The Characterization of Drug-to-Antibody Ratio and Isoforms of ADCs Using LC and MS Technologies

Hydrophobic interaction chromatography (HIC) and MS are leading techniques for the characterization of the critical quality attributes (CQA) of antibody-drug conjugates (ADCs). This includes the average drug-to-antibody ratio (DAR) and drug loading distribution. A workflow that effectively utilizes the synergy between chromatography and detection technologies has been developed and was assessed using cysteine-conjugated ADCs. The DAR of low, moderate and high drug-loaded ADC samples were calculated from the chromatographic peak areas using LC(HIC)/UV or the deconvoluted mass spectra using native LC(SEC)/MS. The results of DAR by both technologies produced comparable results. In addition, the 2D-LC/MS system has been evaluated in combination with HIC and reversed-phase chromatography for structural identification. Individual peaks from the 1st dimension of the HIC separation were isolated online and re-directed to the 2nd dimension reversed-phase column. ADC was detected as the sub-units by MS and the conjugation site was identified via a middle down approach.