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

Evans Blue Inhibits HBV Replication Through a Dual Antiviral Mechanism by Targeting Virus Binding and Capsid Assembly

Chronic hepatitis B (CHB) is a global health problem caused by human hepatitis B virus (HBV). Current treatment with interferons and nucleos(t)ide analogs (NAs) can cause population tolerance and drug resistance. Therefore, new antiviral drugs, especially those targeting host factors, are urgently needed. Here, we identified Evans blue as a new HBV inhibitor by screening an FDA drug library using Huh7D^hNTCP cells and confirmed the antiviral activity in primary human hepatocytes and human sodium taurocholate cotransporting polypeptide (hNTCP)-transfected porcine primary hepatocytes. Our efficacy study showed that Evans blue has an IC₅₀ of 2 μM against HBV infection in Huh7D^hNTCP cells, and no apparent toxicity at up to 1000 μM. The IC₅₀ of Evans blue against HBV in primary human hepatocytes was approximately 5 μM. Mechanism studies revealed that Evans blue has a dual anti-HBV effect. It inhibits both the binding of viral preS1 to host cells through the host factor NTCP and the virus capsid assembly by targeting the host factor BK channel. The K_D of the direct interaction between Evans blue and NTCP is 8.82E-8 M. Evans blue can suppress capsid assembly at micromolar concentrations by reducing the cytosolic calcium ion concentration. Since the antiviral effects on HBV binding and assembly are both achieved through targeting host factors, Evans blue inhibits the infection of nucleos(t)ide analog drug-resistant HBV strains in Huh7D^hNTCP cells. Taken together, our results suggest that Evans blue may be a promising anti-HBV drug candidate in the classes of both entry and assembly inhibitors.

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-human immunodeficiency virus activity of novel aminoglycoside-arginine conjugates at early stages of infection

Conjugates of L-arginine with aminoglycosides have already been described as potent in vitro inhibitors of the HIV-1 Tat-trans-activation responsive element interaction. The polycationic nature of these agents leads us to suggest that they may be active against HIV-1 replication by inhibiting earlier stages of the virus life cycle. We have found that R4K and R3G, kanamycin A, and gentamicin C, conjugated with arginine, inhibited HIV-1 NL4-3 replication at EC50 values of 15 and 30 microM for R3G and R4K, respectively, without a detectable tonic effect on MT-4 cells at concentrations higher than 4000 and about 1000 microM, respectively. Both compounds inhibited the binding of a monoclonal antibody (12G5) directed to CXCR4 as well as the intracellular Ca2+ signal induced by the chemokine SDF-1alpha on CXCR4+ cells, suggesting that aminoglycoside-arginine conjugates interact with CXCR4, the coreceptor used by T-tropic, X4 strains of HIV-1. On the other hand, CB4K, a conjugate of kanamycin A with gamma-guanidinobutyric acid, structurally similar to R4K, failed to display any anti-HIV activity of CXCR4 antagonist activity. An HIV-1 strain that was made resistant to the known CXCR4 antagonist AMD3100 was cross-resistant to both R4K and R3G. However, unlike SDF-1alpha and R4K, R3G inhibited the binding of HIV-1 to MT-4 cells. Aminoglycoside-arginine conjugates inhibit HIV replication by interrupting the early phase of the virus life cycle, namely virus binding to CD4 cells and interaction with CXCR4. R3G and R4K may serve as prototypes of novel anti-HIV agents and should be further studied.

Triazine dyes inhibit HIV-1 entry by binding to envelope glycoproteins

We have attempted to purify envelope (Env) glycoproteins of human immunodeficiency virus (HIV) from the culture supernatants of CHO-Sec cells that secreted truncated 140-kDa precursor and mature 120-kDa Env glycoproteins. The concentrated culture supernatants were applied to a column coupled with cibacron blue 3GA (CB3GA) to separate albumin from the Env proteins because CB3GA, a triazine dye, has been known to have a high affinity to albumin. Unexpectedly, Env proteins as well as albumin bound to the column, and the bound Env proteins were eluted by increasing the ionic strength using KCl. Gp120 was eluted at 0.5-0.9 M of KCl, while a higher concentration (0.9-1.5 M) was necessary for the elution of gp140. The agarose gel coupled with reactive red 120 (RR120), another triazine dye with similar characteristics, also retained both Env proteins, and the bound Env proteins could be eluted in a similar manner. In addition, these agents inhibited syncytium formation caused by HTLV-IIIB and HTLV-IIIMN. Inhibition was also seen when a virus-free fusion assay between Env protein expressed in CHO cells and fluorescent labeled SupT1 cells were used. These findings indicate that triazine dyes bind to the functional regions of Env proteins of HIV-1 that play important role(s) for HIV infection.

Liposomal entrapment of suramin(II): interaction of suramin with phospholipids of various chain lengths

Previously, we reported that the entrapment of suramin in dipalmitoylphosphatidylcholine (DPPC, C16) multilamellar liposomes ranged from 25% to 65% and the addition of 30-50 mol% cholesterol (CHL) greatly reduced entrapment. Entrapment of small molecules similar to suramin, disodium 1,5-naphthalenedisulfonic acid (5.5%) and sodium 3-amino-2,7-naphthalenedisulfonic acid (1.2%), were very low. In the present study, the entrapment and interaction of suramin with dilauroylphosphatidylcholine (DLPC, C12), dimyristoylphosphatidylcholine (DMPC, C14), and distearoylphosphatidylcholine (DSPC, C18) liposomes was investigated. DLPC and DMPC showed 2-3-fold higher entrapment percentages (95.1% and 74.2%, respectively) than DPPC (37%). However, the entrapment with DSPC (29%) was about 25% lower than DPPC. Adding 50 mol% cholesterol greatly reduced suramin entrapment for all phospholipids. The entrapment of polysulfonated dyes such as Evans blue, Direct blue 1, or Trypan blue, which are structurally similar to suramin, was found to be in the same order of DLPC > DMPC > DPPC > DSPC. Differential scanning calorimetry of aqueous dispersions of DLPC and DMPC with suramin showed more apparent interaction than for DPPC and DSPC. These results suggest that a large portion of the associated suramin and other polysulfonated compounds results from binding to the surface of the phospholipid bilayer or intercalation into the liposomal bilayer. The phospholipid chain length effect on entrapment may be due to the lower net van der Waals interaction between hydrocarbon chains for shorter acyl chains which also increases the bilayer intermolecular spacing. Such effects could then increase the ability of suramin to interact with individual phospholipid molecules.

Antiviral therapy for human immunodeficiency virus infections

Depending on the stage of their intervention with the viral replicative cycle, human immunodeficiency virus inhibitors could be divided into the following groups: (i) adsorption inhibitors (i.e., CD4 constructs, polysulfates, polysulfonates, polycarboxylates, and polyoxometalates), (ii) fusion inhibitors (i.e., plant lectins, succinylated or aconitylated albumins, and betulinic acid derivatives), (iii) uncoating inhibitors (i.e., bicyclams), (iv) reverse transcription inhibitors acting either competitively with the substrate binding site (i.e., dideoxynucleoside analogs and acyclic nucleoside phosphonates) or allosterically with a nonsubstrate binding site (i.e., non-nucleoside reverse transcriptase inhibitors), (v) integration inhibitors, (vi) DNA replication inhibitors, (vii) transcription inhibitors (i.e., antisense oligodeoxynucleotides and Tat antagonists), (viii) translation inhibitors (i.e., antisense oligodeoxynucleotides and ribozymes), (ix) maturation inhibitors (i.e., protease inhibitors, myristoylation inhibitors, and glycosylation inhibitors), and finally, (x) budding (assembly/release) inhibitors. Current knowledge, including the therapeutic potential, of these various inhibitors is discussed. In view of their potential clinical the utility, the problem of virus-drug resistance and possible strategies to circumvent this problem are also addressed.

Liposomal entrapment of suramin

The liposomal entrapment of suramin and similar compounds in phospholipid vesicles was examined. For dipalmitoylphosphatidylcholine (DPPC) liposomes, entrapment percentages ranged from 25 to 65% with 3-25 mM phospholipid for aqueous solutions containing 0.07 mM of suramin. Incorporation of 30-50 mol % cholesterol (CHL) into DPPC liposomes reduced the percentage suramin entrapment. Addition of positively-charged stearylamine (5 mol %) to DPPC/CHL liposomes increased the entrapment from 2.3% to 30.3%. Entrapment was not affected by the incorporation of negatively-charged phosphatidylglycerol into DPPC/CHL liposomes. When the amount of suramin was increased from 0.07 to 0.7 mM, the entrapment percentage decreased from 37% to 11% when DPPC was held constant at 6 mM. The entrapment of 0.07 mM Evans blue, a molecule similar in structure to suramin, was 51.6% in DPPC liposomes for 6 mM phospholipid. The entrapment percentage, however, decreased by about 50% when incorporated into 7:3 (DPPC/CHL) liposomes. The liposomal entrapment of disodium 1,5-naphthalenedisulfonic acid (5.5%) and sodium 3-amino-2,7-naphthalene-disulfonic acid (1.2%) was very low compared to that of suramin or Evans blue. Differential scanning calorimetry studies of suramin and an aqueous dispersion of DPPC showed an apparent interaction between them. These observations suggest that a significant portion of the entrapped suramin results from binding of suramin to the surface of or intercalation into the liposomal bilayer. Surface binding or intercalation into the phospholipid bilayer may be attributed to both ionic and hydrophobic interactions. The ionic interaction would arise from the suramin sulfonate groups associating with the cationic choline portion of the phospholipid.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

Phosphorothioate oligodeoxynucleotides--anti-sense inhibitors of gene expression?

Phosphorothioate (PS) oligodeoxynucleotides are relatively nuclease resistant, water soluble analogs of phosphodiester (PO) oligodeoxynucleotides. These molecules are chiral but still hybridize well to their RNA targets. While considered for use as in vivo anti-sense inhibitors of gene expression, their biology, especially in the anti-viral area, is dominated by non-sequence specific effects. This review discusses both the sequence and non-sequence specific biologic effects of PS oligomers, and attempts to more clearly indicate their ultimate therapeutic potential.