Process characterization of the chromatographic steps in the purification process of a recombinant Escherichia coli-expressed protein.

Process development and characterization studies were performed for the chromatographic steps in the purification process of a recombinant Escherichia coli -expressed protein product candidate. The objective of this work was to develop a robust and efficient purification process that would generate material of adequate purity and quantity. A resin screening procedure was developed to aid in picking out the optimal resin for each of the chromatographic columns. It was found that, as a result of resin screening, it was possible to come up with a process with only two column-chromatographic steps. The resulting process used a sulphopropyl (SP) and a quaternary amino (Q) column with intermittent ultrafiltration steps for purification. Effects of different process parameters such as the gradient slope, pH, flow velocity and protein loading on the column performance were evaluated. Buffer pH for the SP column, and buffer pH, gradient slope, protein loading and flow velocity for the Q column, were identified as parameters that could have a significant impact on the performance of the chromatographic step and would require further characterization to improve the robustness of the process. Further process characterization led to the findings that the gradient slope, load pH and buffer pH of the Q column have a significant impact on column performance (>15% change in step yield). All other parameters under consideration did not have any significant impact on pool quality (>10% change in pool purity for the SP column and >5% for the Q column). On the basis of small-scale studies, optimum operating conditions were chosen and the purification process was successfully scaled-up to a large-scale robust process with step yields and product quality that were better than those at the small scale.