DNA nanotechnology as a tool to manipulate lipid bilayer membranes
Meng, Zhuojun
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Meng, Z. (2017). DNA nanotechnology as a tool to manipulate lipid bilayer membranes. University of Groningen.
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Chapter 1
Functionalization of
Lipid Bilayer Membranes
10
1. 1 Lipid bilayer membranes
Lipids play an important role in the physiology and pathophysiology of living systems why they are produced, transported, and recognized by the concerted actions of numerous enzymes, binding proteins, and receptors.1 Micelles are formed by the aggregation of single-chain lipids in a polar solvent (such as water) beyond a particular concentration, known as Critical Micelle Concentration (CMC) (Fig. 1.1A). Therefore, the micelle formation and stability are highly dependent on the lipid concentration and solvent composition (Fig. 1.1B).
Two-chain lipids can hardly be packed into micelles due to the bulky hydrophobic part. They usually form a lipid bilayer membrane, which is a thin polar sheet made of two layers of lipid molecules and is characterized by hydrophobic tails facing inwards towards each other and hydrophilic head groups facing outwards to associate with aqueous solution.2 At this moment, the hydrophobic parts of the molecules are still in contact with water, which leads to an energetically unfavorable state of the bilayer. This is overcome through folding of the bilayer membrane into a liposome with closed edges (Fig. 1.1C).3,4
11 Fig. 1.1 (A) Surface tension as a function of the surfactant concentration. Schematic structure
12
1.2 Classification and Preparation of Liposomes
Depending on the number of bilayers, liposomes can be classified into two categories: unilamellar vesicles (ULV) and multilamellar vesicles (MLV). Unilamellar vesicles can also be classified into three categories on the basis of their sizes, which can vary from nanometer to micrometer range: small unilamellar vesicles (SUV), large unilamellar vesicles (LUV) and giant unilamellar vesicles (GUV). GUVs also include other morphologies such as multilamellar vesicles (MLV), which consist of SUVs or multiple concentric bilayers (Fig. 1.2).
Fig. 1.2 Schematic structure of unilamellar and multilamellar liposomes.
There are four classical methods to prepare liposomes, differing in the way how the lipids are dried from organic solvent and then redispersed in aqueous buffer.5 These steps can be performed individually or jointly.6 These four methods are:
1. Hydration of a Thin Lipid Film.7
2. Reverse-Phase Evaporation Technique.8
3. Solvent (Ether or Ethanol) Injection Technique.9,10 4. Detergent Dialysis.11
13 Since the “Hydration of a Thin Lipid Film” method, is widespread used and easy to handle, it is explained here in more details. Firstly, the lipids are dissolved and mixed in an organic solvent to assure a homogeneous mixture. Once the lipids are thoroughly dispersed in the organic solvent, the solvent is removed using a dry nitrogen stream in a fume hood to yield a lipid film. The lipid film is dried to remove residual organic solvent by using a vacuum desiccator overnight. Afterwards, hydration of the dry lipid film is accomplished by stirring in an aqueous buffer. The temperature of the hydrating buffer should be higher than the gel-liquid crystal transition temperature (Tc) of the lipid. Subsequently, several stirring (above the Tc) and freeze-thawing cycles of the swelling multilayer sample results in MLVs. Finally, the sample is extruded multiple times using an extruder and polycarbonate membranes to obtain unilamellar vesicles (LUVs or SUVs). Fig. 1.3 shows the classical hydration method of liposome preparation.
Fig. 1.3 Schematic diagram of liposome preparation method. (Schematic obtained from www.
14
1.3 Modification and Applications of liposomes
The first discovery of liposomes in 1964 by A. D. Bangham12 was the starting point for these self-assembled containers to become a multifunctional tool in biology, biochemistry and medicine today. Because of the structure, charge, chemical composition and colloidal size can be well controlled by preparation methods, liposomes can be useful in various applications. Vesicles can also be prepared from natural substances and are therefore in many cases nontoxic, biodegradable, biocompatible, targetable and non-immunogenic.13 Due to these properties, liposomes can be used as drug14-16 protein, plasmid17 and gene18-21 delivery vehicles in medicine and diagnosis.
1.3.1 Loading and surface modification
Molecular interactions between the cargo and the lipid bilayer membrane play an important role on liposome formation and cargo encapsulation.22 Liposomes consist of an aqueous core surrounded by a lipid bilayer, sectioning off two separate inner areas. They can carry hydrophobic molecules in their hydrocarbon tail region (between the phospholipid bilayer), or hydrophilic molecules in the core and direct the cargo to the required diseased site in the body with some targeting moieties on the surface.23 The thickness of the lipid bilayer is around 4 to 10 nm, which is a natural barrier for many substances such as sugars and proteins.24 But small hydrophilic substances such as water, gases, ammonia and glycerol can penetrate freely through the bilayer.25-27 Some large hydrophilic substances can be encapsulated in the water core of the liposome during liposome preparation using the common thin layer hydration method. Cationic liposomes, which are made of positively charged lipids, appear to be better suited for DNA delivery due to the natural charge-charge interaction between the positively charged lipid head groups and the negatively charged phosphate groups of the DNA-backbone.28,29 Due to their favorable interactions with negatively charged DNA and cell membranes,30-33 cationic liposome–DNA complexes are increasingly being researched for their use in gene therapy and nucleic acid release.34,35 In order to increase liposomal drug accumulation in the desired cells and
15 tissues, the use of targeted liposomes with surface modification has been suggested.
Surface modification of liposomes with controlled propertied requires the chemical conjugation of peptides, DNA, antibodies or other targeting molecules. Moreover, some “smart” vesicle designs allow the release of the encapsulated cargo by incorporation of transport channels.36-39 Both chemical attachment and physical interactions can be used to achieve surface modification (Fig. 1.4A).
Fig. 1.4 (A) Schematic representation of liposomes surface modifications. (B) Interaction of the
particle with cell surface antigens and receptors.40 (C) Scheme of tetrac tagged liposome and
enhanced delivery by the ligand-mediated targeting strategy.41(Fig. 1.4 B was adapted from
reference 40. Fig. 1.4 C was adapted from reference 41)
To realize active targeting, the liposome surface can be coated with ligands or antibodies that will confer cell type-specificity to ensure that the liposomes are internalized and that their content is released, improving the efficacy and reducing side effects over non-targeted cells (Fig. 1.4B).40 For instance, tetraiodothyroacetic acid (tetrac), a small molecule which binds
16
to integrin αvβ3, was used for the surface modification of liposomes and successfully enhanced the tumor-targeting ability of PEGylated liposome (Fig. 1.4C).41 Although the physical properties of liposomes were not significantly changed, tetrac-tagged liposomes showed significantly higher cancer cell localization than the unmodified PEGylated liposome, and tumor growth was effectively retarded. The ligand-mediated targeting strategy could provide better therapeutic effects with more accurate delivery of nanoparticles.
1.3.1.1 Membrane fusion
Surface modification of lipid bilayers can also be used for membrane fusion which is an essential process of life resulting in the highly regulated transport of bio-molecules both between and within cells.42-44 Membrane fusion is an essential but not a spontaneous process as free energy is required to overcome the electrostatic and steric repulsions between two merging membrane surfaces and to break the hydration shell.45,46 A highly conserved protein machinery, known as SNARE proteins (soluble N-ethylmaleimide sensitive factor attachment protein receptors), facilitates the communication within a cell.47-49 The SNAREs from synaptic vesicles interact with the SNAREs from the target membrane to form a coiled-coil bundle of four helices, pulling the membranes tightly together and initiating fusion.
Design and construction of simplified artificial model systems mimicking natural systems are one of the most promising approaches for studying complex biological mechanisms.50 Several of these systems have been reported for realizing membrane fusion, such as DNA51-53, peptides54, 55, enzymes56 and polymers57. Yang et al. designed an artificial biorthogonal targeting system that was able to target liposomes and other nanoparticles efficiently to the tissue of interest by using coiled coil forming peptides, E4[(EIAALEK)4] (E4) and K4[(KIAALKE)4] (K4) (Fig. 1.5C), which are known to trigger liposomal membrane fusion when tethered to lipid vesicles in the form of lipopeptides.58 The same group proved that E4 peptide-modified liposomes could deliver far-red fluorescent dye TOPRO-3 iodide (E4-Lipo-TP3) and doxorubicin (E4-Lipo-DOX) into HeLa cells
17 expressing K4 peptide (HeLa-K) on the surface. Then, Lipo-TP3 and E4-Lipo-DOX were injected into zebrafish xenografts of HeLa-K (Fig. 1.5A, B). The results showed that E4-liposomes delivered TP3 to the implanted HeLa-K cells (Fig. 1.5D), and E4-Lipo-DOX could suppress cancer proliferation in the xenograft when compared to nontargeted conditions. These data demonstrated that coiled-coil formation enables drug selectivity and efficacy in vivo.
Fig. 1.5 Drug Delivery by E4/K4 Coiled-Coil Formation in Cells (A) and Zebrafish (B). (C)
Schematic representation of coil structure between peptides E and K. (D) E4/K4 coiled-coil formation allows delivering the content in the liposome to cancer cells in the xenograft zebrafish.58 (This figure was reproduced with permission from reference58)
1.3.1.2 Controlled release
Conventional liposomes (Fig. 1.6A) are easily recognized by the mononuclear phagocyte system and are rapidly cleared from the blood stream.59 Many methods have been suggested to achieve long circulation of liposomes in vivo by modification of the liposomal surface with hydrophilic
18
polymers to delay the elimination process, such as coating the surface of liposomes with biocompatible polymers like poly(ethylene glycol) (PEG) linked phospholipids. These can be incorporated into the liposomal bilayer to form a hydrophilic polymer shield over the liposome surface, protecting the liposome from penetration or disintegration by plasma proteins60-65 (Fig. 1.6B). While many varieties have been synthesized by using chemically modified forms of PEG, in some cases it’s necessary to make the liposomes shed their cloak of modified PEG molecules when they reach their target (Fig. 1.6C). In this way they can interact with the target and release their payload. Using imaging technologies, visual evidence of the effect of PEGylation on the circulation kinetics of the liposomes was provided (Fig. 1.6D).66 The images clearly demonstrate that PEGylation significantly enhances the persistence of liposomes in the blood stream. At the same time, the uptake of PEGylated liposomes in organs (liver and spleen) responsible for particle clearance decreased.
Fig. 1.6 Schematic representation of (A) conventional liposome, (B) PEG-liposome and (C)
chemically modified PEG-liposome. (D) The effect of PEGylation on the circulation persistence of liposomes. The liposomes were labeled with Tc-99m, administered in rats, and the rats were imaged with a gamma camera over 24 h. As is evident from the heart (H) image signal, the PEG-liposomes remained in circulation even 24 h post-injection. The accumulation in the liver (L) and the spleen (S) was also lower in the case of PEG-liposomes, as compared to the plain liposomes.66 (Fig. 1.6 D was adapted from reference66)
19 Ligands conjugated with hydrophobic molecules form amphiphiles. The hydrophobic part can insert into the liposome bilayer, exposing the ligand outside of the liposomes for being recognized or for other interactions. For instance, DNA-b-polypropyleneoxide (DNA-ppo) has proven to be stably anchored into the lipid membrane for over at least 24 h. In this way, the containers are encoded with sequence information. The DNA-ppo present on the surface was used for anchoring a photosensitizer by hybridization. Upon light irradiation the PPO was oxidized leading to cargo release (Fig. 1.7).67
Fig. 1.7 Illustration of selective cargo release from DNA block copolymer (DBC) -decorated
phospholipid vesicles. (1) DNA-ppo is stably anchored in unilamellar lipid vesicles; (2) DBC-decorated vesicles are functionalized with conjugated DNA-photosensitizers by hybridization; (3) singlet oxygen is generated by light irradiation; and (4) selective cargo release is induced by the oxidative effect of singlet oxygen.67 (This figure was reproduced with permission from
reference 67)
1.3.2 Stimuli-responsive liposomes
Liposomes can suspend cargos with their peculiar solubility properties and act as a sustained-release system for microencapsulated molecules. After modification, liposomes can be used as stimuli-responsive nanoparticles, which are visionary concepts to deliver and release a drug exactly where it is needed.68,69 There are several ways to trigger cargo release, such as light,70 temperature71,72 and magnetism.73 Often two or more triggers need
20
to be combined to appropriately improve the cargo release kinetics and distribution to reduce side effects.
1.3.2.1 Light responsive vesicle systems
Methods of sensitizing liposomes to light have progressed from the use of organic molecule moieties to the use of metallic plasmon resonant structures which can be broadly categorized as photochemical or photophysical release. Photochemical release can be achieved via photoisomerization, photocleavage and photopolymerization, which all lead to destabilization of the liposome bilayer and release of encapsulated contents (Fig. 1.8A-C).
Fig. 1.8 Release from liposomes mediated by photochemical responses: photoisomerization (A),
photocleavage (B), or photopolymerization (C); and photophysical responses: molecular absorbers (D) and gold nanoparticles (E).
21 On the other hand, photophysical release from liposomes does not rely on any chemical changes of structures within or associated with the bilayer membrane. Examples of photophysical release discussed here take advantage of photothermal conversion of absorbed light with ensuing thermal and/or mechanical processes in the lipid membrane and the surrounding medium. The methods for achieving photophysical release are developed around molecular absorbers (Fig. 1.8D) or gold nanoparticles (Fig. 1.8E).70
1.3.2.2 Temperature responsive vesicle systems
Temperature-responsive liposomes are classified into two types: traditional temperature-responsive liposomes and liposomes modified with responsive polymers. Traditional temperature-responsive liposomes which are composed of temperature-temperature-responsive lipids show the greatest permeation of the lipid membrane at its gel-to-liquid crystalline phase transition temperature.
Moreover, liposomes modified with temperature-responsive polymers exhibit a lower critical solution temperature (LCST) behavior. These polymers are soluble in an aqueous solution below this temperature but dehydrate and aggregate if heated above the LCST. This behavior induces the release of a drug within a polymer-modified liposome. For instance, a temperature-responsive polymer, poly (N-isopropylacrylamide)-co-N,N'-dimethylaminopropylacrylamide (P(NIPAAm-co-DMAPAAm)) was synthesized and used for liposome modification. This research showed that the polymer underwent dehydration and aggregation above 40 °C and that temperature-responsive polymer-modified liposomes had faster cellular uptake and release compared to non-modified liposomes (Fig. 1.9).74
22
Fig. 1.9 Liposomes modified with temperature-responsive polymers are used for cellular
uptake. The copolymer displayed a thermosensitive transition at a lower critical solution temperature (LCST) that is higher than body temperature. Above the LCST, the temperature-responsive liposomes started to aggregate and release their content. The liposomes showed a fixed aqueous layer thickness (FALT) at the surface below the LCST, and the FALT decreased with increasing temperature. Above 37°C, cytosolic release from the temperature-responsive liposomes was higher than that from the PEGylated liposomes, indicating intracellular uptake.74 (This figure was adapted from reference 74)
1.3.2.3 Magnetic responsive vesicle systems
Magnetoliposomes are composed of a lipid bilayer surrounding superparamagnetic iron oxide nanoparticles. Due to the biocompatibility, size, material-dependent physicochemical properties and potential applications as alternative contrast enhancing agents for magnetic resonance imaging, magnetoliposomes are ideal candidates to achieve a spatial and temporal control over drug release.75,76 Superparamagnetic iron oxide nanoparticles (SPION) can be guided to their site of action using an externally applied magnetic field. The subsequent accumulation of SPION in the target site can be exploited for simultaneous drug delivery, MR imaging or hyperthermia therapy of cancer (Fig. 1.10).
23 Fig. 1.10 Superparamagnetic iron oxide nanoparticles can be guided to the site of action using
an externally applied magnetic field.77 (This figure was adapted from reference 77)
In the beginning, liposomes were studied only for their physicochemical properties as models of membrane morphology. Today, they are used as delivery devices to encapsulate cosmetics, drugs, fluorescent detection reagents, and as vehicles to transport nucleic acids, peptides, and proteins to specific cellular sites in vivo. Advances in therapeutic applications of liposomes have been achieved through surface modifications. With these surface modifications, their biological stability could be increased, which includes reduced constituent exchange and leakage as well as reduced unwanted uptake by cells of the mononuclear phagocytic system.78 Targeting components such as antibodies can be attached to liposomal surfaces and were used to create large antigen-specific complexes. In this sense, liposomal derivatives are being used to target cancer cells in vivo, to enhance detectability in immunoassay systems.
24
1.4 Motivation and Thesis Overview
The overall goal of the work described in this thesis was to use DNA nanotechnology as a tool to manipulate lipid bilayer surfaces. Our group synthesized and characterized a new family of DNA amphiphiles containing modified nucleobases. The modification is introduced in uracil and consists of hydrophobic moieties. Through solid phase synthesis, the modified nucleotides can be incorporated in any desired position and several modifications per DNA strands can be introduced.79 The resulting DNA sequences still undergo specific Watson-Crick base pairing. This property combined with the amphiphilic nature of this lipid-DNA qualifies the material as appealing candidate to interact with and manipulate biological membrane structures.
In chapter 2, a powerful new approach was introduced by modifying DNA with lipid chains at four nucleobases to tightly anchor the nucleotide to the lipid membrane. This strategy allows highly stable incorporation of DNA into the liposomal bilayer, thereby limiting dissociation. Several assays were employed proving the incorporation and stable anchoring in the phospholipid bilayer. These measurements involve small vesicles and fluorescence energy transfer. These experiments allow to measure how long the DNA amphiphiles remain in the bilayer.
In chapter 3, efficient fusion of liposomes was studied using lipid-DNA introduced in the chapter before. While the orientation of DNA hybridization played a significant role in the efficacy of full fusion of DNA-grafted vesicles, the number of anchoring units was found to be a crucial factor as well. As compared to vesicles functionalized with single-anchored or double-anchored DNA, liposomes containing quadruple-anchored oligonucleotides were found to be highly fusogenic, achieving considerable full fusion of up to 29% without notable leakage. This study demonstrates the importance of the DNA-anchoring strategy in hybridization-induced vesicle fusion, as not only the structural properties of the unit itself, but also the number of anchoring units determines its favorable fusion-inducing properties. Several fluorescence assays, dynamic light scattering and cryogenic transmission electron microscopy were utilized to prove these results.
25 In chapter 4, we expand the functionality of DNA encoded vesicles significantly. It was demonstrated that strand replacement can be carried out. In this chapter it will be outlined what sequences and what DNA amphiphiles are needed to reach this goal, i.e. changing the surface functionalities of liposomes by the simple addition of oligonucleotides. Moreover, it will be detailed how such a surface modification can be amplified by a simple DNA-triggered supramolecular polymerization. In chapter 5, we investigated whether it is possible to insert the lipid-modified DNA sequences into the membrane of live zebrafish to function as artificial receptor. We demonstrate that oligonucleotides functionalized with a membrane anchor can be immobilized on a zebrafish. Protruding single-stranded DNA atop the fish was functionalized by Watson-Crick base pairing employing complementary DNA sequences. In this way, small molecules and liposomes were guided and attached to the fish surface. The anchoring process can be designed to be reversible allowing exchange of surface functionalities by simple addition of DNA sequences. To achieve this on a fish surface, the strand exchange experiments established in chapter 4 on simple vesicles as model were crucial. Finally, a DNA based amplification process was performed atop of the zebrafish enabling the multiplication of surface functionalities from a single DNA anchoring unit.
26
References
1. Fahy, E.; Subramaniam, S.; Brown, H. A.; Glass, C. K.; Merrill, A. H. Jr.; Murphy, R. C.; Raetz, C. R.; Russell, D. W.; Seyama, Y.; Shaw, W.; Shimizu, T.; Spener, F.; Van Meer, G.; Van Nieuwenhze, M. S.; White, S, H.; Witztum, J. L.; Dennis, E. A.; A comprehensive classification system for lipids. Journal of Lipid Research 2005, 46, 839-861.
2. Margineanu, D. G.; Equilibrium and non-equilibrium approaches in biomembrane thermodynamics. Archives Internationales de Physiologie et de Biochimie 1987, 95, 381-422. 3. Svetina, S.; Zeks, B.; Shape behavior of lipid vesicles as the basis of some cellular processes.
The Anatomical Record 2002, 268, 215-225.
4. Lasic, D. D.; Liposomes in Gene Delivery. 1997, March 13, by CRC Press.
5. Mozafari, M. R.; Liposomes: An Overview of Manufacturing Techniques. Cell Mol. Biol. Lett.
2005, 10, 711-719.
6. Laouini, A.; Jaafar-Maalej, C.; Limayem-Blouza, I.; Sfar, S.; Charcosset, C.; Fessi, H.; Preparation, Characterization and Applications of Liposomes: State of the Art. J. Colloid Sci.
Biotechnol. 2012, 1, 147-168.
7. Bangham, A.; Gier, J. D.; Greville, G.; OSMOTIC PROPERTIES AND WATER PERMEABILITY OF PHOSPHOLIPID LIQUID CRYSTALS. Chem. Phys. Lipids 1967, 1, 225-246.
8. Szoka, F. J.; Papahadjopoulos, D.; Procedure for preparation of liposomes with large internal aqueous space and high capture by reverse-phase evaporation. Proc. Natl. Acad. Sci.
U.S.A. 1978, 75, 4194-4198.
9. Szebeni, J.; Breuer, J. H.; Szelenyi, J. G.; Bathori, G.; Lelkes, G.; Hollan, S. R.; Oxidation and denaturation of hemoglobin encapsulated in liposomes. Biochim. Biophys. Acta 1984, 798, 60-67.
10. Batzri, S.; Korn, E. D.; Single bilayer liposomes prepared without sonication. Biochim.
Biophys. Acta 1973, 298, 1015-1019.
11. Zumbuehl, O.; Weder, H. G.; Liposomes of controllable size in the range of 40 to 180 nm by defined dialysis of lipid/detergent mixed micelles. Biochim. Biophys. Acta 1981, 640, 252-262.
12. Bangham, A. D.; Horne, R.W.; Negative staining of phospholipids and their structural modification by surface active agents as observed in the electron microscope. J Mol Biol
1964, 8, 660-668.
13. Lasic, D. D.; Applications of Liposomes. Handbook of Biological Physics 2005, chapter 10. 14. Chen, Y.; Sen, J.; Bathula, S. R.; Yang, Q.; Fittipaldi, R.; Huang, L.; molecular pharmaceutics
2009, 6, 696-705.
15. Dutta, D.; Pulsipher, A.; Luo, W.; Yousaf, M. N.; Synthetic Chemoselective Rewiring of Cell Surfaces: Generation of Three-Dimensional Tissue Structures J. Am. Chem. Soc. 2011, 133, 8704-8713.
27
16. Chen, H.; Kim, S.; Li, L.; Wang, S.; Park, K.; Cheng, J.; Release of hydrophobic molecules from polymer micelles into cell membranes revealed by Förster resonance energy transfer imaging. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 6596-6601.
17. Samad, A.; Sultana, Y.; Aqil, M.; Liposomal Drug Delivery Systems: An Update Review.
Current Drug Delivery 2007, 4, 297-305.
18. Li, S.; Huang, L.; In vivo gene transfer via intravenous administration of cationic lipid-protamine-DNA (LPD) complexes. Gene Therapy 1997, 4, 891-900.
19. Torchilin, V. P.; Levchenko, T. S.; Rammohan, R.; Volodina, N.; Sternberg, B. P.; D’Souza, G. G. M.; Cell transfection in vitro and in vivo with nontoxic TAT peptide-liposome–DNA complexes. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 1972-1977.
20. Dzau, V. J.; Mann, M. J.; Morishta, R.; Kaneda, Y.; Fusigenic viral liposome for gene therapy in cardiovascular diseases. Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 11421-11425.
21. Shi, N.; Pardridge, W. M.; Noninvasive gene targeting to the brain. Proc. Natl. Acad. Sci.
U.S.A. 2000, 97, 7567-7572.
22. Villasmil-Sánchez, S.; Rabasco, A. M.; González-Rodríguez, M. L.; Thermal and 31P-NMR
studies to elucidate sumatriptan succinate entrapment behavior in
Phosphatidylcholine/Cholesterol liposomes. Comparative 31P-NMR analysis on negatively and positively-charged liposomes. Colloids and Surfaces B: Biointerfaces 2013, 105, 14-23. 23. Mozafari, M. R.; Liposomes: an overview of manufacturing techniques. Cell Mol. Biol. Lett.
2005, 10, 711-719.
24. Gubernator, J.; Active methods of drug loading into liposomes: recent strategies for stable drug entrapment and increased in vivo activity. Expert Opin. Drug Deliv. 2011, 567-582.
25. Cohen, B. E.; Bangham, A. D.; Diffusion of small nonelectrolytes across liposome membranes. Nature 1972, 236, 173-174.
26. Cullis, P. R, Hope, M. J.; Bally, M. B.; Influence of pH gradients on the transbilayer transport of drugs, lipids, peptides and metal ions into large unilamellar vesicles. Biochim.
Biophys. Acta 1997, 1331, 187-211.
27. Lasic, D. D.; Liposomes: from physics to aplications. Biophysical Jounal 1994, 67, 1358-1362.
28. Chonn, A.; Cullis, P. R.; Devine, D. V.; THE ROLE OF SURFACE CHARGE IN THE ACTIVATION AND ALTERNATIVE PATHWAYS OF COMPLEMENT BY LIPOSOME. J Immunol
1991, 46, 4234-4241.
29. Eastman, S. J.; Siegel, C.; Tousignant, J.; Smith, A.E.; Cheng, S.H.; Scheule, R.K.; Biophysical characterization of cationic lipid: DNA complexes. Biochim. Biophys. Acta 1997, 1325, 41-62. 30. Leventis, R.; Silvius, J. R.; Interactions of mammalian cells with lipid dispersions containing novel metabolizable cationic amphiphiles. Biochim. Biophys. Acta 1990, 1023, 124-132.
31. Felgner, P. L.; Gadek, T. R.; Holm, M.; Roman, R.; Chan, H. W.; Wenz, M.; Northrop, J. P.; Ringold, G. M.; Danielson, M.; Lipofection: a highly efficient, lipid-mediated DNA-transfection procedure. Proc. Natl. Acad. Sci. U.S.A. 1987, 84, 7413-7417.
32. Templeton, N. S.; Cationic liposome-mediated gene delivery in vivo. Biosci. Rep. 2002, 22, 283-295.
28
33. Wrobel, I.; Collins, D.; Fusion of cationic liposomes with mammalian cells occurs after endocytosis. Biochim. Biophys. Acta 1995, 1235, 296-304.
34. Shim, G.; Kim, M.; Park, J. Y.; Oh, Y.; Application of cationic liposomes for delivery of nucleic acids. ASIAN JOURNAL OF PHARMACEUTICAL SCIENCES 2013, 8, 72-80.
35. Kang, S. H.; Cho, H.; Shim, G.; Lee, S.; Kim, S.; Choi, H.; Kim, C.; Oh, Y.; Cationic Liposomal Co-delivery of Small Interfering RNA and a MEK Inhibitor for Enhanced Anticancer Efficacy.
Pharm Res. 2011, 28, 3069-3078.
36. Dudia, A.; Koҫer, A.; Subramaniam, V.; Kanger, J. S.; Biofunctionalized Lipid-Polymer Hybrid Nanocontainers with Controlled Permeability. Nano Lett. 2008, 8, 1105-1110. 37. Cisse, I.; Okumus, B.; Joo, C.; Ha, T.; Fueling protein–DNA interactions inside porous nanocontainers. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 12646-12650.
38. Birkner, J. P.; Poolman, B.; Koҫer, A.; Hydrophobic gating of mechanosensitive channel of large conductance evidenced by single-subunit resolution. Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 12944-12949.
39. Louhivuori, M.; Risselada, H. J.; Giessen, van der E.; Marrink, S. J.; Release of content through mechano-sensitive gates in pressurized liposomes. Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 19856-19860.
40. Yhee, J. Y.; Lee, S.; Kim, K.; Advances in targeting strategies for nanoparticles in cancer imaging and therapy. Nanoscale 2014, 6, 13383.
41. Lee, S.; Kim, J.; Shim, G.; Kim, S.; Han, S. E.; Kim, K.; Kwon, I. C.; Choi, Y.; Kim, Y. B.; Kim, C.; Oh, Y.; Tetraiodothyroacetic acid-tagged liposomes for enhanced delivery of anticancer drug to tumor tissue via integrin receptor. J Control Release 2012, 164, 213-220.
42. Ma, M.; Bong, D.; Controlled Fusion of Synthetic Lipid Membrane Vesicles. Acc Chem Res.
2013, 46, 2988-2997.
43. Kumar, P.; Guha, S.; Diederichsen, U.; SNARE protein analog-mediated membrane fusion.
J. Pept. Sci. 2015, 21, 621-629.
44. Kong, L.; Askes, S. H. C.; Bonnet, S.; Kros, A.; Campbell, F.; Temporal Control of Membrane Fusion through Photolabile PEGylation of Liposome Membranes. Angew. Chem. Int. Ed. 2016, 55, 1396-1400.
45. Chernomordik, L. V.; Kozlov, M. M.; Protein-lipid interplay in fusion and fission of biological membranes. Annu. Rev. Biochem. 2003, 72, 175-207.
46. Cohen, F.S.; Melikyan, G. B.; The energetics of membrane fusion from binding, through hemifusion, pore formation and pore enlargement. J. Membr. Biol. 2004, 199, 1-14.
47. Weber, T.; Zemelman, B. V.; Mcnew, J. A.; Westermann, B.; Gmachl, M.; Parlati, F.; Söllner, T. H.; Rothman, J. E.; SNAREpins: minimal machinery for membrane fusion. Cell 1998, 92, 759-772.
48. Jahn, R.; Scheller, R. H.; SNAREs–engines for membrane fusion. Nat. Rev. Mol. Cell Biol.
2006, 7, 631-643.
49. Hong, W. J.; Lev, S.; Tethering the assembly of SNARE complexes. Trends Cell Biol. 2014, 24, 35-43.
50. Kumar, P.; Guha, S.; Diederichsen, U.; SNARE protein analog-mediated membrane fusion.
29
51. Stengel, G.; Zahn, R.; Höök, F.; DNA-induced programmablefusionof phospholipidvesicles.
J. Am. Chem. Soc. 2007, 129, 9584-9585.
52. Chan, Y. H. M.; van Lengerich, B.; Boxer, S. G.; Lipid-anchored DNAmediates vesicle fusion as observed by lipid content mixing. Biointerphases 2008, 3,17-21.
53. Chan, Y. H. M.; van Lengerich, B.; Boxer, S. G.; Effects of linker sequences on vesicle fusion mediated by lipid-anchored DNA oligonucleotide. Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 979-984.
54. Zheng, T.; Voskuhl, J.; Versluis, F.; Zope, H. R.; Tomatsu, I.; Marsden, H. R.; Kros, A. Controlling The Rate of Coiled Coil Driven Membrane Fusion. Chem. Commun. 2013, 49, 3649-3651.
55. Kong, L.; Askes, S. H.; Bonnet, S.; Kros, A.; Campbell, F. Temporal Control of Membrane Fusion through Photolabile PEGylation of Liposome Membranes. Angew. Chem. Int. Ed. 2016, 55, 1396-1400.
56. Mukai, M.; Sasaki, Y.; Kikuchi, J.; Fusion-Triggered Switching of Enzymatic Activity on an Artificial Cell Membrane. Sensors 2012, 12, 5966-5977.
57. Su, W.; Luo, Y.; Yan, Q.; Wu, S.; Han, K.; Zhang, Q.; Gu, Y.; Li, Y.; Photoinduced Fusion of Micro-Vesicles Self-Assembled from Azobenzene-Containing Amphiphilic Diblock Copolymers. Macromol. Rapid Commun. 2007, 28, 1251-1256.
58. Jian Yang, Yasuhito Shimada, René C. L. Olsthoorn, B. Ewa Snaar-Jagalska, Herman P. Spaink, and Alexander Kros, Application of Coiled Coil Peptides in Liposomal Anticancer Drug Delivery Using a Zebrafish Xenograft Model. ACS Nano. 2016, 10, 7428-7435.
59. Nag, O. K.; Awasthi, V.; Surface Engineering of Liposomes for Stealth Behavior.
Pharmaceutics 2013, 5, 542-569.
60. Papahadjopoulos, D.; Allen, T. M.; Gabizon, A.; Sterically stabilized liposomes-improvements in pharmacokinetics and antitumor therapeutic efficacy. Proc. Natl. Acad. Sci.
U.S.A. 1991, 88, 11460-11464.
61. Pashin, Y. V.; Bakhitova, L. M.; Bentkhen, T. I.; Antimutagenic activity of simple phenols and its dependence on the number of hydroxyl groups. Bull Exp Biol Med. 1986, 102, 1121-1123.
62. Woodle, M. C.; Lasic, D. D.; Sterically stabilized liposomes. Biochim. Biophys. Acta 1992, 1113, 171-199.
63. Woodle, M. C.; Newman, M. S.; Cohen, J. A.; Sterically stabilized liposomes: physical and biological properties. J Drug Target 1994, 2, 397-403.
64. Woodle, M. C.; Newman, M. S.; Collins, L. R.; Efficient evaluation of long circulating or stealth liposomes by studies of in vivo blood-circulation kinetics and final organ distribution in rats. Biophys J. 1990, 57, A261.
65. Çağdaş, M.; Sezer, A.D.; Bucak, S.; Liposomes as Potential Drug Carrier Systems for Drug Delivery. Application of Nanotechnology in Drug Delivery. 2014 Chapter 1.
66. Nag, O. K.; Yadav, V. R.; Hedrick, A.; Awasthi, V.; Post-modification of preformed liposomes with novel non-phospholipid poly(ethylene glycol)-conjugated hexadecylcarbam -oylmethyl hexadecanoic acid for enhanced circulation persistence in vivo. Int. J. Pharm.
30
67. Rodríguez-Pulido, A.; Kondrachuk, A. I.; Prusty, D. K.; Gao, J.; Loi, M. A.; Herrmann, A.; Light-Triggered Sequence-Specific Cargo Release from DNA Block Copolymer–Lipid Vesicles.
Angew. Chem. Int. Ed. 2013, 52, 1008-1012.
68. Chiu, H. C.; Lin, Y. W.; Huang, Y. F.; Chuang, C. K.; Chern, C. S.; Polymer Vesicles Containing Small Vesicles within Interior Aqueous Compartments and pH-Responsive Transmembrane Channels. Angew. Chem. Int. Ed. 2008, 47, 1875-1878.
69. Volodkin, D. V.; Skirtach, A. G.; Möhwald, H.; Near-IR Remote Release from Assemblies of Liposomes and Nanoparticles. Angew. Chem. Int. Ed. 2009, 48, 1807-1809.
70. Leung, S. J.; Romanowski, M.; Light-Activated Content Release from Liposomes.
Theranostics 2012, 2, 1020-1036.
71. Li, L.; Hagen, ten T. L.M.; Hossann, M.; Süss, R.; Rhoon, van G. C.; Eggermont, A. M.M.; Haemmerich, D.; Koning, G. A.; Mild hyperthermia triggered doxorubicin release from optimized stealth thermosensitive liposomes improves intratumoral drug delivery and efficacy. J Control Release 2013, 168, 142-150.
72. Tai, L.; Tsai, P.; Wang, Y.; Wang, Y.; Lo, L.; Yang, C.; Thermosensitive liposomes entrapping iron oxide nanoparticles for controllable drugrelease. Nanotechnology 2009, 20, 1-9.
73. Nappini, S.; Bombelli, F. B.; Bonini, M.; Nord, B.; Baglioni. P.; Magnetoliposomes for controlled drug release in the presence of low-frequency magnetic field. Soft Matter 2010, 6, 154-162.
74. Wang, J.; Ayano, E.; Maitani, Y.; Kanazawa, H.; Tunable Surface Properties of Temperature-Responsive Polymer-Modified Liposomes Induce Faster Cellular Uptake, ACS
Omega 2017, 2, 316-325.
75. Monnier, C. A.; Burnand, D.; Rutishauser, B. R.; Lattuada, M.; Petri-Fink, A.; Magnetoliposomes: opportunities and challenges. Eur J Nanomed. 2014, 6, 201-215. 76. Amstad, E.; Kohlbrecher, J.; Müller, E.; Schweizer, T.; Textor, M.; Reimhult, E.; Triggered Release from Liposomes through Magnetic Actuation of Iron Oxide Nanoparticle Containing Membranes. Nano Lett. 2011, 11, 1664-167.
77. Laurent, S.; Saei, A.A.; Behzadi, S.; Panahifar, A.; Mahmoudi, M.; Superparamagnetic iron oxide nanoparticles for delivery of therapeutic agents: opportunities and challenges. Expert
Opin Drug Deliv. 2014, 11, 1449-1470.
78. Woodle, M. C.; Surface-modified liposomes: assessment and characterization for increased stability and prolonged blood circulation. Chem. Phys. Lipids 1993, 64, 249-262. 79. Anaya, M.; Kwak, M.; Musser, A. J.; Müllen, K.; Herrmann, A.; Tunable Hydrophobicity in DNA Micelles: Design, Synthesis, and Characterization of a New Family of DNA Amphiphiles.
