Receptor Occupancy Assays

Flow cytometry-based Receptor Occupancy (RO) assays are rapid, powerful, and customisable tools in precision medicine. RO assays are designed to quantify and characterize the binding capabilities of therapeutic drugs to their target receptors on the cell surface ^{[1, 2]}. RO assays can also be used to assess other bioactive substances such as neurotransmitters and hormones but spotlight in clinical platforms tend to fall on therapeutic drugs due to their vast applications in medicine. These drugs are often antibody-based therapeutics that are used to target specific receptors to manipulate downstream signalling in diseases. Together with pharmacokinetic and pharmacodynamic (PKPD) data, the assessment of specificity of these antibody-based drugs is essential to identify their mechanism of action, adverse events, and effectiveness in patients ^[2].  RO assays are used to determine binding affinity, efficacy, potency, therapeutic dose, and duration of action of these drugs. There are several RO assay formats that can be used to assess these parameters, and the choice of assay depends on the specific research or clinical objectives and mechanisms of action ^[1]. PeploBio offers several RO assay formats, and we provide expert advice to help you choose a suitable assay design for your requirements.

This assay measures the total number of receptors which includes both free and drug‐occupied receptors. A non-competing fluorescent labelled ligand is used to bind, detect, and quantify the target receptors of the drug. Determining the expression levels of specific receptors on different cell types ^{[1, 2]}. This assay format is useful for:

A free receptor assay measures the proportion of specific receptors on the surface of cells or particles that are unoccupied or free. A fluorescently labelled ligand is used to bind the epitope of interest on the target receptor. The assay then quantifies the remaining number of receptors unoccupied by the labelled ligand ^{[1, 2]}. Application of this method includes:

The drug occupied receptor binding RO format is used to measure the extent to which a specific receptor on the surface of cells or particles is bound or occupied by a drug molecule. A fluorescently labelled drug molecule that specifically binds to the target receptor of interest measured in this assay.  This type of assay is valuable in drug development and pharmacology to assess the binding affinity, potency, and effectiveness of a drug candidate in binding to its target receptor ^{[1, 2]}. This RO assay format is crucial for: