Background: Interaction of antiretrovirals with drug transporters such as P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), breast cancer resistance protein (BCRP) and solute carrier organic anion transporter (SLCO) may influence the emergence of viral mutants by altering intracellular drug concentrations. Here we characterize the effect of transporter expression in a variety of cell types such as control CEM, CEM(VBL) (P-gp-overexpressing), CEM(E1000) (MRP1-overexpressing), MT4, control MDCKII, MDCKII(MDR1) (P-gp-overexpressing) and peripheral blood mononuclear cells (PBMCs) on the uptake of [(14)C]efavirenz and [(3)H]nevirapine. We also investigated the lipophilicity of [(14)C]efavirenz and [(3)H]nevirapine.
Methods: The expression of P-gp, MRP1, MRP2, SLCO1A2, 1B1, 1B3, 2B1, 3A1 and 4A1 was assessed by PCR. Inhibitors of P-gp (XR9576, GF120918, dipyridamole) and MRP (MK571, frusemide, dipyridamole), and SLCO substrate or inhibitor (estrone-3-sulphate or montelukast, respectively) were used to study the role of drug transporters in the accumulation of [(14)C]efavirenz and [(3)H]nevirapine. Lipophilicity was measured by the octanol/saline partition coefficient.
Results: CEM cells, MT4 cells and PBMCs express various SLCO isoforms, with SLCO3A1 detected in all of the cells. XR9576, dipyridamole and GF120918 had no effects on the accumulation of [(14)C]efavirenz, while MK571 and frusemide produced variable effects in the cells. The accumulation of [(14)C]efavirenz was significantly decreased in all the cells by montelukast and estrone-3-sulphate.
Conclusions: P-gp expression had no effect on the accumulation of [(14)C]efavirenz and [(3)H]nevirapine. MRP1/2 expression, lipophilicity and SLCO-like transporters (possibly SLCO3A1) may have greater influence on the accumulation of [(14)C]efavirenz than [(3)H]nevirapine.