Plants hold key to developing future cancer treatments
Cancer care relies on complex therapies involving radioactive materials and sophisticated drugs and has come far from past remedies based on plants and herbs.
However, scientists warn there is still a need to understand the botanical roots of tumour treatments – to maintain new sources of drugs and to ensure plant resources are not overexploited. The natural world still has a lot to teach us about tackling disease.
An example is provided by MelanieJayne Howes, a researcher based at Kew Gardens in London. “An effective anticancer drug called paclitaxel was developed from the Pacific yew tree. However, it was based on a chemical that exists in very low yields,” said Howes. “Hundreds of trees had to be cut down to develop the drug. As a result, the tree is now classified as near threatened.”
However, a solution has been provided – by botanists. Howes said: “A similar drug has since been found in higher concentrations in the common yew and this is now used, with much less ecological harm, to make paclitaxel, a treatment for ovarian and breast cancers. Basic research and understanding of plant biology has had a key impact on cancer treatment.”
This point was reiterated by Prof Susan Short of Leeds University. “There are lots of different tumour types and tumour subtypes that are being discovered all the time so we still need new ideas and new drugs,” she said.
Short is leading an extensive UK trial of the cannabis-based medicine Sativex in order to treat patients with recurrent glioblastomas, an aggressive form of brain tumour. The trial will assess the impact of the drug – which is also used to treat multiple sclerosis and is delivered as an oral spray – on people undergoing standard chemotherapy.
“We will be treating patients whose primary brain tumours have grown back after standard treatments, to see if adding this plant-based drug to subsequent chemotherapy helps to keep them alive for longer and to see if it improves their quality of life,” added Short.
Plant-based treatments clearly have a vital role to play in cancer therapies, a point emphasised by Howes. “Even today, scientists have not been able to synthesise some drugs because they are so complex so we still rely on plants for key cancer drugs,” said Howes, whose work involves examining the plants and seeds found at Kew in order to pinpoint new drugs and medi
cines.
As examples of past successes, she pointed to vinblastine and vincristine, two critically important drugs that are used to treat Hodgkin’s lymphoma, melanoma and several other cancers.
The only source of these medicines is from extracts of the rose periwinkle, which is native to Madagascar but grown across the world as an ornamental plant.
“The periwinkle was used originally as a traditional treatment for diabetes but subsequent research showed it had potential anti-cancer properties,” said Howes.
However the efficacy of plant extracts is not restricted to the creation of cancer drugs. Medicines for many other conditions are still isolated from plants and used today.
Galantamine, an extract of snowdrops, is used to treat dementia, while artemisinin, an extract of the plant sweet wormwood – a herb used in Chinese
traditional medicine – was shown by the chemist Tu Youyou to be effective in treating malaria, a discovery that won her a share of the 2015 Nobel prize in physiology or medicine.
The emphasis on the power of plants to help people survive disease for longer and have better quality of life has important consequences outside the treatment of their conditions, added Howes. “If we can show how we can source new medicines from nature by unlocking the useful properties of plants, then we help treat disease, but we also demonstrate the value of biodiversity and provide an incentive for people to protect it.”