In 1998, the U.S. NIH Biomarkers Definitions Working Group defined a biomarker as “a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention.” Since then, biomarkers have grown in popularity and now play a promising role in accelerating the pace and efficiency of drug development, not just in the U.S. but in other regulatory markets as well.
Despite the increasing role of biomarkers, widespread adoption of biomarkers has been impeded by a lack of consistent validation methodology and an unclear regulatory environment. In 2013, the U.S. FDA updated their Guidance for Industry on Bioanalytical Method Validation (BMV) to include a section on biomarkers—a move that was intended to streamline and standardize the biomarker validation process and requirements. Instead, the section on biomarkers generated more debate, in part because this latest draft guidance assumed too much similarity between pharmacokinetics and biomarker assays.
One thing is clear: If a biomarker is being used to support regulatory action as a pivotal determination of the safety and/or effectiveness of a drug, it should be validated rigorously. Here are five key points to consider when validating your biomarker.
1. Establish the scope of the biomarker’s use. Biomarkers have the ability to be used in a wide variety of studies to understand the prediction, cause, diagnosis, progression, regression, or outcome of treatment of disease. As a result, it is extremely important to determine early what the biomarker will ultimately be used for. Is it intended to test for toxicity? Will it measure the efficacy of treatment? The process for validation will vary based on this intended use. During this process, it should also be determined what the volume requirements and sensitivity of the assay are, along with the appropriate matrix and sample collection conditions.
2. Determine what variations could impact the assay. Common variables that could affect the outcome include effect of diurnal cycles, impact of fasting, and reported stability issues.
3. Probe the scientific literature. When working with a particular biomarker, checking established literature for references, specifically for reference points within the study species, is an important step. If there is a valid reference point for the biomarker being used, the next step is to check for commercially available kits. Performance and reliability of commercially available kits should not be taken at face value and should be tested thoroughly prior to use, especially if generated biomarker data is critical to the outcome of the study.
4. Establish validation parameters. It’s important to know the limits of your assay. Appropriate validation parameters include: parallelism, linearity of dilution and prozone; range of response; intra- and interassay precision and relative accuracy; and stability.
5. Account for lot variation. (Only after validation has been completed.) Once the biomarker has been validated thoroughly, reagent/kit lot variation should be considered. More often than not, reference material is recombinant material (and often not of the same species) and does not always behave as its endogenous counterpart in plasma/serum. If you are using multiple lots of kits during a study, quality controls consisting of the endogenous biomarker in the matrix of interest should be used to ensure that different lots of kits will yield comparable results so you don’t generate artefactual variations in the biomarker profile throughout the study.