Identification and Qualification of Critical Reagents to Ensure Robust Cell-Based Potency Assay Performance

Potency is a critical quality attribute for biopharmaceutical drug products, and robust, QC-suitable cell-based potency assays are essential to support drug substance and drug product release throughout the product lifecycle. In alignment with ICH Q2 and USP <1033>, identification, qualification, and control of critical assay reagents are necessary to ensure consistent method performance and robustness.

In this case study, cells, fetal bovine serum (FBS), and ligand were identified as critical reagents during method development. Lot-to-lot consistency and source comparability were evaluated for each reagent. Cell bank variability showed no meaningful impact on assay performance, while FBS variability primarily affected assay dynamic range without impacting relative potency or curve parallelism. In contrast, ligands sourced from different lots and vendors resulted in significant EC50 shifts. Additional characterization studies linked these shifts to differences in aggregate content, confirming the ligand as the most critical reagent requiring enhanced control.

Based on these findings, a comprehensive critical reagent and method control strategy was established. This strategy includes performance-based qualification criteria, ongoing trending and monitoring to detect assay drift, defined owner-laboratory responsibilities for reagent sourcing and inventory management, and change-control procedures for reagent and vendor transitions. Particular emphasis is placed on ligand control strategies, including aggregate profiling, lot-bridging studies, and contingency planning, to maintain consistent assay performance and ensure uninterrupted patient access to commercial products.