A client wanted a thorough analysis of their process’s ability to remove Host Cell Proteins (HCPs) from their CHO-expressed monoclonal antibody (mAb). Even though their HCP-ELISA reported no detectable HCPs in the purified drug substance, SWATH® LC-MS identified one HCP impurity.
The specific HCP was ubiquitin. Ubiquitin is a protein that sticks to protein substrates through ubiquitination, and it is a prevalent posttranslational modification. Ubiquitination marks other proteins for degradation via the proteasome pathway. It can thus affect protein activity and cellular location.
How the client used the LC-MS data
The client discovered and documented ubiquitin in their drug substance with the LC-MS data. They also found out that it is a common HCP in other mAb products. It is still uncertain if they can or should reduce it further. However, now they know the absolute quantity of this specific HCP and can monitor the ubiquitin levels from batch to batch.