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      Influenza antivirals currently in late‐phase clinical trial

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          Abstract

          Influenza antiviral drugs are important for the control of influenza, most specifically for the treatment of influenza patients with severe disease following infection with a seasonal influenza virus, a newly emerging influenza strain, or in the event of a pandemic. Many influenza antivirals that are currently under investigation in late‐stage clinical trials differ in their mechanism of action compared to drugs currently licensed for the treatment of influenza. Nitazoxanide and DAS181 target components of the host cell and alter the ability of the virus to replicate efficiently, while small molecule drugs such as T705, JNJ63623872 and S‐033188 bind to the viral polymerase complex and restrict viral replication. Monoclonal antibodies that are currently in clinical trial for the treatment of influenza most commonly are targeted to the stem region of the haemagglutinin molecule. Early findings from animal models and in vitro studies suggest that many of the new antiviral drugs when tested in combination with oseltamivir have improved effectiveness over monotherapy. Clinical trials assessing both monotherapy and combination therapy are currently under investigation. It is hoped that as new antivirals are licensed, they will improve the standard of care and outcomes for influenza patients with severe disease.

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          Successful treatment of advanced Ebola virus infection with T-705 (favipiravir) in a small animal model.

          Outbreaks of Ebola hemorrhagic fever in sub-Saharan Africa are associated with case fatality rates of up to 90%. Currently, neither a vaccine nor an effective antiviral treatment is available for use in humans. Here, we evaluated the efficacy of the pyrazinecarboxamide derivative T-705 (favipiravir) against Zaire Ebola virus (EBOV) in vitro and in vivo. T-705 suppressed replication of Zaire EBOV in cell culture by 4log units with an IC90 of 110μM. Mice lacking the type I interferon receptor (IFNAR(-)(/)(-)) were used as in vivo model for Zaire EBOV-induced disease. Initiation of T-705 administration at day 6 post infection induced rapid virus clearance, reduced biochemical parameters of disease severity, and prevented a lethal outcome in 100% of the animals. The findings suggest that T-705 is a candidate for treatment of Ebola hemorrhagic fever. Copyright © 2014 The Authors. Published by Elsevier B.V. All rights reserved.
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            A unique cap(m7GpppXm)-dependent influenza virion endonuclease cleaves capped RNAs to generate the primers that initiate viral RNA transcription.

            We propose a mechanism for the priming of influenza viral RNA transcription by capped RNAs in which specific 5'-terminal fragments are cleaved from the capped RNAs by a virion-associated endonuclease. These fragments would serve as the actual primers for the initiation of transcription by the initial incorporation by the initial incorporation of a G residue at their 3' end. We show that virions and purified viral cores contain a unique endonuclease that cleaves RNAs containing a 5' methylated cap structure (m7GpppXm) preferentially at purine residues 10 to 14 nucleotides from the cap, generating fragments with 3'-terminal hydroxyl groups. RNAs containing the 5'-terminal structure GpppG could not be cleaved to produce these specific fragments. Consistent with our proposed mechanism, those capped fragments that function as primers could be linked to a G residue in transcriptase reactions containing alpha-32P-GTP as the only ribonucleoside triphosphate. The pattern of G and C incorporation onto these primer fragments suggests that this incorporation is directed by the second and third bases at the 3' end of the virion RNA template, which has the sequence 3' UCG. Primer fragments with a 3'-terminal A residue were used more efficiently than those with a 3'-terminal G residue, indicating a preference for generating an AGC sequence in the viral mRNA complementary to the 3' end of the virion RNA. Cleavage of the RNA primer and initiation of transcription are not necessarily coupled, because a 5' fragment isolated from one reaction could be used as a primer when added to a second reaction. Uncapped ribopolymer inhibitors of viral RNA transcription inhibited the cleavage of capped RNAs.
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              T-705 (favipiravir) induces lethal mutagenesis in influenza A H1N1 viruses in vitro.

              Several novel anti-influenza compounds are in various phases of clinical development. One of these, T-705 (favipiravir), has a mechanism of action that is not fully understood but is suggested to target influenza virus RNA-dependent RNA polymerase. We investigated the mechanism of T-705 activity against influenza A (H1N1) viruses by applying selective drug pressure over multiple sequential passages in MDCK cells. We found that T-705 treatment did not select specific mutations in potential target proteins, including PB1, PB2, PA, and NP. Phenotypic assays based on cell viability confirmed that no T-705-resistant variants were selected. In the presence of T-705, titers of infectious virus decreased significantly (P < 0.0001) during serial passage in MDCK cells inoculated with seasonal influenza A (H1N1) viruses at a low multiplicity of infection (MOI; 0.0001 PFU/cell) or with 2009 pandemic H1N1 viruses at a high MOI (10 PFU/cell). There was no corresponding decrease in the number of viral RNA copies; therefore, specific virus infectivity (the ratio of infectious virus yield to viral RNA copy number) was reduced. Sequence analysis showed enrichment of G→A and C→T transversion mutations, increased mutation frequency, and a shift of the nucleotide profiles of individual NP gene clones under drug selection pressure. Our results demonstrate that T-705 induces a high rate of mutation that generates a nonviable viral phenotype and that lethal mutagenesis is a key antiviral mechanism of T-705. Our findings also explain the broad spectrum of activity of T-705 against viruses of multiple families.
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                Author and article information

                Contributors
                Aeron.Hurt@influenzacentre.org
                Journal
                Influenza Other Respir Viruses
                Influenza Other Respir Viruses
                10.1111/(ISSN)1750-2659
                IRV
                Influenza and Other Respiratory Viruses
                John Wiley and Sons Inc. (Hoboken )
                1750-2640
                1750-2659
                28 February 2017
                May 2017
                : 11
                : 3 ( doiID: 10.1111/irv.2017.11.issue-3 )
                : 240-246
                Affiliations
                [ 1 ] WHO Collaborating Centre for Reference and Research on Influenza VIDRLPeter Doherty Institute for Infection and Immunity Melbourne VictoriaAustralia
                [ 2 ] University of MelbourneMelbourne School of Population and Global Health Parkville VictoriaAustralia
                Author notes
                [*] [* ] Correspondence

                Assoc. Prof. Aeron C. Hurt, WHO Collaborating Centre for Reference and Research on Influenza, VIDRL, Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia.

                Email: Aeron.Hurt@ 123456influenzacentre.org

                Author information
                http://orcid.org/0000-0003-1826-4314
                Article
                IRV12446
                10.1111/irv.12446
                5410715
                28146320
                f51f2cd8-c13c-4874-bbf7-461dd5f7a08f
                © 2017 The Authors. Influenza and Other Respiratory Viruses Published by John Wiley & Sons Ltd.

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 26 January 2017
                Page count
                Figures: 0, Tables: 1, Pages: 7, Words: 6595
                Funding
                Funded by: Australian Government Department of Health
                Categories
                Expert Commentary
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                Custom metadata
                2.0
                irv12446
                May 2017
                Converter:WILEY_ML3GV2_TO_NLMPMC version:5.0.9 mode:remove_FC converted:27.04.2017

                Infectious disease & Microbiology
                antiviral,clinical trial,development,effectiveness,influenza,influenza virus

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