Breakthrough Performance of Plasmid DNA on Ion-Exchange Membrane Columns Rosa Ma. Montesinos-Cisneros, † Jonathan de la Vega Olivas, ‡ Jaime Ortega, § Roberto Guzma ´ n, | and Armando Tejeda-Mansir* ,⊥ Departamento de Matema ´ticas, Universidad de Sonora, Hermosillo, Sonora, Me ´xico CP 83000, Departamento de Ingenierı ´a Quı ´mica y Metalurgia, Universidad de Sonora, Hermosillo, Sonora, Me ´xico CP 83000, Departamento de Biotecnologı ´a y Bioingenierı ´a, CINVESTAV-IPN, Avenida IPN No. 2508, Me ´xico, D.F. CP 07360, Me ´xico, Chemical and Environmental Engineering Department, University of Arizona, Tucson, Arizona 85721, and Departamento de Investigaciones Cientı ´ficas y Tecnolo ´gicas, Universidad de Sonora, Apartado Postal 593, Hermosillo, Sonora, Me ´xico CP 83000 Breakthrough performance of plasmid DNA adsorption on ion-exchange membrane columns was theoretically and experimentally investigated using batch and fixed-bed systems. System dispersion curves showed the absence of flow non-idealities in the experimental arrangement. Breakthrough curves (BTC) were significantly affected by inlet flow rate and solute concentration. In the theoretical analysis, a model was integrated by the serial coupling of the membrane transport model and the system dispersion model. A transport model that considers finite kinetic rate and column dispersed flow was used in the study. A simplex optimization routine, coupled to the solution of the partial differential model equations, was employed to estimate the maximum adsorption capacity constant, the equilibrium desorption constant, and the forward interaction rate constant, which are the parameters of the membrane transport model. The analysis shows that as inlet concentration or flow rate increases, the deviation of the model from the experimental behavior decreases. The BTCs displacement as inlet concentration increases was explained in terms of a greater degree of column saturation reached and more efficient operation accomplished. The degree of column saturation was not influenced by inlet flow rate. It was necessary to consider in the column model the slight variation in the BTC produced by the axial dispersion, in order to accomplish the experimental curve dispersion. Consequently, the design criteria that for Pe > 40 the column axial dispersion can be neglected should be taken with precaution. Introduction The demand for efficient production methods of plasmid DNA (pDNA) has increased vastly in response to rapid advances in the use of pDNA in gene therapy and vaccines. A prerequisite for the success of these therapies is the development of cost- effective and generic production processes of pDNA (1, 2). In the process synthesis, high-resolution steps such as column chromatography are considered essential to achieve the high purity requirements for this type of products (3-5). Among the different chromatography modes available for plasmid purifica- tion, anion-exchange membrane chromatography has received considerable attention recently (6-10). Membrane columns can operate in convective mode, which can significantly reduce diffusion limitations commonly en- countered in conventional commercial processes using beads. Besides numerous systems for laboratory-scale applications, modular systems of membrane adsorbers for a technical scale in pharmaceutical downstream processing have been reported (7, 11, 12). Numerous comprehensive reviews discuss the fundamentals and applications of membrane chromatography (13-20). Sharp breakthrough curves (BTCs) are obtained in membrane chromatography of small proteins (21-24). However, pro- nounced asymmetric BTCs have been reported for large proteins (24-26). Recently, an analogous BTC asymmetric behavior was reported for pDNA membrane chromatography (27). The steric hindrance and spreading models have been used to explain these results (28). In these studies very dilute feed solutions were used; furthermore, in three of the cases (including the pDNA study (27)) an extremely low residence time in the membrane system was also used. According to Chase (29) this type of operating condition contributes to BTC broadening. In a recent study sharp BTCs up to values of c/c o ) 0.8 were reported for pDNA adsorption on ion-exchange membranes. The dynamic capacity for pDNA was found to be highly dependent on flow rates and concentrations (30). The literature suggests that the frontal adsorption mechanism of DNA in membrane columns is more complex than the corresponding mechanism for proteins and that it is necessary to have a better understanding of the fundamental mechanisms underlying such chromatographic processes. We hypothesized that a study of the hydrodynamic and adsorption behavior of pDNA in a well-designed membrane system using a theoretical- experimental approach, may contribute to this understanding. * To whom correspondence should be addressed. Ph: +52 (662) 259 21 69. Fax: +52 (662) 259 2197. Email: atejeda@guayacan.uson.mx. † Departamento de Matema ´ticas, Universidad de Sonora. ‡ Departamento de Ingenierı ´a Quı ´mica y Metalurgia, Universidad de Sonora. § CINVESTAV-IPN. | University of Arizona. ⊥ Departamento de Investigaciones Cientı ´ficas y Tecnolo ´gicas, Univer- sidad de Sonora. 881 Biotechnol. Prog. 2007, 23, 881-887 10.1021/bp070054d CCC: $37.00 © 2007 American Chemical Society and American Institute of Chemical Engineers Published on Web 06/13/2007