A colorized transmission electron micrograph of Ebola virus, the cause of Ebola hemorrhagic fever. The disease infects people and nonhuman primates and is frequently fatal. The first outbreak of Ebola fever occurred in 1976. Credit: CDC

Ebola virus (EboV) is the cause of sporadic outbreaks of highly fatal infections in Africa that are unpredictable in onset and rapid in progression. There is no effective vaccine or therapy for EboV infection. To address this problem, researchers at Brigham and Women's Hospital (BWH) used a robotic method developed by their colleagues at the National Small Molecule Screening Laboratory at Harvard Medical School to screen tens of thousands of compounds and identified a novel small molecule derived from benzylpiperazine adamantyl diamide that inhibits EboV entry into cells by more than 99 percent. Further studies at the United States Army Research Institute for Infectious Disease at Fort Detrick, MD verified that the newly identified entry inhibitor blocked cell-cell transmission of the virus. They used the inhibitor as a probe to investigate the EboV infection pathway and found that the target of the inhibitor is the cell protein Niemann-Pick C1 (NPC1). This research is published in the August 25, 2011 issue of Nature.

"In 2005, we showed that digestion of the glycoprotein on the surface of EboV particles by the host cell protease cathepsin B is a critical step in infection, but we knew that there was something else at play. Identifying the EboV inhibitor led us to the discovery that NPC1 is the conduit through which the virus is able to breakthrough cell membranes and infect host cells," said James Cunningham, MD, senior author of the paper and researcher in the Division of Hematology at BWH.

Combined with the results of previous studies of the virus glycoprotein structure and function, these findings indicate that EboV infection proceeds by sequential steps in which cathepsin B removes the protective top of the EboV glycoprotein and exposes the critical region that binds to NPC1 and triggers entry of EboV particles into cells.

"Our findings show that EboV infection has features in common with other pathogenic viruses including HIV and SARS that also utilize two host proteins to breakthrough cell membranes and infect host cells," said Cunningham. "It is interesting that NPC1 is critical for the uptake of cholesterol into cells, which is an indication of how the virus exploits normal cell processes to grow and spread. Small molecules that target NPC1 and inhibit EboV infection have the potential to be developed into anti-viral drugs."

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Brigham and Women's Hospital: http://www.brighamandwomens.org