A clinical-stage biopharmaceutical company wanted a thorough analysis of their process’ 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, LC-MS analysis identified one HCP impurity, as can be seen in the table below.
The specific HCP detected by LC-MS – but missed by ELISA – 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, and it can thus affect protein activity and cellular location.
How the client used the LC-MS data
The client wanted to do a risk assessment of discovered and documented ubiquitin in their drug substance with the LC-MS data. During their risk assessment, they found that you also find this common HCP in many other mAb products.
It is still uncertain if they can or should reduce the ubiquitin level further. However, now the client knows the absolute quantity of this specific HCP and can monitor the ubiquitin levels from batch to batch.