Comparative inhibitory effects of suramin and other selected compounds on the infectivity and replication of human T-cell lymphotropic virus (HTLV-III)/lymphadenopathy-associated virus (LAV)

New synergistic antibacterial mechanism of bulky mixed Ti/w hetero-polyoxometalates composed of multi lacunary Keggin structure with oxacillin against vancomycin intermediate-resistant Staphylococcus aureus

Considering the lack of detailed research on the antibacterial mechanism of polyoxometalates, we examined the synergistic effect of novel bulky mixed Ti/W hetero-polyoxometalates (K9.5H2.5 ［α-Ge2Ti4W20O78］・ 29H2O; αTi4, K9H5 ［α-Ge2Ti6W18O77］・16H2O; αTi6, K23H5［α-Ge4Ti12W36O154］・39H2O; αTi12, K9H5 ［β-Ge2Ti6W18O77］・ 45H2O; βTi6) with the antibiotic oxacillin against vancomycin intermediate-resistant Staphylococcus aureus (VISA) using fractional inhibitory concentration (FIC) index and growth curve in this study. All polyoxometalates used in this study showed remarkable synergistic effects with oxacillin. Its synergistic antibacterial mechanism was examined using reverse transcription PCR (RT-PCR) and penicillin binding protein-2' (PBP2') latex agglutination test. The results suggested that these polyoxometalates did not inhibit mecA gene transcription but resulted in PBP2' protein malfunction. From these results, we concluded that the substances producing resistance in VISA were affected by polyoxometalates depending on their molecular size, facilitating a synergistic antibacterial effect with oxacillin.

Structural insights into the inhibition of bacterial RecA by naphthalene polysulfonated compounds

As a promising target for alternative antimicrobials, bacterial recombinase A (RecA) protein has attracted much attention for its roles in antibiotic-driven SOS response and mutagenesis. Naphthalene polysulfonated compounds (NPS) such as suramin have previously been explored as antibiotic adjuvants targeting RecA, although the underlying structural bases for RecA-ligand interactions remain obscure. Based on our in silico predictions and documented activity of NPS in vitro, we conclude that the analyzed NPS likely interact with Tyr103 (Y103) and other key residues in the ATPase activity center (pocket A). For validation, we generated recombinant RecA proteins (wild-type versus Y103 mutant) to determine the binding affinities for RecA protein interactions with suramin and underexamined NPS in isothermal titration calorimetry. The corresponding dissociation constants (K d) ranged from 11.5 to 18.8 μM, and Y103 was experimentally shown to be critical to RecA-NPS interactions.

Screening and Evaluation of Novel Compounds against Hepatitis B Virus Polymerase Using Highly Purified Reverse Transcriptase Domain

Hepatitis B virus (HBV) polymerase seems to be very hard to express and purify sufficiently, which has long hampered the generation of anti-HBV drugs based on the nature of the polymerase. To date, there has been no useful system developed for drug screening against HBV polymerase. In this study, we successfully obtained a highly purified reverse transcriptase (RT) domain of the polymerase, which has a template/primer and substrate binding activity, and established a novel high-throughput screening (HTS) system using purified RT protein for finding novel polymerase inhibitors. To examine whether the assay system provides reliable results, we tested the small scale screening using pharmacologically active compounds. As a result, the pilot screening identified already-known anti-viral polymerase agents. Then, we screened 20,000 chemical compounds and newly identified four hits. Several of these compounds inhibited not only the HBV RT substrate and/ template/primer binding activity, but also Moloney murine leukemia virus RT activity, which has an elongation activity. Finally, these candidates did show to be effective even in the cell-based assay. Our screening system provides a useful tool for searching candidate inhibitors against HBV.

Metal–organic architectures driven by a multifunctional 6-aminouracil spacer: structures, noncovalent interactions, and conductivity

Three new coordination polymers were assembled from a multifunctional 6-aminouracil building block and their structural features & functional properties were investigated.

Antiviral Evaluation of Herbal Drugs

The viral infection and resistance to the existing antiviral drugs are alarming, which is a serious public health concern. Medicinal plants are valuable resources for treatment of viral infections and can be used for the management of infections like herpes simplex virus (HSV), human immunodeficiency virus (HIV), influenza, etc. The antiviral screening of plant extracts should be highly selective, specific, and sensitive for bioactivity guided isolation of the active compounds from the plant extracts. The antiviral screening system should be validated for accuracy, reproducibility, simplicity, and cost effectiveness. This chapter highlights on various aspects for screening and evaluation of antiviral natural components including factors affecting antiviral in vivo studies, host cells, organisms, and culture media followed by different virus-specific assays for antiviral screening of natural products.

Suramin potently inhibits cGAMP synthase, cGAS, in THP1 cells to modulate IFN-β levels

Aim: Persistent activation of STING pathway is the basis for several autoimmune diseases. STING is activated by cGAMP, which is produced by cGAS in the presence of DNA. Results/methodology: HPLC-based medium throughput screening for inhibitors of cGAS identified suramin as a potent inhibitor. Unlike other reported cGAS inhibitors, which bind to the ATP/GTP binding site, suramin displaced the bound DNA from cGAS. Addition of suramin to THP1 cells reduced the levels of IFN-β mRNA and protein. Suramin did not inhibit lipopolysaccharide- or Pam3CSK4-induced IL-6 mRNA expression. Conclusion: Suramin inhibits STING pathway via the inhibition of cGAS enzymatic activity. Suramin or analogs thereof that displace DNA from cGAS could be used as anti-inflammatory drugs.

Anionic Liposomes Inhibit Human Immunodeficiency Virus Type 1 (HIV-1) Infectivity in CD4+ A3.01 and H9 Cells

Immunodeficiency viruses undergo fusion with liposomes containing anionic phospholipids (Larsen etal., 1990). We have investigated the effect of liposomes composed of cardiolipin, phosphatidylserine or phosphatidylinositol, on the infectivity of three strains of HIV-1 in A3.01 and H9 cells, measured by p24 (gag) production in the medium. The infectivity of HIV-1 in A3.01 or H9 cells was inhibited by the presence of cardiolipin liposomes during a 2 h infection period, with IC50's of 23.0, 4.8, and 5.0 μM phospholipid, respectively, for the different strains. Liposomes composed of phosphatidylserine or phosphatidylinositol were ineffective under similar conditions. However, prolonged pre-incubation of the virus with these liposomes also inhibited infectivity. Inhibition of virus binding to cells could not account for the inhibition of infectivity. We propose that the fusion products of HIV-1 and anionic liposomes are impaired in their ability to fuse with the plasma membrane.

Naphthalenesulphonic Acid Derivatives as Potential anti-HIV-1 Agents. Chemistry, Biology and Molecular Modelling of Their Inhibition of Reverse Transcriptase

Activity against human immunodeficiency virus (HIV) in the naphthalenesulphonic acid series is most pronounced in the disulphonic acid series. In this class of compounds, N-acyl derivatives of 4-amino-5-hydroxy-2,7-naphthalenedisulphonic acid demonstrate significant anti-HIV activity at non-toxic doses. The most potent compounds in this group of agents are bis naphthalenedisulphonic acids. A bis derivative containing a decamethylene spacer demonstrated activity against HIV-1, HIV-2 giant cell formation and reverse transcriptase (RT). This compound also demonstrated an in vitro therapeutic index (ratio of 50% cytotoxic concentration to 50% inhibitory antiviral concentration) of 10.6. Molecular modelling analyses of this agent, suramin, and several suramin analogues were undertaken to explain the potent anti-HIV-1 RT activity. These studies were carried out using the molecular decomposition/recomposition strategy, conformational searching, energy minimization and molecular dynamics (MD) simulation. The bis naphthalenedisulphonic acid derivative compound 1, having a flexible decamethylene spacer, was shown to be able to mimic the helical twist of the B-DNA backbone as a low energy conformer state.

Inhibition of gp120 Binding to the CD4 Antigen by Dyes: Mechanism of Effect and Contribution to anti-HIV Activity

Several compounds developed for use as dyes have shown activity against HIV-1. The present study examines one putative mechanism of this anti-HIV activity, inhibition of gp120/CD4 binding, and its contribution to the antiviral effects of three chemical classes of dyes. Although, for most dyes, the ability to inhibit gp120/CD4 binding and the reported anti-HIV activities do not correlate, a group of dyes is identified whose anti-HIV activity does appear to be related to binding inhibition. Qualitative examination of the effect of two of these dyes on the gp120/CD4 binding isotherm suggests that the inhibition is non-competitive. Dyes which act by preventing viral binding may represent prototypes for the development of novel drugs for the treatment or prevention of AIDS.

Inhibition of the Binding of HIV rgp120 to CD4 by Dyes

We have found that several dye compounds have the ability to inhibit the binding of HIV rgpl 20 to the Leu3a epitope of CD4 on PBL. One of these compounds, selected for further testing as the best candidate, can inhibit the growth of HIV In vitro. The tested dyes have varying degrees of specificity and efficacy in inhibiting the binding of rgpl 20. These results may point towards compounds that can be useful therapeutics against HIV.

The X-ray Crystal Structure of the Sulfonated Azo Dye Congo Red, a Non-Peptidic Inhibitor of HIV-1 Protease which also Binds to Reverse Transcriptase and Amyloid Proteins

Congo Red is a sulfonated azo dye and widely used biological stain that has recently been the focus of intense interest because it has been shown to bind to proteins involved in viral recognition and replication. Congo Red also finds wide use as a histological stain for amyloid proteins of the type found in neurodegenerative conditions such as Alzheimer's disease, transmissible spongiform encephalopathies in cattle and mink, and scrapie in sheep. Congo Red has been demonstrated to protect normal prion protein from being converted to the protease-resistant form, an important step in the pathology of the so-called ‘slow viral’ diseases. The range of biological molecules to which Congo Red binds makes it an important lead compound in drug development, for example in the development of new anti-HIV and anti-Alzheimer's therapeutic agents. In this report we present the first high-resolution structure of Congo Red: the low-temperature (173 K) X-ray crystal structure determination of its calcium salt. Two conformations of the molecule are found in the same crystal structure, one in which the central biphenyl group assumes a twisted (25°) conformation, and one in which the biphenyl group is planar and is located on a crystallo-graphic inversion centre. In both conformations the sulfonate groups are oriented anti with respect to the long molecular axis and assume eclipsed conformations with respect to the naphthalene rings. A comparison is made with a published structure [Turned, W.G., and Finch, J.T. (1992) J Mol Biol 227: 1205-1223] in which Congo Red is bound to porcine insulin, this complex serving as a model for amyloid binding. The results illustrate the conformational flexibility possessed by the biphenyl spacer, which allows the hydrophobic portion of the molecule to assume an optimum fit in the hydrophobic binding pockets of target proteins. A model is presented for the binding of Congo Red to the HIV protease in which the sulfonate groups interact with the side-chains of arginine residues. This proposed binding mode is consistent with the observed binding for other sulfonated aromatic inhibitors such as Evans Blue.

Inhibition of HIV-1-Induced Cytopathogenicity, Syncytium Formation, and Virus-Cell Binding by Naphthalenedisulphonic Acids through Interaction with the Viral Envelope gp120 Glycoprotein

Bis-naphthalenedisulphonic acid derivatives with a biphenyl spacer, 4,4′-[4,4′-biphenyldiylbis(sulphonyl-amino)]bis(5-hydroxy-2,7-naphthalenedisulphonic acid) and 3,3′-[4,4′-biphenyldiylbis(sulphonyl-amino)]bis(1,5-naphthalenedisulphonic acid), have previously been reported as potent and selective inhibitors of human immunodeficiency virus type 1 (HIV-1) replication in cell culture. These compounds have also proved inhibitory to syncytium formation in cocultures of MOLT-4 cells with HIV-1-infected HUT-78 cells. They also inhibit the binding of HIV-1 virions to MT-4 cells as determined by a flow cytometric (FACS) method. Further studies on their mechanism of action by the FACS have revealed that the compounds inhibit the binding of anti-gp120 monoclonal antibody to the viral envelope glycoprotein gp120. Binding of OKT4A/Leu3a monoclonal antibody to the cellular CD4 receptor is not affected by the compounds. These results suggest that the anti-HIV-1 activity of the naphthalenedisulphonic acid derivatives can be attributed to inhibition of the gp120-CD4 interaction through binding of the compounds to the viral gp120 antigen.

Proteoglycans act as cellular hepatitis delta virus attachment receptors

The hepatitis delta virus (HDV) is a small, defective RNA virus that requires the presence of the hepatitis B virus (HBV) for its life cycle. Worldwide more than 15 million people are co-infected with HBV and HDV. Although much effort has been made, the early steps of the HBV/HDV entry process, including hepatocyte attachment and receptor interaction are still not fully understood. Numerous possible cellular HBV/HDV binding partners have been described over the last years; however, so far only heparan sulfate proteoglycans have been functionally confirmed as cell-associated HBV attachment factors. Recently, it has been suggested that ionotrophic purinergic receptors (P2XR) participate as receptors in HBV/HDV entry. Using the HBV/HDV susceptible HepaRG cell line and primary human hepatocytes (PHH), we here demonstrate that HDV entry into hepatocytes depends on the interaction with the glycosaminoglycan (GAG) side chains of cellular heparan sulfate proteoglycans. We furthermore provide evidence that P2XR are not involved in HBV/HDV entry and that effects observed with inhibitors for these receptors are a consequence of their negative charge. HDV infection was abrogated by soluble GAGs and other highly sulfated compounds. Enzymatic removal of defined carbohydrate structures from the cell surface using heparinase III or the obstruction of GAG synthesis by sodium chlorate inhibited HDV infection of HepaRG cells. Highly sulfated P2XR antagonists blocked HBV/HDV infection of HepaRG cells and PHH. In contrast, no effect on HBV/HDV infection was found when uncharged P2XR antagonists or agonists were applied. In summary, HDV infection, comparable to HBV infection, requires binding to the carbohydrate side chains of hepatocyte-associated heparan sulfate proteoglycans as attachment receptors, while P2XR are not actively involved.

Purinergic receptor functionality is necessary for infection of human hepatocytes by hepatitis delta virus and hepatitis B virus

Hepatitis B virus (HBV) and hepatitis delta virus (HDV) are major sources of acute and chronic hepatitis. HDV requires the envelope proteins of HBV for the processes of assembly and infection of new cells. Both viruses are able to infect hepatocytes though previous studies have failed to determine the mechanism of entry into such cells. This study began with evidence that suramin, a symmetrical hexasulfated napthylurea, could block HDV entry into primary human hepatocytes (PHH) and was then extrapolated to incorporate findings of others that suramin is one of many compounds that can block activation of purinergic receptors. Thus other inhibitors, pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonate (PPADS) and brilliant blue G (BBG), both structurally unrelated to suramin, were tested and found to inhibit HDV and HBV infections of PHH. BBG, unlike suramin and PPADS, is known to be more specific for just one purinergic receptor, P2X7. These studies provide the first evidence that purinergic receptor functionality is necessary for virus entry. Furthermore, since P2X7 activation is known to be a major component of inflammatory responses, it is proposed that HDV and HBV attachment to susceptible cells, might also contribute to inflammation in the liver, that is, hepatitis.

Assessing changes in vascular permeability in a hamster model of viral hemorrhagic fever

Background

A number of RNA viruses cause viral hemorrhagic fever (VHF), in which proinflammatory mediators released from infected cells induce increased permeability of the endothelial lining of blood vessels, leading to loss of plasma volume, hypotension, multi-organ failure, shock and death. The optimal treatment of VHF should therefore include both the use of antiviral drugs to inhibit viral replication and measures to prevent or correct changes in vascular function. Although rodent models have been used to evaluate treatments for increased vascular permeability (VP) in bacterial sepsis, such studies have not been performed for VHF.

Results

Here, we use an established model of Pichinde virus infection of hamsters to demonstrate how changes in VP can be detected by intravenous infusion of Evans blue dye (EBD), and compare those measurements to changes in hematocrit, serum albumin concentration and serum levels of proinflammatory mediators. We show that EBD injected into sick animals in the late stage of infection is rapidly sequestered in the viscera, while in healthy animals it remains within the plasma, causing the skin to turn a marked blue color. This test could be used in live animals to detect increased VP and to assess the ability of antiviral drugs and vasoactive compounds to prevent its onset. Finally, we describe a multiplexed assay to measure levels of serum factors during the course of Pichinde arenavirus infection and demonstrate that viremia and subsequent increase in white blood cell counts precede the elaboration of inflammatory mediators, which is followed by increased VP and death.

Conclusions

This level of model characterization is essential to the evaluation of novel interventions designed to control the effects of virus-induced hypercytokinemia on host vascular function in VHF, which could lead to improved survival.

Anti-HIV-1 efficacy of extracts from medicinal plants

The anti-HIV-1 activities of butanol, hexane, chloroform and water extracts from four widely used folk medicinal plants (Sophora flavescens, Tulipa edulis, Herba ephedra, and Pachyma hoelen Rumph) were evaluated in this study. The hexane extract of Pachyma hoelen Rumph, PH-4, showed effective inhibition against HIV-1. The 50% effective concentration (EC(50)) of PH-4 was 37.3 microg/ml in the p24 antigen assay and 36.8% in the HIV-1 recombinant RT activity test (at 200 microg/ml). In addition, the PH-4 showed the protective effect on the infected MT-4 cells, with a 58.2% rate of protection. The 50% cytotoxic concentration (CC(50)) of PH-4 was 100.6 microg/ml. These results suggest that PH-4 from Pachyma hoelen Rumph might be the candidate for the chemotherapy agent against HIV-1 infection with further study.

Congo red and protein aggregation in neurodegenerative diseases

Congo red is a commonly used histological dye for amyloid detection. The specificity of this staining results from Congo red's affinity for binding to fibril proteins enriched in beta-sheet conformation. Unexpectedly, recent investigations indicate that the dye also possesses the capacity to interfere with processes of protein misfolding and aggregation, stabilizing native protein monomers or partially folded intermediates, while reducing concentration of more toxic protein oligomers. Inhibitory effects of Congo red upon amyloid toxicity may also range from blockade of channel formation and interference with glycosaminoglycans binding or immune functions, to the modulation of gene expression. Particularly, Congo red exhibits ameliorative effect in models of neurodegenerative disorders, such as Alzheimer's, Parkinson's, Huntington's and prion diseases. Another interesting application of Congo red analogues is the development of imaging probes. Based on their small molecular size and penetrability through blood-brain barrier, Congo red congeners can be used for both antemortem and in vivo visualization and quantification of brain amyloids. Therefore, understanding mechanisms involved in dye-amyloidal fibril binding and inhibition of aggregation will provide instructive guides for the design of future compounds, potentially useful for monitoring and treating neurodegenerative diseases.

Screening of South American plants against human immunodeficiency virus: preliminary fractionation of aqueous extract from Baccharis trinervis

Ethanolic and aqueous extracts of 14 South American medicinal plants were tested for inhibitory activity on human immunodeficiency virus (HIV). Both extracts were relatively non-toxic to human lymphocytic MT-2 cells, but only the aqueous extract of Baccharis trinervis exhibited potent anti-HIV activity in an in vitro MTT assay. To delineate the extract-sensitive phase, some studies of the antiviral properties of the active extract are described in this paper. Based on the results presented here, a separation scheme was devised, which permitted the preliminary fractionation of the extract, with the aim of finding an inhibitor of this virus.

Anti-HIV activity of medicinal plant extracts

As part of our screening of anti-AIDS agents from natural sources, ethanolic and aqueous extracts of 15 medicinal plants widely used in the folk medicine of the Iberian Peninsula were evaluated in vitro. Most of the extracts tested were relatively nontoxic to human lymphocytic MT-2 cells, but only the extracts of Tuberaria lignosa and Sanguisorba minor magnolii exhibited anti-HIV activity in an in vitro MTT assay. The aqueous extracts of these plants showed inhibitory effects against HIV-1 induced infections in MT-2 cells at concentrations ranging from 12.5 to 50 microg/ml and 50 microg/ml, respectively. Both extracts showed no appreciable cytotoxicity at these concentrations.

Carbonyl J Derivatives: A New Class of HIV-1 Integrase Inhibitors

Integration of a DNA copy of the HIV-1 genome is required for viral replication and pathogenicity, and this highly specific molecular process is mediated by the virus-encoded integrase protein. The requirement for integration, combined with the lack of a known analogous process in mammalian cells, makes integrase an attractive target for therapeutic inhibitors of HIV-1 replication. While many reports of HIV-1 IN inhibitors exist, no such compounds have yet emerged to treat HIV-1 infection. As such, new classes of integrase inhibitors are needed. We have combined molecular modeling and combinatorial chemistry to identify and develop a new class of HIV-1 integrase inhibitors, the Carbonyl J [N,N'-bis(2-(5-hydroxy-7-naphthalenesulfonic acid)urea] derivatives. This new class includes a number of compounds with sub-micromolar IC(50) values for inhibiting purified HIV-1 integrase in vitro. Herein we describe the chemical characteristics that are important for integrase inhibition and cell toxicity within the Carbonyl J derivatives. Copyright 2000 Academic Press.

The ribavirin analog ICN 17261 demonstrates reduced toxicity and antiviral effects with retention of both immunomodulatory activity and reduction of hepatitis-induced serum alanine aminotransferase levels

The demonstrated utility of the nucleoside analog ribavirin in the treatment of certain viral diseases can be ascribed to its multiple distinct properties. These properties may vary in relative importance in differing viral disease conditions and include the direct inhibition of viral replication, the promotion of T-cell-mediated immune responses via an enhanced type 1 cytokine response, and a reduction of circulating alanine aminotransferase (ALT) levels associated with hepatic injury. Ribavirin also has certain known toxicities, including the induction of anemia upon chronic administration. To determine if all these properties are linked, we compared the D-nucleoside ribavirin to its L-enantiomer (ICN 17261) with regard to these properties. Strong similarities were seen for these two compounds with respect to induction of type 1 cytokine bias in vitro, enhancement of type 1 cytokine responses in vivo, and the reduction of serum ALT levels in a murine hepatitis model. In contrast, ICN 17261 had no in vitro antiviral activity against a panel of RNA and DNA viruses, while ribavirin exhibited its characteristic activity profile. Importantly, the preliminary in vivo toxicology profile of ICN 17261 is significantly more favorable than that of ribavirin. Administration of 180 mg of ICN 17261 per kg of body weight to rats by oral gavage for 4 weeks generated substantial serum levels of drug but no observable clinical pathology, whereas equivalent doses of ribavirin induced a significant anemia and leukopenia. Thus, structural modification of ribavirin can dissociate its immunomodulatory properties from its antiviral and toxicologic properties, resulting in a compound (ICN 17261) with interesting therapeutic potential.

Interaction of 7-hydroxy-8-(phenylazo)1,3-naphthalenedisulfonate with bovine plasma albumin. Spectroscopic studies

Interaction of Orange G (OG) with bovine plasma albumin (BPA) has been investigated using NMR, UV-visible absorption, CD, and fluorescence techniques. The bound conformation of OG is a compact structure with N9-N10 bond in a non-planar syn conformation. The binding causes a decrease in the 478-nm absorption band of OG. The analysis of the binding isotherm generated from UV-visible absorption measurements gives a dissociation constant of 10 microM and stoichiometry 1:1 for BPA.OG complex. Dissociation constant is invariant in the pH range 5.0-8.0 and is approximately 20 times higher at pH 4.0 than its value at pH 7.0. Near and far UV-CD studies indicate alterations in the helical content and in the tertiary structure of the protein on complexation. The binding induces (-) and (+) CD at 335 nm and 465 nm, respectively. The binding also results into an increase in the steady state fluorescence anisotropy of OG without affecting emission maximum and quantum yield. Fluorescence data indicate that quenching of Trp fluorescence by OG is static in nature and OG selectively binds near Trp-135. Observation of similar rotational correlation time for BPA and BPA.OG complex indicates that the overall globular structure of BPA remains unaltered on binding despite certain internal rearrangement in the protein structure.

Inhibition of NAD(H)/NADP(H)--requiring enzymes by aurintricarboxylic acid

Aurintricarboxylic acid (ATA), an inhibitor of Ca(2+)-dependent endonuclease activity, is often used to implicate a role for increased intracellular calcium in mechanistic toxicology studies. We report here on the ability of ATA to inhibit the activity of several NAD(H)/NADP(H)-requiring enzymes (purified or cellular homogenates), including lactic dehydrogenase, alcohol dehydrogenase, cytochrome c reductase, ethoxycoumarin o-dealkylase, isocitric dehydrogenase, glutathione reductase and glucose-6-phosphate dehydrogenase. These results were compared with the ability of ATA to inhibit micrococcal nuclease and rat liver Ca(2+)-dependent endonuclease activity in similar incubations. With the exception of alcohol dehydrogenase, ATA was a potent inhibitor of each of the purified enzymes, with IC50s ranging from 0.5 to 82 microM. In cell homogenates, however, ATA was from 10 to 100-fold less potent at inhibiting these enzymes. When exogenous protein was added to purified enzyme incubations, the effect of ATA was similarly diminished. Our results demonstrate that ATA inhibits a wide range of NAD(H)/NADP(H)-requiring enzymes in in vitro incubations using purified enzymes, but that the inhibitory effects are markedly reduced in incubations which more closely resemble a cellular milieu.

Antiviral agents in hepatitis B virus transfected cell lines: inhibitory and cytotoxic effect related to time of treatment

The antiviral and cytotoxic effects of ara-arabinoside monophosphate, 2',3', dideoxy-cytidine, ganciclovir, 9-2(-phosphonylmethoxyethyl) adenine, 2',3'-dideoxy-3'-thiacytidine and recombinant interferon-alpha were studied using two human hepatitis B virus transfected hepatoma cell lines, HepG2 2.2.15 and HB 611. After 9 days of exposure, starting on day 3 after seeding, inhibition of extracellular HBV-DNA expressed as ID50 was in the 0.1-1.0 microM range for 2',3'-dideoxy-3'-thiacytidine and 9-2(-phosphonylmethoxyethyl) adenine and > 10 microM for dideoxy-cytidine, ara-arabinoside monophosphate and ganciclovir in both cell lines. At 2.500 U/ml recombinant interferon-alpha showed less than 20% inhibition in both cell lines. The HBV-DNA inhibitory effects of 2',3'-dideoxy-3'-thiacytidine and 9-2(-phosphonylmethoxyethyl) adenine were also investigated after 1 and 3 days of exposure. In that setting ID50's were 10 and 3.3 microM for 2',3'-dideoxy-3'-thiacytidine and > 100 and 30 microM for 9-2(-phosphonylmethoxyethyl) adenine, respectively. No major inhibitory effect on hepatitis B surface antigen and hepatitis B e antigen secretion was observed for any agent in this study, except for 9-2(-phosphonylmethoxyethyl) adenine in HB 611 cells. Cytotoxicity measured by inhibition of [3H-methyl] deoxythymidine incorporation and expressed as CD50 on day 4 was in the 10-100 microM range for ara-arabinoside monophosphate; in the 100-1000 microM range for 9-2(-phosphonylmethoxyethyl) adenine, ganciclovir and dideoxy-cytidine; and > 1000 microM for 2',3'-dideoxy-3'-thiacytidine.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of a flavivirus RNA-dependent RNA polymerase assay to investigate the antiviral activity of selected compounds

We have developed an assay using flavivirus RNA-dependent RNA polymerase to test the inhibitory activity of potential antiviral agents. The effects of antiviral agents on RNA synthesis were examined in this assay using extracts of Vero cells infected with dengue virus type 2 or Kunjin virus. Several different classes of known polymerase inhibitors were tested. The synthesis of double-stranded replicative form RNA was inhibited in a dose-dependent fashion in the presence of the polyoxometalate HPA-23 [(NH4)18(NaW21Sb9O86)17].14 H2O and several structurally related compounds.

Benzopurpurin and related compounds inhibit the binding of gp120 to galactosyl ceramide/sulfatide and infection of human immunodeficiency virus

In an attempt to find compounds capable of inhibiting the binding and infection by human immunodeficiency virus type 1 (HIV-1) in neural cells, we studied the effect of benzopurpurin and related compounds on the binding of gp120 to galactosyl ceramide (GalCer) and sulfatide. In this report, we show that the binding of gp120 to GalCer and sulfatide is inhibited by benzopurpurin and related compounds. These compounds also inhibit the binding and entry of HIV-1 to neural cell line, SK-N-MC. Binding studies indicate that benzopurpurin and related compounds bind to gp120. Studies involving related compounds indicate that the minimal structure required for the inhibition is two naphthalene rings with amine or sulfonic acids attached to a central biphenyl molecule by an azo group. This approach will be useful for screening of potential anti-HIV compounds.

Neutralization of HIV-1 and inhibition of HIV-1-induced syncytia by 1,8-naphthalimide photoactive compound

The antiviral property of a newly designed class of 1,8-naphthalimide photochemical compounds was investigated. One such photoactive compound, 1,14-bis-(N-hexyl-3'-bromo-1,8'-naphthalimide-4'-yl)-1,4,11,14- tetraazatetradecane-5,10-dione (diED66Br), when activated to an excited state by visible light (420 nm), effectively neutralized the in vitro infectivity of human immunodeficiency virus (HIV-1). Light-activated diED66Br also inhibited syncytium formation induced by cells infected with HIV-1. Nonactivated diED66Br was completely ineffective. The neutralizing and syncytium-inhibiting doses of activated diED66Br had no effect on normal human peripheral blood mononuclear cells. Radioimmunoprecipitation analysis indicated that diED66Br neutralizing activity resulted primarily from its ability to inhibit the binding of HIV-1 envelope glycoprotein gp120 to the CD4 cellular receptors. Although the exact molecular mechanism of viral neutralization by diED66Br has not been elucidated, its ability to neutralize HIV-1 infectivity and to inhibit syncytium formation supports further investigations of this photochemical as a potential therapeutic treatment of HIV-1 infection.

Metabolism and mode of selective inhibition of human immunodeficiency virus replication by 3'-azido-2',3'-dideoxy-5-iodouridine and 3'-azido-2',3'-dideoxy-5-bromouridine

3'-Azido-2',3'-dideoxy-5-iodouridine (AzIdUrd) and 3'-azido-2',3'-dideoxy-5-bromouridine (AzBdUrd), previously shown to be potent and selective inhibitors of human immunodeficiency virus replication in vitro were minimally toxic to the uninfected human lymphoid cell line H9 (IC50 = 197 and 590 microM, respectively). Both compounds strongly inhibited the incorporation of [3H]thymidine but not [3H]deoxyadenosine into DNA, and we observed no significant inhibition of [3H]uridine incorporation into RNA or [3H]amino acid incorporation into protein. Exposure of H9 cells to AzIdUrd or AzBdUrd (100 microM, 24 hr) and pulse-labeling with [3H]thymidine resulted in approximately 80% reduction in levels of tritiated dTMP, dTDP, and dTTP relative to control. [125I]AzIdUrd was phosphorylated rapidly in H9 cells with the monophosphate accounting for over 90% of total soluble radioactivity. A relatively low but stable level of AzIdUTP was maintained over a 12-hr period. [125I]AzIdUrd was phosphorylated by a cell free extract of H9 cells at a rate approximately three times that of thymidine and its phosphorylation was inhibited by excess thymidine. AzIdUrd was found to be a competitive inhibitor of cytosolic thymidine kinase with a Ki of 2.63 microM and AzIdUMP a weak competitive inhibitor of thymidylate kinase with a Ki of 55.3 microM. Both AzIdUTP and AzBdUTP were potent competitive inhibitors of HIV-1 reverse transcriptase (Ki = 0.028 and 0.043 microM, respectively) and relatively poor inhibitors of H9 cell DNA polymerase alpha (Ki = 42.0 and 42.7 microM, respectively). Thus, the high therapeutic index of these compounds is due to the sensitivity of the viral reverse transcriptase, coupled with the relative insensitivity of the host cell DNA polymerase alpha.

Quinobene, a new potent anti-HIV agent

A simple synthesis of the sulfonated azo dye Quinobene (3) and its derivatives, as well as the results of their evaluation in anti-HIV screening have been described. Thus, reacting the diazonium salt of 4,4'-diaminostilbene-2,2'-disulfonic acid with 8-hydroxyquinoline-5-sulfonic acid yielded the readily isolable title compound. The lithium and tetramethylammonium salts of Quinobene and its complexes with Cu(II), Zn(II), Mg(II) were also prepared. In vitro tests showed considerable activity of these compounds against HIV-1.

Changes in membrane permeability during Semliki Forest virus induced cell fusion

The infection of Aedes albopictus cells by Semliki Forest virus (SFV) is a non lytic event. Exposure of infected cells to mildly acidic pH (less than 6.2) leads to syncytium formation. This polykaryon formation is accompanied by an influx of protons into the cells (Kempf et al. Biosci. Rep. 7, 761-769, 1987). We have further investigated this permeability change using various fluorescent or radiolabeled compounds. A significant, pH dependent increase of the membrane permeability to low molecular weight compounds (M(r) less than 1000) was observed when infected cells were exposed to a pH less than 6.2. The pH dependence of the permeability change was very similar to the pH dependence of cell-cell fusion. The permeability change was sensitive to divalent cations, protons and anionic antiviral drugs such as trypan blue. The nature of this virus induced, pH dependent permeability change is discussed.

Sulfonic acid polymers as a new class of human immunodeficiency virus inhibitors

Four sulfonic acid polymers [poly(4-styrenesulfonic acid)(PSS), poly(anetholesulfonic acid)(PAS), poly(vinylsulfonic acid)(PVS), poly(2-acrylamido-2-methyl-1-propanesulfonic acid)(PAMPS)] have been found to inhibit the cytopathicity of HIV-1 and HIV-2 in MT-4 cells at concentrations that are not toxic to the host cells. The sulfonic acid polymers also inhibited syncytium formation in co-cultures of MOLT-4 cells with HIV-1- or HIV-2-infected HUT-78 cells. They also inhibited binding of anti-gp120 mAb to HIV-1 gp120 and blocked adsorption of HIV-1 virions to MT-4 cells. PSS and PAS, but not PVS and PAMPS, interfered with the binding of OKT4A/Leu3a to the CD4 receptor. The anti-HIV activity of these polyanionic compounds can be ascribed to inhibition of the gp120-CD4 interaction. Sulfonic acid polymers represent a lead of anti-HIV compounds that warrant further evaluation of their therapeutic potential.

Anti-AIDS drug development: challenges and strategies

A myriad of chemical derivatives has been shown to inhibit in vitro replication of the AIDS virus at concentrations that are nontoxic to the host cells. The majority of these agents acts by either (i) inhibiting enzymes such as reverse transcriptase (RT), protease, or glucosidase, (ii) arresting expression of genes or gene products, or (iii) inhibiting viral processes such as giant cell (syncytia) formation or viral binding to the target cell. The nucleoside RT inhibitors are the most widely studied agents at both the preclinical and the clinical levels. Their inability to cure AIDS has stimulated the discovery of several novel nonnucleoside RT inhibitors, possessing varied structures and demonstrating activity at nanomolar concentrations. These agents demonstrate a unique mode of binding to RT and show a high specificity for HIV-1. Protease inhibitors, soluble CD4 derivatives, oligonucleotides, and many anionic derivatives also demonstrate potent anti-HIV-1 activities. These derivatives possess mechanisms of action different to the nucleosides and exhibit selectivity as exemplified by their high in vitro therapeutic indices. This article discusses the structural parameters that govern activity in these agents, the pros and cons regarding the development of these compounds as putative anti-AIDS agents, and the future promise of searching for newer agents directed at novel targets to inhibit the AIDS virus.

Evaluation of multiple parameters of HIV-1 replication cycle in testing of AIDS drugs in vitro

Evaluation of the activities of antiretroviral agents and an immunoregulatory compound has been made using two models of HIV-1 infection and three measurements of virus expression. Acute infection of Jurkat cells or chronic/inducible infection in U1.1 cells was monitored at multiple time points after drug treatment. The 50% effective concentrations (EC50) of the HIV-1 inhibitors suramin, 3'-azido-3'-deoxythymidine (AZT), and 2',3'-dideoxycytidine, as measured by HIV-1 RNA hybridization in Jurkat cells two days after infection, were comparable to EC50 values obtained in parallel measurements of extracellular p24 levels and percent HIV-1 IF-positive cells. However, these measurements diverged: at seven days after infection the EC50 of AZT was greater than 10 microM when intracellular HIV-1 RNA was assayed, 0.2 microM by IF, and 0.03 microM by p24 assay. Human thymic humoral factor displayed no direct inductive activity in chronic HIV-1 infection in U1.1 cells, while phorbol ester and lymphocyte supernatants induced all parameters. These observations warrant care when interpreting results of only a single assay and suggest that definitive assay of HIV-1 infection requires measurements of multiple parameters of virus expression.

The carotenoid halocynthiaxanthin: A novel inhibitor of the reverse transcriptases of human immunodeficiency viruses type 1 and type 2

We have studied the effects of a natural carotenoid, identified as halocynthiaxanthin, on the enzymatic activities associated with the recombinant preparations of the reverse transcriptases (RTs) of human immunodeficiency viruses (HIV) types 1 and 2. The carotenoid was found to be a potent inhibitor of the RNA-dependent DNA polymerase activity (with 50% inhibition obtained at 5-7 microM halocynthiaxanthin), whereas the DNA-dependent DNA polymerase function of both RTs was significantly less sensitive to the inhibitor. Conversely, the ribonuclease H activity associated with the two HIV RTs was essentially insensitive to the carotenoid. The RNA-dependent DNA polymerase function of RT is the only unique activity found in this enzyme that is not expressed at significant levels in uninfected eukaryotic cells. Therefore, it is possible that this carotenoid may serve as a good candidate for the development of novel potent and specific inhibitors of HIV RT.

1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide (ribavirin) and 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (EICAR) markedly potentiate the inhibitory effect of 2',3'-dideoxyinosine on human immunodeficiency virus in peripheral blood lymphocytes

Ribavirin and EICAR are two antiviral agents that share a similar antiviral activity spectrum and are targeted at inosine 5'-monophosphate (IMP) dehydrogenase. Neither ribavirin nor EICAR inhibit the replication of human immunodeficiency virus (HIV) in peripheral blood lymphocyte cells (PBL) at subtoxic concentrations. However, both compounds markedly potentiate the anti-HIV activity of 2',3'-dideoxyinosine (DDI) in PBL cells without a marked increase of toxicity. Both the increased IMP levels and the decreased guanine nucleotide levels caused by ribavirin and EICAR may be responsible for their potentiating effect on the anti-HIV activity of DDI.

Brain-derived cells contain a specific binding site for Gp120 which is not the CD4 antigen

Infection with the human immunodeficiency virus (HIV-1) often produces a set of neuropsychiatric dysfunctions which have been termed the AIDS dementia complex. This complex appears due to the infection of brain cells by HIV-1. If so, brain cells might be expected to contain a binding site for the same viral envelope glycoprotein that enables HIV-1 to bind to other cells (e.g. CD4+ T-cells), gp120. The present study shows that the cells of the brain-derived U-138MG, U-373MG, SK-N-MC and SK-N-SH cell lines bind gp120 in an inhibitable fashion. Binding of gp120 to these cells is inhibited by the dyes Aurintricarboxylic acid (ATA) and Evans blue (EB), which are known to inhibit specific gp120 and HIV-1 binding, and block HIV-1 infection, in CD4-expressing cells. Binding is not inhibited by Aurin, a dye related to ATA but lacking its anti-HIV effects. As expected, anti-CD4 antibodies are ineffective in blocking gp120 binding to brain-derived cells. These results suggest that human brain-derived cells possess a specific binding site for gp120 that is not the CD4 antigen.

Physical factors contributing to the partition coefficient and retention time of 2',3'-dideoxynucleoside analogues

Acquired immunodeficiency syndrome (AIDS) is an immunosuppressive disease characterized by an immune impairment and a high susceptibility to unusual forms of certain neoplasms. Since the brain is an important site of the infection, it is necessary to explore new classes of drugs that have the ability to penetrate across the blood-brain barrier, and the potency to suppress viral replication within the central nervous system (CNS). Therefore, the ability to predicate the lipophilicity of the potent anti-AIDS drugs may provide useful information about the potential of the drugs to enter CNS. In this paper, the correlations of log P (octanol-buffer partition coefficient) and log tR (retention time in HPLC; Rt was used by Balzarini et al.) with some physical constants like log MW (molecular weight), hydrogen bond forming ability (HB) of the substituents, and the substituent group dipole moments (mu) are analyzed. Good correlations of log P and log tR with log MW, HB, and mu have been obtained.

Effect of Evans blue and trypan blue on syncytia formation and infectivity of human immunodeficiency virus type I and type II in vitro

Polyanionic compounds were used to inhibit infectivity of human immunodeficiency virus in vitro. Suramin, Evans blue, and Trypan blue were shown to inhibit syncytia formation normally observed when HIV-1-infected cells are cocultured with CD4+ cells. The inhibition was more pronounced with Evans blue than with any of the other polyanions studied. The inhibitory effect was significantly weaker in HIV-2 systems. However, the reverse transcriptase activities of both types of viruses were inhibited by Evans blue. Another polyanionic compound, phosphorothioate 28-mer cytidine homopolymer (SdC28) was shown to inhibit syncytium formation induced by HIV-1-and HIV-2-infected cells in an identical manner. Evans blue showed partial blocking of gp120 binding to CD4 in a solid-phase enzyme-linked immunosorbent assay (ELISA). These results suggest that the polyanionic dyes may exert their antiviral effects, at least in part, by interfering with the binding and fusion of HIV with susceptible T cells.