Rare diseases present some unique obstacles for researchers that significantly contribute to the high cost of drug development. Fortunately, innovations in biomarker use have the potential to significantly cut back on these costs while improving data quality.
However, before biomarkers can be used in this research, their associated collection, measurement, and evaluation methods must be validated. The key phases of biomarker method validation include:
Validation begins with method feasibility studies, which take a look at how likely an assay will achieve its intended purpose. This usually includes an early objective assessment of an assay’s working range — its ability to measure the relevant biomarker at a predetermined range of concentrations.
Feasibility studies should also address an assay’s:
- Specificity — Ability to distinguish an analyte from structurally similar substances.
- Selectivity — The degree to which unrelated substances can cause analytical interference.
- Accuracy — The presence of the drug of interest, especially when interacting directly with drug targets.
2. Exploratory Method Validation
During this phase, the assay method is quantitatively characterized with respect to its basic analytical methods.
At least three evaluation runs are performed to determine:
- Accuracy — Defining the exposure-response relationship in the clinical diagnostic environment.
- Precision— Statistical significance of biomarker results in a study.
- Sensitivity — Lowest analyte concentration that can be measured with acceptable accuracy and precision. Level of sensitivity must be feasible in the clinical laboratory with regulatory compliance.
- Relative selectivity — With respect to the binding substrate, including the investigation of likely sources of interference.
- Initial biomarker concentration ranges — Results in normal controls and in the target study population.
- Assay dynamic range — Lower and upper limits within which the analyte is measurable with acceptable levels of accuracy, precision, and total error.
- Biomarker stability — Both short- and long-term and under conditions replicating those of the study. These include collection, transportation, and temperature.
3. Advanced Method Validation
In this phase, the same performance characteristics used in the exploratory phase are evaluated. Biomarker method validation is an iterative process with increased rigor undertaken in a scaled, fit-for-purpose approach. This process progresses as more data is obtained concerning safety, efficacy, pharmacodynamics, differentiation, and surrogate information.
4. In-Study Validation
Once methods have been evaluated and used for sample testing, they become an ideal source of data that reflects accuracy and precision performance from actual assay use. The in-study validation phase ensures that the assay continues to perform according to predefined expectations. Regular in-study validation typically involves the use of QC samples containing known concentrations of analytes used to confirm accuracy and precision.
A biomarker method is fit for purpose when it is capable of distinguishing statistically significant changes based on inter- and intra-subject variation. These qualities are vital when incorporating biomarkers into drug development study design, both for maintaining rigorous scientific standards and for ensuring swift regulatory approval.