Bioprocess Scale-Up Consideration
Yes, it is unavoidable that your manufacturing process will undergo a scale-up at least once in the life cycle of your product. Typically, the first significant bioprocess scale-up goes hand-in-hand with the technology transfer of the process into GMP biologics manufacturing. Scale-Up can be particularly challenging for biologics as there are many variables at play which differ between microbial and mammalian expression systems. At BPAI, we have learned that the challenges are also very different for upstream compared to downstream processing. Many potential pitfalls are associated with scale-up of biologics manufacturing processes, and it is important to avoid these hazards and to provide a successful scale-up. The possible issues often originate from:
- Process design
- Raw materials
- Regulatory requirements.
In our experience as Bioprocess Technology Consultants, it is important to design your biologics manufacturing process with scale-up in mind. Though this concept seems to be intuitive, often processes are developed without consideration of the required scale first in support of clinical trials and later for commercial production. Thus, it is important to understand early on how much product is needed, which is dependent on different aspects such as potency of the product, proposed clinical indication, and thus patient population, as well as dose and route of administration. Even if these details are not always available when the biologics manufacturing processes are developed, a good estimation and an understanding of the intended scale is essential to avoid unnecessary process changes that might be required to replace an un-scalable process step.
An obvious difference between laboratory scale for research, and scaled-up GMP biologics manufacturing is the equipment and bioprocesses that can be used. At BPAI we have a good understanding of these differences and the limitation of certain methods and can therefore help in consideration from the onset of process development. For upstream processes, a good understanding of the differences in parameters like mass transfer, kLa and mixing of bioreactors used at different scales, combined with an understanding of the critical process parameter to control the biologics manufacturing process, help to facilitate bioprocess scale-up. A key factor to remember is that the ratio of surface to volume typically decreases with increasing bioreactor volume, which can be beneficial for some products as it reduces non-specific adsorption or surface induced precipitation. However, other parameters are more difficult to control at scale such as heat transfer to control the bioreactor temperature, or poorer gas exchange that can lead to accumulation of carbon dioxide in mammalian cells, or inefficient oxygenation in microbial systems. In our experience at BPAI, it is not uncommon to see a reduction in yield during scale-up, and we therefore suggest to plan for this as part of your scale-up considerations.
The transition of a process from upstream operations to the downstream process requires the separation of cell mass from the spent medium. Depending on the biologics manufacturing process, the product can either be part of the cell mass or the culture supernatant, but typically only the product containing part is further processed which makes the separation of solids from the liquid stream necessary. Again, understanding the scale-up considerations is critically important at this juncture of the process. At laboratory scale, either depth-filters or bucket centrifuges are primarily used for the initial separation. Though dead-end filtration can be scaled to a certain degree, centrifugation using continuous centrifuges (for example disc stack centrifuges) offers certain economic advantages and is therefore often the method of choice for large-scale biologics manufacturing. Furthermore, using microbial expression systems often requires the processing of the cell mass which eliminates dead-end filtration as potential separation technology. As Bioprocessing Technology Consultants we remind our clients it is vital to keep in mind that the centrifugation technology used for large scale manufacturing is very different from the typical bucket centrifuge and thus, it is important to understand the bioprocess scale-up and validation considerations associated with centrifuges early in the development of a biologics manufacturing process. Failure to do this could result in a repeat of process development for the first unit operations to follow the centrifugation step.
For bioprocess scale-up of downstream processes, it is important to choose the right technology. For example, gel filtration chromatography has a limited capacity compared to other modes in chromatography and alternatives might be required later in the life cycle of the biologics manufacturing process when demands increase. However, the most common issue in scaling up a DSP bioprocess is related to process volume. Large volumes of buffer are frequently required in the preparation of column chromatography steps and unfortunately often the available bioprocess tanks limit the capacity of DSP. The advance of single-use technology has helped to alleviate some of the restrictions that GMP biologics manufacturing sites previously faced, but utilities and storage capacity are still limiting factors.
The cost of specialized resins used in the purification process often require changes in the originally developed process. Changing the order of process steps to ensure a lower protein load and thus a smaller required resin volume later in the purification process is one way to allow use of highly specialized and expensive resins. Another approach is cycling the process over a smaller chromatography column and thus reducing the required resin volume. In order to enable such an approach however, it is critical to understand the stability of the product of interest at this stage of the process. This requires studies at small scale that should be performed during process development. Hence, in our experience as Bioprocessing Technology Consultants, it is even more critical for DSP to understand the intended production scale-up plan for success – sometimes even simple process steps create challenges at production scale. One such example is the adjustment of pH often required during a DSP process. As simple as this is during a laboratory process, production-scale processes require a different approach and the larger volumes increase the time significantly to reach the targeted range.
As a Bioprocessing Technology Consultant, I often get asked what aspect of the biologics manufacturing process goes most easily unnoticed during bioprocess scale-up, and my typical answer is: temperature control. Most processes developed at laboratory scale for research involve hold times. To reduce product degradation during these holds, the product often is placed in a refrigerator. Once you try to use a similar hold in a +1000L process, this becomes a significant challenge: air is a very poor thermal conductor and thus, using a cold room for storage of large volumes will result in a slow reduction of the temperature of the process volume. Using a jacketed mixing tank is the best solution to control and change temperature but cooling of large volumes require a significant cooling capacity that not all GMP biologics manufacturing facilities can supply. Now, if your product of interest requires freezing to ensure stability it becomes a challenge of even larger consideration, and any hold points in the process require careful planning.
Two aspects that I have left out so far are raw materials and regulatory requirements. During process development it is good to keep in mind where a change of material could potentially impact the bioprocess scale-up outcome. It is important to identify critical raw material attributes and to ensure that the appropriate amounts, grades and origins of the raw material are available for GMP biologics manufacturing. Evaluate early on, if a raw material change could impact the process in which case a good raw material control strategy needs to be put in place early on in the life cycle of the product.
I always recommend as a Bioprocessing Technology Consultant to keep the process as simple as possible to limit the number of changes due during bioprocess scale-up. One way to simplify the process is to maximize the efficiency of process steps and thus reducing the number of required step. Often, numerous buffer exchanges are performed during the early stage of process development and reducing these to a minimum by, for example, standardizing buffers used in the process will make scale-up easier.
So, to summarize the key aspects in planning for a successful bioprocess scale-up that we are suggesting from BPAI are:
- Know the intended scale of production
- Review each process step in view of the intended scale
- Keep the process simple; and
- Reduce unnecessary process changes.
Not every scale-up is going to be successful first time but good preparation will increase the likelihood. Planning for a potentially lower upstream yield and anticipating aggregation issues during downstream processing are some of the pieces that will ensure preparedness for bioprocess scale-up challenges. A shake-down or engineering run at the intended scale using the envisioned GMP equipment is a good way to mitigate risks of failure. However, in this fast pace market, companies often choose to skip risk-mitigating non-GMP scale-up runs, putting even greater importance on good planning for bioprocess scale-up. Understanding your biologics manufacturing process and the key process parameters can help manage uncertainty on scale-up. Thus, in summary, designing a bioprocess with commercial production in mind, and ensuring the developed bioprocess is supported at the required scale through careful considerations, will mitigate risks of failure and unwanted changes to the process later in the product development life-cycle.
Bio-Processing Alliance, Inc.