Discovery of berberine, abamectin and ivermectin as antivirals against chikungunya and other alphaviruses

Approved drugs screening against the nsP1 capping enzyme of Venezuelan equine encephalitis virus using an immuno-based assay

Alphaviruses such as the Venezuelan equine encephalitis virus (VEEV) are important human emerging pathogens transmitted by mosquitoes. They possess a unique viral mRNA capping mechanism catalyzed by the viral non-structural protein nsP1, which is essential for virus replication. The alphaviruses capping starts by the methylation of a GTP molecule by the N7-guanine methyltransferase (MTase) activity; nsP1 then forms a covalent link with m⁷GMP releasing pyrophosphate (GT reaction) and the m⁷GMP is next transferred onto the 5'-diphosphate end of the viral mRNA to form a cap-0 structure. The cap-0 structure decreases the detection of foreign viral RNAs, prevents RNA degradation by cellular exonucleases, and promotes viral RNA translation into proteins. Additionally, reverse-genetic studies have demonstrated that viruses mutated in nsP1 catalytic residues are both impaired towards replication and attenuated. The nsP1 protein is thus considered an attractive antiviral target for drug discovery. We have previously demonstrated that the guanylylation of VEEV nsP1 can be monitored by Western blot analysis using an antibody recognizing the cap structure. In this study, we developed a high throughput ELISA screening assay to monitor the GT reaction through m⁷GMP-nsP1 adduct quantitation. This assay was validated using known nsP1 inhibitors before screening 1220 approved compounds. 18 compounds inhibiting the nsP1 guanylylation were identified, and their IC₅₀ determined. Compounds from two series were further characterized and shown to inhibit the nsP1 MTase activity. Conversely, these compounds barely inhibited a cellular MTase demonstrating their specificity towards nsP1. Analogues search and SAR were also initiated to identify the active pharmacophore features. Altogether the results show that this HT enzyme-based assay is a convenient way to select potent and specific hit compounds targeting the viral mRNA capping of Alphaviruses.

Inhibition by Marine Algae of Chikungunya Virus Isolated From Patients in a Recent Disease Outbreak in Rio de Janeiro

Chikungunya virus (CHIKV) infection is one of the most challenging re-emergent diseases caused by a virus, and with no specific antiviral treatment it has now become a major public health concern. In this investigation, 25 blood samples were collected from patients with characteristic CHIKV symptoms and submitted to a virus isolation protocol, which detected 3 CHIKV isolates. These samples were evaluated by sequencing for the characterization of the strains and any homology to viruses circulating in Brazil during a recent outbreak. These viruses were used for the development of antiviral assays. Subsequently, the inhibitory effects of seaweed extracts on CHIKV replication were studied. The marine species of algae tested were Bryothamnion triquetrum, Caulerpa racemosa, Laurencia dendroidea, Osmundaria obtusiloba, Ulva fasciata, and Kappaphycus alvarezii, all of which are found in different countries including Brazil. The results revealed high levels of CHIKV inhibition, including extracts of O. obtusiloba with inhibition values of 1.25 μg/mL and a selectivity index of 420. Viral inhibition was dependent on the time of addition of extract of O. obtusiloba to the infected cells, with the optimal inhibition occurring up to 16 h after infection. Neuron evaluations with O. obtusiloba were performed and demonstrated low toxicity, and in infected neurons we observed high inhibitory activity in a dose-dependent manner. These results indicate that the algal extracts may be promising novel candidates for the development of therapeutic agents against CHIKV infections.

Ivermectin inhibits DNA polymerase UL42 of pseudorabies virus entrance into the nucleus and proliferation of the virus in vitro and vivo

Pseudorabies virus (PRV) is an important viral pathogen of pigs that causes huge losses in pig herds worldwide. Ivermectin is a specific inhibitor of importin-α/β-dependent nuclear transport and shows antiviral potential against several RNA viruses by blocking the nuclear localization of viral proteins. Since the replication of DNA viruses is in the nucleus, ivermectin may be functional against DNA virus infections if the DNA polymerase or other important viral proteins enter the nucleus via the importin-α/β-mediated pathway. Here, we determined whether ivermectin suppresses PRV replication in hamster kidney BHK-21 cells and investigated the effect of ivermectin on the subcellular localization of the PRV UL42 protein, the accessory subunit of PRV DNA polymerase. Also, an in vivo anti-PRV assay was conducted in mice. Our data demonstrate that ivermectin treatment inhibits PRV infection in cells in a dose-dependent manner. Treatment of PRV-infected cells with ivermectin significantly suppressed viral DNA synthesis and progeny virus production. Ivermectin disrupted the nuclear localization of UL42 by targeting the nuclear localization signal of the protein in transfected cells. Ivermectin treatment increased the survival rates of mice infected with PRV and relieved infection as indicated by lower clinical scores and fewer gross lesions in the brain. Together, our results suggest that ivermectin may be a therapeutic or preventative agent against PRV infection.

A compendium of small molecule direct-acting and host-targeting inhibitors as therapies against alphaviruses

Alphaviruses were amongst the first arboviruses to be isolated, characterized and assigned a taxonomic status. They are globally widespread, infecting a large variety of terrestrial animals, birds, insects and even fish. Moreover, they are capable of surviving and circulating in both sylvatic and urban environments, causing considerable human morbidity and mortality. The re-emergence of Chikungunya virus (CHIKV) in almost every part of the world has caused alarm to many health agencies throughout the world. The mosquito vector for this virus, Aedes, is globally distributed in tropical and temperate regions and capable of thriving in both rural and urban landscapes, giving the opportunity for CHIKV to continue expanding into new geographical regions. Despite the importance of alphaviruses as human pathogens, there is currently no targeted antiviral treatment available for alphavirus infection. This mini-review discusses some of the major features in the replication cycle of alphaviruses, highlighting the key viral targets and host components that participate in alphavirus replication and the molecular functions that were used in drug design. Together with describing the importance of these targets, we review the various direct-acting and host-targeting inhibitors, specifically small molecules that have been discovered and developed as potential therapeutics as well as their reported in vitro and in vivo efficacies.

Male germ cells support long-term propagation of Zika virus

Evidence of male-to-female sexual transmission of Zika virus (ZIKV) and viral RNA in semen and sperm months after infection supports a potential role for testicular cells in ZIKV propagation. Here, we demonstrate that germ cells (GCs) are most susceptible to ZIKV. We found that only GCs infected by ZIKV, but not those infected by dengue virus and yellow fever virus, produce high levels of infectious virus. This observation coincides with decreased expression of interferon-stimulated gene Ifi44l in ZIKV-infected GCs, and overexpression of Ifi44l results in reduced ZIKV production. Using primary human testicular tissue, we demonstrate that human GCs are also permissive for ZIKV infection and production. Finally, we identified berberine chloride as a potent inhibitor of ZIKV infection in both murine and human testes. Together, these studies identify a potential cellular source for propagation of ZIKV in testes and a candidate drug for preventing sexual transmission of ZIKV.

Current Strategies for Inhibition of Chikungunya Infection

Increasing incidences of Chikungunya virus (CHIKV) infection and co-infections with Dengue/Zika virus have highlighted the urgency for CHIKV management. Failure in developing effective vaccines or specific antivirals has fuelled further research. This review discusses updated strategies of CHIKV inhibition and provides possible future directions. In addition, it analyzes advances in CHIKV lifecycle, drug-target development, and potential hits obtained by in silico and experimental methods. Molecules identified with anti-CHIKV properties using traditional/rational drug design and their potential to succeed in subsequent stages of drug development have also been discussed. Possibilities of repurposing existing drugs based on their in vitro findings have also been elucidated. Probable modes of interference of these compounds at various stages of infection, including entry and replication, have been highlighted. The use of host factors as targets to identify antivirals against CHIKV has been addressed. While most of the earlier antivirals were effective in the early phases of the CHIKV life cycle, this review is also focused on drug candidates that are effective at multiple stages of its life cycle. Since most of these antivirals require validation in preclinical and clinical models, the challenges regarding this have been discussed and will provide critical information for further research.

Chikungunya: treatments, opportunities and possibilities

The natural progression of chikungunya virus (CHIKV) disease can consist of three stages – acute, post-acute and chronic, each having different clinical features. The acute phase (up to 3 weeks) is characterised by high viremia, fever, rash, polyarthralgia, synovitis and intense inflammation. Complete recovery is achieved in most symptomatic cases after this phase. However, in a large proportion of patients symptoms persist into a post-acute phase and in some may even continue to become chronic. In the post-acute phase, which can last up to 4 months, there is clinical persistence of joint inflammation or relapse after transient improvement. These can lead to musculoskeletal disorders and eventually chronicity of disease. The main symptoms being chronic inflammatory rheumatism that can last for several years in some cases. With the near global reach, debilitating nature and recent outbreaks of CHIKV there has been much research effort put towards combatting it. New antivirals and medications to counteract inflammation are being developed. Development of CHIKV vaccines is also an area with intense research focus.

Vaccine and Therapeutic Options To Control Chikungunya Virus

Beginning in 2004, chikungunya virus (CHIKV) went from an endemic pathogen limited to Africa and Asia that caused periodic outbreaks to a global pathogen. Given that outbreaks caused by CHIKV have continued and expanded, serious consideration must be given to identifying potential options for vaccines and therapeutics. Currently, there are no licensed products in this realm, and control relies completely on the use of personal protective measures and integrated vector control, which are only minimally effective. Therefore, it is prudent to urgently examine further possibilities for control. Vaccines have been shown to be highly effective against vector-borne diseases. However, as CHIKV is known to rapidly spread and generate high attack rates, therapeutics would also be highly valuable. Several candidates are currently being developed; this review describes the multiple options under consideration for future development and assesses their relative advantages and disadvantages.

The medicinal chemistry of Chikungunya virus

Arthropod-borne viruses (arboviruses) are an important threat to human and animal health globally. Among these, zoonotic diseases account for billions of cases of human illness and millions of deaths every year, representing an increasing public health problem. Chikungunya virus belongs to the genus Alphavirus of the family Togariridae, and is transmitted mainly by the bite of female mosquitoes of the Aedes aegypti and/or A. albopictus species. The focus of this review will be on the medicinal chemistry of Chikungunya virus, including synthetic and natural products, as well as rationally designed compounds.

Obatoclax Inhibits Alphavirus Membrane Fusion by Neutralizing the Acidic Environment of Endocytic Compartments

As new pathogenic viruses continue to emerge, it is paramount to have intervention strategies that target a common denominator in these pathogens. The fusion of viral and cellular membranes during viral entry is one such process that is used by many pathogenic viruses, including chikungunya virus, West Nile virus, and influenza virus. Obatoclax, a small-molecule antagonist of the Bcl-2 family of proteins, was previously determined to have activity against influenza A virus and also Sindbis virus. Here, we report it to be active against alphaviruses, like chikungunya virus (50% effective concentration [EC₅₀] = 0.03 μM) and Semliki Forest virus (SFV; EC₅₀ = 0.11 μM). Obatoclax inhibited viral entry processes in an SFV temperature-sensitive mutant entry assay. A neutral red retention assay revealed that obatoclax induces the rapid neutralization of the acidic environment of endolysosomal vesicles and thereby most likely inhibits viral fusion. Characterization of escape mutants revealed that the L369I mutation in the SFV E1 fusion protein was sufficient to confer partial resistance against obatoclax. Other inhibitors that target the Bcl-2 family of antiapoptotic proteins inhibited neither viral entry nor endolysosomal acidification, suggesting that the antiviral mechanism of obatoclax does not depend on its anticancer targets. Obatoclax inhibited the growth of flaviviruses, like Zika virus, West Nile virus, and yellow fever virus, which require low pH for fusion, but not that of pH-independent picornaviruses, like coxsackievirus A9, echovirus 6, and echovirus 7. In conclusion, obatoclax is a novel inhibitor of endosomal acidification that prevents viral fusion and that could be pursued as a potential broad-spectrum antiviral candidate.

Design and Validation of Novel Chikungunya Virus Protease Inhibitors

Chikungunya virus (CHIKV; genus Alphavirus) is the causative agent of chikungunya fever. CHIKV replication can be inhibited by some broad-spectrum antiviral compounds; in contrast, there is very little information about compounds specifically inhibiting the enzymatic activities of CHIKV replication proteins. These proteins are translated in the form of a nonstructural (ns) P1234 polyprotein precursor from the CHIKV positive-strand RNA genome. Active forms of replicase enzymes are generated using the autoproteolytic activity of nsP2. The available three-dimensional (3D) structure of nsP2 protease has made it a target for in silico drug design; however, there is thus far little evidence that the designed compounds indeed inhibit the protease activity of nsP2 and/or suppress CHIKV replication. In this study, a set of 12 compounds, predicted to interact with the active center of nsP2 protease, was designed using target-based modeling. The majority of these compounds were shown to inhibit the ability of nsP2 to process recombinant protein and synthetic peptide substrates. Furthermore, all compounds found to be active in these cell-free assays also suppressed CHIKV replication in cell culture, the 50% effective concentration (EC₅₀) of the most potent inhibitor being ∼1.5 μM. Analysis of stereoisomers of one compound revealed that inhibition of both the nsP2 protease activity and CHIKV replication depended on the conformation of the inhibitor. Combining the data obtained from different assays also indicates that some of the analyzed compounds may suppress CHIKV replication using more than one mechanism.

The Antiviral Alkaloid Berberine Reduces Chikungunya Virus-Induced Mitogen-Activated Protein Kinase Signaling

Chikungunya virus (CHIKV) has infected millions of people in the tropical and subtropical regions since its reemergence in the last decade. We recently identified the nontoxic plant alkaloid berberine as an antiviral substance against CHIKV in a high-throughput screen. Here, we show that berberine is effective in multiple cell types against a variety of CHIKV strains, also at a high multiplicity of infection, consolidating the potential of berberine as an antiviral drug. We excluded any effect of this compound on virus entry or on the activity of the viral replicase. A human phosphokinase array revealed that CHIKV infection specifically activated the major mitogen-activated protein kinase (MAPK) signaling pathways extracellular signal-related kinase (ERK), p38 and c-Jun NH2-terminal kinase (JNK). Upon treatment with berberine, this virus-induced MAPK activation was markedly reduced. Subsequent analyses with specific inhibitors of these kinases indicated that the ERK and JNK signaling cascades are important for the generation of progeny virions. In contrast to specific MAPK inhibitors, berberine lowered virus-induced activation of all major MAPK pathways and resulted in a stronger reduction in viral titers. Further, we assessed the in vivo efficacy of berberine in a mouse model and measured a significant reduction of CHIKV-induced inflammatory disease. In summary, we demonstrate the efficacy of berberine as a drug against CHIKV and highlight the importance of the MAPK signaling pathways in the alphavirus infectious cycle.

IMPORTANCE

Chikungunya virus (CHIKV) is a mosquito-borne virus that causes severe and persistent muscle and joint pain and has recently spread to the Americas. No licensed drug exists to counter this virus. In this study, we report that the alkaloid berberine is antiviral against different CHIKV strains and in multiple human cell lines. We demonstrate that berberine collectively reduced the virus-induced activation of cellular mitogen-activated protein kinase signaling. The relevance of these signaling cascades in the viral life cycle was emphasized by specific inhibitors of these kinase pathways, which decreased the production of progeny virions. Berberine significantly reduced CHIKV-induced inflammatory disease in a mouse model, demonstrating efficacy of the drug in vivo Overall, this work makes a strong case for pursuing berberine as a potential anti-CHIKV therapeutic compound and for exploring the MAPK signaling pathways as antiviral targets against alphavirus infections.

Antiviral effect of theaflavins against caliciviruses

Caliciviruses are contagious pathogens of humans and various animals. They are the most common cause of viral gastroenteritis in humans, and can cause lethal diseases in domestic animals such as cats, rabbits and immunocompromised mice. In this study, we conducted cytopathic effect-based screening of 2080 selected compounds from our in-house library to find antiviral compounds against three culturable caliciviruses: feline calicivirus, murine norovirus (MNV) and porcine sapovirus (PoSaV). We identified active six compounds, of which two compounds, both related to theaflavins, showed broad antiviral activities against all three caliciviruses; three compounds (abamectin, a mixture of avermectin B1a and B1b; avermectin B1a; and (-)-epigallocatechin gallate hydrate) were effective against PoSaV only; and a heterocyclic carboxamide derivative (BFTC) specifically inhibited MNV infectivity in cell cultures. Further studies of the antiviral mechanism and structure-activity relationship of theaflavins suggested the following: (1) theaflavins worked before the viral entry step; (2) the effect of theaflavins was time- and concentration-dependent; and (3) the hydroxyl groups of the benzocycloheptenone ring were probably important for the anti-calicivirus activity of theaflavins. Theaflavins could be used for the calicivirus research, and as potential disinfectants and antiviral reagents to prevent and control calicivirus infections in animals and humans.

Mood stabilizers inhibit cytomegalovirus infection

Cytomegalovirus (CMV) infection can generate debilitating disease in immunocompromised individuals and neonates. It is also the most common infectious cause of congenital birth defects in infected fetuses. Available anti-CMV drugs are partially effective but are limited by some toxicity, potential viral resistance, and are not recommended for fetal exposure. Valproate, valpromide, and valnoctamide have been used for many years to treat epilepsy and mood disorders. We report for the first time that, in contrast to the virus-enhancing actions of valproate, structurally related valpromide and valnoctamide evoke a substantial and specific inhibition of mouse and human CMV in vitro. In vivo, both drugs safely attenuate mouse CMV, improving survival, body weight, and developmental maturation of infected newborns. The compounds appear to act by a novel mechanism that interferes with CMV attachment to the cell. Our work provides a novel potential direction for CMV therapeutics through repositioning of agents already approved for use in psychiatric disorders.

A Screen of FDA-Approved Drugs for Inhibitors of Zika Virus Infection

Currently there are no approved vaccines or specific therapies to prevent or treat Zika virus (ZIKV) infection. We interrogated a library of FDA-approved drugs for their ability to block infection of human HuH-7 cells by a newly isolated ZIKV strain (ZIKV MEX_I_7). More than 20 out of 774 tested compounds decreased ZIKV infection in our in vitro screening assay. Selected compounds were further validated for inhibition of ZIKV infection in human cervical, placental, and neural stem cell lines, as well as primary human amnion cells. Established anti-flaviviral drugs (e.g., bortezomib and mycophenolic acid) and others that had no previously known antiviral activity (e.g., daptomycin) were identified as inhibitors of ZIKV infection. Several drugs reduced ZIKV infection across multiple cell types. This study identifies drugs that could be tested in clinical studies of ZIKV infection and provides a resource of small molecules to study ZIKV pathogenesis.