Characterization and elimination of artificial non-covalent light Chain dimers in reduced CE-SDS analysis of pertuzumab

Capillary electrophoresis sodium dodecyl sulfate (CE-SDS), either in reduced (rCE-SDS) or non-reduced (nrCE-SDS) form, is widely used for purity evaluation and impurity analysis of monoclonal antibody (mAb) drugs. The accuracy of the method may be interfered by artificial species resulted from sample preparation or electrophoresis operation if it is not well optimized. In a routine analysis of pertuzumab for both innovator Perjeta® and biosimilar HLX11 samples, a cluster of unknown peaks located between light chain (LC) and heavy chain (HC) were observed in rCE-SDS and making the purity of (LC + HC)% unacceptable. They can hardly be reduced by regular method optimization such as changing buffer pH, denaturing temperature or incubation time to achieve the (LC + HC)% expectation. Here, the peaks are first characterized and determined to be non-covalently formed LC-LC dimers by multiple techniques including reversed-phase liquid chromatography-mass spectrometry (LC–MS). These artifacts are then eliminated through enhancing capillary separation temperature to 60 °C and decreasing the separation voltage to 9.5 kV, an unusual CE-SDS operation setting. Finally, a developed rCE-SDS method is presented for successful evaluation of pertuzumab purity and impurities, which is further confirmed by an alternative reduced microchip-based gel electrophoresis. In summary, the developed method provided an accurate and reliable purity evaluation and size variant profiling for batch releasing, stability testing and quality study of reduced pertuzumab samples.