On-line monitoring of responses to nutrient feed additions by multi-frequency permittivity measurements in fed-batch cultivations of CHO cells

Abstract

Changes in the nutrient availability of mammalian cell cultures are reflected in the beta-dispersion parameter characteristic frequency (f ( C )) and the on-line dual frequency permittivity signal. Multi-frequency permittivity measurements were therefore evaluated in fed-batch cultivations of two different CHO cell lines. Similar responses to nutrient depletions and discontinuous feed additions were monitored in different cultivation phases and experimental setups. Sudden increases in permittivity and f ( C ) occurred when feed additions were conducted. A constant or declining permittivity value in combination with a decrease in f ( C ) indicated nutrient limitations. f ( C ) correlated well with changes in oxygen uptake rate when cell diameter remained constant, indicating that metabolic activity is reflected in the value of f ( C ). When significant cell size changes occurred during the cultivations, the analysis of the beta-dispersion parameters was rendered complex. For the application of our findings in other systems it will be hence required to conduct additional off-line measurements. Based on these results, it is hypothesized that multi-frequency permittivity measurements can give information on the intracellular or physiological state in fed-batch mode. Similar observations were made when using different cell lines and feeding strategies, indicating that the findings are transferable to other cell lines and systems. The results should lead to an improved understanding of routine fed-batch processes. Additional studies are, however, required to explore how these observations can be used for fed-batch process development and optimization.

Fig. 1

Fed-batch cultivation of cell line CHO I in pilot scale. Feed additions are marked by vertical dashed lines and divide the cultivation in phases FB I–IV. a permittivity and metabolite concentrations. b viability and cell counts (hema). c off-line biovolume (CASY, PCV)/cell size (CASY) measurements. d β-dispersion parameters

Fig. 2

Fed-batch lab scale cultivation of CHO II. Feed additions are marked by vertical arrows and divide cultivation in phases FB I–X. a permittivity and cell counts (hema). b biovolume measurements and cell diameter. c β-dispersion parameters and product concentration; product concentration. increased linearly over time from FB II-FB X: conc (mAb(ProSep A)) = 0.31 × −8.7, R₂ = 0.997 (regression not shown in figure)

Fig. 3

On-line measurements until 200 h of fed-batch cultivation with cell line CHO II (graph presents data for same cultivation also shown in Fig. 2)