By Alice Park
April 22, 2015

When the Ebola outbreak hit last spring, there were a handful of potential treatments at the experimental stage in labs around the world. Some of them—like the drug TKM Ebola—that had shown promise in primates were given to U.S. and European health care workers who had been infected. Assessing how effective these drugs were in humans, however, posed some unique challenges.

That’s because many of the patients who got experimental treatments were also given a number of other therapies—making it impossible to know what was responsible for their recovery. But in a new paper published Wednesday, several of the scientists responsible for developing TKM Ebola, led by Thomas Geisbert of the University of Texas Medical Branch, report that the drug worked on all the monkeys it used it on, even after the monkeys were given a lethal dose of Ebola.

The animals exposed to Ebola that didn’t get the drugs all died at day eight or nine.

The study used an updated version of the drug that is made up of snippets of the Ebola virus’ genome encapsulated in fatty particles. The fragments bind to their matching counterparts on the circulating virus and become a genetic monkey wrench that prevents Ebola from copying itself and infecting more cells.

MORE: WHO Outlines Timeline for Experimental Ebola Drugs

It turns out that the virus responsible for the current outbreak in west Africa differs from the 1976 strain at three points in the Ebola genome, so Geisbert and his team adjusted the drug accordingly. That’s one of advantages of the TKM Ebola approach, he says, compared to therapies such as vaccines or other drugs that rely on antibodies to the virus. These regimens are designed to attack the broadest range of virus strains possible, but in doing so, they may give up some of their virus-fighting potency. With gene sequencing technology becoming more refined and accessible, however, having drugs that are specifically targeted against a particular strain of a virus is actually a realistic goal. “It’s especially important when you look at how big this outbreak is, and it’s continuing for over a year,” says Geisbert of such matched therapies. “With this technology, we could theoretically turn around a new treatment in something like weeks. This outbreak taught us a lot about how to prepare for the future.”

MORE: The Ebola Fighters

These results will still have to be repeated in human patients, to ensure TKM Ebola is both safe and effective, but they strongly hint that the drug could be a critical part of future anti-Ebola strategies. The company that is developing TKM, Tekmira Pharmaceuticals, is now testing this latest form of the drug in Ebola patients in Sierra Leone, west Africa.

Contact us at editors@time.com.

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