Search

Background: Glioblastoma, a notably malignant tumor within the central nervous system, is distinguished by its aggressive behavior. Silvestrol, a robust inhibitor of the RNA helicase eukaryotic initiation factor 4A (eIF4A), has shown significant potential as an anticancer compound. Yet, the impact of silvestrol on glioblastoma, especially its molecular mechanisms, has not been fully elucidated. Methods: This investigation employed a variety of in vitro assays, such as cell counting kit-8 (CCK-8), clonogenic, 5-ethynyl-2′-deoxyuridine (EDU), wound healing, and flow cytometry, to evaluate cell cycle progression, apoptosis, cell viability, and migration. Western blot analysis was also performed to study the apoptosis and extracellular regulated kinase (ERK) pathways. After the ERK pathway was inhibited, differentially expressed genes (DEGs) in U87 cells were identified, followed by an analysis of target genes using the gene expression profiling interactive analysis (GEPIA) database. Results: Silvestrol significantly suppressed the proliferation, migration, and colony formation of glioma cells. It caused cell cycle arrest and enhanced apoptosis in these cells. Additionally, silvestrol stimulated the ERK pathway, with these effects being reversible by an ERK phosphorylation inhibitor. Transcriptome combined with GEPIA, GSCA, UALCAN, TIMER database screened 4 potential drug targets of silvestrol: chromosome 1 open reading frame 226 (C1ORF226), mannosidase beta A (MANBA), IQ motif and Sec7 domain 2 (IQSEC2), neuregulin 1 (NRG-1). Among them, C1ORF226 was lower risk gene while MANBA, IQSEC2, and NRG-1 were high-risk genes. Furthermore, silvestrol notably reduced MANBA mRNA levels, which could be reversed by inhibiting ERK phosphorylation. Furthermore, silvestrol markedly decreased NRG-1 protein levels, with an additional reduction observed when the ERK pathway was blocked. Conclusion: Silvestrol’s anti-glioma effects are primarily due to the suppression of MANBA expression via the ERK pathway and possibly by hindering the translation of NRG-1 protein, thus reducing its expression. The downregulation of MANBA and NRG-1 proteins may be crucial in hindering glioma development and progression. These results highlight the intricate relationship between the ERK pathway and gene expression regulation in silvestrol’s therapeutic effectiveness against glioma. [ABSTRACT FROM AUTHOR]

Context: The emergence of zoonotic viruses in the last decades culminating with COVID-19 and challenges posed by the resistance of RNA viruses to antiviral drugs requires the development of new antiviral drugs. Objective: This review identifies natural products isolated from Asian and Pacific medicinal plants with in vitro and in vivo antiviral activity towards RNA viruses and analyses their distribution, molecular weights, solubility and modes of action. Materials and methods: All data in this review was compiled from Google Scholar, PubMed, Science Direct, Web of Science, ChemSpider, PubChem and library search from 1961 to 2022. Results: Out of about 350 molecules identified, 43 phenolics, 31 alkaloids, and 28 terpenes were very strongly active against at least one type of RNA virus. These natural products are mainly planar and amphiphilic, with a molecular mass between 200 and 400 g/mol and target viral genome replication. Hydroxytyrosol, silvestrol, lycorine, tylophorine and 12-O-tetradecanoylphorbol 13-acetate with IC50 below 0.01 mg/mL and selectivity index (S.I.) above 100 have the potential to be used for the development of anti-RNA virus leads. Discussion and conclusions: The medicinal plants of Asia and the Pacific are a rich source of natural products with the potential to be developed as lead for the treatment of RNA viral infections. [ABSTRACT FROM AUTHOR]

We characterized the in vitro safety and bioavailability profile of silvestrol, a compound effective against various viruses, such as corona- and Ebolaviruses, with an EC50 value of about 5 nM. The cytotoxic profile of silvestrol was assessed in various cancer cell lines, as well as the mutagenic and genotoxic potential with Ames and micronuclei tests, respectively. To identify off-target effects, we investigated whether silvestrol modulates G-protein coupled receptor (GPCR) signaling pathways. To predict the bioavailability of silvestrol, its stability, permeability and cellular uptake were determined. Silvestrol reduced viability in a cell-type-dependent manner, mediated no off-target effects via GPCRs, had no mutagenic potential and minor genotoxic effects at 50 nM. Silvestrol did not disturb cell barrier integrity, showed low membrane permeability, was stable in liver microsomes and exhibited good cellular uptake. Efficient cellular uptake and increased cytotoxicity were observed in cell lines with a low expression level of the transport protein P-glycoprotein, the known efflux transporter of silvestrol. In conclusion, silvestrol showed low permeability but good cellular uptake and high stability. Cell-type-dependent cytotoxicity seems to be caused by the accumulation of silvestrol in cells lacking the ability to expel silvestrol due to low P-glycoprotein levels. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Signaling via the B-cell receptor (BCR) is a key driver and therapeutic target in chronic lymphocytic leukemia (CLL). BCR stimulation of CLL cells induces expression of eIF4A, an initiation factor important for translation of multiple oncoproteins, and reduces expression of PDCD4, a natural inhibitor of eIF4A, suggesting that eIF4A may be a critical nexus controlling protein expression downstream of the BCR in these cells. We, therefore, investigated the effect of eIF4A inhibitors (eIF4Ai) on BCR-induced responses. We demonstrated that eIF4Ai (silvestrol and rocaglamide A) reduced anti-IgM-induced global mRNA translation in CLL cells and also inhibited accumulation of MYC and MCL1, key drivers of proliferation and survival, respectively, without effects on upstream signaling responses (ERK1/2 and AKT phosphorylation). Analysis of normal naïve and non-switched memory B cells, likely counterparts of the two main subsets of CLL, demonstrated that basal RNA translation was higher in memory B cells, but was similarly increased and susceptible to eIF4Ai-mediated inhibition in both. We probed the fate of MYC mRNA in eIF4Ai-treated CLL cells and found that eIF4Ai caused a profound accumulation of MYC mRNA in anti-IgM treated cells. This was mediated by MYC mRNA stabilization and was not observed for MCL1 mRNA. Following drug wash-out, MYC mRNA levels declined but without substantial MYC protein accumulation, indicating that stabilized MYC mRNA remained blocked from translation. In conclusion, BCR-induced regulation of eIF4A may be a critical signal-dependent nexus for therapeutic attack in CLL and other B-cell malignancies, especially those dependent on MYC and/or MCL1. [ABSTRACT FROM AUTHOR]

Purpose: In medulloblastoma (MB), group 3 (G3) patients with MYC amplification tend to exhibit worse prognosis, thus creating a need for novel effective therapies. As the driver and crucial dependency for MYC-amplified G3-MB, MYC has been proven to be a prospective therapeutic target. Here, we aimed to identify novel effective therapeutic strategies against MYC-amplified G3-MB via targeting MYC translation. Materials and Methods: Major components of translation initiation complex eIF4F were subjected to MB tumor dataset analysis, and EIF4A1 was identified to be a potential therapeutic target of MYC-amplified G3-MB. Validation was performed through genetic or pharmacological approaches with multiple patient-derived tumor models of MYC-amplified G3-MB in vitro and in vivo. Underlying mechanisms were further explored by Western blot, quantitative real-time PCR and mass spectrometry (MS) analyses. Results: MB tumor datasets analyses showed that EIF4A1 was significantly up-regulated in G3-MB patients relative to normal cerebella, positively correlated with MYC in G3-MB at transcriptional level and a crucial cancer dependency in MYC-amplified G3-MB cells. Targeting EIF4A1 with a CRISPR/Cas9 approach or small-molecule inhibitor silvestrol effectively attenuated growth in multiple preclinical models of MYC-amplified G3-MB via blocking proliferation and inducing apoptosis. Mechanistically, EIF4A1 inhibition effectively impeded MYC expression at translational level, and its potency was positively associated with MYC level. Whole-proteome MS analysis of silvestrol-treated cells further unveiled other biological functions and pathways influenced by EIF4A1 inhibition. Conclusion: Our investigation shows that interrupting MYC translation by EIF4A1 inhibition could be a potential effective therapeutic approach when treating patients with MYC-amplified G3-MB. [ABSTRACT FROM AUTHOR]

Eukaryotic translation initiation factor 4A (eIF4A) is a helicase that facilitates assembly of the translation preinitiation complex by unwinding structured mRNA 50 untranslated regions. Pateamine A (PatA) and silvestrol are natural products that disrupt eIF4A function and arrest translation, thereby triggering the formation of cytoplasmic aggregates of stalled preinitiation complexes known as stress granules (SGs). Here we examined the effects of eIF4A inhibition by PatA and silvestrol on influenza A virus (IAV) protein synthesis and replication in cell culture. Treatment of infected cells with either PatA or silvestrol at early times post-infection resulted in SG formation, arrest of viral protein synthesis and failure to replicate the viral genome. PatA, which irreversibly binds to eIF4A, sustained long-term blockade of IAV replication following drug withdrawal, and inhibited IAV replication at concentrations that had minimal cytotoxicity. By contrast, the antiviral effects of silvestrol were fully reversible; drug withdrawal caused rapid SG dissolution and resumption of viral protein synthesis. IAV inhibition by silvestrol was invariably associated with cytotoxicity. PatA blocked replication of genetically divergent IAV strains, suggesting common dependence on host eIF4A activity. This study demonstrates that the core host protein synthesis machinery can be targeted to block viral replication. [ABSTRACT FROM AUTHOR]

Nasopharyngeal carcinoma (NPC) is a type of tumour that arises from the epithelial cells that line the surface of the nasopharynx. NPC is treated with radiotherapy and cytotoxic chemotherapeutic drugs such as cisplatin and 5-fluorouracil. However, current strategies are often associated with potential toxicities. This has prompted efforts to identify alternative methods of treatment. The present study aimed to investigate silvestrol and episilvestrol-mediated inhibition of cell proliferation in human NPC cells. The growth kinetics of NPC cells treated with silvestrol or episilvestrol were monitored dynamically using a real-time, impedance-based cell analyzer, and dose-response profiles were generated using a colorimetric cell viability assay. Furthermore, apoptosis was evaluated using flow cytometry and high content analysis. In addition, flow cytometry was performed to determine cell cycle distribution. Finally, the effects of combining silvestrol or episilvestrol with cisplatin on NPC cells was examined. Apoptosis was not observed in silvestrol and episilvestrol-treated NPC cells, although cell cycle perturbation was evident. Treatment with both compounds induced a significant increase in the percentage of cells in the G2/M phase, as compared with the control. In vitro cultures combining silvestrol or episilvestrol with cisplatin showed synergistic effects against NPC cells. The results of the present study suggested that silvestrol and episilvestrol had an anti-tumour activity in NPC cells. Silvestrol and episilvestrol, particularly in combination with cisplatin, merit further investigation, so as to determine the cellular mechanisms underlying their action(s) as anti-NPC agents. [ABSTRACT FROM AUTHOR]

Enhanced protein synthesis capacity is associated with increased tumor cell survival, proliferation, and resistance to chemotherapy. Cancers like multiple myeloma (MM), which display elevated activity in key translation regulatory nodes, such as the PI3K/mammalian target of rapamycin and MYC-eukaryotic initiation factor (elF) 4E pathways, are predicted to be particularly sensitive to therapeutic strategies that target this process. To identify novel vulnerabilities in MM, we undertook a focused RNAi screen in which components of the translation apparatus were targeted. Our screen was designed to identify synthetic lethal relationships between translation factors or regulators and dexamethasone (DEX), a corticosteroid used as frontline therapy in this disease. We find that suppression of all three subunits of the elF4F cap-binding complex synergizes with DEX in MM to induce cell death. Using a suite of small molecules that target various activities of elF4F, we observed that cell survival and DEX resistance are attenuated upon elF4F inhibition in MM cell lines and primary human samples. Levels of MYC and myeloid cell leukemia 1, two known elF4F-responsive transcripts and key survival factors in MM, were reduced upon elF4F inhibition, and their independent suppression also synergized with DEX. Inhibition of elF4F in MM exerts pleotropic effects unraveling a unique therapeutic opportunity. [ABSTRACT FROM AUTHOR]

Protein synthesis is a powerful therapeutic target in leukemias and other cancers, but few pharmacologically viable agents are available that affect this process directly. The plant-derived agent silvestrol specifically inhibits translation initiation by interfering with eIF4A/mRNA assembly with eIF4F. Silvestrol has potent in vitro and in vivo activity in multiple cancer models including acute lymphoblastic leukemia (ALL) and is under pre-clinical development by the US National Cancer Institute, but no information is available about potential mechanisms of resistance. In a separate report, we showed that intraperitoneal silvestrol is approximately 100% bioavailable systemically, although oral doses were only 1% bioavailable despite an apparent lack of metabolism. To explore mechanisms of silvestrol resistance and the possible role of efflux transporters in silvestrol disposition, we characterized multi-drug resistance transporter expression and function in a silvestrol-resistant ALL cell line generated via culture of the 697 ALL cell line in gradually increasing silvestrol concentrations. This resistant cell line, 697-R, shows significant upregulation of ABCB1 mRNA and P-glycoprotein (Pgp) as well as cross-resistance to known Pgp substrates vincristine and romidepsin. Furthermore, 697-R cells readily efflux the fluorescent Pgp substrate rhodamine 123. This effect is prevented by Pgp inhibitors verapamil and cyclosporin A, as well as siRNA to ABCB1, with concomitant re-sensitization to silvestrol. Together, these data indicate that silvestrol is a substrate of Pgp, a potential obstacle that must be considered in the development of silvestrol for oral delivery or targeting to tumors protected by Pgp overexpression. [ABSTRACT FROM AUTHOR]

sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for the quantification of the plant natural product silvestrol in mice, using ansamitocin P-3 as the internal standard. The method was validated in plasma with a lower limit of quantification of 1 ng/mL, accuracy ranging from 87 to 114%, and precision (coefficient of variation) below 15%. The validated method was used to characterize pharmacokinetics in C57BL/6 mice and metabolism in mouse, human and rat plasma, and liver microsomes. Mice were dosed with silvestrol formulated in hydroxypropyl-β-cyclodextrin via intravenous, intraperitoneal, and oral routes followed by blood sampling up to 24 h. Intraperitoneal systemic availability was 100%, but oral administration resulted in only 1.7% bioavailability. Gradual degradation of silvestrol was observed in mouse and human plasma, with approximately 60% of the parent drug remaining after 6 h. In rat plasma, however, silvestrol was completely converted to silvestric acid (SA) within 10 min. Evaluation in microsomes provided further evidence that the main metabolite formed was SA, which subsequently showed no cytotoxic or cytostatic activity in a silvestrol-sensitive lymphoblastic cell line. The ability of the analytical assay to measure tissue levels of silvestrol was evaluated in liver, brain, kidney, and spleen. Results indicated the method was capable of accurately measuring tissue levels of silvestrol and suggested it has a relatively low distribution to brain. Together, these data suggest an overall favorable pharmacokinetic profile of silvestrol in mice and provide crucial information for its continued development toward potential clinical testing. [ABSTRACT FROM AUTHOR]

Simple Summary: Immune checkpoints blockade has emerged as an effective approach to prevent immune escape of tumor cells, and constitutes a powerful anti-cancer therapeutic strategy. Regulation of the expression of genes encoding immune checkpoint inhibitors has thus become an increasingly important field of study. Beyond transcription, gene expression is regulated at several post-transcriptional levels including pre-mRNA 3′-end processing and mRNA translation. More specifically, the eIF4F translation initiation complex represents an important hub for oncogenic signaling in the etiology of different cancers. The eIF4A RNA helicase component of the eIF4F can be inhibited by the widely characterized small molecule inhibitor silvestrol. Here, we evaluated the effect of eIF4A inhibition with silvestrol on the translation of alternatively polyadenylated mRNAs in melanoma cell lines and activated T cells. We show that silvestrol can selectively inhibit the translation of alternatively polyadenylated isoforms of genes encoding key immune-related proteins. Targeting the translation initiation complex eIF4F, which binds the 5′ cap of mRNAs, is a promising anti-cancer approach. Silvestrol, a small molecule inhibitor of eIF4A, the RNA helicase component of eIF4F, inhibits the translation of the mRNA encoding the signal transducer and activator of transcription 1 (STAT1) transcription factor, which, in turn, reduces the transcription of the gene encoding one of the major immune checkpoint proteins, i.e., programmed death ligand-1 (PD-L1) in melanoma cells. A large proportion of human genes produce multiple mRNAs differing in their 3′-ends through the use of alternative polyadenylation (APA) sites, which, when located in alternative last exons, can generate protein isoforms, as in the STAT1 gene. Here, we provide evidence that the STAT1α, but not STAT1β protein isoform generated by APA, is required for silvestrol-dependent inhibition of PD-L1 expression in interferon-γ-treated melanoma cells. Using polysome profiling in activated T cells we find that, beyond STAT1, eIF4A inhibition downregulates the translation of some important immune-related mRNAs, such as the ones encoding TIM-3, LAG-3, IDO1, CD27 or CD137, but with little effect on the ones for BTLA and ADAR-1 and no effect on the ones encoding CTLA-4, PD-1 and CD40-L. We next apply RT-qPCR and 3′-seq (RNA-seq focused on mRNA 3′ ends) on polysomal RNAs to analyze in a high throughput manner the effect of eIF4A inhibition on the translation of APA isoforms. We identify about 150 genes, including TIM-3, LAG-3, AHNAK and SEMA4D, for which silvestrol differentially inhibits the translation of APA isoforms in T cells. It is therefore crucial to consider 3′-end mRNA heterogeneity in the understanding of the anti-tumor activities of eIF4A inhibitors. [ABSTRACT FROM AUTHOR]

Tactical disruption of protein synthesis is an attractive therapeutic strategy, with the first-in-class eIF4A-targeting compound zotatifin in clinical evaluation for cancer and COVID-19. The full cellular impact and mechanisms of these potent molecules are undefined at a proteomic level. Here, we report mass spectrometry analysis of translational reprogramming by rocaglates, cap-dependent initiation disruptors that include zotatifin. We find effects to be far more complex than simple "translational inhibition" as currently defined. Translatome analysis by TMT-pSILAC (tandem mass tag-pulse stable isotope labeling with amino acids in cell culture mass spectrometry) reveals myriad upregulated proteins that drive hitherto unrecognized cytotoxic mechanisms, including GEF-H1-mediated anti-survival RHOA/JNK activation. Surprisingly, these responses are not replicated by eIF4A silencing, indicating a broader translational adaptation than currently understood. Translation machinery analysis by MATRIX (mass spectrometry analysis of active translation factors using ribosome density fractionation and isotopic labeling experiments) identifies rocaglate-specific dependence on specific translation factors including eEF1ε1 that drive translatome remodeling. Our proteome-level interrogation reveals that the complete cellular response to these historical "translation inhibitors" is mediated by comprehensive translational landscape remodeling. [Display omitted] • Rocaglates both inhibit and activate different protein synthesis factors • Downstream translatome remodeling includes substantial translational activation • Rocaglates induce eEF1ε1-dependent proapoptotic GEF-H1/RHOA/JNK signaling in cancer cells • Cytotoxicity not replicated by eIF4A silencing urges re-evaluation of drug mechanisms Tactical protein synthesis inhibition is actively pursued as a cancer therapy that bypasses signaling redundancies limiting current strategies. Ho et al. show that rocaglates, first identified as inhibitors of eIF4A activity, globally reprogram cellular translation at both protein synthesis machinery and translatome levels, inducing cytotoxicity through anti-survival GEF-H1/RHOA/JNK signaling. [ABSTRACT FROM AUTHOR]

The increase in pandemics caused by RNA viruses of zoonotic origin highlights the urgent need for broad-spectrum antivirals against novel and re-emerging RNA viruses. Broad-spectrum antivirals could be deployed as first-line interventions during an outbreak while virus-specific drugs and vaccines are developed and rolled out. Viruses depend on the host's protein synthesis machinery for replication. Several natural compounds that target the cellular DEAD-box RNA helicase eIF4A, a key component of the eukaryotic translation initiation complex eIF4F, have emerged as potential broad-spectrum antivirals. Rocaglates, a group of flavaglines of plant origin that clamp mRNAs with highly structured 5′ untranslated regions (5′UTRs) onto the surface of eIF4A through specific stacking interactions, exhibit the largest selectivity and potential therapeutic indices among all known eIF4A inhibitors. Their unique mechanism of action limits the inhibitory effect of rocaglates to the translation of eIF4A-dependent viral mRNAs and a minor fraction of host mRNAs exhibiting stable RNA secondary structures and/or polypurine sequence stretches in their 5′UTRs, resulting in minimal potential toxic side effects. Maintaining a favorable safety profile while inducing efficient inhibition of a broad spectrum of RNA viruses makes rocaglates into primary candidates for further development as pan-antiviral therapeutics. [ABSTRACT FROM AUTHOR]

Simple Summary: eIF4A-targeted translational inhibitors, such as silvestrol and its analogues, have emerged as strong anticancer therapies. Here, we tested the efficacy of eIF4A inhibition across a large and diverse panel of cancer cell lines and found B cell lymphomas to be the most sensitive group. Moreover, we performed a genetic screen and identified NRF2 activation as a major mechanism of resistance to silvestrol and related eIF4A inhibitors. Mechanistically, NRF2 activation broadly increases protein synthesis, and this effect is more pronounced on specific mRNAs that require eIF4A for translation. Finally, blocking NRF2 function by preventing its deglycation restores silvestrol sensitivity in cells that harbor NRF2 activation. Overall, our findings indicate that eIF4A inhibitors are a feasible therapeutic option against lymphoma and other cancers and that NRF2 activation status may be an important predictor of their efficacy. Inhibition of the eIF4A RNA helicase with silvestrol and related compounds is emerging as a powerful anti-cancer strategy. We find that a synthetic silvestrol analogue (CR-1-31 B) has nanomolar activity across many cancer cell lines. It is especially active against aggressive MYC+/BCL2+ B cell lymphomas and this likely reflects the eIF4A-dependent translation of both MYC and BCL2. We performed a genome-wide CRISPR/Cas9 screen and identified mechanisms of resistance to this new class of therapeutics. We identify three negative NRF2 regulators (KEAP1, CUL3, CAND1) whose inactivation is sufficient to cause CR1-31-B resistance. NRF2 is known to alter the oxidation state of translation factors and cause a broad increase in protein production. We find that NRF2 activation particularly increases the translation of some eIF4A-dependent mRNAs and restores MYC and BCL2 production. We know that NRF2 functions depend on removal of sugar adducts by the frutosamine-3-kinase (FN3K). Accordingly, loss of FN3K results in NRF2 hyper-glycation and inactivation and resensitizes cancer cells to eIF4A inhibition. Together, our findings implicate NRF2 in the translation of eIF4A-dependent mRNAs and point to FN3K inhibition as a new strategy to block NRF2 functions in cancer. [ABSTRACT FROM AUTHOR]

Background: Deregulation of protein translation control is a hallmark of cancers. Eukaryotic initiation factor 4A2 (EIF4A2) is required for mRNA binding to ribosome and plays an important role in translation initiation. However, little is known about its functions in colorectal cancer (CRC). Methods: Analysis of CRC transcriptome data from TCGA identified that EIF4A2 was associated with poor prognosis. Immunohistochemistry study of EIF4A2 was carried out in 297 paired colorectal tumor and adjacent normal tissue samples. In vitro and in vivo cell-biological assays were performed to study the biological functions of EIF4A2 on experimental metastasis and sensitivity to oxaliplatin treatment. Bioinformatic prediction, chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assay were carried out to unveil the transcription factor of EIF4A2 regulation. Results: EIF4A2 Expression is significantly higher in colorectal tumors. Multivariate analysis suggests EIF4A2 as an independent predictor of overall, disease-free and progression-free survival. Dysfunction of EIF4A2 by genetic knock-down or small-molecule inhibitor silvestrol dramatically inhibited CRC invasion and migration, sphere formation and enhanced sensitivity to oxaliplatin treatment in vitro and in vivo. Notably, EIF4A2 knock-down also suppressed lung metastasis in vivo. qRT-PCR and immunoblotting analyses identified c-Myc as a downstream target and effector of EIF4A2. ChIP and dual-luciferase reporter assays validated the bioinformatical prediction of ZNF143 as a specific transcription factor of EIF4A2. Conclusions: EIF4A2 promotes experimental metastasis and oxaliplatin resistance in CRC. Silvestrol inhibits tumor growth and has synergistic effects with oxaliplatin to induce apoptosis in cell-derived xenograft (CDX) and patient-derived xenograft (PDX) models. [ABSTRACT FROM AUTHOR]

Silvestrol, a natural compound that is isolated from plants of the genus Aglaia, is a specific inhibitor of the RNA helicase eIF4A, which unwinds RNA secondary structures in 5′-untranslated regions (UTRs) of mRNAs and allows translation. Silvestrol has a broad antiviral activity against multiple RNA virus families. Here, we show that silvestrol inhibits the replication of chikungunya virus (CHIKV), a positive single-stranded RNA virus. Silvestrol delayed the protein synthesis of non-structural (nsPs) and structural proteins, resulting in a delayed innate response to CHIKV infection. Interferon-α induced STAT1 phosphorylation was not inhibited nor did eIF2α become phosphorylated 16 h post infection in the presence of silvestrol. In addition, the host protein shut-off induced by CHIKV infection was decreased in silvestrol-treated cells. Silvestrol acts by limiting the amount of nsPs, and thereby reducing CHIKV RNA replication. From our results, we propose that inhibition of the host helicase eIF4A might have potential as a therapeutic strategy to treat CHIKV infections. [ABSTRACT FROM AUTHOR]

Every year, there are about 20 Mio hepatitis E virus (HEV) infections and 60,000 deaths that are associated with HEV worldwide. At the present, there exists no specific therapy for HEV. The natural compound silvestrol has a potent antiviral effect against the (−)-strand RNA-virus Ebola virus, and also against the (+)-strand RNA viruses Corona-, Picorna-, and Zika virus. The inhibitory effect on virus spread is due to an inhibition of the DEAD-box RNA helicase eIF4A, which is required to unwind structured 5′-untranslated regions (UTRs). This leads to an impaired translation of viral RNA. The HEV (+)-strand RNA genome contains a 5′-capped, short 5′-UTR. This study aims to analyze the impact of silvestrol on the HEV life cycle. Persistently infected A549 cells were instrumental. This study identifies silvestrol as a potent inhibitor of the release of HEV infectious viral particles. This goes along with a strongly reduced HEV capsid protein translation, retention of viral RNA inside the cytoplasm, and without major cytotoxic effects. Interestingly, in parallel silvestrol affects the activity of the antiviral major vault protein (MVP) by translocation from the cytoplasm to the perinuclear membrane. These data further characterize the complex antiviral activity of silvestrol and show silvestrol’s broad spectrum of function, since HEV is a virus without complex secondary structures in its genome, but it is still affected. [ABSTRACT FROM AUTHOR]

The Zika virus (ZIKV) outbreak in 2016 in South America with specific pathogenic outcomes highlighted the need for new antiviral substances with broad-spectrum activities to react quickly to unexpected outbreaks of emerging viral pathogens. Very recently, the natural compound silvestrol isolated from the plant Aglaia foveolata was found to have very potent antiviral effects against the (−)-strand RNA-virus Ebola virus as well as against Corona- and Picornaviruses with a (+)-strand RNA-genome. This antiviral activity is based on the impaired translation of viral RNA by the inhibition of the DEAD-box RNA helicase eukaryotic initiation factor-4A (eIF4A) which is required to unwind structured 5´-untranslated regions (5′-UTRs) of several proto-oncogenes and thereby facilitate their translation. Zika virus is a flavivirus with a positive-stranded RNA-genome harboring a 5′-capped UTR with distinct secondary structure elements. Therefore, we investigated the effects of silvestrol on ZIKV replication in A549 cells and primary human hepatocytes. Two different ZIKV strains were used. In both infected A549 cells and primary human hepatocytes, silvestrol has the potential to exert a significant inhibition of ZIKV replication for both analyzed strains, even though the ancestor strain from Uganda is less sensitive to silvestrol. Our data might contribute to identify host factors involved in the control of ZIKV infection and help to develop antiviral concepts that can be used to treat a variety of viral infections without the risk of resistances because a host protein is targeted. [ABSTRACT FROM AUTHOR]