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The presence of a plasmid, containing gene sequences for DNA immunotherapy that are not expressed in microbial culture, imposed a degradation in bioreactor performance in cultures of the host E. coli strain. Significant decreases in growth rate (24%) and biomass yield (7%) and a corresponding increase in overflow metabolism were observed in a strain containing a therapeutic sequence (a hepatitis B antigen under the control of a CMV promotor). The observed increase in overflow metabolism was incorporated into a Metabolic Flux Analysis (MFA) model (as acetate secretion). Metabolic flux analysis revealed an increase in TCA cycle flux, consistent with an increased respiration rate observed in plasmid-containing cells. These effects are thought to result from increased ATP synthesis requirements (24%) arising from the expression of the Kanr plasmid marker gene whose product accounted for 18% of the cell protein of the plasmid-containing strain. These factors will necessitate significantly higher aeration and agitation rates or lower nutrient feed rates in high-density cultures than would be expected for plasmid-free cultures.

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We have developed a generic transient transfection process at 100 L scale, using HEK293-EBNA cells and PEI as the transfection reagent for the production of recombinant IgG. The process, including large-scale plasmid preparation, expression at bioreactor scale, capture, purification and, if necessary, endotoxin removal allows reproducible production of more than 0.5 g IgG for in vitro and in vivo studies. We compared the performance of two HEK cell lines, investigated the effect of conditioned medium, optimized the DNA:PEI ratio and implemented a feed strategy to prolong the culture time to increase product yield. The transient transfection protocol developed enables a closed process from seeding culture to protein capture. The challenge of performing a medium exchange before transfection at large scale is solved by applying a continuous centrifugation step between the seeding bioreactor and the production bioreactor. After 7-8 days the harvest and capture is performed in a one-step operation using a Streamline expanded bed chromatography system. Following a polishing step the purified antibody is transferred to the final formulation buffer. The method has shown to be reproducible at 10, 50, and 100 L scale expressing between 5 and 8 mg L -1 IgG.

ABSTRACT:Membrane-bound transporter proteins play an important role in the efflux of drugs from cells and can significantly influence the pharmacokinetics of drug molecules. This study describes the production of large amounts of high-activity transporter membrane vesicles from human embryonic kidney 293-Epstein-Barr virus nuclear antigen cells transiently transfected using a Gateway-adapted pCEP4 plasmid. Transfections were scaled up to 10-liter cell cultures, and vesicle preparations were optimized using ultracentrifugation with a sucrose cushion, which enabled us to produce hundreds of milligrams of membrane vesicles expressing human efflux transporter proteins Pglycoprotein (P-gp)/multidrug resistance 1 (ABCB1), multidrug resistance protein 2 (MRP2) (ABCC2), and breast cancer resistance protein (BCRP) (ABCG2). Assays were developed and optimized for analyzing the ATP-dependent functionality of the transporters using probe substrates and specific inhibitors. Excellent signal/noise ratios of ATP-stimulated uptake for P-gp, MRP2, and BCRP vesicles were obtained, indicating high expression of functioning transporters. The uptake kinetics of the transporters was investigated by determining K m and V max using the model substrates N-methylquinidine (P-gp), estradiol-17␤-glucuronide (MRP2), and estrone-3-sulfate (BCRP). The ATP-dependent transport was inhibited by the model inhibitors verapamil (P-gp), benzbromarone (MRP2), and sulfasalazine (BCRP). The vesicles are thus well suited to screen for possible substrates and inhibitors in high throughput systems or are used for detailed mechanistic investigations of transporter kinetics of specific substances.