Nanoarchitectonics and Simulation on the Molecular-Level Interactions between <i>p-</i>Sulfonic Acid Calix[4]arene and Langmuir Monolayers Representing Healthy and Cancerous Cell Membranes

The design of chemotherapeutic drug carriers requires precise information on their interaction with the plasma membrane since the carriers should be internalized by cells without disrupting or compromising the overall integrity of the membrane. In this study, we employ Langmuir monolayers mimicking the outer leaflet of plasma membranes of healthy and cancerous cells to determine the molecular-level interactions with a water-soluble calixarene derivative, <i>p</i>-sulfonic acid calix[4]arene (SCX4), which is promising as drug carrier. The cancer membrane models comprised either 40% 1,2-dipalmitoyl-<i>sn</i>-glycero-3-phosphocholine (DPPC) or 1,2-dioleoyl-<i>sn</i>-glycero-3-phosphocholine (DOPC), 30% cholesterol (Chol), 20% 1,2-dipalmitoyl-<i>sn</i>-glycero-3-phosphoethanolamine (DPPE), and 10% 1,2-dipalmitoyl-<i>sn</i>-glycero-3-phospho-l-serine (DPPS). The healthy membrane models were composed of 60% DPPC or DOPC, 30% Chol, and 10% DPPE. SCX4 expanded the surface pressure isotherms and decreased compressional moduli in all membrane models, altering their morphologies as seen in Brewster angle microscopy images. A combination of polarization-modulated infrared reflection absorption spectroscopy and molecular dynamics simulations revealed that SCX4 interacts preferentially with lipid headgroups in cancer membrane models through electrostatic interactions with the amine groups of DPPS and DPPE. In healthy membrane models, SCX4 interacts mostly with cholesterol through van der Waals forces. Using a multidimensional projection technique to compare data from the distinct membrane models, we observed that SCX4 effects depend on membrane composition with no preference for cancer or healthy membrane models, which is consistent with its biocompatibility. Furthermore, the interactions and close location of SCX4 to the headgroups indicate that it does not compromise membrane integrity, confirming that SCX4 may be a suitable drug carrier.