Intracellular 'boosting' of darunavir using known transport inhibitors in primary PBMC

center dot Antiretroviral protease inhibitors such as lopinavir and saquinavir have been shown to be substrates of ABCB1. Co-administration with the potent ABCB1 and CYP3A4 inhibitor, ritonavir, has shown improved pharmacokinetics and subsequent therapeutic effects of protease inhibitors. Darunavir is a recently licensed protease inhibitor with potent antiretroviral effects but has yet to be characterized as a potential substrate for drug transporters. WHAT THIS STUDY ADDS center dot Darunavir was shown to be a substrate of ABCB1 using different in vitro models. Inhibition of ABCB1 alone does not increase cellular accumulation of darunavir in PBMCs. However, inhibition of ABCB1 and ABCCs significantly increased cellular accumulation of darunavir whereas inhibition of influx transporters significantly reduced the cellular accumulation of darunavir in PBMCs. AIMS ABCB1, some ABCCs and SLCOs have been reported to affect the intracellular accumulation of various protease inhibitors in vitro and ex vivo. Darunavir is the most recently licensed protease inhibitor and we sought to investigate the ability of transport inhibitors to influence its intracellular accumulation in lymphocytes from healthy volunteers. METHODS The intracellular accumulation of radiolabelled darunavir was assessed using CEM cells and ABCB1-overexpressing CEMVBL cells. Apical and basolateral transport of radiolabelled darunavir through MDCKII monolayers was also studied. Finally the ability of known inhibitors to influence intracellular accumulation of darunavir in peripheral blood mononuclear cells (PBMC) was investigated. RESULTS CEMVBL cells (1.4 +/- 0.6, P < 0.001, 95% CI for the difference = 0.46, 0.80, n = 7) had significantly lower accumulation of darunavir compared with CEM cells (5.6 +/- 0.7, n = 7) and this was reversed by addition of tariquidar (30 nm, 4.6 +/- 0.8, P < 0.001, 95% CI = -0.64, -0.41, n = 4). In MDCKII-ABCBI cells, transport from the basal to the apical compartment was observed and this was also reversible with the addition of tariquidar. In PBMCs, dipyridamole (6.9 +/- 1.3, P < 0.01, 95% CI for the difference = -1.16, -0.30, (n = 8) significantly increased whilst montelukast (5.7 +/- 1.0, P < 0.01, 95% CI for the difference = 0.16, 0.79, n = 8) significantly decreased the intracellular accumulation of darunavir when compared with control (6.2 +/- 1.1, n = 8). CONCLUSIONS Darunavir is a substrate for efflux and influx transporters in PBMC and intracellular concentrations can be manipulated using known inhibitors.