Commercial assay kits biomarker validation

This chapter will attempt to describe the various options available to validate commercial assays used in chug development appropriately to meet the expectations and requirements of each study in which they may be used. In particular, we will examine the use of commercial kits for pharmacodynamic (PD), efficacy and toxicity (biomarkers), and pharmacokinetic (PK) assessments. The PK assessment assays will focus on those molecules that are developed as therapeutic chugs, but which are also compounds that exist endogenously in humans. These chugs are often called new biological entities (NBEs) and examples include growth hormone, insulin, and erythropoietin. 

At a minimum, documentation of the characterization and stability of a standard, such as a certificate of analysis (Co A) and/or a certificate of stability (CoS), is typically available from the suppliers. The certificate should be obtained and recorded. The quantity of reference standard is typically limited in commercial kits designed for research use, and it is not uncommon that the reference material values may differ substantially between lots and manufacturers [16]. Novel biomarkers rarely have established gold standards against which their potency and abundance can be calibrated. A comparison of available sources can be useful, and when validating an assay for advanced applications it is desirable to plan ahead to obtain and reserve a sufficient supply of the same reference material. The example in Fig. 6.5 compares three reference standard curves, each prepared from a concentrated stock solution from a commercial supplier, an in-house reference standard, and a commercial kit, respectively. The instrument responses (optical density, OD) were highest with the standard from the commercial stock, the lowest with the kit, while the in-house reference standard response was intermediate. In this case, either the same commercial stock or the in-house reference standard can be used throughout the clinical study. 

The validation experiments conducted in the course of validating a commercial kit are the same as for any biomarker assay and the full list of possible experiments is given in Table 7.2. 

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