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BIOPHARMING: THE INTERFACE OF PLANT BIOTECHNOLOGY, BIOPHARMACEUTICALS AND FARMING
C Kameswara Rao Foundation for Biotechnology Awareness and Education, Bangalore, India
Introduction Biopharming, is the harvest of bioactive molecules from mass cultured organisms and crops (also called molecular farming), for use as ingredients in industrial products and pharmaceuticals. Bipharming differs from bioprospecting in that the latter is sourced in wild populations.
Bipharming is not a wholly new concept, as antibiotics and enzymes are extracted from mass cultured micro-organisms by the industry for a very long time. A number of drugs such as opium (Papaver somniferum) alkaloids, digioxin (Digitalis species), rauvolfin and reserpine (Rauvolfia serpentina), vincristine (Catharanthus roseus, Vinca rosea), placitaxel (Taxus species), camptothecin (Camptotheca acuminata and Nothopodytes nimmoniana), etc., are extracted from wild or cultivated non-edible plant species. Bioactive compounds such as piperine (Piper nigrum), curcumin (Curcuma domestica, Curcuma longa), papain (Carica papaya), bromelin (Ananas comosus), etc., are obtained from cultivated edible plant species. Modern biopharming differs from the conventional practices in deploying genetically engineered (GE) transgenic crop plants and domesticated animals. An important advantage in modern biopharming is that vaccines and antibodies can also be produced in crop plants, without using embryonated eggs and cell cultures.
Potential of plants as sources of drugs Several hundreds of important drugs come from plants and a few from animals. Currently, plant component of medicine in the developed countries is about 25 per cent, while in the developing countries it is more than 75 per cent. Biopharming involving transgenic crops can enlarge the diversity and effectiveness of plant based medicine.
Drug development Synthetic organic chemists and pharmaceutical scientists have long realized that creating new chemical structures for the total synthesis of drugs has become very tedious and frustrating. This also involves enormous amounts of time and money, with no assurance of success. The best recourse then is searching for bioactive compounds in organisms, taking leads from indigenous systems of medicine.
Most therapeutically active chemical compounds in organisms are products of complex secondary metabolism called Natural Products, which accumulate in specific organs and do not normally re-enter metabolic cycles. More than a million natural products are known and many have clinically demonstrated therapeutic effects.
With time it became clear that a total synthesis of natural products may be improbable (digioxin), or uncertain in effectiveness (vincristine) or may be too time consuming and expensive (quinine). For example, it took 150 years to synthesize a functional stereo-conformational molecule of quinine. Semi-synthesis of natural products is an alternative as is the case with corticosteroids from steroidal saponins and vincristine from vinblastine. Structural modification of a natural product, as was done with quinine, is also an alternative. However, the problems associated with these methods are neither few nor small. This made the deployment of transgenic crops, with genes for bioactive chemicals from other sources, a very promising means of production of bioactive compounds.
Development of drugs from natural sources requires phytochemical, pharmacological and clinical research on medicinal plants to verify the efficacy of indicated traditional uses, in order to provide new chemical structures for drug development. Such research is also required to build up public confidence and promote global acceptance of medicines from plants.
Ethnopharmacology Ethnopharmacology is the area of scientific validation of traditional uses of medicinal plants. Several South American, Chinese, African and Indian and medicinal plant species were subjected to ethnopharmacological evaluation. Some significant examples are Rauvolfia serpentina, the source of rauvolfine and reserpine, the alkaloids that control hypertension; Picrorrhiza kurrooa, that contains picrorrhizine, an established hepato-protector; Azadirachta indica, the neem tree, which contains over 120 chemicals with anti-viral, anti-microbial and insecticidal properties, and several others.
Anti-cancer drugs from plants A number of anti-cancer plant drugs are in clinical use and available across the counter. The more important species are Catharanthus roseus which provides vincristine, vinblastine and vindesine used against solid and haematological malignancies; species of Taxus, which yield placitaxel, Podophyllum hexandrum, the source of podophyllotoxin, and many others.
Diagnostic chemicals from plants Plants also provide diagnostic chemicals such as lectins that can be used in human and animal blood typing. Horse gram (Macrotyloma uniflorum, Dolichos biflorus) seed lectin is the only means of differentiating blood of human A1 subgroup from A2 subgroup, since there are no antisera for this purpose. Similarly the unusual blood group called the Bombay group can be distinguished only by plant lectins, one of them is from Ulex europeus, a temperate species, now a weed in several tropical hill stations. There are no antisera to distinguish the blood of different animals, where plant lectins are a great help.
Some plant lectins are human tissue specific and help in an early diagnosis of organ specific cancers. Some examples are: ricin, the castor bean (Ricinus communis) lectin, to diagnose cervical cancer; the horse gram lectin to diagnose of lung, prostate and endometrial cancers; pea nut (Arachis hypogaea) lectin for colon cancer; and others.
Cultivation of medicinal plants Over exploitation of medicinal plants dwindled their wild populations in different parts of the world, threatening the very existence of these important species. Cultivation of medicinal plants is necessary for sustainable use and conservation, to supply the required quantity of raw material for the industry and to meet with the large export demand for many species. The export of some species of medicinal plants is now prohibited unless they come from cultivation.
Cultivation of medicinal plants is hampered by several problems. Traditional practices demand that medicinal plants are collected from the wild, from a specific area, in a specific season and at a specific time of the day. Biopharming can overcome these restrictions by controlling gene expression.
Neither all species of medicinal plants nor all areas in any country are suitable for cultivation. Many species are slow growing trees with long life cycles posing serious recycling problems. A famous example is the species of Taxus, which provide placitaxel, where six 100-year old trees are needed to treat one single patient. Enormous qualitative and quantitative chemical diversity occurs in each species, from place to place and season to season. It is necessary to screen and select the right population for cultivation, and develop agronomic practices suitable for each species. Cultivation of medicinal plants makes additional demands on the already restricted arable land. Transgenic crops with incorporated genes for active principles can over come most of these problems through controlled gene expression.
Alternatives to cultivation of medicinal plants There are alternatives to cultivation of medicinal plants, such as callus culture, suspension cell culture and fermentation in bioreactors. However, these procedures require the right starting material, are technically sensitive needing close monitoring and so the products are expensive.
Genetically engineered crop plants in biopharming Established crop plants and domesticated animals as biopharm transgenics facilitate easier and large-scale cultivation and do not require new cultivation protocols. They would also yield abundant quantities of the active principles, and are far cheaper than conventional products.
Functional prototypes of transgenic crops with therapeutic potential Functional prototypes of the following genetically engineered crop varieties with genes for therapeutical products have been developed:
· Transgenic rice: a) b-carotene (Golden Rice), b) human milk proteins, c) higher iron content, d) higher content of zinc, e) low phytic acid and f) high phytase.
· Transgenic potato: a) gene from grain amaranth for high protein content, b) antigens of cholera and diarrhoeal pathogens and c) hepatitis B vaccine.
· Transgenic maize: a) AIDS antigens, b) higher content of lysine and tryptophan and c) nutritive value equivalent to that of milk.
· Transgenic fruits and vegetables: a) Bananas, melons, brinjals and tomatoes with subunit vaccines against Rabies, b) AIDS antigens in tomato and c) human glycoprotein in tomato to inhibit Helicobacter pylorii against ulcers and stomach cancer.
· Transgenic tobacco: a) Human haemoglobin, b) human collagen, c) human antibody against Hepatitis B virus and d) 50 per cent lower nicotine.
· GE coffee: Decaffeinated by gene silencing.
·
Transgenic
livestock: a) Goats and pigs with genes for human tissue plasminogen
activator to prevent thrombosis, b) cows that produce a protein to treat human
cases of melanoma and c) cows and pigs that produce heart-healthy omega-3 fatty
acids. · Transgenic poultry: a) Chicken lines producing human antibodies against Hepatitis B virus and b) complex protein drugs in eggs, in far higher quantities and cheaper than in bioreactors.
These transgenic varieties have to pass through the biosecurity regulatory process before commercial cultivation can be taken up. They will also be evaluated for the safety and efficacy of the therapeutics they produce.
Administration of biotherapeutic products from crop plants Therapeutic compounds from biopharming would have to be extracted from transgenic crops. Most drugs can be administered orally. Several antigens pass through the intestinal barrier into the body system unaffected by the digestive process and can be administered orally like Polio vaccine and Triple antigens. Bioactive products from transgenic plants would be administered as injections, oral drops, in capsules or processed or uncooked food or drink, depending upon the nature of the product.
Vaccines and antibodies through biopharming Vaccine production in the conventional system suffers from several disadvantages and demands large time and financial inputs, limiting the volume of production, resulting in high across the counter costs. With the result, pharmaceutical companies opt more for drugs and not so much for vaccines though the societal value of vaccines is far higher than that of drugs, but the economic value is unattractive. Crop transgenics with vaccines and antibodies have lower entry barriers for manufacture and provide better and purer products. There is no need for the cumbersome and expensive cold chain. There is also no need for needles in many cases and so the demand for skilled professionals is minimized. These products are easier to dispense and result in better compliance in use.
Stability of bioproducts in transgenic crops in storage Proteins, carbohydrates, lipids and the natural products in the seeds of crops keep very well for decades. Hence, drugs, vaccines and antibodies produced in crop plants are expected to keep for very long periods. Antibodies and vaccines are being designed to express in parts of plants that are eaten in the raw condition as cooking process may denature them. These will be consumed within a short time after harvest.
Segregation of biopharm crops from non-pharma crops Kernel Visual Distinguishability (KVD) by colour markers, is an option to distinguish transgenic pharma seed from non-pharma seed. Genes for toxic bioproducts are inserted into non-food crops such as jute, sunn-hemp, flax, tobacco, etc., to facilitate easier segregation and to prevent accidental mix up, in order to avoid the risk to non-target populations.
Biosecurity concerns Biopharm crops would be subjected to the same biosecurity regulatory processes as the respective transgenic non-biopharm crop types. They will also be regulated for the safety and efficacy of the therapeutic products they contain. However, biopharm crops are likely to attract a more severe resistance from anti-tech groups.
Future prospects At the moment biopharming is a concept in development, notwithstanding the prototypes already developed. It would take quite some time before any of these products come on to the market. Nevertheless, biopharming to produce drugs, vaccines and antibodies in crop plants and domesticated animals, in a rapid and inexpensive manner, is a very viable and attractive proposition.
February 25, 2008 |