This Is What’s Up:
Simple viral inhibitors have long been the best hope for treating the Flu, but recent research has brought to light that there could be other methods.
There are many steps in the virus life cycle that you can target a drug at: attachment, entry, protein production, genome replication, and exit from the cell. Oseltamivir is a fairly well known antiretroviral drug used to combat the flu. This drug targets and inhibits the viral neuraminidase, which is a protein on the surface of the virus particle that is necessary for assembled viral particles to leave host cells. In other words, without this protein functioning, the virus is trapped inside the cells it’s in, and your immune system can quickly hunt it down and take it out.
While neuraminidase inhibition has worked well in the past, there are some disadvantages to using antiviral drugs such as these. Viruses replicate themselves thousands, if not millions of times a day, and they are pretty sloppy about it. This large number of “offspring” and high mutation rate creates a large pool of genetic variation for natural selection to act on, and thus allows viruses to evolve much faster than most organisms. As a result, viruses such as the flu can develop resistance to medications in relatively short amounts of time. In this case, certain flu strains have gained resistance to drugs such as oseltamivir. There are other antiviral drugs that target different steps in the virus life cycle, but it is only a matter of time before another strain develops resistance to them too.
This is a real public heath issue!
For this reason, many labs have been looking into more effective methods of inhibiting viral replication. Based on previous research, Aoki et al. began looking into methods of inhibiting the neuraminidase receptor on the flu virus that the virus could not evolve an immunity to.
So What’s New?
Previous research by Suzuki et al. suggested that a molecule called anthraquinone has the ability to degrade proteins in the presence of long wavelength ultra violet light. With this in mind, Aoki et al. made an anthraquinone-sialic acid hybrid protein. Sialic acid is a receptor that neuraminidase binds to. Whether or not a flu virus has gained drug resistance, it still must bind to sialic acid to perform its functions in the cell. In this hybrid protein, the sialic acid section targets the anthraquinone to the virus, where it can then be activated with UV light to degrade the neuraminidase it is attached to.
After performing several SDS-Page experiments (these look for the presence/absence of a protein), the authors found that in a test tube, when neuraminidase is mixed with the anthraquinone-sialic acid hybrid protein and then irradiated with UV light, there are significantly diminished amounts of neuraminidase. They also made sure that there was no neuraminidase degradation by either the hybrid or the light alone–it had to be the combination that was causing the effect seen.
How Does It Work?
Aoki et al performed several tests to try to determine just what was going on to degrade the protein. First, they used electron paramagnetic resonance (EPR) to study if any free radicals were being created. The principle that this machine works on is similar to that of an MRI machine, but instead of using it to look at tissue in a human body, it is used to examine the presence of free radicals in small samples. This experiment showed that hydroxyl radicals were being created when the hybrid and the UV light were both present. Hydroxyl radicals are very reactive molecules and help explain the protein degradation that was observed.
The authors wanted to compare the ability of this new hybrid protein to inhibit neuraminidase in comparison to the standard drug (oseltamivir). To do this they performed several “enzyme inhibition assays”. They concluded that while their hybrids did not inhibit neuraminidase as much under standard conditions, it worked better against both normal, and drug-resistant neuraminidase when UV light was added.
What’s It All Mean?
This research by no means provides a solution to drug resistant influenza, but it is an important step forward. Since this method targets a basic function of the virus, technology such as this could be used in further studies to help make drugs that could fight any strain of flu virus! This method of targeting compounds that can degrade proteins could potentially be used to fight many different kinds of drug-resistant viruses.
While this research is promising for the future, it is still in a rather preliminary stage. This experiment was done all in test tubes. It would be nice to see some animal testing in the future. Although this will also face another challenge. How will you irradiate these molecules with UV light once they are in an animal? After all, UV light can only penetrate so far. Since the free radicals that are created are also very toxic to normal animal proteins, future tests will need to examine how localized the protein degradation is.
It seems to me that while this article applies this technology to fighting viruses, it could also be used to fight skin cancer. This could be accomplished by creating hybrid proteins containing anthraquinone and a molecule that binds specifically to receptors on the cancer that are necessary for cell growth. But whatever the use, this technology is part of a growing field in which hybrid toxins can be targeted directly to cells or proteins to be destroyed. And I’m sure that there will be much more emerging in the near future in the way of improvements for these processes and the range of problems they can be used to fix.
Primary Article: Yusuke Aoki, Shuho Tanimoto, Daisuke Takahashi, and Kazunobu Toshima. “Photodegradation and inhibition of drug-resistant influenza virus neuraminidase using anthraquinone–sialic acid hybrids” Chem. Commun. 49.12(2013): 1169-1171. http://pubs.rsc.org/en/content/articlepdf/2013/cc/c2cc38742e.
Supporting: Akane Suzuki, Masashi Hasegawa, Maiko Ishii, Shuichi Matsumura, Kazunobu Toshima. “Anthraquinone derivatives as a new family of protein photocleavers” Bioorganic & Medicinal Chemistry Letters. 15.20(2005): 4624–4627. http://www.sciencedirect.com/science/article/pii/S0960894X05009388.