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Efavirenz Increases MRP1 Efflux Transporter Function while Darunavir/Ritonavir Inhibits MRP1 Expression in Healthy Volunteers
Lawrence Lee*1,2, G Soon1, P Shen1, C Flexner2, and P Pham2
1Natl Univ of Singapore and Natl Hlthcare Group and 2Johns Hopkins Univ, Baltimore, MD, US
Background: The efflux transporter MRP1 is involved
in active transport of ARV and reduces their intracellular accumulation.
Studies have demonstrated in vitro that NNRTI and some NRTI inhibit MRP1
and increases concentrations of some ARV in cells. However, this mechanism of
intracellular pharmacokinetic interaction has not been demonstrated in clinical
settings.
Methods: We recruited 12 healthy volunteers for a darunavir
(DRV) + efavirenz (EFV) drug interaction study. Peripheral blood mononuclear
cells (PBMC) were collected from these subjects at baseline, 10 days after
administration of DRV 900 mg once daily/ritonavir (RTV) 100 mg twice daily, and
14 days after administration of EFV 600 mg once daily. MRP1 expression was
measured by polymerase chain reaction (PCR). Flow cytometry was performed for
MRP1 protein expression using a FITC-conjugated antibody against the MRP1 m6
epitope, after cell permeabilization. MRP1 expression was compared between CD4+
and CD4– cells. MRP1 efflux function was assessed by incubating PBMC
with carboxyfluorescein diacetate (CFDA) with and without the MRP1 inhibitors
MK571 and probenecid, and quantifying intracellular CFDA fluorescence.
Results: There was a marked decrease in MRP1 efflux
function after EFV administration, with a geometric mean ratio of 0.32 compared
to baseline (95%CI 0.28 to 0.37, p <0.001). DRV/RTV administration
had no significant effect, with a geometric mean ratio (GMR) of 0.94 (0.70 to 1.26,
p = 0.62). MRP1 mRNA expression was reduced after DRV/RTV administration
(GMR 0.62 [0.49 to 0.79], p = 0.0012) but not significantly after EFV
administration (GMR 0.88 [0.67 to 1.17], p = 0.35). MRP1 protein
expression was also reduced after DRV/RTV administration (GMR 0.58 [0.52 to 0.65],
p <0.001) but not significantly after EFV administration (GMR 0.82 [0.64
to 1.06], p = 0.10). MRP1 protein expression was 41% higher in CD4+
cells compared to non-CD4 expressing PBMC.
Conclusions: EFV potently inhibited MRP1 efflux
function in vivo and could increase the intracellular concentrations of some
ARV, leading to a synergistic interaction as part of combination ART,
especially in CD4+ lymphocytes. DRV/RTV reduced MRP1 expression but
not function. This clinical study suggests that studying plasma concentrations
alone may underestimate the beneficial interactions of certain combination ARV.
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