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Overlapping substrate and inhibitor specificity of human and murine ABCG2.

ABSTRACT: ABCG2 (also known as breast cancer resistance protein) is an ATP-binding cassette (ABC) transporter localized to the plasma membrane where it mediates the efflux of xenobiotics, including potential therapeutics. Studies investigating Abcg2 function at the blood-brain barrier in mouse models are often compared with human ABCG2 function. It is critical to understand the nature of species differences between mouse and human ABCG2, since extrapolations are made from murine data to humans. Two independent drug-selected cell line pairs expressing human or mouse ABCG2 were compared for efflux of fluorescent substrates using flow cytometry. To this end, we developed and characterized a new mouse Abcg2-expressing subline that demonstrated efflux of known fluorescent ABCG2 substrates and increased resistance to mitoxantrone, which is reduced in the presence of the ABCG2 inhibitor Ko143. Our results indicate that the substrate specificity of human and mouse ABCG2 is very similar. We identified a new human and mouse ABCG2 substrate, a porphyrin analog, purpurin-18 (Pp-18), which is not a substrate for P-glycoprotein or multidrug resistance protein 1. The ability of inhibitors to block efflux activity of ABCG2 was assessed using Pp-18. Inhibitors also demonstrated similar effects on human and mouse ABCG2. Chrysin, benzoflavone, and cyclosporin A inhibited Pp-18 efflux in both human and mouse ABCG2. The similarity of the substrate and inhibitor specificity of human and mouse ABCG2 supports interpretation of mouse models in understanding the clinical, pharmacological, and physiologic roles of ABCG2.

SUBMITTER: Bakhsheshian J

PROVIDER: S-EPMC3781367 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature

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Overlapping substrate and inhibitor specificity of human and murine ABCG2.

Bakhsheshian Joshua J Hall Matthew D MD Robey Robert W RW Herrmann Michelle A MA Chen Jin-Qiu JQ Bates Susan E SE Gottesman Michael M MM

Drug metabolism and disposition: the biological fate of chemicals 20130718 10

ABCG2 (also known as breast cancer resistance protein) is an ATP-binding cassette (ABC) transporter localized to the plasma membrane where it mediates the efflux of xenobiotics, including potential therapeutics. Studies investigating Abcg2 function at the blood-brain barrier in mouse models are often compared with human ABCG2 function. It is critical to understand the nature of species differences between mouse and human ABCG2, since extrapolations are made from murine data to humans. Two indepe ...[more]

PMID: 23868912

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Project description:The mouse has three arylamine N-acetyltransferase genes, (MOUSE)Nat1, (MOUSE)Nat2 and (MOUSE)Nat3. These are believed to correspond to (HUMAN)NAT1, (HUMAN)NAT2 and NATP in humans. (MOUSE)Nat3 encodes an enzyme with poor activity and human NATP is a pseudogene. (MOUSE)Nat2 is orthologous to (HUMAN)NAT1 and their corresponding proteins are functionally similar, but the relationship between (MOUSE)Nat1 and (HUMAN)NAT2 is less clear-cut.To determine whether the (MOUSE)NAT1 and (HUMAN)NAT2 enzymes are functionally equivalent, we expressed and purified (MOUSE)NAT1*1 and analysed its substrate specificity using a panel of arylamines and hydrazines. To understand how specific residues contribute to substrate selectivity, three site-directed mutants of (MOUSE)NAT2*1 were prepared: these were (MOUSE)NAT2_F125S, (MOUSE)NAT2_R127G and (MOUSE)NAT2_R127L. All three exhibited diminished activity towards "(MOUSE)NAT2-specific" arylamines but were more active against hydrazines than (MOUSE)NAT1*1. The inhibitory and colorimetric properties of a selective naphthoquinone inhibitor of (HUMAN)NAT1 and (MOUSE)NAT2 were investigated.Comparing (MOUSE)NAT1*1 with other mammalian NAT enzymes demonstrated that the substrate profiles of (MOUSE)NAT1 and (HUMAN)NAT2 are less similar than previously believed. Three key residues (F125, R127 and Y129) in (HUMAN)NAT1*4 and (MOUSE)NAT2*1 were required for enzyme inhibition and the associated colour change on naphthoquinone binding. In silico modelling of selective ligands into the appropriate NAT active sites further implicated these residues in substrate and inhibitor specificity in mouse and human NAT isoenzymes.Three non-catalytic residues within (HUMAN)NAT1*4 (F125, R127 and Y129) contribute both to substrate recognition and inhibitor binding by participating in distinctive intermolecular interactions and maintaining the steric conformation of the catalytic pocket. These active site residues contribute to the definition of substrate and inhibitor selectivity, an understanding of which is essential for facilitating the design of second generation (HUMAN)NAT1-selective inhibitors for diagnostic, prognostic and therapeutic purposes. In particular, since the expression of (HUMAN)NAT1 is related to the development and progression of oestrogen-receptor-positive breast cancer, these structure-based tools will facilitate the ongoing design of candidate compounds for use in (HUMAN)NAT1-positive breast tumours.

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Dataset Information

Overlapping substrate and inhibitor specificity of human and murine ABCG2.

Publications

Overlapping substrate and inhibitor specificity of human and murine ABCG2.

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