In today's online issue of the journal Public Library of Science Pathogens, a research team led by Sina Bavari and colleagues at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) reports using novel "antisense" drugs to interrupt normal Ebola virus replication. The work was performed in collaboration with AVI BioPharma, a U.S. biotechnology firm.
According to the study's authors, antisense drugs are useful against viral diseases because they are designed to enter cells and eliminate viruses by preventing their replication. The drugs, which act by blocking critical viral genetic sequences, may be more potent than anti-virals such as protease inhibitors, which seek to inhibit a protein needed for viral replication.
Ebola virus causes hemorrhagic fever with case fatality rates as high as 80 percent in humans. The virus, which is infectious by aerosol (although more commonly spread through blood and bodily fluids of infected patients), is of concern both as a global health threat and a potential agent of biological warfare or terrorism. Currently there are no available vaccines or therapies.
"One advantage of this strategy is that it directly targets the virus," said the paper's first author, Kelly L. Warfield. "With Ebola infection, the virus grows so fast that it overtakes the host immune system. What we did, essentially, was to hold off the viral replication long enough for the host to mount an immune response and clear the virus."
Working with a class of compounds known as antisense phosphorodiamidate morpholino oligomers, or PMOs, the team first performed a series of studies to identify PMOs that demonstrated activity against Ebola virus. Next, three of the PMOs were tested in mice, both individually and in combination. The combination of all three was found to be the most effective therapeutic approach in mice, whether the PMOs were administered before or after Ebola infection. Combination therapy was also tested in guinea pigs, where it appeared to be most effective when administered after infection.
To further evaluate the efficacy of the three-PMO combination, four rhesus monkeys were treated with the drug two days prior to Ebola virus exposure. Three of the four were protected from Ebola infection.
"These results, while preliminary, are very encouraging," said Colonel George W. Korch, USAMRIID commander, "especially when you consider that Ebola virus has, to date, been fairly intractable to effective treatment. We look forward to additional findings of success using these PMOs."