Showing papers in "Antiviral Therapy in 1998"

Low plasma concentrations of indinavir are related to virological treatment failure in HIV-1-infected patients on indinavir-containing triple therapy.

Abstract: All human immunodeficiency virus type 1 (HIV-1)-infected patients who started to use indinavir (800 mg three times a day) as part of their triple drug regimen were included in a study to determine the importance of low plasma concentrations of indinavir as a cause of virological treatment failure. The indinavir concentration and a number of patient characteristics at baseline were tested as risk factors for virological treatment failure (defined as a viral load above 200 copies/ml after 24 weeks of treatment) in univariate and multivariate analyses; 65 patients were included. Virological treatment failure occurred in 36.9% of the patients. Multivariate analysis showed that a low plasma concentration of indinavir (odds ratio 0.1), a high viral load at baseline (odds ratio 2.6) and pretreatment with another protease inhibitor (odds ratio 10.0) were independent factors related to virological treatment failure. Monitoring of indinavir plasma concentrations may be an important tool for the optimization of triple drug combination therapy.

Preclinical investigation of L-FMAU as an anti-hepatitis B virus agent.

Abstract: Preclinical aspects of a potent anti-hepatitis B virus (HBV) L-nucleoside, 1-(2-fluoro-5-methyl-beta-L-arabino-furanosyl)uracil (L-FMAU) are described. L-FMAU was prepared from L-ribose derivatives via either L-xylose or L-arabinose. L-FMAU shows potent antiviral activity against hepatitis B virus (EC50 5.0 microM in H1 cells) with high selectivity in vitro. L-FMAU is not incorporated into mitochondrial DNA and no significant lactic acid production was observed in vitro. L-FMAU is phosphorylated by thymidine kinase as well as deoxycytidine kinase, ultimately to the triphosphate, which inhibits HBV DNA polymerase as the mechanism of antiviral action. Preliminary in vivo toxological studies suggest no apparent toxicity for 30 days at 50 mg/kg/day in mice and for 3 months in woodchucks (10 mg/kg/day). L-FMAU also has respectable bioavailability in rats. L-FMAU shows potent anti-HBV activity in vivo against woodchuck hepatitis virus in chronically infected woodchucks and there is no significant virus rebound after cessation of the drug treatment.

Coinfection by hepatitis B virus and hepatitis C virus.

Abstract: Coinfection by hepatotropic viruses can occur due to the fact that hepatitis B virus (HBV) and hepatitis C virus (HCV) share similar routes of transmission. Different clinical features of liver disease can be observed in infected patients, ranging from fulminant, acute and chronic hepatitis to hepatocellular carcinoma (HCC). The relative role of the infecting viruses in determining the final clinical picture is not yet well defined. Several reports indicate that clinical and pathological severity of liver disease among coinfected patients is increased and in patients with HCC, co-occurrence of both viruses is a common event. The potential mechanism of tumour development still remains speculative, although direct and indirect roles for both HBV and HCV have been proposed. At the molecular level, reciprocal interference of virus replication has been repeatedly described and the extent of interference is influenced by the infecting HCV genotype, genotype 1 of HCV having more efficient inhibitory activity on HBV than genotype 2. Sequence similarities between an arginine-rich nucleocapsid motif of both viruses could support these clinical observations. Concerning response rates to interferon therapy, no satisfactory results have been achieved to date, although identification of effective therapeutic schemes, based on virological status of both viruses are warranted.

The immunopathogenesis of HBV infection.

Abstract: Clinical manifestations of hepatitis B virus (HBV) infection are a balance between viral and host factors. The immune response against any virus consists of a coordinated defence of innate immunity and acquired, virus-specific immunity. In acute HBV, immune responses associated with recovery include vigorous, polyclonal CD4 T cells directed against multiple epitopes within HBV; antibodies directed against surface envelope proteins (anti-HBs), the development of which requires the presence of a CD4 response; and HBV-specific cytotoxic T lymphocytes (CTLs). HBV-specific CTLs can induce death of infected hepatocytes as well as produce cytokines. Most individuals with acute HBV recover without evidence of massive liver destruction; this, plus evidence from transgenic animal models, suggests that these cytokines produced by T cells play an important role in controlling HBV replication. Individuals who fail to mount a vigorous response in acute HBV develop chronic infection. In these cases, the persisting ineffective immune response appears to be responsible for liver damage and is likely to initiate the process of hepatic fibrosis. Based on our current understanding of the immune response in acute and chronic HBV, several groups are investigating the prospect of manipulating the immune response in chronic HBV.

Molecular virology of hepatitis C virus: an update with respect to potential antiviral targets.

Abstract: Hepatitis C virus (HCV), a positive-strand enveloped RNA virus, is a major cause of chronic liver disease worldwide. Cis-acting RNA elements and virus-encoded polypeptides required for HCV replication represent attractive targets for the development of antiviral therapies. Internal ribosome entry site-directed translation of HCV genome RNA produces a long polyprotein which is co- and post-translationally processed to yield at least 10 viral proteins. A host signal peptidase is responsible for maturation of the structural proteins located in the N-terminal one-third of the polyprotein. Thus far, four enzymatic activities encoded by the non-structural (NS) proteins have been reported. The NS2-3 region encodes an autoproteinase responsible for cleavage at the 2/3 site. The N-terminal one-third of NS3 functions as the catalytic subunit of a serine proteinase which cleaves at the 3/4A, 4A/4B, 4B/5A and 5A/5B sites, and NS4A is an essential cofactor for some of these cleavages. NS3 also encodes an RNA-stimulated NTPase/RNA helicase at its C terminus, and NS5B has been shown to possess an RNA-dependent RNA polymerase activity. To date, no functions have been reported for NS4B or NS5A in RNA replication, however, NS5A has been implicated in modulating the sensitivity of HCV to interferon. Sequence and structural conservation within the 3' terminal 98 bases of genomic RNA suggest a functional importance in the virus life-cycle and hence another target for antiviral intervention. Recently, HCV infection was shown to be initiated in chimpanzees following intrahepatic inoculation of RNA transcribed from cloned HCV cDNA. The ability to generate large quantities of infectious HCV RNA may facilitate the development of reliable cell culture replication systems useful for the evaluation of antiviral drugs.

Prevalence of hepatitis B and C in Egypt and Africa.

Abstract: Hepatitis B and C are, and will remain for some time, major health problems in Egypt and the entire continent of Africa. Both infections can lead to an acute or silent course of liver disease, progressing from liver impairment to cirrhosis and decompensated liver failure or hepatocellular carcinoma (HCC) in a 20-30 year period. In addition, hepatitis B and C infection rates differ in different settings, and prognosis may be worse in conjunction with schistosomiasis in Egypt, malaria in Sudan and human immunodeficiency virus (HIV) in other African populations. Unlike hepatitis B virus (HBV), for which the prospects for controlling the spread of infection by vaccination are promising, prospects for development of an effective vaccine against hepatitis C virus (HCV) are limited. As well as screening of blood for transfusion and using sterile needles for injection, preventive measures should be undertaken to reduce the risk of contact (often described as community-acquired infection). Until more is known about the unidentified routes of transmission in tropical and subtropical settings it will be difficult to be specific about the kind of measures which may be effective. Success may largely depend on changing habits within the population. Prevention should be the main goal of current efforts until low-cost, effective therapies become available.

Lipid evaluation in HIV-1-positive patients treated with protease inhibitors.

Abstract: There is accumulating evidence that human immunodeficiency virus type 1 (HIV-1) protease inhibitors (PIs) can induce hyperlipidaemia. To evaluate the frequency and type of hyperlipidaemia in PI-tre...

The hepatitis C virus NS3 proteinase: structure and function of a zinc-containing serine proteinase.

Abstract: The hepatitis C virus (HCV) NS3 protein contains a serine proteinase domain implicated in the maturation of the viral polyprotein. NS3 forms a stable heterodimer with NS4A, a viral membrane protein that acts as an activator of the NS3 proteinase. The three-dimensional structure of the NS3 proteinase complexed with an NS4A-derived peptide has been determined. The NS3 proteinase adopts a chymotrypsin-like fold. A beta-strand contributed by NS4A is clamped between two beta-strands within the N terminus of NS3. Consistent with the requirement for extraordinarily long peptide substrates (P6-P4'), the structure of the NS3 proteinase reveals a very long, solvent-exposed substrate-binding site. The primary specificity pocket of the enzyme is shallow and closed at its bottom by Phe-154, explaining the preference of the NS3 proteinase for cysteine residues in the substrate P1 position. Another important feature of the NS3 proteinase is the presence of a tetrahedral zinc-binding site formed by residues Cys-97, Cys-99, Cys-145 and His-149. The zinc-binding site has a role in maintaining the structural stability and guiding the folding of the NS3 serine proteinase domain. Inhibition of the NS3 proteinase activity is regarded as a promising strategy to control the disease caused by HCV. Remarkably, the NS3 proteinase is susceptible to inhibition by the N-terminal cleavage products of substrate peptides corresponding to the NS4A/NS4B, NS4B/NS5A and NS5A/NS5B cleavage sites. The Ki values of the inhibitory products are lower than the K(m) values of the respective substrates and follow the order NS4A < NS5A < NS4B. Starting from the observation that the NS3 proteinase undergoes product inhibition, very potent, active site-directed inhibitors have been generated using a combinatorial peptide chemistry approach.

Opportunistic Infections Shortly after Beginning Highly Active Antiretroviral Therapy

Abstract: The clinical benefit of highly active antiretroviral therapy (HAART) has been attributed to its suppression of viral replication and improvement in the CD4 lymphocyte count. However, the development of clinical symptoms secondary to previously silent opportunistic pathogens shortly after beginning HAART has been reported as a distinct clinical syndrome and seems to be associated with inflammatory phenomena surrounding a rapid restoration of the immune system in previously immunosuppressed patients. Herein, we report nine (3.6%) episodes of opportunistic infections (OI) in 247 human immunodeficiency virus (HIV)-infected patients undergoing HAART in a reference HIV/AIDS institution located in Madrid, Spain. In all instances, OI clustered within the first 3 months after beginning HAART. Episodes of cerebral toxoplasmosis (three cases), Pneumocystis carinii pneumonia (two cases), and herpes zoster (two cases) occurred in persons without a previous AIDS-defining illness, in addition a relapse of cytomegalovirus retinitis and a rebound in Kaposi's sarcoma were seen, respectively, in another two patients. Four of the nine subjects had a CD4 count above 200 cells/mm3 before HAART began. Of these, one developed Pneumocystis pneumonia and one other cerebral toxoplasmosis. In conclusion, prophylaxis and close clinical monitoring of HIV-infected patients should be considered for the first 3 months after beginning HAART, even for subjects without severe immunosuppression.

Sanctuary sites in HIV-1 infection.

Abstract: The existence of sanctuary sites for human immunodeficiency virus type 1 (HIV-1) may potentially endanger the efficacy of antiretroviral therapy in the long term and may even make eradication of HIV-1 from the infected body impossible. Potential 'classic' sanctuary sites for HIV-1 are the central nervous system and the testes, but long-lived cell populations (such as macrophages) or latently infected (resting) CD4 cells may also be considered a sanctuary for HIV-1. These potential sanctuary sites, and putative underlying biochemical mechanisms such as the divergent phosphorylation properties of nucleoside reverse transcriptase inhibitors in different cell populations and the affinity of drugs for the multidrug transporter P-glycoprotein, are discussed.

Finding a role for zalcitabine in the HAART era.

Abstract: Zalcitabine (ddC) is a nucleoside analogue reverse transcriptase inhibitor with demonstrated clinical benefit in combination use. More widespread use of zalcitabine has been limited by a number of ...

Pathogenesis of chronic hepatitis C virus infection.

Abstract: HCV-infected patients with chronic liver disease have evidence of circulating HCV-specific antibodies and a polyclonal, multi-specific T cell response. CD4+ proliferative responses and HCV-specific CTLs directed against one or more viral antigens are readily detected in those individuals who develop chronic HCV infection and appear to compartmentalize within the liver. Cytokines, which are produced locally within the liver and systemically, may play an important role in controlling viral replication and contributing to hepatocellular damage. However, neither the humoral nor cellular immune response, nor the cytokine response appears sufficient to eradicate infection in most patients. In its attempt to clear the virus from the liver, the immune system contributes to the hepatocellular injury seen in the majority of chronically infected patients. A better understanding of the host's immune response may provide further insight on the pathogenetic mechanisms involved in development of chronic hepatitis and aid the development of better therapeutic strategies.

Management of antiretroviral therapy for HIV infection: modelling when to change therapy.

Abstract: OBJECTIVE: To evaluate four strategies for monitoring plasma HIV RNA levels and/or resistance genotypes to decide when to change antiretroviral therapy. The strategies include: (i) 1997 guidelines recommending a therapy switch when plasma RNA exceeds a threshold level; (ii) a viral load policy, using a fixed increase in viral load as the trigger; (iii) a genotype policy, requiring a smaller viral rebound than (ii) and detection of genotypic resistance before switching; and (iv) a proactive policy, switching drug regimens at a predetermined time if viral load has not rebounded. DESIGN AND SETTING: A Monte Carlo simulation tracks patients' viral loads and presence of opportunistic infection during therapy. The model uses clinical and virological data and statistical variation in patient parameters for the evaluation of therapeutic strategies. MAIN OUTCOME MEASURES: To determine which strategies minimize viral rebound detection delay while maintaining a low (prespecified) probability of switching therapy before rebound. RESULTS: 1997 Guidelines and the viral load policy create lengthy delays in detection of rebound, particularly when patients are drug-naive and the detection limit of the viral load assay is 500 copies/ml. A detection limit of 20 copies/ml decreases this delay substantially. Genotyping achieves only minor additional delay reductions. Of the strategies tested, the proactive policy leads to the shortest delays. CONCLUSIONS: This model indicates that prolonged periods may be required for viral load to rebound to detectable levels following prolonged suppression. Proactive switching produces the best outcome in our model because it may reduce the duration of viral replication under pressure of a failing regimen before detection of viral rebound. This strategy should be evaluated in clinical trials.

Transgenic mice as a chemotherapeutic model for hepatitis B virus infection

Abstract: Many transgenic mice carrying either portions of the hepatitis B virus (HBV) genome, or the complete genome, have been developed as models because HBV does not infect any other organisms besides humans and chimpanzees to cause a productive infection and disease. Some of these models have been useful in evaluating chemotherapeutic agents such as interferon-alpha, interleukins-2 and -12, other cytokines and nucleoside analogues for efficacy against HBV. A recently developed transgenic mouse (Guidotti et al., Journal of Virology 69:6158-6169.) which supports the replication of high levels of infectious HBV, provides the opportunity to evaluate the effect of antiviral drugs on various portions of the HBV life cycle in the whole animal. Evaluation of lamivudine, zidovudine and interferon-alpha B/D (IFN-alpha) in this HBV transgenic mouse model are described. Lamivudine and IFN-alpha were highly efficacious in reducing serum HBV DNA. As might be predicted, zidovudine was not efficacious. IFN-alpha was more effective in reducing virus titres in male mice as compared to female mice. This gender difference was not due to lower ability of female mice to express the virus. One anticipates that as this high level HBV transgenic-expressing mouse becomes more fully developed as a chemotherapeutic model, questions about the efficacy of different agents, routes of administration, synergy of antiviral combinations and novel drug therapies will be answered.

Nevirapine/didanosine/lamivudine once daily in HIV-1-infected intravenous drug users.

Abstract: Human immunodeficiency virus (HIV)-infected, active intravenous drug users received once-daily therapy consisting of a combination of didanosine (2',3'-dideoxyinosine or DDI), lamivudine [(-)-beta-L-2',3'-dideoxy-3'-thiacytidine or 3TC] and nevirapine. Preliminary results for the first 24 weeks show that the regimen provides potent immunological and antiviral effects.

Sensitivity and resistance to (+)-calanolide A of wild-type and mutated forms of HIV-1 reverse transcriptase.

Abstract: We have tested both wild-type and drug-resistant mutated, recombinant human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) molecules for sensitivity to each of two non-nucleoside ...

Kinetics of productive and latent HIV infection in lymphatic tissue and peripheral blood during triple-drug combination therapy with or without additional interleukin-2.

Abstract: ObjectiveTo study decay rates of productively and latently infected cells in peripheral blood and lymph nodes during triple antiretroviral therapy and the possible impact of interleukin-2 (IL-2) on...

Antiviral Therapy of Haemorrhagic Fevers and Arbovirus Infections

Abstract: RNA viruses of the families Arena-, Bunya-, Filo-, Flavi-and Togaviridae cause illness in humans ranging from mild, non-specific febrile syndromes to fulminant, lethal haemorrhagic fever. They are ...

Helicase, a target for novel inhibitors of hepatitis C virus.

Abstract: Virus-encoded enzymes of hepatitis C virus (HCV) were identified from its genome sequence. This allows application of drug discovery strategies which rely on inhibition of enzymes unique to HCV. Discovery of high-affinity inhibitors is facilitated by knowledge of the target enzyme's three-dimensional structure. For development of inhibitors of the HCV helicase, which belongs to a class of enzymes for which little structural information is available, the impact of structural information on the drug discovery process is greater than for targets belonging to well-characterized classes of enzyme. Here the structure of the HCV helicase is described. Regions required for enzymatic activity, which are also the preferred sites of drug interaction, are highlighted.

Pharmacological considerations in antiretroviral therapy.

Abstract: Suboptimum drug exposure arising from pharmacological and pharmacokinetic factors is an important reason that combination antiretroviral therapy fails in patients with human immunodeficiency virus type 1 infection. With all three available drug classes, the major causes are drug-drug interactions and interpatient pharmacokinetic variability. Inadequate concentrations of protease inhibitors and non-nucleoside reverse transcriptase inhibitors occur when concurrently administered drugs interfere with their metabolism by the hepatic cytochrome P450 enzyme system, the major metabolic pathway for these drugs. Combined therapy with certain nucleoside reverse transcriptase inhibitors can reduce systemic drug exposure by interfering with the intracellular conversion of administered drugs to their active metabolites. Important causes of interpatient variability in pharmacokinetic parameters include low oral drug bioavailability and individual differences in drug disposition and metabolism. Careful selection and monitoring of combination drug therapy along with individualized rather than standard dosage regimens may minimize these pharmacological problems and help ensure optimum antiviral activity.

Hydroxyurea: mechanisms of HIV-1 inhibition.

Abstract: Hydroxyurea inhibits cellular ribonucleotide reductase, resulting in decreased pools of dNTPs and thus inhibition of DNA synthesis. Studies in vitro have shown that hydroxyurea reduces dNTP pools in cells infected with human immunodeficiency virus type 1 (HIV-1), inhibiting HIV-1 DNA synthesis in infected quiescent and activated primary human lymphocytes and macrophages. Hydroxyurea also potentiates the activity of nucleoside reverse transcriptase inhibitors (NRTIs): the activated triphosphate forms of NRTIs compete with naturally occurring dNTPs for incorporation into nascent viral DNA during reverse transcription. A synergistic effect is observed between hydroxyurea and didanosine (2',3'-dideoxyinosine; DDI). This combination exerts persistent suppression of HIV-1 replication without evidence of viral rebound for over 1 year in HIV-1-infected patients. Didanosine-resistant HIV-1 mutants retain sensitivity to didanosine in the presence of hydroxyurea. The incorporation of didanosine triphosphate by resistant reverse transcriptase is increased in the context of the hydroxyurea-induced depletion of dATP. Although hydroxyurea has a reduced effect on dNTPs competing with the triphosphate forms of pyrimidine NRTIs, it appears to augment the anti-HIV-1 activity of these agents by increasing their intracellular phosphorylation; this may be of particular interest for salvage strategies given recent data indicating disruption of NRTI phosphorylation with specific NRTI treatment regimens. Finally, by exerting a cytostatic effect on CD4 and CD8 T lymphocytes, hydroxyurea may (i) reduce HIV-1 replication by decreasing CD4 T cell proliferation; and (ii) prevent the exhaustion of CD8 T cell populations that may occur as a result of excessive activation in the context of HIV-1 infection.

Evolution of HIV drug Resistance in Zidovudine/Zalcitabine- and Zidovudine/ Didanosine-Experienced Patients Receiving Lamivudine-Containing Combination Therapy:

Abstract: Drug resistance patterns and their correlation to treatment response 24 weeks after addition of lamivudine to a previous zidovudine/zalcitabine or zidovudine/ didanosine combination treatment, or a...

Loss of lamivudine resistance in a zidovudine and lamivudine dual-resistant HIV-1 isolate after discontinuation of in vitro lamivudine drug pressure.

Abstract: We examined the in vitro phenotypic and genotypic profiles of an extensively passaged human immunodeficiency virus type 1 clinical isolate which has been selected for lamivudine resistance, with an...

Hepatitis B Virus Antiviral Drug Resistance: From the Laboratory to the Patient:

Abstract: The development and application of nucleoside (and nucleotide) analogues for the treatment of chronic hepatitis B infection will transform the management of this condition. For instance, treatment ...

Hepatitis delta virus: molecular biology, pathogenesis and immunology.

Abstract: Hepatitis delta virus (HDV) is a unique infectious agent which causes severe liver disease in those infected with its helper virus, hepatitis B virus. No effective antiviral therapy for HDV exists. This review covers recent advances in the molecular biology, pathogenesis and immunology of HDV, with an emphasis on potential targets for the development of successful antiviral agents.

Anti-HIV antiviral activity of stavudine in a thymidine kinase-deficient cellular line.

Abstract: Stavudine (d4T) is a potent inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase. It is known that stavudine is metabolized in cells to the mono-, di- and triphosphate nucleotides but the enzymes responsible for its phosphorylation are as yet unidentified. In particular, there are conflicting results concerning the role of thymidine kinase 1 (TK1) in stavudine metabolism. To gain new insights into this phenomenon we analysed the antiviral activity of stavudine in a TK1-deficient, resistant cell line. The results indicate that TK1 is responsible for the phosphorylation of stavudine but it is not the only enzyme involved in its activation. The other enzyme(s) that might be involved in the metabolism of stavudine, however, are not able to phosphorylate stavudine with the same efficiency as TK1. Since it has been shown that prolonged treatment with zidovudine may induce an in vivo defect in TK1 activity, it is tempting to speculate that patients treated for a long time with zidovudine could be resistant to further treatment with stavudine.

Meta-analysis of antiretroviral effects on HIV-1 RNA, CD4 cell count and progression to AIDS or death.

Abstract: There is uncertainty as to how the effects of antiretroviral treatments on human immunodeficiency virus type 1 (HIV-1) RNA levels and CD4 cell counts can predict reductions in clinical progression to AIDS or death. A meta-analysis was conducted for 27 pairwise comparisons of antiretroviral treatments in 15 randomized trials of antiretroviral treatments. For each trial, three measures of treatment effect were used: (i) 16 week change from baseline in HIV-1 RNA; (ii) 16 week change from baseline in CD4 cell count; and (iii) rate of clinical progression. Treatments which caused greater increases in CD4 cell count and greater reductions in HIV-1 RNA were more effective at reducing the rate of clinical progression (P < 0.05 for each comparison). However, there was variability in the consistency of this correlation between different trials and treatments. The results support the use of both CD4 count and HIV-1 RNA levels as the primary markers of the efficacy of antiretroviral treatment.

Different outcome in the first two patients with an HIV-1 multinucleoside drug-resistant T69SSS insertion in Spain.

Abstract: A novel multidrug-resistance mechanism has been described in human immunodeficiency virus type 1 (HIV-1), which involves the insertion of 6 bp between codons 69 and 70 in the reverse transcriptase ...

Evaluation of mixtures of wild-type HIV-1 and HIV-1 with resistance point mutations against reverse transcriptase inhibitors.

Abstract: The presence of resistance-related mutations in 185 serial proviral DNA samples from 108 HIV-infected patients was monitored using the line probe assay (LiPA) The proportions of wild-type and muta

Immunological effects of antiretroviral therapy.

Abstract: The striking decline in HIV load with highly active antiretroviral combination therapy (HAART) is accompanied by substantial improvements in immune function, even in patients with more advanced disease. These include a general reduction in immune activation with increases in total CD4 and CD8 cell counts, memory and naive T cell subsets and antigen responses to certain opportunistic pathogens. At this time, it appears that HAART-induced improvements in function are limited to those T cells that have not yet been completely depleted by HIV. Long-term studies are needed to determine whether complete functional restoration of the repertoire is possible. Clinically, HAART improves survival and reduces progression of HIV disease. Some patients with active opportunistic disorders demonstrate complete or partial resolution of the infection or malignancy. However, persons with subclinical Mycobacterium avium complex or cytomegalovirus retinitis and those with chronic hepatitis B virus infection may sometimes experience acute flares if prophylactic therapy against the underlying disorder is not included in the regimen.