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      Discovery and Synthesis of a Phosphoramidate Prodrug of a Pyrrolo[2,1- f][triazin-4-amino] Adenine C-Nucleoside (GS-5734) for the Treatment of Ebola and Emerging Viruses

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          Abstract

          The recent Ebola virus (EBOV) outbreak in West Africa was the largest recorded in history with over 28,000 cases, resulting in >11,000 deaths including >500 healthcare workers. A focused screening and lead optimization effort identified 4b (GS-5734) with anti-EBOV EC 50 = 86 nM in macrophages as the clinical candidate. Structure activity relationships established that the 1′-CN group and C-linked nucleobase were critical for optimal anti-EBOV potency and selectivity against host polymerases. A robust diastereoselective synthesis provided sufficient quantities of 4b to enable preclinical efficacy in a non-human-primate EBOV challenge model. Once-daily 10 mg/kg iv treatment on days 3–14 postinfection had a significant effect on viremia and mortality, resulting in 100% survival of infected treated animals [Nature2016, 531, 381−385[ PubMed]]. A phase 2 study (PREVAIL IV) is currently enrolling and will evaluate the effect of 4b on viral shedding from sanctuary sites in EBOV survivors.

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          Therapeutic Efficacy of the Small Molecule GS-5734 against Ebola Virus in Rhesus Monkeys

          Summary The most recent Ebola virus outbreak in West Africa – unprecedented in the number of cases and fatalities, geographic distribution, and number of nations affected – highlights the need for safe, effective, and readily available antiviral agents for treatment and prevention of acute Ebola virus (EBOV) disease (EVD) or sequelae 1 . No antiviral therapeutics have yet received regulatory approval or demonstrated clinical efficacy. Here we describe the discovery of a novel anti-EBOV small molecule antiviral, GS-5734, a monophosphoramidate prodrug of an adenosine analog. GS-5734 exhibits antiviral activity against multiple variants of EBOV in cell-based assays. The pharmacologically active nucleoside triphosphate (NTP) is efficiently formed in multiple human cell types incubated with GS-5734 in vitro, and the NTP acts as an alternate substrate and RNA-chain terminator in primer-extension assays utilizing a surrogate respiratory syncytial virus RNA polymerase. Intravenous administration of GS-5734 to nonhuman primates resulted in persistent NTP levels in peripheral blood mononuclear cells (half-life = 14 h) and distribution to sanctuary sites for viral replication including testes, eye, and brain. In a rhesus monkey model of EVD, once daily intravenous administration of 10 mg/kg GS-5734 for 12 days resulted in profound suppression of EBOV replication and protected 100% of EBOV-infected animals against lethal disease, ameliorating clinical disease signs and pathophysiological markers, even when treatments were initiated three days after virus exposure when systemic viral RNA was detected in two of six treated animals. These results provide the first substantive, post-exposure protection by a small-molecule antiviral compound against EBOV in nonhuman primates. The broad-spectrum antiviral activity of GS-5734 in vitro against other pathogenic RNA viruses – including filoviruses, arenaviruses, and coronaviruses – suggests the potential for expanded indications. GS-5734 is amenable to large-scale manufacturing, and clinical studies investigating the drug safety and pharmacokinetics are ongoing.
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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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              Structure of a covalently trapped catalytic complex of HIV-1 reverse transcriptase: implications for drug resistance.

              A combinatorial disulfide cross-linking strategy was used to prepare a stalled complex of human immunodeficiency virus-type 1 (HIV-1) reverse transcriptase with a DNA template:primer and a deoxynucleoside triphosphate (dNTP), and the crystal structure of the complex was determined at a resolution of 3.2 angstroms. The presence of a dideoxynucleotide at the 3'-primer terminus allows capture of a state in which the substrates are poised for attack on the dNTP. Conformational changes that accompany formation of the catalytic complex produce distinct clusters of the residues that are altered in viruses resistant to nucleoside analog drugs. The positioning of these residues in the neighborhood of the dNTP helps to resolve some long-standing puzzles about the molecular basis of resistance. The resistance mutations are likely to influence binding or reactivity of the inhibitors, relative to normal dNTPs, and the clustering of the mutations correlates with the chemical structure of the drug.
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                Author and article information

                Journal
                J Med Chem
                J. Med. Chem
                jm
                jmcmar
                Journal of Medicinal Chemistry
                American Chemical Society
                0022-2623
                1520-4804
                26 January 2017
                09 March 2017
                : 60
                : 5
                : 1648-1661
                Affiliations
                []Gilead Sciences, Inc. , Foster City, California 94404, United States
                []United States Army Medical Research Institute of Infectious Diseases (USAMRIID) , Frederick, Maryland 21702, United States
                [§ ]University of California—San Diego , San Diego, California 92093, United States
                []Centers for Disease Control and Prevention , Atlanta, Georgia 30333, United States
                Author notes
                [* ]E-mail: richard.mackman@ 123456gilead.com . Tel.: 650 522 5258.
                Article
                10.1021/acs.jmedchem.6b01594
                7202039
                28124907
                037c0e9f-2229-40cc-989f-3061f52be9a5
                Copyright © 2017 American Chemical Society

                This article is made available via the PMC Open Access Subset for unrestricted RESEARCH re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.

                History
                : 27 October 2016
                Categories
                Drug Annotation
                Custom metadata
                jm6b01594
                jm6b01594

                Pharmaceutical chemistry
                Pharmaceutical chemistry

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