Valuable cancer-fighting drugs may soon be no further away than the nearest omelette. The scientists behind Dolly the cloned sheep plan to genetically engineer chickens to enable them to lay eggs carrying human drug products.
The details were announced yesterday in Edinburgh by the groups behind the project, the Roslin Institute in Scotland and the US biotechnology company Viragen. They hope to have an antibody against skin cancer delivered in a chicken egg within a year and will follow up with drugs against lung and intestinal cancers.
The approach may sound like science fiction but it is all fairly straightforward genetic engineering. Many important medicines such as antibiotics and insulin already come from engineered bacteria which carry genes producing these products. Researchers have also successfully engineered sheep, cows, rabbits and goats that produce drugs in their milk.
Bacteria work very well as drug factories and are easily grown and handled in large bioreactors, but there are great advantages in using chickens, according to Dr Helen Sang, who leads the Roslin research team. Many powerful anti-cancer treatments are based on using protein drugs such as interferon.
Proteins are large, complex and difficult to produce in volume in bacteria, making the drugs both expensive and in short supply. "Avian technology promises a much faster, cheaper and virtually unlimited production process marked by the chicken's prolific egg-laying capacity," Dr Sang said.
The drugs arise in the egg white and, while bacteria might produce a few milligrams of drug, a chicken obligingly provides up to 500 milligrams per egg. A good layer can deliver up to 250 eggs a year, and the drug in eggs can be produced, extracted and purified at only a fraction of the cost of building bio-reactors for bacteria.
The process involves installing a foreign gene, a piece of genetic material which can produce a protein, into embryonic chickens. The birds incorporate the foreign DNA into their systems and produce the protein in their eggs.
The genes were isolated and developed by Viragen and are being given to Roslin, which will design the best transfer methods. The first gene will target the skin cancer, melanoma.
