Development and optimization of growth media, feed solutions, and feed strategies is a complex project. More than 200 components (amino acids, trace metals, vitamins, growth factors, carbon sources, etc.) can be found in various commercial growth media formulations. A typical cell culture medium formulation may contain 50 to 60 individual components. Some of these may be critical for cell growth or productivity, others may be toxic at certain levels, and many may be involved in complex interactions in the same or competing pathways within the cell. Media and feed components typically are screened individually or in small combinations in shake flasks, in experiments of a few dozen shake flasks in parallel. This method significantly limits the ability to discover complex interactions among medium components.
EXPERIMENTAL APPROACHA recombinant CHO cell line engineered to express a proprietary antibody was provided by an outside party. Cells were grown in a commercial serum-free medium with L-glutamine and insulin. Cell cultures were grown at 37°C with 5% CO2. Initially, optimal conditions were determined for the growth of CHO cells in a shaker plate model system, and it was shown that cell growth was comparable to shake flasks. A high-throughput liquid handler was used to deliver the samples to the shaker plates according to the combinations derived from a design of experiments software program. For this study, 23 amino acids and derivatives, 4 carbon sources, 10 hydrolysates, 8 lipid solutions, 21 salts, 7 trace metals, 18 vitamin solutions, and 9 other components were prepared in the serum-free medium (without L-glutamine or insulin); pH was adjusted to 7.2 ± 0.2.
Cell count and the viability of cultures in flasks were determined using trypan blue exclusion dye. Viable cell counts for the cultures in the shaker plate system were determined using a high-throughput plate-based imaging method in which a fluorescent viability stain was added, and plates were incubated and scanned using a high-throughput fluorescent microscope. Protein concentration was determined using a bead-based enzyme-linked immunosorbent assay (ELISA)-style immuno-competition assay. Streptavadin beads were prepared with a biotinylated anti-immunoglobulin G (IgG) antibody. Unknowns were competed against a Cy5-labeled IgG and read against an antibody standard.