Source: PTSM: Pharmaceutical Technology Sourcing and Management
Issue 3,Volume 6
Nigel Darby, vice-president of biotechnologies at GE Healthcare Life Sciences and speaker at the Drug, Chemical, and Associated Technologies Association (DCAT) upcoming educational program on biologics, offers insight into the current and future state of upstream and downstream processing of biologics.
Biologic-based drugs are increasingly part of the product-development strategies of pharmaceutical companies. The very nature of biologics such as monoclonal antibodies (mAbs), recombinant proteins, or vaccines require specialized manufacturing conditions compared with the chemical synthesis of small molecules. To gain a perspective on the key issues involved in upstream (i.,e drug substance) manufacturing and downstream processing (i.e., purification), Patricia Van Arnum, editor of Sourcing and Management and senior editor of Pharmaceutical Technology, discussed these issues with Nigel Darby, vice-president of biotechnologies at GE Healthcare Life Sciences (Uppsala, Sweden). Darby will be a speaker at a biologics forum, The Rapid Evolution of Biomanufacturing and the New Supplier Reality organized by the Drug, Chemical, and Associated Technologies Association (DCAT) on Mar. 17 at the Waldorf-Astoria in New York City. The biologics forum is part of series of educational programs organized by DCAT during DCAT Week Mar. 15–18 that focus on pharmaceutical industry market dynamics, manufacturing, and sourcing of pharmaceutical ingredients.
PharmTech: What are the key trends and developments industry-wide in biomanufacturing, specifically in upstream technologies relating to manufacturing the biologic drug substance? How are advances in media and cell-line development contributing to improved yields or process efficiency?
Darby: Cell-culture productivity expressed as product titer has increased to a level of2-4 g/L in established production processes and 4-6 g/L in preclinical and some clinical manufacturing processes. This is a combined effect: optimized expression systems turn the cells into more efficient production systems and culture-media developments, including the feed strategy, lead to significantly increased cell density in the bioreactor. Cells would be capable of even higher yields up to 10 g/L, but this benefit, more often than not, comes with 50–70% prolonged culture time and deletes part of the productivity gains made with high titers. In addition, longer culture times reduce the flexibility in production scheduling and may thus limit the benefits of cell-culture optimization to conditions where culture time can be kept to approximately 12 days.
Overall, however, the improvements made with upstream processes have clearly enabled the manufacturing of ton quantities of therapeutic mAbs as required for some of the legacy mAbs. Twenty years after the first protein drug (tissue plasminogen activator) produced with mammalian cells, cell-culture technology has finally turned into an economic production tool for large-scale operations.
PharmTech: What are key trends and developments in downstream processing (i.e., purification) strategies of a biologic drug substance?
Darby: Downstream processing strategies follow two different trends: with mAbs still being high-dose drugs requiring relatively large-scale manufacturing, filtration steps need to cope with high biomass content in the initial steps and purification resins need to offer higher capacity while maintaining or improving the purification effect. Companies will continue to develop their manufacturing platforms and will aim to use robust downstream methods that work for the majority of their mAbs. As far as development, upstream processing is addressing some challenges: one is trying to reduce the number of main purification steps from three to two. Most recombinant proteins require significantly smaller product quantities (10-100-fold less), and each protein is very much more different than individual antibodies are different from each other. Platform approaches are more difficult to establish with recombinant proteins. Many processes for recombinant proteins still use four purifications steps. Higher capacity will be a benefit even here, but the focus will be on using steps with higher selectivity to reduce the number of steps. For all proteins, flow-through mode steps where impurities are adsorbed (instead of the much larger product amounts) represent a major trend in purification strategies and help to keep the column and buffer volumes small.
PharmTech: Do you see disposables continuing to be an important component of biomanufacturing? In what specific unit operations do you feel that disposables are well-established and in what areas do you see future application?
Darby: Disposable equipment and hardware components play a significant role in manufacturing strategies seeking a high degree of flexibility, short startup time, and quick changeover between production campaigns. In other words, they are important in busy facilities and in lean operations, where all nonvalue-adding activities are removed from the workflow. However, if the facility design, the workflow, and the scale-up strategies are not adopted to the features of disposable equipment, the economical benefits may be difficult to realize. For example, in a very busy facility, the large quantities of disposable equipment to be purchased represent a significant cost factor, the more batches that are run, the higher the cost. The cost benefit can best be realized, if the facility is as small as feasible and the fixed cost part of production has been reduced already at the facility-design stage. Currently, disposable equipment is most widely used to store buffers and intermediate product and also in seed-train operations in the upstream process (relatively simple, low-cost storage bags and GE Wave bioreactors). Virus filters and sterile filters are disposable components in the process. More complex functional equipment such as bioreactors and chromatography columns are still not very widely used in regular production. However, there is a clear trend towards single-use bioreactors (SUBs) wherever production scale does not need to exceed 1000 L. Acceptance of these SUBs is gradually increasing among cell-culture engineers. Disposable chromatography columns have also been introduced and are being considered as 'campaign-use' rather than 'single-use.'
PharmTech: What have been some of the significant advances relating to vaccine development, including cell-culture-based technologies? What are some of the challenges and benefits of using cell-culture technology compared with traditional egg-based technologies?
Darby: Some of the major developments in vaccine technology include novel approaches to the core design of the vaccine. For example, virus-like particles and recombinantly produced components of the infectious organism can trigger an immune response without the presence of the virus, bacteria, or toxin in inactive, weakened, or even live form. These novel vaccine designs carry the promise of excellent safety. Production technology used for vaccines is generally old technology for most legacy products, both upstream and downstream. The introduction of cell-culture-based production of viral vaccines has probably been a trigger for significant new development efforts also for downstream processing of such vaccines. Versatility and relative simplicity of scale up are the main benefits of a cell-culture based production strategy. A major surge in vaccine demand is difficult to respond to with the egg-based production route, if not impossible, if one really aims for high vaccination rates in very large populations. One challenge with the change towards cell-culture-based production is, of course, the need to develop an entirely new downstream process and to adopt to different purity and safety risks upon the change of production source.
PharmTech: Looking ahead five years from now, can you outline some specific areas in which the industry is working to improve upstream and downstream processing in biomanufacturing?
Darby: Following successful increase of productivity from cell culture, the new theme for upstream processing will be the reduction of quality variability in the product, including the reduction of impurities such as aggregates, glycosylation variants, and other product-related impurities. This is a trend that can already be seen in clone-selection strategies and the use of high-throughput methods in the effort of finding the best producer cell as well as in characterization of the product and the impurities. Ideally, cell viability could also be an improvement area.
On the downstream processing side, handling the increased biomass from the reactor is a challenge. The harvesting steps will be more and more combined with precolumn purification, which would allow for two-step purification for mAbs and possible three-step purification for most recombinant proteins. A number of groups are working with alternative purification methods such as extraction, precipitation, and crystallization, looking for replacement of the capture step in the purification train, or more generally for reduction of the overall number of steps. For purification resins, capacity increase will still be a theme in the coming five years, often paired, however, with improved selectivity and operated in flow-through mode.