Next Article in Journal
SOX2 Represses Hepatitis B Virus Replication by Binding to the Viral EnhII/Cp and Inhibiting the Promoter Activation
Next Article in Special Issue
Special Issue “Emerging Viruses: Surveillance, Prevention, Evolution, and Control”
Previous Article in Journal
Serological Survey of Lyssaviruses in Polish Bats in the Frame of Passive Rabies Surveillance Using an Enzyme-Linked Immunosorbent Assay
Previous Article in Special Issue
Late-Relapsing Hepatitis after Yellow Fever
Review

Antivirals Against Chikungunya Virus: Is the Solution in Nature?

1
Laboratory of Virology, Institute of Biomedical Science, ICBIM, Federal University of Uberlândia, Uberlândia, MG 38408-100, Brazil
2
São Paulo State University, Institute of Biosciences, Letters and Exact Sciences (IBILCE), State University of São Paulo, São José do Rio Preto, SP 15054-000, Brazil
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Viruses 2020, 12(3), 272; https://doi.org/10.3390/v12030272
Received: 15 November 2019 / Revised: 3 February 2020 / Accepted: 7 February 2020 / Published: 29 February 2020
(This article belongs to the Special Issue Emerging Viruses: Surveillance, Prevention, Evolution and Control)

Abstract

The worldwide outbreaks of the chikungunya virus (CHIKV) in the last years demonstrated the need for studies to screen antivirals against CHIKV. The virus was first isolated in Tanzania in 1952 and was responsible for outbreaks in Africa and Southwest Asia in subsequent years. Between 2007 and 2014, some cases were documented in Europe and America. The infection is associated with low rates of death; however, it can progress to a chronic disease characterized by severe arthralgias in infected patients. This infection is also associated with Guillain–Barré syndrome. There is no specific antivirus against CHIKV. Treatment of infected patients is palliative and based on analgesics and non-steroidal anti-inflammatory drugs to reduce arthralgias. Several natural molecules have been described as antiviruses against viruses such as dengue, yellow fever, hepatitis C, and influenza. This review aims to summarize the natural compounds that have demonstrated antiviral activity against chikungunya virus in vitro.
Keywords: chikungunya virus; antiviral; natural compounds chikungunya virus; antiviral; natural compounds

1. Introduction

Chikungunya fever is a tropical disease caused by the chikungunya virus (CHIKV) which is transmitted to humans by the bite of an infected mosquito of Aedes sp. The first case of chikungunya fever was reported in 1952 in Tanzania [1]. In February 2005, a major outbreak of chikungunya occurred on the islands of the Indian Ocean [2]. A large number of cases occurred in Europe and India in 2006 and 2007, respectively [2]. Several other countries in Southeast Asia were also affected [3]. In December 2013, autochthonous cases were confirmed in the French part of the Caribbean island of St Maarten [4]. Since then, local transmission has been confirmed in over 60 countries in Asia, Africa, Europe, and the Americas. In 2014, more than 1 million suspected cases were reported in the Americas, with 1,379,788 suspected cases and 191 deaths in the Caribbean islands, Latin American countries, and the United States of America (USA) [5]. Canada, Mexico, and USA have also recorded imported cases. The countries reporting the most cases were Brazil (265,000 suspected cases), and Bolivia and Colombia (19,000 suspected cases each) [6]. The first autochthonous transmission of chikungunya reported in Argentina occurred in 2016 following an outbreak of more than 1000 suspected cases [7]. In the African region, Kenya reported an outbreak of chikungunya resulting in more than 1700 suspected cases. In 2017, Pakistan continues to respond to an outbreak which started in 2016 [8]. These virus outbreaks have raised concerns on studies of CHIKV epidemiology and antiviral research [9].
CHIKV belongs to the Alphavirus genus and the Togaviridae family. It is a positive-sense, single-stranded RNA (12 kb in length) virus, with an enveloped icosahedral capsid [10]. The virus lifecycle starts via the attachment of the viral glycoproteins to the cell membrane receptors, mainly to MXRA8 [11,12] but also to prohibitin (PHB) [13], phosphatidylserine (PtdSer) [14], and glycosaminoglycans (GAGs) [15] receptors in mammalian and to ATP synthase β in mosquito cells [16], forming a pore. Then, a virus capsid is released into the cytoplasm, where the replication process takes place. Viral genome is uncoated and directly translated into nonstructural (NS) proteins nP1–4. The NS proteins form the viral replicase complex that catalyzes the synthesis of a negative strand, a template to synthesize the full-length positive sense genome, and the subgenomic mRNA. The subgenomic mRNA is translated in a polyprotein, which is cleaved to produce the structural proteins C, E3, E2, 6k, and E1, followed by the assembly of the viral components and virus release (Figure 1) [17,18].
Chikungunya fever is characterized by strong fever, arthralgia, backache, headache, and fatigue. In some cases, cutaneous manifestation and neurological complications can occur [19,20]. There is no Food and Drug Administration (FDA) approved specific antiviral or vaccine against CHIKV. Therefore, the treatment of infected patients is based on palliative care, using analgesics for pain and non-steroidal anti-inflammatory drugs to reduce arthralgia in chronic infections [10].
Due to the lack of efficient anti-CHIKV therapy, researches have been developed to identify new drug candidates for the future treatment of chikungunya fever [21]. Among them, antiviral research based on natural molecules is a potential approach. Many natural compounds showed antiviral activity against a variety of human viruses such as dengue (DENV) [22,23,24,25], yellow fever (YFV) [25,26,27], hepatitis C (HCV) [28,29,30,31,32], influenza [33,34], and zika (ZIKV) [33,35,36]. Here, we aim to summarize the natural compounds previously described to possess anti-CHIKV activity (Table 1).

2. Inhibitors of CHIKV Replicative Cycle

2.1. Epigallocatechin Gallate (Green Tea)

Epigallocatechin gallate (EGCG) is the major catechin constituent in green tea that has shown antiviral activity against CHIKV in vitro [37]. HEK 293T cells (human kidney cells) were infected with the pseudo particles CHIKV-mCherry-490 with a multiplicity of infection of 1 (MOI = 1) in the presence or absence of EGCG at 10 μg/mL, which blocked up to 60% of CHIKV entry. Through lentiviral expression of CHIKV glycoprotein, the authors evaluated the antiviral activity of EGCG on entry steps and suggested that EGCG interferes with CHIKV entry due to their effect on CHIKV envelope protein [37].

2.2. Chloroquine

According to the studies of Khan and coworkers, a synthetic compound derived from the natural Chloroquine used to treat malaria infection has shown antiviral activity against CHIKV [38]. To do this, Vero cells were infected with the African East-Central-South (ECSA) CHIKV genotype, DRE-06 strain, and incubated with the compound at 5, 10, or 20 μM to evaluate its antiviral activity. Three treatment strategies were used for the plaque assay: (1) pretreatment of the cells 24 h before infection; (2) concurrent treatment by simultaneously adding virus and chloroquine; and (3) treatment of cells up to 6 h post-CHIKV infection of Vero cells. Chloroquine at 20 μM was nontoxic to the cells and inhibited CHIKV entry by approximately 94% when cells were pretreated, 70% in the concurrent treatment, and 65% in the post-infection treatment. The results suggested that this compound presents strong antiviral activity, mainly when administered 24 h prior to infection [38].

2.3. Apigenin, Chrysin, Luteonin, Narigerin, Silybin, and Prothipendyl

Pohjala and colleagues demonstrated the anti-CHIKV activity of five natural compounds by using either a replicon cell line expressing the nonstructural proteins of CHIKV and the eGFP and Renilla luciferase (Rluc) markers or the full-length virus genetically modified with the reporter Rluc. Firstly, BHK21 (baby hamster kidney) cells were infected with the full length CHIKV-Rluc (MOI = 0.001) and simultaneously treated with different concentrations of each compound ranging from 0.01 to 100 µM for 16 h. The compounds apigenin (inhibitory concentration (IC50) = 70.8 µM), chrysin (IC50 = 126.6 µM), narigenin (IC50 = 118.4 µM), silybin (IC50 = 92.3 µM), and prothipendyl (IC50 = 97.3 µM) significantly inhibited CHIKV-Rluc replication [39].
In addition, Muralli and coworkers also tested the antiviral activity of apigenin and luteonin ethanolic fraction from Cynodon dactylon in Vero cells and found that the fractions inhibited 98% of CHIKV activity at concentration of 50 µg/mL through the cytopathic effect [40]. Using a reverse transcriptase polymerase chain-reaction (RT-PCR) the authors also demonstrated that virus RNA levels decreased under treatment. In another study, apigenin and luteonin were isolated from a fraction of the Cynodon dactylon plant, obtained from the National Institute of Virology of India, and were used to assess the cytotoxicity and antiviral activity in Vero cells. Results showed that concentrations ranging from 5 to 200 μg/mL were nontoxic as determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell proliferation assay (MTT assay). In addition, treatment of cells at 10, 25, and 50 μg/mL showed a reduction of viral activity by decreasing 68%, 88%, and 98% of the cytopathic effect of the virus, respectively [39,40].

2.4. Flavaglines

As CHIKV uses prohibitin as a receptor to entry into mammalian cells [13], Wintachai and colleagues investigated the anti-CHIKV activity of the plant-derived compounds sulfonyl amidines 1M and the flavaglines FL3 and FL23 [41], previously reported to interact with this receptor. These compounds demonstrated antiviral activity against the CHIKV strain E1:226V East-Central-South-Africa (ECSA) genotype of a Thai isolate. The cell line HEK-293T/17 was added to each compound at specific concentrations (1, 5, 10, and 20 nM) for one hour and then infected with 10 pfu/cell of CHIKV. After 20 h, cell pellets were submitted to flow cytometry and the supernatant to a plaque assay to measure CHIKV titers. All three compounds significantly reduced the percentage of viral production in the infected cells at 10 and 20 nM concentrations. Sulfonyl amidine 1M and FL23 at 20 nM reduced viral cytopathic effect by approximately 40%, and FL3 at 20 nM reduced viral yield by 50% [41].

2.5. Compounds from Tectona grandis

The antiviral activity of three isolated and characterized compounds from Tectona grandis had its antiviral activity tested against the CHIKV strains ECSA KC 969208 and Asian KC969207 in Vero cells [42]. The authors determined IC50 of the compounds 2-(butoxycarbonyl) benzoic acid (BCB), 3,7,11,15-tetramethyl-1-hexadecanol (THD), and benzene-1-carboxylic acid-2-hexadeconate (BHCD). They demonstrated that the most potent anti-CHIKV activity was observed for BHCD with selectivity index (SI) of 116 for the Asian strain and 4.66 for ECSA. In silico analyses were performed and showed that the compound possessed strong interactions with CHIKV envelope protein 1 (E1) and poor interactions with nonstructural proteins (nSP) that may suggest that this compound could act on CHIKV entry [42].

2.6. Trigocherrierin A

The work of Bourjot and colleagues showed that compounds isolated from the Trigonostemon cherrieri presented inhibitory activity against CHIKV replication [43]. Vero cells were used in cell proliferation assay (MTS) to evaluate the anti-CHIKV activity of compounds by decreasing the cell death induced by the virus infection [43]. Among the isolated compounds, trigocherrierin A inhibited death of cells caused by the virus with a concentration that induced half of the maximum effect (EC50) of 0.6 ± 0.1 μM, CC50 of 43 ± 16 μM, and the SI of 71.7. Thus, trigocherrierin A has been shown to be the most potent tested compound against CHIKV replication in this study [43].

2.7. Harringtonine

Harringtonine, a natural compound derived from the Japanese plant Cephalotaxus harringtonia, demonstrated antiviral activity against CHIKV replication [44]. The authors investigated the anti-CHIKV activity of this compound by using the cell lines BHK-21, C6/36 (embryonic tissue cells of the Aedes albopictus mosquito), and HSMM (human skeletal muscle myoblasts) and the virus strains CHIKV-0708 (Singapore 07/2008, lacking the A226V mutation in E1 protein) and CHIKV-122508 (SGEHICHD 122508, having the A226V mutation in the E1 protein) [44]. In BHK-21 cells, harringtonine at 1 and 10 μM showed potent anti-CHIKV action, inhibiting up to 90% of viral replication with cell viability higher than 80%. Aiming to investigate the harringtonine mechanism of action, the authors performed a time addition assay. Compounds were added at different concentrations, prior to infection (−2 h) and at 0, 2, 6, 12, and 16 h post infection (h.p.i.). Treatments showed inhibition of CHIKV replication at 2 h.p.i, indicating that harringtonine inhibits the early steps of the CHIKV replicative cycle. Additionally, cells were infected and treated for 6 h, and western blot and qRT-PCR assays were performed. The results showed that harringtonine reduced negative- and positive-sense RNAs of CHIKV and the production of nSP3 and E2 proteins [44].

2.8. Diterpene Ester (phorbol-12,13-didecanoate)

Twenty-nine diterpenoids isolated from Euphorbiaceae species had their antiviral activity tested against CHIKV (Indian Ocean strain 899) in vitro through MTS assay [45,46]. First, media with serial dilutions of each compound was added to empty 96-well microplate, and then, each well was added of media containing Vero cells (2.5 × 103 cells per well) and CHIKV for 6–7 days. Among the tested compounds, phorbol-12,13-didecanoate was shown to be the strongest candidate as an antivirus against CHIKV replication, with an EC50 6.0 ± 0.9 nM [45,46].

2.9. Daphanane Diterpenoid Ortho Esters

A panel of diterpenoids or thioesters isolated from Trigonostemon cherrieri was used to evaluate the antiviral activity against CHIKV [47]. Vero cells were used to determine the cytotoxicity of compounds, and antiviral properties were accessed by plaque assay. Among the tested compounds, Trigoocherrins A, B, and F were shown to be potent inhibitors of CHIKV replication with SIs of 23, 36, and 8, respectively [45].

2.10. Aplysiatoxin-Related Compounds

Five bioactive compounds from the cyanobacteria Trichodesmiumery thraeuma had their antiviral activity evaluated [47]. Cell viability was measured and a dose-dependent anti-CHIKV assay was performed to access the antiviral activity of the compounds under pre- or post-treatment conditions. The Debromo analogues 2 and 5 showed significant antiviral activity in post-treatment of infected BHK 21 cells with EC50 of 1.3 and 2.7 μM and SI of 10.9 and 9.2, respectively. The authors suggested that the antiviral activity of these compounds blocks the replication step of the CHIKV replicative cycle [47].

2.11. Tannic Acid

Tannic acid (TA) is a compound found in different species of plants, but its structure varies according to their sources. It previously demonstrated antiviral activity against viruses as Herpes (HSV) and HCV [48,49]. The anti-CHIKV activity of TA was investigated by KONISHI and HOTTA by performing plaque reduction assay using BHK-21 cells [50]. TA reduced 50% of the virus infectivity in lower concentrations and demonstrated inhibition of virus post-entry steps in BHK-21 cells. To investigate which chemical group of TA is associated with its antiviral activity, the authors tested TA analogues on their virus-inhibiting capacities. The results demonstrated that phenolic hydroxyl groups may be related to the antiviral activity, since the displacement of these groups make the molecule ineffective [50].

2.12. Silymarin

Silymarin is a polyphenolic compound from flavonoids family, is extracted from Silybum marianum, and is described to possesses antiviral activity against HCV [51]. A study tested the activity of silymarin on CHIKV genotype ECSA with A226V mutation in E1 protein from a clinical strain isolated in an outbreak in 2008. BHK-21 and Vero cells were used to evaluate different steps of the viral replicative cycle, and silymarin showed inhibition of post-entry stages of CHIKV with an EC50 of 16.9 µg/mL and SI of 25.1. By using a stable cell line expressing CHIKV replicon and EGFP and Rluc markers [39], it was demonstrated that silymarin suppressed 93.4% of CHIKV replication. Western blot assay was performed, showing that silymarin treatment decreased the amounts of nSP1, nSP3, and E2 proteins [52].

2.13. Baicalein, Fisetin, and Quercetagetin

Baicalein, fisetin, and quercetagetin are compounds from the flavonoids family that exhibited antiviral activity against DENV [22] and enterovirus A71 [53]. Lani and colleagues infected Vero cells with the CHIKV genotype ECSA strain from the outbreak of 2008 and evaluated their effects in reducing the cytopathic effect resulting from viral infection [54]. All three compounds were found to inhibit CHIKV replication in a dose-dependent manner and reduced E2, nSP1, and nSP3 protein synthesis, as showed by Western blot analysis. Baicalein and quercetagetin showed anti-CHIKV activity by inactivating the virus, preventing the attachment of the virus to the host cells and blocking post-entry stages, with EC50 of 1.891 µg/mL and 13.85 µg/mL, respectively. Fisetin only inhibited post-entry steps with EC50 of 8.44 µg/mL [54].

2.14. Bryostatin

Bryostatin is a macrolide lactone derived from a marine animal named Bugula neritina [55]. It was described by the antineoplastic activity [56], affects Alzheimer’s disease [57], and has been related to the eradication of human immunodeficiency virus reservoirs [58]. The anti-CHIKV activities of the Bryostatin analogs salicylate-derived analog 1, C26-capped analog 2, and C26-capped analog 3 were assessed by evaluating the cytopathic effect (CPE) caused by CHIKV Indian Ocean lineage strain 899 replication under treatment with these three compounds [59]. All of the Bryostatin analogs inhibited the CHIKV replicative cycle, decreasing infectious progeny and viral RNA copies, confirmed by supernatant titration and RT-PCR. A time-addition assay showed that these compounds inhibited late stages of CHIKV replication, with EC50 rates of 4 µM, 8 µM, and 7.5 µM, respectively. Additionally, salicylate-derived analog 1 but not the other compounds blocked entry of CHIKV pseudoparticles into Buffalo green monkey kidney cells (BGM) [59].

2.15. Prostatin

Bourjot and coworkers described the effect of prostratin, a compound derived from Trigonostemon howii, on CHIKV infection in Vero cells by a CPE assay (EC50 = 2.6 µM) [60]. Another work used CHIKV lineage Indian Ocean 899 to infected Vero, BGM, or Human embryonic lung fibroblasts (HEL) cells at MOI of 0.001 under the treatment with prostratin and obtained EC50 of 8 µM, 7.6 µM, and 7.1 µM, respectively. Using a delay treatment associated with a RT-PCR or CHIKV pseudoparticle techniques, it was demonstrated that prostratin decreased both the number of CHIKV genome copies and the production of infectious progeny virus particles. A western blot assay was used to detect CHIKV proteins and showed that prostratin also reduced the accumulation of nSP1 and capsid proteins [60].

2.16. Berberine

Berberine is a compound found in plants from the Berberis genus, family Berberidaceae, that previously demonstrated antiviral activity against other viruses [61]. Varghese and colleagues analyzed the antiviral effect of berberine on the CHIKV replication cycle using the CHIKV lineage LR2006 OPY1 with the Rluc marker to infect HEK-293T, HOS (humam bone osteosarcoma), and CRL-2522 cells. The berberine EC50 for each cell line were 4.5, 12.2, and 35.3 µM, respectively. This compound was also active against the different CHIKV strains LR2006 OPY1, SGP11, and CNR20235, showing EC50 of 37.6, 44.2, and 50.9 µM, respectively. Berberine showed no inhibition on CHIKV entry or replication but decreased viral RNA and viral protein synthesis, suggesting that berberine is indirectly perturbing CHIKV replication by affecting host components [61].

2.17. Avermectin Derivates

Avermectin is naturally produced in Streptomyces avermitilis bacteria and showed different biological properties including antiparasitic [62], antiviral [63], and antibacterial [64,65] activities. Ivermectin (IVN) and abamectin (ABN) are chemically modified derivatives of avermectin. The activity of these derivatives on the CHIKV replication cycle was described in a study that used BHK-21 with CHIKV containing the Rluc gene [66]. IVN and ABN demonstrated EC50 of 0.6 µM and 1.5 µM, respectively, and strongly reduced nSP1 and nSP3 even in high MOIs. A time-of-addition assay demonstrated that IVN and ABN interfered in earlier stages of CHIKV cycle but not when cells were pretreated. Alternatively, the activity of these compounds was decreased in the later stages of the CHIKV replicative cycle [66].

3. Prospects

The aim of this review was to summarize data from literature concerning the natural compounds described to possess anti-CHIKV activity. Altogether, data is heterogeneous since authors developed a variety of assays using different cell lines and CHIKV strains or replicons. Some studies did not elucidate the mechanism of action (MOA) of the compound, retaining their information as EC50, CC50, and/or SI. For most of the compounds presented in this review, it would be desirable to demonstrate the MOA in order to elucidate the biochemical and molecular basis of the compound–virus or compound–cell interactions and to be able to predict and promote strategies for pharmacological outcomes in further studies [67]. Also, the investigation of the effects of each compound in different cell lines would provide important information concerning the effects of these compounds on the host cells [68,69]. Besides that, all data summarized here represent a relevant source of knowledge concerning the antiviral potential of molecules isolated from nature.
From the natural compounds cited in this review, chloroquine was the only compound tested in vivo, in non-human primates, and in human clinical trials. Chloroquine is already used for the treatment of malaria [70]. However, despite the in vitro results, chloroquine demonstrated no relevant results in vivo in decreasing viremia or in reducing clinical manifestations during acute stage of CHIKV infection [71]. Therefore, the results demonstrated by in vitro analysis were not correlated with the in vivo analysis that showed that chloroquine was not suitable for patients with CHIKV. Additionally, the remaining compounds described here have not been tested in vivo yet, representing a delay in anti-CHIKV drug development.
Apart from the chloroquine case, all compounds that demonstrated antiviral activity have the potential to be further investigated by their therapeutically properties against chikungunya fever. Furthermore, natural compounds may present as a source of molecules with potent biological activities that could be used as templates to the development of novel antivirals.

4. Conclusions

The spread of CHIKV in the last years demonstrated the need to develop effective antiviruses to treat chikungunya fever and to prevent future outbreaks. In this context, natural compounds have shown potent antiviral activity against a range of viruses. This review summarized the natural compounds described to possess anti-CHIKV activity by blocking early and/or late stages of virus replication in vitro. Apart from the great antiviral activity of the described compounds, further research is needed for the development of future treatments.

Funding

We would like to thank the Royal Society–Newton Advanced Fellowship (grant reference NA 150195), CNPQ (National Counsel of Technological and Scientific Development–grant 445021/2014-4), FAPEMIG (Minas Gerais Research Foundation - APQ-00587-14, SICONV 793988/2013 and APQ-03385-18) and CAPES (Coordination for the Improvement of Higher Education Personnel–Code 001), for financial support. ACGJ also thanks the CNPq for the productivity fellowship (311219/2019-5).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Ross, R.W. The virus: Isolation, Pathogenic properties and relationship to the epidemic. Newala Epidemic 1956, 177–191. [Google Scholar]
  2. Panning, M.; Grywna, K.; van Esbroeck, M.; Emmerich, P.; Drosten, C. Chikungunya Fever in Travelers Returning to Europe from the Indian Ocean Region, 2006. Emerg. Infect. Dis. 2008, 14, 416–422. [Google Scholar] [CrossRef] [PubMed]
  3. Schuffenecker, I.; Frangeul, L.; Vaney, M.; Iteman, I.; Michault, A.; Lavenir, R.; Pardigon, N.; Reynes, J.; Biscornet, L.; Diancourt, L. Genome Microevolution of Chikungunya Viruses Causing the Indian Ocean Outbreak. PLoS Med. 2006, 3, 1058–1070. [Google Scholar] [CrossRef]
  4. Henry, M.; Francis, L.; Asin, V.; Polson-Edwards, K.; Olowokure, B. Chikungunya virus outbreak in Sint Maarten, 2013-2014. Rev. Panam. Salud Publica Pan Am. J. Public Health 2017, 41, e61. [Google Scholar] [CrossRef]
  5. Morens, D.M.; Fauci, A.S. Chikungunya at the Door — Déjà Vu All Over Again? N. Engl. J. Med. 2014, 371, 885–887. [Google Scholar] [CrossRef] [PubMed]
  6. PAHO PAHO WHO. Chikungunya. Data, Maps and Statistics. Available online: https://www.paho.org/hq/index.php%3Foption%3Dcom_topics%26view%3Drdmore%26cid%3D5927%26item%3Dchikungunya%26type%3Dstatistics%26Itemid%3D40931%26lang%3Den (accessed on 28 December 2019).
  7. Carbajo, A.E.; Vezzani, D. Waiting for chikungunya fever in Argentina: Spatio-temporal risk maps. Mem. Inst. Oswaldo Cruz 2015, 110, 259–262. [Google Scholar] [CrossRef] [PubMed]
  8. Badar, N.; Salman, M.; Ansari, J.; Ikram, A.; Qazi, J.; Alam, M.M. Epidemiological trend of chikungunya outbreak in Pakistan: 2016-2018. PLoS Negl. Trop. Dis. 2019, 13, 2018–2019. [Google Scholar] [CrossRef] [PubMed]
  9. Renault, P.; Solet, J.; Sissoko, D.; Balleydier, E.; Larrieu, S.; Filleul, L.; Lassalle, C.; Thiria, J.; Rachou, E.; De Valk, H.; et al. A Major Epidemic of Chikungunya Virus Infection on Réunion Island. Am. Soc. Trop. Med. Hyg. 2007, 77, 727–731. [Google Scholar] [CrossRef]
  10. Thiberville, S.D.; Moyen, N.; Dupuis-Maguiraga, L.; Nougairede, A.; Gould, E.A.; Roques, P.; de Lamballerie, X. Chikungunya fever: Epidemiology, clinical syndrome, pathogenesis and therapy. Antivir. Res. 2013, 99, 345–370. [Google Scholar] [CrossRef]
  11. Song, H.; Zhao, Z.; Chai, Y.; Jin, X.; Li, C.; Yuan, F.; Liu, S.; Gao, Z.; Wang, H.; Song, J.; et al. Molecular Basis of Arthritogenic Alphavirus Receptor MXRA8 Binding to Chikungunya Virus Envelope Protein. Cell 2019, 177, 1714–1724.e12. [Google Scholar] [CrossRef]
  12. Zhang, R.; Earnest, J.T.; Kim, A.S.; Winkler, E.S.; Desai, P.; Adams, L.J.; Hu, G.; Bullock, C.; Gold, B.; Cherry, S.; et al. Expression of the Mxra8 Receptor Promotes Alphavirus Infection and Pathogenesis in Mice and Drosophila. Cell Rep. 2019, 28, 2647–2658.e5. [Google Scholar] [CrossRef] [PubMed]
  13. Wintachai, P.; Wikan, N.; Kuadkitkan, A.; Jaimipuk, T.; Ubol, S.; Pulmanausakakil, R.; Auewarakul, P.; Kasinrerk, W.; Weng, W.-Y.; Panyasrivanit, M.; et al. Identification of Prohibitin as a Chikungunya Virus Receptor Protein. J. Med. Virol. 2012, 84, 1757–1770. [Google Scholar] [CrossRef] [PubMed]
  14. Moller-Tank, S.; Kondratowicz, A.S.; Davey, R.A.; Rennert, P.D.; Maury, W. Role of the Phosphatidylserine Receptor TIM-1 in Enveloped-Virus Entry. J. Virol. 2013, 87, 8327–8341. [Google Scholar] [CrossRef] [PubMed]
  15. Silva, L.A.; Khomandiak, S.; Ashbrook, A.W.; Weller, R.; Heise, M.T.; Morrison, T.E.; Dermody, T.S.; Lyles, D.S. A Single-Amino-Acid Polymorphism in Chikungunya Virus E2 Glycoprotein Influences Glycosaminoglycan Utilization. J. Virol. 2014, 88, 2385–2397. [Google Scholar] [CrossRef] [PubMed]
  16. Fongsaran, C.; Jirakanwisal, K.; Kuadkitkan, A.; Wikan, N.; Wintachai, P.; Thepparit, C.; Ubol, S.; Phaonakrop, N.; Roytrakul, S.; Smith, D.R. Involvement of ATP synthase β subunit in chikungunya virus entry into insect cells. Arch. Virol. 2014, 159, 3353–3364. [Google Scholar] [CrossRef]
  17. Abdelnabi, R.; Neyts, J.; Delang, L. Towards antivirals against chikungunya virus. Antivir. Res. 2015, 121, 59–68. [Google Scholar] [CrossRef]
  18. Gould, E.A.; Coutard, B.; Malet, H.; Morin, B.; Jamal, S.; Weaver, S.; Gorbalenya, A.; Moureau, G.; Baronti, C.; Delogu, I.; et al. Understanding the alphaviruses: Recent research on important emerging pathogens and progress towards their control. Antivir. Res. 2010, 87, 111–124. [Google Scholar] [CrossRef]
  19. De Lima, M.E.S.; Bachur, T.P.R.; Aragão, G.F. Guillain-Barre syndrome and its correlation with dengue, Zika and chikungunya viruses infection based on a literature review of reported cases in Brazil. Acta Trop. 2019, 197, 105064. [Google Scholar] [CrossRef]
  20. W.H.O. Chikungunya. Available online: https://www.who.int/news-room/fact-sheets/detail/chikungunya (accessed on 28 December 2019).
  21. Yactayo, S.; Staples, J.E.; Millot, V.; Cibrelus, L.; Ramon-Pardo, P. Epidemiology of Chikungunya in the Americas. J. Infect. Dis. 2016, 214, S441–S445. [Google Scholar] [CrossRef]
  22. Zandi, K.; Teoh, B.-T.; Sam, S.-S.; Wong, P.-F.; Mustafa, M.R.; AbuBakar, S. Novel antiviral activity of baicalein against dengue virus. BMC Complement. Altern. Med. 2012, 12, 1185. [Google Scholar] [CrossRef]
  23. Jain, J.; Kumar, A.; Narayanan, V.; Ramaswamy, R.S.; Sathiyarajeswaran, P.; Shree Devi, M.S.; Kannan, M.; Sunil, S. Antiviral activity of ethanolic extract of Nilavembu Kudineer against dengue and chikungunya virus through in vitro evaluation. J. Ayurveda Integr. Med. 2019. [Google Scholar] [CrossRef] [PubMed]
  24. Gómez-Calderón, C.; Mesa-Castro, C.; Robledo, S.; Gómez, S.; Bolivar-Avila, S.; Diaz-Castillo, F.; Martínez-Gutierrez, M. Antiviral effect of compounds derived from the seeds of Mammea americana and Tabernaemontana cymosa on Dengue and Chikungunya virus infections. BMC Complement. Altern. Med. 2017, 17, 57. [Google Scholar] [CrossRef] [PubMed]
  25. Mastrangelo, E.; Pezzullo, M.; De burghgraeve, T.; Kaptein, S.; Pastorino, B.; Dallmeier, K.; De lamballerie, X.; Neyts, J.; Hanson, A.M.; Frick, D.N.; et al. Ivermectin is a potent inhibitor of flavivirus replication specifically targeting NS3 helicase activity: New prospects for an old drug. J. Antimicrob. Chemother. 2012, 67, 1884–1894. [Google Scholar] [CrossRef] [PubMed]
  26. Julander, J.G. Experimental therapies for yellow fever. Antivir. Res. 2013, 97, 169–179. [Google Scholar] [CrossRef] [PubMed]
  27. Danielle, V.; Muller, M.; Rinaldi, R.; Cristina, A.; Cintra, O.; Aurélio, M.; Alves-paiva, R.D.M.; Tadeu, L.; Figueiredo, M.; Vilela, S.; et al. Toxicon Crotoxin and phospholipases A 2 from Crotalus durissus terri fi cus showed antiviral activity against dengue and yellow fever viruses. Toxicon 2012, 59, 507–515. [Google Scholar]
  28. Calland, N.; Dubuisson, J.; Rouillé, Y.; Séron, K. Hepatitis C virus and natural compounds: A new antiviral approach? Viruses 2012, 4, 2197–2217. [Google Scholar] [CrossRef]
  29. Campos, G.R.F.; Bittar, C.; Jardim, A.C.G.; Shimizu, J.F.; Batista, M.N.; Paganini, E.R.; de Assis, L.R.; Bartlett, C.; Harris, M.; da Bolzani, V.S.; et al. Hepatitis C virus in vitro replication is efficiently inhibited by acridone Fac4. J. Gen. Virol. 2017, 98, 1693–1701. [Google Scholar] [CrossRef]
  30. Stankiewicz-drogon, A.; Palchykovska, L.G.; Kostina, V.G.; Alexeeva, I.V.; Shved, A.D.; Boguszewska-chachulska, A.M. New acridone-4-carboxylic acid derivatives as potential inhibitors of Hepatitis C virus infection. Bioorg. Med. Chem. 2008, 16, 8846–8852. [Google Scholar] [CrossRef]
  31. Jardim, A.C.G.; Igloi, Z.; Shimizu, J.F.; Santos, V.A.F.F.M.; Felippe, L.G.; Mazzeu, B.F.; Amako, Y.; Furlan, M.; Harris, M.; Rahal, P. Natural compounds isolated from Brazilian plants are potent inhibitors of hepatitis C virus replication in vitro. Antivir. Res. 2015, 115, 39–47. [Google Scholar] [CrossRef]
  32. Shimizu, J.F.; Lima, C.S.; Pereira, C.M.; Bittar, C.; Batista, M.N.; Nazaré, A.C.; Polaquini, C.R.; Zothner, C.; Harris, M.; Rahal, P.; et al. Flavonoids from Pterogyne nitens Inhibit Hepatitis C Virus Entry. Sci. Rep. 2017, 7, 16127. [Google Scholar] [CrossRef]
  33. Varghese, F.S.; Rausalu, K.; Hakanen, M.; Saul, S.; Kümmerer, B.M.; Susi, P.; Merits, A.; Ahola, T. Obatoclax Inhibits Alphavirus Membrane Fusion by Neutralizing the Acidic Environment of Endocytic Compartments. Antimicrob. Agents Chemother. 2017, 61, 1–17. [Google Scholar] [CrossRef] [PubMed]
  34. Song, J.M.; Lee, K.H.; Seong, B.L. Antiviral effect of catechins in green tea on influenza virus. Antivir. Res. 2005, 68, 66–74. [Google Scholar] [CrossRef] [PubMed]
  35. Li, C.; Deng, Y.; Wang, S.; Ma, F.; Aliyari, R.; Huang, X.-Y.; Zhang, N.-N.; Watanabe, M.; Dong, H.-L.; Liu, P.; et al. 25-Hydroxycholesterol Protects Host against Zika Virus Infection and Its Associated Microcephaly in a Mouse Model. Immunity 2017, 46, 446–456. [Google Scholar] [CrossRef] [PubMed]
  36. Carneiro, B.M.; Batista, M.N.; Braga, A.C.S.; Nogueira, M.L.; Rahal, P. The green tea molecule EGCG inhibits Zika virus entry. Virology 2016, 496, 215–218. [Google Scholar] [CrossRef] [PubMed]
  37. Weber, C.; Sliva, K.; Von Rhein, C.; Kümmerer, B.M.; Schnierle, B.S. The green tea catechin, epigallocatechin gallate inhibits chikungunya virus infection. Antivir. Res. 2015, 113, 1–3. [Google Scholar] [CrossRef]
  38. Khan, M.; Santhosh, S.R.; Tiwari, M.; Rao, P.V.L.; Parida, M. Assessment of In Vitro Prophylactic and Therapeutic Efficacy of Chloroquine Against Chikungunya Virus in Vero Cells. J. Med. Virol. 2010, 824, 817–824. [Google Scholar] [CrossRef]
  39. Pohjala, L.; Utt, A.; Varjak, M.; Lulla, A.; Merits, A.; Ahola, T.; Tammela, P. Inhibitors of Alphavirus Entry and Replication Identified with a Stable Chikungunya Replicon Cell Line and Virus-Based Assays. PLoS ONE 2011, 6, e28923. [Google Scholar] [CrossRef]
  40. Murali, K.S.; Sivasubramanian, S.; Vincent, S.; Murugan, S.B.; Giridaran, B.; Dinesh, S.; Gunasekaran, P.; Krishnasamy, K.; Sathishkumar, R. Anti—chikungunya activity of luteolin and apigenin rich fraction from Cynodon dactylon. Asian Pac. J. Trop. Med. 2015, 8, 352–358. [Google Scholar] [CrossRef]
  41. Wintachai, P.; Thuaud, F.; Basmadjian, C.; Roytrakul, S.; Ubol, S.; Désaubry, L.; Smith, D.R. Assessment of flavaglines as potential chikungunya virus entry inhibitors. Microbiol. Immunol. 2015, 59, 129–141. [Google Scholar] [CrossRef]
  42. Sangeetha, K.; Purushothaman, I.; Rajarajan, S. Spectral characterisation, antiviral activities, in silico ADMET and molecular docking of the compounds isolated from Tectona grandis to chikungunya virus. Biomed. Pharmacother. 2017, 87, 302–310. [Google Scholar]
  43. Bourjot, M.; Leyssen, P.; Neyts, J.; Dumontet, V.; Litaudon, M. Trigocherrierin A, a potent inhibitor of chikungunya virus replication. Molecules 2014, 19, 3617–3627. [Google Scholar] [CrossRef] [PubMed]
  44. Kaur, P.; Thiruchelvan, M.; Lee, R.C.H.; Chen, H.; Chen, K.C.; Ng, M.L.; Chu, J.J.H. Inhibition of Chikungunya virus replication by harringtonine, a novel antiviral that suppresses viral protein expression. Antimicrob. Agents Chemother. 2013, 57, 155–167. [Google Scholar] [CrossRef] [PubMed]
  45. Allard, P.M.; Leyssen, P.; Martin, M.T.; Bourjot, M.; Dumontet, V.; Eydoux, C.; Guillemot, J.C.; Canard, B.; Poullain, C.; Guéritte, F.; et al. Antiviral chlorinated daphnane diterpenoid orthoesters from the bark and wood of Trigonostemon cherrieri. Phytochemistry 2012, 84, 160–168. [Google Scholar] [CrossRef]
  46. Nothias-Scaglia, L.-F.; Pannecouque, C.; Renucci, F.; Delang, L.; Neyts, J.; Roussi, F.; Costa, J.; Leyssen, P.; Litaudon, M.; Paolini, J. Antiviral Activity of Diterpene Esters on Chikungunya Virus and HIV Replication. J. Nat. Prod. 2015, 78, 1277–1283. [Google Scholar] [CrossRef]
  47. Gupta, D.K.; Kaur, P.; Leong, S.T.; Tan, L.T.; Prinsep, M.R.; Chu, J.J.H. Anti-Chikungunya viral activities of aplysiatoxin-related compounds from the marine cyanobacterium Trichodesmium erythraeum. Mar. Drugs 2014, 12, 115–127. [Google Scholar] [CrossRef] [PubMed]
  48. Liu, S.; Chen, R.; Hagedorn, C.H. Tannic Acid Inhibits Hepatitis C Virus Entry into Huh7.5 Cells. PLoS ONE 2015, 10, e0131358. [Google Scholar] [CrossRef]
  49. Orłowski, P.; Kowalczyk, A.; Tomaszewska, E.; Ranoszek-Soliwoda, K.; Węgrzyn, A.; Grzesiak, J.; Celichowski, G.; Grobelny, J.; Eriksson, K.; Krzyzowska, M. Antiviral Activity of Tannic Acid Modified Silver Nanoparticles: Potential to Activate Immune Response in Herpes Genitalis. Viruses 2018, 10, 524. [Google Scholar] [CrossRef]
  50. Konishi, E.; Hotta, S. Effects of Tannic Acid and Its Related Compounds upon Chikungunya Virus. Microbiol. Immunol. 1979, 23, 659–667. [Google Scholar] [CrossRef]
  51. Wagoner, J.; Negash, A.; Kane, O.J.; Martinez, L.E.; Nahmias, Y.; Bourne, N.; Owen, D.M.; Grove, J.; Brimacombe, C.; McKeating, J.A.; et al. Multiple effects of silymarin on the hepatitis C virus lifecycle. Hepatol. Baltim. Md 2010, 51, 1912–1921. [Google Scholar] [CrossRef]
  52. Lani, R.; Hassandarvish, P.; Chiam, C.W.; Moghaddam, E.; Chu, J.J.H.; Rausalu, K.; Merits, A.; Higgs, S.; Vanlandingham, D.; Abu Bakar, S.; et al. Antiviral activity of silymarin against chikungunya virus. Sci. Rep. 2015, 5, 11421. [Google Scholar] [CrossRef]
  53. Li, X.; Liu, Y.; Wu, T.; Jin, Y.; Cheng, J.; Wan, C.; Qian, W.; Xing, F.; Shi, W. The Antiviral Effect of Baicalin on Enterovirus 71 In Vitro. Viruses 2015, 7, 4756–4771. [Google Scholar] [CrossRef] [PubMed]
  54. Lani, R.; Hassandarvish, P.; Shu, M.-H.; Phoon, W.H.; Chu, J.J.H.; Higgs, S.; Vanlandingham, D.; Abu Bakar, S.; Zandi, K. Antiviral activity of selected flavonoids against Chikungunya virus. Antivir. Res. 2016, 133, 50–61. [Google Scholar] [CrossRef] [PubMed]
  55. Halford, B. THE BRYOSTATINS’ TALE. Chem. Eng. News Arch. 2011, 89, 10–17. [Google Scholar] [CrossRef]
  56. Plimack, E.R.; Tan, T.; Wong, Y.-N.; von Mehren, M.M.; Malizzia, L.; Roethke, S.K.; Litwin, S.; Li, T.; Hudes, G.R.; Haas, N.B. A Phase I Study of Temsirolimus and Bryostatin-1 in Patients With Metastatic Renal Cell Carcinoma and Soft Tissue Sarcoma. Oncologist 2014, 19, 354–355. [Google Scholar] [CrossRef]
  57. Schrott, L.M.; Jackson, K.; Yi, P.; Dietz, F.; Johnson, G.S.; Basting, T.F.; Purdum, G.; Tyler, T.; Rios, J.D.; Castor, T.P.; et al. Acute oral Bryostatin-1 administration improves learning deficits in the APP/PS1 transgenic mouse model of Alzheimer’s disease. Curr. Alzheimer Res. 2015, 12, 22–31. [Google Scholar] [CrossRef]
  58. Mehla, R.; Bivalkar-Mehla, S.; Zhang, R.; Handy, I.; Albrecht, H.; Giri, S.; Nagarkatti, P.; Nagarkatti, M.; Chauhan, A. Bryostatin Modulates Latent HIV-1 Infection via PKC and AMPK Signaling but Inhibits Acute Infection in a Receptor Independent Manner. PLoS ONE 2010, 5, e11160. [Google Scholar] [CrossRef]
  59. Abdelnabi, R.; Staveness, D.; Near, K.E.; Wender, P.A.; Delang, L.; Neyts, J.; Leyssen, P. Comparative analysis of the anti-chikungunya virus activity of novel bryostatin analogs confirms the existence of a PKC-independent mechanism. Biochem. Pharmacol. 2016, 120, 15–21. [Google Scholar] [CrossRef]
  60. Bourjot, M.; Delang, L.; Nguyen, V.H.; Neyts, J.; Guéritte, F.; Leyssen, P.; Litaudon, M. Prostratin and 12- O -Tetradecanoylphorbol 13-Acetate Are Potent and Selective Inhibitors of Chikungunya Virus Replication. J. Nat. Prod. 2012, 75, 2183–2187. [Google Scholar] [CrossRef]
  61. Varghese, F.S.; Thaa, B.; Amrun, S.N.; Simarmata, D.; Rausalu, K.; Nyman, T.A.; Merits, A.; McInerney, G.M.; Ng, L.F.P.; Ahola, T. The Antiviral Alkaloid Berberine Reduces Chikungunya Virus-Induced Mitogen-Activated Protein Kinase Signaling. J. Virol. 2016, 90, 9743–9757. [Google Scholar] [CrossRef]
  62. Campbell, W.C.; Fisher, M.H.; Stapley, E.O.; Albers-Schönberg, G.; Jacob, T.A. Ivermectin: A potent new antiparasitic agent. Science 1983, 221, 823–828. [Google Scholar] [CrossRef]
  63. Wagstaff, K.M.; Sivakumaran, H.; Heaton, S.M.; Harrich, D.; Jans, D.A. Ivermectin is a specific inhibitor of importin α/β-mediated nuclear import able to inhibit replication of HIV-1 and dengue virus. Biochem. J. 2012, 443, 851–856. [Google Scholar] [CrossRef] [PubMed]
  64. Muhammed Ameen, S.; Drancourt, M. Ivermectin lacks antituberculous activity. J. Antimicrob. Chemother. 2013, 68, 1936–1937. [Google Scholar] [CrossRef]
  65. Laing, R.; Gillan, V.; Devaney, E. Ivermectin – Old Drug, New Tricks? Trends Parasitol. 2017, 33, 463–472. [Google Scholar] [CrossRef] [PubMed]
  66. Varghese, F.S.; Kaukinen, P.; Gläsker, S.; Bespalov, M.; Hanski, L.; Wennerberg, K.; Kümmerer, B.M.; Ahola, T. Discovery of berberine, abamectin and ivermectin as antivirals against chikungunya and other alphaviruses. Antivir. Res. 2016, 117–124. [Google Scholar] [CrossRef] [PubMed]
  67. National Research Council (US) Committee on Applications of Toxicogenomic Technologies to Predictive Toxicology. Application to the Study of Mechanisms of Action; National Academies Press: Washington, DC, USA, 2007.
  68. Kaur, G.; Dufour, J.M. Cell lines. Spermatogenesis 2012, 2, 1–5. [Google Scholar] [CrossRef] [PubMed]
  69. Ulrich, A.B.; Pour, P.M. Cell Lines. In Encyclopedia of Genetics; Brenner, S., Miller, J.H., Eds.; Academic Press: New York, NY, USA, 2001; pp. 310–311. [Google Scholar]
  70. Slater, A.F. Chloroquine: Mechanism of drug action and resistance in Plasmodium falciparum. Pharmacol. Ther. 1993, 57, 203–235. [Google Scholar] [CrossRef]
  71. Roques, P.; Thiberville, S.-D.; Dupuis-Maguiraga, L.; Lum, F.-M.; Labadie, K.; Martinon, F.; Gras, G.; Lebon, P.; Ng, L.F.P.; de Lamballerie, X.; et al. Paradoxical Effect of Chloroquine Treatment in Enhancing Chikungunya Virus Infection. Viruses 2018, 10, 268. [Google Scholar] [CrossRef]
Figure 1. Schematic representation of chikungunya virus (CHIKV) replication cycle: Natural compounds with antiviral activity against CHIKV are indicated in each step of virus replication cycle (entry, replication, and release).
Figure 1. Schematic representation of chikungunya virus (CHIKV) replication cycle: Natural compounds with antiviral activity against CHIKV are indicated in each step of virus replication cycle (entry, replication, and release).
Viruses 12 00272 g001
Table 1. Natural compounds with antiviral activity against CHIKV.
Table 1. Natural compounds with antiviral activity against CHIKV.
CompoundStructureInhibitionSI or EC50Cell Line
Abamectin [66] Viruses 12 00272 i001Replication1.5 µMBHK-21
Apigenin [39,40] Viruses 12 00272 i002Infection/Replication70.8 µMBHK 21
Baicalein [54] Viruses 12 00272 i003Infection and replication1.891 µg/mLBHK-21
Baicalein [54] Viruses 12 00272 i004Entry, binding6.997 µMVero
Berberine [61] Viruses 12 00272 i005Replication (interfering in host components)≤35.3 µMCRL-2522, HEK-293T, and HOS
BHCD [42] Viruses 12 00272 i006Entry116 (Asian strain) and 4.66 (ECSA)Vero and in silico
C26-capped bryostatin analog 2 [59] Viruses 12 00272 i007Replication8 µMVero
C26-capped bryostatin analog 3 [59] Viruses 12 00272 i008Replication7.5 µMVero
Chloroquine [38] Viruses 12 00272 i009Entry37.14Vero
Chrysin [39] Viruses 12 00272 i010Infection126.6 µMBHK 21
EGCG [37] Viruses 12 00272 i011Entry steps; cell attachment6.54 µg/mLHEK 293T
Fisetin [54] Viruses 12 00272 i012Replication8.44 µg/mLBHK-21
Harringtonine [44] Viruses 12 00272 i013Early stages of replication0.24 µMBHK 21
Ivermectin [66] Viruses 12 00272 i014Replication0.6 µMBHK-21
Luteolin [40] Viruses 12 00272 i015ReplicationNSVero
Narigenin [39] Viruses 12 00272 i016Infection118.4 µMBHK 21
Prostratin [60] Viruses 12 00272 i017Replication and release2,6 µM and ± 8 µMVero, BGM, and HEL
Prothipendyl [39] Viruses 12 00272 i018Replication97.3 µMBHK 21
Quercetagetin [54] Viruses 12 00272 i019Entry and binding43.52 µMVero
Quercetagetin [54] Viruses 12 00272 i019Entry and replication13.85 µg/mLBHK-21
Salicylate-derived bryostatin analog [59] Viruses 12 00272 i020Entry and replication4 µMVero
Silybin [39] Viruses 12 00272 i021Infection92.3 µMBHK 21
Silymarin [52] Viruses 12 00272 i022Replication16.9 µg/mLBHK-21 and Vero
Tannic Acid [50] Viruses 12 00272 i023ReplicationNSBHK-21
Phorbol-12,13-dideca-noate [46] Viruses 12 00272 i024Replication6 ± 0.9 nMVero
Trigocherrierin [43] Viruses 12 00272 i025Replication0.6 ± 0.1 µMVero
NS = Not shown, data not shown.
Back to TopTop