Abstract
P-Glycoprotein (P-gp) is a member of the ABC (ATP binding cassette) super-family of transport proteins, which in addition to their physiological role in tissue protection, actively extrude a large variety of therapeutically administered drugs from the malignant cells and thus are responsible for multiple drug resistance (MDR) in cancer patients [1]. Since the discovery of P-gp more than 30 years ago many studies have shown that MDR can be reversed by the use of inhibitors, often denoted as MDR modulators.