Fundamentals of large-molecule protein therapeutic bioanalysis using ligand-binding assays.

This article provides an overview of ligand-binding assays, including the origin and evolution of the primary concepts, in addition to reviewing commonly used assay formats. The birth of ligand-binding assays began with a radioimmunoassay developed to measure insulin in 1960. Fundamental to ligand-binding assay design is the requirement of at least one protein that interacts with the analyte of interest. Enzyme immunoassay has largely supplanted radioimmunoassay as the ligand-binding assay of choice in today's laboratory environment. This article illustrates various assay formats such as competitive, sandwich and bridging, in addition to, describing critical reagents necessary for their design. The utility of ligand-binding assays in therapeutic protein development and comparison to alternative bioanalysis platforms is discussed.