Systematic development and optimization of a cIEF method for the charge variants analysis of moderately basic to basic monoclonal antibodies using the Analytical Quality by Design strategy

This study proposes a Capillary IsoElectric Focusing Analytical Procedure Platform for the charge heterogeneity characterization of monoclonal antibodies. The Analytical Quality by Design approach was implemented to define a robust Method Operable Design Region using Infliximab as the primary model compound. The Analytical Target Profile consisted in a robust Analytical Procedure Platform able to measure the monoclonal antibody isoforms pI values with a bias lower than 4%. Risk Management tools were used to evaluate and control the risk of Analytical Target Profile failure. Risk Analysis identified several potential Critical Procedure Parameters, including urea and methyl cellulose concentrations, cathodic/anodic stabilizer levels, carrier ampholytes composition. The carrier ampholytes composition was optimized utilizing a mixture design. A Scheffé mixture model allowed the selection of experiments, and the Partial Least Squares regression provided high predictive power models for the three defined responses, i.e. the calibration biases at the bracketing markers of Infliximab (pI 9.5 and pI 7.0) and the overall fit of the pI vs. migration time relationship. Within the Method Operable Design Region, the optimized conditions were achieved using as the specific carrier ampholyte a blend constituted of 1.5% at pH 3–10, 1.5% at pH 5–8, and 2.0% at pH 8–10.5. The validation results demonstrated the robustness of the Analytical Procedure Platform, with a bias in pI measurement lower than 0.3% for the markers bracketing the Infliximab isoforms. In addition, the method was validated for linearity, trueness and precision as degree of repeatability in the quantification of the charge variants of Infliximab. Under the same optimized experimental conditions, the method was applied to successfully profile Bevacizumab, Daratumumab, Trastuzumab and Durvalumab. By including molecules exhibiting a broader range of physicochemical properties compared to the Infliximab model, the study confirms the versatility of the proposed Capillary IsoElectric Focusing method for moderately basic to basic antibodies. This work provides a refined, regulatory-compliant conventional electrokinetic methodology for biopharmaceutical quality control.