Engineering enhanced performance in affinity purification

Biopharmaceuticals represent the fastest growing area of drug development. These treatments include monoclonal antibody-based drugs for rheumatoid arthritis and cancer, along with newer concepts such as the prostate cancer immunotherapy, Provenge. The success of biologics (link is external) is almost twice that of small molecule pharmaceuticals, with 13% of biopharmaceuticals that enter phase I trials going on to launch. With the biopharmaceutical industry as a whole estimated to be worth $163billion and a current annual growth rate of 8% that is predicted to continue for the foreseeable future, changes are now being driven in the traditional technologies to keep step with the developments of this sector.

Affinity chromatography column

Developing biopharmaceuticals does not follow the same simple, synthetic pathways as for small molecule drug development and today the purification of these biomolecules is often complicated and expensive. Between 60 and 80% of the downstream processing costs for biopharmaceuticals are attributed to the affinity purification process, where the biomolecule is purified from the complex cell background in which it has been manufactured, and a large component of these costs are taken up by the cost of affinity resins.

Protein A affinity purification is the accepted industry standard for purifying monoclonal antibodies, yet multiple problems (link is external) present with industry use of this affinity ligand. The exorbitant costs of protein A affinity resins on an industrial scale mean that biomanufacturers typically use multiple cycles of affinity purification per batch of product, to allow for the use of smaller protein A affinity purification columns thus keeping cost down. However, reusing the protein A resins leads to fouling of the protein A affinity resin. Similarly, repeated exposure to the harsh chemical conditions of elution and column cleaning procedures results in degradation and leaching of the affinity ligands, reducing column capacity and stunting optimal process performance.

Ensuring protein A resins maintain performance over multiple cycles requires extensive process monitoring. To limit these processes with the initiation of smart monitoring systems would require an increased understanding of the factors that influence protein A affinity purification performance loss, though this knowledge is not currently available.

For the affinity purification of non-antibody products, affinity ligands (link is external) are lacking. Monoclonal antibodies have proven typically too fragile to withstand the elution and cleaning procedures, prove sensitive to protease attack and exhibit difficulties with discrete antibody affinities preventing target elution without damaging the product from some systems, such as in cell purification screens. Taken together with their high production costs we can see that antibodies are less than ideal ligands for affinity purification processes. 

Affimer affinity purification

One strategy that has been used to isolate the increasing array of non-antibody biopharmaceuticals is to tag target proteins and capture based upon the affinity-tag. An immediate disadvantage of this approach is the addition of potentially unnecessary steps to any workflow. Protein tagging is often undesirable in itself- particularly for therapeutic proteins where the affinity-tag may induce immunogenicity. Subsequently there can be a need to remove the affinity-tag at a later stage, increasing both manufacturing costs and process-development timelines. Tag-free affinity purification simplifies process-development, by reducing the number of process steps and the time required, making it more cost-effective and scalable for large scale production.

Over the past five years interest has rapidly increased in the development of downstream technologies, such as affinity purification. Driven partly as a response to the well-documented bottlenecks created by improvements in upstream efficiencies, it is also due in part to the number and variety of new biopharmaceuticals entering development and clinical trials, and the rise of biosimilars. 

The need to engineer new affinity ligands for use in affinity purification protocols rather than depending upon natural affinity ligands is clear. Engineered affinity ligands have the potential to isolate higher capacities of a wider variety of targets with the ability to calibrate the target affinity to the required application, allowing vital process innovation. The rapid development times of alternative affinity reagents in affinity purification can reduce project-development timelines limiting costs and offer an essential competitive advantage, for example in the production of biosimilars. This potential for new biopharmaceuticals and drugs to be easily purified at lower cost, through the use of prokaryotic systems is a major factor in the increased interest in and uptake of alternative affinity reagents for affinity purification applications across both research and industrial fields.