Claims rhubarb pigment 'could help cancer crumble'

Behind the Headlines

Tuesday October 20 2015

Eating lots of rhubarb will not help treat cancers such as leukaemia

Rhubarb's colour comes from the pigment physcion

The front page of the Daily Express announces that, "Rhubarb can save your life," while other headlines state, "cancer-killing drug of rhubarb [will be available] 'within years' " – but these claims are unsupported by the facts. Tests were only carried out on cancer cells in the laboratory and in mice.

Researchers found that when a concentrated form of the chemical physcion (also reported to be called parietin) – which gives rhubarb stems their colour – was added to leukaemia cells in the lab, half of them died within two days. A modified form of physcion was also able to reduce tumour growth in mice injected with human cancer cells.

Although these results are encouraging, much more research will be needed to determine whether this chemical can be developed into an effective and safe drug for treating cancer in humans.

While rhubarb may make a tasty crumble, we can't say from this research that eating it could "save your life". And as a spokesperson for Cancer Research UK rightly points out: "Even if it's proven that parietin can treat cancer in people, it's unlikely that anyone could eat enough rhubarb to get the benefits." 

Where did the story come from?

The study was carried out by researchers from Emory University School of Medicine in the US, and other universities in the US and China.

It was funded by the US National Institutes of Health, a Pharmacological Sciences Training Grant, the US Department of Defense, National Natural Science Funds of China, Charles Harris Run For Leukemia, Inc., the Hematology Tissue Bank of the Emory University School of Medicine, and the Georgia Cancer Coalition.

The study was published in the peer-reviewed journal, Nature Cell Biology.

The Express' headline overplays what we can say based on this research, and contradicts quotes from an independent expert included in its own reporting. 

While the chemical from rhubarb that was tested was able to kill cancer cells in the lab, we do not know whether it would safely be able to do the same in the human body. Even if it did, it is unlikely eating rhubarb would have the effect of "saving your life", as the headline implies.

The Mail Online's reporting is more restrained and presents a more accurate summary of the implications of the research. 

What kind of research was this?

This laboratory and animal study looked at the role of a protein called 6-phosphogluconate dehydrogenase (6PGD) in cancer cells. This protein is involved in a pathway that helps give cancer cells the energy and building blocks they need to divide rapidly and create new cancer cells, and so form tumours. 

The researchers wanted to confirm 6PGD was important for cancer cell growth and look for chemicals that could stop it working to see how this would impact cancer cells.

This type of detailed laboratory investigation helps researchers understand how cancers grow and spread, and find ways they might be able to stop them. These experiments are important first steps towards developing new treatments for cancer.

However, not all chemicals that show promise in the lab will be safe or effective when they are used in animals. This is why these chemicals need to go through rigorous testing to ensure they are safe before they are tried in humans. 

What did the research involve?

The researchers grew human cancer cells in the lab and looked at what happened if they used genetic methods to stop the 6PGD being produced. They also looked at what happened if these cells were injected into mice. They carried out detailed experiments to look at exactly how 6PGD affected the cancer cells.

Next, the researchers screened a "library" of 2,000 chemicals to see if any of them were able to stop 6PGD working, but not affect other similar proteins in the cells. 

Once they identified chemicals able to block 6PGD, they tested what effect they had on human cancer cells and normal human cells in the lab. They also looked at what effect the chemicals had if given by daily injection over four weeks to mice that had previously been injected with human cancer cells. 

What were the basic results?

The researchers found using genetic techniques to stop 6PGD working did not stop normal skin cells dividing. 

However, it did stop human leukaemia cells, lung cancer, and head and neck cancer cells in the lab dividing as much as they normally would. If these genetically manipulated lung cancer cells were injected into mice, they generated smaller and slower-growing tumours than untreated lung cancer cells.

When the researchers screened their "library" of chemicals, they found a chemical called physcion could stop 6PGD working, but not affect similar proteins in the cells. 

They also identified a chemical derived from physcion called S3, which had a similar effect and was better able to dissolve in water – this is important if a chemical is to be used as a drug.

Adding physcion to human leukaemia cells, lung cancer, or head and neck cancer cells grown in the lab, or human leukaemia cells taken directly from a patient, stopped them dividing as much as they normally would. 

At the highest concentration tested, physcion caused about half of the leukaemia cells taken directly from a patient to die over 24 to 48 hours. Physcion did not have this effect on normal human cells in the lab.

S3 had similar results to physcion in the lab tests. Giving daily S3 injections for four weeks to mice injected with human lung cancer reduced tumour growth and the total weight of tumours compared with a control inactive injection. 

The researchers found similar results in mice injected with leukaemia cells or head and neck cancer cells. The S3 injections did not appear to cause obvious side effects in the mice.  

How did the researchers interpret the results?

The researchers concluded their findings "suggest that 6PGD is commonly important for cell proliferation and tumour growth". 

They said they have "identified and developed 6PGD inhibitors, physcion and its derivative S3, that effectively inhibited 6PGD, cancer cell proliferation and tumour growth in [mice injected with human cancer cells] without obvious toxicity, suggesting that 6PGD could be an anticancer target".

Conclusion

This study found that a chemical found in rhubarb called physcion, and related chemicals, are able to reduce cancer cell growth in the lab and in mice. They do this by blocking a protein called 6PGD.

While the chemical is found in rhubarb – where it produces an orange pigment – it was concentrated for use in this study and a slightly modified form was used in the mice. 

As yet, these chemicals have only been tested on human cancer cells in the laboratory and injected into mice. We therefore can't conclude eating rhubarb is going to "save your life", as implied by the Daily Express' front page.

Overall, these findings open another avenue for investigating potential cancer treatments. Much more research will be needed to make sure these chemicals are effective and safe enough to progress to testing in humans.

We will need to wait to see the results of these studies before we know whether these chemicals could become anti-cancer drugs in the future. This early stage of research is vital for the development of new cancer drugs, but unfortunately not all of the chemicals that show promise at this stage will go on to be successful cancer treatments.

Analysis by Bazian. Edited by NHS Choices. Follow NHS Choices on Twitter. Join the Healthy Evidence forum.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Cancer-killing drug made of rhubarb will be ready 'within years'. Daily Express, October 20 2015

Could rhubarb crumble help fight cancer? Orange-coloured compound in vegetable kills tumours cells. Mail Online, October 19 2015

Links to the science

Lin R, Elf S, Shan C, et al. 6-Phosphogluconate dehydrogenase links oxidative PPP, lipogenesis and tumour growth by inhibiting LKB1–AMPK signalling. Nature Cell Biology. Published online October 19 2015

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