Receptor occupancy (RO) analysis of flow cytometry is a robust analysis method designed to identify, quantify and monitor the binding of therapeutic drugs to their targets. In drug clinical research, RO analysis can assist in dose setting, help to evaluate the minimum biological effect level of biological agents, reasonable dosage, and establish a reasonable dosing schedule.
RO analysis can be used for safety assessment to evaluate the possibility of toxic and side effects caused by long-term saturation of RO. RO is usually regarded as pharmacodynamic (PD) biomarker data and combined with traditional pharmacokinetic (PK) evaluation, it is used to model the PK/PD relationship. It is a macromolecule acting on cell surface targets The cornerstone of drug PK/PD modeling.
There are two basic types of analysis commonly used for RO assessment. An indirect method of assessing the proportion of unoccupied or unbound (called “free”) sites using fluorescently labeled antibodies that compete with drug molecules (usually fluorescently-labeled versions of drug molecules). This analysis will report the level of freely available receptors after administration. The second method is to directly assess the level of the combined drug. In this test, fluorescently labeled antibodies that recognize drug molecules (called “bound”) are used. Both detection methods can be used to evaluate the ratio of positive cells to background controls (such as fluorescence minus one control, isotype control), or to measure the average fluorescence intensity (MFI) or median fluorescence intensity (MdFI) expressed by the receptor.
The “free” and “combined” analysis modes and many of its variant modes have been commonly used in preclinical and clinical development and post-marketing research, which illustrates the importance and practicality of these analyses in the drug development process. Because the expression level of receptors may change during the administration process, for a rigorous test, it is necessary to monitor the changes in the total receptor level during the administration process at the same time. For some drugs, if the mechanism of action is to regulate the level of cell surface receptors, the detection of total receptor levels is necessary. Therefore, the detection of total receptors is also required in many applications.
PD-1, PD-L1, CD19, CD20, CD33, CD38, CD39, CD40, CD47, TIM-3, TIGIT, OX40, VISTA, LAG-3