The emergence of biologic-based therapeutics has transformed the treatment of cancer, autoimmune disease and other disorders. These biologically active molecules can alter the immune response and change disease trajectories, so many of the tests that are used to assess their function must examine biological functions. These molecules typically bind to specific receptors on immune cells, which may block or activate a specific response depending on the mode of action.
Receptor occupancy (RO) assays measure binding of a specific molecule or drug to a receptor expressed on a specific cell, and this is a quantitative assay that can be used to evaluate receptor binding and other pharmacodynamic characteristics of experimental therapies. Currently, flow cytometry is a widely used approach for RO assays because it is a fast, flexible and precise platform that can be customized for different molecules and cell types and can be used in a high-throughput platform to screen numerous candidate molecules. Flow cytometry RO assays can also complement other flow cytometry assays such as immunophenotyping analysis or other functional assays that assess mechanisms of action.
Flow cytometry-based RO assays are well-suited to measuring binding of therapeutic antibodies to specific cell surface receptors. Rituximab is an FDA-approved monoclonal antibody that is used to treat a variety of autoimmune diseases and blood cancers. Rituximab binds to the molecule CD20, which is expressed on the surface of B cells, and flow cytometry-based assays can be used to measure receptor occupancy of CD20 by comparing binding of unlabeled Rituximab with different concentrations of fluorescently conjugated Rituximab to a B cell line (shown above in the Daudi Cell Line).
[VIDEO] Advantages For Using Flow Cytometry To Evaluate Receptor Occupancy
Flow cytometry is a unique platform that allows users to measure a wide range of characteristics and develop an understanding of an experimental molecule’s biological activity before testing in animal models or clinical trials. Consider using a flow cytometry-based Receptor Occupancy assay as you develop and characterize novel drugs or biologics.