In vivo antibody response and in vitro CTL activation induced by selected measles vaccine candidates, prepared with purified Quil A components

Semipurified Quil A and purified Quil A were used to prepare well-characterized subunit vaccine candidates against measles. Variation in the relative amounts of the measles virus (MV) fusion (F) protein, Quil A-components and lipids did not influence induction of antibody responses in mice, but had a pronounced effect on the capacity to induce cytotoxic T cell (CTL) activity of a CD8(+) MV F-protein specific human T cell clone in vitro. A characteristic MV iscom preparation based on the combined use of HPLC-purified Quil A-components QA-3 and QA-22 (QA-3/22) efficiently induced CTL activity in vitro. Comparable results were obtained by mixing beta-propiolactone inactivated MV with iscom-matrix QA-3/22 or free QA-22. On the basis of the data presented it was concluded that these three preparations are interesting MV vaccine candidates for further evaluation in pre-clinical experiments in a primate model.

Use of cotton rats to evaluate the efficacy of antivirals in treatment of measles virus infections

No practical animal models for the testing of chemotherapeutic or biologic agents identified in cell culture assays as being active against measles virus (MV) are currently available. Cotton rats may serve this purpose. To evaluate this possibility, 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (EICAR) and poly(acrylamidomethyl propanesulfonate) (PAMPS), two compounds that have been reported to inhibit MV in vitro, and ribavirin, an established antiviral drug with MV-inhibitory activity, were evaluated for their antiviral activities against MV and respiratory syncytial virus (RSV) in tissue culture and in hispid cotton rats. A single administration of PAMPS markedly inhibited pulmonary RSV or MV replication (>3 log(10) reduction in pulmonary titer compared to that for controls), but only if this compound was administered intranasally at about the time of virus inoculation. Both EICAR and ribavirin exhibited therapeutic activity against RSV and MV in cotton rats when they were administered parenterally. However, both of these compounds were less effective against MV. On the basis of the pulmonary virus titers on day 4 after virus inoculation, the minimal efficacious dose of EICAR against MV (120 mg/kg of body weight/day when delivered intraperitoneally twice daily) appeared to be three times lower against this virus than that of ribavirin delivered at a similar dose (i.e., 360 mg/kg/day). These findings correlated with those obtained in vitro. The data obtained suggest that cotton rats may indeed be useful for the initial evaluation of the activities of antiviral agents against MV.

Multiple antiviral activities of cyanovirin-N: blocking of human immunodeficiency virus type 1 gp120 interaction with CD4 and coreceptor and inhibition of diverse enveloped viruses

Cyanovirin-N (CV-N) is a cyanobacterial protein with potent neutralizing activity against human immunodeficiency virus (HIV). CV-N has been shown to bind HIV type 1 (HIV-1) gp120 with high affinity; moreover, it blocks the envelope glycoprotein-mediated membrane fusion reaction associated with HIV-1 entry. However, the inhibitory mechanism(s) remains unclear. In this study, we show that CV-N blocked binding of gp120 to cell-associated CD4. Consistent with this, pretreatment of gp120 with CV-N inhibited soluble CD4 (sCD4)-dependent binding of gp120 to cell-associated CCR5. To investigate possible effects of CV-N at post-CD4 binding steps, we used an assay that measures sCD4 activation of the HIV-1 envelope glycoprotein for fusion with CCR5-expressing cells. CV-N displayed equivalently potent inhibitory effects when added before or after sCD4 activation, suggesting that CV-N also has blocking action at the level of gp120 interaction with coreceptor. This effect was shown not to be due to CV-N-induced coreceptor down-modulation after the CD4 binding step. The multiple activities against the HIV-1 envelope glycoprotein prompted us to examine other enveloped viruses. CV-N potently blocked infection by feline immunodeficiency virus, which utilizes the chemokine receptor CXCR4 as an entry receptor but is CD4 independent. CV-N also inhibited fusion and/or infection by human herpesvirus 6 and measles virus but not by vaccinia virus. Thus, CV-N has broad-spectrum antiviral activity, both for multiple steps in the HIV entry mechanism and for diverse enveloped viruses. This broad specificity has implications for potential clinical utility of CV-N.

Recombinant measles virus requiring an exogenous protease for activation of infectivity

Proteolytic cleavage of the fusion protein (F) is an important control mechanism of the biological activity of paramyxoviruses. The sequence R-R-H-K-R(112) at the cleavage site of the F protein of measles virus (MV) was altered by site-directed mutagenesis to R-N-H-N-R(112), which is not recognized by the ubiquitous cellular protease furin. When transiently expressed in cell cultures standard F protein was cleaved, whereas the mutant remained in the uncleaved form. Syncytium formation by the mutant that was analysed after coexpression with haemagglutinin protein depended on the presence of trypsin. Recombinant MV containing the mutation required trypsin activation for fusion and infectivity in cell culture. Intranasal infection of transgenic mice susceptible to MV infection (Ifnar(tm)-CD46Ge) resulted in a moderately productive infection and inflammation of the lung. In contrast to parental virus, intracerebral inoculation did not induce neural disease. The possible effects of the change in cleavage activation on tissue tropism and pathogenicity are discussed.

Inactivation of human viruses by povidone-iodine in comparison with other antiseptics

Inactivation of a range of viruses, such as adeno-, mumps, rota-, polio- (types 1 and 3), coxsackie-, rhino-, herpes simplex, rubella, measles, influenza and human immunodeficiency viruses, by povidone-iodine (PVP-I) and other commercially available antiseptics in Japan was studied in accordance with the standardized protocol in vitro. In these experiments, antiseptics such as PVP-I solution, PVP-I gargle, PVP-I cream, chlorhexidine gluconate, alkyldiaminoethyl-glycine hydrochloride, benzalkonium chloride (BAC) and benzethonium chloride (BEC) were used. PVP-I was effective against all the virus species tested. PVP-I drug products, which were examined in these experiments, inactivated all the viruses within a short period of time. Rubella, measles, mumps viruses and HIV were sensitive to all of the antiseptics, and rotavirus was inactivated by BAC and BEC, while adeno-, polio- and rhinoviruses did not respond to the other antiseptics. PVP-I had a wider virucidal spectrum, covering both enveloped and nonenveloped viruses, than the other commercially available antiseptics.

Antiproliferative action of interferon-alpha requires components of T-cell-receptor signalling

Signal transduction through both cytokine and lymphocyte antigen receptors shares some common pathways by which they initiate cellular responses, such as activation of mitogen-activated protein kinase(s). However, other signalling components appear to be uniquely coupled to each receptor. For example, the interferon receptors transduce regulatory signals through the JAK/STAT pathway, resulting in an inhibition of growth and of antiviral effects, whereas this pathway apparently plays no role in T-cell-receptor (TCR)-dependent gene expression. Conversely, signal transduction through the TCR requires the tyrosine kinases Lck and ZAP-70 and the tyrosine phosphatase CD45. Here we show that, unexpectedly, transmission of growth-inhibitory signals by interferon-alpha (IFN-alpha) in T cells requires the expression and association of CD45, Lck and ZAP-70 with the IFN-alpha-receptor signalling complex.

Inhibition of HIV-1, HIV-2 and SIV envelope glycoprotein-mediated cell fusion by calmodulin

Calmodulin, an EF-hand protein, inhibited the fusion between CD4+ human cells and cells stably expressing HIV-1 envelope proteins. Fusion was also inhibited when HIV-1, HIV-2 or SIV envelope glycoproteins were expressed by vaccinia virus (VV) recombinants, but calmodulin did not inhibit syncytia formation induced by measles virus glycoproteins. Calmodulin also inhibited fusion induced by vPE17, a VV-recombinant expressing a truncated form of HIV-1gp160 which lacks the two known calmodulin-binding sites located in the cytoplasmic domain of gp41. The inhibitory activity was specific to calmodulin among the EF-hand proteins. These observations may be important in understanding the mechanism of retroviral envelope glycoprotein-mediated cell fusion. Several possible mechanisms of action are discussed.

Inhibition effect of shengma-gegen-tang on measles virus in Vero cells and human peripheral blood mononuclear cells

Shengma-Gegen-Tang has long been used against measles virus in human peripheral blood mononuclear cells (PBMC) as well as in Vero cells. One hundred micrograms/ml Shengma-Gegen-Tang in PBMC displays significant anti-measles activity, whereas the same concentration in Vero cells does not. After eight days of infection, the release of virus is significantly suppressed by Shengma-Gegen-Tang in the case of PBMC. In addition, Shengma-Gegen-Tang has a selective stimulation to the secretion of cytokine TNF-alpha in PBMC. Time kinetic analysis indicated that the stimulation of secretion was rapid and could be detected only 2 hrs following the treatment of the PBMC. It rose to an optimal level in 8-12 hrs. These findings suggest that the magnification of anti-measles virus activity of this agent is lymphocyte dependent and may well be mediated by TNF-alpha.

Evaluation of the antiviral activity of N-(phosphonoacetyl)-L-aspartate against paramyxoviruses in tissue culture and against respiratory syncytial virus in cotton rats

N-(phosphonoacetyl)-L-aspartate (PALA), a potent inhibitor of L-aspartic acid transcarbamoylase, was evaluated for cytotoxicity and antiviral activity against three different paramyxoviruses in tissue culture, and for antiviral efficacy and toxicity in vivo using a cotton rat-respiratory syncytial virus (RSV) model. Significant in vitro cytotoxicity was observed in proliferating cultures of HEp-2 (IC50 = 250 micrograms/ml) and Vero cells (IC50 = 32 micrograms/ml), but was less evident in cultures containing confluent monolayers (i.e., stationary cells) of these cells, or in cultures of Madin Darby canine kidney (MDCK) cells (these IC50 values were all > or = 750 micrograms/ml, with 1000 micrograms/ml being the maximum concentration tested). Mean selective indices (ratio of the median cytotoxic dose: median efficacious dose) of 1, 72 and 146 were obtained against parainfluenza virus type 3, RSV and measles virus, respectively, when PALA was tested against these viruses using confluent HEp-2 and Vero cell monolayers. In cotton rats, significant reductions in pulmonary titers (0.8-1.4 log10/g lung) compared to pulmonary viral titers in placebo-treated control animals, were consistently seen in cotton rats given > or = 10 mg of PALA/kg/day (b.i.d.) intraperitoneally on days 1-3 postinfection with either subtype A or B RSV. No toxic effects were noted even in animals given 100 mg of PALA/kg/day for 7 consecutive days.

Engineered serine protease inhibitor prevents furin-catalyzed activation of the fusion glycoprotein and production of infectious measles virus

We have identified the major cellular endoprotease that activates the fusion (F) glycoprotein of measles virus (MV) and have engineered a serine protease inhibitor (serpin) to target the endoprotease and inhibit the production of infectious MV. The F-protein precursor of MV was not cleaved efficiently into the mature F protein in human colon carcinoma cells lacking functional furin, indicating that furin is the major enzyme responsible for activation of the MV F protein. A human serpin alpha 1-antitrypsin variant was engineered to specifically inhibit furin. When expressed from a recombinant vaccinia virus in primate cells infected by MV, the engineered serpin (alpha 1-PDX) specifically inhibited furin-catalyzed cleavage of the F-protein precursor without affecting synthesis of other MV proteins. We generated human glioma cells stably expressing alpha 1-PDX. MV infection in these cells did not result in syncytia. The infected cells produced all the MV proteins, but the F-protein precursor remained largely uncleaved. This did not prevent virus assembly. However, the released virions contained inactive F-protein precursor rather than mature F protein, and infectious-virus titers were reduced by 3 to 4 orders of magnitude. These results show that a mature F protein is not required for the assembly of MV but is crucial for virus infectivity. The engineered serpin may offer a novel molecular antiviral approach against MV.

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.

Efficient MHC class II-restricted presentation of measles virus to T cells relies on its targeting to its cellular receptor human CD46 and involves an endosomal pathway

The role of the measles virus (MV) receptor, human CD46, in the uptake of MV and antigen presentation by Major Histocompatibility Complex (MHC) class II molecules was investigated. Expression of CD46 in murine B cells resulted in cells highly efficient in capturing UV-inactivated MV particles and presenting both envelope hemagglutinin H and nucleoprotein N to specific T cell hybridomas. Although MV fuse with the plasma membrane of its target cells, presentation of both MV-H and -N was sensitive to inhibition by chloroquine but was not affected by a tripeptide which prevents virus-cell fusion. Whereas 50 microM of chloroquine was required to inhibit presentation of MV-H, purified H or soluble N, only a two-fold lower concentration was required to inhibit that of MV-N. This shows that some CD46-mediated captured MV particles are endocytosed, then disrupted and processed in an endosome/lysosome compartment.

Antigenic determinants of measles virus hemagglutinin associated with neurovirulence

The biological activity of monoclonal antibodies specific for the hemagglutinin protein of measles virus strain CAM recognizing six epitope groups according to their binding properties to measles virus strain CAM/R401 was investigated in vivo in our rat model of measles encephalitis. When injected intraperitoneally into measles virus-infected suckling rats, some monoclonal antibodies modified the disease process and prevented the necrotizing encephalopathy seen in untreated animals. The analysis of measles virus brain isolates revealed emergence of variants that resisted neutralization with the passively transferred selecting monoclonal antibody but not with other monoclonal antibodies. Monoclonal antibody escape mutants were also isolated in vitro, and their neurovirulence varied in the animal model. Sequence data from the hemagglutinin gene of measles virus localize a major antigenic surface determinant of the hemagglutinin protein between amino acid residues 368 and 396, which may be functionally important for neurovirulence. The data indicate that the interaction of antibodies with the measles virus H protein plays an important role in the selection of neurovirulent variants. These variants have biological properties different from those of the parent CAM virus.

Isolation and structure of woodorien, a new glucoside having antiviral activity, from Woodwardia orientalis

Hot aqueous and methanol extracts of the rhizomes of Woodwardia orientalis were tested for their in vitro antiviral activity against herpes simplex virus type 1 (HSV-1), poliovirus type 1, and measles virus by plaque reduction assay. The aqueous extract of W. orientalis reduced the plaque forming ability of HSV-1 and poliovirus more strongly than did the methanol extract. By bioassay-directed fractionation of the aqueous extract, a new glucoside, woodorien (1), along with five known compounds were isolated from an EtOAc-soluble fraction that had antiviral activity. The structures of these compounds were determined by the use of two dimensional (2D) NMR techniques (1H-1H correlation spectroscopy (COSY), 1H-13C COSY and heteronuclear multiple-bond multiple-quantum coherence (HMBC)). Woodorien (1) was the most potent inhibitor against HSV-1 among the isolated compounds.

Isolation and structure of woodorien, a new glucoside having antiviral activity, from Woodwardia orientalis

Hot aqueous and methanol extracts of the rhizomes of Woodwardia orientalis were tested for their in vitro antiviral activity against herpes simplex virus type 1 (HSV-1), poliovirus type 1, and measles virus by plaque reduction assay. The aqueous extract of W. orientalis reduced the plaque forming ability of HSV-1 and poliovirus more strongly than did the methanol extract. By bioassay-directed fractionation of the aqueous extract, a new glucoside, woodorien (1), along with five known compounds were isolated from an EtOAc-soluble fraction that had antiviral activity. The structures of these compounds were determined by the use of two dimensional (2D) NMR techniques (1H-1H correlation spectroscopy (COSY), 1H-13C COSY and heteronuclear multiple-bond multiple-quantum coherence (HMBC)). Woodorien (1) was the most potent inhibitor against HSV-1 among the isolated compounds.

Antiviral traditional medicines against herpes simplex virus (HSV-1), poliovirus, and measles virus in vitro and their therapeutic efficacies for HSV-1 infection in mice

One hundred forty-two kinds of traditional medicines, which have been historically used in China, Indonesia, and Japan, were examined for the antiviral activity of their hot water (HW) extracts against herpes simplex virus type 1 (HSV-1), poliovirus type 1, and measles virus by plaque reduction assay. Thirty-two, 55, and 30 HW-extracts of them showed anti-HSV-1, antipoliovirus, and anti-measles virus activities, respectively. Among the 32 HW-extracts with anti-HSV-1 activity, 3 HW-extracts had anti-HSV-1 activity alone and the others showed anti-HSV-1 activity with anti-poliovirus and/or anti-measles virus activities. The 32 HW-extracts were further examined for their therapeutic efficacies of HSV-1 infection in mice. The mice were infected cutaneously with HSV-1 and HW-extracts were orally administered three times daily. Twelve HW-extracts, currently used for the treatment of various diseases other than viral infection, were found to be significantly effective in limiting the development of skin lesions and/or in prolonging the mean survival times of HSV-1-infected mice. These results suggested that 12 of 142 HW-extracts that exhibited therapeutic efficacy in an animal infection model were possible candidates for anti-HSV-1 traditional medicine.

Inhibitory effect of the calcium antagonist, verapamil, on measles and vaccinia replication in cell culture

Kidney cell lines MA104 and BGM were infected with vaccinia and measles viruses respectively in the presence of 45Ca. Increased 45Ca level was detected in the virally infected cells as compared with control cells. An enhancement of 28 +/- 6% and 37 +/- 13% was shown in vaccinia and measles respectively following 5 h of infection. The effect of the calcium antagonist verapamil was studied in both vaccinia- and measles-infected cells. In one-step growth experiments, the mean inhibitory effect of 90 microM verapamil on viral yield after 13 h was 97 +/- 1% in the case of vaccinia. In the measles virus after 47 h a mean of 76 +/- 5% inhibition was detected. The suitability of verapamil as a potential antiviral agent is suggested and requires further investigation.

Effect of prostaglandin E2 (PGE2) and cyclic adenosine monophosphate (cAMP) upon actin cytoskeleton in human pulmonary fibroblasts (ICP-23) infected by measles virus

The evolution of the actin cytoskeleton after trypsinization and recultivation as well as the effect of the PGE2 modulator and that of the secondary messenger, the cyclic AMP upon the same cytoskeletal proteins in human pulmonary fibroblasts (ICP-23) were studied. The substances were administered simultaneously and after one hour of viral adsorption. Using epifluorescence for pointing out filamentous actin the modifications occurring in this cytoskeletal protein when contacting trypsin and the virus and when PGE2 and cAMP are administered in the experimental variants are observed. Actin arrangement is obviously modified by the viral infection but the restrictive effect of PGE2 and cAMP upon virus replication is correlated with modifications occurring in the actin cytoskeleton.

Antibody-dependent transcriptional regulation of measles virus in persistently infected neural cells

Application of neutralizing anti-hemagglutinin antibodies to mouse neuroblastoma cells (NS20Y/MS) persistently infected with measles virus (MV) leads to a significant reduction of viral structural proteins within 6 days. While the transcriptional gradient for MV-specific mRNAs remained unaffected upon antibody treatment, the total amount of MV-specific transcripts dropped by 80% after 24 h. The expression of genomic RNA was affected similarly, with slightly slower time kinetics. Both transcription and expression of the viral structural proteins could be completely reactivated when viral antibodies were removed from the tissue culture. The same findings could be obtained in rat glioma cells persistently infected with subacute sclerosing panencephalitis virus (C6/SSPE) but not in cells of nonneural origin. The data indicate that antibody-induced antigenic modulation affects the early stages of viral transcription within a few hours after the addition of antibodies and leads to an almost complete repression of viral gene expression in cells of neural origin.

Effect of interferon-alpha on measles virus replication in human peripheral blood mononuclear cells

We analyzed the effect of exogenous human leukocyte interferon (IFN)-alpha on measles virus (MV) replication in human peripheral blood mononuclear cells (PBMC). The release of infectious virus was progressively reduced by increasing concentrations of IFN-alpha, and blocked with an IFN-alpha concentration of 1000 U/ml. In order to detect a possible target of this inhibitory effect, viral transcription and translation events were analyzed. The synthesis of MV mRNAs was reduced, but not blocked, in the presence of IFN-alpha. However, this effect was not specific on the viral RNAs, but due to a general inhibition of RNA synthesis in IFN-treated PBMC. The expression of viral polypeptides was also inhibited in a dose-dependent manner by exogenous IFN-alpha, but a low level of protein synthesis was detected by both Western blotting and immunofluorescence techniques, even with the maximum amount of IFN-alpha used (1000 U/ml). These findings account for a partial maintenance of the viral replicative cycle, even when the production of infectious virus is blocked. Moreover, the effect of IFN-alpha is not specifically targeted on the virus macromolecular synthesis.

Prostaglandin E2 (PGE2) effect upon ICP-23 human pulmonary fibroblasts growth in culture and on measles virus multiplication in this cell type

The influence of PGE2 in different concentrations (10(-4)M, 10(-6)M, 10(-8)M) and of 1 mM AMPc upon ICP-23 human pulmonary fibroblasts and also the influence of PGE2 upon measles virus multiplication in the same cell type were studied. PGE2 inhibited fibroblasts growth in all administered concentrations, depending on them. AMPc adding to human fibroblasts in culture progressively stimulated cells growth in the first 24 hours, produced a steady growth during 24-48-hour interval and slightly inhibited cellular divisions between 48 and 72 hours. PGE2, added in the same concentrations to measles virus--infected ICP-23 cells, concomitantly with virus administration and after 1 hour of viral adsorption influenced viral multiplication, depending on substance concentration and culturing period. Obtained data suggested that PGE2 in physiological concentrations (10(-6)M, 10(-8)M) initially has a weak inhibitory effect (titration after 6 days), but then stimulates viral production (9 days). The initial inhibition is more marked when the substance is added concomitantly with virus administration.

Stimulation of measles virus replication by cyclic guanosine monophosphate

Measles virus (MV) replication in acutely infected human cells was markedly stimulated following exposure to guanosine 3',5'-monophosphate (cyclic GMP). Addition of cyclic GMP to tissue culture fluids immediately following infection with the virus resulted in acceleration of virus-mediated cell fusion, increased synthesis of virus-specified proteins and a 50-fold increase in infectious particle production. No evidence of altered viral protein phosphorylation was found. The results suggest that cyclic GMP stimulates multiple stages of the MV replication cycle.

Identification of interferon-resistant subpopulations in several strains of measles virus: positive selection by growth of the virus in brain tissue

Subacute sclerosing panencephalitis (SSPE) is a chronic and usually fatal central nervous system disease caused by a persistent infection with measles virus. The pathogenic mechanisms of the disease are poorly understood, but restricted expression of viral antigens within the infected tissue appears to be involved. We have previously proposed that interferon (IFN) plays a role in the pathogenesis of SSPE by interacting with viral subpopulations that are relatively resistant to IFN-mediated inhibition. Such IFN-resistant viral subpopulations have now been identified in six independent strains of measles virus, two derived from patients with measles and four derived from patients with SSPE. By means of a replicative-plating procedure, these IFN-resistant viruses were found to be heterogeneous with respect to their growth in the presence of high levels of IFN. One viral form replicates fully, with complete destruction of the infected-cell culture, whereas the other form induces a restricted, self-limited form of cytopathic effect, similar to that seen with cell-associated strains of measles virus isolated from SSPE patients. Passage of a virus stock containing both of these viral forms through the central nervous system tissue of newborn hamsters strongly selects for the viral form associated with the self-limiting type of cytopathic effect. The presence of this form of IFN-resistant virus coupled with chronic production of IFN within the central nervous system may account for viral persistence in SSPE patients.

Effect of drugs which inhibit cholesterol synthesis on syncytia formation in vero cells infected with measles virus

We found that nontoxic doses of two inhibitors of cholesterol synthesis, namely W-7 and cerulenin, delayed syncytia formation in vero cells infected with measles virus. To correlate syncytia formation and lipidic membrane changes induced by these drugs, we labelled cell lipids with [14C]acetate. Measles virus infection increased the incorporation of radiolabel into fatty acids, triacylglycerol, cholesterol ester, and decreased its incorporation into cholesterol and 1,2-diacylglycerol. The ratios phosphatidylcholine/sphingomyelin and free cholesterol/lanosterol-dihydrolanosterol also decreased during the infection. W-7 and cerulenin greatly altered lipid metabolism. Both decreased the phosphatidylcholine to sphingomyelin and the cholesterol to lanosterol-dihydrolanosterol ratios. Z-D-Phe-L-Phe-L-Gly, a tripeptide which corresponds to the N-terminal sequence of the viral fusion protein (responsible for syncytia formation) and which inhibits virus-induced cell fusion without affecting virus synthesis also perturbed cholesterol metabolism. The tripeptide reversed the phosphatidylcholine to sphingomyelin ratio in infected cells. At non-toxic doses, W-7 inhibited the synthesis of infectious virus. Cerulenin which inhibited strongly the lipid synthesis did not. Finally, the well characterized inhibitors of cholesterol synthesis, mevinolin, ketoconazole and miconazole were shown to inhibit the syncytia formation. We conclude that the inhibition of syncytia by W-7 and cerulenin is associated with their capacity to alter the cholesterol metabolism, whereas the antiviral effect of W-7 does not seem related to this capacity.

Inhibitory effect of selected antiviral compounds on measles (SSPE) virus replication in vitro

A variety of antiviral compounds were examined for their inhibitory effect on measles (SSPE) virus plaque formation in VERO cells. The following compounds inhibited SSPE virus (strain Niigata-1) replication at concentrations that were significantly lower than their minimum cytotoxic concentrations: neplanocin A, neplanocin C, carbocyclic 3-deazaadenosine, 9-(trans-2', trans-3'-dihydroxycyclopent-4'-enyl)adenine, 9-(trans-2',trans-3'-dihydroxycyclopent-4'-enyl)-3-deazaadenine, (RS)-3-adenin-9-yl-2-hydroxypropanoic acid isobutyl ester, carbodine, cyclopentenyl cytosine, 3-deazaguanine, pyrazofurin, ribavirin and 6-azauridine. As the most selective inhibitors of SSPE virus replication emerged pyrazofurin, 3-deazaguanine, 6-azauridine and ribavirin. These compounds were further examined for their relative potency against a number of measles (SSPE) virus strains. Their order of (decreasing) potency was pyrazofurin greater than 6-azauridine approximately 3-deazaguanine greater than ribavirin. Amantadine, inosiplex and glycyrrhizin, that were also included in these assays, did not show appreciable activity against any of the measles (SSPE) virus strains.