38


November/December 2009


Facing the challenges in bio-pharmaceutical production: developments in ion exchange media to bring down cost of goods.


Noriko Shoji1 , Akiko Matsui1 , Masakatsu Omote1 1 YMC Co. Ltd., Ishikawa, Japan; 2 , Naohiro Kuriyama1 , Britta Blödorn², Daniel Kune², Charles A. White2 YMC Europe GmbH, Dinslaken, Germany As the bio-pharmaceutical industry matures, terms like “cost of goods” are becoming more and more important.


Up to now, strain optimisation for high productivity and upstream purification were the bottleneck for most bio-processes. However, with the progress made in recent years, titers in fermentation processes have increased significantly. Obviously, this increased volumetric productivity will help reducing the cost of goods, but it also has an impact on the downstream processing. Therefore, improved downstream processing media are required to process the increased product load in the same timeframe. Recently, new materials, based on fully synthetic polymer based matrices became available and show important advantages over traditional polysaccharide-derived media. In the following article the focus is on ion exchange chromatography (IEX) as an important step in the biopharmaceutical process.


Basics of Ion Exchange Chromatography


IEX has been used for many years for analysis and purification of bio-molecules1


.


Its simple concept of charge induced reversible binding has several important advantages, two of which are: binding is fast and media show a high capacity. Also, compared with other chromatographic methods, such as hydrophobic interaction chromatography (HIC) or mixed mode resins, method development is straightforward. The binding/elution behaviour can be described by a simple “on/off” mechanism. The molecules will bind to the chromatographic support at low ionic strength at a pH below (for cation exchange) or above (for anion exchange) its isoelectric point. Release will take place at increased ionic strength or by pH shift.


In both cases, there is a distinct and narrow zone of pH / salt concentration, which determines whether there is binding or not. This also means that isocratic elution is not possible with IEX. Simple salt (step) gradients are most commonly used for elution. Stationary phases are generally resistant to a wide range of pH. All these characteristics make the technique ideal for


Process step Important material characteristics Capture


Typical Application


- Particle sizes between 45-200 µm, sometimes higher - High dynamic binding capacity at high flow rates (up to 1000 cm/h and more) - Good flow characteristics.


(Intermediate) - Particle size ca. 30-75 µm Purification - Low non-specific binding


Polishing


- Narrow particle size distribution Particle size between <10 – 30 µm


Table 1 Media Characteristics for Typical Steps in Bioprocessing


the two main process steps of capture and (intermediate) purification. In addition final polishing steps can also be performed with IEX. The differences between these three steps are summarised in table 1.


In a capture step the target compound is extracted and concentrated from the (homogenised) fermentation broth where it is present in low concentrations. The main aim in this step is to concentrate the target compound, achieve complete recovery of the target compound and the removal of bulk impurities (including protease etc.). In this step, high purity of the resulting concentrates is an advantage, but is not essential. During (intermediate) purification


the separation of the target compound from the main impurities is a key factor and purity aspects become more important.


Even though IEX is a comparatively simple method, there are still several parameters to keep in mind when developing a cost effective large-scale production process. In the following section, some key factors having an impact on the efficiency of an IEX- process step are discussed.


Capture step: In a capture step, the target compound is extracted and concentrated from the (homogenised) fermentation broth, where it is present in comparatively low concentrations in the range from 1-10 g/L


- Harvest of fermentation supernatants (capturing)


- Purification of material up to 90+% purity,


- Reduction of endotoxins Purification of up to 99+%


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