SOURCES OF BIOPHARMACEUTICALS

The bulk of biopharmaceuticals currently on the market are produced by genetic engineering using various recombinant expression systems. While a wide range of potential protein production systems are available, most of the recombinant proteins that have gained marketing approval to date are produced either in recombinant Eschericia coli or in recombinant mammalian cell lines. Such recombinant systems are invariably constructed by the introduction of a gene or cDNA coding for the protein of interest into a well-characterized strain of the chosen producer cell. Examples include E. coli K12 and Chinese hamster ovary strain K1 (CHO-K1). Gene/cDNA transfer is normally achieved by using an appropriate expression plasmid, or other standard gene-manipulating techniques. Each recombinant production system displays its own unique set of advantages and disadvantages.

Many microorganisms represent attractive potential production systems for therapeutic proteins. They can usually be cultured in large quantities, inexpensively and in a short time, by standard methods of fermentation. Production facilities can be constructed in any world region, and the scale of production can be varied as required. The expression of recombinant proteins in cells in which they do not naturally occur is termed ‘heterologous protein production’. By far the most common microbial species used to produce heterologous proteins of therapeutic interest is Eschericia coli. The first biopharmaceutical produced by genetic engineering to gain marketing approval (in 1982) was recombinant human insulin (trade name Humulin), produced in E. Coli.

Technical advances facilitating genetic manipulation of animal cells now allow routine production of therapeutic proteins in such systems. The major advantage of these systems is their ability to carry out post-translational modification of the protein product. As a result, many biopharmaceuticals that are naturally glycosylated are now produced in animal cell lines. Chinese hamster ovary (CHO) and baby hamster kidney (BHK) cells have become particularly popular in this regard.

Attention has also focused upon a variety of additional production systems for recombinant biopharmaceuticals. Yeast cells (particularly Saccharomyces cerevisiae) display a number of characteristics that make them attractive in this regard.

Fungi have elicited interest as heterologous protein producers, as many have a long history of use in the production of various industrial enzymes, such as a-amylase and glucoamylase. Suitable fermentation technology therefore already exists. In general, fungi are capable of high-level expression of various proteins, many of which they secrete into their extracellular media. The extracellular production of a biopharmaceutical would be distinctly advantageous in terms of subsequent downstream processing.

The production of heterologous proteins in transgenic animals has gained much attention in the recent past. The generation of transgenic animals is most often undertaken by directly microinjecting exogenous DNA into an egg cell. In some instances, this DNA will be stably integrated into the genetic complement of the cell. After fertilization, the ova may be implanted into a surrogate mother. Each cell of the resultant transgenic animal will harbour a copy of the transferred DNA. As this includes the animal’s germ cells, the novel genetic information introduced can be passed on from one generation to the next.

The production of pharmaceutical proteins using transgenic plants has also gained some attention over the last decade.

A wide range of proteins have been produced at laboratory scale in recombinant insect cell culture systems. The approach generally entails the infection of cultured insect cells with an engineered baculovirus (a viral family that naturally infects insects) carrying the gene coding for the desired protein, placed under the influence of a powerful viral promoter.

Answer the questions.

1. What does it mean "recombinant production system"?

2. When was the first biopharmaceutical produced by genetic engineering? What it was?

3. What awake interest in the production of various industrial enzymes?

4. How can the genetic information be passed?

5. What is an engineered baculovirus?