Effect of phosphate concentration on the yield and purity of DNA separated from RNA by hydroxyapatite chromatography

DNA spike studies for demonstrating improved clearance on chromatographic media

DNA spike clearance methods were used to demonstrate improved clearance factors on anion exchange and hydrophobic interaction columns used in the production of human therapeutic proteins. DNA clearance at large-scale was first measured for a monoclonal antibody expressed in Chinese Hamster Ovary (CHO) cells and an antibody fragment expressed in Escherichia coli. Small-scale spike experiments were then performed on individual chromatographic steps using host-specific DNA paired with TaqMan PCR assay methods. This approach has advantages of improved specificity, sensitivity, cost and throughput compared to other types of spike clearance methods. The anion exchange column used in the monoclonal antibody process was shown to have very high capacity for CHO DNA, resulting in greater than 7.1 log reduction. The anion exchange and hydrophobic interaction columns used in the antibody fragment process were shown to have high E. coli DNA clearance capability, with greater than 5.1 and 5.3 logs clearance, respectively. Compared to the large-scale process, higher log reduction values were achieved in small-scale spike clearance studies by challenging the chromatographic steps with load DNA levels 2-5 logs higher than the large-scale process levels. Using highly specific and sensitive spike clearance methods, we demonstrated consistently high DNA clearance factors for each of the production processes that meet industry and regulatory standards for human therapeutics. The method is applicable to a broad range of industrial scale processes where demonstration of the robustness of DNA clearance is necessary to support development or licensure of biopharmaceutical products.

Continuous isolation of plasmid DNA by annular chromatography

Continuous chromatographic separations, especially of multicomponent mixtures, constitute interesting options for biotechnological downstream processing. Taking the separation of plasmid DNA from clearified lysates on hydroxyapatite as a pertinent example, we discuss the potential of continuous annular chromatography (CAC) in comparison with conventional (preparative) batch chromatography. In CAC the column is realized in the form of a thin (5 mm, height 210 mm) slowly rotating annulus. The performance of such a CAC column is compared to that of an ("analytical") batch column of similar thickness (diameter) and length (4 x 250 mm) and that of a ("preparative") batch column of similar cross-sectional surface area and height (50 x 210 mm). The quality of the obtained plasmid as defined by the appearance of the corresponding agarose gels (native and linearized plasmid), the 260/280 ratio and the biological activity (transient transfection of HEK 293 cells) was found to be identical in all three cases. The yields are also shown to be equivalent. The loading factor is found to be the most decisive parameter for the transfer of a given separation method between the continuous and the batch columns. Under nonoptimized conditions, plate numbers tended to be lower in the continuous compared to the batch columns. This is shown to be largely due to an artifact created by the CAC design (collection of averaged fractions at the outlets) and can be overcome by optimizing the rotation speed. Surprisingly the large batch column consistently gave better plate numbers than either the small batch or the CAC column. Compared to the preparative batch column, wall effects are more pronounced in the CAC (respectively the small diameter batch column), which may translate into better bed stability but conceivably also contributes to an increase in plate height, due to the reduction in bed density usually observed in the proximity of the wall. The CAC is shown to be a powerful approach to continuous chromatography, which allows a direct and straightforward upscale of chromatographic bioseparation methods.

Separation of high-molecular mass RNAs by high-performance liquid chromatography on hydroxyapatite

High-molecular-mass RNAs [transfer-(t-), 5S-, 18S- and 28S-RNA] in 25 mM sodium acetate buffer (pH 6.0) were separated by high-performance liquid chromatography (HPLC) on hydroxyapatite using a linear gradient (120 min-duration) from 0.03 to 0.147 M of phosphate buffer (pH 7.0) containing 0.3 M potassium chloride and 1 mM sodium azide with a slope of 2 mM/ml at a flow-rate of 0.5 ml/min. When the RNAs were dissolved in 4 M guanidine isothiocyanate-25 mM sodium acetate buffer (pH 6.0)-0.1 M beta-mercaptoethanol (4 M GIT), t-, 5S- and 18S- or 28S-RNAs but not 18S- and 28S-RNAs were separated. RNAs extracted from rat superior cervical ganglia with 4 M GIT could be separated. Thus, HPLC on hydroxyapatite is a rapid and accurate means of quantifying and/or preparing high-molecular-mass RNAs such as t- and ribosomal RNAs.