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Abstract Mimotope peptides selected from combinatorial peptide libraries can be used as capture reagents for immunoassay detection of therapeutic monoclonal antibodies (mAbs). We report the use of phage display libraries to identify peptide ligands (VeritopesTM) that bind natalizumab, a therapeutic mAb indicated for use in multiple sclerosis. PKNPSKF is identified as a novel natalizumab-binding motif, and peptides containing this motif demonstrated utility as capture reagents in enzyme-linked immunosorbent assays (ELISAs). A peptide containing the identified motif was shown to be competitive with the natural ligand (α4-integrin) and a neutralizing anti-idiotype antibody for natalizumab binding, indicating that VeritopesTM act as surrogate ligands that bind the antigen binding site of natalizumab. Affinity maturation further confirmed the motif sequence and yielded peptides with greater apparent affinity by ELISA. VeritopesTM are promising assay reagents for therapeutic drug level monitoring.

Capture reagents are critical to affinity-based bioanalytical methods. The potential bias of capture reagents, for or against certain subpopulations of the target of interest, may lead to inaccurate quantitation. This issue is more profound for sensitive measurements, such as post-translational modification (PTM) profiling of therapeutic proteins from complex matrix. Here, a recently developed affinity purification coupled mass spectrometric method was utilized to assess the full sequence of a circulating therapeutic aglycosylated IgG1 (MAB3) in human subject, using two different capture reagents. We monitored all PTMs known to be related to MAB3 drug quality (three representative PTMs are shown in this paper). The results validated the comparability of these two reagents. [ABSTRACT FROM AUTHOR]