Two drugs already on the market for other purposes can halt Ebola virus in mice. The findings open the way for further testing of the drugs, clomiphene and toremifene, against the deadly virus.
Scientists screened more than 2,000 drugs against Ebola, a process that required the highest level of safety precautions because the virus is so lethal. Several drugs called selective estrogen receptor modulators showed promise, including clomiphene, marketed as Clomid and prescribed to treat infertility, and toremifene, used to treat advanced breast cancer.
In the June 19 Science Translational Medicine, researchers report that each drug prevented Ebola virus from commandeering cells in lab-dish experiments. The researchers also injected mice with one form of the Ebola virus, and nine of 10 mice given clomiphene one hour after exposure survived a month-long observation period. Five of 10 mice getting toremifene died within 10 days, but the other five survived the month. All mice given the virus without the drugs died within a week.
The drugs bottled up Ebola in a cell compartment called an endosome, which the virus uses as a way station when it invades a cell. How the drugs thwart the virus there is unclear, says study coauthor Gene Olinger, a virologist at the U.S. Army Medical Research Institute of Infectious Diseases in Frederick, Md. But the results suggest that the drugs might stop other versions of the Ebola virus and the related Marburg virus, another deadly pathogen. In theory, the drugs would be given to patients and health care workers in an outbreak, he says.
“This is an interesting study, and it’s the way one wants to go with these viruses,” says Stephan Becker, a virologist at Philipps University in Marburg, Germany. Ebola burst on the scene in 1976 with deadly outbreaks in Zaire and Sudan. But it has been a sporadic menace, racking up about 2,300 victims worldwide. Despite a stunning mortality rate, Becker says, the small numbers suggest that the best strategy against Ebola is to repurpose drugs already cleared for other uses.
While testing an established drug for a new use is faster than starting from scratch, Olinger says, approval of these drugs for Ebola might still take five to 10 years. There is currently no cure for an Ebola infection.