Analytical and Functional Characterization of Plasmid DNA Topological Forms and Multimers

Plasmid DNA (pDNA) is an essential tool in genetic engineering that has gained prevalence in cell and gene therapies. Plasmids exist as supercoiled (SC), open circular (OC), and linear forms. Plasmid multimerization can also occur during the manufacturing process. Even though the SC forms are thought to provide optimal knock-in (KI) efficiency, there is no strong consensus on the effect of the topological forms and multimers on the functional activity. In addition, the results obtained for conventional pDNAs (>5 kbp) do not necessarily translate to smaller pDNAs (∼3 kbp). In this study, a workflow was developed for the analytical and functional characterization of pDNA topological forms and multimers. An anion exchange chromatography (AEC) method was first developed to quantify the topological forms and multimers. Four AEC columns were initially compared, one of which was found to provide superior chromatographic performance. The effect of mobile phase pH, various salts, column temperature, and acetonitrile content on the separation performance was systematically studied. The method performance, including precision and accuracy, was evaluated. The final AEC method was compared to capillary gel electrophoresis (CGE) by analyzing several pDNA sequences and lots. A forced degradation study revealed unexpectedly high degradation of the SC forms. Finally, the KI efficiency was compared for the SC and OC forms, and the multimers.