Achieving Cost-Effective Bioprocesses

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Although many of the newest methods to optimize process economics focus squarely on the implementation of single-use systems and the realization of continuous processing, there are other methods of cost cutting that could help a bioprocess become more sustainable. Operators should look to methods to optimize the use of solvents, get the most from their resins, explore hybrid approaches and miniature bioreactors for improved process understanding, and investigate alternatives to mammalian vectors to improve cost calculations.

Optimization of media volumes
Resin prices can range from low single-digit thousands of dollars per liter for ion exchangers to tens of thousands of dollars per liter for affinity resins, estimates Kevin Isett, CEO and founder of Avitide, which makes high-affinity resins. The costs associated with chromatography resins can significantly contribute to overall manufacturing costs, especially if two or three chromatographic steps are required in a bioprocess, according to Alex Xenopoulos, principal research scientist at MilliporeSigma. Isett explains that resin manufacturers historically demanded a “premium” price for resins that could withstand rigorous cleaning and sanitation conditions and facilitated a better unit economy by allowing manufacturers to use less expensive sanitization buffers. According to Cobra Biologics’ Technical Director Tony Hitchcock, cost has to be delicately balanced with overall purity achieved, binding capacities, and the number of cycles that can be performed with the resin.

One strategy to lower the overall cost of bioprocessing is to minimize resin-related costs. “For a large commercial process producing one ton of antibody per year, chromatographic resins contribute about 10% of the downstream cost, while filters contribute up to 30%, because of the single-use nature of depth, virus, and sterile filters,” notes Xenopoulos. “For a smaller, single-use process producing 50 kg of antibody per year, the percentage of cost contributed by chromatographic resins goes down to a few percentage points, because capital and labor now constitute a larger fraction of the total cost.”

Rathore et al. estimate that in a typical monoclonal antibody (mAb) platform process, 60% of downstream costs come from chromatography (1); the cost of a typical Protein A resin is 50% higher than the cost of traditional chromatographic media. Although Gjoka et al. agree that economic optimization of chromatography is critical, these authors estimate that Protein A resin is closer to “an order of magnitude more expensive than other non-affinity sorbents (including most ion exchangers)” (2).

The switch to single-use systems has been highly cited as a way to reduce costs in biomanufacturing. Although Xenopoulos mentions that the use of disposables generally increases the consumable component of the cost of bioprocessing, single-use chromatography devices, such as prepacked columns and membrane adsorbers, could offer overall “cost advantages because of the elimination of column packing and media washing and storage steps.” Hitchcock points out that at smaller processing volumes, single-use products can reduce the amount of liquids that are typically used in cleaning operations.

Resin reuse
Cycling of resins can occur, and resin reuse typically lowers the cost burden of a process. A resin can be used for up to 200–300 cycles, and smaller columns are typically used to facilitate resin reuse. Validating even more reuses of resins can reduce costs further, says Xenopoulos, although he says that the benefit above 50 reuses is quite small and the cost of validation should be taken into account. Not all resins have the same number of reuses, adds Isett: “Ligand stability, resin matrix, and chemistries employed to immobilize the ligands are key determinants to the reusability of any bioprocess resin.”

Reusing resin, although potentially cost-effective, increases total purification time, decreasing throughput (1). Long-term use of a resin has also been associated with a resin’s decreased efficiency in terms of product recovery as a result of resin fouling, ligand degradation, or reduction in pore surface area. Using a simple depth filter before loading, notes Xenopoulos, can reduce the incidence of resin fouling and maximize the number of potential resin reuses.

Improving resin selectivity
Improving resin selectivity could potentially help operators eliminate a downstream chromatographic step entirely, says Xenopoulos, or at the least, reduce the load on downstream steps. It’s a double-edged sword, however: although selecting a resin with a high binding capacity can limit the amount of resin used, “such high-performance resins usually have a higher per-liter cost,” asserts Xenopoulos. Newer separation technologies may play a major role in improving process economics, notes Isett. “Identifying highly selective, product-specific resins can enable reduced purification unit operations, afford efficient step-elution schemes, and permit flow-through polish applications, which will ultimately have the largest beneficial impact on resin usage and media/buffer volume costs in batch and continuous downstream processing.”

Finally, other small changes in a bioprocess (e.g., proper selection of wash and elution buffers to maximize product recovery, optimizing solution conditions such as dilution or pH changes, using flow-through conditions, and potentially, overloading a column beyond nominal binding capacity) can reduce resin volume and could possibly improve the performance of some of the chromatographic steps, says Xenopoulos.

Additionally, some manufacturers use in-line mixing and dilution of buffer components, which could help reduce the amount of media used in downstream processing, notes Benoit Mothes, scientific and innovation downstream processing head at Sanofi in France. Mothes says that regarding buffers, adoption of “in-line dilution and in-line concentration will be the next improvement to reduce the amount of media in downstream processing.”
 

Continuous operations
Harnessing continuous downstream operations has been cited as a good way to both improve the utilization of chromatography resins and decrease the demand on filters (3, 4). Multi-column systems, in particular, allow resins to enjoy the longest lifespan (3). Adds Xenopoulos, “Continuous, multi-column chromatography has certainly been shown to reduce resin volume used by significant amounts, up to 80%. The benefits depend on factors such as product titer, batch time, and cycling schedule and are higher when the resin is reused multiple times during cycling.”

Klutz et al. found that in upstream operations for the manufacture of mAbs, however, continuous processes use more fermentation media for perfusion than did fed-batch operations (84 pounds per grams mAb vs. 59 pounds per grams mAb, respectively), making it more expensive to use continuous processes upstream. Downstream continuous operations, nevertheless, were more efficient from a cost perspective-which the authors attributed to better utilization of chromatography resins in downstream operations. Plus, using fed-batch operations upstream instead of continuous perfusion did not affect overall yield, according to Klutz and his colleagues: “In all cases, fed-batch fermentation is more cost efficient than the perfusion fermentation at the same level of cell-specific productivity.” Klutz et al. concluded that a hybrid approach-consisting of fed-batch operations upstream and continuous chromatography downstream-was the most cost-effective model, corresponding to a 15% reduction in cost of goods (CoGs) (3).

As a whole, it appears a hybrid approach uses the least amount of media. Although hybrid methods “lack the elegance of completely continuous templates,” according to Xenopoulos, they do address cost pressures related to high cell-culture media usage.

Although the aforementioned study by Klutz el al. did not find an increase in productivity associated with continuous perfusion, other experts in the field say that the productivity increase outweighs the amount of media consumption in continuous upstream operations. “Continuous processing provides clear advantages in terms of space-time-yields,” says Christel Fenge, vice-president of marketing and product management, fermentation technology, Sartorius Stedim Biotech. In other words, “the amount of material produced per unit time and volume is higher compared with conventional fed-batch processes.” Xenopoulos concurs that while continuous perfusion uses more media-which he estimates can total 1–10 bioreactor volumes per day-he says the increased cost is “somewhat mitigated” by the increased productivity, as measured by the cost per gram of product. Scott Waniger, vice-president of bioservices at the Cell Culture Company, also asserts that generating greater production “makes up for the additional raw material consumption of relatively inexpensive liquid tissue culture media."

To control overall costs, “there is also an effort to reduce the cost of the media itself, with development efforts directly targeted to perfusion cell culture media,” notes Xenopoulos.  “Biomanufacturers usually work with media vendors, but sometimes invest in internal development of media, showing the importance of this aspect.” In an attempt to reduce cell-culture media volume used, some companies opt to use richer media, which Xenopoulos says can unfortunately also increase media cost per liter. An additional strategy to optimize media consumption, says Waniger, is to perform an offline analysis of spent media to characterize the consumption and production of media elements. “The resulting information allows for identification of the components that are limited, and have been consumed by the cell line,” Waniger articulates. "With this knowledge, the operator can add concentrated amounts of nutrients as a supplement to replace any specific ones that have been exhausted."
 

Buffer recycling
Jungbauer and Walch write that buffer recycling positively impacts process economics (5). The reuse of buffers could decrease waste streams and save money that goes into wastewater treatment efforts. The authors suggest the use of multi-column separations, integrated continuous countercurrent chromatography, and countercurrent tangential flow chromatography as effective ways in which buffers can be recycled. They note that continuous processes and the introduction of filtration into chromatography systems would allow for a substantial reduction in solvent consumption.

Unlike resins and other solvents, expert consensus is that buffers don’t significantly contribute to overall biopharmaceutical manufacturing costs. “Cost savings of recycling would most probably be countered by the cost of the recycling equipment and by the need to validate and test the recycled buffers,” notes Xenopoulos. “Buffer recycling could address environmental concerns of disposal, especially if a particularly exotic buffer is used.” Hitchcock adds that the operation and validation challenges associated with buffer recycling may not make it "worthwhile for a majority of production processes."

Rather than focus on salvaging buffers, Sanofi’s Accelerated Seamless Antibody Purification (ASAP) platform focuses on avoiding the use of nonvaluable buffers as a technique to reduce downstream purification costs. “Most of purification processes include a minimum of three chromatographic steps made in a sequence of distinct unit operations,” says Mothes, who runs the ASAP program in France. He says that unit operations cannot normally be operated in a continuous mode, “as adjustment of pH, molarity, and protein concentration are necessary between each chromatographic or filtration step.” The ASAP platform, however, eliminates the need to perform what he calls these “non-added-value unit operations” and shortens process cycle time to less than three hours. Use of the system facilitates a reduction in the buffer volumes that are necessary for processing, notes Mothes. While a typical mAb purification relies on a total of nine buffers, the ASAP model requires only four. Mothes adds that Sanofi’s process will “provide an entirely purified mAb in a few hours while reducing the volume of resin used” and will enable the reduction of buffer volumes because of the platform’s small columns and singular process skid.

Other factors that influence cost
Additional costs related to biopharmaceutical manufacturing can be tied to events that occur after an actual product is manufactured. These factors can relate to drug safety, speed to clinic, and time to market, notes Fenge. Hitchcock estimates that 80% or more of costs are locked up in the manufacturing design of a product; therefore, “understanding the implications of choices within the development phase” and manufacturing processes is key. He adds, “Once these choices have been made, there is often only a limited amount of cost reductions that can really be achieved.”

Fenge mentions that incorporating a fully integrated upstream platform early-combined with a similar downstream strategy-can help reduce development-related costs. “By selecting tools that are efficient in their own right but that have also been designed to work together can significantly reduce the resources and time needed to develop processes and can ensure low cost of goods in manufacturing with reliable high productivity and consistent product quality. For example, by deciding to use an expression platform with a track record of high-productivity cell lines that has a proven performance from small- to large-scale bioreactors, the risk of delays and high costs associated with determining optimum process parameters and control strategies are considerably reduced, and a rapid path into [the] clinic is provided."

Costs related to outsourcing must also be managed, and Waniger suggests taking extra measures to ensure that the technology transfer, method performance, and manufacturing process are all addressed in the original request for proposal (RFP). “CDMOs [contract and development manufacturing organizations] may unintentionally add costs to projects where the RFP does not fully describe the needs of the manufacturing process,” Waniger says. “Ultimately, these costs are passed on to the patient.” Waniger also suggests conducting comprehensive stability studies on the final product, which he says will maximize product shelf life and reduce the frequency of batch production.

"The pace of discovering novel drugs and engineering highly productive biopharmaceutical production systems, in large part, has outpaced the engineering of high-performance separation ligands and resins,” concludes Isett, who believes that the industry should put an increased focus on optimizing downstream operations to make biopharmaceutical manufacturing more cost-effective overall. "This is particularly true for vaccine and biosimiliar companies, where sensitivities to manufacturing costs/pressures are more pronounced."

References
1. A. Rathore et al., BioPharm Int. 28 (3), pp. 28–33 (March 2015).
2. X. Gjoka et al., J. of Chrom. A 1416, pp. 38–46 (Oct. 16, 2015).
3. S. Klutz et al., Chem. Eng. Sci. 141, pp. 63–74 (2016).
4. A. Xenopoulos, J. Biotechnol. 213, pp. 42–53 (2015).
5. A. Jungbauer and N. Walch, Curr. Opin. Chem. Eng. 10, pp. 1–7 (2015).

Article DetailsBioPharm International
Vol. 29, No. 3
Pages 14–19
Citation: When referring to this article, please cite it as R. Hernandez, "Achieving Cost-Effective Bioprocesses," BioPharm International29 (3) 2016.