Effect of Peroxide- Versus Alkoxyl-Induced Chemical Oxidation on the Structure, Stability, Aggregation, and Function of a Therapeutic Monoclonal Antibody

Current guidelines indicate that the effects of oxidation should be included as part of forced degradation studies on protein drugs. We probed the effect of 3 commonly used oxidants, hydrogen peroxide, tert-butyl hydroperoxide, and 2,2'-Azobis(2-amidinopropane) dihydrochloride (AAPH), on a therapeutic monoclonal IgG1 antibody (mAb8). Upon oxidation, mAb8 did not show noticeable changes in its secondary structure but showed minor changes in tertiary structure. Significant decrease in conformational stability was observed for all the 3 oxidized forms. Both hydrogen peroxide and tert-butyl hydroperoxide destabilized mainly the CH2 domain, whereas AAPH destabilized the variable domain in addition to CH2. Increased aggregation was found for AAPH-oxidized mAb8. In addition, a significant decrease in Fc receptor binding was observed for all 3 oxidized forms. Antibody dependent cell-mediated cytotoxicity, binding to target protein receptor, and cell proliferation activity were significantly reduced in the case of AAPH-oxidized mAb8. The presence of free methionine in the formulation buffer seems to alleviate the effect of oxidation. The results of this study show that the 3 oxidants differ in terms of their effects on the structure and function of mAb8 because of chemical modification of different sets of residues located in Fab versus Fc.