Impact of oxidative degradation on the bioavailability of subcutaneously administered adalimumab

Subcutaneous (SC) administration of therapeutic antibodies enhances patient convenience and healthcare resource efficiency compared to intravenous (IV) delivery, but therapy can be limited by incomplete bioavailability (BA) of SC biotherapeutics. This limitation may be attributed to processes inherent to the unique composition of SC tissue, including the potential presence of reactive oxygen species (ROS) within the SC microenvironment, which can induce chemical and structural instability and functional impairment. This study investigated the impact of oxidation on the SC BA of adalimumab (Humira® biosimilar) as a representative IgG1 therapeutic protein. Two models of oxidation, mimicking some of those ROS encountered in the SC tissue, were applied to adalimumab, then the resulting oxidized variants were characterized and subsequently administered SC to rats to evaluate changes in SC BA. HPLC-MS/MS analysis identified methionine residues within CH2-CH3 interface as the primary sites of oxidation. Oxidation at these sites correlated with reduced conformational stability, alterations in the charge variant profile, and diminished binding affinity to the neonatal Fc receptor (FcRn). SC administration of oxidized species at 18% (w/w), diluted with excess unstressed IgG, to rats resulted in a slight decrease in SC BA, although not statistically significant. Additionally, oxidized AdmAb showed prolonged retention at the SC injection site, which may be associated with reduced conformational stability and higher propensity to aggregation and precipitation, although the underlaying mechanism requires further studies. Collectively, these findings demonstrate that oxidation can substantially alter the biophysical stability and FcRn binding affinity, while administering a moderate proportion of those oxidized species 18% (w/w) results in minimal changes in PK profile and overall SC BA.