Method validation of protein biomarkers in support of drug development or clinical diagnosis/prognosis

Protein biomarkers are used for various purposes in drug development and clinical diagnosis and prognosis. In this review, a fit-for-purpose method validation approach is discussed that fulfills the needs of exploratory and advanced applications in both the pharmaceutical and diagnostic arenas. Method validation for protein biomarkers is typically applied to ligand binding assays (LBA) although hyphenated mass spectrometric methods can be used as adjunct methodologies to confirm LBA specificity or provide valuable information during early discovery or demonstrative phases of a novel biomarker. Pre-analytic variables of protein biomarkers, such as the purpose of the intended application, analyte(s), biological matrix, availability of reference standard, calibrator matrix, assay platform, and sample collection/handling, must be considered in any method development and validation plan. Method validation for exploratory applications involves basic experiments for assay range finding, accuracy and precision, selectivity, specificity, and minimal stability. For advanced method validation, more rigorous tests with a wider scope are performed. These tests include additional patient population ranges, more runs on accuracy and precision from multiple analysts/reagent lots/instruments, selectivity and specificity tests using patient samples, and stability tests subjected to conceivable conditions over long-term use. Differences in biomarker method validation for drug development vs. clinical diagnosis and issues of using developmental commercial kits are discussed. The co-development of biomarkers for drug development and diagnostics presents collaborative opportunities between the pharmaceutical and diagnostic sectors.