Beyond Binding Kinetics: Stoichiometry via SPR can identify novel binding modes, assess ligand quality and inform functional design in biopharmaceutical discovery.

Biological therapeutics have seen a dramatic increase in molecular complexity and biological mechanisms. Antibody drug conjugates (ADCs) and multi‐specific formats are filling therapeutic pipelines and fundamentally changing traditional platform approaches to biologics discovery. These new entities pose unique challenges for characterization; as with traditional mAbs they are generally triaged through the discovery process by a series of functional assays including ELISA, FACS and binding kinetics however, we have implemented an additional and often underutilized SPR measure to characterize the function and quality of these entities: binding stoichiometry. Here we will discuss the special requirements for quality stoichiometry measures and show how stoichiometry can be used to 1) identify novel binding modes for a mAb that may have implications to ADC function, 2) identify signs of molecular instability, 3) aid in engineering functional biotherapeutic molecules and 4) assess simultaneous binding of analytes in multi‐specific formats. These examples will show an important measure that can be used to identify liabilities and to demonstrate function of biotherapeutic candidates. Support or Funding Information All authors are employees of AbbVie. The design, study conduct, and financial support for this research were provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the publication.