Development and validation of a multiplexed drug level assay in support of combination biologics therapy clinical studies.

Clinical development of biotherapeutics for combination therapy requires monitoring the concentrations of both drugs in biological samples. Traditionally, two assays are required to measure drug levels one at a time, which poses challenges in sample management, data reporting, and cost. The Meso Scale Discovery (MSD®) U-PLEX platform provides a simple and flexible way to create custom multiplex ligand binding assays (LBAs). We developed and fully validated a two-plex assay on the U-PLEX platform where two therapeutic monoclonal antibodies (mAbs) in Merck's pipeline, which we call MK-A and MK-B in this manuscript, can be measured simultaneously in one sample. Our results demonstrated that the multiplexed pharmacokinetic (PK) assay has performances, including accuracy, precision, and cross-reactivity, that meet requirements in regulatory guidance. Furthermore, results of MK-A from the multiplex assay are comparable to results from a previously validated MK-A single-plex assay with 80% of samples tested in both assays having concentration differences < 30% relative to the mean of the two measurements. The multiplex assay was used to support a phase I MK-A/MK-B combination therapy clinical study and generated results consistent with historical MK-A monotherapy PK data. The ability to measure both biotherapeutics in a multiplexed assay is beneficial in that it improves consistency and efficiency while reduces sample volume and cost. With the number of combination therapies increasing in development, multiplexed assays can potentially have wide applications in biologics bioanalysis.