LC–MS Approach to Decipher a Light Chain Chromatographic Peak Splitting of a Monoclonal Antibody

Purpose Monoclonal antibodies (mAbs), like other protein therapeutics, are prone to various forms of degradation, some of which are difficult to distinguish from the native form yet may alter potency. A generalizable LC–MS approach was developed to enable quantitative analysis of isoAsp. In-depth understanding of product quality attributes (PQAs) enables optimization of the manufacturing process, better formulation selection, and decreases risk associated with product handling in the clinic or during shipment. Methods Reversed-phase chromatographic peak splitting was observed when a mAb was exposed to elevated temperatures. Multiple LC–MS based methods were applied to identify the reason for peak splitting. The approach involved the use of complementary HPLC columns, multiple enzymatic digestions and different MS/MS ion dissociation methods. In addition, mAb potency was measured by enzyme-linked immunosorbent assay (ELISA). Results The split peaks had identical masses, and the root cause of the peak splitting was identified as isomerization of an aspartic acid located in the complementarity-determining region (CDR) of the light chain. And the early eluting and late eluting peaks were collected and performed enzymatic digestion to confirm the isoAsp enrichment in the early eluting peak. In addition, decreased potency was observed in the same heat-stressed sample, and the increased isoAsp levels in the CDR correlate well with a decrease of potency. Conclusion Liquid chromatography-mass spectrometry (LC–MS) has been utilized extensively to assess PQAs of biological therapeutics. In this study, a generalizable LC–MS-based approach was developed to enable identification and quantitation of the isoAsp-containing peptides.