THE first drug to combat the Sars virus could be available for treating patients within months, after new research in the United States.
Early trials at the US National Institutes of Health suggest that the antiviral therapy, developed by AVI BioPharma in Oregon, is highly effective at killing the coronavirus that is thought to cause Sars.
If the full results, which are expected in two weeks, confirm the findings, the drug could be given to patients within “months rather than years”, Denis Burger, AVI’s chief executive, told The Times yesterday.
The drug, which has been designed using the coronavirus’s genetic sequence, is particularly promising because similar chemicals are already effective against viruses in the same family as Sars. More than 250 patients have also been treated with similar drugs in trials over the past three years, without side effects. This safety record, and the urgency of the Sars outbreak, means that regulatory approval should be swift, according to Dr Burger. “If we continue to see this sort of efficacy, we would have to start considering the risk-benefit ratio for seriously ill patients,” he said.
“Because of the concern about Sars, and because of the safety record of these chemicals, it is going to get a lot of quick attention. I would think it would take months, and not very many months at that.”
The drug uses a new technique known as antisense therapy, which is designed to attack RNA viruses such as hepatitis, West Nile virus, Norwalk virus and coronaviruses, the group to which Sars is thought to belong. These viruses consist of single strands of RNA, the messenger chemical normally used by genes to produce proteins. Antisense drugs are small segments of RNA designed in mirror image of the RNA virus they seek to attack. They bind to crucial sections of the virus, preventing it from replicating in human cells.
“A good analogy is a zipper,” Dr Burger said. “The RNA virus is like one half of the zipper, and if you can create another half that fits together with it perfectly, you can neutralise it.”
Last year, AVI created an antisense therapy in just two weeks that protected penguins at Milwaukee Zoo against an outbreak of the West Nile virus, and it has been testing antisense therapies for cancer and cardiovascular disease for three years. It took the company just ten days to develop an antisense drug for the Sars coronavirus, after its genetic code was sequenced by the Michael Smith Genome Science Centre in Vancouver, Canada. “Once you have the sequence, it takes just somewhere between one to two weeks to make the drug,” Dr Burger said. “It’s a polymer that’s like a mirror image of the genome sequence.
“The reason we believe it’s really possible to be effective is that we’ve already developed agents against other viruses in the same group.”
Genetic tests have already shown that the Sars drug will not interfere with any critical RNA processes in human cells, but that it targets crucial sections of the coronavirus.
“This should also mean that mutation isn’t a big problem,” Dr Burger said. “The agent attacks a critical part of the virus, and if this section mutates, the changes would make it into an ineffective virus.”
One potential pitfall could be doubt over whether the coronavirus alone is enough to cause Sars. Frank Plummer, of the Canadian National Microbiology Laboratory, identified the virus in only 40 per cent of Sars patients, and said this week that the association between the two was “weak”.
“We don’t understand this disease well enough yet,” Dr Burger said. “It is possible that this therapy won’t stop replication effectively enough. But this is the most promising candidate for addressing this disease yet, because it’s a drug that’s largely proven in other contexts.”
It is also possible that drug regulators would be reluctant to sanction the therapy without full clinical trials, which could take years. The lack of a cure for Sars, however, means that it is more likely that an experimental treatment might be approved for use in emergencies with seriously ill patients.
