Ion exchange chromatography (IEX) is a historical technique widely used for the detailed characterization of therapeutic proteins and can be considered as a reference and powerful technique for the qualitative and quantitative evaluation of charge variants. When applying salt gradient IEX approach for mono-clonal antibodies (mAbs) characterization, this approach is described as time-consuming to develop and product-specific. The goal of this study was to tackle these two bottle-necks. The optimization was performed by computer simulation using DryLab modeling software and a custom made model.

By modeling the retention of several commercial mAbs and their variants in IEX, we proved that the mobile phase temperature was not relevant for tuning selectivity, while optimal salt gradient program can be easily found based on only two initial gradients of different slopes. Last but not least, the dependence of retention vs. pH being polynomial, three initial runs at different pH were required to optimize mobile phase pH. Finally, only 9 h of initial experiments were necessary to simultaneously optimize salt gradient profile and pH in IEX. The data can then be treated with commercial modeling software to find out the optimal conditions to be used, and accuracy of retention times prediction was excellent (less than 1% variation between predicted and experimental values).

Second, we also proved that generic IEX conditions can be applied for the characterization of mAbs possessing a wide range of pI, from 6.7 to 9.1. For this purpose, a strong cation exchange column has to be employed at a pH below 6 and using a proportion of NaCl up to 0.2 M. Under these conditions, all the mAbs were properly eluted from the column. Therefore, salt gradient CEX can be considered as a generic multi-product approach.

The cation exhange pH gradient approach was evaluated for the characterization of 10 model monoclonal antibodies including panitumumab, natalizumab, cetuximab, bevacizumab, trastuzumab, rituximab, palivizumab, adalimumab, denosumab and ofatumumab.

This work shows that retention and resolution can be modelled in cation exchange pH gradient mode, based on only four initial runs (i.e. two gradient times and two mobile phase temperature). Only 6 h were required for a complete method optimization when using a 100 mm × 4.6 mm strong cation exchange column. Optimization was performed by computer simulation using DryLab modeling software. The accuracy of predictions was excellent, with an average difference between predicted and experimental retention times of about 1%.

The 10 model antibodies were successfully eluted in both pH and salt gradient modes, proving that both modes of elution can be considered as multi-product charge sensitive separation methods. For most of the compounds, the variants were better resolved in the salt gradient mode and the peak capacities were also higher in the salt gradient approach. These observations confirm that pH gradient approach may be of lower interest than salt gradient cation exchange chromatography for antibody characterization.