Measurement of High Protein Concentrations by Optical Rotation: A Case Study for Monitoring of Monoclonal Antibody Drug Downstream Processes

Background: Recent advancements in cell engineering and bioreactor engineering have enabled high monoclonal antibody (mAb) concentrations in harvested solutions for the downstream process (DSP). Methods: As many unit operations such as capture chromatography, polish chromatography, membrane filtration, virus inactivation, virus filtration, and concentration by ultrafiltration are involved in DSP, it is crucial to monitor the process carefully in order to perform reliable and stable DSP operations. One of the most important signals (process parameter) to be monitored is the protein concentration CP. Although various methods are available, most of them are not suited for measuring high CP. In this paper, we have developed a method for measuring very high CP by optical rotation (OR). Result: Linear correlations were confirmed between OR and Cp in the range CP = 0 to 80 g/L for mAbs with high repeatability and small variation coefficients. This method was applied to the monitoring of CP in the opaque (colored) solution during the cell culture. The CP by OR was in good agreement with those by the standard Protein A HPLC method. Conclusion: Monitoring of high CP by OR is expected to be an efficient process analytical tool (PAT) for DSP.