Antibody-drug conjugates (ADCs) are increasingly recognized as a promising class of targeted therapeutics, combining antibody specificity with the potency of cytotoxic drugs. Ensuring consistent safety and efficacy remains critical, as variability in drug-to-antibody ratios (DAR) and conjugation sites can affect therapeutic performance and safety profiles. The development of site-specific ADCs using non-natural amino acids (nnAAs) offers significant therapeutic advantages. A novel CHO cell platform engineered to incorporate nnAAs via orthogonal tRNA/tRNA ligase systems provides a mechanism for targeted drug attachment.

However, introducing nnAAs into the antibody sequence and the associated modifications to CHO cells present unique challenges. Mass spectrometry (MS) revealed that sequence variants are highly sensitive to cell culture conditions. Additionally, modifications impacting conjugation efficiency and DAR values were observed. Analytical methods to detect nnAA misincorporation and impurities from raw materials are essential to mitigate these issues.

Further investigation suggested that suppression of the amber stop codon might lead to host cell protein (HCP) modifications with nnAAs. A strategy combining bioinformatics predictions, MS analysis, and targeted pull-downs was employed to understand modifications within the host cell proteome.

This work highlights the analytical complexities of nnAA incorporation and underscores the critical role of advanced MS techniques in ensuring product quality. These insights will guide future cell line development and bioprocess quality control efforts.

Hirsh Nanda

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