Fluorescence studies on the interaction between chlorpromazine and model cell membranes
In this work, the interaction between a commonly used multifunctional fluorescent drug chlorpromazine (CPZ) and model cell membranes (liposomes, giant unilamellar vesicles and supported lipid membranes) was investigated using various fluorescence-based techniques (steady-state and time-resolved spectroscopy, confocal microscopy and flow cytometry). It was found that CPZ could substantially quench the fluorescence of lipid membrane fluorophores while the drug’s own fluorescence signal was significantly enhanced upon membrane interaction. The drug contact-induced fluorescence quenching response of the membrane fluorophores can be explained by the coexistence of both static and dynamic quenching processes, while the fluorescence enhancement of CPZ is attributed to the change of environmental polarity. Both fatty acid (tail)- and headgroup-labeled fluorophores in lipid membrane were quenched immediately after the introduction of CPZ, indicating that the CPZ molecules reside at the lipid interfacial region and can interact with both the lipid headgroups and tails. Besides, the fluorescence quenching was partly recoverable by water washing, indicating that the association of the CPZ molecules with the lipid membrane is not very strong. On the other hand, the significantly enhanced fluorescence intensity of CPZ after insertion into the less polar lipid bilayer enabled us to directly visualize the location of the drug molecules interacting with cell membranes. The current study provides important molecular-level knowledge on CPZ–cell membrane interactions using various model cell membranes, and represents a typical example of deciphering the drug and cell membrane interaction mechanisms using various fluorescence-based techniques.