Abstract
Breast cancer resistance protein (BCRP) is a recently discovered ATP-binding cassette drug transporter. Hence, the full spectrum of therapeutic agents that interact with BCRP remains to be elucidated. Because human immunodeficiency virus protease inhibitors (HPIs) are well known P-glycoprotein (P-gp) substrates, and there is an overlap in substrate specificity between P-gp and BCRP, this study was performed to investigate whether HPIs are substrates and/or inhibitors of BCRP. First, the effect of HPIs on BCRP efflux activity in human embryonic kidney (HEK) cells stably expressing wild-type BCRP (482R) and its two mutants (482T and 482G) was studied by measuring intracellular mitoxantrone fluorescence using flow cytometry. We found that ritonavir, saquinavir, and nelfinavir were effective inhibitors of wild-type BCRP (482R) with IC50 values of 19.5 ± 0.8 μM, 19.5 ± 7.6 μM, and 12.5 ± 4.1 μM, respectively. Ritonavir, saquinavir, and nelfinavir inhibited 482T and 482G with IC50 values that were approximately 2 times greater than that for 482R. Indinavir and amprenavir had no significant inhibition on BCRP activity. Direct efflux of radiolabeled HPIs in HEK cells was measured to determine whether the HPIs are substrates of BCRP. None of the HPIs were found to be transported by BCRP. Together, ritonavir, saquinavir, nelfinavir, indinavir, and amprenavir are not substrates for BCRP. However, ritonavir, saquinavir, and nelfinavir are effective inhibitors of the transporter. These results suggest that BCRP may play an important role in drug-drug interactions involving coadministration of the HPIs with drugs that are substrates of the transporter.
Footnotes
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We gratefully acknowledge financial support from National Institutes of Health Grant HD044404 (to Q.M. and J.D.U.) and New Investigator Award from American Association of Colleges of Pharmacy (to Q.M.). Part of this work was presented as a poster at the American Association of Pharmaceutical Scientists Workshop in Peachtree City, GA, February 10–12, 2003.
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DOI: 10.1124/jpet.104.065342.
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ABBREVIATIONS: BCRP, breast cancer resistance protein; P-gp, P-glycoprotein; HIV, human immunodeficiency virus; HPI, human immunodeficiency virus protease inhibitor; MX, mitoxantrone; FTC, fumitremorgin C; DMSO, dimethyl sulfoxide; DMEM, Dulbecco's modified Eagle's medium; FBS, fetal bovine serum; HEK, human embryonic kidney; TBS-T, Tris-buffered saline-Tween 20; mAb, monoclonal antibody; MRP, multidrug-resistance protein; GF120918, N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide.
- Received January 9, 2004.
- Accepted March 8, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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