Grafting Chromatographic Monoliths With Charged Linear Polymers for Highly Productive and Selective Protein or Plasmid DNA Purification

Meta Špela Kodermac, Sara Rotar, Darko Dolenc, Klemen Božič, Aleš Štrancar and Urh Černigoj

Separation and Purification Technology, vol. 353, Part A.

Abstract:

Increased requirements for plasmid DNA (pDNA) in gene therapy and vaccination efforts bring the need for efficient large-scale production processes with high purity and productivity. Chromatographic purification of pDNA is often a bottleneck due to low dynamic binding capacities (DBC), pDNA recovery and/or low selectivity of columns. Ion exchangers (IEX) with charged groups on surface extenders (polyions formed by a grafting reaction and subsequents modification) have attracted attention due to their greatly enhanced productivity compared with traditional IEX.

The ultimate goal of our investigation was to increase the DBC for pDNA on a monolith stationary phase by grafting the surface with linear polymethacrylate brushes (grafted chains), while retaining high pDNA recovery and chromatographic selectivity between pDNA and RNA impurities. The inner walls of the Convective Interaction Media® monolith channels were successfully coated with polyglycidyl methacrylate linear chains of varying densities and lengths by employing a controlled radical polymerization reaction. Glycidyl groups throughout the length of the formed grafted chains were converted to cation- (CEX) or anion-exchanging (AEX) moieties. Preliminary chromatographic evaluation of novel grafted CEX columns for different model proteins exhibited 10-times higher DBC with high elution recovery (99 %). Similar DBC improvement was proven for 7.3 kilobase pair pDNA, where the DBC10 increased from 1.8 mg pDNA per mL of non-grafted chromatographic support up to 15.2 mg per the most densely distributed and the longest grafted chains, modified with weak AEX groups. However, the DBC increase was partially at the expense of pDNA elution recovery, which presumably decreased due to entanglement of pDNA molecules inside the dense grafted layer.

To confirm the hypothesis, we have prepared a series of columns differing in length and density of grafted chains and tested them for pDNA capture. A satisfactory compromise between high pDNA DBC and elution recovery was found with relatively long and low density grafted chains. The optimal grafted AEX column with 1 mL bed volume was evaluated for pDNA capture from neutralized E. coli lysate. With a capacity of 13.5 mg pDNA per mL support, ≥95 % elution recovery, and complete RNA clearance, the pDNA was successfully purified at loading flow rate of at least 15 column volumes per min. According to our knowledge and literature search, these process characteristics would enable one of the highest pDNA isolation productivities to be achieved with currently tested IEX.

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