Commercial production of therapeutic proteins using mammalian cells
requires complex process solutions, and consistency of these process
solutions is critical to maintaining product titer and quality between
batches. Inconsistencies between process solutions prepared at bench and
commercial scale may be due to differences in mixing time, temperature,
and pH which can lead to precipitation and subsequent removal via
filtration of critical solution components such as trace metals.
Pourbaix diagrams provide a useful tool to model the solubility of trace
metals and were applied to troubleshoot the scale-up of nutrient feed
preparation after inconsistencies in product titer were observed between
bench- and manufacturing-scale batches. Pourbaix diagrams modeled the
solubility of key metals in solution at various stages of the nutrient
feed preparation and identified copper precipitation as the likely root
cause of inconsistent media stability at commercial scale. Copper
precipitation increased proportionally with temperature in bench-scale
preparations of nutrient feed and temperature was identified as the root
cause of copper precipitation at the commercial scale. Additionally,
cell culture copper titration studies performed in bench-scale
bioreactors linked copper-deficient mammalian cell culture to
inconsistent titers at the commercial scale. Pourbaix diagrams can
predict when trace metals are at risk of precipitating and can be used
to mitigate risk during the scale-up of complex media preparations.