Introduction
The antibody drug market has continued to expand in recent years, and antibody drugs held 6 of the top 10 blockbuster drug spots for 2015. The most promising antibody drug candidates for next-generation biopharmaceuticals are ADCs (antibody-drug conjugates). ADCs have a structure in which a cytotoxic drug is chemically bonded to an antibody (IgG).

Since low-molecular drugs are more hydrophobic than monoclonal antibodies, differences in hydrophobicity arise when the numbers of bonded drug molecules differ. This property can be utilized to determine the drug-to-antibody ratio (DAR) by hydrophobic interaction chromatography (HIC). In this application note an ADC was analyzed using a TSKgel Butyl-NPR column, which can be used with either UHPLC or HPLC instruments. The antibody drug market has continued to expand in recent years, and antibody drugs held 6 of the top 10 blockbuster drug spots for 2015. The most promising antibody drug candidates for next-generation biopharmaceuticals are ADCs (antibody-drug conjugates). ADCs have a structure in which a cytotoxic drug is chemically bonded to an antibody (IgG). Because there are numerous binding sites for a low-molecular weight drug on an antibody (Cys, Lys residues, etc.), heterogeneity arises with respect to the number of bonds and binding sites. It is necessary to study in detail the effect that this heterogeneity has on the medicinal effects and safety of ADCs.