Detection of circulating blood biomarkers is commonly accomplished by sandwich ELISA using one antibody for capture and another antibody for detection. But what if that biomarker is also a target for a therapeutic monoclonal antibody (mAb)?
In a clinical sample, such a biomarker would exist in both bound and unbound forms in the presence of potentially higher amounts of the therapeutic mAb. Moreover, the binding of the therapeutic mAb to the target may change the body’s natural clearance, thereby altering the biomarker concentration in response to treatment.
Quantification of both bound and unbound biomarkers would produce important data to not only show efficacy of the mAb, but to potentially facilitate establishment of dosing levels when used in preclinical or clinical settings.
“Development of a high-throughput assay detecting a biomarker independent of the presence of a therapeutic mAb is challenging,” says Jana Chain, staff scientist at the laboratory for experimental medicine at Eli Lilly and Company.
In response to this challenge, Lilly has developed an immunoassay for quantifying total biomarker in the presence of high levels of mAb targeting the biomarker of interest. The assay utilizes a capture antibody to a noncompeting, mid-region epitope. First, the bound and unbound biomarkers are captured on a plate coated with the noncompeting antibody. Next, the biomarker is eluted with acid, then transferred and bound to a second plate. A biotinylated version of the same noncompeting antibody is then utilized for detection.
This novel format allows for quantitation of ng/mL levels of biomarkers in the presence of ug/mL levels of therapeutic mAbs. To date, Lilly has validated this assay format for three therapeutic monoclonal antibodies currently in clinical trials. “Developing an assay that enables us to quickly and efficiently screen clinical trial samples for efficacy of our therapeutic proteins is in line with our company’s strategy to improve outcomes for individual patients,” says Chain.