We at MolecularFarming.com see Tobacco as the ideal Molecular Crop. [ Easily Genetically engineered, large leaf mass, NONFOOD crop] The article below, to which we contributed, sums up our view of the huge potential

Feature article for Tobacco Journal International © T.J.I. 2002 & Peter McGrath

Molecular farming - Tobacco's future? - by Peter McGrath Gaucher disease is a rare genetic disorder which, in Europe, affects between 1 in 20,000 to 1 in 60,000 people. It can be treated with an enzyme known as GCase. However, as GCase is currently produced by culturing Chinese hamster ovary cells, even limited quantities are expensive to produce. In Europe's top treatment facility at Trieste, Italy, 82 lucky children are receiving the drug. In Israel, however, Gaucher disease affects as many as 1 in 700 of the population. Because of the expense of producing GCase, these cases usually go untreated.

Production capacity crisis

Initially isolated from human placentas, GCase produced using hamster cells is just one of hundreds of new drugs that have been developed during the recent biotechnology boom. Pharmaceutical companies, however, have a major problem. Current production systems do not have enough capacity to produce the required quantities of all these new medicines. In fact, some experts are predicting that, by 2005, demand for these protein-based pharmaceuticals will be four-times greater than manufacturing capacity.

"The really significant development of the last year or two has been the surge in demand for protein-type medical drugs worldwide," explains Professor Maelor Davies of the Kentucky Tobacco Research and Development Center. "Now often referred to as a 'crisis', this demand will be difficult to address with conventional fermentation-based production of proteins as many of the new pharmaceuticals are required in quantities much greater than typical protein medicinals."

Although systems using genetically modified animals which produce therapeutic proteins in their milk, for example, are being tested, there are fears that viruses and prions (such as the one that causes BSE or 'mad cow disease') being passed from animals to humans, could create more problems than they solve. For these reasons, scientists are turning towards transgenic plants to produce their 'designer drugs'. Among the candidate crops, tobacco features highly.

Tobacco's role

"The tobacco plant is most suited to large-scale production of active agents," says Dr. Stefan Schillberg of the Fraunhofer Institute for Molecular Biotechnology and Applied Ecology in Germany. "It can easily be genetically modified and cultivated at low cost. Tobacco generates a great volume of biomass per hectare per year, and thus produces a very high yield of the final product."

In fact, there are already many crops of genetically-modified, pharmaceutical-protein-producing tobacco being grown around the world. "After some 15 years or more of being able to express new proteins in plants, we are particularly pleased to see this development of a market at last," adds Professor Davies.

One such crop is being grown this summer in Italy. The Italian government, strongly opposed to genetically modified crops for food use, has approved the experimental production of one hectare of tobacco which will produce the GCase enzyme needed by Gaucher disease patients. Dr. Stefano Marchetti of Italy's University of Udine explains that the GCase will be purified from the tobacco seeds and he hopes to get clearance for clinical trials to start later this year.

Clinical trials of other tobacco-produced pharmaceuticals, however, are already well advanced. At Guy's Hospital, London, for example, Professor Julian Ma is now conducting Phase III trials, involving several hundred people, to test the efficacy of a treatment against dental caries. In this case, the active protein is applied directly to the teeth and prevents the disease-causing agent, Streptococcus mutans, from attacking the surface enamel.

"Based on just one treatment a year for children in the UK, we would need 200 kg of antibodies each year, or 1180 kg in the USA," says Prof. Ma, who explains that the only possible way to produce this amount is to use transgenic plants. Like the GCase enzyme, the antibodies currently being used in the Phase III trials are being produced in tobacco plants, grown in both Italy and the US. In this case, though, it is the leaves that are harvested rather than the seeds. The research is being carried out in collaboration with Plant Biotechnology Inc. of Mountain View, California, and the novel drug, known as CaroRX, is likely to be among the first field-produced pharmacological reagents to be commercialised.

Molecular farming

The production of various types of medicinal proteins in plants has been given various names, including 'biopharming', but the industry seems to have settled on 'molecular farming' as the label of choice.

"Medical molecular farming is the growing and harvesting of genetically engineered crops of transgenic plants with the object of producing biopharmaceuticals, sometimes called 'farmaceuticals'. The idea is to use these molecular crops as biological factories to generate drugs that are difficult or expensive to produce in any other way," explains Brian Marshall, who runs the Molecular Farming website (www.molecularfarming.com).

At least 350 candidate genes for molecular farming have been identified and different companies are investigating the use of different crops. As well as tobacco, there are already reports of biopharmaceuticals being produced in crops such as alfalfa, banana, carrots, potatoes and tomatoes. Avidin, however, the first of these products to reach the market, is being produced in corn. Even so, Brian Marshall agrees with Dr. Schellberg in that tobacco will have an important role to play in the development of the molecular farming revolution - and, conversely, that molecular farming will have an important part to play in the future of tobacco production.

"Tobacco plants are especially suited to molecular farming, and by 2010 will be more valuable as a source of biopharmaceuticals than of tobacco," he says, adding that the industry could be worth $50 billion within the next 7 or 8 years.

To support his case, Brian Marshall has analysed the scientific literature and compared the yield of various biopharmaceuticals produced in tobacco plants with their current market values. Human epidermal growth hormone, for example, used in wound repair, is produced at a rate of 0.01% of the plants' total soluble protein (TSP), giving a one acre crop of tobacco an estimated value of $175,000. The more expensive Human protein C, an anticoagulant, is also produced at 0.01% TSP, with an estimated value of $2,000,000 per acre. Likewise, an acre of tobacco producing 0.02% human serum albumen, the most widely used intravenous protein, could provide $2,000,000-worth of product.

New methods

In all these cases, the gene of interest has been inserted into the genetic material present in the nucleus of each of the plants' cells. This is the traditional method of genetically engineering plants and, to date, all commercially released crops have been produced this way. However, there is a new approach to genetically modifying plants which involves inserting the gene of interest into the genome of the chloroplast, the green structures present within each cell that are responsible for converting light energy into sugars. Transforming the plant this way boosts TSP levels. Unfortunately, scientists have found the technique to be difficult to apply to many crop species, but the transformation of tobacco chloroplasts is now routine in several laboratories, including that of Professor Henry Daniell at the University of Florida. In fact, he has reported human serum albumen to be produced at up to 11% of the TSP, 500 times higher than in regular transgenic plants. With such high production levels, Professor Daniell believes that, by using tobacco, the cost of drug production could fall by between 100 and 1000 times.

Another advantage of the chloroplast production system is that there is no chance of the introduced genes escaping via pollen to fertilise adjacent crops for the simple reason that pollen grains do not contain chloroplasts. Of course, harvesting tobacco leaves before the plant flowers also avoids this possibility, but another system in the advanced stages of development goes one step further.

CropTech, currently relocating from Blacksburg, Virginia, to a purpose-built site near Charleston, South Carolina, have patented their MeGa-PharM plant-based protein manufacturing system, which is based on a so-called 'inducible promoter'. In this case, the gene of interest is introduced into the plant, but does not produce the desired protein until the plant is wounded. This is done by shredding the leaves immediately after harvest and then incubating them for 24 to 48 hours before extracting the protein. The advantages of such a system are that even proteins detrimental to cell functioning can be produced. It is also regarded as safe for the environment as pharmaceuticals are not produced in the field, but in carefully controlled post-harvest processing facilities.

CropTech are currently using their MeGA-PharM system to produce proteins for several top-tier biotech companies, including Amgen and Immunex, as well as pursuing pre-clinical development of two of their own proprietary products.

Risks

Despite the obvious benefits of producing pharmaceuticals in plants, however, there have been some dissenting voices. A recent report has revealed that there are around 300 molecular farming trials currently being carried out in the US alone and, although the USDA keeps a list, it does not reveal the location of the crop or the type of protein being produced.

"Just one mistake by a biotech company and we'll be eating other people's prescription drugs in our cornflakes," warns Larry Bohlen, director of health and environment programs at Friends of the Earth, USA, one of the authors of the report.

Although this is unlikely with tobacco-produced pharmaceuticals, there are still hurdles to be overcome as companies try to convince the regulatory authorities that a drug produced by a plant rich in toxic secondary metabolites is safe to use.

Perhaps for this reason, it is no surprise that the first clinical trials involve pharmaceuticals, such as the anti-caries CaroRX, that are not ingested or injected. To avoid the consumer backlash seen in Europe and elsewhere against genetically modified crops, companies producing biopharmaceuticals are also eager to maintain a division in the public's thinking between crops grown for food and pharmacological purposes.

The future

It is estimated that more than a thousand protein-based therapeutics are at various stages of development and, in 2000 alone, the FDA approved 21 new biotechnology drugs and vaccines. This figure is bound to increase as more products begin to be commercialised. As we have seen, current production capacity cannot cope with the expected demand and more and more tobacco growers, therefore, will be producing crops for medicinal purposes.

In many cases, the economics of plant-based production systems have still to be worked out. Even so, with such efficient and relatively cheap 'biofactories', perhaps the 1 in 700 children born in Israel with Gaucher disease, along with many other patients of many other ailments around the world, will have a brighter future ahead of them.

-end-

Author bio

Nowadays, he uses his scientific background to produce news and feature articles for both print and electronic publications, specialising in scientific, agricultural and environmental issues. His work has appeared in a diverse range of magazines, including the New Scientist and BBC Wildlife, as well as the UK agricultural publications The Grower, Potato Review and Farmers' Weekly. His work has also been published in various US magazines, as well as websites such as the New Agriculturalist and People and Planet

For more details of his scientific and journalistic career to date (as well as some examples of his photographic work), please visit his website at www.petermcgrath.net.

Peter McGrath is married and currently lives in the south of Italy.

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