PROCESS PERFORMANCE AND MEDIA COMPONENTS INTERACTION
The initial cause for the shift away from serum in cell-culture processes was because of its complexity and ill-defined composition.
Manufacturers had to struggle with inconsistent process performance, which ultimately affected product quality.
The development of CDM containing complex component formulations has meant cell viability, cell growth, and good product titer
can be maintained without the use of serum. CDM provides many benefits for the manufacture of biotherapeutics, not the least
of which are regulatory compliance, simplified downstream processing, and consistency of both processes and products. Although
CDM can be costly, these performance benefits are important in driving improved manufacturing processes and therefore drug-development
costs down.
As the understanding for specific nutrient requirements for various production cell lines increases, media formulations are
being developed to achieve optimal performance. To enhance culture performance, CDM is often supplemented with defined feeds
and supplements at predetermined stages in the growth and productivity cycle. However, optimization of these strategies can
be time-consuming and success of this strategy is often dependant on the basal medium formulation.
Hydrolysates, a common cell culture supplement and feed, share a number of components with CDM. The additional availability
of these common media components to the cell can have an additive effect, stimulating cell growth and productivity. Alternatively,
the additive effect may have a negative impact on cell performance as a result of unintentional overdosing of certain components.
Figure 3: Supplementing two commercial chemially defined media (CDM) at 100% and 80% strength with 8g/L cotton seed hydrolysate
(CSH) resulted in enhanced Chinese hamster ovary (CHO) cell viability (a and c) and productivity (b and d).
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To demonstrate the interaction of basal media components and supplements on biological systems, CHOK1 cells expressing a recombinant
protein, were cultured in two independently sourced CDM at full strength and 80% strength, either alone or supplemented with
plant-derived protein hydrolysate. The results showed supplementation of chemically defined media with plant-derived protein
hydrolysates affected cell culture performance in a medium-dependent manner. Interestingly, supplementation with hydrolysate
of diluted CDM achieved equivalent or enhanced cell culture performance compared with full strength supplemented CDM (see
Figure 3).
COMBINATIONS OF SUPPLEMENTS AND CELL GROWTH
Cell culture media for the production of biologicals are becoming more complex. As described above, the addition of media
feeds and supplements to enhance cell culture performance must be carefully matched with the basal media because of component
interactions.
With the nutritional requirements for individual production cell lines and clones becoming better understood, the response
to culture media and supplements must be examined in a case-by-case basis. With the implementation of design of experiment
and high throughput screening of media components it is becoming increasingly possible to design and optimize supplements
and feeding strategies that address the specific nutrient requirements for each cell line and clone.
Figure 4: Addition of the yeast extract and human serum albumin (HSA) supplements both alone and in combination enhanced total
Chinese hamster ovary (CHO) cell density, which significantly affected product titer.
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Addition of certain supplements in combination has recently been shown to have a positive effect on specific cell growth and
productivity. An example of cell culture supplement interaction having a positive effect of cell performance has been observed
when ultrafiltered yeast extract and recombinant human serum albumin (rHSA) were co-supplemented in CHO CDM. The ultrafiltered
yeast extract, a consistent animal-free hydrolysate, at 1 g/L in combination with rHSA 1 g/L were shown to have a positive
effect on growth and productivity when added alone compared with the CDM control. Moreover, when these supplements were added
in combination, a synergistic response was observed for both CHO cell growth and productivity (see Figure 4).
Figure 5: Chinese hamster ovary (CHO) cell response to supplementing with yeast extract (YE) was shown to be dependant on
background media. In contrast, cell performance was consistently improved when supplementing with the optimized dosage of
yeast extract (YE) and human serum albumin (HSA). CDM is chemically defined medium.
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Interaction of media components and the importance of optimizing supplement and feed addition according to the basal or platform
media employed were further investigated. A single CHO clone was tested in two independent CDM supplemented with a range of
concentrations of ultrafiltered yeast hydrolysate and an optimized dosage of ultrafiltered yeast hydrolysate (YE) and rHSA.
In CDM–A, CHO cell growth decreased with increasing hydrolysate concentration while product titer and specific productivity
(Qp) increased. The optimized combination of YE and rHSA demonstrated the greatest overall performance benefit (see Figures
5a and 5b). In contrast, addition of YE alone in CDM–B had little effect on the already poor cell growth. In the presence
of the combination of YE and rHSA, however, CHO cell growth displayed rates comparable to that of CDM–A. The combination of
supplements again delivered best overall performance with respect to CHO cell growth and productivity (see Figures 5c and
5d).
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