Abstract
Isoelectric point markers from five sources have been compared and evaluated to replace the Bio-Rad brand markers (pI 6.2 and 7.5) used for pI determination of the charge isoforms of a therapeutic monoclonal cancer antibody (pI range of 6.3–7.2) in a capillary isoelectric focusing (cIEF) identity assay. Two of the five sources were found to be optimal replacement markers for the antibody molecule. Isoelectric point markers manufactured by Fluka (pI 5.5 and 7.6) and synthetic peptide markers prepared in-house (pI 5.91 and 7.27) produced antibody cIEF profiles, pI values, and percent corrected peak areas most comparable to the Bio-Rad marker results. Marker robustness was demonstrated by evaluating the markers using different CE instruments, marker lots, and capillary lots, as well as evaluating the markers at multiple Amgen sites.
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