19 research outputs found

    Comparison of the interaction of doxorubicin, daunorubicin, idarubicin and idarubicinol with large unilamellar vesicles Circular dichroism study

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    AbstractDoxorubicin, daunorubicin and other anthracycline antibiotics constitute one of the most important groups of drugs used today in cancer chemotherapy. The details of the drug interactions with membranes are of particular importance in the understanding of their kinetics of passive diffusion through the membrane which is itself basic in the context of multidrug resistance (MDR) of cancer cells. Anthracyclines are amphiphilic molecules possessing dihydroxyanthraquinone ring system which is neutral under the physiological conditions. Their lipophilicity depends on the substituents. The amino sugar moiety bears the positive electrostatic charge localised at the protonated amino nitrogen. The four anthracyclines used in this study doxorubicin, daunorubicin, idarubicin and idarubicinol (an idarubicin metabolite readily formed inside the cells) have the same amino sugar moiety, daunosamine, with pKa of 8.4. Thus, all drugs studied will exhibit very similar electrostatic interactions with membranes, while the major differences in overall drug-membrane behaviour will result from their hydrophobic features. Circular dichroism (CD) spectroscopy was used to understand more precisely the conformational aspects of the drug–membrane systems. Large unilamellar vesicles (LUV) consisting of phosphatidylcholine, phosphatidic acid (PA) and cholesterol, were used. The anthracycline–LUV interactions depend on the molar ratio of phospholipids per drug. At low molar ratios drug:PA, these interactions depend also on the anthracycline lipophilicity. Thus, both doxorubicin and daunorubicin bind to membranes as monomers and their CD signal in the visible is positive. However, doxorubicin with its very low lipophilicity binds to the LUV through electrostatic interactions, with the dihydroxyanthraquinone moiety being in the aqueous phase, while daunorubicin, which is more lipophilic is unable to bind only through electrostatic interactions and actually the hydrophobic interactions are the only detected. The highly hydrophobic idarubicin, forms within the bilayer a rather complex entity involving 2–3 molecules of idarubicin associated in the right-handed conformation, one cholesterol molecule and also molecule(s) of phosphatidic acid, as this special oligomeric species is not detected in the absence of negatively-charged phospholipids. Idarubicinol differs from idarubicin with CH(13)–OH instead of C(13)O and its interactions with LUV are distinctly different. Its CD signal in the visible becomes negative and no self associations of the molecule within the bilayer could be detected. The variation of the sign of the Cotton effect (positive to negative) may derive from the changes in the C(6a)–C(7)–O(7)–C(1′) dihedral angle. It is noteworthy that C(13)–OH group, which strongly favours formation of the dimeric species in aqueous solutions when compared to idarubicin prevent association inside the LUV bilayer. At high ratios of phospholipids per drug all of them are embedded within the bilayer as monomer

    Analysis of Multidrug Transporter in Living Cells. Inhibition of P-glycoprotein-mediated Efflux of Anthracyclines by Ionophores

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    One of the major obstacles of chemotherapy is that, after repeated treatments, cellular resistance to the drug appears. The problem is that the tumor cells become resistant not only to the drugs which have been used during the treatment but also to other drugs which are structurally and functionally unrelated. This is termed ‘multidrug resistance’ (MDR). MDR is frequently associated with decreased drug accumulation resulting from enhanced drug efflux. This is correlated with the presence of a membrane protein, P-glycoprotein, which pumps a wide variety of drugs out of cells thus reducing their toxicity. The search for molecules able to reverse MDR is very important. We here report that mobile ionophores such as valinomycin, nonactin, nigericin, monensin, calcimycin, lasalocid inhibit the efflux of anthracycline by P-glycoprotein whereas, channel-forming ionophores such as gramicidin do not. Cyclosporin which is also a strong Ca2+ chelating agent also inhibits the P-glycoprotein-mediated efflux of anthracycline

    Degradation of Anthracycline Antitumor Compounds Catalysed by Metal Ions

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    The influence of some metal ions on the degradation of anthracyclines was examined. One of the degradation products is the 7,8-dehydro-9,10-desacetyldoxorubicinone, D* (Â¥), usually formed by hydrolysis at slightly basic pH. D* is a lipophilic compound with no cytostatic properties. Its formation could be responsible for the lack of antitumor activity of the parent compound. The coordination of metal ions to anthracycline derivatives is required to have degradation products. Cations such as Na+, K+, or Ca2+ do not induce the D* formation however metals which can form stable complexes with doxorubicin afford D*. Iron(III) and copper(II) form appreciable amount of D* at slightly acidic pH. Terbium(III) forms D* but its complex is stable only at slightly basic pH. Palladium(II) which does not form D*. The influence of the coordination mode of metal ions to anthracycline on the D* formation is discussed

    Transport de différents substrats par la P-glycoprotéine (P-gp) et la MRP1. Rôle du glutathion

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    La résistance multiple aux antitumoraux qui peut apparaître lors de traitements anticancéreux est devenue un obstacle majeur à l'éfficacité de ces traitements. Fréquemment, le phénomène de résistance est associé à la surexpression de protéines membranaires telles que la P-glycoprotéine et la MRP1.The development of multidrug resistance is a major obstacle in the chemotherapeutic treatment of many human cancers. This phenomenon is generally associated to the overexpression of membrane proteins like P-glycoprotein or MRP1.PARIS13-BU Sciences (930792102) / SudocSudocFranceF

    Kinetic Analysis of Rhodamines Efflux Mediated by the Multidrug Resistance Protein (MRP1)

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    Characterization of rhodamine 123 as functional assay for MDR has been primarily focused on P-glycoprotein-mediated MDR. Several studies have suggested that Rh123 is also a substrate for MRP1. However, no quantitative studies of the MRP1-mediated efflux of rhodamines have, up to now, been performed. Measurement of the kinetic characteristics of substrate transport is a powerful approach to enhancing our understanding of their function and mechanism. In the present study, we have used a continuous fluorescence assay with four rhodamine dyes (rhodamine 6G, tetramethylrosamine, tetramethylrhodamine ethyl ester, and tetramethylrhodamine methyl ester) to quantify drug transport by MRP1 in living GLC4/ADR cells. The formation of a substrate concentration gradient was observed. MRP1-mediated transport of rhodamine was glutathione-dependent. The kinetics parameter, k(a) = V(M)/k(m), was very similar for the four rhodamine analogs but ∼10-fold less than the values of the same parameter determined previously for the MRP1-mediated efflux of anthracycline. The findings presented here are the first to show quantitative information about the kinetics parameters for MRP1-mediated efflux of rhodamine dyes
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