Development of a phenyl membrane chromatography-based process yielding pharmaceutical grade plasmid deoxyribonucleic acid for mammalian cells transfection.

Production of plasmid DNA pharmaceuticals requires fast, robust and cost effective methodologies able to deliver high amounts of the target molecule in short periods of time. Membrane adsorbers can be tailored and operated to suit such criteria. This study focuses on the impact of pDNA samples produced by a membrane chromatography-based purification methodology on the transfection efficiency of CHO cells. Chromatographies were performed with 5mL of plasmid-containing clarified bacterial lysate each on a Sartorius® Phenyl 3mL spiral cartridge using a bind and elute mode to purify the GFP expressing pVAX1/GFP model plasmid. The developed methodology could deliver up to 285µg pDNA samples per run that were virtually RNA free (over 99% removal) and chromatographic step yields of 85%. The purified samples had a reduced content of OC pDNA (∼15% less in average). Additionally, robustness of the process was assessed up to nine chromatographic runs without noticing any relevant loss in chromatographic performance and transfection capabilities. The increase of productivity was also studied by increasing the flow rate 5 fold-a maximum productivity of 100µg pDNA/(hmL-BV) was achieved. The pDNA samples produced led to transfection efficiencies that were comparable among all experiments-72% and within 4% relative standard deviation when samples were produced using a lower throughput. Transfection efficiencies obtained by the membrane process were comparable to a combined HIC/SEC bead-based purification process, with values ranging within 74-113% of the values obtained from the latter.

Impact of plasmid quality on lipoplex-mediated transfection.

This work investigates the impact of quality attributes (impurity content, plasmid charge, and compactness) of plasmid DNA isolated with different purification methodologies on the characteristics of lipoplexes prepared thereof (size, zeta potential, stability) and on their ability to transfect mammalian cells. A 3.7 kb plasmid with a green fluorescence protein (GFP) reporter gene, Lipofectamine®-based liposomes, and Chinese Hamster Ovary (CHO) cells were used as models. The plasmid was purified by hydrophobic interaction chromatography (HIC)/gel filtration, and with three commercial kits, which combine the use of chaotropic salts with silica membranes/glass fiber fleeces. The HIC-based protocol delivered a plasmid with the smallest hydrodynamic diameter (144 nm) and zeta potential (-46.5 mV), which is virtually free from impurities. When formulated with Lipofectamine®, this plasmid originated the smallest (146 nm), most charged (+13 mV), and most stable lipoplexes. In vitro transfection experiments further showed that these lipoplexes performed better in terms of plasmid uptake (∼500,000 vs. ∼100,000-200,000 copy number/cell), transfection efficiency (50% vs. 20%-40%), and GFP expression levels (twofold higher) when compared with lipoplexes prepared with plasmids isolated using commercial kits. Overall our observations highlight the potential impact that plasmid purification methodologies can have on the outcome of gene transfer experiments and trials.