An in silico structural approach to critical quality attributes assessment of biopharmaceutical products

“Quality by design” (QbD) is a key approach in modern pharmaceutical development, applied during the development, the manufacturing and the whole life cycle of the product, included the post approval phase, for assuring the quality in terms of efficacy and safety. In detail, QbD process includes the critical quality attributes (CQAs) assessment, providing a comprehensive understanding of the product itself and the manufacturing process. CQAs are defined as “all the physical, chemical, biological, or microbiological properties or characteristics that should be within an appropriate limit, range, or distribution to ensure the desired product quality” (ICH Q8). They have a potential impact on bioactivity, PK, immunogenicity and safety and are associated with the drug substance and drug product. In the context of biotechnological products, the introduction of a structural investigation in an early identification of potential CQAs (pCQAs) can be very useful to QbD approach. Identification of pCQAs of biomolecules can lead the characterization process during the development phase in order to ensure the desired drug quality profile. Monoclonal antibodies (mAbs), fusion proteins and antibody-drug conjugates (ADC) represent one of the most innovative class of biopharmaceuticals, due to their ability to specifically recognize unique epitopes inducing specific therapeutic responses. CQAs assessment for these biopharmaceuticals is a complex analysis due to the lack of structural information. Actually, there is only one fully-crystallized human IgG1 (PDB entry: 1HZH) and, in absence of whole structures, it is challenging to understand the impact of structural insights on the therapeutic response. On these basis, the purpose of this study was to develop an in silico strategy to build the atomistic model of the whole structure of an IgG1, focusing on lambda and kappa light chains. To reach this goal, we used a structural chimeric approach that, using the Homology Modeling (HM) tool by MOE software, allowed us to build the full atomistic model of two therapeutic and commercially available IgG1: adalimumab (kappa chain) and avelumab (lambda chain). This allowed us to investigate structural differences between two isotypes, kappa and lambda, and understand the impact of these different characteristics on the antibody structure and function. Our results try to fill the gap between biological and structural properties on biotechnological products, created by lack of full immunoglobulin crystal structures. Moreover, this innovative structural approach can be used in CQAs assessment during the pharmaceutical development and production phases, giving an important resource to pharmaceutical companies. DISCLOSURES Merck Serono, Guidonia Montecelio-Rome, Italy is an affiliate of Merck KGaA, Darmstadt, Germany. Please note that avelumab has been approved in various countries for the treatment of metastatic Merkel cell carcinoma and in the US for treatment of advanced urothelial carcinoma progressed after platinum-containing treatment.