AAPS PharmSci360 2024 -- Receptor occupancy (RO) assays allow for the quantification of binding of therapeutics to their intended targets on the surface of different cell subsets. Flow cytometry-based RO assays are a strong tool for preclinical and clinical development, providing rapid, high-throughput and quantitative measure for PK/PD modelling. Research challenges remain however when RO assays are developed and validated for rare low expressing targets. Herein we present an example of such an assay, its challenges, and the steps taken to resolve performance issues with impact on data and RO calculations.

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