A Novel Total Drug Assay for Quantification of Anti-C5 Therapeutic Monoclonal Antibody in the Presence of Abundant Target

Overcoming Soluble Target Interference in Measurement of Total Bispecific Therapeutic Antibody Concentrations

The measurement of therapeutic drug concentrations is used to assess drug exposure and the relationship between therapeutic pharmacokinetics (PK) and pharmacodynamics (PD), which help determine the optimal dose for patients. Ligand binding assays (LBAs) are often the method of choice for evaluation of drug concentration and use either the therapeutic target protein or antibodies to the therapeutic as capture and/or detection reagents. Due to the bivalency of antibody therapeutics, heterogeneous states of the drug/target complex can exist in the presence of soluble targets which can complicate measurement of unbound drug. In the case of bispecific antibodies, measurement of drug can be even more complicated and depend upon the levels of both targets to each arm. Measuring the total drug allows for PKPD modeling prediction of human dose projections in addition to overcoming challenges associated with measuring free drug for bispecific antibodies. Here, we present a study in which a sandwich ELISA format was used to measure total anti-KLK5/KLK7 antibody concentrations. This assay utilized a non-blocking anti-idiotype (ID) antibody to one arm of the antibody for capture and an antibody to target bound to the other arm of the antibody for detection. Our qualified assay showed acceptable precision, accuracy, dilutional linearity, and reproducibility and enabled detection of a total bispecific antibody at high levels of two targets. To confirm that our assay was detecting total drug, a subset of samples was evaluated in a generic total LC-MS/MS assay.

Assay pH and critical reagent optimization in measuring concentrations of a monoclonal antibody and its target

Aim: To mitigate assay interference in the drug and target assays to support the development of monoclonal antibody REGN-Z. Results: Mild acidic assay conditions and capture and detection antibodies with different affinities and t_1/2 under different assay pHs were used to mitigate interference in the total drug and total target assays. A free target assay was also developed using a lower-affinity capture antibody with a much slower association and dissociation rate. The impact of sample incubation, dilution and storage on the accurate detection of the free target was also evaluated. Conclusion: The total drug, total and free target assays can accurately quantitate drug and target concentrations when tested with a subset of clinical study samples.