Guidelines For Defining A Control Strategy Framework For Accelerated mAb Programs
By BioPhorum
Accelerating chemistry, manufacturing, and control (CMC) development for early-stage molecules that have shown exceptional performance in preclinical or clinical studies is critical to bringing promising treatments to patients as quickly as possible. While acceleration helps get treatments to patients faster, it poses challenges to the CMC development of the molecule because it allows less time for the generation of product-specific CMC knowledge as the project advances rapidly through the later phases of clinical trials. This requires that CMC teams maintain a strong focus on the generation of a robust product quality-driven control strategy that ensures the safety and efficacy of the compound despite the reduced timeline for the generation of product-specific knowledge.
Acceleration during process characterization is particularly relevant to control strategy development. This can be achieved by reaching a consensus on how to prioritize both the process parameters for characterization and the analytical testing used to determine impacts on the product. Consensus on parameter importance allows the development team to focus process characterization studies on the limited number of potentially impactful parameters and leverage scientific knowledge and a risk-based approach to classify remaining parameters as non-impactful.
This article presents a brief introduction to process parameter risks within typical evaluation ranges. The aim is to provide CMC teams with a foundation that can be combined with internal platform and product-specific knowledge to guide the design of efficient work packages to appropriately characterize processes for accelerated programs. It assembles an industrywide “platform” knowledge base on the impact of parameters across unit operations in a standard mAb process. It also will help development teams identify potentially impactful parameters and provide clear justifications to inform CMC decisions on parameter risk.
There are many phases and process parameters to consider, but here we will concentrate on potentially impactful and non-impactful process parameters that may inform:
- the production bioreactor unit operation (from the cell culture/upstream process phase)
- bind and eluate chromatography (from the purification/downstream process phase)
- filling (from the drug product process phase)
- analytics.
Production Bioreactor
The production bioreactor unit operation serves to continue the robust growth and viability of the culture from the inoculum expansion unit operations while also providing an environment for the cell culture to produce significant quantities of the product of interest. Therefore, the parameters considered here will have a great impact on the (potential) critical quality attribute (pCQAs). Maintaining robust culture growth and viability ensures high productivity and reproducible product quality.
Tables 1 and 2 indicate the parameters that were found to commonly impact or not commonly impact process performance across the production bioreactor unit operation. While the parameters (within the ranges detailed) in Table 2 were deemed to have no impact, the failure mode of some of these parameters may impact a parameter that does impact the process performance and product quality. For example, a failure in the media fill volume or inoculum volume will impact the viable cell density (VCD) at inoculation.
Table 1: Production bioreactor: impactful process parameters.
Key: pCQA — (potential) critical quality attribute, PP — process parameter, VCD — viable cell density
Table 2: Production bioreactor: non-impactful process parameters.
Key: CHO — Chinese hamster ovary, VCD — viable cell density
Bind And Elute Chromatography
The main goals of a bind and elute chromatography step are product and process impurity clearance robustness while maintaining yield. Impurities include rHCP, rProA, aggregation, fragmentation, and product charge heterogeneity. Typically, bind and elute chromatography refers to the target molecule binding to the column under load conditions where product and/or process impurities flow directly through the column or bind tighter to the resin than the mAb. The product is then eluted from the column by changing the buffer conditions.
Cation Exchange Chromatography (CEX)
During bind and elute mode, a gradient from lower to higher salt concentration is typically used to preferentially separate aggregates and other impurities from the mAb, which has a weaker affinity for the resin under higher salt concentration conditions. Elution buffer pH also can impact product binding and impurity separation. Higher elution buffer pH can lower impurity clearance due to potential co-elution of aggregates, while lower elution buffer pH can impact product elution from the column. Load conductivity is usually ≤6 mS/cm but can be product-dependent and impact yield and impurity clearance.
Mixed-Mode Cation Exchange Chromatography (MMCEX)
Mixed-mode cation exchange chromatography uses a mixed-mode cationic ligand that can promote electrostatic, hydrogen bonding, and hydrophobic interactions to enhance impurity removal. An example of an MMCEX resin for product purification would be Capto MMC. Loading conductivity can be higher than traditional CEX to activate the combination of ionic and hydrophobic groups on the resin to allow for selective impurity clearance (aggregates, rHCP). Column loading might be lower than traditional CEX resins due to three modes of binding potential with MMCEX resin (electrostatic, hydrophobic, and hydrogen bonding). Impurities can be removed from MMCEX resin using a caustic with salt buffer (or two separate buffers; one high salt and one caustic buffer) for a regeneration protocol.
Hydrophobic Interaction Chromatography
For the bind and elute operation, a gradient of higher to lower concentration of kosmotropic salt will be used in the separation of product from impurities such as aggregates and rHCP. Impurity removal can be a function of column loading, which is similar to MMCEX and CEX bind and elute modes. Load pH is typically operated near a neutral pH of ~7.
Tables 3 and 4 indicate the parameters that were found to commonly impact or not commonly impact process performance across the bind and elute chromatography step.
Additional wash steps for impurity removal for the bind and elute mode were not considered in this assessment since these wash steps will be protein and process dependent. Additional wash steps could contain some impactful parameters based on the evaluation range and impact on pCQAs, yield, or viral clearance.
Table 3: Bind and elute chromatography: impactful parameters.
Key: LMW — low molecular weight, pCQA — (potential) critical quality attribute
Table 4: Bind and elute chromatography: non-impactful parameters.
Key: CIP — clean in place, CV — column volume, FT — flow through
Filling
In this unit operation, the sterile-filtered bulk solution is aseptically filled in presterilized containers at the target fill volume/fill weight under a highly controlled cleanroom environment. Depending on the final dosage form, the filled container may be either fully stoppered and sealed as finished product (such as a vial or a prefilled syringe) or the closure is partially stoppered to prepare it for the lyophilization operation.
The primary container and closure characteristics vary widely in terms of their material of construction, design, and size. In addition, these components may pass through multiple preparatory steps such as washing, drying, lubrication (in the case of a prefilled syringe and cartridge), depyrogenation (or dry heat sterilization), steam sterilization, etc., before being used for filling. Besides primary containers and closures, as part of a product contamination control strategy, each product-contact material (such as filter, tubing, connector, and filling needle) is prepared in such a way that sterility and a low endotoxin level in the finished product are ensured. This step ends with the visual inspection of filled and sealed liquid product or moving half-stoppered vials into the lyophilizer for lyophilized product.
Tables 5 and 6 indicate the parameters that were found to commonly impact or not commonly impact process performance across the filling unit operation.
Table 5: Filling operation: impactful parameters.
Key: DP — drug product, PFS — prefilled syringe
Table 6: Filling operation: non-impactful parameters.
Analytics
Analytical Control Strategy
The design and implementation of an appropriate analytical testing strategy is an integral component of the overall control strategy to ensure process consistency and product quality. The analytical control strategy generally consists of in-process testing, release and stability specification, and extended characterization. For an accelerated program, the level of product understanding may not be as comprehensive as during a traditional development program. This, along with potentially limited manufacturing history (or batches) and long-term real-time stability data, poses significant challenges in finalizing the analytical control strategy for an accelerated program. The sections below provide guidance to consider when designing in-process testing and release and stability testing for early-phase development. They include approaches to develop rational later-stage or commercial specifications in accelerated programs.
In-Process Testing
In-process testing is implemented throughout the manufacturing process to ensure process consistency and product quality. There are two types of in-process testing: testing to measure process performance indicators and product quality (CQAs).
In addition to regulatory expected CQAs (e.g., safety testing, microbial control), the strategy for in-process testing of CQAs should be determined based on process characterization risk assessment and study outcomes, with consideration for how each unit operation modulates CQAs. We expect that acceptance criteria or action limits also will be defined for any in-process test at the respective unit operation to assess the consistency of the process. In-process testing may also be used for process analytical technology applications or to eliminate the need for testing of CQAs at release, where justified, depending on the point of control. The initial strategy and rationale for testing are outlined in Table 7 and represent an approach in which process and product understanding are still emerging. We expect that some of this testing (e.g., rDNA, rProA) may be eliminated at later stages of development, where process capability to remove these impurities has been demonstrated. Note that there are variations between companies as to which unit operation this testing starts to take place.
Table 7: Minimum recommended drug substance in-process evaluation for process characterization studies.
Key: HMWS — high molecular weight species, LMWS — low molecular weight species
Release And Stability Test Methods For Early Phase
At early stages of development, both the process and product understanding are very limited. The setting of release and stability specifications is dealt with in greater depth in the BioPhorum companion article Harmonized approaches for setting and justifying commercial specifications of biological drugs.1 Beyond standard compendial test methods, we recommend that analytical method development consider methods for release and stability testing that may also be implemented rapidly to accelerate evaluation of process conditions.
For example, an antigen-binding enzyme-linked immunosorbent assay may serve as both an identity method and an indicator of biological activity to rapidly enable support of early manufacturing batches, with an intent to migrate to a cell-based bioassay for potency that is more relevant to the mechanism of action later in development due to its longer development time. Where possible, platform methods previously qualified or validated for the same therapeutic modality (e.g., a general size-exclusion chromatography method) are also recommended. As process and product understanding increase, additional method development may be required to monitor newly identified CQAs. Project planning should anticipate the need to bridge methods accordingly.
Considerations In Developing Commercial Specifications For Accelerated Programs
As the program progresses to the late stage of development or marketing application, a commercial-ready specification needs to be proposed by the sponsor. A holistic review of the data and knowledge accumulated throughout the development stages of the program is needed to set up an appropriate commercial specification that considers the manufacturing capability, clinical experience, product stability profile, and understanding of the structure-function relationship, etc.
As mentioned, for an accelerated program, the challenge mainly arises from the limited characterization and understanding of both the manufacturing process and the product, as well as less manufacturing experience (i.e., fewer manufacturing batches) and a lack of a long-term, real-time stability profile. As a result, there are some additional considerations beyond the conventional approach of specification setting to take into account while combining data from the manufacturing capability, clinical experience, structure-function relationship understanding, product stability profile, etc.
Conclusion
Accelerating CMC program development to meet patient needs requires streamlined approaches to process characterization and control strategy definition. This article discusses a base-level list of process parameters for a small sample of unit operations across the different process phases.
Potentially impactful and non-impactful parameters are identified based on the collective experience of the group and are intended to supplement product-specific knowledge and considerations. We acknowledge the importance of appropriate analytical controls, though the specifics are outside the scope of this article. The collective understanding of manufacturing operations across Chinese hamster ovary-based antibody production has been leveraged to enable the establishment of meaningful controls to ensure product quality and safety.
This article summarizes some of the main points from a recent BioPhorum publication on this topic, which also includes a discussion on a wide range of phases and process parameters. To learn more, check out the full paper, Guidelines to aid control strategy definition for accelerated programs
Reference
1. Le Page, C., Kelley, W., et al. Harmonized approaches for setting and justifying commercial specifications of biological drugs. BioPhorum, 2024.