Development of a rapid reversed-phase liquid chromatographic method for total free thiol quantitation in protein therapeutics.

Free thiols, or unpaired cysteines, are important product quality attributes in the therapeutic proteins due to their potential impact on the protein structure, bioactivity and stability. While many free thiol quantitation methods were developed for specific therapeutic formats, an unmet need still exists for a multiproduct, high-throughput method for free thiol quantitation. In this study, a workflow was established that combines N-cyclohexylmaleimide (NcHM) derivatization and high-throughput reversed-phase ultra-high performance liquid chromatography (RP-UHPLC) separation with superficially porous particle (SPP) column for quantitating total free thiols in monoclonal antibodies (mAbs), fragment antigen-binding (Fab), and bispecific antibodies (BsAbs). The NcHM derivatization increases the hydrophobicity of the free thiol variants and allows the further separation and quantitation with RP-UHPLC. A thorough evaluation of sample preparation, column selection, chromatographic condition and LC-MS peak identification was performed to optimize and characterize the method outputs. Method optimization resulted in a 42-minute total analysis time. Method qualification demonstrated suitable accuracy, precision, linearity, specificity and robustness. This high-throughput method is not only used for quantitation of total free thiols for both in-process testing and drug substance/drug product batch testing, but also for provide the positional distribution of the free thiols in the protein.