A single-dose treatment against malaria worked in mice to cure them of the disease. The drug also worked to block infection in healthy mice and to stop transmission, according to a study published in Nature today. The fact that the drug can act against so many stages of malaria is pretty new, but what's even more exciting is the compound's mode of action: it kills malaria in a completely new way, researchers say. The feature would make it a welcome addition to our roster of antimalarials — a roster that's threatened by drug resistance.
Researchers sifted through a library of about 4,700 compounds to find this one
Malaria is an infectious disease that's transmitted through mosquito bites; it's also a leading cause of death in a number of developing countries. Approximately 3.4 billion people live in areas where malaria poses a real threat. As a result, there were 207 million cases of malaria in 2012 — and 627,000 deaths. There are drugs that can be used to prevent malaria, and even treat it, but drug resistance is halting the use of certain treatments in some areas.
A long search
Searching for a new drug is all about trial and error. To find this particular compound, researchers sifted through a library of about 4,700 compounds, testing them to see if they were capable of killing the malaria parasite in a lab setting. When they found something that worked, they tweaked the drug candidate to see if it could perform more effectively. "We went through a lot of these cycles of testing and designing new compounds," says Ian Gilbert, a medicinal chemist at the University of Dundee in the UK, and a co-author of the study. "Eventually we optimized to the compound which is the subject of the paper." For now, that compound's unwieldy name is DDD107498.
To make sure DDD107498 really had potential, the researchers tested it on mice that had already been infected with malaria. A single dose was enough to provoke a 90 percent reduction in the number of parasites in their blood. The scientists also gave the compound to healthy mice that were subsequently exposed to malaria. DDD107498 helped the mice evade infection with a single dose, but it's unclear how long that effect would last in humans. Finally, the researchers looked at whether the compound could prevent the transmission from an infected mouse to a mosquito. A day after receiving the treatment, mice were put in contact with mosquitoes. The scientists noted a 91 percent reduction in infected mosquitoes.
"It has the ability to be a one-dose [drug], in combination with another molecule."
"What's exciting about this molecule is obviously the fact that it has the ability to be a one-dose [drug], in combination with another molecule to cure blood stage malaria," says Kevin Read, a drug researcher also at the University of Dundee and a co-author of the study. The fact that the compound has the ability to block transmission and protect against infection is equally thrilling. But the way in which DDD107498 kills malaria might be its most interesting feature. It halts the production of proteins — which are necessary for the parasite's survival. No other malaria drug does that right now, Read says. "So, in principle, there's no resistance out there already to this mechanism."
The drug hasn't been tested in humans yet, so it may not be nearly as good in the field. But Read says DDD107498 looks promising. "From all the pre-clinical or non-clinical data we've generated, it is comparable or better than any of the current marketed anti-malarials in those studies." And at $1 per treatment, the price of the drug should fall "within the range of what's acceptable," he says.
"It looks like an excellent study, and the results look very important," says Philip Rosenthal, a malaria drug researcher at The University of California-San Francisco who didn't participate in the study. This is a big shift for Rosenthal's field. Five years ago, "we had very little going on in anti-malarial drug discovery," he says. Now, there's quite a bit going on for malaria researchers, and a number of promising compounds are moving along. DDD107498 "is another player, and it's got a number of positive features," he says.
Other treatments have to be taken for a few days
One of the features is the drug's potency. It's very active against cultured malaria parasites, Rosenthal says. But what's perhaps most intriguing about DDD107498 is that the drug works against the mechanism that enables protein synthesis the malaria parasite's cells. No other malaria drug does that right now, Read says. "Considering challenges of treating malaria, which is often in rural areas and developing countries, a single dose would be a big plus," he says. "In addition, because of it's long half life, it may also work to prevent malaria with once a week dosing, which is also a benefit."
Still, no drug is perfect. The data suggests that DDD107498 doesn't kill malaria as quickly as some other drugs, Rosenthal says. And when the researchers tested it to see how long it might take for resistance to develop, the results weren't as promising as he would like. The parasites figured out a way to become resistant to the compound "relatively easily," he says. That shouldn't be "deal-killer," however. "Its slow onset of action probably means it should be combined with a faster-acting drug," he says.
But it's slow-acting
The compound is going through safety testing now. If everything goes well, it should hit human trials within the next year, Read says. Chances are, it will have to be used in combination with other malaria drugs, Gilbert says. "All anti-malarials are given in combination because it slows down resistance."
"When you're treating infectious diseases, you know that drug resistance is always a potential problem, so having a number of choices to treat malaria is a good thing," Rosenthal says. In this case, the drug's new mode of action may hold lead to an entirely new weapon against malaria. "Obviously it's got a long way to go," Read says. But the compound is "very exciting," nonetheless.