For at least the last decade, protein purification has increasingly been viewed as a process bottleneck—not just for individual unit operations, but for the entire purification train. Current wisdom holds that production titers will continue to rise, and with them, the height and number of hurdles encountered downstream. While this belief is certainly true for some products, particularly long-lived drugs manufactured at extremely high scale, it is something of a simplification. Downstream bottlenecks are neither universal nor inevitable.
Downstream bottlenecks differ according to the product’s development stage, notes Alan Hunter, Ph.D., senior principal scientist at Pfizer. Since processes are designed with equipment and facilities in mind, early-stage clinical manufacturing tends to encounter limitations in those areas, particularly when outsourcing is involved. Dr. Hunter advises that, in those situations, drug developers should “try to be more proactive in planning and designing processes to fit into the contractor’s capacity.”
Analytics represent another early-stage downstream hurdle. HPLC analysis of column fractions, for example, takes between 20 and 40 minutes each. “Throw in GMP requirements and the delay can reach a day for ten to twenty fractions.” The answer, explains Dr. Hunter, is to minimize the number of fractions, or collect them intelligently, so as to minimize the number of samples.
Later clinical stages processors should have had the time to solve facility and equipment issues, but here, capacities of chromatography resins and virus filters can become intractable—not from an engineering standpoint, but from the perspective of economics.
Virus filters are easily scaled, but their price tag (around $25,000 per run) and their single use add significantly to process costs. Protein A resins are also scalable and expensive—up to $10,000 per liter (around $1.5 million for one column’s worth). Protein A is recyclable, but the regeneration process is expensive and time-consuming.
Nearly every top mAb manufacturer is looking for alternatives to protein A capture, but these efforts are not always in harmony with process requirements at various development stages. “If you want to eliminate the use of protein A you would like to establish the alternatives relatively early, but early is precisely when you really need protein A, to crank out antibodies and get them into the clinic,” Dr. Hunter continues.
Most severe bottlenecks occur in facilities that are between 10 and 20 years old, where designers could not anticipate huge upstream productivity enhancements. “High titers affect all downstream unit operations, with the possible exception of centrifuges,” notes Günter Jagschies, Ph.D., senior director for strategic customer relations at GE Healthcare Life Sciences.
Nevertheless, Dr. Jagschies believes that downstream capacity issues may be over-hyped since very few products are manufactured at mega scales. “Most mAbs reaching the market over the next few years will require only up to about 200 kg per year.” The advent of biosimilars will further reduce the need for large-scale production of blockbuster biotherapies.
“When people talk about severe bottlenecks, they’re usually referring to first-generation processes. Resins and membranes being introduced today, which belong to the second and third generations of purification tools, offer up to five times the throughput of first-generation technologies.” For example, Enbrel is currently manufactured at three facilities, which, according to Dr. Jagschies, would not be necessary if Amgen/Wyeth employed current-generation downstream technology.
Experts also questions the degree to which higher titers are unduly stressing downstream operations. While titers are indeed rising, biopharmaceuticals are becoming more potent, which reduces dosing and in many situations batch size as well. In fact, bioprocessors may soon find themselves in the enviable situation where downstream capacities catch up. Further improvements in cell culture productivity will continue, but their impact will be to improve upstream efficiencies or perhaps to shrink expression and fermentation operations.