Friday February 22 2013
Strains of flu can develop resistance to antiviral drugs
‘Flu drug shows promise in overcoming resistance’, reports BBC news, saying that scientists have found a way to permanently block the flu virus from spreading to other cells.
This was early stage laboratory and animal research examining the effectiveness of a possible new antiviral treatment for flu. Currently there are two anti-flu drugs available on the market in the UK, oseltamivir (brand name Tamiflu) and zanamivir, (brand name Relenza). Both of these drugs work by blocking a viral enzyme which helps the flu virus to infect new cells.
The problem is that widespread use of these drugs is allowing flu viruses to develop resistance to them. New drugs are always going to be needed to fight such infections, just as new vaccines are regularly needed.
The new drug works in a similar way to the existing drugs: slowing down the process by which flu viruses spread to new cells. In the laboratory, researchers found that the new chemical was similarly or more effective than Relenza at stopping the flu virus from spreading between cells. Importantly, it also worked against flu strains that are resistant to the current flu drugs.
This current research into a new antiviral drug is in its very early stages. Even if further tests in animals and then humans go well, it may be several years before it is available.
Where did the story come from?
The study was carried out by researchers from University of British Columbia and other institutions in Canada, the UK and Australia. Funding was provided by the Canadian Institutes for Health Research, the Pfizer CDRD Innovation Fund, the Canadian Foundation for Innovation, and the BC Knowledge Development fund.
The study was published in the peer-reviewed scientific journal, Science Express.
BBC News and the Metro covered the study well, but the Daily Express’s claim that this could lead to a super-vaccine that could ‘wipe out flu for good’ is irresponsible. This style of casually worded, overhyped coverage can lead to popular misunderstandings about science and medicine.
What kind of research was this?
This was laboratory research into a possible new type of flu drug with a slightly different method of action from the two flu drugs currently available. Researchers tested the effectiveness of this new chemical in both animal models and cells in the laboratory.
The two anti-flu (antiviral) drugs currently used in the UK – oseltamivir (Tamiflu) and zanamivir (Relenza) – both work by blocking a viral enzyme (neuraminidase) which is involved in helping the virus to infect other cells.
The drugs can be given up to two days after a person has been exposed to flu (people who have been in close contact with someone with influenza, or have just started to have flu symptoms). They would normally only be given to someone who was considered to be at higher risk of having complications from flu, such as those with a weakened immune system.
As these two flu drugs become more widely used, flu viruses will inevitably develop resistance to them, so there is a need for new flu drugs that act in different ways in the future.
The current research into the development of a possible new antiviral drug is in its very early stages.
What did the research involve?
The researchers describe the process by which the influenza virus infects cells as being akin to ‘biological lock picking’. First, a protein on the surface of the virus attaches it to uninfected cells. This protein helps the virus ‘unlock’ the cell by interacting with specific chemicals (sialic acids) on the cell surface. Once inside the cell, the virus replicates and exudes the enzyme neuraminidase to breaks apart the sialic acids. This allows the copied viruses to spread onto other non-infected cells.
Oseltamivir and zanamivir act by interacting with and blocking the action of the enzyme neuraminidase, preventing the replicated viruses escaping from cells to infect other cells.
The new chemicals (based on sialic acids) act on the same process as Tamiflu and Relenza, but they form a stronger type of bond with the neuraminidase than Tamiflu and Relenza. By doing this, the chemicals block an intermediate step in the process where neuraminidase breaks apart the sialic acids.
The researchers think that flu viruses will be less likely to develop resistance to these newer chemicals, because they are more similar to the sialic acids the flu viruses need to bind to to infect cells.
The researchers examined the effectiveness of these chemicals compared to Relenza in the laboratory, using cells taken from a dog’s kidney, and in live mice. They also looked at how effective it was against viral strains which have previously demonstrated resistance to Tamiflu and Relenza.
What were the basic results?
The researchers tested different forms of the new chemicals in the laboratory, and found that one of them was similarly effective to the drugs Relenza and Tamiflu at reducing the activity of the flu virus neuraminidase in non-resistant strains.
This chemical was also effective against flu virus strains that have demonstrated resistance to both the current flu drugs. It also performed similarly to or better than Relenza at stopping the flu virus from spreading between cells in the laboratory, depending on the type of flu virus used.
When the chemical was given to mice that had been infected with lethal amounts of flu virus, the new chemical prolonged survival of the mice, to a similar extent to Relenza. The mice did not show any adverse effects of the drugs.
How did the researchers interpret the results?
The researchers conclude that the similar method of action of the new chemical to the current flu drugs, but its altered resistance profile, makes it an ‘attractive candidate’ as an anti-flu drug.
There are currently only two flu drugs authorised for use in the UK. As they become more widely used, flu viruses will inevitably develop resistance to them. This is particularly likely to be a problem for the more widely used Tamiflu.
Research exploring new flu drugs that act in different ways could be very useful as flu can be a deadly disease, particularly in vulnerable population groups.
This new research demonstrates that a new chemical has the potential to be developed into a flu drug as it was found to be similarly or more effective than Relenza at stopping the spread of the flu virus in the laboratory, including flu strains that have been resistant to the current flu drugs. The chemical was also similarly effective to Relenza at prolonging survival in mice infected with a lethal dose of flu.
However, it is important to be aware that the current research into the development of a new anti-flu drug is in its very early stages. If more animal research confirms these findings, safety and effectiveness testing would be needed in humans before it is better known whether this new chemical could one day have the potential to be authorised as an anti-flu drug for use in the UK.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.