Zika virus (ZIKV) has been linked to the development of microcephaly in newborns, as well as Guillain-Barré syndrome. There are currently no drugs available to treat ZIKV infection, and accordingly, there is an unmet medical need for the discovery of new therapies. High-throughput drug screening efforts focusing on indirect readouts of cell viability are prone to a higher frequency of false positives in cases where the virus is viable in the cell but the cytopathic effect (CPE) is reduced or delayed. Here, we describe a fast and label-free phenotypic high-content imaging assay to detect cells affected by the virus-induced CPE using automated imaging and analysis. Protection from the CPE correlates with a decrease in viral antigen production, as observed by immunofluorescence. We trained our assay using a collection of nucleoside analogues with activity against ZIKV; the previously reported antiviral activities of 2'--methylribonucleosides and ribavirin against the Zika virus in Vero cells were confirmed using our developed method. To validate the ability of our assay to reveal new anti-ZIKV compounds, we profiled a novel library of 24 natural product derivatives and found compound 1 to be an inhibitor of the ZIKV-induced cytopathic effect; the activity of the compound was confirmed in human fetal neural stem cells (NSCs). The described technique can be easily leveraged as a primary screening assay for profiling of the activities of large compound libraries against ZIKV and can be expanded to other ZIKV strains and other cell lines displaying morphological changes upon ZIKV infection.
Zika virus (ZIKV), an emerging flavivirus that causes neurodevelopmental impairment to fetuses and has been linked to Guillain-Barré syndrome continues to threaten global health due to the absence of targeted prophylaxis or treatment. Nucleoside analogues are good examples of efficient anti-viral inhibitors, and prodrug strategies using phosphate masking groups (ProTides) have been employed to improve the bioavailability of ribonucleoside analogues. Here, we synthesized and tested a small library of 13 ProTides against ZIKV in human neural stem cells. Strong activity was observed for 2′-C-methyluridine and 2′-C-ethynyluridine ProTides with an aryloxyl phosphoramidate masking group. Substitution of a 2-(methylthio) ethyl phosphoramidate for the aryloxyl phosphoramidate ProTide group of 2′-C-methyluridine completely abolished antiviral activity of the compound. The aryloxyl phosphoramidate ProTide of 2′-C-methyluridine outperformed the hepatitis C virus (HCV) drug sofosbuvir in suppression of viral titers and protection from cytopathic effect, while the former compound’s triphosphate active metabolite was better incorporated by purified ZIKV NS5 polymerase over time. These findings suggest both a nucleobase and ProTide group bias for the anti-ZIKV activity of nucleoside analogue ProTides in a disease-relevant cell model.
Zika virus (ZIKV) has been linked to the development of microcephaly in newborns, as well as Guillain-Barré syndrome. There are currently no drugs available to treat infection, and accordingly there is an unmet medical need for discovery of new therapies. High-throughput drug screening efforts focusing on indirect readouts of cell viability are prone to a higher frequency of false positives in cases where the virus is viable in the cell but the cytopathic effect is reduced or delayed. Here, we describe a fast and label-free phenotypic high-content imaging assay used to detect cells affected by the viral-induced cytopathic effect (CPE) using automated imaging and analysis. Protection from CPE correlates with a decrease in viral antigen production as observed by immunofluorescence. We trained our assay using a collection of nucleoside analogues against ZIKV; the previously reported antiviral activities of 2’-C-methylribonucleosides and ribavirin against the Zika virus in Vero cells were confirmed using our developed method. Profiling of a novel library of 24 natural product derivatives using our assay revealed compound 1 as an inhibitor of ZIKV-induced cytopathic effect; activity of the compound was confirmed in human fetal neural stem cells (NSCs). The described technique can be easily leveraged as a primary screening assay for profiling large compound libraries against ZIKV, and can be expanded to other ZIKV strains and other cell lines displaying morphological changes upon ZIKV infection.
Zika virus (ZIKV), an emerging flavivirus which causes neurodevelopmental impairment 22 to fetuses and has been linked to Guillain-Barré syndrome, continues to threaten global health due 23 to the absence of targeted prophylaxis or treatment. Nucleoside analogues are good examples of 24 efficient anti-viral inhibitors, and prodrug strategies using phosphate masking groups (ProTides) 25 have been employed to improve the bioavailability of ribonucleoside analogues. Here, we 26 synthesized and tested a library of 13 ProTides against ZIKV in human neural stem cells. Strong 27 activity was observed for 2'-C-methyluridine and 2'-C-ethynyluridine ProTides with an aryloxyl 28 phosphoramidate masking group. Conversion of the aryloxyl phosphoramidate ProTide group of 29 2'-C-methyluridine to a 2-(methylthio)ethyl phosphoramidate completely abolished antiviral 30 activity of the compound. The aryloxyl phosphoramidate ProTide of 2'-C-methyluridine 31 outperformed the hepatitis C virus (HCV) drug sofosbuvir in suppression of viral titers and 32 protection from cytopathic effect, while the former compound's triphosphate active metabolite was 33 better incorporated by purified ZIKV NS5 polymerase over time. Molecular superpositioning 34 revealed different orientations of residues opposite the 2'-fluoro group of sofosbuvir. These findings 35 suggest both a nucleobase and ProTide group bias for the anti-ZIKV activity of nucleoside analogue 36 ProTides in a disease-relevant cell model. 37 38 cells, RNA-dependent RNA polymerase 39 40 1. Introduction 41The explosive spread of Zika virus (ZIKV) during the 2015-2016 epidemics in Latin America 42 attracted worldwide attention to this previously neglected disease. The lack of effective vaccines or 43 small molecules to prevent or treat this infection remains a cause for concern and emphasizes the 44 urgent need for new therapeutic options [1]. ZIKV, an emerging flavivirus infection, causes several 48 manifestations of the disease, and in rare cases, ZIKV infection has been linked to the 49 neuroinflammatory Guillain-Barré syndrome [2]. 50 Viral polymerases remain attractive drug targets for the development of selective antiviral 51 therapies [3-5]. Generally, clinically-approved inhibitors that target these proteins fall into two broad 52 classes [6,7]. The first class consists of nucleoside analogues that mimic the natural substrate of the 53 enzyme. Upon analogue incorporation by the virally-encoded polymerase, DNA or RNA synthesis 54 is abrogated by preventing further nucleotide incorporation (chain termination), thereby arresting 55 viral replication. The second class is known as non-nucleoside inhibitors, which bind allosterically 56 and arrest viral nucleic acid synthesis by distorting the polymerase active site geometry to interfere 57 with nucleotide binding or nucleotide incorporation. 58 A common prodrug strategy used for antiviral ribonucleoside analogues involves the chemical 59 synthesis of nucleoside analogue monophosphates with metabolically-removable masking groups 60 [8...
DEAtC is a tricyclic 2’-deoxycytidine analogue that can be incorporated into oligonucleotides by solid-phase synthesis and that exhibits a large fluorescence enhancement when correctly base-paired with guanine base in a DNA–DNA duplex. The synthesis of DEAtC begins with 5-amino-2-methylbenzothiazole and provides the DEAtC nucleobase analogue over four synthetic steps. This nucleobase analogue is then silylated using BSA and conjugated to Hoffer’s chlorosugar to provide the protected DEAtC nucleoside in good yield. Following protective group removal and chromatographic isolation of the β-anomer, dimethoxytritylation and phosphoramidite synthesis offered the monomer for solid-phase DNA synthesis. Solid-phase DNA synthesis conditions using extended coupling of the DEAtC amidite and a short deprotection time are used to maximize efficiency. By following the protocol described in this unit, the DEAtC fluorescent probe can be synthesized and incorporated into any desired synthetic DNA oligonucleotide.
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