Development and characterization of a free therapeutic ligand binding assay with assistance from kinetics modeling.

Bioanalytical data from early human studies conducted in normal volunteers are often used for building pharmacokinetic/pharmacodynamic models that can predict outcomes of future studies in diseased patients. Thus, it is important to develop and validate reliable and accurate bioanalytical assays that instill confidence that the intended therapeutic species (total or free) are being measured. Assays quantifying the free therapeutic species, the partially bound (for multivalent therapeutics) and unbound species, require much more characterization than assays that quantify the total therapeutic species. We have developed an immunoassay to measure free BMS-962476, an Adnectin protein therapeutic against soluble proprotein convertase subtilisin kexin (PCSK)-9, and performed an in-depth characterization of the accuracy of this assay with the assistance of modeling. The experimental data correlates with modeled data within 15% at all clinically relevant levels of PCSK9 in normal and diseased populations.