Multidrug resistance (MDR) in tumour cells is often caused by the overexpression of two transporters the P-glycoprotein (P-gp) and the multidrug resistance-associated protein (MRP1) which actively pump out multiple chemically unrelated substrates across the plasma membrane. A clear distinction in the mechanism of translocation of substrates by MRP1 or P- gp is indicated by the finding that, in most of cases, the MRP1-mediated transport of ...