Characterization of the Degradation Products of a Color-Changed Monoclonal Antibody: Tryptophan-Derived Chromophores

We describe the characterization of degradation products responsible for color change in near UV–visible light-irradiated and heat-stressed monoclonal antibody (mAb) drug product in liquid formulation. The treated samples were characterized using reversed-phase HPLC and size-exclusion HPLC with absorption spectroscopy. Both methods showed color change was due to chromophores formed on the mAb but not associated with the formulation excipients in both light-irradiated and heat-stressed mAb samples. These chromophores were further located by a new peptide mapping methodology with a combination of mass spectrometry and absorption spectroscopy. Mass spectrometry identified the major tryptophan oxidation products as kynurenine (Kyn), N-formylkynurenine (NFK), and hydroxytryptophan (OH-Trp). The absorption spectra showed that each of the tryptophan oxidation products exhibited a distinct absorption band above 280 nm shifted to the longer wavelengths in the order of OH-Trp < NFK < Kyn. The Kyn-containing peptide...