Daunorubicin and doxorubicin molecular interplay with 2D membrane models

The anthracyclines daunorubicin and doxorubicin are widely used antineoplastic agents due to their therapeutic activity against a broad variety of human cancers. Although, the classical model to explain anthracyclines' cytotoxicity has been based in the direct interference with nucleic acid function, evidence suggests that the plasma membrane is also involved in the drug's mechanism of action. In this work, the interaction of these drugs with two-dimensional membrane models were studied in order to gain further insights at the molecular level regarding anthracyclines membrane interactions. For that purpose, Langmuir monolayers composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), sphingomyelin (SM) and cholesterol (Chol) were used, since these are the most common lipids found in biological membranes. Several biophysical techniques were employed: surface pressure (π) - area (A) isotherms measurements were used to investigate the adsorption and penetration of drugs, polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) to acquire structural information and Brewster angle microscopy (BAM) to record images of the monolayers on the micrometer scale. The interactions of anthracyclines were assessed by alterations in the monolayers' shape, characteristic parameters (C_s^-1 values and area per lipid molecule at 30mN·m^-1 and under maximum packing conditions) and morphology of each 2D model studied. The presence of the drugs in the interface led to the production of less ordered monolayers, as evidenced by the decrease in the compressibility modulus. In addition, the drugs' effect on the membrane organization is related with their chemical structure and depends on the membraneś phase. For lower surface pressures, both electrostatic and hydrophobic interactions led to significant modifications in the monolayer order. With further compression, the impact of such interactions is reduced, resulting in the squeezing-out of some drug molecules from the interface. Furthermore, BAM images showed a clear anticancer drug interplay with the lipid monolayer by changes in the domains shape and appearance of bright dots, which are located in the frontier between the condensed and expanded lipid phases.