An Automated and Qualified Platform Method for Site-Specific Succinimide and Deamidation Quantitation Using Low-pH Peptide Mapping

mAbs undergo several post-translational modifications, including the formation of succinimide from the deamidation of asparagine or the isomerization of aspartic acid. Because of the potential impact of succinimide formation on the biological activity of mAbs, detection and quantification of this species is a key area of interest for the pharmaceutical industry. However, studies assessing succinimide stability have been limited, and methods developed to monitor succinimide are either product specific or not robust. Here, we report the development of a platform low-pH peptide-mapping method using a combination of low-pH-resistant Lys-C and modified trypsin to maintain succinimide stability, eliminate deamidation assay artifact, and achieve efficient mAb digestion equivalent to conventional tryptic peptide-mapping method under alkaline condition. Using this method, succinimide stability in serum was accurately assessed in vitro study and the half-life was determined to be 1.5 days. With potential patient exposure to succinimide intermediate, a reliable method was developed to measure site-specific deamidation and succinimide intermediate. Coupled with a single quadrupole mass detector, our method was automated from digestion to data processing and applicable in a good manufacturing practice environment. The method was fully qualified to demonstrate accuracy, precision, linearity, and robustness.