Interactions of alkylphosphocholines with model membranes : the Langmuir monolayer study

Alkylphosphocholines (APCs) belong to a class of synthetic antitumor lipids, which are new-generation anticancer agents. In contrast to traditional antitumor drugs, they do not attack the cell nucleus but, rather, the cellular membrane; however, their mechanism of action is not fully understood. This work compared the interactions of selected APCs [namely, hexadecylphosphocholine (miltefosine), octadecylphosphocholine and erucylphosphocholine] with the most important membrane lipids [cholesterol, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)] and examined their influence on a model membrane of tumor and normal cells. As a simple model of membranes, Langmuir monolayers prepared by mixing cholesterol either with a saturated phosphatidylcholine (DPPC), for a normal cell membrane, or with an unsaturated one (POPC), for a tumor cell membrane, have been applied. The APC–lipid interactions, based on experimental surface pressure (π) versus mean molecular area (A) isotherms, were analyzed qualitatively (with mean molecular area values) as well as quantitatively (with the \Delta G^{exc} function). Strong attractive interactions were observed for mixtures of APCs with cholesterol, contrary to the investigated phosphatidylcholines, for which the interactions were found to be weak with a tendency to separation of film components. In ternary monolayers it has been found that the investigated model systems (cholesterol/DPPC/APC vs cholesterol/POPC/APC) differ significantly as regards the interactions between film-forming molecules. The results demonstrate stronger interactions between the components of cholesterol/POPC/APC monolayers compared to cholesterol/POPC film, mimicking tumor cell membranes. In contrast, the interactions in cholesterol/DPPC/APC films were found to be weaker than those in the cholesterol/DPPC system, serving as a model of healthy cell membranes, thus proving that the incorporation of APCs is, from a thermodynamic point of view, unfavorable for binary cholesterol/DPPC monolayers. It can be concluded that the composition of healthy cell membranes is a natural barrier preventing the incorporation of APCs into normal cells

Interactions between antitumor alkylphosphocholines and membrane sphingolipids in Langmuir monolayers

Alkylphosphocholines (APCs) are new generation, highly selective antineoplastic drugs, whose mechanism of action is not fully understood. It is known that in contrast to traditional chemotherapeutics, APCs do not induce cell death by apoptosis or necrosis as a result of DNA damage, but target cellular membranes and affect their biophysical properties. However, it is still unknown which membrane component attracts APC molecules selectively to cancer cells. In order to get insight into this issue, systematic investigations on the interactions between APCs and particular membrane components are highly required. Such experiments can be performed with the Langmuir monolayer technique, serving as a biomembrane model. Because of overexpression of gangliosides in tumor progression and the ability of APCs to insert into membrane rafts, two sphingolipids, i.e. sphingomyelin (SM) and ganglioside GM1 have been examined as potential membrane targets. In this respect, their interactions with three alkylphosphocholines, differing in their hydrophobic part: hexadecylphosphocholine (HePC), octadecylphosphocholine (OcPC) and erucylphosphocholine (ErPC) have been studied and the following systems have been analysed: SM(or GM1)/HePC, SM(or GM1)/OcPC and SM(or GM1)/ErPC. It was found that all the investigated APCs show strong affinity to ganglioside in contrast to sphingomyelin. Differences in interaction of APCs with both investigated sphingolipids were studied based on experimental surface pressure ( \pi ) versus mean molecular area (A) isotherms, and analyzed qualitatively (with mean molecular area values) as well as quantitatively (with \Delta G^{exc} function). The obtained results have also been analysed taking into consideration geometry of interacting molecules. Our results suggest that gangliosides may be molecular targets for APCs, attracting them to tumor cells. Although the interactions with sphingomyelin were found to be unfavourable, further studies on more complex system, containing APCs mixed with sphingomyelin and cholesterol, are required to better understand the role of lipid rafts in the selectivity of APCs

Langmuir monolayer characteristics of erucylphosphocholine : a novel anti-tumor drug

Erucylphosphocholine, an alkylphosphocholine anticancer drug, was employed for Langmuir monolayer characterization and liquid crystalline studies. Differential scanning calorimetry measurements together with texture observation with polarizing microscope revealed the presence of nematic phase. Film forming properties of erucylphosphocholine at the air/water interface were thoroughly investigated by means of surface pressure–area ( º –A) and electric surface potential–area ( ¢ V – A ) isotherms. The influence of such factors as subphase temper- ature, ionic strength, speed of compression, number of molecules spread at the surface on the characteristics of the º – A isotherms was investigated. Erucylphosphocholine was found to form very stable Langmuir monolayers, which are almost not influenced by experimental conditions. The liquid character of its monolayers was confirmed with both compressibility modulus values and homogeneous Brewster angle microscopy images

Affinity of alkylphosphocholines to biological membrane of prostate cancer : studies in natural and model systems

The effectiveness of two alkylphosphocholines (APCs), hexadecylphosphocholine (miltefosine) and erucylphosphocholine to combat prostate cancer has been studied in vitro with artificial cancerous membrane, modelled with the Langmuir monolayer technique, and on cell line (Du-145). Studies performed with the Langmuir method indicate that both the investigated drugs have the affinity to the monolayer mimicking prostate cancer membrane (composed of cholesterol:POPC = 0.428) and the drug-membrane interactions are stronger for erucylphosphocholine as compared to hexadecylphosphocholine. Moreover, both studied drugs were found to fluidize the model membrane, which may lead to apoptosis. Indeed, biological studies confirmed that in Du-145 cell line both investigated alkylphosphocholines cause cell death primarily by apoptosis while necrotic cells constitute only a small percentage of APC-treated cells

Cyclosporin A in membrane lipids environment : implications for antimalarial activity of the drug : the Langmuir monolayer studies

Cyclosporin A (CsA), a hydrophobic cyclic peptide produced by the fungus Tolypocladium inflatum, is well known for its high efficiency as an immunosuppressor for transplanted organs and anti-inflammatory properties; however, it is also active as antiparasitic (antimalarial) drug. Antimalarial mechanism of CsA action lacks a detailed understanding at molecular level. Due to a high lipophilicity of CsA, it is able to interact with lipids of cellular membrane; however, molecular targets of this drug are still unknown. To get a deeper insight into the mode of antimalarial activity of CsA, it is of utmost importance to examine its interactions with membrane components. To reach this goal, the Langmuir monolayer technique, which serves as a very useful, easy to handle and controllable model of biomembranes, has been employed. In this work, the interactions between CsA and main membrane lipids, i.e., cholesterol (Chol), 2-oleoyl-1-palmitoyl-3-phosphocholine (POPC), and sphingomyelin (SM), have been investigated. Attractive interactions are observed only for CsA mixtures with SM, while repulsive forces occur in systems containing remaining membrane lipids. Taking into consideration mutual interactions between membrane lipids (Chol–SM; Chol–POPC and SM–POPC), the behavior of CsA in model erythrocyte membrane of normal and infected cells has been analyzed. Our results prove strong affinity of CsA to SM in membrane environment. Since normal and parasitized erythrocytes differ significantly in the level of SM, this phospholipid may be considered as a molecular target for antimalarial activity of CsA

Drug-induced phospholipidosis – causes, effects, identification

Adverse reactions of drugs are a significant problem in pharmacotherapy. The observed side effects may have multiple causes. They may depend on the dose and type of medicine used. They can occur during therapy or appear with a delay, after its completion. They may disappear after discontinuation of treatment or persist. In this review, we summarize the vast literature in the area of phospholipidosis, which is a major consequence of the use of cationic amphiphilic drugs (CAD). Their specific chemical structure causes the accumulation of phospholipids inside the lysosomes, which affects their proper function, however, the mechanism of phospholipidosis at the molecular level is not fully understood. Several hypotheses on the mechanism of phospholipidosis formation have been put forward - they mainly concern: the formation of complexes between phospholipids and CAD drugs, competitive inhibition of lysosomal phospholipases by CAD and increased biosynthesis of phospholipids and cholesterol under the influence of the drug. As a result of the accumulation of phospholipids in lysosomes, the so-called lamellar bodies may appear in tissues days or weeks after in vivo CAD administration, and this process is dose-dependent. Phospholipidosis is believed to be a reversible process and is assumed to be an adaptive - but not toxic - response to drugs. If the concentration of CAD or a toxic substance accumulated in lysosomes exceeds a critical value, apoptosis and autophagy may be activated. Phospholipidosis can also be caused by drugs other than CAD, oxysterols and some nanoparticles. Phospholipidosis is one of the least known complications of pharmacotherapy - methods of its detection at the initial stage as well as the full spectrum of functional disorders of the body are still being sought. Identification of phospholipidosis in cells is possible by means of electron microscopy studies confirming the presence of lamellar bodies in tissues from biopsies or by means of real-time PCR techniques examining the expression of genes correlated with the occurrence of phospholipidosis. A potential biomarker detecting this process in the blood and urine of patients is bis(monoacylglycero)phosphate (BMP). Drug-induced phospholipidosis can be detected at the preclinical stage. However, the accumulation of phospholipids and the formation of lamellar bodies found in in vitro or in animal studies does not necessarily mean organ damage in the human body. In recent years, there has been an increase in interest in the mechanism of the phospholipidosis and in the study of new drugs in terms of causing this undesirable effect. This review presents an overview of the most important studies to date related to the mechanism of phospholipidosis formation, methods of its identification and effects at the cellular level as well as on the whole organism

Site of the hydroxyl group determines the surface behavior of bipolar chain-oxidized cholesterol derivatives - langmuir monolayer studies supplemented with theoretical calculations

Cholesterol oxidation products (called oxysterols) are involved in many biological processes, showing both negative (e.g., neurodegenerative) and positive (e.g., antiviral and antimicrobial) effects. The physiological activity of oxysterols is undoubtedly closely related to their structure (i.e., the type and location of the additional polar group in the cholesterol skeleton). In this paper, we focus on determining how a seemingly minor structural change (introduction of a hydroxyl moiety at C(24), C(25), or C(27) in the isooctyl chain of cholesterol) affects the organization of the resulting molecules at the phase boundary. In our research, we supplemented the classic Langmuir monolayer technique, based on the surface pressure and electric surface potential isotherms, with microscopic (BAM) and spectroscopic (PM-IRRAS) techniques, as well as theoretical calculations (DFT and MD). This allowed us to show that 24-OH behaves more like cholesterol and forms stable, rigid monolayers. On the other hand, 27-OH, similar to 25-OH, undergoes the phase transition from monolayer to bilayer structures. Theoretical calculations enabled us to conclude that the formation of bilayers from 27-OH or 25-OH is possible due to the hydrogen bonding between adjacent oxysterol molecules. This observation may help to understand the factors responsible for the unique biological activity (including antiviral and antimicrobial) of 27-OH and 25-OH compared to other oxysterols