Search

Identification of critical quality attributes (CQAs) is an important step for development of biopharmaceuticals with intended performance. An accurate CQA assessment is needed to ensure product quality and focusing on development efforts where control is needed. The assignment of criticality is based on safety and efficacy. Efficacy is related to PK and bioactivity. Here, we developed a novel approach based on antibody-antigen complex structure and modeling as a complementary method for bioactivity assessment. To validate this approach, common product related quality attributes and mutagenesis data from several IgGs were assessed using available antibody-antigen complex structures, and results were compared with experimental data from bioactivity or binding affinity measurements. A stepwise evaluation scheme for structural based analysis is proposed; based on systematic assessment following the scheme, good correlation has been observed between structural analysis and experimental data. This demonstrates that such an approach can be applied as a complementary tool for bioactivity assessment. Main applications are 1) To decouple multiple attributes to achieve amino acid resolution for bioactivity assessment, 2) To assess bioactivity of attributes that cannot be experimentally generated, 3) To provide molecular mechanism for experimental observation and understand structure function relationship. Examples are provided to illustrate these applications.

Guide ribonucleic acid (gRNA) is a critical reagent in clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 genome editing. The single stranded guide RNA (sgRNA) is the most commonly used gRNA in application. Evaluation of the impurity profile of synthetic sgRNA is important for any CRISPR genome editing experiments. However, the large molecular size, complex impurity profile and unique secondary structure pose many challenges in the analysis of sgRNA by ion pairing reversed-phase liquid chromatography (IP-RPLC), the commonly used method. In this work, we developed a generic IP-RPLC method for guide RNA analysis. We found that large pore size of stationary phase was the most critical column parameter to achieve high resolution separation of sgRNA while particle structure, particle size and surface chemistry had less impact. Our results indicated that charge interaction was the most critical mechanism for retention and mass transfer had less impact on the performance of separation. An IP-RPLC/mass spectrometry (MS) method was also developed with a specific practice to reduce adducts and enable intact MS analysis of sgRNAs. The generic IP-RPLC method demonstrates its feasibility to serve as a release, stability, characterization and in-process control testing method for synthetic sgRNA products.

Reversed-phase liquid chromatography (RPLC) has been commonly used in IgG2 disulfide isoforms analysis. Recently, the columns packed with large pore superficially porous particles (SPP) have become available commercially. This work explores the application of this SPP technology in IgG2 disulfide isoforms separation. A high throughput and improved resolution RPLC method is developed with the optimization of column selection, gradient, temperature and flow rate. Compared with the small particles RP-UHPLC columns, large pore SPP columns provide unique selectivity and several new peaks were resolved and identified to be the free thiol variants of the IgG2 disulfide isoforms. The optimized method enables the detailed characterization of cysteines related variants in a single and fast method.

The identification and quantification of post-translational modifications (PTMs) is a crucial step required during the development of therapeutic proteins. In particular, the characterization of charge variants separated by cation exchange chromatography (CEX) is a tedious process commonly performed with an off-line manual fraction collection followed by peptide mapping. To improve the efficiency of this time-consuming approach, a generic on-line multi-dimensional LC/MS approach was developed for the characterization of various monoclonal antibody (mAb) isotypes and a bi-specific antibody (BsAb). Fractions collected from 1D CEX analysis were consecutively reduced on a 2D reversed phase liquid chromatography (RPLC) column (polyphenyl), digested within 1–2 min using a 3D immobilized trypsin cartridge, and finally the obtained peptides were separated on another 4D RPLC column (C18), and simultaneously identified with a Q Exactive™ mass spectrometer. 2D RPLC columns and 3D trypsin cartridges from different suppliers were compared, as well as the effects of reducing agents. The effect of 2D and 4D RPLC column temperature, and 2D RPLC column mass load were also systematically studied. Under optimal conditions, the multi-dimensional LC/MS system described in this paper is a robust tool for the on-line digestion of proteins and shows high repeatability. Similar levels of oxidation and deamidation were measured using the off-line and on-line approaches for the same stressed samples. The lower amounts of deamidation and isomerization measured at some asparagine and aspartic acid residues by the on-line approach compared to the manual off-line procedure suggest reduced artifacts using the on-line methodology. The multi-dimensional LC/MS described here enables fast, on-line, automated characterization of therapeutic antibodies without the need for off-line fraction collection and sample pre-treatment (manual approach). The entire workflow can be completed within less than one day, compared to weeks with the manual off-line procedure.

Bispecific antibodies (BsAbs) combine the specificities of two antibodies to target different antigens. While production and in vivo assembly of BsAb using a single-cell host is less resource intensive compared to two-cell production, in particular mispaired light chain antibody species are a unique and undesired side product. Different pairing strategies may be employed to increase correct BsAb content, however, the potential presence of mispaired species must be both identified and quantified. Quantitative analysis by mass spectrometry is limited to chromatographic separation of the antibody assemblies due to their similar biophysical properties. This is particularly challenging for distinguishing correctly paired and light chain-scrambled mispaired antibodies which have the same molecular weight. Traditionally, imaged capillary isoelectric focusing (iCIEF) has been employed for analyzing charge-based heterogeneities, but this technique lacks resolution. Here we describe a powerful analytical platform using native weak cation exchange chromatography coupled to a high-resolution mass spectrometer, charge variant mass spectrometry (CV-MS), to characterize bispecific and mispaired antibody species. We investigate elution order through analytical methods and molecular modeling in an effort to understand the intrinsic charge, size and shape differences of these molecules. Although isoelectric points of the variants are similar, localized charge patches are hypothesized to offer sufficient micro-variations to be able to resolve and then identify isobars using CV-MS.