By Shankar Vedantam
Washington Post Staff Writer
Saturday, February 7, 2009
Federal officials yesterday approved for the first time the sale of a drug made in animals genetically modified to secrete the compound in their milk.
The drug comes from goats whose DNA was altered to produce a drug needed by patients with a rare blood disorder.
Using animals as factories to produce medications needed by humans has been a long-standing goal, and federal officials emphasized that the technique not only has vast potential for patients, but also that it can be carried out without harm to the animals.
The drug approved by the Food and Drug Administration yesterday, called ATryn, is used to untangle blood clots in patients who lack sufficient quantities of a protein called antithrombin. Patients with hereditary antithrombin deficiency are at high risk during surgeries and childbirth, and the drug would be given in hospital settings. About one in 5,000 Americans has the hereditary disorder.
"This is very exciting, it is novel and has great potential for where we can go with this new technology," said Bernadette Dunham, who directs the FDA's Center for Veterinary Medicine.
The drug is made by GTC Biotherapeutics of Framingham, Mass. Company scientists combined human DNA for antithrombin with goat DNA in such a way that goat's milk glands would express human antithrombin.
"The mammary gland is designed by nature to make proteins for offspring in a substance that we call milk, so all we have done is provide the extra bit of coding so it makes this particular protein," said Thomas E. Newberry, a vice president at GTC Biotherapeutics.
Researchers are seeking to produce drugs in animals because they can be manufactured faster and more cheaply than by synthetic processes, Newberry said. Antithrombin, for example, can be extracted from plasma in donated blood. But if all the blood donations in the country were used to extract antithrombin, scientists would have about 220 pounds of the protein a year. The same amount can be by made with 150 goats, and the company already has 200 animals producing the protein, Newberry said.
Other animals could have been used, he said, but the company chose goats because it takes only 18 months to raise a goat altered to produce milk laced with antithrombin. Rabbits would breed faster and cows would produce more milk, but Newberry said goats offered the largest supply at the quickest pace. The company has about 1,500 goats, he said, and is exploring the manufacture of other therapeutic products.
FDA officials said that although their primary responsibility was to make sure the antithrombin produced in goats was safe, the agency had also taken care to assure itself that they were not harmed.
"Even though the Animal Welfare Act is under [Department of Agriculture] jurisdiction, we look at target animal safety," Dunham said. "In this case, we had an opportunity to go back seven generations to make sure throughout the review that they were healthy."
Basil Golding, who directs the Division of Hematology at the FDA's Center for Biologics Evaluation and Research, said that manufacturing drugs using animals is safer than trying to get antithrombin DNA directly into humans with antithrombin deficiency.
"In the goat, it is expressed in the mammary gland, so it is not affecting the whole goat. So there is very little chance of doing harm," he said. "If you were delivering it to a human, it would be expressed in many cells of the body. If there was a safety issue, there would be more chance of doing harm."
Martin Stephens, vice president for animal research issues at the Humane Society of the United States, acknowledged that the manufacturing technique had not harmed the goats, but said he was still troubled by the development: "It does represent a dark cloud on the horizon in that we would rather not see more uses of animals drummed up," he said.