M.malarkodi,nagamani.n.k, S.khaja Indar, Sowmya Jois asked:




Proteins of therapeutic importance, like those used in the treatment, diagnosis of human diseases; can be produced in plants using recombinant DNA technology. Scaling-up of these transgenic plants to fields results in industrial production of proteins. The area of research combining molecular biotechnology and agriculture is called ‘molecular farming’ or ‘pharming’. It focuses on developing practical and feasible methods of producing recombinant proteins which are used in the treatment, diagnosis of number of human diseases. Recombinant therapeutic drugs like- human erythropoietin, tissue plasminogen activator, cerezyme are currently on the market and many others are in various stages of human clinical trials.

The use of transgenic animal cell lines and microorganisms (e.coli) are still preferred in production of recombinant pharmaceutical proteins. However, the constantly increasing demand for therapeutic proteins has forced to think of other alternatives. Here transgenic plants become attractive systems for production of human therapeutic proteins because of the reduced risk of mammalian viral contaminants, eukaryotic protein processing, low cost productions, large scale production and supply, reduced time to market and the low maintenance requirements. Plant-based strategies also have advantages in the speed and ease at which the feasibility testing and scaling-up to fields can be done.

Many recombinants proteins produced in plants are ideal for laboratory experiments

like tobacco or Arabidopsis thaliana. However, molecular pharming moves towards commercialization of the recombinant products. Thus many issues are considered like selecting host species, selecting the target tissue in which the proteins would accumulate, expression strategies to ensure amplification of the product, down stream processing procedures like extraction and purification, all these however, depends on the protein desired and the state (soluble, secretary) at which it is required.

To achieve specific protein in plants, the DNA encoding the particular protein is inserted into the plant cells so as to enable transformation. Two major strategies have been developed for efficient transformation of the desired gene- stable integration of the gene and use of plant viruses as transient vectors. Stable integration occurs when foreign DNA is incorporated into the plant genome, a promoter associated with it directs the cell to produce that protein and accumulate it only in specific tissues like seeds. Viruses are used alternatively for direct expression of specific proteins without genetically modifying the host plant. The transformation and expression systems used to engineer these proteins in plants contributes to the stability, yield, cost of purification, and quality of the proteins

The proteins produced in transgenic plants for therapeutic use, are of three main types-antibodies, vaccines, other proteins: Antibodies directed against dental caries, rheumatoid arthritis, cholera, E.coli diarrhea, malaria, certain cancers, Norwalk virus, HIV, rhinovirus, influenza, hepatitis B virus, and herpes simplex virus are known to be produced in transgenic plants. Some of these demonstrating therapeutic values are currently on clinical trials. One of the most advanced products is an anti-streptococcus mutans secretary antibody for the prevention of dental caries. Proteins antigens from various pathogens have been expressed in plants and used as vaccines to produce immune responses resulting in protection against diseases in humans. Plant-derived vaccines against Vibrio cholera, enterotoxigenic E.coli, hepatitis B virus, rabies virus, and rotavirus have been produced. Antigens specific to an individual patient’s tumor are expressed in tobacco, harvested, purified and administered into the patient. This is virus-based system in tobacco to produce personalized vaccines against cancer; the entire process takes as little as four weeks. Edible vaccines enabling oral delivery of the vaccines within foods are also successful as a low-cost delivery mechanism for immunizations against various diseases especially in developing countries. Edible vaccines are known to have successfully immunized test animals against enterotoxigenic E.col, Vibrio cholerae, hepatitis B virus, Norwalk virus, rabies virus, respiratory syncytial virus F and rotavirus. Edible vaccines productions are tested in potatoes, watermelon, squash, tomatoes, bananas, and carrots. Plants are being tested as production systems for a range of other proteins which are of therapeutic importance to be used either directly in foods or after purification like- trichosanthin: inhibits tumor growth, glucocerebrosidase enzyme: deficiency of which results in an inherited Gaucher’s disease, human serum albumin: used in treatment of burns and in liver cirrhosis.

A wide range of therapeutic proteins have been expressed in transgenic plants in the hope of producing an economically viable system for large-scale production. Although active recombinant proteins have been produced, one problem associated with production in plant systems is that these often give relatively low yield upon recovery of product. Various strategies are being devised to overcome this problem, use of novel purification systems and chloroplast transformations being the foremost among them. Despite these difficulties, plants hold out great promise as production systems for therapeutic proteins.

Thus advancement in plant molecular biotechnology does not only help farmers to obtain a more than adequate harvest from the sown crops, but also in producing proteins of therapeutic importance in transgenic plants. The last decade has seen a dramatic progress in plant biotechnology, leading to the development of molecular farming. The scientific community is positive that the next decade will see products approved as pharmaceuticals; with this the molecular farming will finally come of age.

 

 

REFERENCES:

1. Paul Christou and Harry Klee, editors-in-chief, handbook of Plant biotechnology, volume 2.

2. J. Hammond, P. McGarvey and V.Yusbov (Editions), Plant biotechnology- New products and applications.

3. Bruce R. Thomas, Allen Van Deynze, Kent J. Braford, Agricultural biotechnology in California series, ANR Publications, title of the article “Production of Therapeutic Proteins in Plants”, anrcatalog.ucdavis.edu/pdf/8078.pdf.

4. S.S. Purohit, Third edition, Biotechnology: Fundamentals and Applications.



 

 



CHREST