Potent inhibition of arenavirus infection by a novel fusion inhibitor

Several arenaviruses, including Lassa and Lujo viruses in Africa and five New World arenavirus (NWA) species in the Americas, cause life-threatening viral hemorrhagic fevers. In the absence of licensed antiviral therapies, these viruses pose a significant public health risk. The envelope glycoprotein complex (GPC) mediates arenavirus entry through a pH-dependent fusion of the viral and host endosomal membranes. It thus is recognized as a viable target for small-molecule fusion inhibitors. Here, we report on the antiviral activity and pre-clinical development of the novel broad-spectrum arenavirus fusion inhibitors, ARN-75039 and ARN-75041. In Tacaribe virus (TCRV) pseudotyped and native virus assays, the ARN compounds were active in the low to sub-nanomolar range with selectivity indices exceeding 1000. Pharmacokinetic analysis of the orally administered compounds revealed an extended half-life in mice supporting once-daily dosing, and the compounds were well tolerated at the highest tested dose of 100 mg/kg. In a proof-of-concept prophylactic efficacy study, doses of 10 and 35 mg/kg of either compound dramatically improved survival outcome and potently inhibited TCRV replication in serum and various tissues. Additionally, in contrast to surviving mice that received ribavirin or placebo, animals treated with ARN-75039 or ARN-75041 were cured of TCRV infection. In a follow-up study with ARN-75039, impressive therapeutic efficacy was demonstrated under conditions where treatment was withheld until after the onset of disease. Taken together, the data strongly support the continued development of ARN-75039 as a candidate therapeutic for the treatment of severe arenaviral diseases.

[Use of ribavirin in viruses other than hepatitis C. A review of the evidence]

Ribavirin is a molecule with antiviral activity against different viruses. In clinical practice, it has made its niche almost exclusively for the treatment of the hepatitis C virus. However, there are other diseases in which it could be of benefit and it has the advantage of being suitable for oral, intravenous and inhaled administration. We conducted a review of the indications of the main drug agencies (Spanish, European and American) and other possible indications, mainly haemorrhagic fevers and coronavirus.

[Chemotherapy for Bolivian hemorrhagic fever in experimentally infected guinea pigs]

The efficacy of the antiviral agents nucleoside analogues manufactured in Russia and foreign countries against Bolivian hemorrhagic fever in the treatment and rapid prevention regimens was studied in guinea pigs. In rapid prevention and treatment of guinea pigs, the intraperitoneal injection of 1/10 of the equivalent dose of vero-ribavirin for this animal species was ascertained to protect 70% of the animals infected with Machupo virus strain Carvallo in doses 8 and 10 LD50.

Transferrin receptor 1 is a cellular receptor for New World haemorrhagic fever arenaviruses

The transferrin receptor 1 (TfR1) has been identified as the cellular receptor for four New World arenaviruses — the Junin, Machupo, Guanarito and Sabia viruses. This class of arenaviruses is important because they cause fatal haemorrhagic fevers. Treating cultured cells with an antibody against TfR1 blocks viral entry and replication. Antibodies that limit arenavirus replication without interfering with host iron metabolism may be effective in controlling outbreaks of New World haemorrhagic fever.

At least five arenaviruses cause viral haemorrhagic fevers in humans. Lassa virus, an Old World arenavirus, uses the cellular receptor α-dystroglycan to infect cells¹. Machupo, Guanarito, Junin and Sabia viruses are New World haemorrhagic fever viruses that do not use α-dystroglycan². Here we show a specific, high-affinity association between transferrin receptor 1 (TfR1) and the entry glycoprotein (GP) of Machupo virus. Expression of human TfR1, but not human transferrin receptor 2, in hamster cell lines markedly enhanced the infection of viruses pseudotyped with the GP of Machupo, Guanarito and Junin viruses, but not with those of Lassa or lymphocytic choriomeningitis viruses. An anti-TfR1 antibody efficiently inhibited the replication of Machupo, Guanarito, Junin and Sabia viruses, but not that of Lassa virus. Iron depletion of culture medium enhanced, and iron supplementation decreased, the efficiency of infection by Junin and Machupo but not Lassa pseudoviruses. These data indicate that TfR1 is a cellular receptor for New World haemorrhagic fever arenaviruses.

Identification and characterization of potent small molecule inhibitor of hemorrhagic fever New World arenaviruses

Category A arenaviruses as defined by the National Institute of Allergy and Infectious Diseases (NIAID) are human pathogens that could be weaponized by bioterrorists. Many of these deadly viruses require biosafety level-4 (BSL-4) containment for all laboratory work, which limits traditional laboratory high-throughput screening (HTS) for identification of small molecule inhibitors. For those reasons, a related BSL-2 New World arenavirus, Tacaribe virus, 67-78% identical to Junín virus at the amino acid level, was used in a HTS campaign where approximately 400,000 small molecule compounds were screened in a Tacaribe virus-induced cytopathic effect (CPE) assay. Compounds identified in this screen showed antiviral activity and specificity against not only Tacaribe virus, but also the Category A New World arenaviruses (Junín, Machupo, and Guanarito). Drug resistant variants were isolated, suggesting that these compounds act through inhibition of a viral protein, the viral glycoprotein (GP2), and not through cellular toxicity mechanisms. A lead compound, ST-294, has been chosen for drug development. This potent and selective compound, with good bioavailability, demonstrated protective anti-viral efficacy in a Tacaribe mouse challenge model. This series of compounds represent a new class of inhibitors that may warrant further development for potential inclusion in a strategic stockpile.

Interferon alfacon-1 protects hamsters from lethal pichinde virus infection

Hemorrhagic fever of arenaviral origin is a frequently fatal infectious disease of considerable priority to the biodefense mission. Historically, the treatment of arenaviral infections with alpha interferons has not yielded favorable results. Here we present evidence that interferon alfacon-1, a nonnaturally occurring bioengineered alpha interferon approved for the treatment of chronic hepatitis C, is active against Pichinde and Tacaribe arenaviruses in cell culture. In the hamster model of Pichinde virus (PCV) infection, interferon alfacon-1 treatment significantly protected animals from death, prolonged the survival of those that eventually died, reduced virus titers, and limited liver damage characteristic of PCV-induced disease. Moreover, interferon alfacon-1 also demonstrated therapeutic activity, to a lesser degree, when the initiation of treatment was delayed up to 2 days post-virus challenge. Despite the observed advantages of interferon alfacon-1 therapy, efforts to stimulate the immune system with the known interferon inducer poly(I:C12U) (Ampligen) offered only limited protection against lethal PCV challenge. Taken together, these data suggest that the increased potency of the bio-optimized interferon alfacon-1 molecule may be critical to the observed antiviral effects. These data are the first report demonstrating efficacious treatment of acute arenaviral disease with alpha interferon therapy, and further study is warranted.

Differential inhibitory action of two azoic compounds against arenaviruses

The action of five azo-based compounds against the arenaviruses Junin (JUNV) and Tacaribe (TCRV) was evaluated in vitro by a virus yield inhibition assay in Vero cells and a cell-free virion inactivation assay. The compound 2-azo-(1'-(2'-nitroso)naphthyl)-benzoate (ANNB) was the most effective inhibitor of arenavirus production in Vero cells with EC(50) (effective concentration 50%) values in the range 6.5-26.2 microM and without inactivating properties. By contrast, the azodicarbonamide (ADA) was very effective in inactivating both arenaviruses with IC(50) (inactivating concentration 50%) values of 7.6 and 5.3 microM against JUNV and TCRV, respectively. The virucidal activity of ADA was time- and temperature-dependent. ANNB had no inhibitory action on virus binding or penetration of target cells and did not affect the synthesis of viral proteins. The most likely event susceptible to ANNB would be the process of intracellular virion assembly.

Mode of inactivation of arenaviruses by disulfide-based compounds

Several disulfide-based compounds, including intermolecular aromatic disulfides of the type Ph-S-S-Ph and dithianes with the sulfur atoms tethered in a ring structure, have shown effective inhibitory activity against the arenaviruses Junin (JUNV), agent of Argentine hemorrhagic fever, and Tacaribe (TCRV). These compounds showed a strong virucidal effect with inactivating concentration 50% (IC(50)) values in the range 0.6-5.0 microM, and also were effective to reduce virus yields from infected cells. The mode of inactivating action of two active compounds, the aromatic bis disulfide NSC20625 and the dithiane NSC624152, was further studied. Both compounds were able to inactivate arenaviruses after a few minutes of direct contact with virions, in a concentration- and time-dependent manner. The ability of drug-treated virus to perform several steps of the replication cycle was analyzed. The killed virus particles were found to bind and enter to Vero cells with the same efficacy as infectious native virions, but the ability of inactivated virions to synthesize viral proteins in Vero cells was abolished. Thus, treatment of JUNV and TCRV with these compounds destroyed virion infectivity, generating particles which entered the host cell but were unable to complete the viral biosynthetic processes.

New neplanocin analogues. 6. Synthesis and potent antiviral activity of 6'-homoneplanocin A1

The design, synthesis, and antiviral activities of 6'-homoneplanocin A (HNPA, 3) and its congeners having nucleobases other than adenine, such as 3-deazaadenine (4), guanine (5), thymine (6), and cytosine (7), were described. Starting from the known cyclopentenone derivative 8, the optically active (mesyloxy)cyclopentene derivative 15 was prepared, which was condensed with nucleobases then deprotected to give target compounds 3-7. Of these compounds, HNPA showed an antiviral activity spectrum that was comparable to, and an antiviral specificity that was higher than, that of neplanocin A. HNPA proved particularly active against human cytomegalovirus, vaccinia virus, parainfluenza virus, vesicular stomatitis virus, and arenaviruses, which is compatible with an antiviral action targeted at S-adenosylhomocysteine hydrolase. HNPA appears to be a promising candidate drug for the treatment of these viruses.

[The immunity indices of BALB/c mice immunized with an inactivated antigen of the Machupo virus]

The paper presents the data characterizing parameters of specific and nonspecific immunity in BALB/c mice immunized with gamma-ray-inactivated Machupo virus antigen or its formalinized antigen. The gamma-ray inactivated preparation was shown to be more immunogenic for BALB/c mice. A certain relationship between the time course of activity of nonspecific immunity factors in the immunized animals and the protective activity of the preparation under study was also noted. The decisive role of the T-cell part of the immune system was demonstrated in the resistance of this model animal to Machupo virus infection.

The effects of oligosaccharide trimming inhibitors on glycoprotein expression and infectivity of Junin virus

The effects of specific inhibitors of glycoprotein trimming reactions on Junin virus (JV) replication were investigated. Bromoconduritol, an inhibitor of glucosidase II, significantly reduced infective virus production (DE50: 1.1 mM) and viral protein expression. Neither 1-deoxynojirimycin, an inhibitor of both glucosidases I and II, nor 1-deoxymannojirimycin and swainsonine, inhibitors of mannosidase I and II, respectively, showed any activity against JV multiplication. These results are the first evidence that the acquisition of a complex form of the envelope glycoprotein oligosaccharide chains is not essential for JV infectivity. The effect of bromoconduritol was reversible and probably due to the formation of an unstable intermediate oligosaccharide structure which may be more sensitive to degradative proteolysis.

Metal-based formulations with high microbicidal activity

Substances were evaluated for their relative potencies in inactivating Junin virus, Escherichia coli, and spores of Bacillus subtilis. Under the conditions of our test, glutaraldehyde was the most efficient agent among all substances currently recommended for disinfecting and sterilizing medical devices. Either copper or iron ions by themselves were able to inactivate virus with an efficiency similar to that of substances currently used for disinfection and sterilization. The microbicidal effect of metals, however, was enhanced further by the addition of peroxide. The mixtures of copper and peroxide described here were more efficient than glutaraldehyde in inactivating viruses and bacteria. The addition of a metal chelator to metal-peroxide mixtures further increased the microbicidal potency of the reagent. The formulations described in this study should be harmless to people but able to quickly and efficiently inactivate microorganisms, particularly viruses.

[Lysosomotropic compounds inhibiting the multiplication of Junin virus]

A number of lysosomotropic compounds of diverse chemical structure, ammonium chloride, procaine and chlorpheniramine, were found to inhibit the infection of Vero cells by Junín virus. Viral replication was almost totally inhibited by 15 mM ammonium chloride, when added either before or within the first hour of infection and a significant inhibition (97.8%) was observed when it was added 8 hours after infection. These results agree with a model which postulates that arenavirus entry occurs by receptor-mediated endocytosis.

Antiviral immunotoxins: antibody-mediated delivery of gelonin inhibits Pichinde virus replication in vitro

Immunotoxins were produced and evaluated for antiviral activity against Pichinde virus, a member of the family Arenaviridae. Immunoglobulins were conjugated to the ribosome-inactivating protein, gelonin, through a disulfide linkage to form the immunotoxins. Immunotoxins were produced utilizing monoclonal antibodies, immunoglobulin-binding proteins and hyperimmune sera. An immunotoxin consisting of hyperimmune rabbit sera conjugated with gelonin displayed strong antiviral activity against Pichinde virus, as did a protein G-gelonin indirect immunotoxin in combination with nonconjugated hyperimmune sera. Hyperimmune rabbit sera conjugated with gelonin caused no detectable cytotoxicity in non-infected Vero cells as measured by [3H]leucine incorporation. The 50% effective dose for the immunotoxin was 0.018 microM compared with 86 microM for ribavirin.

Protective effect of a low-dose of cyclophosphamide in experimental infection of guinea pigs with Junin virus

Administration of cyclophosphamide (CY) to guinea pigs infected with a lethal strain of Junin virus (JV) delayed the time of death, with survival of a small number of animals. Virological studies showed a temporary decrease of virus concentration in blood and viscera shortly after the CY injection. In the pathological study no differences were found in the organic lesions present in CY-treated and nontreated animals, with the exception of the pulmonary alterations. In CY-treated guinea pigs the lungs appeared almost normal, but in the control, nontreated animals severe alterations with the pattern of the "respiratory distress syndrome of the adult" were consistently present. In in vitro experiments, incorporation of serum collected from guinea pigs injected 30 minutes before exsanguination with CY to cell cultures, infected with JV, prevented virus replication. On the basis of these results it is suggested that the delay of time of death and eventual survival of CY-treated guinea pigs after JV infection depends on a direct antiviral effect of the drug rather than on its known immunosuppressive action. In addition, the absence of pulmonary alterations in CY-treated animals was tentatively considered to be dependent on the marked polymorphonuclear leukocyte depletion induced by the drug.

Ribavirin effect on experimental Junin virus-induced encephalitis

Junin virus, the etiological agent of Argentine hemorrhagic fever, produces in man a disease mainly characterized by hemorrhagic alterations, commonly accompanied by neurological symptoms, and leading to 10% mortality. Intracerebral inoculation in 10-day-old rats or intraperitoneal inoculation in 2-day-old rats leads to high mortality due to severe encephalitis. Here, the effect of Ribavirin on these experimental models was tested in order to evaluate the degree of protection achieved against neuropathological manifestations. In intracerebrally infected 10-day-old rats the drug was administered 2 hr before virus inoculation. Doses ranged from 30 to 90 mg/kg body weight. Protection reached 40% for the 60 and 90 mg doses. Intraperitoneally infected 2-day-old rats received the drug in five 30-mg daily doses, starting the same day as virus inoculation. Survival was 73%. Viral replication within peritoneal macrophages dropped markedly, leading to much lower CNS viral titres. Together with results reported in primates, our findings support further studies on Ribavirin, with a view to eventual trials in humans.

[Pathogenic Machupo and Lassa arenaviruses: the biochemical properties of virion RNA and proteins]

Lassa virus purified in the isodensity sucrose concentration gradient had the following buoyant densities: 1.17 g/cm3 (sucrose), 1.19 g/cm3 (cesium chloride), 1.16 g/cm3 (urografin). Similar parameters were obtained for Machupo virus. Virion RNAs of these viruses contained 5 sedimentation classes of molecules: 30-31S, 28S, 22-24S, 18S, and 4-6S. Experiments on hybridization of individual sedimentation classes of RNA with an excess of poly(A)-containing RNA from the infected cells as well as inhibition of synthesis of 28S and 18S virion RNAs with low concentrations (0.005-0.5 micrograms/ml) of actinomycin D showed the genetic information for virus proteins to be coded for in two segments: 30-31S and 22-24S. The method of self-annealing demonstrated molecules with complementary sequence ("plus" and "minus" strands) in genome RNAs. In addition to previously described major proteins (78K, 64K, 37K), high performance liquid gel-penetrating chromatography of Machupo virus structural proteins revealed a minor protein with molecular weight of 50 kilodaltons. Pulse-chase experiments demonstrated in the infected cells a precursor-product metabolic bond between glycosylated proteins 78K and 37K. Lassa virus contained 3 structural major proteins with molecular weights 60, 48, and 34 kilodaltons (K). The 60K protein was detected in the nucleocapsid fraction, and 48 K protein in the soluble subvirion fraction. Proteins 60K and 34K were immunoprecipitated in greatest amounts in the infected cells.

Abrogation of Junin virus encephalitis by critical cyclophosphamide timing and dosage

Junin virus-induced encephalitis in suckling mouse is a delayed-type hypersensitivity reaction, whose immunopathologic nature has been proven by suppressing the thymus-dependent response. Cyclophosphamide (CY) given at day +6 post-infection (p.i.) has been shown to modulate infection, presumably by TDTH lymphocyte inactivation. To determine critical timing and i.p. drug dose, brain histology and survival were studied in 3-day-old Balb/c mice, inoculated i.c. with Junin virus. Optimal protection was achieved with a non-toxic, 50 mg/kg CY dose at day 6 p.i. (+6): no brain tissue damage was detected in animals killed at day +12, when the necropsied controls exhibited widespread lesions. Other timings (day +3, +4, +5) proved less effective. As regards alternative dosage at day +6, 30 mg was useless, and severe leptomeningitis was evident, whereas 40 mg significantly lowered mortality, and lesions were much milder and less constant. It seems that the 50 mg/kg CY dose must be administered at a critical time p.i. to inactivate sensitized TDTH lymphocytes and to reduce mortality and CNS pathology significantly.

Therapeutic effect of the antiviral agent ribavirin in Junín virus infection of primates

In order to assess the effect of the antiviral Ribavirin on the course of Junín virus infection in Callithrix jacchus, seven inoculated monkeys were treated with 15 mg of the drug, twice a day, starting 6 days after infection when all animals were viremic. The three untreated controls showed typical signs of Junín virus infection at 14 days pi and their mean time of death was 18 days. In contrast, no signs of illness were detected in Ribavirin-treated animals until 24 days pi, when marmosets showed signs of neurological involvement: 5 of these animals died (mean day of death: 36) but the two remaining treated monkeys improved and survived infection without sequelae. The comparison of survival rates (0% vs 28%) and the delay of the mean day of death observed indicates that the Ribavirin treatment used has therapeutic effect on Junín virus infection in vivo.

Effect of ribavirin and tributylribavirin on argentine hemorrhagic fever (Junin virus) in guinea pigs

Subcutaneous injections of ribavirin into guinea pigs infected intraperitoneally or intracerebrally with Junin virus significantly increased the mean time to death but did not enhance survival of the animals. We found similar results with tributylribavirin. Virus replication was delayed, but not prevented, in ribavirin-treated infected guinea pigs. The animals usually died with high virus titers in their brains and frequently were paralyzed.

[Characteristics of the subvirion components formed after the treatment of Machupo virus with a nonionic detergent]

Machupo virus labeled with radioactive precursors of RNA or protein synthesis was purified by isodensity ultracentrifugation in sucrose concentration gradient. The purified virus was disrupted with NP-40 nonionic detergent in the presence of 1 M KCl, and subvirion fractions were separated by ultracentrifugation in urografin density gradient. This treatment resulted in formation of two subvirion components with a buoyant density 1.25-1.26 and 1.10-1.12 g/cm3 in urografin concentration gradient. The subvirion fraction with the density of 1.25-1.26 g/cm3 contained high-molecular virion RNAs, a major protein of molecular weight of 64 kD, and seemed to be the virion nucleocapsid. The solubilised fraction (1.10-1.12 g/cm3) contained glycosylated protein 37 kD which seems to be a surface glycoprotein.

[Effect of actinomycin D on the reproduction of the Machupo virus]

The effect of inhibitors of mRNA synthesis (actinomycin D and alpha-amanitin) and DNA replication (mitomycin C and ethidium bromide) on Machupo virus reproduction was studied. Actinomycin D (1.0-4.0 micrograms/ml) and alpha-amanitin (10.0 micrograms/ml) added immediately after adsorption reduced the infectious virus titre by 2 lg or more. Actinomycin D inhibited virus reproduction not only at the early but also at the later stages of infection. Mitomycin C and ethidium bromide did not inhibit Machupo virus reproduction. The cells treated with actinomycin D at early and late stages of infection were found to contain immunoprecipitable virus-specific proteins 78, 64, and 37 KD described previously. The total amount of virus-specific proteins in the inhibitor-treated cells was reduced 3.7 and 2,6-fold after addition of actinomycin at 0 and 12 h postinfection, respectively, as compared with untreated cells. The mechanism of action of actinomycin D on the Machupo virus reproduction is discussed.

Replication of Junin virus in the presence of tunicamycin

In the presence of tunicamycin (TM), an antibiotic which inhibits glycosylation, Junin virus-infected cells released 70% as much virus as control cultures, as measured by [35S]-methionine appearing in a sucrose gradient virus particle fraction. In this same fraction, the incorporation of [14C]-glucosamine was inhibited 85% by TM, accompanied by a dramatic decrease in the envelope glycoprotein, Gp38, and a marked decrease in virus infectivity. These results indicate that the presence of Gp38 on the viral surface is essential for viral infectivity. In contrast, maturation and release of virus particles do not seem to be affected by the absence of Gp38 from the viral envelope.

Effect of glucosamine on the replication of the arenavirus Junín in Vero cells

When Vero cells infected with Junín virus are cultured in the presence of 16 mM glucosamine, no infectious virus is produced and no surface antigens or virions are detected. Cytoplasmic viral antigen, however, is synthesized normally.