By Nial Wheate – University of Sydney.
Extracts from a berry can improve the effectiveness of a chemotherapy drug, according to research published today in the Journal of Clinical Pathology.
But it’s best to view this finding with caution because while nutraceuticals (foods that provide health or medical benefits) are often touted like this, their promise doesn’t always hold up.
Today’s study, which looked at the impact of chokeberry (native to North America) extract on the cancer drug gemcitabine, adds weight to the idea that nutraceuticals can help fight disease. Indeed, there’s now a whole area of study focused on the application of plant extracts to treat illness.
Unfortunately, the promising initial results of nutraceutics in the lab often fail to translate into effectiveness in humans. The results of the study published today, for instance, are too preliminary to support the authors’ call that “micronutrient supplementation should be considered as part of cancer therapy strategies”.
‘Natural’ drugs in chemotherapy
Naturally derived drugs are not new to cancer chemotherapy; three of the most important families of such drugs are extracted from natural sources. The most useful medicines for the treatment of breast cancer, for instance, are paclitaxel and docetaxel, which come from the Yew tree.
The drugs doxorubicin and daunorubicin, which are also used to treat breast cancer, come from a bacteria originally found in the ground outside a 13th century Italian castle. And vinblastine and vincristine, which treat a variety of cancers, were originally extracted from the Madagascar periwinkle plant.
What of all them have in common is that they are not useful in their natural form; you can’t treat breast cancer by eating Yew tree bark. They’re only effective in their purified form and when delivered as a scientifically designed medicine.
The chokeberry results
Like much other research into nutraceuticals, the paper has several limitations. The authors found chokeberry extract did not kill cancerous or normal cells by itself; it only worked when they combined it with the drug gemcitabine. They concluded the chemicals in the berry have a supra-additive, or synergistic effect with the gemcitabine, but other explanations are possible.
While chokeberry extract is known to have some potentially useful chemicals – the authors highlight flavonoids and anthocyanins – it’s not certain if any of them are actually responsible for the observed anticancer effects.
This question could easily have been addressed by testing each chemical individually to see if a similar synergistic effect was obtained. That’s the missing step between nutriceuticals and the drugs mentioned above.
In addition, the active compounds in nutraceuticals typically aren’t in a high enough dose to be effective. They may also be poorly absorbed during digestion or may be processed by the liver before they get into blood circulation – things that research that only uses cancer cells in a laboratory can’t ascertain.
Many natural products that display remarkable results in the laboratory fail to improve disease outcome in more advanced and stringent studies. One such example is curcumin, an antioxidant found in the spice turmeric, which has shown potential to treat many diseases, including cancer. But turmeric has not yet been found to be effective enough in animal and human trials to justify its use in chemotherapy. Most studies now focus on the use of pure, laboratory-synthesised curcumin for cancer treatment, rather than the natural turmeric spice.
And there’s another reason to be cautious. Nutraceuticals are high in vitamins and other key nutrients needed for cell growth so they can also promote cancer proliferation.
One example is the anticancer drug methotrexate, which only works when a key nutrient is missing from the patient’s diet. High levels of folic acid can interfere with the drug’s ability to kill the cancer.
Other studies have shown that key chemicals found in many nutraceuticals, like antioxidants, can speed up cancer growth. In one study researchers found that vitamin E and the antioxidant supplement, acetylcysteine, increased lung cancer growth in mice.
While the results of many nutraceutical studies are scientifically interesting, they’re almost always too preliminary to justify recommending cancer patients supplement their treatment. Only when further testing has shown effectiveness in animals and in human clinical trials, and their mechanisms of action have been determined can we justify the use of specific nutraceuticals in therapy.
Nial Wheate in the past has received funding from the ACT Cancer Council, Tenovus Scotland, Medical Research Scotland, Scottish Crucible and the Scottish Universities Life Sciences Alliance for research into anticancer drugs.