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Chemistry Letters 10/2012; 41. · 1.59 Impact Factor
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ABSTRACT: Treatment with docetaxel is the standard of care as first line chemotherapy in castration resistant prostate cancer. Due to serious side effects from the commercially available Taxotere formulation, we aimed to develop a safe and effective nanoparticle formulation of docetaxel. Liquid crystal nanoparticles (LCNPs), based on phosphatidyl choline, glycerol dioleate and polysorbate 80 dispersed in excess aqueous solution, were produced by simple procedures as carriers of docetaxel. Their effect on tumor growth in male SCID mice inoculated with PC-3 cells was compared to the effect of Taxotere and empty LCNP vehicle. Immunohistochemistry was performed to evaluate cell proliferation, angiogenesis and apoptosis in tumor tissue. Docetaxel and lipid excipients were dispersed into well-defined LCNP, stable during long-term storage. Mice subjected to LCNP/docetaxel formulation showed a better tumor regression than mice treated with Taxotere, with an indication of better tolerability. Immunohistochemical staining showed a decreased expression of Ki-67 in tumors from LCNP/docetaxel treated animals, especially in the cores of the tumors, suggesting better penetration/absorption compared to Taxotere. A new lipid-based nanoparticle formulation has been developed as carrier for docetaxel. Treatment effects in SCID mice indicate that this may be an interesting alternative to the current marketed formulation product.
European journal of pharmaceutical sciences: official journal of the European Federation for Pharmaceutical Sciences 10/2010; 41(2):369-75. · 2.61 Impact Factor
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ABSTRACT: Lipid-based liquid crystalline nanoparticles (LCNPs) are interesting candidates for drug delivery applications, for instance as solubilizing or encapsulating carriers for intravenous (i.v.) drugs. Here it is important that the carriers are safe and tolerable and do not have, e.g. hemolytic activity. In the present study we have studied LCNP particles of different compositions with respect to their mixing behavior and membrane destabilizing effects in model and cell membrane systems. Different types of non-lamellar LCNPs were studied including cubic phase nanoparticles (Cubosome) based on glycerol monooleate (GMO), hexagonal phase nanoparticles (Hexosome) based on diglycerol monooleate (DGMO) and glycerol dioleate (GDO), sponge phase nanoparticles based on DGMO/GDO/polysorbate 80 (P80) and non-lamellar nanoparticles based on soy phosphatidylcholine (SPC)/GDO. Importantly, the LCNPs based on the long-chain monoacyl lipid, GMO, were shown to display a very fast and complete lipid mixing with model membranes composed of multilamellar SPC liposomes as assessed by a fluorescence energy transfer (FRET) assay. The result correlated well with pronounced hemolytic properties observed when the GMO-based LCNPs were mixed with rat whole blood. In sharp contrast, LCNPs based on mixtures of the long-chain diacyl lipids, SPC and GDO, were found to be practically inert towards both hemolysis in rat whole blood as well as lipid mixing with SPC model membranes. The LCNP dispersions based on a mixture of long-chain monoacyl and diacyl lipids, DGMO/GDO, displayed an intermediate behavior compared to the GMO and SPC/GDO-based systems with respect to both hemolysis and lipid mixing. It is concluded that GMO-based LCNPs are unsuitable for parenteral drug delivery applications (e.g. i.v. administration) while the SPC/GDO-based LCNPs exhibit good properties with limited lipid mixing and hemolytic activity. The correlation between results from lipid mixing or FRET experiments and the in vitro hemolysis data indicates that FRET assays can be one useful screening tool for parenteral drug delivery systems. It is argued that the hemolytic potential is correlated with chemical activity of the monomers in the mixtures.
International journal of pharmaceutics 03/2010; 391(1-2):284-91. · 2.96 Impact Factor
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ABSTRACT: The kinetics of structure change when dispersions of two different types of lipid-based liquid-crystalline phases, one lamellar and one reversed, are mixed has been investigated using synchrotron small-angle X-ray diffraction and ellipsometry. The systems studied were (i) cubic-phase nanoparticles (CPNPs) based on glycerol monooleate (GMO) stabilized with a nonionic block copolymer, Pluronic F-127; (ii) CPNPs based on phytantriol (PtOH) stabilized with D-alpha-Tocopheryl polyethylene glycol 1000 succinate (Vitamin E TPGS); and (iii) hexagonal-phase nanoparticles (HPNPs) based on a lipid mixture of diglycerol monooleate/glycerol dioleate, stabilized by Pluronic F-127. Time-resolved small-angle X-ray diffraction was used to track structural changes within nonlamellar nanoparticles when they interact with uni- and multilamellar vesicles of dioleoylphosphatidylcholine and dipalmitoylphatidylcholine. The results are very dependent on the type of nanoparticles under investigation. For GMO-based CPNPs, a strong interaction is observed on mixing with vesicular dispersions that leads to large changes in unit size dimensions as well as a later transition from cubic to lamellar structure. These results are in good agreement with previous studies on the interaction of GMO-based CPNPs with planar bilayers using neutron reflectivity, where the diffraction peak shifted with time upon mixing. The structural changes are much less prominent for the PtOH-based CPNPs and the HPNPs upon mixing with phospholipid vesicles. These results are correlated with those from measurement studying interactions between the liquid-crystalline nanoparticles and supported phospholipid bilayers by ellipsometry. Also, here the GMO-based CPNPs show more pronounced and rapid adsorption and interaction with the supported bilayer surface than do the other types of nonlamellar nanoparticles. The interaction also depends on the bilayer properties, where significantly slower lipid mixing is observed for a bilayer in the gel state compared to a bilayer in the liquid-crystalline phase. This study is not only relevant for drug-delivery applications but also shows the potential of synchrotron small-angle X-ray diffraction in studying time-dependent structural changes as a consequence of the interaction between different lipid self-assembled aggregates in complex systems.
Langmuir 05/2009; 25(7):3999-4008. · 4.19 Impact Factor
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ABSTRACT: Somatostatin (SST) is a peptide hormone active in the regulation of the endocrine system via different somatostatin receptors subtypes. It inhibits the release of multiple secondary peptide hormones, affecting neurotransmission and cell proliferation. SST has a high therapeutic potential in the treatment of disease, such as acromegali, acute pancreatitis and gastroenteropathic endocrine tumors. However, its practical use is hampered by a short in vivo half-life of only a few minutes in man. For this reason more long-lived SST analogues, including octreotide and lanreotide, have been developed. Here we have used native SST as a model compound for a different approach of extending plasma half-lives of in vivo labile biomolecules. Through association of the peptide hormone with lipid-based liquid crystalline nanoparticle (LCNP) carriers, the terminal half-life of SST injected intravenously in rats is shown to be significantly extended from less than 10min to more than 1h. The effect on the in vivo circulation behavior depends on the mode of peptide association to the lipid particles and related physicochemical properties are discussed on the basis of in vitro light scattering, z-potential and adsorption measurements. It is concluded that application of the LCNP delivery system represents an interesting alternative to chemical modifications of in vivo sensitive therapeutically interesting peptides.
European journal of pharmaceutical sciences: official journal of the European Federation for Pharmaceutical Sciences 12/2008; 36(4-5):377-85. · 2.61 Impact Factor
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ABSTRACT: The structural/phase behaviour of self-assembled lyotropic liquid crystals formed in mixtures of a phospholipid and alpha-tocopherol (vitamin E) is presented.
Physical Chemistry Chemical Physics 12/2008; 10(43):6483-5. · 3.57 Impact Factor
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ABSTRACT: Lipid nanoparticles of nonlamellar lyotropic phases have a wide solubilizing and encapsulating spectrum for a range of substances thanks to their nanostructured interior featuring both lipophilic and hydrophilic domains. As a consequence, these systems have emerged as promising drug delivery systems in various pharmaceutical and diagnostic applications. Here we present the phase behavior and dispersion properties of a novel three-component lipid system composed of diglycerol monooleate (DGMO), glycerol dioleate (GDO), and polysorbate 80 (P80) which shows several advantageous features relating to drug delivery applications including: spontaneous dispersion formation with a narrow size distribution and tunable particle phase-structure. The obtained phase diagram shows the presence of lamellar (L(alpha)), hexagonal (H(2)), and reverse bicontinuous cubic (V(2)) liquid crystalline phases and an inverse micellar (L(2)) solution. A particularly interesting observation is the presence of a phase region where two liquid phases coexist, most likely the L(2) and L(3) ("sponge phase"). These two phase structures appear also to coexist in the submicron particles formed in the dilute water region, where the L(3) element appears to stabilize nanoparticles with inner L(2) structure. Increasing the fraction of the dispersing P80 component results in the growth of the more water rich L(3) "surface phase" at the expense of the size of the inner L(2) core.
Langmuir 08/2006; 22(14):6328-34. · 4.19 Impact Factor
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ABSTRACT: A unique set of nanoparticle dispersions of self-assembled lipid mesophases with distinctive reversed cubic, hexagonal, and sponge phase structures has been prepared by use of original lipid combinations and a simple, generally applicable and scalable method. All key properties, particle size distributions, shape, phase structure, and stability, are controlled predictably and reproducibly. The results suggest the cross-disciplinary use of nonlamellar particle structures in science and technology as, for instance, biomimetics, in vivo drug delivery vehicles for diagnostic and therapeutic agents, protein crystallization matrices, and soft nanoporous materials.
Nano Letters 09/2005; 5(8):1615-9. · 13.20 Impact Factor
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ABSTRACT: The first part of this study concerns the aqueous phase behavior of mixtures of diglycerol monooleate (DGMO) and glycerol dioleate (GDO) examined by X-ray diffraction (XRD). The ternary phase diagram displays a multitude of liquid crystalline phases (polymorphism). With increasing GDO content the following phase sequence was observed: lamellar (L(alpha)); two reversed bicontinuous cubic phases (Q(230) and Q(224)); reversed hexagonal (H(II)); the reversed micellar (L(2)) phase. The second part deals with the preparation and characterization of aqueous dispersions of the reversed hexagonal phase in the presence of the nonionic triblock copolymer Pluronic F127. Submicrometer-sized monocrystalline H(II) phase particles were obtained, as evidenced by cryo-transmission electron microscopy (cryo-TEM), laser diffraction, and XRD, by use of a simple and reproducible preparation method including a heat-treatment step. Moreover, the particle size distributions of the H(II) phase nanoparticle dispersions were narrow as determined by laser diffraction measurements. Using XRD, we show that the polymeric stabilizer is depleted from the core of the hexagonal particles and preferentially located at the surface. It is concluded that the preferential distribution of stabilizing agents at particle surfaces is a prerequisite for the formation of structurally well-defined and kinetically stable H(II) phase particles (Hexosome).
Langmuir 06/2005; 21(11):5159-65. · 4.19 Impact Factor
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ABSTRACT: Methods and compositions for producing lipid-based cubic phase nanoparticles were first discovered in the 1990s. Since then a number of studies have been presented, but little is known about how to control key properties such as particle size, morphology, and stability of cubic phase dispersions. In the present work we give examples of how these properties can be tuned by composition and processing conditions. Importantly we show that stable particle dispersions with consistent size and structure can be produced by a simple processing scheme comprising a homogenization and heat treatment step.
Langmuir 04/2005; 21(6):2569-77. · 4.19 Impact Factor
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ABSTRACT: A cubic liquid crystalline phase forming system based on the phospholipid dioleoylphosphatidylethanolamine (DOPE) which is fortified with small amounts of PEGylated (poly(ethylene) glycol) glycerol monooleate (PEG(660)-GMO) is characterized. The cubic phase formed by the DOPE/PEG(660)-GMO/water system coexists with water in the dilute part of the phase diagram and can be fragmented into colloidal size particles with retained cubic phase structure.
Journal of the American Chemical Society 03/2005; 127(4):1076-7. · 9.91 Impact Factor
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ABSTRACT: The phase behavior of dilute mixtures of dioleoylphosphatidylethanolamine (DOPE) and reduced TritonX100 (TX100(r)) has been investigated at pH 7.4 and 10. Using simple turbidity measurements and optical observations, together with cryo-transmission electron microscopy (cryo-TEM), we estimate the phase boundaries. We show that at both pH 7.4 and 10, a very large amount of surfactant is needed for the onset of micelle formation (X(TX100(r)) approximately 0.60-0.70) as well as for a complete solubilization of DOPE into mixed micelles (X(TX100(r)) > 0.94). We find that the micelles that are formed at high TX100(r) concentrations are of spherical shape. Increasing the pH from 7.4 to 10 has a comparably small effect on the transition from a lamellar (Lalpha) to a micellar (L1) phase. However, the reversed hexagonal phase (H(II)) that is present at low surfactant content at pH 7.4 is absent at pH 10. This is due to the partial negative charge of DOPE at pH 10. We determine the fraction of charged DOPE (alpha = 0.34) at pH 10 in a 150 mM NaCl buffer using zeta-potential (zeta-potential) measurements in combination with a Poisson-Boltzmann (PB) model. The intrinsic pK(a) of the primary amino group of DOPE, in a pure DOPE membrane, is estimated to 9.15 +/- 0.2.
Colloids and Surfaces B Biointerfaces 04/2004; 34(2):69-76. · 3.46 Impact Factor
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ABSTRACT: Poly(ethylene glycol) (PEG) decorated lipid bilayers are widely used in biomembrane and pharmaceutical research. The success of PEG-lipid stabilized liposomes in drug delivery is one of the key factors for the interest in these polymer/lipid systems. From a more fundamental point of view, it is essential to understand the effect of the surface grafted polymers on the physical-chemical properties of the lipid bilayer. Herein we have used cryo-transmission electron microscopy and dynamic light scattering to characterize the aggregate structure and phase behavior of mixtures of PEG-lipids and distearoylphosphatidylcholine or dipalmitoylphosphatidylcholine. The PEG-lipids contain PEG of molecular weight 2000 or 5000. We show that the transition from a dispersed lamellar phase (liposomes) to a micellar phase consisting of small spherical micelles occurs via the formation of small discoidal micelles. The onset of disk formation already takes place at low PEG-lipid concentrations (<5 mol %) and the size of the disks decreases as more PEG-lipid is added to the lipid mixture. We show that the results from cryo-transmission electron microscopy correlate well with those obtained from dynamic light scattering and that the disks are well described by an ideal disk model. Increasing the temperature, from 25 degrees C to above the gel-to-liquid crystalline phase transition temperature for the respective lipid mixtures, has a relatively small effect on the aggregate structure.
Biophysical Journal 12/2003; 85(6):3839-47. · 3.65 Impact Factor
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ABSTRACT: A sugar-based (reduced glucose) gemini surfactant forms vesicles in dilute aqueous solution near neutral pH. At lower pH, there is a vesicle-to-micelle transition within a narrow pH region (pH 6.0-5.6). The vesicles are transformed into large cylindrical micelles that in turn are transformed into small globular micelles at even lower pH. In the vesicular pH region, the vesicles are positively charged at pH < 7 and exhibit a good colloidal stability. However, close to pH 7, the vesicles become unstable and rapidly flocculate and eventually sediment out from the solution. We find that the flocculation correlates with low vesicle zeta-potentials and the behavior is thus well predicted by the classical DLVO theory of colloidal stability. Surprisingly, we find that the vesicles are easily redispersed by increasing the pH to above pH 7.5. We show that this is due to a vesicle surface charge reversal resulting in negatively charged vesicles at pH > 7.1. Adsorption, or binding, of hydroxide ions to the vesicular surface is likely the cause for the charge reversal, and a hydroxide ion binding constant is calculated using a Poisson-Boltzmann model.
Journal of the American Chemical Society 02/2003; 125(3):757-60. · 9.91 Impact Factor
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ABSTRACT: In this work we report on the characteristics of dilute mixtures of poly(ethylene glycol) derivatized lipids (PEG lipids) in aqueous solution. We show that for PEG lipids with PEG of molecular weight 750, 2000, and 5000 covalently coupled to DSPE (distearoyl phosphatidylethanolamine), spherical micelles are formed. The hydrodynamic radii and aggregation numbers of the micelles are determined as a function of temperature. The hydrodynamic thickness of the polymer layer is also determined, and the experimental values are compared with theoretically predicted values using a starlike polymer scaling model. We show a quantitative agreement between the experimental and theoretically predicted values. The phospholipid anchor carries a negative charge, and the surface potential of the micelles is estimated using a fluorescent probe titration technique. The experimental values are compared with values of the surface potential calculated using a program that solves the Poisson−Boltzmann equation numerically for the spherical geometry. A reasonable agreement between the experiments and the calculations is found. Based on the range of the electrostatic interaction, we infer that the steric repulsion caused by the overlap of the polymeric coronas dominates the intermicellar interactions. In addition to spherical micelles, we also observe some interesting aggregates in samples containing PEG(750)-DSPE which are found to be of lamellar character. For the PEG(2000) and PEG(5000) lipids no lamellar aggregates are observed, but it is found that micellar solutions of these lipids are only metastable at temperatures below approximately 60 °C.
08/2001;
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ABSTRACT: The adsorption of the triblock copolymer F127, poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide), EO98PO67EO98, onto immobilized small unilamellar vesicles (SUVs) of egg phosphatidylcholine (EPC) has been studied by means of a quartz crystal microbalance (QCM). With this technique we first show that SUVs of EPC adsorb on gold to form a monolayer of vesicles. This supported monolayer of vesicles was then used to follow the adsorption of the F127 polymer onto the lipid membrane surface. The adsorption of F127 was found to be a rapid process, and the measured polymer binding isotherm was fitted to a Freundlich type of isotherm. The maximum, or plateau, adsorbed amount was determined to be of a magnitude similar to that found for adsorption of F127 on hydrophobic surfaces. Furthermore, the desorption of the triblock copolymers from the membrane surface was followed after rinsing the SUV monolayer with pure buffer. It was found that the desorption process displayed essentially the same rapid kinetics as the adsorption process, indicating a weak interaction between the polymers and the lipid membrane. The determined polymer binding isotherm was used to correlate the adsorbed amount of polymer with the polymer-induced leakage of carboxy fluorescein (CF) from the SUVs. It was found that the membrane permeability was increased severalfold already at low surface coverage and that the maximum magnitude of the CF release rate was obtained at, or close to, F127 concentrations giving rise to the maximum adsorbed amount of polymer. In addition, the increased membrane permeability induced by the triblock copolymers was compared with the effect of adding a conventional ethylene oxide (EO) surfactant, Triton X-100, to the SUVs. The result emphasizes the dramatic effect of F127 on the bilayer permeability.
05/2001;
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ABSTRACT: The interactions between sterically stabilized (EPC/PEG-lipid) liposomes and the nonionic surfactants octyl glucoside (OG) and octa(ethylene glycol) n-dodecyl monoether (C12E8) have been studied. Cryogenic transmission electron microscopy revealed that poly(ethylene glycol)-lipids (PEG-lipids) affected the OG-mediated solubilization of the liposomes. Long-lived small bilayer disks were observed at OG concentrations saturating the bilayers. In addition, the macroscopic phase separation observed in EPC/OG systems, at OG concentrations such that the bilayers were close to being solubilized, was entirely inhibited by the inclusion of PEG-lipids in the membrane. OG was more efficient in destabilizing sterically stabilized liposomes than conventional ones, whereas for C12E8 the effective molar ratio of surfactant to lipid at bilayer saturation was essentially the same for both types of liposomes. Furthermore, the results reported illuminate the effect of PEG-lipids on, and the mechanism of, surfactant-induced growth of small unilamellar vesicles.
08/2000;
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ABSTRACT: The interactions of five poly(oxyethylene)−poly(oxypropylene)−poly(oxyethylene) (PEO−PPO−PEO), Pluronic, copolymers and phosphatidylcholine liposomes of varying composition have been studied. Structural studies were performed by means of cryo-transmission electron microscopy (c-TEM) and reveal that inclusion of low amounts (2 mol %) of Pluronics gives rise to significant morphological changes of the liposome preparations. Pluronics with large poly(oxyethylene) (PEO) blocks, such as F127, F108, and F87, induce the formation of bilayer disks, whereas those with comparably short PEO blocks, P105 and P85, tend to to promote a reduction in the liposome size. Inclusion of cholesterol in the liposomal preparations reduces the incorporation of copolymers in the lipid bilayer and thus reduces, and in some cases even abolishes, the morphological changes observed in the absence of cholesterol. The effect of the copolymers on liposome permeability was also investigated. All investigated copolymers were found to increase the leakage of carboxyfluorescein from preformed liposomes. This was true also in the case of cholesterol-containing liposomes despite the fact that no change in the liposome structure could be observed by means of c-TEM. The magnitude of the induced leakage was found to correlate well with the hydrophobicity, as measured by the cmc, of the respective Pluronic. By raising the temperature or decreasing the solvency of the copolymer in the solution, the effect of the copolymer on liposome leakage was found to increase significantly.
07/1999;
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ABSTRACT: The permeability of liposomal membranes was studied as a function of the amount of incorporated PEG-lipid. The fluorescent dyes ethidium, propidium and 5(6)-carboxy fluorescein were used as markers for measurements of spontaneous leakage. The results show that addition of up to 8 mol% of PEG(2000)-DSPE into liposomal membranes of DSPC/Cho and EPC/Cho reduces the permeability of carboxyfluorescein in buffer solution. In contrast, the leakage of the more amphiphilic dye ethidium was not to any measurable extent affected by PEG-lipid inclusion. Another important difference was that ethidum leakage showed a clear dependence on temperature whereas leakage of carboxyfluorescein from pegylated liposomes did not. We conclude that the mechanisms by which the two dyes permeate the liposomal bilayer are qualitatively different. Both ethidium and carboxyfluorescein did interact with human serum components in a way that made measurements in serum unreliable. The more hydrophilic ethidium analogue propidium was shown not to interact with human serum components to any detectable extent. This made propidium suitable for permeability determinations in human serum. It was found that liposomes composed of pure EPC or EPC with 5 mol% DSPE-PEG, displayed a dramatic increase in permeability when subjected to a medium composed of 20% human serum in buffer. Addition of 40 mol% cholesterol to the EPC bilayers reduced the observed release rate in human serum substantially, whereas no stabilizing effect was observed upon PEG-lipid inclusion.
Chemistry and Physics of Lipids 01/1999; · 2.57 Impact Factor
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ABSTRACT: Liposomes are of interest as drug delivery tools for therapy of cancer and infectious diseases. We investigated conjugation of epidermal growth factor, EGF, to liposomes using the micelle-transfer method. EGF was conjugated to the distal end of PEG-DSPE lipid molecules in a micellar solution and the EGF-PEG-DSPE lipids were then transferred to preformed liposomes, either empty or containing the DNA-binding compound, water soluble acridine, WSA. We found that the optimal transfer conditions were a 1-h incubation at 60 degrees C. The final conjugate, (125)I-EGF-liposome-WSA, contained approximately 5 mol % PEG, 10-15 EGF molecules at the liposome surface, and 10(4) to 10(5) encapsulated WSA molecules could be loaded. The conjugate was shown to have EGF-receptor-specific cellular binding in cultured human glioma cells.
Bioconjugate Chemistry 13(4):737-43. · 4.93 Impact Factor
