Researchers in Sierra Leone today started a new phase II trial of an experimental drug in Ebola patients. The first participant received an injection of the therapeutic, called TKM-Ebola, this morning at an Ebola treatment unit in Port Loko*. The trial may expand to other sites; the study team hopes to have an answer fast so that it can either move on to another drug or start a phase III study of TKM-Ebola.

Produced by Tekmira Pharmaceuticals in Burnaby, Canada, TKM-Ebola is made of synthetic, small interfering RNAs packaged into lipid nanoparticles. The RNAs target three of Ebola’s seven genes, blocking the virus’s replication. TKM-Ebola has been shown to work well in monkeys; the efficacy trial in humans is only starting now because there was not enough of the drug available earlier. Also, the RNAs have been adapted to the strain circulating at the moment.

The study does not have a placebo arm; all patients at the trial site are eligible for the drug, and researchers hope to determine whether it works by comparing them with patients treated elsewhere.

However, not every Ebola patient at the unit may actually get the drug because of practical reasons. The treatment is given as a 2-hour infusion every day for a week; patients need to be watched for 8 hours after the infusion because of worries that the drug could produce a dangerous inflammatory response known as a cytokine storm. Doctors and nurses can only spend so much time in their protective equipment in the tropical heat, which means they may not be able to serve everyone. "Staff have a very narrow window, and if there are several patients that are eligible in the morning, we have to choose one randomly,” says Trudie Lang, a global health researcher at the University of Oxford in the United Kingdom and one of the study's leaders. Patients at the trial site who don't receive the drug could also be used as controls in the study.

The trial aims to enroll up to 100 patients, but Lang says that it may arrive at an answer much earlier. "We are looking for a big effect, and if there is a big yes or a big no, we hope to see that sooner.” If there is a clear signal that the drug does nothing, the team wants to try to test another experimental drug before Sierra Leone brings down the number of cases to zero. Neighboring Liberia has not seen new cases in more than 2 weeks; although Sierra Leone's epidemic has slowed considerably, there are still about 10 new cases every day.

If TKM-Ebola does seem to work, the team wants to go straight to a bigger phase III clinical trial. It’s "essential that we push forward with clinical trials while we still have a realistic chance of getting answers about which, if any, of the candidate treatments can save lives in this, and in future outbreaks,” said principal investigator Peter Horby in a statement released today by the Wellcome Trust, a charity that is funding the trial.

In Liberia, Horby’s group had previously tested brincidofovir, a drug developed for cytomegalovirus and adenovirus that also showed anti-Ebola activity in the lab. That trial had to be stopped last month when Chimerix, the company producing the drug, withdrew their support. There were too few Ebola cases in Liberia, and the scientists weren't able to expand the trial to Sierra Leone, Lang says. Only a handful of patients were treated; those data will be released in the coming months. "It will be important when we can step back from the business of running this trial to explore what went wrong and what went well in setting up trials during this epidemic,“ she says.

So far, no drug has been proven to be effective against Ebola. A study of the Japanese influenza drug favipiravir is going on in Guinea, and scientists have reported a first weak signal that it may be helping some patients. A trial to use serum from recovered Ebola patients as a therapy for others is ongoing in Guinea, and the U.S. National Institutes of Health has said it is planning a trial of an antibody cocktail called ZMapp.

*Update: This story originally said the trial had started in an Ebola treatment unit in Kerry Town, as its file in the Pan African Clinical Trials Registry indicated. It actually started in Port Loko and may be expanded later to Kerry Town.

*The Ebola Files: Science and Science Translational Medicine have made a collection of research and news articles on the Ebola virus and the current outbreak freely available to researchers and the general public.