Monoclonal antibodies (mAbs) are pivotal therapeutic agents for various diseases, and effective treatment hinges on attaining a specific threshold concentration of mAbs in patients. With the rising adoption of combination therapy involving multiple mAbs, there arises a clinical demand for multiplexing assays capable of measuring the concentrations of these mAbs. However, minimizing the complexity of serum samples while achieving rapid and accurate quantification is difficult. In this work, we introduced a novel method termed nano-surface and molecular orientation limited (nSMOL) proteolysis for the fragment of antigen binding (Fab) region-selective proteolysis of co-administered trastuzumab and pertuzumab based on the pore size difference between the protease nanoparticles (∼200 nm) and the resin-captured antibody (∼100 nm). The hydrolyzed peptide fragments were then quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS). In this process, the digestion time is shortened, and the produced digestive peptides are greatly reduced, thereby minimizing sample complexity and increasing detection accuracy. Assay linearity was confirmed within the ranges of 0.200-200 μg mL-1 for trastuzumab and 0.300-200 μg mL-1 for pertuzumab. The intra- and inter-day precision was within 9.52% and 8.32%, except for 12.5% and 10.8% for the lower limit of quantitation, and the accuracy (bias%) was within 6.3%. Additionally, other validation parameters were evaluated, and all the results met the acceptance criteria of the guiding principles. Our method demonstrated accuracy and selectivity for the simultaneous determination of trastuzumab and pertuzumab in clinical samples, addressing the limitation of ligand binding assays incapable of simultaneously quantifying mAbs targeting the same receptor. This proposed assay provides a promising technical approach for realizing clinical individualized precise treatment, especially for co-administered mAbs.
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