NMR-based structural integrity analysis of therapeutic monoclonal antibodies: a comparative study of Humira and its biosimilars

The analytical comparability of biologic products and their biosimilars, including higher-order structure (HOS) assessment, ensures product quality and is required for regulatory approval. In this study, nuclear magnetic resonance (NMR) spectroscopy was used to evaluate the HOS of Humira (adalimumab) and its biosimilars under normal and photo-stressed conditions. Under normal conditions, 1D and 2D NMR spectra showed strong structural similarity among all products. However, photo-stressed samples exhibited distinct structural differences, including increased methionine oxidation, and localized conformational changes, most notably in the reference product. These changes correlated with findings from size-exclusion chromatography, capillary isoelectric focusing, and mass spectrometry (MS), which revealed size and charge heterogeneity, as well as site-specific methionine oxidation in the heavy chains. The differences in photostability were found to be influenced by container closure systems (CCSs) and formulations. In contrast, circular dichroism spectral analysis showed minimal variation in secondary structures among stressed and unstressed samples. These results underscore the utility of NMR as a sensitive tool for comparative structural analysis of monoclonal antibodies and their biosimilars, particularly under stress conditions, and highlight the impact of formulation and CCS on product stability.