N+1 Engineering of an Aspartate Isomerization Hotspot in the Complementarity-Determining Region of a Monoclonal Antibody

Aspartate (Asp) isomerization is a common degradation pathway and a potential critical quality attribute that needs to be well characterized during the optimization and development of therapeutic antibodies. A putative Asp-serine (Ser) isomerization motif was identified in the complementarity-determining region of a humanized monoclonal antibody and shown to be a developability risk using accelerated stability analyses. To address this issue, we explored different antibody engineering strategies. Direct engineering of the Asp residue resulted in a greater than 5× loss of antigen-binding affinity and bioactivity, indicating a critical role for this residue. In contrast, rational engineering of the Ser residue at the n+1 position had a negligible impact on antigen binding affinity and bioactivity compared with the parent molecule. Furthermore, the n+1 engineering strategy effectively eliminated Asp isomerization as determined by accelerated stability analysis. This outcome affirms that the rate of Asp isomerization is strongly dependent on the identity of the n+1 residue. This report highlights a systematic antibody engineering strategy for mitigating an Asp isomerization developability risk during lead optimization.