Pressure tuning infrared spectroscopic study of cisplatin-induced structural changes in a phosphatidylserine model membrane

Effect of Cisplatin and Its Cationic Analogues in the Phase Behavior and Permeability of Model Lipid Bilayers

Increasing evidence suggests a critical role of lipids in both the mechanisms of toxicity and resistance of cells to platinum(II) complexes. In particular, cisplatin and other analogues were reported to interact with lipids and transiently promote lipid phase changes both in the bulk membranes and in specific membrane domains. However, these processes are complex and not fully understood. In this work, cisplatin and its cationic species formed at pH 7.4 in low chloride concentrations were tested for their ability to induce phase changes in model membranes with different lipid compositions. Fluorescent probes that partition to different lipid phases were used to report on the fluidity of the membrane, and a leakage assay was performed to evaluate the effect of cisplatin in the permeability of these vesicles. The results showed that platinum(II) complex effects on membrane fluidity depend on membrane lipid composition and properties, promoting a stronger decrease in the fluidity of membranes containing gel phase. Moreover, at high concentration, these complexes were prone to alter the permeability of lipid membranes without inducing their collapse or aggregation.

The Role of Plasma Membrane Viscosity in the Response and Resistance of Cancer Cells to Oxaliplatin

Simple Summary

Understanding the role of the plasma membrane in the responses of cancer cells to chemotherapy is important because the cell membrane is directly involved in drug transport and the regulation of numerous biological processes. However, the role of the plasma membrane in cell resistance to platinum drugs like oxaliplatin is not fully understood. In this study we identified the changes to plasma membrane viscosity and lipid composition induced by oxaliplatin in responsive, cultured cancer cells and in mouse tumors. It was also found that the acquisition of chemoresistance is accompanied by modification of membrane lipids in ways that preserve the viscous properties unchanged upon further treatment. Therefore, new therapeutic approaches could be developed to reverse chemoresistance based on membrane lipid modifications and the de-stabilisation of membrane viscosity.

Abstract

Maintenance of the biophysical properties of membranes is essential for cell survival upon external perturbations. However, the links between a fluid membrane state and the drug resistance of cancer cells remain elusive. Here, we investigated the role of membrane viscosity and lipid composition in the responses of cancer cells to oxaliplatin and the development of chemoresistance. Plasma membrane viscosity was monitored in live colorectal cancer cells and tumor xenografts using two-photon excited fluorescence lifetime imaging microscopy (FLIM) using the fluorescent molecular rotor BODIPY 2. The lipid profile was analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS). It was found that the plasma membrane viscosity increased upon oxaliplatin treatment, both in vitro and in vivo, and that this correlated with lower phosphatidylcholine and higher cholesterol content. The emergence of resistance to oxaliplatin was accompanied by homeostatic adaptation of the membrane lipidome, and the recovery of lower viscosity. These results suggest that maintaining a constant plasma membrane viscosity via remodeling of the lipid profile is crucial for drug resistance in cancer.

Mapping cisplatin-induced viscosity alterations in cancer cells using molecular rotor and fluorescence lifetime imaging microscopy

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.

Shirazi F. FTIR Biospectroscopy Investigation on Cisplatin Cytotoxicity in Three Pairs of Sensitive and Resistant Cell Line

Fourier Transformed Infrared Spectroscopy (FTIR) has extensively been used for biological applications. Cisplatin is one the most useful antineoplastic chemotherapy drugs for a variety of different human cancers. One of the clinical problems in its application, which would consequently affect the therapeutic outcome of its application, is the occurrence of resistance to this agent. In this project three different pairs of sensitive and resistant cell lines of human ovarian A2780 and its resistant pair of A2780-CP, human ovarian OV2008 and its resistant pair of C13, and finally human lung carcinoma of HTB56 and its resistant pair of HTB56-CP were grown in the laboratory under the standard procedure. Saline was exposed to control cells, whereas 1, 5 and 10 µg/mL of cisplatin was exposed to experimental cells, for 1 h. Cells were then collected and lyophilized from which spectra were taken. According to our results, we could not trigger a well-recognized cells biomolecular band at 1015 cm(-1), being modified after exposure to cisplatin in all cell lines. On the other hand, there was a clear dose-dependent increase in protein β-sheet structure related peaks shift in resistant cell lines after exposure to cisplatin. This would probably indicate an easier protein interaction site for cisplatin in the resistant cell lines, which would probably inhibit cisplatin from binding to DNA, as the cytotoxic target. As a conclusion, FTIR biospectroscopy has proven its potency to identify the interactions, as well as the false engagement cellular sites for cisplatin in sensitive and resistant cell lines.

Platinum and Palladium Polyamine Complexes as Anticancer Agents: The Structural Factor

Since the introduction of cisplatin to oncology in 1978, Pt(II) and Pd(II) compounds have been intensively studied with a view to develop the improved anticancer agents. Polynuclear polyamine complexes, in particular, have attracted special attention, since they were found to yield DNA adducts not available to conventional drugs (through long-distance intra- and interstrand cross-links) and to often circumvent acquired cisplatin resistance. Moreover, the cytotoxic potency of these polyamine-bridged chelates is strictly regulated by their structural characteristics, which renders this series of compounds worth investigating and their synthesis being carefully tailored in order to develop third-generation drugs coupling an increased spectrum of activity to a lower toxicity. The present paper addresses the latest developments in the design of novel antitumor agents based on platinum and palladium, particularly polynuclear chelates with variable length aliphatic polyamines as bridging ligands, highlighting the close relationship between their structural preferences and cytotoxic ability. In particular, studies by vibrational spectroscopy techniques are emphasised, allowing to elucidate the structure-activity relationships (SARs) ruling anticancer activity.

Cisplatin-induced apoptosis involves membrane fluidification via inhibition of NHE1 in human colon cancer cells

We have previously shown that cisplatin triggers an early acid sphingomyelinase (aSMase)-dependent ceramide generation concomitantly with an increase in membrane fluidity and induces apoptosis in HT29 cells. The present study further explores the role and origin of membrane fluidification in cisplatin-induced apoptosis. The rapid increase in membrane fluidity following cisplatin treatment was inhibited by membrane-stabilizing agents such as cholesterol or monosialoganglioside-1. In HT29 cells, these compounds prevented the early aggregation of Fas death receptor and of membrane lipid rafts on cell surface and significantly inhibited cisplatin-induced apoptosis without altering drug intracellular uptake or cisplatin DNA adducts formation. Early after cisplatin treatment, Na+/H+ membrane exchanger-1 (NHE1) was inhibited leading to intracellular acidification, aSMase was activated, and ceramide was detected at the cell membrane. Treatment of HT29 cells with Staphylococcus aureus sphingomyelinase increased membrane fluidity. Moreover, pretreatment with cariporide, a specific inhibitor of NHE1, inhibited cisplatin-induced intracellular acidification, aSMase activation, ceramide membrane generation, membrane fluidification, and apoptosis. Finally, NHE1-expressing PS120 cells were more sensitive to cisplatin than NHE1-deficient PS120 cells. Altogether, these findings suggest that the apoptotic pathway triggered by cisplatin involves a very early NHE1-dependent intracellular acidification leading to aSMase activation and increase in membrane fluidity. These events are independent of cisplatin-induced DNA adducts formation. The membrane exchanger NHE1 may be another potential target of cisplatin, increasing cell sensitivity to this compound.

Mechanisms of transport across cell membranes of complexes contained in antitumour drugs

Various mechanism of antitumour drug transport across cell membranes has been described. Particular attention has been paid to a passive transport, active transport and multidrug resistance of complexes contained in antitumour drugs. A drug supply to the target site depends on the blood circulation within the tumour, on characteristic drug diffusion in the tissue, and also on binding protein. The physiologic transfer of hydrophilic compounds across the membrane is usually intermediated by means of a specific receptor or a carrier in that membrane, which facilitates the transport of compounds to and from the cell. Some drugs, e.g. doxorubicin and annamycin, can pass across the membrane by intermediacy of liposomes which exhibit a great activity in penetrating into tumour cells. The efficiency of antitumour drugs is limited by the appearance of resistance, i.e. by the lack of sensitivity of the cell to the administered drug. The presence in the membrane of specific proteins belonging to the ABC carriers group is postulated in a resistance theory; they would be responsible for 'pumping out' lipophilic drug molecules from the cell. Participation of high-energy ATP molecule is required by P-glycoprotein (Pgp) and by MRP protein described in this paper for their action. The mechanisms that are responsible for the cell resistance to drugs have been presented by analysing the resistance to antimetabolites, particularly to folate and fluoropyrimidine analogues, to alkylating agents, e.g. cisplatinum, and to heterocyclic compounds being responsible for so-called multidrug resistance.

The electrostatics of lipid surfaces

Charged lipids constitute a substantial fraction of all membrane lipids. Their charges vary in quantity and distribution within their headgroup regions. In long range interactions, their charges' value and electrostatic potential in the vicinity of the membrane surface can be approximated by the Guy-Chapman theory. This theory treats the interface as a charged structureless plain surrounded by uniform environments. However, if one considers intermolecular interactions, such assumptions need to be revised. The interface is in reality a thick region containing the residual charges of lipid headgroups. Their arrangement depends on the type of lipid present in the membrane. The variety of lipids and their biological functions suggests that charge distribution determines the extent and type of interaction with surface associated molecules. Numerous examples show that protein behavior at the lipid bilayer surface is determined by the type of lipid present, indicating protein specificity towards certain surface locations and local properties (determined by lipid composition) of a particular type. Such specificity is achieved by a combination of electrostatic, hydrophobic and enthropic effects. Comparing lipid biological activity, it can be stated that residual charge distribution is one of the factors of intermolecular recognition leading to the specific interaction of lipid molecules and selected proteins in various processes, particularly those involved with signal transduction pathways. Such specificity enables a variety of processes occurring simultaneously on the same membrane surface to function without cross-reaction interference.

Interaction of the anti-cancer drug cisplatin with phosphatidylserine in intact and semi-intact cells

The anti-cancer drug cisplatin (cis-diamminedichloroplatinum(II)) forms a stable coordination complex with phosphatidylserine (PS) in model membrane systems (Speelmans et al., Biochemistry 36 (1997) 10545-10550). Because a similar interaction in vivo would be expected to have important physiological implications we studied cisplatin-PS interaction in human erythrocytes and tumor cell lines. Although cisplatin was efficiently taken up by intact erythrocytes, a cisplatin-PS complex was only detected in cells which had lysed as a result of prolonged storage or hypotonic shock. Despite the use of highly sensitive detection methods, and despite efficient cellular uptake of cisplatin, a complex could also not be detected in four human tumor cell lines, unless cells were permeabilized. In experiments in which cisplatin was incubated with PS-containing liposomes in the presence of an alternative cellular substrate, such as reduced glutathione, the relative affinity of cisplatin for PS was found to be low. Moreover, loading erythrocyte ghosts with physiological concentrations of glutathione strongly reduced cisplatin-PS complexation. Thus, in intact (tumor) cells a complex is not detected, most likely, because of the presence of higher affinity substrates. Though a transient complexation of cisplatin to PS cannot be excluded, our data suggest that cisplatin-PS does not play a direct role in the cellular (cyto)toxicity of cisplatin.

Cisplatin complexes with phosphatidylserine in membranes

Upon incubation of the anticancer drug cisplatin [cis-diamminedichloroplatinum(II)] with model membranes composed of phosphatidylserine (PS), a stable product is formed that has been isolated after chloroform/methanol extraction of the sample. The product formation is specific for PS and does not occur with other major membrane phospholipids. The rate and extent of product formation is dependent on the pH, chloride ion concentration, and temperature, with the highest rate at pH 6.0, in the absence of Cl- and at 37 degrees C, indicating that positively charged aquated cisplatin is the reactive species. Over 80% of PS is converted within 15 h under these conditions with a halftime of 5 h. PS can be regenerated by an excess of glutathione. Mass spectrometry experiments demonstrate that interaction of cisplatin with PS involves a loss of two chloride ions and coordination of platinum to the amine and carboxyl group of the serine moiety. Cisplatin forms complexes specifically with PS not only in model membranes but also in the plasma membrane of human erythrocytes. Since PS is essential in several cellular processes, its interaction with cisplatin may have important physiological implications.