Potency Assays: Cell-Based vs Binding—Which and Why


Published on 08/12/2025

Potency Assays: Cell-Based vs Binding—Which and Why

In the realm of biotechnology and pharmaceuticals, potency assays play a crucial role in ensuring the efficacy and safety of biologics and advanced therapy medicinal products (ATMPs). As regulatory agencies such as the FDA, EMA, and MHRA increasingly scrutinize these methods, understanding the distinctions between cell-based assays and binding assays is fundamental for compliance and quality assurance. This article provides a step-by-step guide tailored for pharmaceutical professionals, detailing the execution of potency assays, including viral clearance validation, spiking studies, and considerations around closed and single-use systems.

Understanding Potency Assays

Potency assays are analytical procedures that assess the biological activity of a therapeutic product, reflecting its effectiveness. The primary objective of these assays is to quantify the active moiety in relation to its intended effect. Ensuring the accuracy and reliability of potency measurements is critical for both product release and regulatory approval. According to ICH Q5A(R2) guidelines, potency should be evaluated as part of quality control to demonstrate consistency across different production lots.

There are two primary types of potency assays utilized in the industry: cell-based assays and binding assays. Each type offers distinct advantages and challenges that must be evaluated in light of specific product requirements and regulatory expectations.

Cell-Based Assays

Cell-based assays utilize living cells to measure the biological activity of a product. These assays are highly relevant for biologics that operate through a mechanism of action involving cellular interaction, such as monoclonal antibodies and vaccines.

  • Advantages of Cell-Based Assays:
    • Can assess complex mechanisms of action in a physiologically relevant environment.
    • May provide more accurate representation of in vivo efficacy.
    • Allows for the assessment of critical quality attributes (CQAs) related to potency.
  • Challenges of Cell-Based Assays:
    • More complex to design and validate compared to binding assays.
    • Increased variability due to cell line characteristics and culture conditions.
    • Longer time frames for results, impacting timelines.

Binding Assays

Binding assays, on the other hand, measure the affinity of a product to its target receptor or ligand without the need for living cells. These assays can be performed using techniques like ELISA (enzyme-linked immunosorbent assay) or radiolabeled binding assays.

  • Advantages of Binding Assays:
    • Simpler and faster to conduct than cell-based assays.
    • Less variability and can be highly reproducible.
    • Typically easier to scale for large batch analyses.
  • Challenges of Binding Assays:
    • May not correlate well with in vivo activity.
    • Does not account for post-translational modifications affecting activity.
    • Risk of over-reliance on these assays without considering biological context.

Viral Clearance Validation in Potency Assays

In addition to their roles in measuring potency, both cell-based and binding assays require robust validation to address safety concerns, particularly regarding viral contamination. Viral clearance validation is critical for biologics manufactured in systems at risk of contamination. As part of ^[PHYS] the validation process and in compliance with ICH guidelines, manufacturers must demonstrate that their processes effectively eliminate viruses.

This involves conducting spiking studies where known quantities of viruses are introduced into the manufacturing process to evaluate the effectiveness of the viral clearance steps. The results of these studies are essential for both regulatory submissions and internal quality assurance processes.

Conducting Spiking Studies

Spiking studies are a crucial component of viral clearance validation. They simulate potential viral contamination scenarios, thus allowing manufacturers to assess the robustness of their processes against viral loads. The following steps outline the process of conducting spiking studies:

  • Step 1: Selection of Viral Agents

    Select appropriate viral agents that represent potential contaminants based on the product’s source and production method.

  • Step 2: Establishing Spiking Levels

    Determine spiking levels that reflect worst-case scenarios, ensuring that the quantity of virus introduced is representative of potential exposure during manufacturing.

  • Step 3: Implementation of the Spiking Procedure

    Introduce the viral agents at specific points within the manufacturing process while ensuring all environmental controls are maintained.

  • Step 4: Evaluation of Viral Clearance

    Analyze how effectively the viral clearance measures eliminate the contaminating agents, using analytical methods compliant with industry standards.

  • Step 5: Documentation and Reporting

    Document all procedures, results, and analyses comprehensively. Ensure proper reporting as per regulatory guidelines.

Closed and Single-Use Systems in Potency Assays

Closed systems and single-use systems have revolutionized manufacturing processes in the pharmaceutical industry, particularly regarding aseptic controls as outlined in Annex 1 of the EU GMP guidelines. These systems minimize the risk of contamination and facilitate the maintenance of sterility throughout production, especially relevant for cell-based potency assays.

Closed systems involve a manufacturing environment where materials are transferred without exposure to the external environment. Single-use systems are designed to be used once and then discarded, which drastically reduces cleaning requirements and the risk of cross-contamination between batches.

Implementation of Closed and Single-Use Systems

To implement effective closed and single-use systems within potency assays, consider the following steps:

  • Step 1: Assess Product Requirements

    Identify the specific needs of the product being validated and how closed or single-use systems can support those requirements.

  • Step 2: Evaluate Equipment Options

    Choose the appropriate equipment and materials that conform to regulatory expectations while allowing seamless integration with existing processes.

  • Step 3: Design Process Flow

    Map out the process flow, ensuring all critical control points are addressed to maintain closed or single-use conditions.

  • Step 4: Conduct Validation Studies

    Undertake comprehensive validation studies to confirm the integrity and functionality of closed and single-use systems in the context of potency assays.

  • Step 5: Train Personnel

    Ensure all personnel are trained on the operability and benefits of closed and single-use systems to align with best practices in aseptic processing.

Integrating Potency Assays with Quality Systems

For successful implementation and oversight of potency assays, it is critical to integrate processes into the Quality Management System (QMS). A robust QMS encompasses all necessary procedures, documentation, and controls to ensure compliance with FDA process validation and other regulatory criteria.

Tailoring PPQ and CPV for ATMPs

As biologics and ATMPs often have unique challenges, it’s essential to tailor the Protocols for Product Quality (PPQ) and Continued Process Verification (CPV) to these specific scenarios. The following steps are integral to this customization:

  • Step 1: Conduct a Risk Assessment

    Perform a thorough risk assessment on the production processes that evaluate potential failures and their impact on product quality.

  • Step 2: Define Critical Quality Attributes

    Identify and characterize potency identity CQAs that are essential for evaluating the safety and efficacy of the ATMP.

  • Step 3: Create Focused Protocols

    Develop PPQ and CPV protocols that are reflective of the nuances associated with ATMP manufacturing and the discovered CQAs.

  • Step 4: Incorporate Continuous Feedback Loops

    Implement mechanisms for real-time monitoring and feedback to keep PPQ and CPV current with evolving regulatory and scientific understanding.

  • Step 5: Documentation and Periodic Review

    Maintain thorough documentation and establish a timetable for periodic reviews to ensure the ongoing effectiveness of tailored protocols.

Conclusion

In conclusion, the selection between cell-based assays and binding assays for potency testing depends on a variety of factors, including the nature of the biologic product, regulatory requirements, and the desired accuracy of the potency measurement. With the consideration of viral clearance validation, spiking studies, and the use of closed and single-use systems, companies can establish robust processes that adhere to good manufacturing practices while ensuring product safety and efficacy.

Finally, by tailoring the PPQ and CPV specific to the nuances of ATMPs, organizations can foster a continuous improvement culture that aligns with both industry innovation and regulatory expectations. As the landscape of biologics and their validation evolves, staying informed and adaptable will remain paramount in navigating the complexities of potency assays.