PT  - JOURNAL ARTICLE
AU  - Anshul Gupta
AU  - Yi Zhang
AU  - Jashvant D. Unadkat
AU  - Qingcheng Mao
TI  - HIV Protease Inhibitors Are Inhibitors but Not Substrates of the Human Breast Cancer Resistance Protein (BCRP/ABCG2)
AID  - 10.1124/jpet.104.065342
DP  - 2004 Jul 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 334--341
VI  - 310
IP  - 1
4099  - http://jpet.aspetjournals.org/content/310/1/334.short
4100  - http://jpet.aspetjournals.org/content/310/1/334.full
SO  - J Pharmacol Exp Ther2004 Jul 01; 310
AB  - 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. The American Society for Pharmacology and Experimental Therapeutics