Montelukast Is a Potent and Durable Inhibitor of Multidrug Resistance Protein 2-Mediated Efflux of Taxol and Saquinavir

The ATP binding cassette (ABC)-transporters are energy dependent efflux pumps which regulate the pharmacokinetics of both anti-cancer chemotherapeutic agents, e.g. taxol, and of human immunodeficiency virus-1 (HIV-1) protease inhibitors (HPIs), e.g. saquinavir. Increased expression of several ABC-transporters, especially P-glycoprotein (P-gp) and multidrug resistance protein 2 (MRP2), are observed in multidrug resistant (MDR) tumor cells and on HIV-1 infected lymphocytes. In addition, due to their apical expression on vascular endothelial barriers, both P-gp and MRP2 are of crucial importance towards dictating drug access into sequestered tissues. However, although a number of P-gp inhibitors are currently in clinical trials, possible inhibitors of MRP2 are not being thoroughly investigated. The experimental leukotriene receptor antagonist (LTRA), MK-571 is known to be a potent inhibitor of MRP transporters. Using the MRP2 over-expressing Madin-Darby canine kidney cell line, MDCKII-MRP2, we evaluated whether the clinically approved LTRAs, e.g. montelukast (Singulair (TM)) and zafirlukast (Accolate (TM)), can similarly suppress MRP2-mediated efflux. We compared the efficacy of increasing concentrations (20-100 mu M) of MK-571, montelukast, and zafirlukast, in suppressing the efflux of calcein-AM, a fluorescent MRP substrate, and the radiolabeled [H-3-] drugs, taxol and saquinavir. Montelukast was the most potent inhibitor (p<0.01) of MRP2-mediated efflux of all three substrates. Montelukast also increased (p<0.01) the duration of intracellular retention of both taxol and saquinavir. More than 50% of the drugs were retained in cells even after 90 min post removal of montelukast from the medium. Our findings implicate that montelukast, a relatively safe anti-asthmatic agent, may be used as an adjunct therapy to suppress the efflux of taxol and saquinavir from MRP2 overexpressing cells.