Application of a novel drug-tolerant target assay for measuring target engagement when only one epitope remains after therapeutic antibodies bind their targets.

The measurement of proteins with a limited number of available non-overlapping epitopes recognizable by antibodies represents a common challenge for the development of drug-tolerant clinical biomarker assays. For target proteins with two dominant epitopes, only one epitope remains when the other is occupied by the therapeutic antibody. Alternative strategies for overcoming this obstacle have been described in the literature; however, these methods have potential limitations. We have developed a novel method for measuring target engagement when only one epitope remains after therapeutic antibodies bind their analytes. The method combines Affinity Capture Elution (ACE) followed by simultaneous capture and detection of the protein of interest. This novel method has been named ACE-Sandwich. The application of this method is not dependent on the immunoglobulin G subclass of the therapeutic antibody, nor does this method require sample pretreatment. Furthermore, the ACE-Sandwich method is highly sensitive, reproducible, and tolerant to high concentrations of therapeutic antibody.