The multidrug-resistant phenotype associated with overexpression of the new ABC half-transporter, MXR (ABCG2).

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Litman T, Brangi M, Hudson E, Fetsch P, Abati A, Ross DD, Miyake K, Resau JH, Bates SE

The multidrug-resistant phenotype associated with overexpression of the new ABC half-transporter, MXR (ABCG2).

J Cell Sci. 2000 Jun;113 ( Pt 11):2011-21.

PubMed ID

10806112 [ View in PubMed

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Abstract

Mechanisms of drug resistance other than P-glycoprotein are of increasing interest as the list of newly identified members of the ABC transport family has grown. We sought to characterize the phenotype of the newly discovered ABC transporter encoded by the mitoxantrone resistance gene, MXR, also known as ABCP1 or BCRP. The pharmacodynamics of mitoxantrone and 12 other fluorescent drugs were evaluated by confocal microscopy in four multidrug-resistant human colon (S1) and breast (MCF-7) cancer cell lines. We utilized two sublines, MCF-7 AdVp3000 and S1-M1-80, and detected overexpression of MXR by PCR, immunoblot assay and immunohistochemistry. These MXR overexpressing sublines were compared to cell lines with P-glycoprotein- and MRP-mediated resistance. High levels of cross-resistance were observed for mitoxantrone, the anthracyclines, bisantrene and topotecan. Reduced levels of mitoxantrone, daunorubicin, bisantrene, topotecan, rhodamine 123 and prazosin were observed in the two sublines with high MXR expression. Neither the P-glycoprotein substrates vinblastine, paclitaxel, verapamil and calcein-AM, nor the MRP substrate calcein, were extruded from MCF-7 AdVp3000 and S1-M1-80 cells. Thus, the multidrug-resistant phenotype due to MXR expression is overlapping with, but distinct from, that due to P-glycoprotein. Further, cells that overexpress the MXR protein seem to be more resistant to mitoxantrone and topotecan than cells with P-glycoprotein-mediated multidrug resistance. Our studies suggest that the ABC half-transporter, MXR, is a potent, new mechanism for conferring multiple drug resistance. Definition of its mechanism of transport and its role in clinical oncology is required.

DrugBank Data that Cites this Article

Drug Transporters

Drug	Transporter	Kind	Organism	Pharmacological Action	Actions
Mitoxantrone	ATP-binding cassette sub-family G member 2	Protein	Humans	Unknown	Substrate	Details