The MRP‐transporters decrease intracellular levels of anti‐HIV drugs Saquinavir and Zidovudine in endothelial cells (ECs): Specific inhibition of MRP‐mediated efflux by Leukotriene (LT) receptor antagonists.

Vascular ECs pose a formidable barrier to anti‐HIV drug efficacy in sub‐endothelial reservoirs. The multidrug resistance (MDR) transporters, P‐glycoprotein (P‐gp) and MDR‐associated proteins (MRPs) can efflux both HIV‐1 protease inhibitors (PIs) and nucleoside reverse‐transcriptase inhibitors (NRTIs). Functional expression of P‐gp and MRPs (−1,−2, −4 & −5) were evaluated in human ECs obtained from aorta (HAEC), pulmonary artery (HPAECs), and dermal (DMVECs), and brain (BMVECs) microvessels. Semi‐quantitative RT‐PCR showed constitutively higher expression of MRP mRNAs in ECs, but low levels of P‐gp mRNAs were observed. The fluorescent dye Calcein, a substrate for P‐gp and MRP, and competitive inhibitors of P‐gp or MRPs (e.g. Verapamil and MK‐571, respectively) were used to determine transporter specific function. Calcein efflux from ECs was blocked by MK‐571 (6.25–25 μM) but not by Verapamil (20–60 μM). Cotreatment with MK‐571 showed higher intracellular accumulation of 3 H‐saquinavir (a PI) and 3 H‐Zidovudine (an NRTI). Interestingly, similar to the LT‐receptor antagonist MK‐571, its clinically approved analogs Montelukast (Singulair TM ) and Zafirlukast (Accolate TM ) were a lso able to suppress MRP‐mediated efflux of Saquinavir and Zidovudine from ECs. Our findings implicate that PI and NRTI levels in HIV‐reservoirs may be augmented by inhibition of their MRP‐mediated efflux from vascular EC barriers.