October 22, 2015

expert reaction to study investigating anti-viral properties of substance engineered from lectin from bananas

The ability of specific molecules to turn different signals on or off in cells is the subject of a paper published in the journal Cell. A group of scientists describe their work in which they mutate the protein lectin in bananas, an action which reportedly stops lectin’s inflammatory properties but which maintain’s its anti-viral action.

Prof. Jonathan Stoye, Group Leader and Virologist, The Francis Crick Institute, said:

“This is an elegant piece of work separating two biological activities of banana lectin, potentially allowing the use of the protein’s antiviral activity.  However, I would be somewhat concerned that although the inflammatory properties of BanLec have been abolished, it would still bind to normal cellular proteins in the body with unforeseen consequences.”

Prof. Wendy Barclay, Chair in Influenza Virology, Imperial College London, said:

“This piece of research not only takes forward a new strategy for combatting a wide range of viruses but elegantly shows why it works. Lectins are proteins made usually by plants that bind very specifically to sugars. Many viruses are covered in sugars and so these lectins can act to block them and stop them infecting cells. However there was a problem because our own cells are also covered in sugars and previous attempts at this strategy have suffered from dangerous side effects whereby the lectin also triggered toxic effects. This new study shows how the lectin can be re-engineered to be specific for the virus and explains at the structural level how that works. It is beautiful science with a truly translational impact. Let’s hope it can go further than just testing in mice!”

Dr Ben Neuman, virologist, University of Reading, said:

“Inside the fruit of a banana is a small protein called banana lectin that is really good at sticking to chains of sugar molecules.  It just so happens that most of the world’s deadliest viruses, including MERS, Flu, Ebola and HIV are covered in exactly the sort of sugar molecules that banana lectin prefers. When these viruses are covered in lectin they become harmless.

“So, banana lectins can be used as a biological barrier to mop up stray viruses so they do not cause harm.  Banana lectin has been shown to block HIV from infecting cells, and it would probably work just as well against other sugar-coated viruses like MERS, Flu, SARS and even Ebola.

“Banana lectins might work well to stop infections through the skin, for example as an anti-HIV coating on condoms, but they would not be useful inside the body since all our cells are covered in the same chains of sugar molecules as viruses.

“Don’t go smearing yourself in banana goop just yet – there is a side effect. Banana lectins can make resting cells start to divide, which could lead to itchiness and swelling that could paradoxically make it easier for a virus like HIV to enter the body by disturbing the natural barrier of the skin. Skin works by being dead on top and alive underneath, but if the living cells grow too quickly, they can push through to the surface, where they can be infected.

“In this new study, the researchers changed the banana lectin just enough to stop the side effects, while keeping its virus-blocking properties intact. The modified banana lectin actually worked better than other commercial antivirals at blocking infection by several different kinds of HIV.

“In the end, it doesn’t really matter where an antiviral drug comes from, as long as it works.”

Prof. Ron Eccles, Director, Common Cold Centre and Healthcare Clinical Trials, Cardiff University, said:

“We really need new antivirals to fight diseases like common cold and flu and the research published on a new antiviral engineered from a substance in bananas could give hope for new antiviral drugs in the future. However, eating more bananas is not going to be of any benefit in treating colds and flu, as the new substance has been engineered from chemicals in bananas and is not present in the real stuff. Still, it does give us some food for thought.”

Prof. Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“Each new virus outbreak is a timely reminder of our need for antivirals that can work against a range of viruses. Lectins have that potential as they are able to bind to the sugars that are present on the surface of a range of viruses including HIV, influenza and Ebola, many of which have caused or have the potential to cause severe epidemics or even pandemics.

“There are a range of lectins out there – different lectins recognise different viruses because each virus has a different pattern of sugars on its surface.

“Crucially, many of these lectins have the potential to be used as an antiviral, but progressing them from the test-tube into humans is not easy. Often there are manufacturing challenges and sometimes unwanted side effects.

“BanLec was previously shown to be a potent virus inhibitor but it also caused inflammation – a nasty side-effect that would limit its usefulness as a treatment.

“Using some nifty bio-engineering the researchers were able to silence the unwanted side effects, but maintain the virus killing ability. It was able to potently inhibit viruses like influenza, hepatitis C and HIV grown in culture.

“Great news – but will it work in humans? This is the key question and there are lots of hurdles that still need to be overcome before antiviral lectins find their way into clinic. For one thing, there’s a risk that our immune system will recognise this as foreign and mount an immune response to it, potentially rendering it ineffective. But even so, given recent events, generating antivirals that can work against a range of viruses is well worth pursuing.

“Also, it’s worth noting that there is no evidence that bananas have any noticeable antiviral effect.”

‘Engineering a Therapeutic Lectin: Uncoupling Mitogenicity from Antiviral Activity’ by Michael D. Swanson et al. published in Cell on Thursday 22 October 2015. 

Declared interests

Prof. Jonathan Stoye, Prof. Wendy Barclay and Prof. Ron Eccles declare that they have no relevant interests.

Prof. Jonathan Ball: “I am collaborating in research aimed at developing human lectins as antiviral agents and am named inventor on a patent related to the use of human lectins as antivirals (L-ficolin as an inhibitor of hepatitis c virus entry; Patent GB1407115.3, Inventors AW Tarr & JK Ball).”