Immunotoxin sensitivity of Chinese hamster ovary cells expressing human transferrin receptors with differing internalization rates

 Previous studies have shown that immunotoxin action is dependent upon selective binding to the target cell, internalization and then passage into the cytosol. It is important to define precisely how these critical steps are controlled so that the underlying relationship of each to high cytotoxic effectiveness is understood. In order to evaluate the contribution of internalization rate and receptor number on immunotoxin potency, the effects of an anti-(transferrin receptor, TfR)/ricin A chain immunotoxin, 7D3-A, were assessed on a parent Chinese hamster ovary cell line developed in our laboratory with no TfR (TfR^neg) and two lines transfected with either wild-type TfR (Tfr^wt) or an internalization-deficient (TfR^{δ7 – 58del}) mutated human TfR. Potent, receptor-mediated cytotoxicity resulted from the action of 7D3-A on TfR^wt cells (ID₅₀<1 nM) while both TfR^neg cells and TfR^{δ7 – 58del} were only minimally affected (ID₅₀>100 nM). Butyrate up-regulation substantially increased receptor expression on the TfR^wt and TfR^{δ7 – 58del} cells, but no corresponding rise in sensitivity to 7D3-A was observed. In contrast, immunotoxin potency was increased by co-treatment of TfR^wt cells with the carboxylic ionophore monensin and the effect was even more pronounced for TfR^{δ7 – 58del} cells. We conclude that internalization rate or intracellular destination is a much more important determinant of immunotoxin efficacy than receptor number. Received: 15 March 1996 / Accepted: 28 May 1996     

Development of a mathematical model for evaluating the dynamics of normal and apoptotic Chinese hamster ovary cells

A metabolic flux based methodology was developed for modeling the metabolism of a Chinese hamster ovary cell line. The elimination of insignificant fluxes resulted in a simplified metabolic network which was the basis for modeling the significant metabolites. Employing kinetic rate expressions for growing and non-growing subpopulations, a logistic model was developed for cell growth and dynamic models were formulated to describe culture composition and monoclonal antibody (MAb) secretion. The model was validated for a range of nutrient concentrations. Good agreement was obtained between model predictions and experimental data. The ultimate goal of this study is to establish a comprehensive dynamic model which may be used for model-based optimization of the cell culture for MAb production in both batch and fed-batch systems.     

Systematic development of temperature shift strategies for Chinese hamster ovary cells based on short duration cultures and kinetic modeling

Temperature shift (TS) to a hypothermic condition has been widely used during protein production processes that use Chinese hamster ovary (CHO) cells. The effect of temperature on cell growth, metabolites, protein titer and quality depends on cell line, product, and other bioreactor conditions. Due to the large numbers of experiments, which typically last 2–3 weeks each, limited systematic TS studies have been reported with multiple shift temperatures and steps at different times. Here, we systematically studied the effect of temperature on cell culture performance for the production of two monoclonal antibodies by industrial GS and DG44 CHO cell lines. Three 2–8 day short-duration methods were developed and validated for researching the effect of many different temperatures on CHO cell culture and quality attributes. We found that minor temperature differences (1–1.5 °C) affected cell culture performance. The kinetic parameters extracted from the short duration data were subsequently used to compute and predict cell culture performance in extended duration of 10–14 days with multiple TS conditions for both CHO cell lines. These short-duration culture methods with kinetic modeling tools may be used for effective TS optimization to achieve the best profiles for cell growth, metabolites, titer and quality attributes. Although only three short-duration methods were developed with two CHO cell lines, similar short-duration methods with kinetic modeling may be applied for different hosts, including both microbial and other mammalian cells.