Image courtesy Frederick A. Murphy, CDC
Published August 22, 2011
There's no cure for the common cold—yet.
A new drug can scout out and kill numerous types of viruses infecting human and animal cells, researchers have announced. It's the first time a single drug has been shown to work against a range of viruses, from those that cause seasonal sniffles to more fatal diseases.
"Several decades ago the discovery and production of antibiotics revolutionized the way bacterial infections were treated," said study co-author Todd Rider, a senior staff scientist at the Massachusetts Institute of Technology's Lincoln Laboratory and Division of Comparative Medicine.
"We hope that this will similarly revolutionize the way viral infections are treated. That covers everything from cold and flu viruses to more serious clinical pathogens like HIV and hepatitis viruses and ultimately even more deadly viruses like Ebola and smallpox."
(Watch video: "How Flu Viruses Attack.")
Alien-Like Viruses Tough to Beat
Though there are plenty of drugs to treat bacterial infections, there are few that can battle viruses. The antiviral drugs that have been developed are highly specific, with each drug targeting just one strain of a virus, which can easily mutate and become resistant to the medication.
So Rider and colleagues took a different approach—tailoring their new drug to work with the body's built-in defense mechanism.
Viruses operate "sort of like the aliens in the Alien movies," Rider said. "They'll enter a cell, replicate inside the cell, and ultimately burst out of the cell," killing it.
While taking over cells, viruses produce what's called long double-stranded RNA, a complex acid that controls the virus's chemical activities and is not produced in healthy human cells, according to the study, published July 27 in the journal PLoS ONE.
Human bodies do have natural defenses against viruses: They produce proteins that latch onto double-stranded RNA and prevent the virus from replicating itself. But many viruses have evolved ways to shut down these proteins.
New Drug Packs Double Whammy
Rider and his team developed a drug that combines the natural-defense protein with another protein that triggers a cell's suicide switch. All human cells have these suicide switches, which are usually activated when cells start to become cancerous, Rider said.
The result is like the mythological centaur, said Marie Pizzorno, a molecular virologist at Pennsylvania's Bucknell University.
"The horse is one piece of a protein that normally we make and that can recognize the [long double-stranded RNA] made by the virus, and the man is something that triggers the cell-death pathway," she said.
The new drug, called DRACO, works by searching for cells in the body that contain long double-stranded RNA—a surefire sign of a virus. If the drug finds a viral infection, it tells the cell to self-destruct.
Since our body doesn't use these proteins together naturally, combining them in drug form may outsmart even the most adaptable of viruses, added Pizzorno, who was not involved in the new study.
"Viruses have figured out how to handle our normal defenses, [but] by activating these two pathways with one protein, they've hopefully prevented the viruses from getting around it."
If the drug does not find double-stranded RNA in the body, it eventually flushes out with no side effects, study leader Rider added. (See a human-body interactive.)
Common-Cold Drug Still a Decade Away
So far, the drug has proven to be effective and nontoxic in killing 15 types of virus—including the ones that cause dengue hemorrhagic fever and H1N1 influenza, or swine flu—in 11 types of mammalian cells, including human.
The drug also cured 100 percent of mice injected with a lethal dose of H1N1, and there are ongoing trials in mice with other viruses.
The next step will be to see if the drug can kill viruses in bigger animals, such as rabbits, guinea pigs, and ultimately monkeys, Rider said.
Then, if the drug is still safe and effective, the U.S. Food and Drug Administration may approve human clinical trials, Rider said. Still, it will be "at least a decade before you can buy this at the drugstore."
Even with all these steps yet to go, the new drug has promise, Bucknell's Pizzorno added.
"It's a really innovative way to consider doing an antiviral," she said. "I don't think anyone has ever thought of this before."
I can see a way this could go wrong in the trials. There's perhaps a reason cells don't suicide as soon as they're infected - quite possibly the internal battle is won by the cell and its antiviral proteins some percentage of the time. This drug, by killing all infected cells, could have some serious side effects.
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