ABSTRACT
Eden Biodesign Ltd.
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Media compositions used for cultivating recombinant cell lines not only directly influence the cells' physiological phenotype
and fermentation performance, and quality of the expressed product, but the development of novel media formulations also provide
a mechanism of generating manufacturing intellectual property for a particular product. Biopharmaceutical companies and media
suppliers are therefore recognizing the strategic importance of continued investment in the development of novel media formulations.
Historically, raw materials involved in the production of biologics have included complex animal-derived components. Although
a decade has passed since cases of bovine spongiform encephalopathy and the resulting transmissible spongiform encephalopathies
were reported, their association with raw materials is still a major concern. Establishing a well-defined media formulation
containing no animal-derived components is the ultimate aim for most biopharmaceutical companies. There are now well researched,
chemically defined alternatives available that promise to meet these goals.
In recent years, a market surge in biopharmaceuticals has warranted extensive research and development in advanced cell culturing
techniques and subsequent methods of optimizing bioprocesses. Media development is one of the most critical stages in biopharmaceutical
manufacturing. Indeed media components have such a strong impact, they can account for up to 30% of the total production cost.1 This area of development offers the potential to dramatically improve yield and quality of the expressed product.2
The ideal cell culture medium, whether for use in mammalian or microbial systems, is one that provides process consistency,
robustness, and batch-to-batch reproducibility. Essentially, a raw material must meet most, if not all, criteria listed below.3
- It will produce maximum product yield or biomass per gram of substrate used.
- It will produce the maximum product concentration or biomass.
- It will permit the maximum rate of product formation.
- There will be a minimum yield of undesired products.
- It will be of a consistent quality and be readily available throughout the year.
- It will cause minimal problems during media preparation and sterilization.
- It will cause minimal problems during other steps of the production process, particularly fermentation, extraction, purification,
and waste treatment.
For many years, economic constraints have dictated media composition. This has led to the widespread use of complex, readily
available raw materials, making large-scale fermentations reliant on cheap sources of carbon and nitrogen, which are often
by-products of other industries such as corn steep liquor from the corn-starch industry and beet molasses from the sugar industry.
Combining such complex components with animal-derived hydrolysates has increased the scope of product manufacture, creating
high yielding processes at minimal costs. The abundance of biosynthetic precursors and growth-promoting agents make complex
media the composition of choice, primarily because they accelerate growth and enhance productivity. Complex raw materials
usually are derived from animal-sourced processes, such as hydrolysed peptones and sera. They also may be non-animal–derived,
such as the by-products beet molasses and corn steep liquor. They can contain numerous individual components, some of which
are semi-characterized and many more are uncharacterized. In many cases, biomass yields are greater with complex and semi-defined
media than with chemically defined media. However, data from physiological studies is more difficult to interpret and can
be clouded or influenced by many intrinsic parameters.
Growth precursors found in such complex components may be channelled directly into anabolic pathways, thus saving metabolic
energy.4 This offers an immediate advantage in terms of culture metabolism but ultimately makes process definition and development
problematic.
Fermentations using complex media have worked successfully for many years, and strain selection is often based around current
media and cultivation conditions. Media development, however, is largely empirical, with little research into defining such
raw materials. For example, a modified strain of the yeast Saccharomyces cerevisiae, which had been labelled the ultimate solution to lignocellulose-derived xylose, was found to require yeast extract, additional
hexose sugar, and oxygenation,5 thus making growth in a chemically defined media difficult without intensive investigation. Therefore, the final industrial
environment must be considered to prevent unanticipated costs at later stages. Both S. cerevisiae and Escherichia coli have extensive biosynthetic capacity and can grow well in defined media. In contrast, the biosynthetic capacity of many lactic
acid bacteria are limited and they require complex or extensively supplemented media for efficient growth.6
The quest for increased productivity combined with patient safety has encouraged biopharmaceutical companies to invest more
time and money into their processes and for raw material suppliers to explore new chemically defined versions of media.
