High-throughput Carbonyl Content Method of Therapeutic mAb using size-exclusion chromatography with ultraviolet and fluorescence detection

In-Depth Characterization of Acidic Variants Induced by Metal-Catalyzed Oxidation in a Recombinant Monoclonal Antibody

Characterization of antibody charge heterogeneity is an important task for antibody drug development. Recently, a correlation between acidic charge heterogeneity and metal-catalyzed oxidation has been observed for antibody drugs. However, to date, the acidic variants induced by metal-catalyzed oxidation have not been elucidated. In addition, it is challenging to satisfactorily explain the induced acidic charge heterogeneity, as the existing analytical workflows, which relied on either untargeted or targeted peptide mapping analysis, could lead to incomplete identification of the acidic variants. In this work, we present a new characterization workflow by combining untargeted and targeted analyses to thoroughly identify and characterize the induced acidic variants in a highly oxidized IgG1 antibody. As a part of this workflow, a tryptic peptide mapping method was also developed for accurate determination of the relative extent of site-specific carbonylation, where a new hydrazone reduction procedure was established to minimize under-quantitation artifacts caused by incomplete reduction of hydrazones during sample preparation. In summary, we identified 28 site-specific oxidation products, which are located on 26 residues and of 11 different modification types, as the sources of the induced acidic charge heterogeneity. Many of the oxidation products were reported for the first time in antibody drugs. More importantly, this study provides new insights to understanding acidic charge heterogeneity of antibody drugs in the biotechnology industry. Additionally, the characterization workflow presented in this study can be applied as a platform approach in the biotechnology industry to better address the need for in-depth characterization of antibody charge variants.

In silico prediction of post-translational modifications in therapeutic antibodies

Monoclonal antibodies are susceptible to chemical and enzymatic modifications during manufacturing, storage, and shipping. Deamidation, isomerization, and oxidation can compromise the potency, efficacy, and safety of therapeutic antibodies. Recently, in silico tools have been used to identify liable residues and engineer antibodies with better chemical stability. Computational approaches for predicting deamidation, isomerization, oxidation, glycation, carbonylation, sulfation, and hydroxylation are reviewed here. Although liable motifs have been used to improve the chemical stability of antibodies, the accuracy of in silico predictions can be improved using machine learning and molecular dynamic simulations. In addition, there are opportunities to improve predictions for specific stress conditions, develop in silico prediction of novel modifications in antibodies, and predict the impact of modifications on physical stability and antigen-binding.

Identification and characterization of carbonylation sites in trastuzumab biosimilars

Detection of metal catalyzed carbonylation in proteins is traditionally based on derivatization followed by detection and quantification via spectroscopy or immunodetection. However, these measure only cumulative carbonylation and do not identify the specific sites of modification within the protein. Recently, fluorescein thiosemicarbazide (FTC) based semi-microplate method was adapted for high throughput monitoring of carbonyl content during mAb process development, using size-exclusion chromatography followed by ultraviolet and fluorescence detection. Here, we have examined carbonylation in originators and 4 biosimilars of an IgG1 therapeutic monoclonal antibody, trastuzumab, a first line of therapy for HER2 positive breast cancer. The hyphenated RP-ESI-MS/MS detection was able to identify the location of each of the carbonylated amino acids for all products. The result is a comprehensive map of a total of 27 unique identified carbonylation sites of trastuzumab found across multiple batches of originator as well as marketed biosimilars. Our results demonstrate that although the different carbonylation sites are spread across different domains throughout the mAb sequence, the complementarity determining regions (CDRs) are free of carbonylation and all identified sites lie within the framework region of the variable domain. Moreover, the constant- heavy domain 3 (CH₃) region seems to be particularly resistant to process induced carbonylation.