Abstract
.Significance: Despite the importance of the cell membrane in regulation of drug activity, the influence of drug treatments on its physical properties is still poorly understood. The combination of fluorescence lifetime imaging microscopy (FLIM) with specific viscosity-sensitive fluorescent molecular rotors allows the quantification of membrane viscosity with high spatiotemporal resolution, down to the individual cell organelles.Aim: The aim of our work was to analyze microviscosity of the plasma membrane of living cancer cells during chemotherapy with cisplatin using FLIM and correlate the observed changes with lipid composition and cell’s response to treatment.Approach: FLIM together with viscosity-sensitive boron dipyrromethene-based fluorescent molecular rotor was used to map the fluidity of the cell’s membrane. Chemical analysis of membrane lipid composition was performed with time-of-flight secondary ion mass spectrometry (ToF-SIMS).Results: We detected a significant steady increase in membrane viscosity in viable cancer cells, both in cell monolayers and tumor spheroids, upon prolonged treatment with cisplatin, as well as in cisplatin-adapted cell line. ToF-SIMS revealed correlative changes in lipid profile of cisplatin-treated cells.Conclusions: These results suggest an involvement of membrane viscosity in the cell adaptation to the drug and in the acquisition of drug resistance.
Highlights
Viscosity, a reciprocal of fluidity, plays an important role in the functioning of living cells, as it is one of the key parameters for the regulation of their morphological and physiological state
The specific questions we addressed here are: (1) does cisplatin cause any changes in viscosity of cellular plasma membranes when used at therapeutically relevant concentrations; (2) how common are these effects for different cancer cell lines cultured as a monolayer and in multicellular structures; (3) are these changes associated with cell survival and/or cell death; and (4) if membrane lipid composition is the underlying reason for the observed changes in viscosity
3.1 Viscosity in Monolayer Cells upon Cisplatin Treatment Using fluorescence lifetime imaging microscopy (FLIM) with fluorescent molecular rotor boron dipyrromethene (BODIPY) 2, plasma membrane viscosity in cancer cells was measured during chemotherapy with cisplatin that was applied to the cell monolayers
Summary
A reciprocal of fluidity, plays an important role in the functioning of living cells, as it is one of the key parameters for the regulation of their morphological and physiological state. The viscosity of the cytoplasmic membrane is thought to be involved in controlling the transport of molecules, permeability, biosynthesis, and catalytic activity of membrane enzymes.[1]. Membrane viscosity depends on both lipid composition and organization. A lower degree of fatty acid unsaturation, greater length of phospholipid acyl chains, and increased cholesterol content make a more viscous membrane.[1,2] In addition, the plasma membrane is highly heterogeneous, as suggested in the “lipid raft hypothesis,” whereby cholesterol-rich, highly ordered lipid “islands” act as organizing hubs for membrane-embedded proteins.[3] The complex interplay between all these factors allow living cells to maintain membrane viscosity within narrow limits, specific to each cell type, which is key to cell homeostasis and survival.[3,4,5,6,7]
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