A Generic HPLC Method for Absolute Quantification of Oxidation in Monoclonal Antibodies and Fc-Fusion Proteins Using UV and MS Detection

Oxidation of biopharmaceuticals may affect their bioactivity, serum half-life, and (bio)chemical stability. The Fc domain of IgG monoclonal antibodies (mAbs) contains two methionine residues which are susceptible to oxidation. Here, we present a middle-down approach employing the cysteine protease IdeS under reducing conditions to obtain three mAb subunits of approximately 25 kDa:Fc/2, Fd', and LC. These subunits were separated by ion-pair reversed-phase high-performance liquid chromatography (IPRP-HPLC) and detected by UV spectroscopy as well as Orbitrap mass spectrometry (MS), as well as MS upon all-ion fragmentation (AIF-MS). We evaluated the feasibility of three strategies for absolute quantification of oxidation in the Fc region of hydrogen peroxide-stressed Rituximab, using a single, commercially available software platform both for data acquisition and evaluation: UV spectroscopy, full-scan MS, and monitoring of product ions obtained by AIF-MS. IN spectroscopy showed the lowest limits of quantification (LOQ) (0.96 ng mu L-1) and featured the lowest relative process standard deviation (V-x0%) of 7.2% compared to MS and AIF-MS with LOQ. of 1.24-4.32 ng mu L-1 and relative process standard deviations of 9.0-14%, respectively. Our approach is generic in that it allows monitoring and quantification of oxidation in the Fc regions of fully human and humanized IgGl mAbs as well as of Fc-fusion proteins. This is exemplified by limits of detection, of 1.2%, 1.0%, and 1.2% of oxidation in drug products containing the biopharmaceuticals Rituximab, Adalimumab, and Etanercept, respectively. The presented method is an attractive alternative to conventional time-intensive peptide mapping which is prone to artificial oxidation due to extensive sample preparation.