Brendan Fish, Ph.D., director of bioprocess sciences at MedImmune, began his presentation by saying that the difference in complexity between a small molecule and a monoclonal antibody is similar to the difference between a skateboard and a Formula 1 car. He said that although biologic products and processes are complex, fermentation titers are rising and the question has moved to whether downstream processing (DSP) can cope with the new capacity, time, cost, and purity challenges.
An increase in productivity upstream increases the proportion of costs borne by downstream processing. For example, if yields go from 1 g/L to 10 g/L, the proportion of DSP costs rises from 38% to 70%. “Purifying all that protein is a significant burden,” he said.
Other issues impacting downstream processing are the potential purification capacity crunch, the ratio between the number of fermentors and DSP suites, and liquid-handling capacities (large amounts of buffer are required for multiple cycles on large chromatography columns).
These challenges can be met in various ways, Dr. Fish commented, including implementation of platform technologies. In addition, “we are also beginning to understand design space through generation of large process datasets.” Clearly, it is important to keep things simple and avoid nonscalable steps. “It is useful to apply the principles of quality by design, which we are doing increasingly at MedImmune,” Dr. Fish added. Other ways of beating the capacity crunch include the use of disposables and the adoption of high-capacity chromatography matrices.
Chromatography is still the quickest and most cost-effective way to produce large amounts of therapeutic protein. Dealing with large amounts of protein, however, has stimulated the search for improvements to matrix-binding capacity. “The suppliers are aware of the capacity crunch and are trying to help, with several commercial matrices exhibiting capacities in excess of 100 g/L,” Dr. Fish noted.
Multicolumn chromatography is a useful approach that involves collecting fractions and reprocessing them with valve-switching. This process, while new to biotech labs, is common in small molecule development and food technology. MedImmune is also looking at high-throughput process development and at ways of removing aggregates. Other technologies of interest for the future could include precipitation, phase extraction, and monolith columns.
Looking forward, Dr. Fish said that the DSP capacity crunch may not fully materialize, because higher titers might promote a move away from the blockbuster drug model based around large-capacity fermentors. Flexibility and appropriateness of facility scale combined with DSP technological advances are likely to drive the biotech processes of the future.
Finally, John Moys, head of technical support for North Europe at Sartorius Stedim Biotech, discussed some of the advantages of membrane technology, where major improvements are predicted. He specifically focused on the Sartobind membrane adsorber technologies for which many different chemistries are available now.
“Membranes are better than conventional bead technologies for polishing because you get a higher flow rate with the open structure,” Moys said. A comparison study carried out at Amgen has shown that membranes are quicker (2–2.5 hours versus 8–9 hours) than gels and take less buffer in polishing of a monoclonal antibody. “Scale-up of membranes is still challenging, but is being addressed,” he added.
The Sartorius Stedim Hydrosart® ultrafiltration cassette range is a cellulosic membrane with low protein adsorption that can be cleaned with sodium hydroxide at up to 1 molar concentrations at elevated temperatures. In virus removal, an orthogonal approach is now needed before Phase I—the technologies being used are UVC inactivation, chromatography, and nanofiltration.
For UVC, inactivation must be done without damaging the product—the UVivatec® achieves this through a helical reactor design that allows uniform irradiation through radial mixing based on Dean vortices, Moys said. This technology was developed by Bayer Technology Services and is exclusively distributed by Sartorius Stedim Biotech.
With nanofiltration, Moys said that there can be a fine line between virus and product, with biomolecules having the potential to block a filter. Virosart® is a disposable nanofilter that can give a log reduction value of virus of greater than four, he explained. For final filtration, the latest advances involve polyethersulphone membranes that allow higher surface area and therefore a higher flow rate and throughput performance.