PHARMACEUTICAL PRODUCTION IN TRANSGENIC ANIMALS

PHARMACEUTICAL PRODUCTION IN TRANSGENIC ANIMALS

PHARMACEUTICAL PRODUCTION IN TRANSGENIC ANIMALS

Biotechnology Information Series (Bio-10) North Central Regional Extension Publication Iowa State University - University Extension

A New Kind of Farming
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A new brand of farming is emerging from the research and development labs of several universities and small biotechnology companies - so new they're even changing the spelling to "pharming."

Pharming is the production of human pharmaceuticals in farm animals that is presently in the development stage with possible commercialization by the year 2000. It has been gaining application among biotechnologists since the development of transgenic "super mice" in 1982 and the development of the first mice to produce a human drug, tPA (tissue plasminogen activator to treat blood clots), in 1987. Transgenic organisms have been modified by genetic engineering to contain DNA from an external source. The first drugs produced by this approach are about to enter clinical trials as part of the FDA review process. These transgenic animals will likely be raised by the pharmaceutical companies and will certainly be kept separate from the food supply.

Genetic Engineering
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During the 1970s, advances in DNA manipulation techniques provided a significant, economical alternative source for many drugs made of protein. Previously, these protein drugs were available in extremely limited supplies; for example, human cadavers were the source for human growth hormone, and insulin to treat diabetes was collected from slaughtered pigs.

By genetic engineering, the DNA gene for a protein drug of interest can be transferred into another organism that will produce large amounts of the drug. This technique (illustrated in Figure 1), can be used to impart new production characteristics to an organism, as well as to trigger the production of a protein drug:

1. The gene of interest is isolated on a strand of DNA.
2. DNA is cut at specific points by restriction enzymes. The enzymes recognize certain sequences of bases on the DNA strand and cut where those sequences appear.
3. The cut DNA joins with a vector, which may be a virus or part of a bacterial cell called a plasmid. The vector carries the gene of interest into the organism that will produce the protein.
4. Transformation occurs when the gene carried by the vector is incorporated into the DNA of another organism where it initiates the action desired (production of a drug, etc.).

[Figure 1]

The first successful products of the genetic engineering process were protein drugs like insulin and growth hormone. These drugs do not have to be produced by mammals to be active in mammals. An inexpensive, easy-to-grow culture of genetically engineered bacteria like the common E. coli can manufacture these protein drugs.

[Figure 2]

Other human drugs, such as tPA for blood clots, erythropoietin for anemia, and blood clotting factors VIII and IX for hemophilia, require modifications that only cells of higher organisms like mammals can provide. The higher costs of maintaining mammalian cell cultures that produce only small amounts of the drugs have been an enormous barrier to the commercial development of this type of cell culture production method.

Animal Pharming
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By genetic engineering, the DNA gene for a protein drug of interest can be transferred into another organism for production. Which organism to use for production is a technical and economic decision. For certain protein drugs that require complex modifications or are needed in large supply, production in transgenic animals seems most efficient. The farm animal becomes a production facility with many advantages - it is reproducible, has a flexible production capacity through the number of animals bred, and maintains its own fuel supply. Best of all, in most animal drug production, the drug is delivered from the animal in a very convenient form - in the milk!

Procedure

A transgenic animal for pharmaceutical production should (1) produce the desired drug at high levels without endangering its own health and (2) pass its ability to produce the drug at high levels to its offspring.

The current strategy to achieve these objectives is to couple the DNA gene for the protein drug with a DNA signal directing production in the mammary gland. The new gene, while present in every cell of the animal, functions only in the mammary gland so the protein drug is made only in the milk. Since the mammary gland and milk are essentially "outside" the main life support systems of the animal, there is virtually no danger of disease or harm to the animal in making the "foreign" protein drug.

After the DNA gene for the protein drug has been coupled with the mammary directing signal, this DNA is injected into fertilized cow, sheep, goat, or mouse embryos with the aid of a very fine needle, a tool called a micromanipulator, and a microscope (Figure 2). The injected embryos are then implanted into recipient surrogate mothers where, hopefully, they survive and are born normally.

Commercialization Issues
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Success in creating a transgenic animal that can produce the drug is far from guaranteed. About 10 to 30 percent of mouse embryos produce transgenics, but less than 5 percent of goats, sheep, or cows do. Production of the drug is measured during lactation after the animal is raised to maturity and bred. Because of the long time periods involved and low success rates, developing transgenic animals is currently very expensive, as the dollar amounts in Table 1 indicate.

Although most protein drugs are made in milk, a notable exception is human hemoglobin that is being made in swine blood to provide a blood substitute for human transfusions. Because hemoglobin is naturally a blood protein, it is likely to be one of few exceptions to the usual method of production in milk. Furthermore, the economics of blood production are less favorable, because to recover human hemoglobin, the animal producing it must be slaughtered.

Drugs currently made by or being developed in transgenic animals are listed in Table 1. Notice that pharming is expected to increase the value of animals dramatically. In general, animal pharming is considered to be 5 to 10 times more economical on a continuing basis and 2 to 3 times cheaper in start-up costs than cell culture production methods.
[Table 1]

Drug Animal Value/Animal/Yr*
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AAT sheep $15,000
tPA goat 75,000
Factor VIII sheep 37,000
Factor IX sheep 20,000
Hemoglobin pig 3,000
Lactoferrin cow 20,000
CFTR sheep, mouse 75,000
Human Protein C pig 1,000,000

*Current market price of the drug and supply produced by one animal.

Drug descriptions:

AAT alpha-1-antitrypsin, inherited deficiency leads to
emphysema
tPA tissue plasminogen activator, treatment for
blood clots
Factors VIII, blood clotting factors, treatment for hemophilia
XI
Hemoglobin blood substitute for human transfusion
Lactoferrin infant formula additive
CFTR cystic fibrosis transmembrane conductance
regulator, treatment of CF
Human Protein C anticoagulant, treatment for blood clots

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Regulatory and Ethical Issues
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Production of human pharmaceuticals in farm animals has many technical barriers to overcome, although most technologists agree that these technical difficulties will be easily resolved in the 1990s. As a production method, animal pharming is entirely unprecedented and is likely to undergo significant evaluation by the Food and Drug Administration (FDA). Human drugs purified from animal milk or blood are likely to require exceptional levels of safety testing before animal and human health concerns are addressed to the satisfaction of consumers.

At a more fundamental level, many people are genuinely concerned about animal welfare and biotechnology's redefinition of the relationship between humans and animals. Genetic engineering and transgenic animal research are essentially human endeavors to improve the availability, quality, and safety of drugs; to enhance human health; and to improve animal health. Animal breeding has gone on for centuries, but the ability to change the DNA of the animal brings breeding to a revolutionary new level.