Benzamidine ML336 inhibits plus and minus strand RNA synthesis of Venezuelan equine encephalitis virus without affecting host RNA production

Venezuelan equine encephalitis virus (VEEV) is an alphavirus that is endemic to the Americas. VEEV outbreaks occur periodically and cause encephalitis in both humans and equids. There are currently no therapeutics or vaccines for treatment of VEEV in humans. Our group has previously reported on the development of a benzamidine VEEV inhibitor, ML336, which shows potent antiviral activity in both in vitro and in vivo models of infection. In cell culture experiments, ML336 inhibits viral RNA synthesis when added 2-4 h post-infection, and mutations conferring resistance occur within the viral nonstructural proteins (nsP2 and nsP4). We hypothesized that ML336 targets an activity of the viral replicase complex and inhibits viral RNA synthesis. To test this hypothesis, we employed various biochemical and cellular assays. Using structural analogues of ML336, we demonstrate that the cellular antiviral activity of these compounds correlates with their inhibition of viral RNA synthesis. For instance, the IC50 of ML336 for VEEV RNA synthesis inhibition was determined as 1.1 nM, indicating potent anti-RNA synthesis activity in the low nanomolar range. While ML336 efficiently inhibited VEEV RNA synthesis, a much weaker effect was observed against the Old World alphavirus Chikungunya virus (IC50 > 4 μM), agreeing with previous data from a cell based assay. Using a tritium incorporation assay, we demonstrated that there was no significant inhibition of cellular transcription. With a combination of fluorography, strand-specific qRT-PCR, and tritium incorporation, we demonstrated that ML336 inhibits the synthesis of the positive sense genomic, negative sense template, and subgenomic RNAs of VEEV. Based on these results, we propose that the mechanism of action for this class of antiviral compounds is inhibition of viral RNA synthesis through interaction with the viral replicase complex.

Discovery of a novel compound with anti-venezuelan equine encephalitis virus activity that targets the nonstructural protein 2

Alphaviruses present serious health threats as emerging and re-emerging viruses. Venezuelan equine encephalitis virus (VEEV), a New World alphavirus, can cause encephalitis in humans and horses, but there are no therapeutics for treatment. To date, compounds reported as anti-VEEV or anti-alphavirus inhibitors have shown moderate activity. To discover new classes of anti-VEEV inhibitors with novel viral targets, we used a high-throughput screen based on the measurement of cell protection from live VEEV TC-83-induced cytopathic effect to screen a 340,000 compound library. Of those, we identified five novel anti-VEEV compounds and chose a quinazolinone compound, CID15997213 (IC₅₀ = 0.84 µM), for further characterization. The antiviral effect of CID15997213 was alphavirus-specific, inhibiting VEEV and Western equine encephalitis virus, but not Eastern equine encephalitis virus. In vitro assays confirmed inhibition of viral RNA, protein, and progeny synthesis. No antiviral activity was detected against a select group of RNA viruses. We found mutations conferring the resistance to the compound in the N-terminal domain of nsP2 and confirmed the target residues using a reverse genetic approach. Time of addition studies showed that the compound inhibits the middle stage of replication when viral genome replication is most active. In mice, the compound showed complete protection from lethal VEEV disease at 50 mg/kg/day. Collectively, these results reveal a potent anti-VEEV compound that uniquely targets the viral nsP2 N-terminal domain. While the function of nsP2 has yet to be characterized, our studies suggest that the protein might play a critical role in viral replication, and further, may represent an innovative opportunity to develop therapeutic interventions for alphavirus infection.

Alphaviruses occur worldwide, causing significant diseases such as encephalitis or arthritis in humans and animals. In addition, some alphaviruses, such as VEEV, pose a biothreat due to their high infectivity and lack of available treatments. To discover small molecule inhibitors with lead development potential, we used a cell-based assay to screen 348,140 compounds for inhibition of a VEEV-induced cytopathic effect. The screen revealed a scaffold with high inhibitory VEEV cellular potency and low cytotoxicity liability. While most previously reported anti-alphavirus compounds inhibit host proteins, evidence supported that this scaffold targeted the VEEV nsP2 protein, and that inhibition was associated with viral replication. Interestingly, compound resistance studies with VEEV mapped activity to the N-terminal domain of nsP2, to which no known function has been attributed. Ultimately, this discovery has delivered a small molecule-derived class of potent VEEV inhibitors whose activity is coupled to the nsP2 viral protein, a novel target with a previously unestablished biological role that is now implicated in viral replication.

Modulation of GSK-3β activity in Venezuelan equine encephalitis virus infection

Alphaviruses, including Venezuelan Equine Encephalitis Virus (VEEV), cause disease in both equine and humans that exhibit overt encephalitis in a significant percentage of cases. Features of the host immune response and tissue-specific responses may contribute to fatal outcomes as well as the development of encephalitis. It has previously been shown that VEEV infection of mice induces transcription of pro-inflammatory cytokines genes (e.g., IFN-γ, IL-6, IL-12, iNOS and TNF-α) within 6 h. GSK-3β is a host protein that is known to modulate pro-inflammatory gene expression and has been a therapeutic target in neurodegenerative disorders such as Alzheimer's. Hence inhibition of GSK-3β in the context of encephalitic viral infections has been useful in a neuroprotective capacity. Small molecule GSK-3β inhibitors and GSK-3β siRNA experiments indicated that GSK-3β was important for VEEV replication. Thirty-eight second generation BIO derivatives were tested and BIOder was found to be the most potent inhibitor, with an IC₅₀ of ∼0.5 µM and a CC₅₀ of >100 µM. BIOder was a more potent inhibitor of GSK-3β than BIO, as demonstrated through in vitro kinase assays from uninfected and infected cells. Size exclusion chromatography experiments demonstrated that GSK-3β is found in three distinct complexes in VEEV infected cells, whereas GSK-3β is only present in one complex in uninfected cells. Cells treated with BIOder demonstrated an increase in the anti-apoptotic gene, survivin, and a decrease in the pro-apoptotic gene, BID, suggesting that modulation of pro- and anti-apoptotic genes contributes to the protective effect of BIOder treatment. Finally, BIOder partially protected mice from VEEV induced mortality. Our studies demonstrate the utility of GSK-3β inhibitors for modulating VEEV infection.

[Development of methodology for predictably significant evaluation of the protective efficacy of antiviral agents]

The paper provides a theoretical analysis for determining whether the antiviral nonspecific drugs being tested are promising to solve biosafety problems in the treatment of exotic viral infections. The essence of the proposed concept of evaluation of protective effectiveness is to analyze the effect of a test drug on the pathogenesis of experimental infection from the fact that it is effective in adequately eliminating the animal-simulated leading syndrome of human disease. The given approaches to using adequacy criteria to select the species of animals meeting the goals of tests in terms of pathogenetic and pharmacological parameters determine a new methodology for evaluating the efficacy of protective agents. Basic requirements for a testing procedure are presented. The prognostic value of evaluation of the protective efficacy of antiviral agents for man will depend on the approximation of the pathogenetic features and external manifestation of disease in the selected animal species to human Infection. The paper also covers the comparative characteristics of the course of Ebola fever and Venezuelan equine encephalomyelitis in man and some species of monkey.

[Experimental and clinicolaboratory evaluation of complex therapy efficacy in arboviral infections]

Search for drugs efficient in prophylaxis and treatment of dangerous infections (especially arboviral ones) is rather actual, since no specific therapy is available. Many-year investigations of interferon inductors showed that they had immunomodulating, antiviral and antiinflammatory effects and were low toxic. The present study demonstrated that the protective effect was the following: Venezuelan equine encephalitis (VEE)--cycloferon > amixin = ridostin, Rift Valley fever (RVF)--cycloferon > amixin > ridostin, predator pox (PP)--cycloferon > amixin = ridostin, that was obvious that cycloferon was the most active agent in the treatment of VEE, RVF and PP, thus making it possible to acknowledge its priority in prophylaxis and therapy of dangerous viral infections (DVI). Ribavirin in combination with cycloferon solution or cycloferon tablets provided shorter periods of the fever, minimized the intoxication syndrome, promoted earlier resolution of hemorrhagic eruption and lowered the frequency of complications, which was in favour of the disease prognosis.

Treatment of mice with human monoclonal antibody 24h after lethal aerosol challenge with virulent Venezuelan equine encephalitis virus prevents disease but not infection

We recently described a Venezuelan equine encephalitis virus (VEEV)-specific human monoclonal antibody (MAb), F5 nIgG, that recognizes a new neutralization epitope on the VEEV E2 envelope glycoprotein. In this study, we investigated the ability of F5 nIgG given prophylactically or therapeutically to protect mice from subcutaneous or aerosolized VEEV infection. F5 nIgG had potent ability to protect mice from infection by either route when administered 24h before exposure; however, mice treated 24h after aerosol exposure developed central nervous system infections but exhibited no clinical signs of disease. Infectious virus, viral antigen and RNA were detected in brains of both treated and untreated mice 2-6 days after aerosol exposure but were cleared from the brains of treated animals by 14-28 days after infection. This fully human MAb could be useful for prophylaxis or immediate therapy for individuals exposed to VEEV accidentally in the laboratory or during a deliberate release.

Bioterrorism and the nervous system

Recent events of war, terrorist attacks, and mail-borne anthrax exposure have produced increasing awareness of potential bioterrorism attacks in the United States and other parts of the world. Physicians and healthcare personnel play a key role in identifying potential bioterrorist attacks. Early recognition and preparedness for bioterrorism-associated illnesses is especially important for neurologists because most bioterrorism agents can directly or indirectly affect the nervous system. This article reviews the neurologic manifestations, diagnosis, and treatments of syndromes caused by potential bioterrorism agents, as well as the potential side effects of vaccines against some of these agents.

Antibody and interleukin-12 treatment in murine models of encephalitogenic flavivirus (St. Louis encephalitis, tick-borne encephalitis) and alphavirus (Venezuelan equine encephalitis) infection

Early and sustained treatment with interleukin-12 (IL-12) ameliorated disease in a mouse model of infection with the encephalitogenic flavivirus, St. Louis encephalitis virus (SLEV, Japanese encephalitis serogroup). However, this effect was not reproduced in murine infections with either the flavivirus tick-bore encephalitis virus (TBEV) or the alphavirus Venezuelan equine encephalitis virus (VEEV). IL-12 exacerbated TBEV disease when used in conjunction with monoclonal antibody (mAb), suggesting an enhancement of immunopathology, and was without clinical effects in VEEV infection. These data confirm the need to fully understand the pathogenesis of viral infection before cytokine intervention may be employed as a broad-spectrum antiviral therapy.

Melatonin prolongs survival of immunodepressed mice infected with the Venezuelan equine encephalomyelitis virus

Male albino mice immunodepressed after the injection of dexamethasone (DEX) were inoculated intraperitoneally with the Guajira strain of Venezuelan equine encephalomyelitis (VEE) virus. Melatonin (MLT) was administered daily, at a dose of 500 micrograms/kg bodyweight, for 3 days before virus inoculation and 10 days after. Serum levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-2 (IL-2) were determined in all the experimental groups (control, DEX, DEX + MLT, DEX + VEE, DEX + VEE + MLT, VEE and MLT). At day 6 after the virus inoculation, the survival rate was significantly increased from 0% in group DEX + VEE to 32.5% in the group of immunodepressed infected mice treated with MLT (DEX + VEE + MLT). By day 10 a survival rate of 10% was found in group DEX + VEE + MLT and 0% in group VEE. No alterations in IL-2 serum levels were observed. MLT increased GM-CSF in control and in DEX-treated mice. In the VEE virus-infected mice treated with DEX, serum levels of GM-CSF increased progressively from day 1 to 5 postinoculation. In contrast, the levels of GM-CSF in infected immunodepressed mice treated with MLT decreased significantly from day 1 to 5 postinoculation. At day 5 after viral inoculation, no differences were detected in the cerebral viral titres in groups VEE, DEX + VEE and DEX + MLT + VEE. These results show that MLT does not inhibit VEE viral replication in the brain of immunodepressed mice.

Pegylated alpha interferon is an effective treatment for virulent venezuelan equine encephalitis virus and has profound effects on the host immune response to infection

Venezuelan equine encephalitis virus (VEEV) is a highly infectious alphavirus endemic in parts of Central and South America. The disease is transmitted by mosquitoes, and the natural reservoir is the small rodent population, with epidemics occurring in horses and occasionally humans. Following infection, VEEV replicates in lymphoid tissues prior to invasion of the central nervous system. Treatment of VEEV-infected BALB/c mice with polyethylene glycol-conjugated alpha interferon (PEG IFN-alpha) results in a greatly enhanced survival from either a subcutaneous or an aerosol infection. Virus is undetectable within PEG IFN-alpha-treated individuals by day 30 postinfection (p.i.). Treatment results in a number of changes to the immune response characteristics normally associated with VEEV infection. Increased macrophage activation occurs in PEG IFN-alpha-treated BALB/c mice infected with VEEV. The rapid activation of splenic CD4, CD8, and B cells by day 2 p.i. normally associated with VEEV infection is absent in PEG IFN-alpha-treated mice. The high tumor necrosis factor alpha production by macrophages from untreated mice is greatly diminished in PEG IFN-alpha-treated mice. These results suggest key immunological mechanisms targeted by this lethal alphavirus that can be modulated by prolonged exposure to IFN-alpha.

[Study of the treatment-prophylactic effect of immunomodulators in experimental infections, caused by Marburg, Ebola, and Venezuelan equine encephalitis viruses]

Therapeutic and prophylactic effects of immunomodifiers ridostin, reaferon, and polyribonate used alone and in various combinations were assessed in experiments on guinea pigs infected with Venezuelan equine encephalomyelitis (VEE) (strain Trinidad), Marburg (strain Popp), and Ebola (M/C-8 variant of Zaire strain) viruses at doses 5 to 20 respiratory LD50 through the respiratory airways. Urgent prophylactic simultaneous intramuscular and intranasal administration of ridostin protected the animals infected with Marburg virus (p = 0.1) and prolonged their life span by 2.4 days (p = 0.15). In Ebola infection a combination of ridostin and reaferon appreciably prolonged the mean life span: by 2.9 days (p = 0.04). In VEE ridostin alone or in combination with reaferone appreciably increased the share of survivors; ridostin with reaferon and polyribonate notably prolonged the mean life span of infected animals. None of these drugs or combinations produced an appreciable therapeutic effect in any of the studied infections.

Melatonin protects mice infected with Venezuelan equine encephalomyelitis virus

We investigated whether the administration of melatonin (MLT) reduces the death rate and evolution of the disease in mice infected with Venezuelan equine encephalomyelitis (VEE) virus. Our results show that, MLT protects mice infected with the virus. The mortality rate was reduced from 100% to 16% merely by increasing the dose from 0 to 1000 micrograms/MLT per kg body weight MLT significantly postponed the onset of the disease and death by several days. In surviving mice very high titres of VEE virus IgM antibodies were found seven weeks after virus inoculation. MLT significantly reduced VEE virus levels in blood and brain of infected mice and increased the survival rate when the length of pretreatment was augmented from 3 to 7 or 10 days before virus inoculation. Serum levels of interleukin-2 were not affected by MLT administration. In control mice receiving MLT as well as in infected mice treated or non-treated with MLT, interferon gamma levels in sera were increased. Interleukin-4 concentrations were found to be elevated in sera of non-infected mice receiving MLT, but did not differ from controls in infected mice treated or non-treated with the hormone. MLT reduced the degree of cell destruction produced by VEE virus in culture plates of chicken embryo fibroblasts. The protective effect of MLT warrants further investigation of the possibility of using this hormone for the treatment of humans and equines infected with VEE virus.

[The efficacy of the therapeutic and prophylactic actions of immunomodulators in experimental infection due to the causative agent of Venezuelan equine encephalomyelitis]

The investigation of the prevention and treatment action of some immunomodulators (ridostin, reaferon and polyribonate) used alone and in combinations was conducted on laboratory animals infected aerogenically by Venezuelan equine encephalitis (VEE) virus. A lower death rate of the aerogenically infected mice (10-30 respiratory LD50) was observed after intramuscular injection of ridostin. The preventive affect of ridostin and ridostin + reaferon administered intranasally and intramuscularly was achieved in the aerogenically infected guinea pigs (10 respiratory LD50). The results of the study on the early virus reproduction in the animals were used for the choice of the treatment scheme. The immunomodulators had no effect when the treatment was started 1 day after the VEE virus infection.

[The antiviral activity of inhibitors of ADP ribosylation in experimental alpha- and bunyavirus infections]

The prophylactic and therapeutic effects of ADP-ribosylation inhibitors, 3,N-acetylaminobenzamide and 3,N-butyrylaminobenzamide, were studied in mice inoculated with an alphavirus or a bunyavirus. Both drugs were shown to have high levels of antiviral activity when given as a single subcutaneous injection in a dose of 10 mg/kg while increasing the number of injections did not increase their efficacy or might even decrease it.

[The effect of the peroxidation of ribamidil-containing liposomes on the results of chemotherapy in experimental viral infections]

A relationship between ribamydil concentration and the intensity of accumulation of peroxidation products was found while storing ribamydil-containing liposomes which indicated a significant pro-oxidant activity of ribamydil. Increasing lethality of guinea pigs and white mice infected with Venezuelan equine encephalomyelitis virus was shown while using liposomal ribamydil containing from 4.78 to 6.82 nmol. ml-1 malonic dialdehyde which appeared to be associated with disordered function of the antioxidant system of the experimental animals.

[The antiviral efficacy of ribamidil in an experimental infection of animals with the Venezuelan equine encephalomyelitis virus]

Considerable differences in antiviral efficacy of ribamydil were demonstrated in various animals experimentally infected with Venezuelan equine encephalomyelitis virus. The infection in baboons was quite similar to the manifestations of this disease in man as reported in the literature. With ribamydil used prophylactically, manifestations of the infection in monkeys were less marked.

Indirect mouse model for the evaluation of potential antiviral compounds: results with Venezuelan equine encephalomyelitis virus

An indirect mouse model was utilized to evaluate the antiviral activity of several compounds against Venezuelan equine encephalomyelitis (VEE) virus infection in mice. Mice were given various dosages of lysine-stabilized polyriboinosinic acid-polyribocytidylic acid, a tilorone analogue, kethoxal, or mepacrine before and/or shortly after receiving one of several dose levels of attenuated strain TC-83 VEE virus. Twenty-one days later, the same mice were rechallenged intracranially with virulent Trinidad donkey strain VEE virus. Susceptibility to rechallenge was interpreted as evidence of drug effectiveness in completely preventing the initial immunizing virus infection. In contrast, if a drug lacked antiviral effectiveness, the initial attenuated infection stimulated sufficient immunity to protect mice against the virulent rechallenge. Both of the interferon inducers, lysine-stabilized polyriboinosinic acid-polyribocytidylic acid and tilorone analogue 11,567, possessed significant (P < 0.01) antiviral activity based upon this indirect model, whereas mepacrine and kethoxal were inactive. Results using the indirect method were confirmed by using the conventional direct method for evaluating the effectiveness of potentially useful antiviral compounds. The indirect mouse model described should prove useful for studying drug efficacy against certain viruses that are lethal only by intracranial inoculation.

[Antiviral activity of a poly A-poly U complex administered by various routes]

Interferon-inducing and antiviral activity of a synthetic polyribonucleotide, polyaenylic and polyuridylic acid complex (poly A--poly U) was studied comparatively on a model of experimental infection of albino mice caused by Venezuela Horse Encephalomyeliti Viruos (VHEV) using oral and intraperitoneal administration of the complex. It was shown that dm-interferon induction and antiviral effect comparatively high doses of poly A--poly U (Reanal) were required (1 mg/mouse). The highest antiviral effect was observed after a two-fold administration of the drug (24 hours and immediately before infection). It was more evident after intraperitoneal administration of the inductor. The interferon titers in the animal blood serum after intraperitoneal or oral administration of poly A--poly U were almost the same 58=60+/- +/- 18.9 IU50/ml).