Choosing the right target
Antiviral drugs that target certain kinds of viral proteins can suppress the emergence of antiviral resistance.
Treating a viral infection with a drug sometimes has an unwanted side effect — the virus quickly becomes resistant to the drug. Viruses whose genetic information is encoded in molecules of RNA mutate faster than DNA viruses and are particularly good at developing resistance to drugs. This is because the process of copying the RNA is prone to errors, and by chance some of these errors, or mutations, may allow the virus to resist the drug’s effects.
Treating viral infections with most drugs destroys the viruses that are susceptible to the drug and inadvertently ‘selects’ for viruses that are resistant to the drug’s effects. These drug-resistant viruses are harder to treat and often require physicians to switch between different drugs. Sometimes these new drug-resistant viruses spread and these new infections cannot be treated with drugs that would have worked in the past. So far, the best strategy to prevent drug-resistant viruses from growing in patients is to use multiple drugs, such as the life-saving treatments for HIV infection. However, for many viral infections — such as those that cause the common cold, dengue fever, Ebola, and polio — no drugs are yet available to treat infected people. Moreover, there are concerns that, if a new drug is used on its own, the viruses will quickly develop resistance to the drug and render it ineffective.
Elizabeth Tanner and co-workers now show that an antiviral drug that interferes with the formation of the outer layer (or capsid) of the poliovirus inhibits the emergence of drug resistance. The drug, called V-073, is currently being tested as a treatment for poliovirus and will be useful in the worldwide eradication effort. Tanner and co-workers show that treating poliovirus-infected mice with V-073 does not select for drug-resistant strains of the virus — and provide evidence that this occurs because the drug targets an assemblage of proteins.
The poliovirus capsid is assembled from a mix of proteins from different naturally occurring strains of the virus within the infected cell. A new strain of virus is always ‘born’ into a cell that is already infected by other viruses, which could be thought of as its parents, cousins and siblings. A new drug-resistant virus will therefore be forced to mix its capsid proteins with those of its ‘family’ members, who are all drug-sensitive. These hybrid capsids will remain vulnerable to the drug — and in this way, the resistant strains do not become the dominant form of the virus.
Tanner and co-workers also discovered a way to screen for drugs that have a similar resistance-blocking effect. These drugs would target capsids, or other viral structures made up of a mix of proteins from different virus strains. Such drugs might be useful against other viruses including the ones that cause the common cold, hepatitis C, or dengue fever.
To find out more
Listen to Elizabeth Tanner talk about drugs that tackle viral infections in episode 16 of the eLife podcast.
Read the eLife research paper on which this eLife digest is based: “Dominant drug targets suppress the emergence of antiviral resistance” (November 3, 2014)
