Screen Uncovers Malaria Drug

The antihistamine astemizole could prove a promising antimalarial agent, according to a new study.

Finding new antimalarials among existing drugs could accelerate the process of developing new treatments for the disease. David J. Sullivan Jr. and coworkers at Johns Hopkins University screened a library of nearly 2,700 existing drugs to find compounds that inhibit the malaria parasite, Plasmodium falciparum.

"If we found something that has activity, we could more easily go into testing directly in humans because the drug has already passed lots of tests for toxicity," Sullivan says. "In this case, it's been used in tens of millions of people."

After eliminating topical drugs, known antimalarials, drugs that are toxic to cells, and compounds previously reported to inhibit the malaria parasite, the researchers found 87 potential new antimalarial agents, the most promising of which is astemizole (Nat. Chem. Bio., published online July 2, dx.doi.org/10.1038/nchembio806).

Astemizole inhibits the growth of three P. falciparum strains that have varying sensitivity to the antimalarial chloroquine. The principal human metabolite of astemizole, desmethylastemizole, lasts in the bloodstream for several days and is even more potent against the malaria parasite than astemizole itself.

Astemizole does have some "blemishes" as a drug, Sullivan says, such as interactions with other drugs, including other antimalarials, and rare cases of heart arrhythmia. Although no longer used in the U.S. or Europe, it continues to be used in generic form in more than 30 other countries.

"It would be a tragedy if a safe drug with antimalarial properties were available but not developed to determine potential use in humans," says Graham V. Brown, a malaria expert at the University of Melbourne, in Australia. "Let's hope that funds can be found to make rapid use of this preliminary data to take the project further."