P-glycoprotein (P-gp), an efflux membrane transporter, is widely distributed throughout the body including the apical surface of epithelial cells lining the colon, small intestine, pancreatic duct, bile duct, kidney proximal tubule, and the adrenal gland. It is also located in the endothelial cells of the blood brain barrier (BBB). P-gp contributes greatly in the extrusion of many drugs from the blood into the intestinal lumen. P-gp is also responsible for promoting drug excretion from hepatocytes and renal tubules to adjacent luminal space. Therefore, P-gp can potentially reduce the absorption and oral bioavailability and shorten the retention time of a number of drugs. In addition, it has a role in limiting cellular uptake of drugs from blood circulation into the brain while being present in the BBB. P-gp is overexpressed in cancer cells, leading to drug efflux. It prevents cell internalization of chemotherapeutic agents, making the chemotherapy almost ineffective in many cases. Hence, this protein is one of the major obstacles to chemotherapy. Various strategies are currently being developed to overcome the difficulties associated with P-gp in optimal drug delivery, including inhibition of P-gp.
Several techniques are available for screening chemical entities for their ability to inhibit P-gp. These techniques are also useful for detecting the substrate specificity to the P-gp and the significance of the protein in altering pharmacokinetics, further contributing to the selection of drug candidates and optimization of drug discovery settings. Based on the ultimate objective of the study, the strategic application of these methods will help in high throughput and better optimization.
In vitro assessment of P-gp inhibition is important for choosing drug candidates that are not likely to cause P-gp-mediated drug-drug interaction (DDI) during the drug discovery stage. Scientists from Creative Bioarray have established several in vitro systems for P-gp inhibition assays to predict P-gp-mediated DDI.