The Overall Partitioning of Anthracyclines into Phosphatidyl‐Containing Model Membranes Depends Neither on the Drug Charge Nor the Presence of Anionic Phospholipids

Abstract

Anthracyclines are potent anticancer agents. Their use is limited by the problem of multidrug resistance (MDR) associated with a decreased intracellular accumulation of drug correlated with the presence, in the membrane of resistant cells, of the P-glycoprotein responsible for an active efflux of the drug. The activity of a drug depends upon its intracellular concentration which itself depends on the kinetics (a) of passive influx (b) of passive efflux and (c) of the P-glycoprotein-mediated efflux of drug across the cell membrane. The ability of an anthracycline to overcome MDR depends largely on the first point.The passive drug uptake is governed by their incorporation into the lipid matrix and both electrostatic and hydrophobic forces seem necessary for the stabilization of anthracyclines into lipid bilayers. The aim of the present study was to determine the relative importance of these two interactions.Using microspectrofluorometry and the observation that the fluorescence of anthracycline is enhanced when the dihydroanthraquinone part is embedded within the lipid bilayer, we have determined the partition coefficient (alternatively, the binding constant) of 12 anthracycline derivatives in large unilamellar vesicles.The anthracyclines were (a) doxorubicin, daunorubicin and idarubicin which, at pH 7.2, bear a single positive charge at the level of the amino group o n the sugar, (b) their corresponding neutral 3'-hydroxy derivatives where the amino group in the sugar has been replaced by a hydroxyl, (c) the three 13-hydroxy derivatives, doxorubicinol, daunorubicinol and idarubicinol, (d) pirarubicin and (e) two permanently positively charged derivatives. The large unilamellar vesicles contained phosphatidylcholine with various amounts of phosphatidic acid which is negatively charged and of cholesterol.We came to the conclusion that the efficiency of drug incorporation in the bilayers depends neither on the presence of a positive charge on the drug nor on the presence of anionic phospholipid but on the hydrophobicity of the molecule: the neutral and the positively charged form have the same ability to partition into the bilayer. However, the percentage of each form present should depend on the electrostatic parameters.

On the Interaction of Doxorubicin with Oleate Ions: Fluorescence Spectroscopy and Liquid-Liquid Extraction Study

“…Fluorescence increase has been reported upon embedding of the fluorescent molecule into lipidic vesicles or liposomes. 6) Taken together, all these spectral observations at pH 8.6 indicate that DOX molecular form could avoid the aqueous medium by partial insertion into aggregated oleates or by complete embedding into oleate vesicles (Figs. 4c, d, respectively).…”

“…Fluorescence Interpretation At pH 6.5, the interaction is mainly indicated by an important quenching of the drug fluorescence in presence of OA Ϫ (static quenching). At this pH, DOX carries a positively charged NH 3 ϩ group that favors electrostatic interaction with the negative charge on the hydrophilic head of an oleate molecule 6) (Fig. 4a).…”

“…of the neutral form percentage, is in favor of the stacking phenomenon. 5,6) It has been recently shown that lipophilicity of cationic drugs 7,8) can be increased by association with an anion, namely with a long chain ion of a fatty acid. 9,10) Nevertheless, no study is devoted to the molecular interaction between the drug and the ion.…”

Subcellular Level Resolution Fluorescence Measurements in Yeast Cells by Image Analysis

“…Most probably these structures were the mitochondrial membranes. Potential ability of DR binding to biological membranes was demonstrated on artificial membranes by others (Gallois, et al 1996). Membrane binding may also explain the diffuse fluorescence of DR in the mitochondrial region as distinct from the dot-like pattern of the mitochondrial DNA staining by DAPI (Fig.…”

Anthelmintics Are Substrates and Activators of Nematode P Glycoprotein

“…In particular, the interactions of drugs with PLs influence drug absorption, tissue distribution, subcellular distribution, and protein activity (2). The amount of xenobiotics embedded within the bilayer may depend on the presence of anionic PLs (15). In nematodes, phosphatidic acid is more abundant in resistant parasites (47).…”