Creating a New Medium to Help Meet the Variable Nutritional Requirements of Chinese Hamster Ovary (CHO) Cell Clones

It is widely known that different recombinant protein expressing Chinese Hamster Ovary (CHO) cell clones can have variable nutritional requirements. Sigma-Aldrich has previously developed an Animal-Component Free Medium (CHO-AF, Product Code C5467) that for many CHO clones yields excellent growth and productivity. However, with some CHO clones it yields less than optimal performance. Therefore the need has arisen to create a second-generation medium that will complement CHO-AF. The Dihydrofolate Reductase (DHFR) gene amplification system has become very popular for use in CHO clones. The DHFR system allows the gene of interest to be amplified with increasing concentration of methotrexate, leading to increased protein expression. The recombinant cell lines used in the optimization of this new medium were all DHFR clones expressing a variety of protein products, including a rIgG and rhM-CSF. Each cell line poses a unique challenge, as demonstrated by the differences in amino acid utilization rates. Based on cell growth, r-protein production, and the amino acid consumption rates, CHO DHFR-Medium (Product Code C8862), was developed. The base formulation for CHO DHFR- was very different from that of CHO-AF, allowing for the development of a complementary animal-component free medium. Experiments have shown that CHO DHFR- promotes better growth and protein production than CHO-AF with many CHO clones, but there are still other cases where using CHO-AF is advantageous. The development of this new medium resulted in growth and recombinant protein production rates surpassing that of other commercially available media. Finally, the application of these two CHO animal-component free media in spinner flasks and 5-L bioreactors is discussed.