Proof of site-specificity of antibody-drug conjugates produced by chemical conjugation technology: AJICAP first generation

[Display omitted] •The simple synthesis of site-specific DAR2 Antibody Drug Conjugates by a chemical conjugation method is presented.•Peptide mapping to identify the defined site of conjugation on the antibody.•The drug-linker unit is conjugated to a single site on the Fc portion of the antibody at site K248.•The peptide mapping method and strategy is described. Antibody-drug conjugates (ADCs) have become major biopharmaceutical drugs in the field of oncology. Traditional ADCs possess a stochastic distribution of cytotoxic payloads linked to several different amino acid residues of the antibody. This heterogeneous nature of stochastic ADCs results in a complex conjugation-site characterization. To improve upon traditional ADC technology, we have developed a chemical conjugation platform, termed AJICAP™, for site-specific modification of native antibodies using a class of IgG Fc-affinity reagents (Yamada et al., 2019). Here, we report further investigation focusing on peptide mapping of the AJICAP™-ADC to confirm the exact conjugation position of the first generation AJICAP™-ADC. Neutral pH pretreatment for peptide mapping prevented undesired PTMs such as succinimide ring hydrolysis. Mirroring comparison using the purified ADC visibly indicated that Lys248 in the Fc region was conjugated to the drug-linker. MS/MS analysis also provided evidence to support Lys248 conjugation. Finally, extracted ion-chromatogram methodology suggested the site-specificity of AJICAP™ conjugation. Purified ADCs by preparative HIC-HPLC showed clear visual results and more than 93% sequence coverage by a single enzymatic digestion. The analytical strategy described herein demonstrated a robust analytical methodology for revealing the conjugation site of ADCs.