ABSTRACT
Filoviruses, consisting of Ebola virus (EBOV) and Marburg virus (MARV), are among the most lethal infectious threats to mankind. Infections by these viruses can cause severe hemorrhagic fevers in humans and nonhuman primates with high mortality rates. Since there is currently no vaccine or antiviral therapy approved for humans, there is an urgent need to develop prophylactic and therapeutic options for use during filoviral outbreaks and bioterrorist attacks. One of the ideal targets against filoviral infection and diseases is at the entry step, which is mediated by the filoviral glycoprotein (GP). In this report, we screened a chemical library of small molecules and identified numerous inhibitors, which are known G protein-coupled receptor (GPCR) antagonists targeting different GPCRs, including histamine receptors, 5-HT (serotonin) receptors, muscarinic acetylcholine receptor, and adrenergic receptor. These inhibitors can effectively block replication of both infectious EBOV and MARV, indicating a broad antiviral activity of the GPCR antagonists. The time-of-addition experiment and microscopic studies suggest that GPCR antagonists block filoviral entry at a step following the initial attachment but prior to viral/cell membrane fusion. These results strongly suggest that GPCRs play a critical role in filoviral entry and GPCR antagonists can be developed as an effective anti-EBOV/MARV therapy.
IMPORTANCE Infection of Ebola virus and Marburg virus can cause severe illness in humans with a high mortality rate, and currently there is no FDA-approved vaccine or therapeutic treatment available. The 2013-2015 epidemic in West Africa underscores a lack of our understanding in the infection and pathogenesis of these viruses and the urgency of drug discovery and development. In this study, we have identified numerous inhibitors that are known G protein-coupled receptor (GPCR) antagonists targeting different GPCRs. These inhibitors can effectively block replication of both infectious EBOV and MARV, indicating a broad antiviral activity of the GPCR antagonists. Our results strongly suggest that GPCRs play a critical role in filoviral entry and GPCR antagonists can be developed as an effective anti-EBOV/MARV therapy.
INTRODUCTION
The Filoviridae family consists of Ebola virus (EBOV) and Marburg virus (MARV), which can cause severe hemorrhagic fever in human and nonhuman primates with mortality rates of up to 90%. The viral outbreaks are sporadic and unpredictable and so far have been limited to Africa (1). It is thought that fruit bats are the natural reservoirs of EBOV (2). Although several vaccines and therapeutic options have been developed and shown to be effective in nonhuman primate models (3–5), there is currently no vaccine or treatment approved for filoviral infections in humans. The 2013-2015 West Africa Ebola epidemic, with more than 25,000 people infected and more than 12,000 deaths, underlines the global challenge of treating and controlling the infections and diseases associated with these viruses.
One of the potential targets to block filoviral infection is at the entry step, which is mediated by a single viral glycoprotein (GP). GP is composed of two subunits, GP1, which is responsible for attachment and binding to receptor(s) on susceptible cells, and GP2, which mediates viral and cell membrane fusion. GP on the surface of virions is present as a homotrimer of GP1/GP2 heterodimer (1). Following the initial attachment of virions to the host cell surface, likely through the interaction of GP with heparan sulfate and other closely related glycosaminoglycans (GAGs) (6, 7), virions are believed to enter the cell by a process of endocytosis into the endosome, where fusion of virus and cell membranes occurs. Although numerous other host factors have been implicated in Ebola/Marburg virus entry, the entry mechanism of filovirus is still poorly understood.
In this study, we demonstrate that several classes of G protein-coupled receptor (GPCR) antagonists can effectively inhibit entry of both EBOV and MARV. This finding has important implications in our understanding of the role of GPCRs in filoviral entry and in the development of GPCR antagonists as a potential antifiloviral therapeutic option.
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