SERR study of the interaction of anthracyclines with mono- and bilayers of charged phospholipids

The interaction of positively charged anthracyclines, pirarubicin, and adriamycin with planar monolayers and bilayers of zwitterionic and anionic phospholipids (POPC and DPPA) is reported, by using a surface pressure technique and surface-enhanced resonance Raman scattering(SERRS). The results are compared with those of previous study concerning the pirarubicin-POPC interaction. The surface pressure technique enabled us to determine the speed of penetration and the amount of anthracycline trapped in phospholipid monolayers. The behavior of both anthracyclines was different, depending on their hydrophilic-lipophilic balance and the charges of phospholipids. We observed,in particular, that the presence of anionic DPPA in the monolayer does not enhance the percentage of pirarubicin at the interface as compared to the adsorption in a pure POPC monolayer. This could be due to the formation of a screen by pirarubicin adsorbed on the polar head groups of anionic phospholipids. These molecules would prevent the other molecules of pirarubicin dissolved in the bulk from penetrating more deeply into the phospholipids. These monolayers were transferred by a Langmuir-Blodgett technique onto silver-coated prisms, in order to study them by SERRS and have information on the orientation of the anthracycline in the phospholipid bilayer thus obtained. The spectrum of a phospholipid bilayer containing anionic DPPA (POPC-DPPA 80-20 mol %), put in contact with an aqueous solution of pirarubicin showed that this anthracycline is able to cross the bilayer and is lying parallel to silver after crossing. This result confirms the hypothesis of the screen formed by pirarubicin adsorbed on DPPA polar head groups, proposed after the surface pressure study. Adriamycin in contact with a POPC bilayer is able to cross this bilayer too. It does not remain in the bilayer, probably because of its weak hydrophobicity, and is lying on silver after crossing. In the presence of anionic DPPA in the bilayer, adriamycin remains adsorbed on the polar head groups of the second monolayer (in contact with water) and does not penetrate into the bilayer.