Shiro Shigeta

Inhibitory effect of dextran sulfate and heparin on the replication of human immunodeficiency virus (HIV) in vitro.

The polyanionic substances dextran sulfate and heparin were investigated for their antiviral effect on the human immunodeficiency virus (HIV) in vitro. Dextran sulfate and heparin effected a 50% reduction in the cytopathogenicity of HIV for MT-4 cells at a concentration of 4.7 and 7.5 micrograms/ml, respectively. In Molt-4 (clone 8) cells, these values were slightly higher (14.1 and 15.6 micrograms/ml, respectively). No toxicity for the host cells was noted with these compounds at a concentration up to 400 micrograms/ml, so that the selectivity indexes, as based on the ratio of the 50% cytotoxic dose to the 50% antiviral effective dose, were well in excess of 100. These findings may have far reaching implications both diagnostically, when attempts are made to isolate HIV from heparinized blood samples, as therapeutically, to the extent that dextran sulfate or heparin may be useful in blocking HIV replication in vivo.

INHIBITORY EFFECT OF GLYCYRRHIZIN ON THE IN VITRO INFECTIVITY AND CYTOPATHIC ACTIVITY OF THE HUMAN IMMUNODEFICIENCY VIRUS [HIV (HTLV-III/LAV)]

Glycyrrhizin (GL), one of the plant extracts, was investigated for its antiviral action on the human immunodeficiency virus [HIV (HTLV-III/LAV)] in vitro, using cytopathic effect and plaque forming assay system in MT-4 cells (a HTLV-I-carrying cell line). Cloned Molt-4 cells (clone No. 8), which are sensitive to HIV and fuse to giant cells after infection, were also used as a parameter for cytopathic effect of HIV. GL completely inhibited HIV-induced plaque formation in MT-4 cells at a concentration of 0.6 mM, the 50% inhibitory dose being 0.15 mM. GL completely inhibited the cytopathic effect of HIV and the HIV-specific antigen expression in MT-4 cells at a concentration of 0.3 and 0.6 mM, respectively. Furthermore, GL inhibited giant cell formation of HIV-infected Molt-4 clone No. 8 cells. GL had no direct effect on the reverse transcriptase of HIV. Its mechanism of anti-HIV action remains to be elucidated.

Mechanism of inhibitory effect of glycyrrhizin on replication of human immunodeficiency virus (HIV)

Glycyrrhizin (GL) achieved a dose-dependent inhibition of the replication of human immunodeficiency virus type 1 (HIV-1) in MOLT-4 (clone No. 8) cells within the concentration range of 0.075 to 0.6 mM. Within this concentration range, GL also effected a dose-dependent reduction in the protein kinase C (PKC) activity of MOLT-4 (clone No. 8) cells. A well-known PKC inhibitor, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), also proved inhibitory to HIV-1 replication in MOLT-4 (clone No. 8) cells. PKC inhibition may thus be considered as one of the mechanisms by which GL inhibits HIV-1 replication. In addition, GL may also owe its anti-HIV-1 activity, at least in part, to an interference with virus-cell binding, since the compound at 1.2 mM partially inhibited the adsorption of radiolabeled HIV-1 particles to MT-4 cells. At this concentration GL also suppressed giant cell formation induced by co-culturing MOLT-4 (clone No. 8) cells with MOLT-4/HTLV-IIIB cells, whereas the PKC inhibitor H-7 failed to do so.

4′-Ethynyl Nucleoside Analogs: Potent Inhibitors of Multidrug-Resistant Human Immunodeficiency Virus Variants In Vitro

ABSTRACT A series of 4′-ethynyl (4′-E) nucleoside analogs were designed, synthesized, and identified as being active against a wide spectrum of human immunodeficiency viruses (HIV), including a variety of laboratory strains of HIV-1, HIV-2, and primary clinical HIV-1 isolates. Among such analogs examined, 4′-E-2′-deoxycytidine (4′-E-dC), 4′-E-2′-deoxyadenosine (4′-E-dA), 4′-E-2′-deoxyribofuranosyl-2,6-diaminopurine, and 4′-E-2′-deoxyguanosine were the most potent and blocked HIV-1 replication with 50% effective concentrations ranging from 0.0003 to 0.01 μM in vitro with favorable cellular toxicity profiles (selectivity indices ranging 458 to 2,600). These 4′-E analogs also suppressed replication of various drug-resistant HIV-1 clones, including HIV-1M41L/T215Y, HIV-1K65R, HIV-1L74V, HIV-1M41L/T69S-S-G/T215Y, and HIV-1A62V/V75I/F77L/F116Y/Q151M. Moreover, these analogs inhibited the replication of multidrug-resistant clinical HIV-1 strains carrying a variety of drug resistance-related amino acid substitutions isolated from HIV-1-infected individuals for whom 10 or 11 different anti-HIV-1 agents had failed. The 4′-E analogs also blocked the replication of a non-nucleoside reverse transcriptase inhibitor-resistant clone, HIV-1Y181C, and showed an HIV-1 inhibition profile similar to that of zidovudine in time-of-drug-addition assays. The antiviral activity of 4′-E-thymidine and 4′-E-dC was blocked by the addition of thymidine and 2′-deoxycytidine, respectively, while that of 4′-E-dA was not affected by 2′-deoxyadenosine, similar to the antiviral activity reversion feature of 2′,3′-dideoxynucleosides, strongly suggesting that 4′-Eanalogs belong to the family of nucleoside reverse transcriptase inhibitors. Further development of 4′-E analogs as potential therapeutics for infection with multidrug-resistant HIV-1 is warranted.

Antiviral activity of glycyrrhizin against varicella-zoster virus in vitro

One of the plant extracts, glycyrrhizin (GL) was investigated for its antiviral action on varicella-zoster virus (VZV) in vitro. When human embryonic fibroblast (HEF) cells were treated with GL after inoculation of virus (post-treatment), the average 50%-inhibitory dose (ID50) for five VZV strains was 0.71 mM, and the selectivity index (ratio of ID50 for host-cell DNA synthesis to ID50 for VZV replication) was 30. GL was also effective against VZV replication when HEF cells were treated 24 h before the inoculation (pretreatment). Furthermore, at a concentration of 2.4 mM GL inactivated more than 99% of virus particles within 30 min at 37 degrees C. In combination with other anti-herpes drugs (acyclovir, adenine arabinoside, bromovinyldeoxyuridine, and phosphonoformate) or human native beta-interferon, GL had an additive or slightly synergistic effect on VZV replication. The mechanism of anti-VZV action is still unclear. We postulate that GL inhibits the penetration, uncoating or release of virus particles.

An application of tetrazolium (MTT) colorimetric assay for the screening of anti-herpes simplex virus compounds

A rapid and sensitive procedure was developed for in vitro evaluation of anti-herpes simplex virus (HSV) agents. The procedure is based on spectrophotometrical assessment for viability of virus- and mock-infected cells via in situ reduction of a tetrazolium dye MTT, which has already been used for the detection of anti-human immunodeficiency virus (HIV) agents (Pauwels et al., 1988). Monolayer cells such as human embryonic fibroblast, VERO, or HeLa cells were not suitable for this purpose. Among the non-adherent cell lines examined for susceptibility to HSV type 1 (HSV-1), a B-lymphoblastoid cell line NC-37 was found to be the most sensitive. The cell line was found to have a good correlation between the viable cell number and the reduction of MTT. In addition, centrifugation of the virus-infected cells resulted in further increase of the sensitivity of NC-37 cells to HSV-1. After optimization, the method proved to be as sensitive as plaque reduction. The system simplifies significantly the assay procedures and thus permits the evaluation of larger numbers of compounds for anti-HSV-1 activity.

Analysis of anti-rotavirus activity of extract from Stevia rebaudiana

Anti-human rotavirus (HRV) activity of hot water extracts from Stevia rebaudiana (SE) was examined. SE inhibited the replication of all four serotypes of HRV in vitro. This inhibitory effect of SE was not reduced on the prior exposure of SE to HCl for 30 min at pH 2. Binding assay with radiolabeled purified viruses indicated that the inhibitory mechanism of SE is the blockade of virus binding. The SE inhibited the binding of anti-VP7 monoclonal antibody to HRV-infected MA104 cells. The inhibitory components of SE were found to be heterogeneous anionic polysaccharides with different ion charges. The component analyses suggested that the purified fraction named as Stevian with the highest inhibitory activity consists of the anionic polysaccharide with molecular weight of 9800, and contains Ser and Ala as amino acids. Analyses of sugar residues suggest uronic acid(s) as sugar components. It did not contain amino and neutral sugars and sulfate residues. These findings suggest that SE may bind to 37 kD VP7 and interfere with the binding of VP7 to the cellular receptors by steric hindrance, which results in the blockade of the virus attachment to cells.

In vitro antiviral activities of sulfated polysaccharides from a marine microalga (Cochlodinium polykrikoides) against human immunodeficiency virus and other enveloped viruses

A marine microalga, Cochlodinium polykrikoides, produces extracellular sulfated polysaccharides. Isolation and purification of the polysaccharides were accomplished by precipitation with ethanol and Cetavlon, followed by DEAE-cellulose column chromatography (polysaccharides A1 and A2). These polysaccharides, which were homogeneous when analysed by both ultracentrifugal and electrophoretic methods, were composed of mannose, galactose, glucose and uronic acid, together with sulfate groups (S = 7-8% w/w). Both A1 and A2 inhibited the cytopathic effect of influenza virus types A and B in MDCK cells, that of respiratory syncytial virus types A and B in HEp-2 cells, that of human immunodeficiency virus type 1 in MT-4 cells; and, except A1 for herpes simplex virus type 1 and A2 for parainfluenza virus type 2 in HMV-2 cells, the cochlodinium polysaccharides showed no antiviral activity against parainfluenza virus types 2 and 3, measles virus, mumps virus or herpes simplex virus type 1 in HMV-2 cells. No cytotoxicity for host cells was observed with these polysaccharides at a concentration of 100 micrograms ml-1. Inhibitory effects on various viruses were achieved at concentrations that were not markedly inhibitory to the blood coagulation process.

Antiviral activity of NMSO3 against respiratory syncytial virus infection in vitro and in vivo.

NMSO3, a sulfated sialyl lipid was evaluated for its efficacy against respiratory syncytial virus (RSV) and other myxovirus infections in cell culture. The median effective concentration (50% effective concentration, EC(50)) of NMSO3 against replication of the Long strain of RSV in HEp-2 cells was 0.2 and 0.32 microM by optical ELISA and the plaque reduction method, respectively. On the other hand, the corresponding values for ribavirin were 10.5 and 11.2 microM, respectively. NMSO3 showed potent activity against other laboratory strains as well as fresh clinical isolates of RSV, and the average EC(50) was similar to that for Long strain. NMSO3 exhibited minimal cytotoxicity against HEp-2, MDCK, HMV-2 and Vero cells for which the median cytotoxic concentration (CC(50)) was more than 685 microM. The selectivity index [SI=(CC(50) for HEp-2/EC(50))] of NMSO3 for RSV exceeded 2978 and that of ribavirin was 6. The EC(50) of NMSO3 against influenza virus (FluV) A (H3N2) was 23.8 by the MTT method using HMV-2 cells, and 17.8 microM by the TCID(50) method using MDCK cells. NMSO3 did not inhibit replication of influenza B virus, parainfluenza virus type 2 and canine distemper virus at 103 microM. NMSO3 inhibited RSV infection of HEp-2 cells when it was added between 0 and 1.5 h after virus infection. By a temperature shift experiment during the period of contact between the virus and cells, NMSO3 inhibited both the binding of RSV to the cells and its penetration into the cells. Prophylactic and therapeutic efficacy of NMSO3 against RSV infection in cotton rats was examined. Intraperitoneal administration of 100 mg/kg per day of NMSO3 to cotton rats from 1 day before or 1 h after to 3 days after the RSV infection, once a day every day, decreased the RSV titer in lungs to 10(-1.26) to 10(-1.63) compared to the control rats which were infected with RSV and left untreated.

MTT colorimetric assay system for the screening of anti-orthomyxo- and anti-paramyxoviral agents

A rapid and sensitive method was developed for screening potential antiviral agents against orthomyxo- and paramyxoviruses, using the MTT method with cell culture suspensions. The cell lines used for the assay were as follows: MDCK cells for the influenza A virus (Fluv. A), HeLa cells for the respiratory syncytial virus (RSV), and Vero cells for the measles virus (MSV). Test compounds were diluted and plated in 96-well round-bottomed microtiter plates. Trypsinized cell suspensions and viruses were added to each well, the plates were then centrifuged (700 x g, 5 min, room temperature), and incubated for several days. The MTT assay was carried out after the degeneration of virus-infected cells became evident. The optical density (OD) of formazan was determined using a computer-controlled microplate reader. With this assay system, the EC50 values of Ribavirin (used as the reference compound) were 3.7 micrograms/ml for Fluv. A, 4.5 micrograms/ml for RSV, and 12.3 micrograms/ml for MSV, respectively. These EC50 values were equivalent to those obtained using the plaque reduction assay. The confluent cell culture system was inadequate for antiviral assays against RSV and MSV when the MTT method was used, because the inhibition of formazan formation was not observed in viral-infected cells. Moreover, the suspension method is more sensitive to the cytotoxicity of antiviral agents than the confluent cell culture system.