What you should know about potency assays

Linsey Reavie

by Linsey Reavie

For licensing of biopharmaceuticals, development and validation of a potency assay(s) should be included in the specifications for the drug substance (DS) and/or drug product (DP) [1]. A potency assay is the quantitative measure of biological activity, ideally it measures the ability of the product to elicit a specific response in a disease-relevant system (Figure 1; [1-4]). The activity measured in the assay must therefore represent the intended biological effect (mechanism of action) and be related to the clinical response (if possible).

Importantly, the potency assay should be capable discriminating product batches based on the following key criteria:

  • Amount of the active ingredient is sufficient to induce the biological effect

  • Sub-potent batches can be identified (including storage under accelerated conditions as well as forced degradation studies)

  • Consistency of the DP is ensured, e.g. batch-to-batch and during the proposed shelf-life

Figure 1: Overview on key features of a potency assay

Upfront thinking and strategic planning are essential to decide:

  • Which assays are required to form a characterization package,

  • Are used for manufacturing and release, and/or

  • Demonstrate an appropriate link to the intended clinical effect (Figure 2).

Depending on the complexity of the product, a combination of multiple methods may be needed to adequately define potency during development (Figure 2). Based on our experience, this scenario applies quite often to cell and gene therapies, also called advanced therapy medicinal products (ATMPs) in the EU. Certain assays may be needed to control process changes, whereas others are more suitable for release testing. If the intended potency assay is not a direct measure of the product’s mechanism of action, then a clear correlation of the measured activity and biological effect must be demonstrated in additional assays during characterization.

Thus, defining potency and selection of appropriate assay(s) becomes a central figure during product development.

Figure 2: Potency along the value chain.

If indeed a matrix of assays is required for adequate control of the product, it is important to note that at least one assay must be quantitative. In the development of a product release assay, standardization, robustness and validation should be carefully considered [5, 6]. Can the quantitative assay that best represents the product’s biological activity (or has been solidly linked to that effect) be validated on the principles of accuracy, sensitivity, specificity, reproducibility and robustness? Are there adequate assay controls (e.g. WHO reference materials or commercially available material) to establish a validated assay? To get started, one might begin with identifying key assay parameters (e.g. viability, production, concentration, functionality) and available assays to meet these criteria. Several scenarios can then be constructed and potentially discussed with regulatory agencies to seek agreement on the best approach for the product.


Our team at Biopharma Excellence has helped multiple clients to develop and/or refine their approach to potency assays. We are happy to help you with any questions and facilitate the development of your potency approach so that it is in-line with regulatory expectations. We would be pleased to support you – do not hesitate to contact us for more information.


  1. ICH Q6B. Specifications: Test Procedures and Acceptance Criteria for Biotechnological/ biological Products. ICH Harmonised Tripartite Guideline 1999; Available from: https://database.ich.org/sites/default/files/Q6B%20Guideline.pdf

  2. EMA/CAT/852602/2018. Guideline on quality, non-clinical and clinical requirements for investigational advanced therapy medicinal products in clinical trials. 2019; Available from: https://www.ema.europa.eu/en/documents/scientific-guideline/draft-guideline-quality-non-clinical-clinical-requirements-investigational-advanced-therapy_en.pdf

  3. EMA/CHMP/BWP/271475/2006 rev.1. Guideline on potency testing of cell based immunotherapy medicinal products for the treatment of cancer. 2016; Available from: https://www.ema.europa.eu/en/documents/scientific-guideline/guideline-potency-testing-cell-based-immunotherapy-medicinal-products-treatment-cancer-revision-1_en.pdf

  4. CBER/FDA, Guidance for Industry Potency Tests for Cellular and Gene Therapy Products 2011.

  5. CDER. Bioanalytical Method Validation Guidance for Industry. 2018  April 2019]; Available from: https://www.fda.gov/downloads/Drugs/Guidances/ucm070107.pdf

  6. EMEA/CHMP/EWP/192217/2009 Rev. 1 Corr. 2. Guideline on bioanalytical method validation. 2011  May 2019]; Available from: https://www.ema.europa.eu/en/documents/scientific-guideline/guideline-bioanalytical-method-validation_en.pdf

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