A compound extracted from tangerine peel can kill certain human cancer cells, research shows.
The key compound is found in the peel
A team from Leicester School of Pharmacy found Salvestrol Q40 was turned into a toxic compound in cancer cells, destroying them.
Salvestrol Q40 is found at higher concentrations in tangerine peel, than in the flesh of the fruit.
The researchers suggest the modern trend to throw away peel may have contributed to a rise in some cancers.
Lead researcher Dr Hoon Tan said his work was still at an early stage, but together with his colleagues he has formed a company to investigate further the potential to develop natural anti-cancer therapies.
He said: "It is very exciting to find a compound in food that can target cancers specifically."
Plant immune system
Salvestrol 40 is a type of phytoalexin - a chemical produced by plants to repel attackers, such as insects or fungi.
It is converted into a toxic compound by the P450 CYP1B1 enzyme, found in much higher levels in cancer cells.
As a result, the researchers found, it proved to be 20 times more toxic to cancer cells than their healthy equivalents.
Dr Tan said Salvestrol was found in other fruit and vegetables, such as the brassica family, which includes broccoli and brussels sprouts.
However, the compound tends to be produced at higher levels when infection levels among crops are high.
Therefore, the use of modern pesticides and fungicides, which have cut the risk of infections, have also led to a drop in Salvestrol levels in food.
Dr Julie Sharp, Cancer Research UK's science information manager, said: "Many naturally occurring substances have anticancer properties, but while this research shows that salvestrols have an effect on cells in the laboratory, there is no evidence that they have a similar effect in patients.
"Clinical trials would be needed to tell us if these substances could be developed into a cancer treatment."