ABCB1 and cancer: The effects of dietary rosemary on the activity of the human drug efflux transporter P-glycoprotein (MDR1, ABCB1) and multidrug resistance protein 1 (MRP1, ABCC1) were explored by employing P-glycoprotein-overexpressing hMRP1 gene-transfected KB/MRP cells and human cancer KB-C2 cells.