Rapid charge variant analysis of monoclonal antibodies to support lead candidate biopharmaceutical development

Biopharmaceuticals are complex therapeutic proteins produced in living cells that undergo a variety of enzymatic and non-enzymatic posttranslational modifications both intracellularly and also following secretion into the condition media. Characterization of these posttranslational modifications is a regulatory requirement to ensure that the molecule meets the required levels of quality to ensure patient safety. Ion exchange chromatography, particularly cation exchange, is routinely used for the determination of the charge variant profile of monoclonal antibodies (mAbs) using either an increasing concentration of salt or the generation of a pH gradient to facilitate elution of the mAb charge variants from the cation exchange phase. In this study, salt and pH gradient elution modes were compared to develop an optimized separation for the mAb standard reference material from NIST on a strong cation exchange phase. Separation using the pH gradient approach was found to outperform salt gradient separation. The developed pH gradient method was transformed into an ultra-fast separation method to facilitate rapid molecular profiling and triage during lead candidate and cell line development activities. The ultrafast method was validated and showed excellent performance for linearity and precision as well as applicability for the analysis of a variety of mAbs with different pI-values. The method has proven suitable for the integration into process analytical technology (PAT) frameworks and was found to be powerful in combination with automated data analysis strategies for obtaining low end-to-end processing time. This was demonstrated by the acquisition and analysis of in total 45 runs within only 5 h. The method was next applied for profiling in-house produced candidate biosimilars of trastuzumab and enabled the assessment of the charge variant profile of these candidates in <25 min. Differences identified for trastuzumab expressed using a stable CHO cell line were found to result from incomplete cleavage of the signal peptide from the light chain as determined using high resolution reversed-phase LC-MS following digestion with IdeS protease and disulphide bond reduction. The proposed method is well suited for molecular triage during cell line development or indeed for potential process analytical technology application during larger scale manufacture.