L-Methionine sulfoximine (MSX) inhibits the activity of glutamine synthetase (GS), an enzyme essential for the production of glutamine. MSX can be used as a media supplement to aid selection and amplification processes in recombinant mammalian cell lines that use GS as a selective marker.
In order to provide customers with a MSX product of known origin and history, SAFC has developed PharmaGrade MSX (Cat No. 76078). PharmaGrade MSX is cGMP/IPEC compliant and offers total supply chain transparency.
In this study, we compare the efficacy of PharmaGrade MSX (Cat No. 76078) with the efficacy of the original Sigma-Aldrich MSX product (Cat No. M5379) by measuring inhibition of GS activity. In order to study the products’ efficacy, two methods were employed. In the first method, two producing CHO clones (that use MSX for selection pressure) were cultured in media supplemented with one of the two MSX products for 4 weeks. The clones were then placed in an assay to determine if both types of MSX were equally effective in preserving productivity after 4 weeks of passage. Growth characteristics during the passage phase of this experiment were recorded to confirm that no cell toxicity (non-specific to GS inhibition) was present with either MSX product. In the second method, a parental cell line, CHO K1, was used.