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  • Title: Efficiency of P-glycoprotein-mediated exclusion of rhodamine dyes from multidrug-resistant cells is determined by their passive transmembrane movement rate.
    Author: Eytan GD, Regev R, Oren G, Hurwitz CD, Assaraf YG.
    Journal: Eur J Biochem; 1997 Aug 15; 248(1):104-12. PubMed ID: 9310367.
    Abstract:
    The aim of the present study was to examine the relationship between the rate of the passive transmembrane movement of multidrug resistance (MDR)-type substrates and the ability of P-glycoprotein to extrude them from MDR cells. For this purpose, seven rhodamine dyes were examined for their P-glycoprotein-mediated exclusion from MDR cells, their localization in wild-type drug-sensitive cells, their capacity to stimulate the ATPase activity of P-glycoprotein reconstituted in proteoliposomes, and their transmembrane movement rate in artificial liposomes. All these rhodamine dyes were accumulated in wild-type drug-sensitive cells and were localized mainly in the mitochondria. All the dyes tested were substrates of reconstituted P-glycoprotein and cellular P-glycoprotein and were excluded to a variable degree from MDR cells. The transmembrane movement rate proved the major factor determining the efficacy of the P-glycoprotein-mediated exclusion of rhodamine dyes from MDR cells. Thus, rhodamine B, the poorest cellular P-glycoprotein substrate, exhibited a high affinity toward reconstituted P-glycoprotein, but was the fastest membrane-traversing dye. In contrast, tetramethylrosamine, the best cellular MDR probe, exhibited high affinity toward reconstituted P-glycoprotein and slow transmembrane movement rate. Therefore, an anticancer drug with a fast transmembrane movement rate is expected to overcome the MDR phenomenon. Furthermore, the widely used MDR marker, rhodamine 123, was a poor cellular MDR substrate compared with other rhodamine dyes, especially tetramethylrosamine, which was a superior cellular MDR substrate for functional dye-exclusion studies.
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