Cancer patients of the future could be treated with a powerful "magic bullet" that attacks tumours with a cyanide cocktail derived from the cassava plant, scientists disclosed yesterday at the British Association's annual meeting.
Researchers from Imperial College in London have devised a way of using cyanide, one of the most dangerous and fast-acting poisons, selectively to destroy cancer cells yet leave healthy tissue untouched.
The key ingredient of the therapy is an enzyme derived from the cassava plant, which converts a harmless sugar molecule into the poison. Scientists have attached the enzyme to an artificial antibody specifically designed to target tumour cells only.
The idea is to inject the combination of antibody and enzyme into the site of a tumour and then flush the cancer with the sugar, which would cause cyanide to be released into the cancer cells.
Mahendra Deonarain, a lecturer in biochemistry, said the approach meant it would be possible to use cyanide safely against many kinds of tumours, with the advantage that patients were unlikely to develop drug resistance, a frequent drawback with more conventional cancer drugs.
Cyanide is such an effective poison because it interrupts the vital oxygen supply that enables living tissues to generate energy. "It suffocates you from the inside out," Dr Deonarain said.
Because the poison cripples such an important part of a cell's vital machinery, it would probably be impossible for tumour cells to develop a way of avoiding being killed.
Dr Deonarain said: "The advantage of this we think is that we can target cells specifically and against any type of cancer cell, depending on what antibody we use. We also believe that we cannot have any drug resistance to cyanide.
"Current cancer treatments are often toxic, with side-effects that limit their use. Also, cancers develop resistance to the therapies. Our approach suggests a more specific, safer treatment for a disease which touches one in three people at some point in their lives," Dr Deonarain said.
Cassava plants use an enzyme called linamerase to convert the sugar linamerin into cyanide as an elaborate form of self-defence against insects and other predators.
Although cyanide is deadly, it quickly dissipates in the human body.
Dr Deonarain said that the technique ensured most of the cyanide remained near the site of the tumour.
Any seepage away from the cancer was soon degraded by the liver, he said.
Studies in the test tube have shown that the approach can destroy tumour cells but leave normal cells untouched. "For the first time we've been able to show we can kill cancer cells using this prodrug activation approach, as we call it," Dr Deonarain said.
Clinical trials on patients could begin within the next five years, he said.