LAUSR

Abstract The interactions of an anticancer drug pirarubicin (THP) with a series of phosphatidylethanolamine (PE) lipids differing in the length and unsaturation degree of acyl chains were investigated using the Langmuir technique supplemented with Brewster angle microscopy (BAM) and thermodynamic analysis of compression-expansion cycles. The incorporation of the drug from the subphase into the lipid monolayer treated as a simple model of urothelial cancer cell membranes leads to the increase in the areas per molecule at lower surface pressures, while further compression of the monolayer at the air-water interface results in the expulsion of the drug. In the case of 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE) undergoing liquid expanded – liquid condensed (LE-LC) phase transition the isotherms in the presence and absence of THP are essentially indiscernible at higher surface pressures and the drug was found to locate in between the domains. For other lipids (1,2-distearoyl-sn-glycero-3-phosphoethanolamine, DSPE, 1-stearoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine, SOPE and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine, DOPE) the isotherms recorded in the presence of THP were characterized by areas per molecule smaller than those for the isotherms obtained for lipids on a pure buffer. It shows that the drug, despite squeezing out from the lipid monolayer, is still interacting strongly with lipid molecules. The formation of THP/lipid aggregates takes place as shown by the results of the thermodynamic analysis for the compression-expansion cycles. It may explain a disruptive effect of THP on the lipid packing, which is supported by a decreased value of Cs−1max. The most significant interactions were observed for 1,2-dilinoleoyl-sn-glycero-3-phosphoethanolamine (DLOPE). Due to the tilt of the acyl chains caused by the presence of two double bonds in each chain, a pocket is formed allowing THP to effectively penetrate the hydrophobic part of the DLOPE monolayer even at higher surface pressures without squeezing-out effect. Interestingly, this penetration is not accompanied by any formation of lipid-drug aggregates as shown by thermodynamic analysis of hysteresis. Moreover, THP is also able to effectively incorporate into the preformed DLOPE layers. These results are important for the detailed explanation of the molecular mechanisms of the passive transport of THP through the urothelial cancer cell membranes, which are especially enriched in the longer chain, double unsaturated PE lipids such as DLOPE.