As a result, there is a trend towards studies of adsorptive membrane technology for antibody purification. Membrane chromatography is one possible solution to achieve high dynamic capacity at high throughput in affinity and ion-exchange chromatography processes. However, to achieve a high enough dynamic binding capacity for a single-cycle capture step using current resin beads, one needs to use low volumetric throughput (i.e., high residence time), which limits productivity. One embodiment uses cation exchange (CEX), followed by anion exchange (AEX), and then hydrophobic interaction chromatography (HIC) to significantly reduce purification costs. Within the last 10 years there have been efforts to replace Protein A chromatography with less-costly non-affinity methods, such as ion-exchange chromatography steps in series. Relative to other, non-affinity chromatography media, Protein A resins cost almost an order of magnitude more. In the case of monoclonal antibody (mAb) production, Protein A affinity resins are used as the selective material, with a cost that accounts for over half of the total material costs of purification. Oftentimes, an expensive affinity chromatography medium is used for protein capture. It often is used in the primary recovery step, where the goals are to reduce the processing volume and provide some level of purification by capturing the target protein, and in intermediate and final purification steps that result in a purified injectable therapeutic protein. To provide affordable drug treatments to patients, especially for chronic and high dose treatments, the biopharmaceutical industry needs highly productive unit operations in the downstream train.Ĭhromatography is a standard unit operation used industrially for the downstream processing of protein therapeutics. The drugs in the MRDPs are predicted to reach or exceed US $500 million in annual sales by 2013.Ĭommonly, a majority percentage of the total cost of manufacturing a biotherapeutic is attributed to the downstream recovery and purification process. According to a recent market analysis by Goodman, the average share of biopharmaceuticals in the major prescription drug portfolios (MRDP) of the 14 largest pharmaceutical companies is estimated to increase to 40% in 2013. The global market for protein-based therapeutics is expected to grow at an average annual rate of 15%. Results show that this unique ATRP formulation can be used to fabricate cation-exchange membrane adsorbers with dynamic binding capacities as high as 70 mg/mL at a throughput of 100 CV/min and unprecedented productivity of 300 mg/mL/min. Dynamic binding capacities were measured for flow rates ranging from 13 to 109 column volumes (CV)/min. Static and dynamic binding capacities were measured using lysozyme protein to allow comparisons with reported performance data for commercial cation-exchange materials. Uniformity of modification within the membranes was visualized with confocal laser scanning microscopy. Success with modification was supported by chemical analysis using Fourier-transform infrared spectroscopy and indirectly by measurement of pure water flux as a function of polymerization time.
A special formulation was used in which the monomer was protected by a crown ether to enable surface-initiated ATRP of this cationic polyelectrolyte. Membranes with three reported nominal pore sizes (0.2, 0.45, 1.0 μm) were modified with poly(3-sulfopropyl methacrylate, potassium salt) tentacles, to create a high density of protein binding sites. The work is motivated by the need for a more economical and rapid capture step in downstream processing of protein therapeutics.
This paper describes the surface modification of macroporous membranes using ATRP (atom transfer radical polymerization) to create cation-exchange adsorbers with high protein binding capacity at high product throughput.
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