Drug-to-Antibody Ratio/Protein Conjugation

Drug antibody ratio (DAR) is an important parameter of antibody drug conjugates (ADC) and refers to the average drug to antibody ratio for a given preparation of ADC. The significance of DAR in biotherapeutics is a primarily as a measure of drug loading for an ADC. Using a combination of intact mass measurement of the ADC as well as peptide mapping, an accurate DAR can be determined with site localization.

Diagram showing the formation of a cysteine-linked antibody-drug conjugate from a linker and drug attached to a monoclonal antibody, with a chemical structure example.

Figure 1. Workflow for drug-to-antibody/protein conjugation ratio calculation.

Mass spectra comparing an unconjugated monoclonal antibody and an antibody-drug conjugate, showing DAR distribution and calculated average DAR value.

Figure 2. Comparison of Sigma-mAb to Sigma-ADC following conjugation.