Checkbiotech Is it possible to reduce the costs of expensive pharmaceuticals by producing them in plants? A Canadian research group thinks so and has started with rice seeds.
Biopharmaceuticals are nowadays still mostly produced either in bacteria or in mammalian cells. The great disadvantage of bacterial systems is that proper protein folding and modification like glycosylation (addition of sugar moieties) is not assured. Mammalian systems on the other hand are very cost intensive and have the risk of carrying viruses that are able to infect humans. That is why many researchers aim at using plants as inexpensive and safe bioreactors.
The drawback of many of these attempts is very low protein yield which makes purification still too expensive. But recently researchers have discovered that seeds are a promising alternative, as transgenic proteins seem to accumulate at a higher level. A second advantage is that seeds can be stored for weeks and even months without the product being degraded or destroyed, which would make manufacturing and transportation much easier. In addition there already exist well-established seed fractionation procedures for the major crops.
However public concern about possible outcrossing of transgenes is high, which is why self-containment has to be ensured. “As rice is primarily a self-pollinated crop, it offers particular attraction in terms of containment of transgenes, in addition to providing obvious advantages associated with producing protein-based medicines in seeds for direct administration to human patients (novel drug delivery).†explained Dr. Ravinder Sardana from the Department of Cellular and Molecular Medicine at the University of Ottawa.
An additional advantage is that rice is edible, which could in certain cases eliminate the need for purification of the product. This is why Dr. Sardana´s research group chose rice seeds to produce a widely used and so far very expensive drug, the cytokine Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF). Cytokines are molecular messages that organisms use to communicate. For instance in humans, cytokines can be released to let the immune system know there is an infection.
This cytokine is essential in fighting infections by regulating production and function of granulocytes and macrophages. Abnormally low numbers of these immune cells, a state called neutropenia, is a common result of cancer chemotherapy. However, neutropenia can also result from other causes such as hereditary diseases or viral infection. Recombinant GM-CSF is clinically used also after bone marrow transplantation to accelerate immune system recovery and has a number of other possible applications, such as in HIV patients. But the high costs of producing it in yeast and E.coli so far limits its widespread use.
In their work, which was published in a recent issue of Transgenic Research, the authors introduced the full coding sequence of the human GM-CSF gene attached to a special rice promoter into rice cells by the help of Agrobacterium.
After breeding a couple of plants, they confirmed the presence of their target by several methods. An important outcome was that the cytokine accounted for 1.3% of total protein in the rice varieties, which is much higher than in the attempts tried before with tobacco and sugarcane plants. In addition this is enough to imagine reasonable low production costs for commercial use.
The second fundamental question was of course, if the purified cytokine is active and usable. Therefore the researchers tested a human cell line which is known to grow only in the presence of GM-CSF. They showed that cells indeed grew when adding rice seed extract and when they compared cell numbers with a sample where they used commercially available GM-CSF, they found it to be similar. This was an important finding because it showed that rice-produced GM-CSF can be used as a biopharmaceutical.
As previously mentioned, modification of a protein, in this case glycosylation, is an important issue. The authors show in their publication, that the protein is indeed glycosylated, although they want to spend more time to find out, if the glycosylation pattern of this plant-derived protein is the same as in human. Previous research on GM-CSF showed that modification is not essential for its activity, but it could well influence activity levels and immune system answers.
To further improve their findings, Dr. Sardana´s group is considering coupling the gene to another promoter, which already showed to augment protein yields to 4% of total protein. This would decrease production costs further.
So there is some fine-tuning, which can be done, but as the authors explain in their publication in Transgenic Research, “This is the first report where an additional protein, biologically active human recombinant protein GM-CSF, has been produced in the seeds of transgenic rice plants.†The method was already patented by the group, which is the first step to go for commercial production of GM-CSF in rice.
Frauke Focke is a Science Writer for Checkbiotech in Basel, Switzerland.
Publication:
Ravinder Sardana et. al. Biologically active human GM-CSF produced in the seeds of transgenic rice plants. Transgenic Res. 2007 Dec;16(6):713-21.
CONTACT:
Dr. Anil Dudani
Department of Cellular and Molecular Medicine,
Faculty of Medicine,
University of Ottawa,
451 Smyth Road,
Ottawa, ON,
Canada, K1H 8M5
anil_dudani@hc-sc.gc.ca
