Quantitative assessment of HIV-1 protease inhibitor interactions with drug efflux transporters in the blood-brain barrier

Purpose. To quantitatively characterize the drug efflux interactions of various HIV-1 protease inhibitors in an in vitro model of the blood-brain barrier (BBB) and to compare that with HIV-1 protease inhibitor stimulated P-glycoprotein (P-gp)-ATPase activity. Methods. Cellular accumulation of the P-gp sensitive probe, rhodamine 123 (R123), and the mixed P-gp/multidrug resistance-associated protein (MRP) probe, 2′,7′-bis(2-carboxyethyl) -5(6)-carboxyfluorescein (BCECF), were evaluated in primary cultured bovine brain microvessel endothelial cells (BBMEC) in the presence of various concentrations of HIV-1 protease inhibitors. The potency (IC₅₀) and efficacy (I_max) of the drugs in the cell accumulation assays for P-gp and/or MRP was determined and compared to activity in a P-gp ATPase assay. Results. For R123 (P-gp probe), the rank order potency for inhibiting R123 accumulation in the BBMEC was saquinavir = nelfinavir > ritonavir = amprenavir > indinavir. This correlated well with the rank order affinity in the P-gp ATPase assay. The rank order potency for MRP-related drug efflux transporters, was nelfinavir > ritonavir > saquinavir > amprenavir > indinavir. Conclusions. HIV-1 protease inhibitors potently interact with both P-gp and MRP-related transporters in BBMEC. Characterization of the interactions between the HIV-1 protease inhibitors and drug efflux transporters in brain microvessel endothelial cells will provide insight into potential drug-drug interactions and permeability issues in the BBB.