Method validation and application of protein biomarkers: basic similarities and differences from biotherapeutics.

Protein drug development and biomarkers share common bioanalytical technologies that are applied for different purposes. A fit-for-purpose approach should be used for biomarker assays at various stages of novel biomarker development and their application to drug development. Biomarker quantifications can be absolute or relative, depending upon the characteristics of the standard curve, which include the reference standard, substituted matrix and parallelism. Appropriate method-validation experiments should be carried out on sample collection, relative accuracy and precision, range finding, parallelism, selectivity, specificity and stability in order to meet the need for exploratory or advanced application that is specified for a study. The interaction of a biotherapeutic with the target ligand or inter-related biomarkers should be taken into consideration for method platform choice and validation. Direct adoption of commercial diagnostic kits can produce confounding data. Therefore, kit comparison, modification and appropriate validation experiments are often carried out to meet the specific purpose for drug development. Multiplex assays and physicochemical methods can complement the single-analyte ligand-binding assay for protein drugs and biomarkers.