Novel indole-2-carboxamide compounds are potent broad-spectrum antivirals active against western equine encephalitis virus in vivo.

Neurotropic alphaviruses, including western, eastern, and Venezuelan equine encephalitis viruses, cause serious and potentially fatal central nervous system infections in humans for which no currently approved therapies exist. We previously identified a series of thieno[3,2-b]pyrrole derivatives as novel inhibitors of neurotropic alphavirus replication, using a cell-based phenotypic assay (W. Peng et al., J. Infect. Dis. 199:950-957, 2009, doi:http://dx.doi.org/10.1086/597275), and subsequently developed second- and third-generation indole-2-carboxamide derivatives with improved potency, solubility, and metabolic stability (J. A. Sindac et al., J. Med. Chem. 55:3535-3545, 2012, doi:http://dx.doi.org/10.1021/jm300214e; J. A. Sindac et al., J. Med. Chem. 56:9222-9241, 2013, http://dx.doi.org/10.1021/jm401330r). In this report, we describe the antiviral activity of the most promising third-generation lead compound, CCG205432, and closely related analogs CCG206381 and CCG209023. These compounds have half-maximal inhibitory concentrations of ∼1 µM and selectivity indices of >100 in cell-based assays using western equine encephalitis virus replicons. Furthermore, CCG205432 retains similar potency against fully infectious virus in cultured human neuronal cells. These compounds show broad inhibitory activity against a range of RNA viruses in culture, including members of the Togaviridae, Bunyaviridae, Picornaviridae, and Paramyxoviridae families. Although their exact molecular target remains unknown, mechanism-of-action studies reveal that these novel indole-based compounds target a host factor that modulates cap-dependent translation. Finally, we demonstrate that both CCG205432 and CCG209023 dampen clinical disease severity and enhance survival of mice given a lethal western equine encephalitis virus challenge. These studies demonstrate that indole-2-carboxamide compounds are viable candidates for continued preclinical development as inhibitors of neurotropic alphaviruses and, potentially, of other RNA viruses. IMPORTANCE There are currently no approved drugs to treat infections with alphaviruses. We previously identified a novel series of compounds with activity against these potentially devastating pathogens (J. A. Sindac et al., J. Med. Chem. 55:3535-3545, 2012, doi:http://dx.doi.org/10.1021/jm300214e; W. Peng et al., J. Infect. Dis. 199:950-957, 2009, doi:http://dx.doi.org/10.1086/597275; J. A. Sindac et al., J. Med. Chem. 56:9222-9241, 2013, http://dx.doi.org/10.1021/jm401330r). We have now produced third-generation compounds with enhanced potency, and this manuscript provides detailed information on the antiviral activity of these advanced-generation compounds, including activity in an animal model. The results of this study represent a notable achievement in the continued development of this novel class of antiviral inhibitors.

Optimization of novel indole-2-carboxamide inhibitors of neurotropic alphavirus replication.

Neurotropic alphaviruses, which include western equine encephalitis virus (WEEV) and Fort Morgan virus, are mosquito-borne pathogens that infect the central nervous system causing acute and potentially fatal encephalitis. We previously reported a novel series of indole-2-carboxamides as alphavirus replication inhibitors, one of which conferred protection against neuroadapted Sindbis virus infection in mice. We describe here further development of this series, resulting in 10-fold improvement in potency in a WEEV replicon assay and up to 40-fold increases in half-lives in mouse liver microsomes. Using a rhodamine123 uptake assay in MDR1-MDCKII cells, we were able to identify structural modifications that markedly reduce recognition by P-glycoprotein, the key efflux transporter at the blood-brain barrier. In a preliminary mouse PK study, we were able to demonstrate that two new analogues could achieve higher and/or longer plasma drug exposures than our previous lead and that one compound achieved measurable drug levels in the brain.

Evaluation of antiviral activity of aqueous extracts from Achyrocline satureioides against Western equine encephalitis virus.

Achyrocline satureioides (Asteraceae) is a medicinal plant traditionally used in Argentina for the treatment of intestinal infections and various digestive disorders. Its infusion is widely utilised for respiratory problems and viral infections. The objective of this study was to investigate cytotoxicity, virucidal and antiviral properties of the cold aqueous extract (CAE) and hot aqueous extract (HAE) of this plant against Western equine encephalitis virus (WEEV). Cytotoxicity in Vero cells was evaluated by maximum non-cytotoxic concentration (MNCC), neutral red (NR) uptake and MTT reduction methods. To study the antiviral activity of aqueous extracts, plaque reduction assay was performed after pre-treatment of host cells, adsorption, penetration and post-penetration of the virus. Extracellular virus inactivation was also analysed by the same method. Extracts showed strong inhibitory activity after virus penetration with selective index values of 32 (NR) and 63.3 (MTT) for the CAE, and 16.2 (NR) and 24.3 (MTT) for the HAE. Both extracts exhibited virucidal action with lower efficacy than their antiviral properties. The present results demonstrate that aqueous extracts of A. satureioides are active against WEEV. Further studies are needed in order to identify which compounds could be responsible for this effect, and how they exert antiviral action.

Effect of exogenous interferon and an interferon inducer on western equine encephalitis virus disease in a hamster model.

Mice are used as models for western equine encephalitis virus (WEEV) infection, but high mortality is generally only seen with intracranial or intranasal challenge, while peripheral inoculation results in approximately 50% mortality and is not dose-dependent. Hamsters were therefore studied as a model for WEEV infection. Hamsters were highly sensitive to intraperitoneal (i.p.) infection with WEEV. Disease progression was rapid, and virus titers in serum, brain, liver, and kidney of infected hamsters peaked between 2 and 4 days post-virus inoculation (dpi). Foci of virus infection were detected in neurons of the cerebral cortex and midbrain. Pre-treatment i.p. with either interferon alfacon-1 (5 microg/kg/day) or with Ampligen (3.2 mg/kg/day) resulted in complete survival, reduced brain titers, and improved weight gain. This model of WEEV infection in hamsters appears to serve as a suitable model for the evaluation of potential therapeutic agents for the treatment of WEE disease.

Encephalitis virus persistence in California birds: experimental infections in mourning doves (Zenaidura macroura).

After-hatching and hatching year, mourning doves were infected by inoculation with either western equine encephalomyelitis (WEE) or St. Louis encephalitis (SLE) viruses; some birds in each group also were treated with the immunosuppressant cyclophosphamide before and during infection. Cyclophosphamide treatment significantly increased the WEE viremia but did not alterthe antibody response. In contrast, cyclophosphamide-treated and -untreated doves did not develop a detectable SLE viremia but became antibody positive. Antibody peaked at 10 wk after inoculation for both viruses and remained detectable in most birds throughout the 26-wk study. When treated with cyclophosphamide the following spring, birds did not relapse and develop a detectable viremia. Previously infected birds were protected when challenged with conspecific virus (i.e., none produced a detectable viremia), but there was no anamnestic antibody response to reinfection. In agreement with our failure to detect relapses, all birds were negative for viral RNA when sera, spleen, lung, and kidney tissues were tested by reverse transcriptase-polymerase chain reaction after necropsy. Our results indicated that adult mourning doves were an incompetent host for SLE virus and probably do not serve as a suitable overwintering or dispersal host for either WEE and SLE viruses.

Inhibition by Agaricus blazei Murill fractions of cytopathic effect induced by western equine encephalitis (WEE) virus on VERO cells in vitro.

Anti-viral activities of Agaricus blazei Murill were investigated. The water extracts of the cultured mycelia and fruiting bodies were fractionated with different concentrations of ethanol. To several viruses which have cytopathic effects (CPE) on VERO cells, inhibition of these effects by the ethanol fractions was tested. Strong inhibition of CPE induced by western equine encephalitis (WEE) virus was observed in the mycelial fractions but not those of fruiting bodies.

Effect of the anesthetizing agent triethylamine on western equine encephalomyelitis and St. Louis encephalitis viral titers in mosquitoes (Diptera: Culicidae).

Triethylamine (TEA) is a chemical compound that provides an effective means to anesthetize mosquitoes. The mosquitoes remain alive but are incapacitated for several hours; they do not recover following treatment. There was no effect on the titers of infectious virus recovered from western equine encephalomyelitis or St. Louis encephalitis virus-infected Culex tarsalis Coquillett and Aedes dorsalis (Meigen) that were anesthetized with TEA prior to storage at -70 degrees C. Furthermore, TEA had no effect on isoenzyme profiles of uninfected Cx. tarsalis.

Antiviral activities of pyrimidine nucleoside analogues: some structure--activity relationships.

Seventeen nucleoside derivatives (derived from arabinosylcytosine, resp. cytidine, 5-fluorouracil and uracil) were tested by agar-diffusion plaque-inhibition test for their antiviral activity with herpes simplex, vaccinia, fowl plague, Newcastle disease and western equine encephalomyelitis viruses. The highest antiviral activity against DNA viruses exhibited arabinosylcytosine, N4-acylarabinosylcytosines, arabinosylthiouracil, cyclocytidine and its 5'-chloroderivative. RNA viruses were inhibited by 5-fluorouridine only, whereas other tested compounds were ineffective or showing marginal activity only. By search for relationship between chemical structure and antiviral activity a tendency was found of higher antiviral activity at lower lipophilicity. This is probably due to better transport of the studied compounds into cell. The chemical structure, however, is the main reason of antiviral activity.

[Stimulation of arbovirus reproduction in cell cultures by hormones]. / Stimuliatsiia reproduktsii arbovirusov v kletochnykh kul'turakh gormonami.

The possibility of stimulation of reproduction and antigen production of arboviruses (tick-borne encephalitis, Japanese encephalitis, western equine encephalomyelitis) in cell cultures (SPEV, chick embryo fibroblasts) by using various hormones (insulin, ACTH, hydrocortisone) and optimal temperatures was demonstrated. The stimulating effect depended upon the type of cell culture, virus, method of cell treatment, and manifested by a significant increase of the hemagglutinating and infectious activity of the replicating viruses. Differences in the structure of populations, biophysical and antigenic properties of the viruses associated with the conditions of their reproduction in vitro were observed.

Western equine encephalitis mimicking herpes simplex encephalitis.

A patient with severe encephalitis had focal findings suggesting herpes simplex encephalitis. After brain biopsy and administration of vidarabine, the patient's condition improved but was ultimately diagnosed as a case of western equine encephalitis. Further complicating laboratory diagnosis, an endogenous murine coronavirus was isolated from newborn mice inoculated with the patient's brain biopsy tissue. This case illustrates the need for caution in attributing therapeutic responses to antiviral agents or in attributing human illness to viruses that are actually endogenous to animals and tissue culture used in diagnostic virology.

Antiviral activity of benzothiazole and benzothiazolinethione derivatives in cell cultures.

The virus inhibitory activity of benzothiazole, benzothiazolinethione and naphthothiazole derivatives was tested with vaccinia virus, Newcastle disease virus (NDV) and western equine encephalomyelitis (WEE) virus in the agar-diffusion plaque-inhibition test. Among 58 compounds examined, 5 showed medium activity and selectivity with vaccinia virus. The highest selective effect was found with 3-(2-ethylthio-6-benzothiazolylaminomethyl)-2-benzothiazolinethione. A much lower inhibitory effect was observed with several derivatives against WEE virus. One derivative (2-mercaptobenzothiazole) showed a low inhibitory effect against NDV.

Isolation of the structural proteins of western equine encephalitis virus by isoelectric focusing.

Western equine encephalitis virus was disrupted with Triton X-100 and subjected to isoelectric focusing in a sucrose or urea gradient. The two envelope proteins, E1 and E2 were not well separated in a sucrose gradient, while the E1 and E2 proteins were distinguished as two major peaks which focused in a urea gradient at about pH 7.5 and 10, respectively. Isolated E1 protein refocused at pH 6.5 in a sucrose gradient isoelectric focusing column. When Western equine encephalitis virus was treated with Triton X-100 in 0.01 M phosphate buffer (pH6), hemagglutinating E1 protein was solubilized, which isoelectrofocused at pH 6.5. Purified nucleocapsids focused at pH 4 in a sucrose gradient on an isoelectric focusing column. After ribonuclease treatment of the purified nucleocapsid more than 95 per cent of the viral RNA was acid-soluble, and hte nucleocapsid protein isoelectrofocused at about pH 4.

Photochemical inactivation of DNA and RNA viruses by psoralen derivatives.

Western equine encephalitis virus, and RNA virus, and herpes simplex virus type I, a DNA virus, were efficiently inactivated in less than I min by exposure to long-wave ultraviolet light (320 to 380 nm) in the presence of several psoralen derivatives. The psoralen photochemical reaction was chosen for study due to its known specificity for nucleic acids. Neither the light nor any of the drugs alone caused appreciable inactivation. The inactivation kinetics and dependence on light intensity and on different derivatives of psoralen were studied. The high solubility of a new aminomethyl psoralen derivative was found to be advantageous in the photochemical inactivation of the RNA virus, but was not in the case of the more easily inactivated DNA virus. Within its limited solubility range trimethylpsoralen was superior to its aminomethyl derivative on a molar basis for the inactivation of both types of viruses under most of the conditions studied.

Antiviral effect of tebrofen.

Tebrofen inhibited the replication of western equine encephalomyelitis (WEE) virus in multicycle experiments in chick embryo cell cell cultures. The compound did not inhibit the replication of vaccinia and Newcastle disease viruses.

Sensitivities of neurotropic arboviruses to human interferon.

The sensitivities of selected neurotropic arboviruses (St. Louis encephalitis, Western equine encephaltis, and La Crosse viruses) to human interferon and polyriboinosinic-polyribocytidylic acid (poly I-poly C) were determined in primary human fetal glial cell cultures. The sensitivities were measured by an end point (inhibition of virus yield). All of the viruses were sensitive to human interferon and poly I-poly C; St. Louis encephalitis and Western equine encephalitis viruses were inhibited at concentrations of interferon actually measured in the brains of persons who died from these infections. For St. Louis encephalitis and Western equine encephalitis viruses, viral replication and induction of interferon varied among cell cultures derived from individual fetuses. The present experiments may provide an approach toward understanding the problem of different host susceptibilities to neurotropic arbovirus infections.

Lead aggravates viral disease and represses the antiviral activity of interferon inducers.

Lead acetate was administered continuously in the drinking water to CD-1 male mice beginning at 4 weeks of age. An LD(10-20) of the lytic viruses or 300 plaque-forming units of RLV was inoculated intrapertioneally at 6 weeks of age. Lead increased the response of the mice to all classes of viruses against which it was tested: an RNA picornavirus-encephalomyocarditis (EMCV), a DNA herpesvirus-pseudoribies, an RNA leukemia-virus-Rauscher leukemia (RLV), an RNA arbovirus B-St. Louis encephalitis, and an RNA arbovirus A-western encephalitis. Most studies were performed between lead and EMCV. Increases in EMCV mortality in lead treated mice over controls ranged from 2x at a lead level of 0.004M to 7x (100% mortality) at a 0.1M lead level. Splenomegaly with spleens 800 to 1100 mg in weight containing high titers of RLV occurred in lead (0.03M)-treated mice 3 and 6 weeks after RLV inoculation; spleens or RLV controls were normal in weight (200 mg) and were free of virus. Lead did not reduce the protective effect of mouse interferon (IF) against the lethal action of EMCV, but it did repress the EMCV antiviral effect of poly I/poly C (PIC) and of Newcastle disease virus (NDV) against EMCV mortality. These data indicate several new facts concerning adverse effects lead may have on an animal: (1) lead aggravates viral disease, most likely in part, through reduced IF synthesis; (2) lead represses the anti-EMCV protective effects of both PIC and of NDV, which, in other reports, were shown to induce IF in radioresistant macrophages (PIC) or in radiosensitive lymphocytes (NDV); (3) lead may then be said to repress IF induction in two kinds of cells; (4) however, lead does not inhibit IF action.