The drug can identify cells that have been infected by any type of virus, then kill those cells to terminate the infection. It's been tested against 15 viruses, and found to be effective against all of them — including the rhinoviruses that cause the common cold, H1N1 influenza, a stomach virus, a polio virus, dengue fever and several other types of hemorrhagic fever.
The drug works by targeting a type of RNA produced only in cells that have been infected by viruses.
"In theory, it should work against all viruses," says senior staff scientist Todd Rider. Because of this, it could potentially be used to combat outbreaks of new viruses, such as the 2003 SARS epidemic, he says.
Rider's therapeutic agents, dubbed DRACOs (Double-stranded RNA Activated Caspase Oligomerizers) are inspired by living cells’ own defense systems.
When viruses infect a cell, they take over its cellular machinery in order to create more copies of the virus. During this process, they create long strings of double-stranded RNA (dsRNA), which isn't found in human or other animal cells.
As part of their natural defenses, human cells have proteins that latch onto dsRNA, setting off a cascade of reactions that prevents the virus from replicating. However, many viruses can outsmart that system by blocking one of the steps further down the cascade.
But Rider's combined a dsRNA-binding protein with another protein that induces cells to undergo apoptosis - programmed cell suicide — in the same way as when a cell determines it's becoming cancerous. Therefore, when one end of the DRACO binds to dsRNA, it signals the other end of the DRACO to initiate cell suicide.
Combining those two elements is a great idea, says Karla Kirkegaard, professor of microbiology and immunology at Stanford University.
"Viruses are pretty good at developing resistance to things we try against them, but in this case, it’s hard to think of a simple pathway to drug resistance," she says.
Each DRACO also includes a 'delivery tag', taken from naturally occurring proteins, that allows it to cross cell membranes and enter any human or animal cell. However, if no dsRNA is present, DRACO leaves the cell unharmed.
Most of the tests reported in this study were carried out on human and animal cells cultured in the lab, but the researchers also tested DRACO in mice infected with the H1N1 influenza virus - and found they were completely cured.
They're now testing DRACO against more viruses in mice and beginning to get promising results. Rider says he hopes to license the technology for trials in larger animals and for eventual human clinical trials.