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Viruses ; 14(3)2022 03 03.
Article in English | MEDLINE | ID: covidwho-1732235


Rocaglates are potent broad-spectrum antiviral compounds with a promising safety profile. They inhibit viral protein synthesis for different RNA viruses by clamping the 5'-UTRs of mRNAs onto the surface of the RNA helicase eIF4A. Apart from the natural rocaglate silvestrol, synthetic rocaglates like zotatifin or CR-1-31-B have been developed. Here, we compared the effects of rocaglates on viral 5'-UTR-mediated reporter gene expression and binding to an eIF4A-polypurine complex. Furthermore, we analyzed the cytotoxicity of rocaglates on several human immune cells and compared their antiviral activities in coronavirus-infected cells. Finally, the potential for developing viral resistance was evaluated by passaging human coronavirus 229E (HCoV-229E) in the presence of increasing concentrations of rocaglates in MRC-5 cells. Importantly, no decrease in rocaglate-sensitivity was observed, suggesting that virus escape mutants are unlikely to emerge if the host factor eIF4A is targeted. In summary, all three rocaglates are promising antivirals with differences in cytotoxicity against human immune cells, RNA-clamping efficiency, and antiviral activity. In detail, zotatifin showed reduced RNA-clamping efficiency and antiviral activity compared to silvestrol and CR-1-31-B, but was less cytotoxic for immune cells. Our results underline the potential of rocaglates as broad-spectrum antivirals with no indications for the emergence of escape mutations in HCoV-229E.

Antineoplastic Agents , Coronavirus , 5' Untranslated Regions , Antineoplastic Agents/pharmacology , Antiviral Agents/pharmacology , Constriction , Humans
Antiviral Res ; 186: 105012, 2021 02.
Article in English | MEDLINE | ID: covidwho-1064809


Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of COVID-19, a severe respiratory disease with varying clinical presentations and outcomes, and responsible for a major pandemic that started in early 2020. With no vaccines or effective antiviral treatments available, the quest for novel therapeutic solutions remains an urgent priority. Rocaglates, a class of plant-derived cyclopenta[b]benzofurans, exhibit broad-spectrum antiviral activity against multiple RNA viruses including coronaviruses. Specifically, rocaglates inhibit eukaryotic initiation factor 4A (eIF4A)-dependent mRNA translation initiation, resulting in strongly reduced viral RNA translation. Here, we assessed the antiviral activity of the synthetic rocaglate CR-31-B (-) against SARS-CoV-2 using both in vitro and ex vivo cell culture models. In Vero E6 cells, CR-31-B (-) inhibited SARS-CoV-2 replication with an EC50 of ~1.8 nM. In primary human airway epithelial cells, CR-31-B (-) reduced viral titers to undetectable levels at a concentration of 100 nM. Reduced virus reproduction was accompanied by substantially reduced viral protein accumulation and replication/transcription complex formation. The data reveal a potent anti-SARS-CoV-2 activity by CR-31-B (-), corroborating previous results obtained for other coronaviruses and supporting the idea that rocaglates may be used in first-line antiviral intervention strategies against novel and emerging RNA virus outbreaks.

Antiviral Agents/pharmacology , Benzofurans/pharmacology , Hydroxamic Acids/pharmacology , SARS-CoV-2/drug effects , Virus Replication/drug effects , Animals , Antiviral Agents/chemistry , Benzofurans/chemistry , Bronchi/virology , Cells, Cultured , Chlorocebus aethiops , Eukaryotic Initiation Factor-4A/antagonists & inhibitors , Humans , Hydroxamic Acids/chemistry , Respiratory Mucosa/virology , SARS-CoV-2/genetics , SARS-CoV-2/physiology , Vero Cells , Viral Load/drug effects , Viral Replication Compartments/drug effects
Antiviral Res ; 175: 104706, 2020 03.
Article in English | MEDLINE | ID: covidwho-2162


Rocaglates, a class of natural compounds isolated from plants of the genus Aglaia, are potent inhibitors of translation initiation. They are proposed to form stacking interactions with polypurine sequences in the 5'-untranslated region (UTR) of selected mRNAs, thereby clamping the RNA substrate onto eIF4A and causing inhibition of the translation initiation complex. Since virus replication relies on the host translation machinery, it is not surprising that the rocaglate Silvestrol has broad-spectrum antiviral activity. Unfortunately, synthesis of Silvestrol is sophisticated and time-consuming, thus hampering the prospects for further antiviral drug development. Here, we present the less complex structured synthetic rocaglate CR-31-B (-) as a novel compound with potent broad-spectrum antiviral activity in primary cells and in an ex vivo bronchial epithelial cell system. CR-31-B (-) inhibited the replication of corona-, Zika-, Lassa-, Crimean Congo hemorrhagic fever viruses and, to a lesser extent, hepatitis E virus (HEV) at non-cytotoxic low nanomolar concentrations. Since HEV has a polypurine-free 5'-UTR that folds into a stable hairpin structure, we hypothesized that RNA clamping by Silvestrol and its derivatives may also occur in a polypurine-independent but structure-dependent manner. Interestingly, the HEV 5'-UTR conferred sensitivity towards Silvestrol but not to CR-31-B (-). However, if an exposed polypurine stretch was introduced into the HEV 5'-UTR, CR-31-B (-) became an active inhibitor comparable to Silvestrol. Moreover, thermodynamic destabilization of the HEV 5'-UTR led to reduced translational inhibition by Silvestrol, suggesting differences between rocaglates in their mode of action, most probably by engaging Silvestrol's additional dioxane moiety.

Antiviral Agents/pharmacology , Benzofurans/pharmacology , Triterpenes/pharmacology , Virus Replication/drug effects , Viruses/drug effects , A549 Cells , Animals , Antiviral Agents/chemical synthesis , Benzofurans/chemical synthesis , Bronchi/cytology , Cell Culture Techniques , Cells, Cultured , Epithelial Cells/virology , Eukaryotic Initiation Factor-4A/antagonists & inhibitors , Hepatocytes/virology , Humans , Mice , Viruses/classification