Quantification of in vivo site-specific Asp isomerization and Asn deamidation of mAbs in animal serum using IP-LC-MS.

Background: Isomerization of aspartic acid and deamidation of asparagine are two common amino acid modifications that are of particular concern if located within the complementarity-determining region of therapeutic antibodies. Questions arise as to the extent of modification occurring in circulation due to potential exposure of the therapeutic antibody to different pH regimes. Results: To enable evaluation of site-specific isomerization and deamidation of human mAbs in vivo, immunoprecipitation ( IP) has been combined with LC-MS providing selective enrichment, separation and detection of naive and modified forms of tryptic peptides comprising complementarity-determining region sequences. Conclusion: IP-LC-MS can be applied to simultaneously quantify in vivo drug concentrations and measure the extent of isomerization or deamidation in PK studies conducted during the drug discovery stage.