Combination of antitumor ether lipid with lipids of complementary molecular shape reduces its hemolytic activity

Advantages of the classical thermodynamic analysis of single-and multi-component Langmuir monolayers from molecules of biomedical importance-theory and applications

The Langmuir monolayer technique has been successfully used for decades to model biological membranes and processes occurring at their interfaces. Classically, this method involves surface pressure measurements to study interactions within membrane components as well as between external bioactive molecules (e.g. drugs) and the membrane. In recent years, surface-sensitive techniques were developed to investigate monolayers in situ; however, the obtained results are in many cases insufficient for a full characterization of biomolecule-membrane interactions. As result, description of systems using parameters such as mixing or excess thermodynamic functions is still relevant, valuable and irreplaceable in biophysical research. This review article summarizes the theory of thermodynamics of single- and multi-component Langmuir monolayers. In addition, recent applications of this approach to characterize surface behaviour and interactions (e.g. orientation of bipolar molecules, drug-membrane affinity, lateral membrane heterogeneity) are presented.

The Past and the Future of Langmuir and Langmuir-Blodgett Films

The Langmuir-Blodgett (LB) technique, through which monolayers are transferred from the air/water interface onto a solid substrate, was the first method to allow for the controlled assembly of organic molecules. With its almost 100 year history, it has been the inspiration for most methods to functionalize surfaces and produce nanocoatings, in addition to serving to explore concepts in molecular electronics and nanoarchitectonics. This paper provides an overview of the history of Langmuir monolayers and LB films, including the potential use in devices and a discussion on why LB films are seldom considered for practical applications today. Emphasis is then given to two areas where these films offer unique opportunities, namely, in mimicking cell membrane models and exploiting nanoarchitectonics concepts to produce sensors, investigate molecular recognitions, and assemble molecular machines. The most promising topics for the short- and long-term prospects of the LB technique are also highlighted.

Predicting the packing parameter for lipids in monolayers with the use of molecular dynamics

Lipid molecules form the backbone of biological membranes. Due to their amphiphilic structure, they can self-organize in a plethora of different structures when in contact with water. The type of self-assembled structure and its curvature depend on so-called shape factor or critical packing parameter, CPP, that can be derived knowing the molecular volume of a lipid (V), optimal surface area (a₀) and critical chain length (l_c) (see Intermolecular and Surface Forces by Jacob N. Israelachvili, Third Edition, 2011). The value of CPP allows not only to predict the type of self-assembled structure but also is a key factor for molecular interactions, which play a great role both in physiological and pathological conditions. The greatest difficulties arise when calculating the a₀ parameter, and although for some typical membrane lipids these values have been determined, there are a number of derivatives for which this parameter, and thus CPP, are unknown. The value of CPP allows not only to predict the type of self-assembled structure but also is a key factor for molecular interactions, which play a great role both in physiological and pathological conditions. So far, the determination of the packing parameter required the use of theoretical models with assumptions deviating from the physical conditions. Here we report a method based on molecular dynamics, which was applied to simulate lipid membranes consisting of cholesterol, oxysterols, sphingolipids, phosphatidylcholines, and phosphatidylethanolamines. For lipid molecules for which CPPs have already been determined, high compliance has been demonstrated. This proves that the method presented herein can be successfully used to determine packing parameters for other membrane lipids and amphiphilic molecules.

Anticancer Agent Edelfosine Exhibits a High Affinity for Cholesterol and Disorganizes Liquid-Ordered Membrane Structures

Edelfosine is an anticancer drug with an asymmetric structure because, being a derivative of glycerol, it possesses two hydrophobic substituents of very different lengths. We showed that edelfosine destabilizes liquid-ordered membranes formed by either 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine, sphingomyelin (SM), and cholesterol (1:1:1 molar ratio) or SM and cholesterol (2:1 molar ratio). This was observed by differential scanning calorimetry in which phase transition arises from either of these membrane systems after the addition of edelfosine. The alteration in the liquid-ordered domains was characterized by using a small-angle X-ray diffraction that revealed the formation of gel phases as a consequence of the addition of edelfosine at low temperatures and by a wide-angle X-ray diffraction that confirmed changes in the membranes, indicating the formation of these gel phases. The increase in phase transition derived by the edelfosine addition was further confirmed by Fourier-transform infrared spectroscopy. The effect of edelfosine was compared with that of structurally analogue lipids: platelet-activating factor and 1-palmitoyl-2-acetyl- sn-glycero-3-phosphocholine, which also have the capacity of destabilizing liquid-ordered domains, although they are less potent than edelfosine for this activity, and lysophosphatidylcholine, which lacks this capacity. It was concluded that edelfosine may be associated with cholesterol favorably competing with sphingomyelin, and that this sets sphingomyelin free to undergo a phase transition. Finally, the experimental observations can be described by molecular dynamics calculations in terms of intermolecular interaction energies in phospholipid-cholesterol membranes. Higher interaction energies between asymmetric phospholipids and cholesterol than between sphingomyelin and cholesterol were obtained. These results are interesting because they biophysically characterize one of the main molecular mechanisms to trigger apoptosis of the cancer cells.

Miltefosine-loaded lipid nanoparticles: Improving miltefosine stability and reducing its hemolytic potential toward erythtocytes and its cytotoxic effect on macrophages

The toxic effects of miltefosine on the epithelial cells of the gastrointestinal tract and its hemolytic action on erythrocytes have limited its use as an antileishmanial agent. As part of our search for new strategies to overcome the side effects of miltefosine during the treatment of leishmaniasis, we have developed stable miltefosine-loaded lipid nanoparticles in an attempt to reduce the toxic effects of the drug. We have evaluated lipid nanoparticles containing varying amounts of miltefosine and cholesterol, prepared by sonication, in terms of their physicochemical properties, preliminary stability, hemolytic potential toward erythrocytes, and cytotoxicity to macrophages and to promastigote and amastigote forms of Leishmania (L.) chagasi. Miltefosine loading into lipid nanoparticles was 100% for low drug concentrations (7.0 to 20.0mg/mL). Particle size decreased from 143nm (control) to between 43 and 69nm. From fluorescence studies, it was observed that the presence of miltefosine and cholesterol (below 103μM) promoted ordering effects in the phospholipid region of the nanoparticles. The formulation containing 15mg/mL miltefosine was stable for at least six months at 4°C and in simulated gastrointestinal fluids, and did not promote epithelial gastrointestinal irritability in Balb/C mice. When loaded into lipid nanoparticles, the hemolytic potential of miltefosine and its cytotoxicity to macrophages diminished, while its antiparasitic activity remained unaltered. The results suggested that miltefosine-loaded lipid nanoparticles may be promising for the treatment of leishmaniasis and might be suitable for oral and parenteral use.

Evidences for anti-mycobacterium activities of lipids and surfactants

Tuberculosis is the most widespread and deadly airborne disease caused by Mycobacterium tuberculosis. The two-pronged lethal effect on the bacteria using lipids/surfactants and anti-tubercular drugs may render the miniaturization of dose owing to synergistic and tandem effect of both. The current research has been focused on screening and evaluating various lipids/surfactants possessing inherent anti-mycobacterium activity that can ferry the anti-tubercular drugs. In vitro anti-mycobacterium activity was evaluated using agar well diffusion method. Furthermore, time-concentration dependent killing and DNA/RNA content release studies were performed to correlate the findings. The exact mechanism of bacterial killing was further elucidated by electron/atomic force microscopy studies. Finally, to negate any toxicity, in vitro hemolysis and toxicity studies were performed. The study revealed that capmul MCM C-8, labrasol and acconon C-80 possessed highest in vitro anti-mycobacterium activity. Electron/atomic force microscopy results confirmed in vitro studies and verified the killing of Mycobacterium owing to the release of cytoplasmic content after cell wall fragmentation and disruption. Moreover, the least hemolysis and hundred percent survivals rate of mice using the excipients demonstrated the safety aspects of explored excipients that can ferry the anti-tubercular drugs. The present study concluded the safe, efficient and synergistic activity of the explored excipients and anti-tubercular drugs in controlling the menace of tuberculosis.

Liposomal codelivery of a synergistic combination of bioactive lipids in the treatment of acute myeloid leukemia

Aim: The aim of this work was to develop a liposomal formulation to facilitate delivery of a synergistic safingol/C2-ceramide combination in the treatment of acute myeloid leukemia (AML). Materials & methods: Liposomes were prepared using the extrusion method and the bioactive lipids were encapsulated passively. Drug concentrations were determined by liquid chromatography tandem mass spectrometry. Antileukemic activity was evaluated using human leukemic cell lines, patient samples and U937 leukemic xenograft models. Results: A stable liposome formulation was developed to coencapsulate safingol and C2-ceramide at 1:1 molar ratio with >90% encapsulation efficiency. The liposomal safingol/C2-ceramide was effective in AML cell lines, patient samples and murine xenograft models of AML, compared with liposomal safingol or liposomal C2-ceramide alone despite a dose reduction of 33%. Conclusion: Our study provided proof-of-concept evidence to deliver synergistic combination of bioactive lipid to achieve complete remission in AML.

Original submitted: 27 February 2013; Revised submitted: 25 June 2013

Surface masking shapes the traffic of the neuropeptide Y Y2 receptor

The neuropeptide Y (NPY) Y2 receptor shows a large masked surface population in adherent CHO cells or in forebrain cell aggregates, but not in dispersed cells or in particulates from these sources. This is related to adhesion via acidic motifs in the extracellular N-terminal domain. Masking of the Y2 receptor is lifted by non-permeabilizing mechanical dispersion of cells, which also increases internalization of Y2 agonists. Mechanical dispersion and detachment by EDTA expose the same number of surface sites. As we have already shown, phenylarsine oxide (PAO), a cysteine-bridging agent, and to a lesser extent also the cysteine alkylator N-ethylmaleimide, unmask the surface Y2 sites without cell detachment or permeabilization. We now demonstrate that unmasking by permeabilizing but non-detaching treatment with cholesterol-binding detergents digitonin and edelfosine compares with and overlaps that of PAO. The caveolar/raft cholesterol-targeting macrolide filipin III however produces only partial unmasking. Depletion of the surface sites by N-terminally clipped Y2 agonists indicates larger accessibility for a short highly helical peptide. These findings indicate presence of a dynamic masked pool including majority of the cell surface Y2 receptors in adherent CHO cells. This compartmentalization is obviously involved in the low internalization of Y2 receptors in these cells.

Effect of edelfosine on tumor and normal cells model membranes--a comparative study

This work is aimed at comparing the effect of edelfosine (Ed) on normal and tumor cell membrane imitated by the Langmuir monolayers prepared from cholesterol and phosphatidylcholines. To keep the differences in the fluidity of these membranes, model membrane of normal cell has been composed from saturated phospholipid (DPPC) and contained a higher proportion of cholesterol (cholesterol:DPPC=0.67) than tumor cell model membranes prepared from unsaturated phosphatidylcholine (cholesterol:POPC=0.25). The results proved that the incorporation of edelfosine modifies the organization and interactions between molecules in both model systems. The interactions in cholesterol/DPPC/edelfosine monolayers are stronger than in cholesterol/DPPC film. On the other hand, the interactions in cholesterol/POPC/edelfosine system are weaker than in cholesterol/POPC monolayer, thus the incorporation of edelfosine is, from thermodynamical point of view, unfavorable for binary cholesterol/POPC monolayer. Edelfosine has been found to increase the fluidity of model membranes, however, at a lower concentration (up to 5% of edelfosine in model system) this compound affects only the condensation of tumor cell model membrane, while practically does not modify the organization of normal model system. It has been suggested that edelfosine inserts into tumor cellular membranes more easily than into normal cell membrane and cholesterol/edelfosine interactions determine the interactions between molecules in the investigated mixed monolayers.

The anti-tumor alkylphospholipid perifosine is internalized by an ATP-dependent translocase activity across the plasma membrane of human KB carcinoma cells

Perifosine is a promising anticancer alkylphospholipid (ALP) that induces apoptosis in tumor cells. Here we report evidences against a role of endocytosis in perifosine uptake by human KB carcinoma cells. We have generated a KB cell line resistant to perifosine (KB PER(R) clone10), which shows cross-resistance to the ALPs miltefosine and edelfosine, a marked impairment in the uptake of (14)C-perifosine at both 37 degrees C and 4 degrees C, and no signs for active efflux of the drug. KB PER(R) clone10 cells show a similar rate of raft-dependent endocytosis with respect to the parental cells, and silencing of both clathrin and dynamin in the latter causes only minor changes in the rate of perifosine uptake. Perifosine uptake is a temperature- and ATP-dependent, N-ethylmaleimide- and orthovanadate-sensitive process in parental cells. Accumulation of (14)C-perifosine and the fluorescent phospholipid analogue 6-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)aminocaproyl]-phosphatidylethanolamine (NBD-PE) is inhibited by perifosine in a concentration-dependent manner in parental cells. Moreover, NBD-PE accumulation is slower in PER(R) clone10 cells and correlated with phosphatidylserine exposure in their plasma membrane surface. Together, all these data suggest a role of plasma membrane translocation by a putative phospholipid translocase, rather than endocytosis, as the true mechanism for ALPs uptake in KB carcinoma cells.

A liposomal formulation of doxorubicin, composed of hexadecylphosphocholine (HePC): physicochemical characterization and cytotoxic activity against human cancer cell lines

The overall goal of this study was to prepare a novel liposomal formulation of doxorubicin, composed of hexadecylphosphocholine (HePC), as a combined formulation and to study its activity against cancer cells and peripheral blood mononuclear cells (PBMCs), in terms of efficacy and toxicity. Liposomes composed of HePC/egg phosphatidylcholine/stearylamine (HePC/EPC/SA) 10:10:0.1 (molar ratio) (1) and EPC/SA 10:0.1 (molar ratio) (2) were prepared and doxorubicin was encapsulated using the pH gradient method. Determination of lipids and doxorubicin has been achieved by high-performance thin-layer chromatography coupled with a flame-ionization detector. Prepared liposomes were characterized for their size distribution and their zeta-potential at each step of the preparation procedure. In vitro release studies have been evaluated in buffer and culture medium at 25 and 37 degrees C for 24 hours period. Liposomal formulations, free doxorubicin and HePC were tested against cancer cell lines and PBMCs, using sulforhodamine B (SRB) assay. Doxorubicin was encapsulated into the liposomes 1 and 2 at a drug to lipid molar ratio of 1.08 and 0.77, respectively, with an entrapping efficiency almost 100% in both cases. Doxorubicin was retained into liposome 1 up to 70% at 25 degrees C in TES, while up to 80% was released from 1 when liposomes were incubated at 37 degrees C either in culture medium or in the TES buffer at 24 hours. The activity of doxorubicin was retained or slightly improved when entrapped into liposomes 1 and 2, while liposomal formulation 1 encapsulating doxorubicin was found to be less toxic against normal cells (PBMCs). The combination of HePC and doxorubicin in one combined formulations justified as an improvement of the therapeutic index (TI) of doxorubicin in terms of efficacy and toxicity.

Antileishmanial and trypanocidal activities of new miltefosine liposomal formulations

Liposomes composed of hexadecylphosphocholine/egg phosphatidylcholine/stearylamine (HePC/EPC/SA) 10:10:0.1, 10:10:0.5 and 10:10:1 (molar ratio) (1-3) were prepared and lyophilized. The liposomes were physicochemically characterized (size and zeta-potential) and they were found stable at 4 degrees C over a period of 4 weeks. In vitro, liposomes 1 and 2 were about twice more active than HePC against Leishmania donovani WT whereas liposomes 3 were about three times more active than HePC on HePC-resistant promastigotes. Although liposomes 1-3 were inactive on the in vitro intramacrophage amastigote model, the ability of the liposomes to accumulate within the liver where parasites are located justifies a further in vivo evaluation. We observed that liposome 1 was twice more active than HePC against Trypanosoma brucei brucei bloodstream forms maintained in vitro. In vivo results showed that liposomal HePC seemed to be less toxic than the free drug despite the absence of significant antitrypanosomal activity.

A comparative study of the effect of the antineoplastic ether lipid 1-O-octadecyl-2-O-methyl-glycero-3-phosphocholine and some homologous compounds on PKCα and PKCɛ

The effects of the anti-neoplastic ether lipid ET-18-OCH3 and some structural homologues on the activity of protein kinase C alpha (PKC alpha) were studied and compared with the effects the same had on the activity of PKC epsilon. ET-18-OCH3 progressively inhibited the activity of PKC alpha as the concentration was increased up to 30 mol% of the total lipid, above which the effect was one of activation. The experiments carried out with the homologues showed that the methoxy group bound at the sn-2 position of the glycerol of ET-18-OCH3 is essential for both the initial inhibitory effect and the subsequent activation effect. On the other hand, variations in the type of bond linking substitutions in the sn-1 position, ether or ester, do not seem to play an important role in determining the activity of the enzyme. The effects were different on PKC epsilon since ET-18-OCH3 had a triphasic effect, activating the enzyme at low concentrations, inhibiting it at slightly higher concentrations and then activating it again at higher concentrations. In this case, when the homologues were used, it was observed that the presence of the methoxy group linked to the sn-2 position of glycerol and the type of bond linking substitutions to the sn-1 position were important for activating the enzyme, so that only homologues with ester bonds as LPC and PAPC were able to induce the initial activation step in a way similar to ET-18-OCH3. Substitution of the phosphocholine group of ET-18-OCH3 by phosphoserine led to a greater activation of PKC alpha, an effect that comes from the Ca(2+)-phospholipid binding site probably because of the specific interaction of this site with the phosphoserine group. The action of ET-18-OCH3 and its homologues, as demonstrated in this paper, may permit the selective inhibition or activation of PKC alpha and PKC epsilon by using the most suitable range of concentrations.

Activity, pharmacokinetics and tissue distribution of TLC ELL-12 (liposomal antitumor ether lipid) in rats with transplantable, s.c. methylnitrosourea-induced tumors

TLC ELL-12 is a liposomal formulation of the novel antineoplastic compound 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (L-ET-18-OCH(3)). The purpose of these studies was to evaluate the activity and tissue distribution of L-ET-18-OCH(3) when administered i.v. as TLC ELL-12 to rats bearing solid tumors. Growth-inhibitory activity of L-ET-18-OCH(3) and TLC ELL-12 against methylnitrosourea (MNU)-induced tumors grown in vitro was evaluated. Female Buffalo rats were injected s.c. with transplantable MNU-induced tumor cells. Four days later, animals were treated i.v. with L-ET-18-OCH(3) administered as TLC ELL-12 once daily for 5 consecutive days. Another group of MNU-tumor bearing rats was given a single 12.5 mg/kg dose of TLC ELL-12 containing [14C]L-ET-18-OCH(3) by i.v. injection into a tail vein. The 50% growth inhibitory concentration for TLC ELL-12 against MNU tumor cells in vitro was 63 microM (about 30 microg/ml). Tumor growth was significantly inhibited in ELL-12-treated rats versus controls. After a single dose, whole blood L-ET-18-OCH(3) concentrations declined in a multiphasic fashion with C(max) and terminal half-life values of approximately 91.1 microg L-ET-18-OCH(3)/ml and 13.1 h, respectively. Tumor L-ET-18-OCH(3) levels increased through the first 16-24 h post-dosing to about 23 microg/g and remained elevated at the terminal time point with little evidence of metabolism. Concentration-time profiles for selected tissues indicate rapid distribution of L-ET-18-OCH(3) from the circulation into tissues with highest concentrations in spleen, liver, lungs, kidneys and gastrointestinal tract. L-ET-18-OCH(3) as TLC ELL-12 shows both in vitro and in vivo activity against the MNU tumor line. When i.v. administered, L-ET-18-OCH(3) from ELL-12 is well distributed and slowly eliminated by metabolism in tissues.

Toxicity and disposition of TLC ELL-12 (liposomal antitumor ether lipid) in Sprague-Dawley rats

TLC ELL-12 is a liposomal formulation of the antineoplastic L-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine [L-ET-18-OCH3 (EL)]. The purpose of these studies was to characterize the toxicity and disposition of [N-methyl-14C] L-ET-18-OCH3 administered as TLC ELL-12. Rats received TLC ELL-12 by i.v. infusion into a tail vein as a single 12.5 or 62.5 mg/kg dose or as five daily doses at 12.5 mg/kg (cumulative dose of 62.5 mg/kg). Whole blood and tissue samples were collected over 24 h, and assayed for total and EL-specific radioactivity. The amounts of radioactivity in urine, bile, injection site and carcass were determined for up to 48 h. TLC ELL-12 was well tolerated in male and female rats in single doses up to 37.5 mg/kg. The minimum lethal dose was 112.5 mg/kg. Doses of 12.5 mg/kg (no observed adverse effects) and 62.5 mg/kg (approximate maximum tolerated dose) were chosen for further study. The pharmacokinetics of EL given as TLC ELL-12 were non-linear with a disproportionate increase in AUC at the higher dose. Daily dosing at 12.5 mg/kg did not result in accumulation in the blood. The highest concentrations of EL at 24 h after dosing were in the spleen and liver. Virtually no radioactivity was recovered in the urine or bile of rats, most remaining in the carcass and injection site (tail). After a 12.5 mg/kg dose of TLC ELL-12, the levels of EL in the blood and most tissues examined were well above the levels that inhibit tumor growth and may therefore be therapeutically active.

The influence of cholesterol and charge on the membrane domains of alkylphospholipid liposomes as studied by EPR

Alkylphospholipids are physiologically active derivatives of lipids effective in the treatment of breast cancer. Among them, octadecyl-(1,1-dimethyl-4-piperidino-4-yl)-phosphate (OPP) was demonstrated recently to have the strongest antitumor effect in micellar as well as in sterically stabilised liposome suspension with a low cholesterol content. In this work electron paramagnetic resonance (EPR) was used to study the influence of cholesterol, charge, and sterical stabilisation by PEG2000DSPE on the domain structure and fluidity characteristics of the membrane of OPP liposomes. As a spin probe 5-doxylpalmitoyl methyl ester was used. By computer simulation of the EPR spectra it was found that the experimental spectra are composed of three spectral components, which were attributed to three types of domains with different fluidity characteristics. The EPR parameters as well as the proportions of the individual domains were found to be mainly dependent on the amount of cholesterol, and only to a minor degree on charge and sterical stabilisation. There was a pronounced increase in the proportion of membrane domains with low order parameter, when the molar ratio of cholesterol to OPP was decreased below 1. At the same time the order parameters of all domains decreased, pointing to a transition from a less to a more fluid membrane organisation. These results coincide with an improved therapeutic activity of formulations with a low molar ratio of cholesterol to OPP and indicates that the fluidity characteristics of the membrane may be important for the effectiveness of liposomal alkylphospholipids against breast cancer cells.

Correlation between the effect of the anti-neoplastic ether lipid 1-O-octadecyl-2-O-methyl-glycero-3-phosphocholine on the membrane and the activity of protein kinase Calpha

The antineoplastic ether phospholipid 1-O-octadecyl-2-O-methyl-sn-glycero-3-phophocholine (ET-18-OCH3) was incorporated into dimyristoylglycerophosphocholine (Myr2Gro-PCho)/dimyristoylglycerophosphoserine (Myr2Gro-PSer) (4 : 1 molar ratio) mixtures. Electron microscopy showed that the addition of ET-18-OCH3 reduced the size of the vesicles. Small vesicles could be detected even at 60 mol% ET-18-OCH3. Sedimentation studies showed the increasing presence of phospholipids in the supernatant, while turbidity measurements indicated a decrease in absorbance as the ET-18-OCH3 concentration was increased. These findings may be explained by the formation of small vesicles and/or mixed micelles. Infrared spectroscopy showed that at 60 mol% the fluidity of the membrane was considerably increased at temperatures below the phase transition, with only a small increase in the proportion of gauche isomers after the gel-to-fluid phase transition of this sample. On the other hand, protein kinase Calpha (PKCalpha) activity progressively decreased when ET-18-OCH3 was incorporated into multilamellar vesicles, reaching a minimum value at 20 mol%, this inhibition being attributed to the modification of the membrane produced by a cone-shaped molecule. At higher concentrations, however, ET-18-OCH3 activated the enzyme with a maximum being attained at 50 mol%. This activation being attributed to the formation of small vesicles and/or micelles. At still higher concentrations of ET-18-OCH3 the enzyme was once again inhibited, inhibition being almost complete at 80 mol%. When PKC was assayed using large unilamellar vesicles a slight activation was observed at very low ET-18-OCH3 concentrations.

Polycyclic aromatic compounds as anticancer agents: structure-activity relationships of chrysene and pyrene derivatives

A large number of diamides and diamines were synthesized using 6-amino chrysene and 1-amino pyrene as starting materials. A structure activity study with cis-platinum as internal control against animal and human tumor lines was carried out in vitro. This study indicated that the in vitro cytotoxicity toward these lines depends on the functionality present in the molecules. The diamino compounds were found to be more potent than the diamides, and these were equally active irrespective of the end heterocyclic group, whereas the activity of the diamides was strongly dependent on the terminal unit. In general, the diamides containing chrysene as the chromophore were more active than those with a pyrene ring. The size of the end heterocyclic ring, along with the nature of the spacer connecting the polycyclic ring to the heterocyclic ring, seemed to affect the biological activity in certain cell lines. Hemolysis experiments on a lead compound established that it had activities similar to those described for membrane-stabilizing agents. This agent also demonstrated the capacity to produce differentiation in leukemia cell lines.

Cholesterol-induced alterations of the packing properties of gangliosides: an EPR study

The effect of cholesterol (Chol) on two kinds of glycolipid assemblies, one composed of monosialogangliosides (GM1a) and the other formed by a natural mixture of bovine brain gangliosides (TBG), has been analysed. The experimental approach involves spin label electron paramagnetic resonance (EPR) in aqueous lipid dispersions. The employment of a hydrosoluble spin label and a 'quencher' of the EPR signal that is not able to permeate lipid interfaces, allowed us to conclude that GM1a/Chol mixtures give rise to vesicles at Chol proportions for which TBG/Chol mixtures form micelles. The use of different liposoluble spin labels reveals that cholesterol produces a straightening of the hydrocarbon chains in both lipid systems. In GM1a/Chol mixtures, this feature is more pronounced and it is coupled with a decrease in polarity at the chain ends.

Liposomal ET-18-OCH3 Induces Cytochrome c-Mediated Apoptosis Independently of CD95 (APO-1/Fas) Signaling

ELL-12, a liposome formulation of the ether-lipid 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET-18-OCH3), is a nonmyelosuppressive antiproliferative agent that is more effective and less toxic than the ether lipid itself in tumor model systems. We found that ELL-12 induced apoptosis in Jurkat, H9, and U-937 cells that was preceded by activation of executioner caspases. In addition, ELL-12 triggered release of cytochrome c from mitochondria to the cytoplasm before caspase-9 activation. Apoptosis, activation of caspases, and cytochromec release were blocked by Bcl-xL overexpression in Jurkat T cells, suggesting a critical role for mitochondria in ELL-12–triggered cell death. Furthermore, ELL-12 had no effect on expression of CD95 ligand, and inhibition of the Fas signaling pathway with antagonistic anti-CD95 antibody did not affect apoptosis induced by ELL-12. Hence, ELL-12 could be a promising adjunct for the treatment of tumors in addition to myelosuppressive chemotherapeutic drugs and/or those that use the CD95-ligand/receptor system to trigger apoptosis.

Differential effects of free and liposome-associated 1-O-octadecyl-2-O-methylglycerophosphocholine on protein kinase C

Incorporation of ET-18-OCH3 into well-characterized liposomes known as ELL-12 has eliminated its gastrointestinal and hemolytic toxicity without loss of growth inhibiting activity. ET-18-OCH3, but not ELL-12, blunted the increase in membrane protein kinase C (PKC) activity induced by 12-O-tetradecanoylphorbol 13-myristate (TPA) and markedly reduced levels of PKC alpha in NIH 3T3 fibroblasts. Furthermore, prolonged treatment with ELL-12 neither inhibited TPA-induced translocations of PKC alpha and PKC delta to the particulate fraction nor caused down-regulation, and did not affect the cellular distribution of TPA-insensitive PKC zeta. In Jurkat T cells, where ELL-12 markedly induced apoptosis that was blocked by an inhibitor of caspase-3-like activities, it had no effect on PKC activity or translocation induced by TPA. Thus, it seems unlikely that PKC is involved in the therapeutic effects of ELL-12.

Stability of association of 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine with liposomes is composition dependent

The ether lipid, 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET-18-OCH3), has anticancer activity, but it has serious side-effects, including hemolysis, which prevent its optimal use. We surmised if ET-18-OCH3 could be stably associated with liposomes, less free ET-18-OCH3 would be available for lytic interaction with red cells. Liposome composition variables investigated included acyl chain saturation, phospholipid head group and mole ratio of Chol and ET-18-OCH3. It was found that attenuation of hemolysis was strongly liposome composition dependent. Some ET-18-OCH3 liposome compositions were minimally hemolytic. For example, whereas the HI5 (drug concentration required to cause 5% human red cell lysis) was 5-6 microM for free ET-18-OCH3, it was approximately 250 microM for DOPC (dioleoylphosphatidylcholine):Chol (cholesterol):DOPE-GA (glutaric acid derivatized DOPE):ET-18-OCH3, (4:3:1:2) and 640 microM for DOPE (dioleyolphosphatidylethanolamine):Chol:DOPE-GA:ET-18-OCH3 (4:3:1:2) liposomes. Efflux of carboxyfluorescein (CF) from liposomes and Langmuir trough determinations of mean molecular area of lipids in monolayers (MMAM) were used as indicators of membrane packing and stability. Incorporation of ET-18-OCH3 in liposomes reduced the MMAM. Reduction in CF permeation was correlated with reduction in hemolysis. The most stable liposomes included components, such as cholesterol, DOPC and DOPE, which have complementary shapes to ET-18-OCH3.

Growth inhibitory effects of liposome-associated 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine

The growth inhibitory effects of 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET-18-OCH3) and various liposome compositions of ET-18-OCH3 were compared in a standardized growth inhibition assay utilizing a diverse tumor cell line panel including cell lines expressing multidrug resistance. ET-18-OCH3 and ELL-12 (4:3:1:2, dioleoylphosphatidylcholine/ cholesterol/dioleoylphosphatidylethanolamine-glutaric acid/ET-18-OCH3), an optimal liposomal ET-18-OCH3 formulation, inhibited growth in the micromolar range in drug-sensitive and -resistant cells. In general, ET-18-OCH3-liposomes were about twofold less growth inhibitory than ET-18-OCH3. However, the known hemolytic effects of ET-18-OCH3 were greatly reduced, up to 20 or more times, by liposome association. The effects of ET-18-OCH3 and ELL-12 were compared in intracellular [Ca2+] modulation and DNA fragmentation assays. ET-18-OCH3 elicited both concentration- and serum-dependent transient and permanent increases in intracellular [Ca2+]. In contrast, ELL-12 did not modulate intracellular [Ca2+]. ET-18-OCH3 and ELL-12 similarly affected DNA fragmentation, which may be indicative of apoptosis. The results suggest that, although the specific growth inhibitory effects of ET-18-OCH3 and ELL-12 are similar, associating ET-18-OCH3 with stable well-characterized liposomes eliminates nonspecific cell membrane-associated lytic effects.