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 sequelae1. 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.

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 [Nature 2016, 531, 381−385]. 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.

HIGHLIGHTS NTZ amplifies RNA sensor and type I interferon activities and induces GADD34 expression NTZ inhibits infectious Ebola virus (EBOV) via RIG-I and PKR, but not GADD34 NTZ inhibits a second negative-strand RNA virus, VSV, via RIG-I and GADD34, but not PKR NTZ holds promise as an oral therapy against EBOV Jasenosky et al., iScience 19, SUMMARYHere, we show that the US Food and Drug Administration-approved oral drug nitazoxanide (NTZ) broadly amplifies the host innate immune response to viruses and inhibits Ebola virus (EBOV) replication. We find that NTZ enhances retinoic-acid-inducible protein I (RIG-I)-like-receptor, mitochondrial antiviral signaling protein, interferon regulatory factor 3, and interferon activities and induces transcription of the antiviral phosphatase GADD34. NTZ significantly inhibits EBOV replication in human cells through its effects on RIG-I and protein kinase R (PKR), suggesting that it counteracts EBOV VP35 protein's ability to block RIG-I and PKR sensing of EBOV. NTZ also inhibits a second negative-strand RNA virus, vesicular stomatitis virus (VSV), through RIG-I and GADD34, but not PKR, consistent with VSV's distinct host innate immune evasion mechanisms. Thus, NTZ counteracts varied virus-specific immune evasion strategies by generally enhancing the RNA sensing and interferon axis that is triggered by foreign cytoplasmic RNA exposure, and holds promise as an oral therapy against EBOV.

Catecholamines play an important role in controlling white adipose tissue function and development. ␤-and ␣2-adrenergic receptors (ARs) couple positively and negatively, respectively, to adenylyl cyclase and are coexpressed in human adipocytes. Previous studies have demonstrated increased adipocyte ␣2/␤-AR balance in obesity, and it has been proposed that increased ␣2-ARs in adipose tissue with or without decreased ␤-ARs may contribute mechanistically to the development of increased fat mass. To critically test this hypothesis, adipocyte ␣2/␤-AR balance was genetically manipulated in mice. Human ␣2A-ARs were transgenically expressed in the adipose tissue of mice that were either homozygous (؊/؊) or heterozygous (؉/؊) for a disrupted ␤3-AR allele. Mice expressing ␣2-ARs in fat, in the absence of ␤3-ARs (␤3-AR ؊/؊ background), developed high fat diet-induced obesity. Strikingly, this effect was due entirely to adipocyte hyperplasia and required the presence of ␣2-ARs, the absence of ␤3-ARs, and a high fat diet. Of note, obese ␣2-transgenic, ␤3 ؊/؊ mice failed to develop insulin resistance, which may reflect the fact that expanded fat mass was due to adipocyte hyperplasia and not adipocyte hypertrophy. In summary, we have demonstrated that increased ␣2/␤-AR balance in adipocytes promotes obesity by stimulating adipocyte hyperplasia. This study also demonstrates one way in which two genes (␣2 and ␤3-AR) and diet interact to influence fat mass.

A longstanding and still-increasing threat to the effective treatment of infectious diseases is resistance to antimicrobial countermeasures. Potentially, the targeting of host proteins and pathways essential for the detrimental effects of pathogens offers an approach that may discover broad-spectrum anti-pathogen countermeasures and circumvent the effects of pathogen mutations leading to resistance. Here we report implementation of a strategy for discovering broad-spectrum host-oriented therapies against multiple pathogenic agents by multiplex screening of drugs for protection against the detrimental effects of multiple pathogens, identification of host cell pathways inhibited by the drug, and screening for effects of the agent on other pathogens exploiting the same pathway. We show that a clinically used antimalarial drug, Amodiaquine, discovered by this strategy, protects host cells against infection by multiple toxins and viruses by inhibiting host cathepsin B. Our results reveal the practicality of discovering broadly acting anti-pathogen countermeasures that target host proteins exploited by pathogens.