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Cell productivity in fed-batch processes can be increased by cell cycle arrest through mild hypothermia. However, hypothermia can simultaneously reduce cell growth, which is regulated by the cell cycle. Consequently, the time point for the temperature shift is important and requires optimization while considering the cell cycle. An unstructured cell cycle model which includes the distribution of proliferating (G1, S, G2/M) and arrested cells (G0) has been proposed in order to predict the time point of temperature shift in fed-batch cultures. A model development and analysis framework that enables the evaluation of the required model parameters is described. The parameters are estimated from (fed)-batch cultivations, carried out at 37 °C and at 33 °C in order to characterize temperature dependency. The batch cultures are also used to evaluate substrate depletion and fed-batch cultures are used to study the impact of metabolite accumulation on the cell cycle. The reliability of the proposed framework for parameter estimation is validated using a mAb-producing hybridoma cell culture and the model predicts hypothermic transitions within the cell population at different shift time points. In conclusion, this framework can be used to optimize the time point of the temperature shift, which is commonly adjusted in industrial fed-batch processes in order to obtain a good balance between temperature induced growth limitation and cell cycle specific enhanced productivity.

Background Large scale mammalian cell culture systems, especially fed-batch systems, are currently utilised to manufacture monoclonal antibodies (MAbs) in order to meet the continuously growing global demand [1]. Nutrient deprivation and toxic metabolite accumulation commonly encountered in such systems influence the cell cycle and trigger apoptosis, resulting in shorter culture times and a lower final MAb titre. Control of the cell cycle has been previously studied in order to achieve higher titre through apoptosis inhibition by bcl-2 overexpression and cell cycle arrest in G1/G0 by p21 transfection. However, the above mentioned strategies have not always been successful; no improvement in titre was often observed though bcl-2 over-expression helped prolong the culture viability whereby the majority of cells were arrested at G1/G0 to avoid apoptosis [2-4]. Thus, a systematic insight of the dynamic relation between metabolic stress, cell cycle and apoptosis is still required. To this end, we aim to establish a novel map of the dynamic interplay between cell cycle and apoptosis at the genetic level, and provide a link with the culture conditions at the metabolic level.