In Vitro and In Vivo Inhibition of the Infectivity of Human Enterovirus 71 by a Sulfonated Food Azo Dye, Brilliant Black BN

Hand, foot, and mouth disease (HFMD), a highly contagious disease in children, is caused by human enteroviruses, including enterovirus 71 (EV71), coxsackievirus A16 (CVA16), and coxsackievirus A6 (CVA6). Although HFMD is usually mild and self-limiting, EV71 infection occasionally leads to fatal neurological disorders. Currently, no commercial antiviral drugs for HFMD treatment are available. Here, numerous sulfonated azo dyes, widely used as food additives, were identified as having potent antiviral activities against human enteroviruses. Among them, brilliant black BN (E151) was able to inhibit all EV71, CVA16, and CVA6 strains tested. In rhabdomyosarcoma cells, the 50% inhibitory concentrations of the dye E151 for various strains of EV71 ranged from 2.39 μM to 28.12 μM, whereas its 50% cytotoxic concentration was 1,870 μM. Food azo dyes, including E151, interacted with the vertex of the 5-fold axis of EV71 and prevented viral entry. Their efficacy in viral inhibition was regulated by amino acids at VP1-98, VP1-145, and/or VP1-246. Dye E151 not only prevented EV71 attachment but also eluted attached viruses in a concentration-dependent manner. Moreover, E151 inhibited the interaction between EV71 and its cellular uncoating factor cyclophilin A. In vivo studies demonstrated that E151 at a dose of 200 mg/kg of body weight/day given on the initial 4 days of challenge protected AG129 mice challenged with 10× the 50% lethal dose of wild-type EV71 isolates. Taken together, these data highlight E151 as a promising antiviral agent against EV71 infection.IMPORTANCE Human enterovirus 71 (EV71) is one of the causative agents of hand, foot, and mouth disease in children and is responsible for thousands of deaths in the past 20 years. Food azo dyes have been widely used since the nineteenth century; however, their biological effects on humans and microbes residing in humans are poorly understood. Here, we discovered that one of these dyes, brilliant black BN (E151), was particularly effective in inhibiting the infectivity of EV71 in both cell culture and mouse model studies. Mechanistic studies demonstrated that these sulfonated dyes mainly competed with EV71 attachment factors for viral binding to block viral attachment/entry to host cells. As no commercial antiviral drugs against EV71 are currently available, our findings open an avenue to exploit the development of permitted food dye E151 as a potential anti-EV71 agent.

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.

A novel mechanism for inhibition of HIV-1 reverse transcriptase

The human immunodeficiency virus (HIV) epidemic is an important medical problem. Although combination drug regimens have produced dramatic decreases in viral load, current therapies do not provide a cure for HIV infection. We have used structure-based design and combinatorial medicinal chemistry to identify potent and selective HIV-1 reverse transcriptase (RT) inhibitors that may work by a mechanism distinct from that of current HIV drugs. The most potent of these compounds (compound 4, 2-naphthalenesulfonic acid, 4-hydroxy-7-[[[[5-hydroxy-6-[(4-cinnamylphenyl)azo]-7-sulfo-2-naphthalenyl]amino]carbonyl]amino]-3-[(4-cinnamylphenyl)azo], disodium salt) has an IC(50) of 90 nM for inhibition of polymerase chain extension, a K(d) of 40 nM for inhibition of DNA-RT binding, and an IC(50) of 25-100 nM for inhibition of RNaseH cleavage. The parent compound (1) was as effective against 10 nucleoside and non-nucleoside resistant HIV-1 RT mutants as it was against the wild-type enzyme. Compound 4 inhibited HIV-1 RT and murine leukemia virus (MLV) RT, but it did not inhibit T(4) DNA polymerase, T(7) DNA polymerase, or the Klenow fragment at concentrations up to 200 nM. Finally, compound 4 protected cells from HIV-1 infection at a concentration more than 40 times lower than the concentration at which it caused cellular toxicity.

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.

Chemotherapy of human immunodeficiency virus (HIV) infection: anti-HIV agents targeted at early stages in the virus replicative cycle

Several compounds have been identified that inhibit an early stage in the replicative cycle of the human immunodeficiency virus (HIV): i) virus adsorption: polysulfates, polysulfonates, polycarboxylates, polyphosphates, and polyoxometalates; or ii) virus-cell fusion: plant lectins, negatively charged albumins and betulinic acid derivatives; iii) virus fusion/uncoating: bicyclam derivatives; iv) reverse transcription: dideoxynucleoside analogues, acyclic nucleoside phosphonates and non-nucleoside reverse transcriptase inhibitors. In principle, HIV may develop resistance to any of these specific anti-HIV agents. However, virus breakthrough can be completely prevented if these agents, alone or in combination, are added to the HIV-infected cells from the beginning at sufficiently high ('knock-out') concentrations.

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.