When working on biotherapeutic process development, the analysis of spent cell culture media is often a daily practice during the optimization of bioreactor conditions and media composition. The introduction of parallel microbioreactor systems has decreased the complexity and costs of process development by allowing for concurrent studies of multiple bioreactor and media variables. However, the bioreactors’ small volumes (typically less than 250 mL) limit the volume of media one can extract for daily sampling. We describe a means to analyze spent media with an integrated microchip capillary electrophoresis mass spectrometer (CE-MS) analyzer with minimal sample volume requirements and rapid analysis time. The platform was evaluated with a parallel microbioreactor system (ambr® 250) culturing a Chinese hamster ovary (CHO) cell line stressed by varying levels of ammonia (NH3).
The spent media analysis identified net increases in the levels of the amino acids (AA) Ala, Arg, Asp, Glu, Gly, His, Ile, Leu, Lys, Phe, Thr, Trp, Tyr, and Val in all bioreactors, with Gly levels showing increases in excess of 8-fold initial levels in all bioreactors. Other media components either steadily decreased in concentration or were completely depleted by the end of culture. For example, Asn was depleted in all of the unstressed and 10 mM NH3-stressed bioreactors, but was approximately twice as high as the initial levels in the 30 mM NH3-stressed bioreactors at the end of the culture periods. Also, the 30 mM NH3-stressed condition may have caused either complete degradation or rapid consumption of choline, since it was no longer present starting at the t = 36 h sampling. Overall, the monitored media components were observed to have independent trajectories based on feeding and consumption by the cells, and depending on the stressed condition. The capability to have more frequent spent media analyses would allow for real-time observation of these process changes and associated control strategies.