Imaged capillary isoelectric focusing (icIEF) is a gold standard method for characterizing the charge heterogeneity of protein therapeutics. A broad range of protein therapeutics such as monoclonal antibodies, antibody-drug conjugates (ADCs), and fusion proteins are routinely analyzed by icIEF due to its high resolution and high reproducibility. Platform methods, which can be applied without modification to the analysis of different protein therapeutics, save valuable time and resources in method development and quality control. Here, we provide platform methods for icIEF analysis of three classes of protein therapeutics, a biosimilar to the monoclonal antibody trastuzumab, recombinant human erythropoietin (rhEPO), and a fusion protein. The details of sample preparation and separation conditions for each molecule are described in this chapter.
Keywords: Biosimilar; Erythropoietin; Fusion protein; Imaged capillary isoelectric focusing (icIEF); Monoclonal antibody; Protein therapeutic; Trastuzumab.