POTENCY TESTING


failure rate, as well as relative potency results are also essential components of assay maintenance, especially in a QC environment.


Trending and periodic review of method parameters, such as EC50


“ , signal-to-noise ratio, assay


Phase Appropriate Potency Assay Development and Validation


Development of a biopharmaceutical product requires significant time and resources and carries a high level of uncertainty. Therefore, it is pragmatic to adopt a phase appropriate strategy for potency method development and validation. During the early stage of development, a binding assay (if appropriate based on MOA) is often preferred over a cell- based potency assay since a binding assay is much easier to develop and implement in a QC environment. However, as the project advances, especially when moving into pivotal clinical trials, a cell-based potency assay is often necessary and is typically preferred by regulatory authorities since it is more physiologically relevant and can sometimes reveal differences in product quality that are not detected in binding assays. It is important to note that some products may have multiple MOAs. In such a case, multiple assays may need to be established to sufficiently demonstrate product efficacy as well as lot- to-lot comparability. As an example, for monoclonal antibodies that are expected to


function through direct inhibition of receptor- induced proliferation, as well as Fc


function


(such as ADCC and Complement Dependent Cytotoxicity [CDC]), a toolbox containing a cell proliferation assay, an ADCC assay, a CDC assay, and an array of chemio-physical assays may be necessary to support both product development and quality control. Once sufficient knowledge has been obtained on product consistency and correlations between results from these different potency assays have been established, it is possible that only one of the assays is selected as a lot release assay to support routine manufacturing campaigns.


Once a potency assay is developed, the sponsor needs to perform a method qualification or validation to demonstrate suitability for intended use. Method qualification/validation also often follows a “phase appropriate” approach. During the early phase of clinical trials, the potency method should at minimum be qualified to demonstrate sufficient accuracy, precision, linearity, and range. The focus on accuracy and precision ensures meaningful interpretation of dose escalation studies. Comprehensive method validation


11 American Pharmaceutical Review | Biopharmaceutical Supplement 2014


should be implemented as the product moves into Phase III clinical trials and in anticipation of commercialization. A late phase validation study is typically more extensive than that of an early phase qualification and performed under a written protocol that clearly defines the scope of the validation, the target acceptance criteria, and data analysis plan. Multiple analysts and instruments are often employed, and the number of necessary assay runs is justified based on assay variability and intrinsic bias (if known). Method accuracy can be established by testing a sample with known relative potency prepared from the reference standard. In addition, representative routine sample types (drug substance, drug product, etc) should also be tested to confirm suitability of sample handling procedures and method precision. Representative degraded samples—obtained through long term or forced degradation studies—are also frequently included for testing during method validation to confirm the method’s stability-indicating property. Although method robustness may have been established using results generated during method development, a Design of Experiment can often be included within the validation to demonstrate tolerance to varying critical assay conditions.


After successful completion of the method validation, proper assay maintenance should be performed to prevent assay drift. Critical reagents need to be qualified prior to use, and new lots of reference standard need to be calibrated and bridged to the old lot of reference standard. Trending and periodic review of method parameters, such as EC50


,


signal-to-noise ratio, assay failure rate, as well as relative potency results are also essential components of assay maintenance, especially in a QC environment.


Final Comments


Potency determination is a critical part of product quality control. Potency assays may present in many different formats based on the MOA of the product. Phase appropriate method development and validation strategies help to reduce patient and business risk and are an integral part of product development.


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