caused by the Epstein Barr virus (EPV), characterised by lymphadenopathy, fever and sore throat. Most cases of symptomatic IM occur in older teenagers or young adults. Usually IM is a benign self-limiting illness and requires only symptomatic treatment. However, occasionally the disease course can be complicated or prolonged and lead to decreased productivity in terms of school or work. Antiviral medications have been used to treat IM, but the use of antivirals for IM is controversial. They may be effective by preventing viral replication which helps to keep the virus inactive. However, there are no guidelines for antivirals in IM.

OBJECTIVES

To assess the effects of antiviral therapy for infectious mononucleosis (IM).

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, Issue 3, March 2016), which contains the Cochrane Acute Respiratory Infections (ARI) Group's Specialised Register, MEDLINE (1946 to 15 April 2016), Embase (1974 to 15 April 2016), CINAHL (1981 to 15 April 2016), LILACS (1982 to 15 April 2016) and Web of Science (1955 to 15 April 2016). We searched the World Health Organization (WHO) International Clinical Trials Registry Platform and ClinicalTrials.gov for completed and ongoing trials.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing antivirals versus placebo or no treatment in IM. We included trials of immunocompetent participants of any age or sex with clinical and laboratory-confirmed diagnosis of IM, who had symptoms for up to 14 days. Our primary outcomes were time to clinical recovery and adverse events and side effects of medication. Secondary outcomes included duration of abnormal clinical examination, complications, viral shedding, health-related quality of life, days missing from school or work and economic outcomes.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for inclusion, assessed the included studies' risk of bias and extracted data using a customised data extraction sheet. We used the GRADE criteria to rate the quality of the evidence. We pooled heterogeneous data where possible, and presented the results narratively where we could not statistically combine data.

MAIN RESULTS

We included seven RCTs with a total of 333 participants in our review. Three trials studied hospitalised patients, two trials were conducted in an outpatient setting, while the trial setting was unclear in two studies. Participants' ages ranged from two years to young adults. The type of antiviral, administration route, and treatment duration varied between the trials. The antivirals in the included studies were acyclovir, valomaciclovir and valacyclovir. Follow-up varied from 20 days to six months. The diagnosis of IM was based on clinical symptoms and laboratory parameters.The risk of bias for all included studies was either unclear or high risk of bias. The quality of evidence was graded as very low for all outcomes and so the results should be interpreted with caution. There were statistically significant improvements in the treatment group for two of the 12 outcomes. These improvements may be of limited clinical significance.There was a mean reduction in 'time to clinical recovery as assessed by physician' of five days in the treatment group but with wide confidence intervals (CIs) (95% CI -8.04 to -1.08; two studies, 87 participants). Prospective studies indicate that clinical signs and symptoms may take one month or more to resolve and that fatigue may be persistent in approximately 10% of patients at six-month follow-up, so this may not be a clinically meaningful result.Trial results for the outcome 'adverse events and side effects of medication' were reported narratively in only five studies. In some reports authors were unsure whether an adverse event was related to medication or complication of disease. These results could not be pooled due to the potential for double counting results but overall, the majority of trials reporting this outcome did not find any significant difference between treatment and control groups.There was a mean reduction in 'duration of lymphadenopathy' of nine days (95% CI -11.75 to -6.14, two studies, 61 participants) in favour of the treatment group.In terms of viral shedding, the overall effect from six studies was that viral shedding was suppressed while on antiviral treatment, but this effect was not sustained when treatment stopped.For all other outcomes there was no statistically significant difference between antiviral treatment and control groups.

AUTHORS' CONCLUSIONS

The effectiveness of antiviral agents (acyclovir, valomaciclovir and valacyclovir) in acute IM is uncertain. The quality of the evidence is very low. The majority of included studies were at unclear or high risk of bias and so questions remain about the effectiveness of this intervention. Although two of the 12 outcomes have results that favour treatment over control, the quality of the evidence of these results is very low and may not be clinically meaningful. Alongside the lack of evidence of effectiveness, decision makers need to consider the potential adverse events and possible associated costs, and antiviral resistance. Further research in this area is warranted.

Approved Antiviral Drugs over the Past 50 Years

Since the first antiviral drug, idoxuridine, was approved in 1963, 90 antiviral drugs categorized into 13 functional groups have been formally approved for the treatment of the following 9 human infectious diseases: (i) HIV infections (protease inhibitors, integrase inhibitors, entry inhibitors, nucleoside reverse transcriptase inhibitors, nonnucleoside reverse transcriptase inhibitors, and acyclic nucleoside phosphonate analogues), (ii) hepatitis B virus (HBV) infections (lamivudine, interferons, nucleoside analogues, and acyclic nucleoside phosphonate analogues), (iii) hepatitis C virus (HCV) infections (ribavirin, interferons, NS3/4A protease inhibitors, NS5A inhibitors, and NS5B polymerase inhibitors), (iv) herpesvirus infections (5-substituted 2'-deoxyuridine analogues, entry inhibitors, nucleoside analogues, pyrophosphate analogues, and acyclic guanosine analogues), (v) influenza virus infections (ribavirin, matrix 2 protein inhibitors, RNA polymerase inhibitors, and neuraminidase inhibitors), (vi) human cytomegalovirus infections (acyclic guanosine analogues, acyclic nucleoside phosphonate analogues, pyrophosphate analogues, and oligonucleotides), (vii) varicella-zoster virus infections (acyclic guanosine analogues, nucleoside analogues, 5-substituted 2'-deoxyuridine analogues, and antibodies), (viii) respiratory syncytial virus infections (ribavirin and antibodies), and (ix) external anogenital warts caused by human papillomavirus infections (imiquimod, sinecatechins, and podofilox). Here, we present for the first time a comprehensive overview of antiviral drugs approved over the past 50 years, shedding light on the development of effective antiviral treatments against current and emerging infectious diseases worldwide.

Inhibitory effects of some derivatives of glycyrrhizic acid against Epstein-Barr virus infection: structure-activity relationships

Glycyrrhizic acid (18β-GL or GL) is a herbal drug with a broad spectrum of antiviral activities and pharmacological effects and multiple sites of action. Previously we showed that GL inhibits Epstein-Barr virus (EBV) infection in vitro by interfering with an early step of the EBV replication cycle (possibly attachment/penetration). Here we tested the effects of 15 GL derivatives against EBV infection by scoring the numbers of cell expressing viral antigens and quantifying EBV DNA copy numbers in superinfected Raji cells. The derivatives were made either by transformation of GL on carboxyl and hydroxyl groups or by conjugation of amino acid residues into the carbohydrate part. We identified seven compounds active against EBV and all showed dose-dependent inhibition as determined by both assays. Among these active compounds, the introduction of amino acid residues into the GL carbohydrate part enhanced the antiviral activity in three of the seven active compounds. However, when Glu(OH)-OMe was substituted by Glu(OMe)-OMe, its antiviral activity was completely abolished. Introduction of potassium or ammonium salt to GL reduced the antiviral activity with no significant effect on cytotoxicity. The α-isomer (18α-GL) of 18β-GL was as potent as the β-form, but its sodium salt lost antiviral activity. The metabolic product of GL, 18β-glycyrrhetinic acid (18β-GA or GA), was 7.5-fold more active against EBV than its parental compound GL but, concomitantly, exhibited increased cytotoxicity resulting in a decreased therapeutic index.

A randomized trial of ganciclovir versus ganciclovir plus immune globulin for prophylaxis against Epstein-Barr virus related posttransplant lymphoproliferative disorder

BACKGROUND

Transplant recipients who are Epstein-Barr virus (EBV)-seronegative and receive organs from seropositive donors (EBV D+/R-) are at increased risk for posttransplant lymphoproliferative disorder (PTLD) and may benefit from antiviral prophylaxis. We performed a multi-center trial assessing two different antiviral regimens and their effect on EBV replication.

METHODS

EBV D+/R- solid organ transplant recipients were randomized to receive either ganciclovir and placebo or ganciclovir and immunoglobulin (IG) for 3 months. Following this, patients were unblinded and IG patients received additional IG therapy until 6 months. EBV viral loads were done at least monthly. RESULTS.: Thirty-four patients (25 pediatric, 9 adult) completed the protocol (16 placebo; 18 IG). The incidence of a detectable viral load within the first year posttransplant was 13/16 (81.3%) in the ganciclovir arm vs. 13/18 (72.2%) in the ganciclovir and IG arm (P=0.8). Time to first detectable viral load, and time to high-level viral load were not significantly different. By repeated measures ANOVA analysis, and by estimation of viral load AUC, no significant effect of randomization group was observed on EBV viral loads. PTLD developed in 3 (8.8%) patients (all in IG arm; P=0.23).

CONCLUSIONS

No significant difference in EBV viral load suppression was observed when ganciclovir was compared with ganciclovir and IG in high-risk EBV D+/R- patients.

Factors associated with the occurrence of AIDS-related non-Hodgkin lymphoma in the era of highly active antiretroviral therapy: Aquitaine Cohort, France

BACKGROUND

High grade non-Hodgkin lymphoma (NHL) remains the most common Acquired Immune Deficiency Syndrome (AIDS)-associated neoplasia and an important cause of mortality in people living with human immunodeficiency virus (HIV) infection in industrialized countries in the era of highly active antiretroviral therapy (HAART).

METHOD

A case-control study was implemented in a large cohort of HIV-infected patients. Case patients had newly diagnosed NHL, and control subjects were matched for CD4(+) cell count, calendar period, sex, and length of follow-up.

RESULTS

Variables associated with a decreased risk of NHL were the use of HAART during follow-up for at least 6 months (odds ratio [OR], 0.46; 95% confidence interval [CI], 0.21-0.98), receipt of a diagnosis of AIDS before the censoring date (OR, 0.37; 95% CI, 0.18-0.76), and undetectable level of HIV RNA during follow-up (OR, 0.34; 95% CI, 0.15-0.77). The use of antiherpetic drug for at least 6 months was associated with a nonsignificant decreased risk of NHL (OR, 0.40; 95% CI, 0.11-1.44; P=.16). In multivariate analysis, variables significantly associated with a decreased risk of NHL were the use of HAART for at least 6 months during follow-up (OR, 0.37; 95% CI, 0.16-0.87) and receipt of an AIDS-related diagnosis before the censoring date (OR, 0.44; 95% CI, 0.21-0.93). Age, transmission group, hepatitis B and C coinfections, CD4(+) and CD8(+) cell count nadir, and previous history of herpes virus infection were not associated with an increased risk for NHL.

CONCLUSION

The use of HAART for at least 6 months was associated with a decreased risk of NHL, whereas uncontrolled HIV RNA load may be associated with an increased risk. The role of antiherpetic drugs needs further investigation.

Mechanism of action of glycyrrhizic acid in inhibition of Epstein-Barr virus replication in vitro

We report here that glycyrrhizic acid (GL), a component of licorice root (Glycyrrhiza radix), is active against EBV replication in superinfected Raji cells in a dose-dependent fashion. The IC(50) values for viral inhibition and cell growth were 0.04 and 4.8mM, respectively. The selectivity index (ratio of IC(50) for cell growth to IC(50) for viral DNA synthesis) was 120. Time of addition experiments suggested that GL interferes with an early step of EBV replication cycle (possibly penetration). GL had no effect on viral adsorption, nor did it inactivate EBV particles. Thus, GL represents a new class of anti-EBV compounds with a mode of action different from that of the nucleoside analogs that inhibit viral DNA polymerase.

Epstein-Barr virus-related post-transplant lymphoproliferative disease in solid organ transplant recipients, 1988-97: a Canadian multi-centre experience

The aim of this work was to obtain information on the magnitude of the problem, disease characteristics, and clinical practices relating to post-transplant lymphoproliferative disease (PTLD) in Canadian institutions. Adult and pediatric Canadian solid organ transplant groups were sent a questionnaire between July and October 1998. Analyzable data were obtained from 33 transplant groups. For the period 1988-97, 90 cases of PTLD were seen among 4283 solid organ transplant recipients. The incidence of PTLD varied from 0 to 14.6%, with the highest rates in children. Lymph nodes were the sites most frequently affected. Among the classifiable lesions, the majority were monoclonal. The lesions were of B-cell origin in 42.2% and of T-cell in 15.6%. The lesions were classified as monomorphic in 31.1%, polymorphic 18.9%, and hyperplastic in 1.1%. Tumors were reported as low grade in 26.7% and high grade in 10%. The majority of patients (71.1%) received reduced immunosuppression. Anti-viral agents were used in 52.2%. Chemotherapy was used in 27.8%, while immune globulin was used in 22.2%. Surgical resection was used in 20.0%, radiotherapy in 14.4%, and interferon-alpha therapy in 12.2%. The results showed that 48.9% of the patients had died, while 25.6% and 8.9% were regarded as having complete remission and partial remission, respectively. In conclusion, the incidence of PTLD varies widely across Canadian centres. Children are disproportionately affected and the mortality rate is high. Management practices vary significantly, and the need for information sharing was identified as one way of optimizing management.

Synthesis, hydrolysis and anti-EBV activity of a series of 3'-modified cycloSal-BVDUMP pronucleotides

A series of cycloSal-BVDUMP phosphate triesters has been prepared. The prototype compound was 3-methyl-cycloSal-BVDUMP 2. Furthermore, a series of 3'-O-acyl-modified derivatives having carboxylic acids with different lipophilicity or a L-configurated alpha-amino acid (phenylalanine) was prepared. The hydrolysis properties in phosphate buffer PBS as well as in PBS containing pig liver esterase (PLE) will be described. Finally, the biological activity against EBV has been determined.

Value of long-term administration of acyclovir and similar agents for protecting against AIDS-related lymphoma: case-control and historical cohort studies

Acyclovir or similar agents with activity against Epstein-Barr virus (EBV) theoretically may prevent non-Hodgkin's lymphoma (NHL) in AIDS. A case-control study of 29 patients with AIDS-related NHL and 58 matched control subjects assessed the frequency with which daily acyclovir (>/=800 mg/d) or similar agents were used for > or =1 year. In a historical cohort of 304 patients with AIDS for > or =2 years, the prevalence of NHL was assessed among 3 groups of patients: those who received long-term treatment with high-dose acyclovir (or similar agents) or low-dose or intermittent acyclovir; those treated with ganciclovir/foscarnet for <1 year; and those who had not previously been treated with acyclovir, ganciclovir, or foscarnet. In the case-control study, 22 patients (72.4%) with NHL never received acyclovir or similar drugs versus 19 control subjects (32.8%; P=. 002); 2 patients (6.9%) with NHL received acyclovir (> or =800 mg/d) for > or =1 year versus 27 (46.6%) of control subjects (P=.0001). In the cohort study, 6 (6.8%) of 88 patients who received acyclovir (> or =800 mg/d) for > or =1 year developed NHL versus 15 (15.5%) of 97 patients who received intermittent or lower-dose acyclovir and 30 (25.2%) of 119 patients who never received these agents (P=.002). Long-term administration (>1 year) of high-dose acyclovir or similar agents with anti-EBV activity may prevent NHL in patients with AIDS. A prospective, randomized study is warranted to confirm these results.

Epstein-Barr virus-induced posttransplant lymphoproliferative disorders. ASTS/ASTP EBV-PTLD Task Force and The Mayo Clinic Organized International Consensus Development Meeting

Epstein-Barr virus-induced posttransplant lymphoproliferative disease (EBV-PTLD) continues to be a major complication after solid organ transplantation in high-risk patients. Despite the identification of risk factors that predispose patients to develop EBV-PTLD, limitations in our knowledge of its pathogenesis, variable criteria for establishing the diagnosis, and lack of randomized studies addressing the prevention and treatment of EBV-PTLD hamper the optimal management of this transplant complication. This review summarizes the current knowledge of EBV-PTLD and, as a result of two separate international meetings on this topic, and provides recommendations for future areas of study.

Inhibition of Epstein-Barr virus replication by a benzimidazole L-riboside: novel antiviral mechanism of 5, 6-dichloro-2-(isopropylamino)-1-beta-L-ribofuranosyl-1H-benzimidazole

Although a number of antiviral drugs inhibit replication of Epstein-Barr virus (EBV) in cell culture, and acyclovir (ACV) suppresses replication in vivo, currently available drugs have not proven effective for treatment of EBV-associated diseases other than oral hairy leukoplakia. Benzimidazole riboside compounds represent a new class of antiviral compounds that are potent inhibitors of human cytomegalovirus (HCMV) replication but not of other herpesviruses. Here we characterize the effects of two compounds in this class against lytic replication of EBV induced in a Burkitt lymphoma cell line latently infected with EBV. We analyzed linear forms of EBV genomes, indicative of lytic replication, and episomal forms present in latently infected cells by terminal probe analysis followed by Southern blot hybridization as well as the high-molecular-weight unprocessed viral DNA by pulsed-field gel electrophoresis. D-Ribofuranosyl benzimidazole compounds that act as inhibitors of HCMV DNA maturation, including BDCRB (5, 6-dichloro-2-bromo-1-beta-D-ribofuranosyl-1H-benzimidazole), did not affect the accumulation of high-molecular-weight or monomeric forms of EBV DNA in the induced cells. In contrast, the generation of linear EBV DNA as well as precursor viral DNA was sensitive to the L-riboside 1263W94 [5, 6-dichloro-2-(isopropylamino)-1-beta-L-ribofuranosyl-1H-benzimidazole]. The 50% inhibitory concentration range for 1263W94 was 0.15 to 1. 1 microM, compared with 10 microM for ACV. Thus, 1263W94 is a potent inhibitor of EBV. In addition, 1263W94 inhibited the phosphorylation and the accumulation of the essential EBV replicative cofactor, early antigen D.

Unique inhibitory effect of 1-(2'-deoxy-2'-fluoro-beta-L-arabinofuranosyl)-5-methyluracil 5'-triphosphate on Epstein-Barr virus and human DNA polymerases

1-(2'-Deoxy-2'-fluoro-beta-L-arabinofuranosyl)-5-methyluracil (L-FMAU) was shown to have potent antiviral activity against Epstein-Barr virus (EBV) without any cellular toxicity at concentrations up to 200 microM (Yao et al., Biochem Pharmacol 51: 941-947, 1996). The 5'-triphosphate of L-FMAU was not a substrate for EBV or cellular DNA polymerases, but could inhibit the elongation reaction, 3'-to-5' exonuclease activity, and nucleotide turnover catalyzed by EBV DNA polymerase. DNA synthesis catalyzed by human DNA polymerases was inhibited to a lesser extent. The inhibition pattern of EBV DNA polymerase by L-FMAU-5'-triphosphate (L-FMAU-TP) was consistent with an uncompetitive mechanism when dNTP or template-primer were used as the variable substrates. The Ki values were 38+/-10 microM for the elongation reaction, and about 50+/-10 microM for both nucleotide exchange and 3'-to-5' exonuclease reactions, values that were 10-20 times less than that for GMP. L-FMAU-TP is the first nucleoside 5'-triphosphate shown to have such unique behavior toward DNA polymerases. EBV DNA polymerase could be one of the targets for the inhibitory effect of L-FMAU-TP on EBV replication.

Inhibition of the Synthesis of Proteins Needed for Epstein-Barr Virus Replication by Antisense RNA against the Zta Gene

Antisense RNA complementary to the Epstein-Barr virus (EBV) Zta gene, an immediate-early gene encoding a transactivator, was applied to inhibit EBV protein synthesis during its lytic cycle. A DNA fragment containing the Zta gene sequence was inserted into an expression vector, pMAMneo, in a sense and antisense direction under a dexamethasone-inducible murine mammary tumor virus LTR promoter, resulting in the construction of plasmids pZ(+) and pZ(-), respectively. Synthesis of Zta protein was reduced in pZ(-)-transfected cells upon dexamethasone induction. Because D-form early antigen and DNA polymerase are essential for viral DNA replication, the contents of these two viral proteins were examined. Amounts of the two lytic proteins were observed to be significantly repressed in pZ(-)-transfected cells. In contrast, both proteins were normally expressed in the sense plasmid pZ(+) or cells transfected with vector alone. Above results demonstrate that Zta antisense RNA can reduce the production of Zta protein and the other lytic proteins, possibly resulting in the inhibition of EBV replication. Copyright 1997 S. Karger AG, Basel

Inhibition of Epstein-Barr virus replication by a novel L-nucleoside, 2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil

A novel L-nucleoside analog, 2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil (L-FMAU), was found to be a potent and selective inhibitor of Epstein-Barr virus (EBV) replication. The decrease in the amount of viral production was concentration dependent with a 90% inhibitory concentration of approximately 5 muM. Upon removal of the drug from treated cells, virus production resumed in 21 days. Metabolism studies indicated that L-FMAU could be converted to its mono-,di- and triphosphate metabolites in both EBV producing and non-producing cells than in EBV non-producing cells. The mechanism of selectivity of L-FMAU against EBV producing cells. However, the amount of L-FMAU nucleotides formed was three times larger in EBV producing cells than in EBV non-producing cells. The mechanism of selectivity of L-FMAU against EBV does not appear to be due solely to the preferential phosphorylation of L-FMAU in EBV producing cells. The triphosphate of L-FMAU could not be utilized as a substrate by EBV DNA polymerase or the human DNA polymerases alpha, beta, gamma, or delta. Therefore, the incorporation of L-FMAU residues into viral DNA may not be the mechanism of antiviral activity. This compound appears to have a mechanism of action different from that of any other antiherpes virus nucleoside analogs. In addition, L-FMAU has very low cytotoxicity with 50% inhibition of cell growth occurring at a concentration of 1mM. Given the potent inhibitory activity of this compound against EBV and its inability to be incorporated into cellular DNA, L-FMAU analogs should be explored as a new class of anti-EBV agents.

Substrate specificity of Epstein-Barr virus thymidine kinase

Purified recombinant protein encoded by the BXLF-I open reading frame of the Epstein-Barr virus genome has thymidine kinase activity. The substrate behaviors of various nucleosides toward this enzyme were tested. Halogenated deoxyuridines, zidovudine, and bromovinyldeoxyuridine are efficient substrates, while acyclovir and dihydroxypropylmethylguanine are relatively poor substrates for the Epstein-Barr virus thymidine kinase.

Potent inhibition of Epstein-Barr virus by phosphorothioate oligodeoxynucleotides without sequence specification

We found that 28-mer phosphorothioate oligodeoxynucleotides (S-oligos) with and without sequence specificity complementary to Epstein-Barr virus (EBV) genes are potent inhibitors of EBV replication in cell culture. The decrease in the amount of EBV DNA, the activity of intracellular viral DNA polymerase, and virus production were dose dependent, with a 90% inhibitory dose of approximately 0.5 microM. No inhibition of cell growth was observed with the S-oligos at concentrations up to 20 microM. The mechanism of action appears to be the inhibition of EBV DNA synthesis. The reversibility of anti-EBV action is dependent on the dose and duration of drug exposure. S-oligos should be considered a new class of anti-EBV agents.

Structure-activity relationship between (E)-5-(2-bromovinyl)- and 5-vinyl-1-beta-D-arabinofuranosyluracil (BV-araU, V-araU) in inhibition of Epstein-Barr virus replication

The structure-activity relationship between (E)-5-(2-bromovinyl)- and 5-vinyl-1-beta-D-arabinofuranosyluracil (BV-araU and V-araU) in inhibition of Epstein-Barr virus (EBV) was evaluated. Both V-araU and BV-araU effectively inhibited EBV replication in virus-producer P3HR-1(LS) cells, as determined by DNA-DNA hybridization. The 50% effective doses (ED50) for viral DNA replication were 0.005 and 0.3 microM for V-araU and BV-araU, respectively. The in vitro therapeutic index was 4000 for V-araU and 1300 for BV-araU. Synthesis of EBV-induced polypeptides with molecular weights of 145,000 (145, 140, 130, and 110 kDa) was significantly inhibited by both drugs. Only V-araU inhibited the synthesis of 85-, 55-, and 32-kDa polypeptides by approx. 50%. Kinetic analysis of inhibition and reversibility of EBV DNA replication after removal of the drugs indicated that BV-araU has a more prolonged inhibitory effect than V-araU. These results indicate that the substitution of H by Br in the 5-vinyl group results in marked reduction in anti-EBV activity while prolonging the drug effect and diminishing cytotoxicity.

Identification and functional characterization of Epstein-Barr virus DNA polymerase by in vitro transcription-translation of a cloned gene

In order to identify the gene encoding the Epstein-Barr virus (EBV) DNA polymerase, a portion of the BamHI-A fragment containing the fifth leftward open reading frame (BALF5) of the EBV genome was cloned into SP6 and T7 promoter-containing vectors for in vitro transcription-translation. The RNA synthesized in vitro was used to program rabbit reticulocyte lysates, which were analyzed for the synthesis of the putative polymerase polypeptide (110 kDa) and assayed directly for EBV DNA polymerase activity. The polypeptide synthesized by the full-length BALF5 genomic fragment had a molecular mass of 110 kDa. 5'-truncated BALF5 with the first and second ATGs deleted produced 95- and 83-kDa polypeptides, respectively. All three translation products were enzymatically active and displayed resistance to high salt concentrations. The identity of the largest polypeptide as the viral polymerase was established by (i) immunoprecipitation with EBV-positive sera from patients with nasopharyngeal carcinoma and by a rabbit polyclonal antiserum prepared with a synthetic peptide derived from the DNA sequence of BALF5; (ii) identification of a polypeptide of identical size (110 kDa) immunoprecipitated from superinfected Raji cell extracts by these antibodies; and (iii) salt-resistant enzymatic activity which was neutralized by the rabbit EBV antiserum. Thus, BALF5 encodes a functional polymerase identical to that induced in superinfected Raji cells.

Ganciclovir. A review of its antiviral activity, pharmacokinetic properties and therapeutic efficacy in cytomegalovirus infections

Ganciclovir is a nucleoside analogue with antiviral activity in vitro against members of the herpes group and some other DNA viruses. It has demonstrated efficacy against human cytomegalovirus infections and should be considered a first-line therapy in the treatment of life- or sight-threatening cytomegalovirus infection in immunocompromised patients. Clinical efficacy varies with the underlying aetiology of immunocompromise and the site of disease, and prompt diagnosis and early treatment initiation appear to improve the response. In patients with cytomegalovirus pneumonia, particularly bone marrow transplant recipients, concomitant administration of cytomegalovirus immune globulin may significantly improve clinical outcome. Maintenance therapy to prevent recurrence is usually required by bone marrow transplant recipients until the recovery of adequate immune function, whereas AIDS patients may require indefinite ganciclovir maintenance therapy to prevent disease progression, as ganciclovir (like other antivirals) does not eradicate latent viral infection. Haematological effects occur relatively frequently during ganciclovir administration but are usually reversible. Ganciclovir has not been directly compared with other antiviral drugs because of the absence until recently of other effective treatments. However, comparative studies with foscarnet, particularly in cytomegalovirus retinitis, will be of considerable interest. Thus, ganciclovir represents a major advance in the therapy of severe cytomegalovirus infections in immunocompromised patients. Comparative studies, and investigation of ways of reducing toxicity (intravitreal administration; concomitant use of stimulants of haematopoiesis; use in conjunction with other antivirals with differing mechanisms of action), may further expand its eventual role.

Characterization of the Epstein-Barr virus-encoded thymidine kinase expressed in heterologous eucaryotic and procaryotic systems

The establishment of mammalian and procaryotic systems which express the Epstein-Barr virus (EBV) thymidine kinase (TK) has been reported previously (E. Littler, J. Zeuthen, A. A. McBride, E. Trøst-Sørensen, K. L. Powell, J. E. Walsh-Arrand, and J. R. Arrand, EMBO J. 5:1959-1966, 1986). The EBV TK activity expressed in both of these systems was characterized by in vitro assays and found to resemble that of the herpes simplex virus TK both in its broad range of nucleoside and nucleotide utilization and also in its ability to accept antiviral nucleoside analogs as substrates. Further results are presented which suggest that these in vitro systems may prove suitable for studying the potential anti-EBV activity of other candidate antiviral compounds.

Comparison of two bromovinyl nucleoside analogs, 1-beta-D-arabinofuranosyl-E-5-(2-bromovinyl)uracil and E-5-(2-bromovinyl)-2'-deoxyuridine, with acyclovir in inhibition of Epstein-Barr virus replication

The effect of 1-beta-D-arabinofuranosyl-E-5-(2-bromovinyl)uracil (BV-araU), a new antiviral drug, on Epstein-Barr virus (EBV) was studied and compared with those of E-5-(2-bromovinyl)-2'-deoxyuridine (BVdU) and acyclovir (ACV). BV-araU effectively inhibited EBV replication both in superinfected Raji cells and in virus producer P3HR-1(LS) cells, as determined by density gradient centrifugation, in situ cytohybridization with an EBV DNA probe, and cRNA-DNA hybridization. The 50% effective doses for viral DNA replication were 0.26, 0.06, and 0.3 microM for BV-araU, BVdU, and ACV, respectively. The relative efficacy on the basis of the in vitro therapeutic index was BVdU (6,500) greater than BV-araU (1,500) greater than ACV (850). Synthesis of EBV-induced polypeptides with molecular weights of 145,000 and 140,000 was inhibited by these drugs. Kinetic analysis of reversibility of inhibition of EBV DNA replication after removal of the drugs indicated that BV-araU, like BVdU, has a more prolonged inhibitory effect than ACV. These results indicate that the 2' OH group in the arabinosyl configuration of BV-araU results in marked reduction in anti-EBV activity while slightly diminishing cytotoxicity.

Anti-human immunodeficiency virus agent 3'-azido-3'-deoxythymidine inhibits replication of Epstein-Barr virus

We show that the anti-human immunodeficiency virus agent, 3'-azido-3'-deoxythymidine (AZT), which suppresses infectivity and cytopathic effects of human immunodeficiency virus, also effectively inhibits Epstein-Barr virus (EBV) DNA replication. However, AZT has no effect on four other human herpesviruses: cytomegalovirus, varicella-zoster virus, and herpes simplex virus types 1 and 2. The combination of acyclovir and AZT, while it is not synergistic, has an additive effect against EBV replication. AZT may prove to be a useful drug for treatment of coinfections with human immunodeficiency virus and EBV.

In vitro activity of cefmetazole, cefotetan, amoxicillin-clavulanic acid, and other antimicrobial agents against anaerobic bacteria from endometrial cultures of women with pelvic infections

The MICs of the new antimicrobial agents cefmetazole, cefotetan, and amoxicillin-clauvulanic acid were compared with the MICs of other antimicrobial agents against anaerobic bacteria from endometrial cultures from women with pelvic inflammatory disease or endometritis. The activity of cefmetazole was similar to that of cefoxitin and generally greater than that of cefotetan. Amoxicillin-clavulanic acid was generally more active than all cephamycins tested.

Metabolic activation of 9([2-hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine in human lymphoblastoid cell lines infected with Epstein-Barr virus

9-([2-Hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine (BW B759U) is more potent and has a more prolonged inhibitory effect against Epstein-Barr virus (EBV) in vitro than does acyclovir (ACV). To assess the mechanism of this difference, we first compared the extent of phosphorylation of the two drugs in superinfected Raji cells. BW B759U is phosphorylated to levels 100-fold higher than is ACV. In addition, lower levels of phosphorylation of BW B759U and ACV were observed in uninfected Raji cells. Studies on the kinetics of formation of BW B759U triphosphate in superinfected Raji cells indicated that drug-phosphorylating activity was detected as early as 3 h after superinfection; this activity was steadily maintained for the first 7 h, followed by a burst of activity between 7 and 10 h and a doubling of phosphorylation between 10 and 25 h. During the superinfection cycle, the pool sizes of deoxyribonucleoside and ribonucleoside triphosphates were increased and reached their maxima at 10 h after infection. The maximal amount of triphosphorylated drug in a virus producer cell, P3HR-1 (LS), was obtained at 21 h after drug treatment. During long-term drug treatment, approximately 44 and 77% reduction in EBV genome copies per cell was observed on days 3 and 7, respectively. In a separate experiment, after treatment of P3HR-1 (LS) cells with BW B759U for 36 h, 4.2 pmol of BW B759U triphosphate per 10(6) cells was achieved. After the cells were released into drug-free medium, drug triphosphate was rapidly decreased to 11% of the original level in 1 day. Thereafter, the decrease was slow but steady, down to 0.22 pmol/10(6) P3HR-1 cells by 5 days. We calculated that 0.22 pmol of BW B759U triphosphate per 10(6) cells represents a cellular concentration of 0.22 microM, which is theoretically enough to inhibit EBV replication. This is based upon a comparison with the 50% effective dose of BW B759U (0.05 microM) for inhibition of genome replication and a Ki of 0.08 microM for BW B759U triphosphate inhibition of EBV DNA polymerase.

Effect of (E)-5-(2-bromovinyl)-2'-deoxyuridine on replication of Epstein-Barr virus in human lymphoblastoid cell lines

The effect of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) on replication of Epstein-Barr virus (EBV) was investigated and compared with Acyclovir (ACV). Both drugs inhibited EBV replication very rapidly. However, the inhibitory effect of ACV was readily reversed after removal of the drug, in contrast to the more prolonged effect exerted by BVDU, which persisted for more than 21 days. The 50% inhibitory doses of BVDU for virus replication (ED50) and lymphoblastoid cell growth (ID50) were 0.06 microM and 390 microM, respectively; the in vitro therapeutic index (ID50/ED50) was 6,500. Synthesis of EBV-induced polypeptides with molecular weights of 145K, 140K and 110K was partially reduced by BVDU. When superinfected Raji cells were exposed to 125I-labeled (E)-5-(2-iodovinyl)-2'-deoxyuridine (IVDU), larger amounts of (125I)IVDU were incorporated into viral DNA than cellular DNA.