P-gp modulator-7 (Compound 9e) is an inhibitor of P-glycoprotein (P-gp). It uniquely occupies the channel entrance of P-gp in a T-shaped conformation, blocking the peristaltic extrusion mechanism of transmembrane domains TM12 and TM9. This action inhibits P-gp from pumping drugs out of cells and reverses multidrug resistance (MDR) in tumor cells. P-gp modulator-7 shows promise for cancer research.