Potency assays in biological products are essential tools for evaluating the biological activity of medicines such as recombinant proteins, monoclonal antibodies, vaccines, and cell and gene therapies.
The amount of active substance present in a sample does not always indicate whether a biological medicine retains its function. For this reason, potency assays enable the quantitative assessment of whether a product maintains the biological activity associated with its mechanism of action.
Their application goes far beyond batch release. Potency assays can be used throughout the different stages of development, in stability studies, comparability assessments, and product characterization, as well as in routine manufacturing control.
What is a potency assay?
A potency assay is a test designed to measure the biological activity of a product and determine whether it retains the functional properties required to produce the intended effect.
Potency should not be confused with the amount of product present in a sample. A biological medicine may contain the expected concentration of a given protein while simultaneously having undergone structural or functional changes that reduce its activity.
For this reason, the assessment of biological products generally combines different analytical strategies. While physicochemical methods can be used to study characteristics such as identity, purity, or structure, potency assays provide information about the biological function of the product.
What do potency assays measure?
Depending on the characteristics of the medicine and its mechanism of action, a potency assay can measure different types of biological activity.
The main approaches include:
- Cell-based assays.
- Biochemical methods.
- Enzyme activity assays.
- Ligand-receptor binding assays.
- Functional assays related to the mechanism of action.
Cell-based assays are particularly relevant because they allow biological responses to be evaluated in a cellular system. However, the selection of the method must be scientifically justified and should depend on the characteristics of the product, its mechanism of action, and the critical attributes associated with its activity.
When appropriate international or national standards are available, results can be expressed in units of activity relative to those reference materials. The World Health Organization (WHO) establishes and maintains international biological standards that help harmonize the measurement of biological activity and facilitate the comparison of results between different laboratories and products. When suitable reference standards are not available, appropriately characterized in-house reference materials can be established.
Potency assays during the development of biological products
Potency assays should not be considered merely as a test that is introduced at the end of development. Their use from the early stages can provide relevant information about the relationship between product characteristics, the manufacturing process, and biological activity.
During development, these methods can help identify changes that may not necessarily be evident through certain physicochemical analyses.
This is particularly important when changes are introduced into the manufacturing process, such as changes to:
- Raw materials.
- Equipment.
- Facilities.
- Manufacturing parameters.
- Culture conditions.
- Purification steps.
A process change may alter certain product attributes without necessarily producing evident differences in all physicochemical analyses. Functional assays can help determine whether these changes have an impact on biological activity.
Potency assays and comparability
Comparability is one of the areas in which potency assays can provide particularly relevant information.
When a manufacturing process is modified, it is necessary to assess whether the product manufactured before and after the change retains comparable characteristics. Different analytical techniques are used for this purpose, including physicochemical methods and functional assays.
A potency assay can help determine whether a process change affects the biological activity of the product and, together with other analytical methods, contribute to the overall comparability assessment.
Therefore, these assays can be used to evaluate consistency between different batches and assess the impact of changes introduced during development and manufacturing.
Potency assays in cell and gene therapies
In cell and gene therapies, potency assessment can present additional complexity.
The control strategy may include not only a final release assay, but also controls associated with the manufacturing process, raw materials, materials, in-process testing, and other complementary assays.
For these products, potency may be associated with complex mechanisms of action and, in some cases, multiple functional attributes. Therefore, determining what should be measured and how it should be measured requires an analytical strategy tailored to the specific characteristics of the product.
The challenge of linking the assay to the mechanism of action
One of the main challenges in developing a potency assay is establishing a method that is sufficiently representative of the biological activity of the product while also being suitable for reproducible use in a quality control environment.
Biological products may have complex or multiple mechanisms of action. In certain situations, a single assay may not provide all the information required.
In these cases, it may be appropriate to use a combination of complementary methods to assess different aspects of biological activity.
It is not always necessary to reproduce exactly in the laboratory what occurs in the body. The key is to establish a scientifically justified relationship between the attribute measured by the assay and the biological properties relevant to the product.
As development progresses, the amount of information available about the product and its mechanism of action also increases. This allows the method to be refined, critical variables to be identified, and acceptance criteria to be established based on the data generated.
Accuracy and robustness of potency assays
When a potency assay is incorporated into routine quality control, its analytical performance becomes particularly important.
The method should provide sufficiently accurate, specific, reproducible, and robust results to detect relevant variations in product activity.
This can be particularly challenging for certain cell-based bioassays, where different factors can introduce variability, including:
- Cell status.
- Passage number.
- Incubation times.
- Reagents used.
- Environmental conditions.
- Equipment.
- Operators.
Therefore, procedure standardization, control of critical materials, and an appropriate reference material strategy are essential for obtaining consistent results.
Potency assays and stability studies
Potency assays also play an important role in the stability studies of biological products.
During storage, a biological medicine may undergo changes that affect its structure or function. Some of these changes may have an impact on biological activity even when certain physicochemical attributes remain within established acceptance criteria.
Periodic assessment of potency makes it possible to monitor how product activity changes during storage and provides relevant information for establishing and justifying shelf life and storage conditions.
For this reason, potency assays in biological products can form part of a stability strategy alongside other analytical methods designed to characterize changes in the product over time.
The importance of potency assays in quality control
Potency assays are a key tool for linking the analytical characterization of a biological medicine with its functional activity.
Their value is not limited to determining whether a batch meets a release criterion. They can also provide information during development, support comparability assessments, contribute to stability evaluation, and help monitor manufacturing process consistency.
The selection and development of the assay should be based on the specific characteristics of each product. In particular, there should be a scientifically justified relationship between the activity measured by the assay and the biological properties relevant to the medicine.
As biological products become increasingly complex, having appropriately developed, characterized, and controlled potency methods is essential for reliably assessing their biological activity.
Frequently asked questions
- What is a potency assay?
A potency assay is a test used to quantitatively measure the biological activity of a product. It helps determine whether a biological medicine retains functional activity related to its mechanism of action. - What is the difference between potency and the amount of active substance?
The amount of active substance indicates how much product is present in a sample, whereas potency evaluates its biological activity. A product may contain the expected amount of active substance while nevertheless showing reduced functional activity. - What are potency assays used for in biological products?
Potency assays are used to evaluate the biological activity of products such as recombinant proteins, monoclonal antibodies, vaccines, and cell and gene therapies. They can be used during development, comparability assessments, stability studies, and quality control. - What types of potency assays are there?
Depending on the product and its mechanism of action, different approaches can be used, including cell-based assays, biochemical methods, enzyme activity assays, and ligand-receptor binding assays, among other functional methods.
