Nandu Deorkar, Ph.D., MBA, Vice President, Research & Development, Avantor
Monoclonal antibody drugs (mAbs) make up more than 50 percent of the biologics on the market today, as well as a significant amount of pipeline drugs.Much of the bottleneck when it comes to delivering mAb therapeutics is within the downstream processing stage. The downstream process typically takes place over a period of a few weeks. It involves many unit operations, from multiple chromatographic steps to filtration steps, as well as more than a dozen buffers and cleaning solutions. Since downstream processing accounts for 60–80 percent of the total cost of producing a mAbs, it’s essential that biopharma manufacturers find ways to remove bottlenecks and improve downstream processing yields.
Pharma Manufacturing recently spoke with Nandu Deorkar, vice president, R&D at Avantor, to learn more about the process chromatography challenges faced by the industry and what Avantor’s new protein A resin brings to table in terms of efficiency and performance.
Q: What is the objective of downstream process chromatography and how is this typically accomplished?
A: The primary objective with downstream chromatography is to remove any process-related contaminants produced in the upstream process. The second objective is to remove any product-related impurities that could be safety issues. Ultimately, the goal is to make the drug substance out of raw ingredients that meet the efficacy and safety standards for use to make finished drug products.
Q: So why is it that biopharma still faces challenges in terms of process chromatography when it comes to downstream processing?
A: There are multiple problems. First, variations in the upstream process (for example, cell culture for mAbs or fermentation for recombinant proteins) need to be addressed by the downstream process. In order for the downstream process to be robust enough to address those variations, it has to be designed with extra safety factors built in, which can make the process less efficient. Suppose you have a chromatography column with the capacity to purify a hundred grams of protein per liter at an optimal condition. Because of built-in safety factors, you might only be able to purify 60 grams per liter, making it less efficient than it otherwise could be.
Second, most downstream operations are not 100 percent continuous. There are other unit operations that need to be conducted with high-quality raw materials and precise process control in order for downstream chromatography to accomplish the required purification. Auxiliary steps of downstream purification are required, like making sure the product that you are loading onto the column has a certain buffer composition, pH and conductivity. The downstream process starts with buffer conditioning using another filtration system or tangential filtration system to accomplish these necessary steps.
The downstream operation grows in size and complexity when one considers the impact of these auxiliary operations. For example, in a two- or three-step chromatographic system, there will be three chromatography steps and another three or four auxiliary steps for each column, ultimately requiring from nine to 12 steps to complete the process. The operation itself becomes larger and complex, factoring in the management of all of the raw materials, systems and steps required to support the end-to-end process.
Q: Given those challenges, what has the industry done to overcome them?
A: A platform approach can be an effective way to overcome downstream challenges. With a given type of molecule or chromatographic step, a platform approach can help drive standardization, which can help achieve process efficiencies. Companies can take different platform approaches, but the goal and some of the tools are similar.
For example, downstream purification of mAbs often includes the use of a protein A chromatographic resin for affinity chromatography. Since this step has been shown to provide very good purification, typically only one or two standardized polishing steps (such as cationic exchange followed by ion exchange) are needed after protein A.
Q: How does Avantor’s protein A improve downstream operations?
A: We looked at this as a safety factor-based calculation. For example, if an existing process can only process 40 grams of a mAb in one cycle, efficiencies can be achieved and operational complexity reduced through increasing the volume of material purified.
The J.T.Baker® BAKERBOND® PROchievA™ resin can help reduce the number of cycles by increasing the dynamic binding capacity of the material, making it possible to load more than 60 or 70 grams of mAb into the process and leading to increased productivity. We have also optimized the protein A ligand to have specificity to the Fc region of IgG. We can utilize the specificity of protein A and select additives to remove key impurities that in turn reduces the burden on the next step.
Finally, we have developed additives which, along with our optimized protein A ligand, are shown to improve protein A resin lifetime. Sucrose, for example, is shown to increase stability of the PROchievA™ resin and the use of a high alkaline cleaning solution, such as sodium hydroxide up to 1.0M.
Q: As manufacturers are scaling-up operations and the size of single-use bioreactors in upstream bioprocessing increases, what changes do you anticipate in chromatography equipment?
A: The most traditional way to scale up operations is to increase the size of the equipment as the amount of material increases, but that has limitations. A more advantageous way to scale up — an approach that both suppliers and manufacturers are taking — is to look at the protein A resin used in the chromatography process. By increasing the dynamic binding capacity of the resin, operators can accomplish more with the same size equipment. Additionally, manufacturers have also taken a look at semi-continuous operation. Instead of increasing the size of the column, manufacturers are increasing the flow through the columns and performing multiple cycles. The increase in flow limits the increase in overall run-time.
Q: I’d imagine both of these options are more economical than simply increasing equipment size?
A: Yes, especially because it’s not just the equipment footprint that increases. When you increase the column size, you have to increase the facility size, the power usage, and everything that goes along with using and maintaining that column. It adds complexity.
Q: How can manufacturers further improve downstream bioprocessing?
A: One option, as I mentioned, involves reducing the number of steps. If manufacturers can reduce the chromatography steps by using a selective resin or a resin washing mechanism, which will immediately reduce complexity.
A second option is utilizing a single-use system. A single-use system for buffer preparation and media preparation eliminates time-consuming and costly cleaning steps, making these processes available on-demand to improve overall efficiency.
A third option is to go to a continuous downstream process. The current standard workflow involves eluting the material from a first column, then storing it in a holding tank before it is prepared and loaded into a second column. This process is not truly continuous because of the holding step. At Avantor, we have been testing several molecules for their ability to elute directly from the first column into the second column, without the intermediate storage step in a tank. Using this approach, the loading efficiency of the resin appears to be a little bit lower compared to just doing one column at a time, but overall much faster and easier, with the added benefit of decreasing material consumption (water, buffers and cleaning solutions).