Production And Purification

Typically, the biotechnology-based pharmaceuticals are proteins. Therapeutic proteins are available from a number of different sources, for example, animal tissues, plants, microorganisms, and cell culture systems. However, most commercially available therapeutic proteins are produced by large-scale fermentation using either recombinant microorganisms or mammalian cells as sources. In contrast to extraction from, for example, animal material, one of the advantages of recombinant technology is the possibility of producing pure substances in large quantities. In addition, recombinant technology makes it possible to produce substances that previously were impossible to produce in sufficient quantities. Another advantage of recombinant technology is the possibility to introduce chemical modifications to alter the physicochemical or pharmacokinetic characteristics of a protein to improve the stability or the therapeutic effect. This will be exemplified later. To clone a DNA molecule, it must be introduced into a host cell, where it is allowed to be replicated. This amplification of the original DNA sequence enables the production of proteins by large-scale fermentation.

The proteins obtained by fermentation are either secreted by the host cells into the culture medium or maintained intracellularly. In the subsequent downstream processing, extracellular proteins are normally much simpler to purify than intracellular proteins, as there is no requirement to disrupt the cells to harvest the protein. The protein product is present—often in low concentrations—in a crude, very complex mixture of cell fragments including subcellular components as well as a vast number of other cellular proteins. Compared to microbial sources, mammalian cell cultures; for example, Chinese hamster ovary (CHO) cells are generally more complex production systems, since various supplements, such as serum, often have to be added to the culture media in addition to the nutritional requirements. Addition of serum increases the risk of contamination of the final bulk protein with blood-borne pathogens. However, for a number of therapeutic proteins, mammalian cells are the cell system of choice since mammalian cells, unlike microorganisms, are capable of conducting important posttranslational reactions such as glycosylation.

The challenge for the bulk production of pharmaceutical proteins lies in the development of a purification process to isolate the protein of interest to obtain a highly purified and properly folded protein, which is a prerequisite for making a safe and therapeutic efficient medicine of optimal quality. A typical overall purification process is outlined in Figure 1.

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