Practice question

Over-expression of ATP-binding cassette transporters such as P-glycoprotein (encoded by MDR1) actively effluxes a wide range of hydrophobic drugs from the cytoplasm, reducing their intracellular concentration below the therapeutic threshold. This mechanism is a major cause of multidrug resistance in cancer chemotherapy. Inhibition of these pumps is therefore an active area of pharmacological research aimed at restoring drug sensitivity.