An Approach to Bioactivity Assessment for Critical Quality Attribute Identification Based on Antibody-Antigen Complex Structure.

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.