Scientists have announced that a chemical defence system used by some plants to poison predators with cyanide is being turned into a new weapon against cancer.

In nature this defence mechanism is activated in the cassava plant, the almond tree and the hydrangea. When these plants are attacked and damaged, an enzyme and sugar, which are normally kept apart in system of the plants, come together to produce the poison.

Scientists have now adapted the process by genetically engineering the enzyme to include an antibody, which recognises and targets certain cancers. It homes in on the tumour and sticks to it . Sugar is then applied, which reacts with the enzyme to release cyanide and kill the cancer cells. Healthy tissue around it is unharmed.

Researchers at Imperial College, London, have already successfully tested the system, called Agent (Antibody Guided Enzyme Nitrile Therapy) on bowel cancer cells in the laboratory.

Dr Mahendra Deonarain, who led the study said: “Traditional chemotherapy drugs cause serious side effects and tumours develop resistance to them. The beauty of cyanide is that although it is poisonous it is not as toxic as some chemotherapy drugs. You can give it in high concentrations locally and it will kill the tumours but not surrounding cells. It's also impossible for a tumour to develop resistance against cyanide.”