Lipid polymorphism: the molecular basis of nonbilayer phases

Nanomaterials Boost CAR-T Therapy for Solid Tumors

T cell engineering, particularly via chimeric antigen receptor (CAR) modifications for enhancing tumor specificity, has shown efficacy in treating hematologic malignancies. The extension of CAR-T cell therapy to solid tumors, however, is impeded by several challenges: The absence of tumor-specific antigens, antigen heterogeneity, a complex immunosuppressive tumor microenvironment, and physical barriers to cell infiltration. Additionally, limitations in CAR-T cell manufacturing capacity and the high costs associated with these therapies restrict their widespread application. The integration of nanomaterials into CAR-T cell production and application offers a promising avenue to mitigate these challenges. Utilizing nanomaterials in the production of CAR-T cells can decrease product variability and lower production expenses, positively impacting the targeting and persistence of CAR-T cells in treatment and minimizing adverse effects. This review comprehensively evaluates the use of various nanomaterials in the production of CAR-T cells, genetic modification, and in vivo delivery. It discusses their underlying mechanisms and potential for clinical application, with a focus on improving specificity and safety in CAR-T cell therapy.

Biological recognition and cellular trafficking of targeted RNA-lipid nanoparticles

Lipid nanoparticles (LNPs) have unlocked the potential of ribonucleic acid (RNA) therapeutics and vaccines. Production and large-scale manufacturing methods for RNA-LNPs have been established and rapidly accelerate. Despite this, basic research on LNPs is still required, due to their high assembly complexity and fairly new development, including research on lipid organization, transfection optimization, and in vivo behavior. Understanding fundamental aspects of LNPs that is, how lipid composition and physicochemical properties affect their biodistribution, cell recognition, and transfection, could propel their clinical development and facilitate overcoming current challenges. Herein, we review recent developments in the field of LNP technology and summarize the main findings focusing on nano-bio interactions.

In vitro and in vivo evaluation of clinically-approved ionizable cationic lipids shows divergent results between mRNA transfection and vaccine efficacy

Ionizable cationic lipids (ICLs) play an essential role in the effectiveness of lipid nanoparticles (LNPs) for delivery of mRNA therapeutics and vaccines; therefore, critical evaluations of their biological performance would extend the existing knowledge in the field. In the present study, we examined the effects of the three clinically-approved ICLs, Dlin-MC3-DMA, ALC-0315 and SM-102, as well as DODAP, on the in vitro and in vivo performance of LNPs for mRNA delivery and vaccine efficacy. mRNA-LNPs containing these lipids were successfully prepared, which were all found to be very similar in their physicochemical properties and mRNA encapsulation efficiencies. Furthermore, the results of the in vitro studies indicated that these mRNA-LNPs were efficiently taken up by immortalized and primary immune cells with comparable efficiency; however, SM-102-based LNPs were superior in inducing protein expression and antigen-specific T cell proliferation. In contrast, in vivo studies revealed that LNPs containing ALC-0315 and SM-102 yielded almost identical protein expression levels in zebrafish embryos, which were significantly higher than Dlin-MC3-DMA-based LNPs. Additionally, a mouse immunization study demonstrated that a single-dose subcutaneous administration of the mRNA-LNPs resulted in a high production of intracellular cytokines by antigen-specific T cells, but no significant differences among the three clinically-approved ICLs were observed, suggesting a weak correlation between in vitro and in vivo outcomes. This study provides strong evidence that ICLs modulate the performance of mRNA-LNPs and that in vitro data does not adequately predict their behavior in vivo.

Enhanced immunogenicity induced by mRNA vaccines with various lipid nanoparticles as carriers for SARS-CoV-2 infection

mRNA vaccines have emerged as a highly promising approach for preventing cancer and infectious diseases, attributed to their superior immunogenicity, rapid development speed, and quality-controlled scale production. While homologous mRNA vaccine administration is currently the most prevalent method employed in clinical settings, heterologous administration is a promising avenue worth exploring. In this report, two types of mRNA vaccine formulations for SARS-CoV-2 infection were developed based on different lipid nanoparticle (LNP) delivery systems, and heterologous and homologous mRNA vaccinations were administered to explore the levels of immune responses comparatively. First, five novel H-series ionizable lipids were synthesized and confirmed by NMR and MS. Subsequently, six SARS-CoV-2 receptor-binding domain (RBD) mRNA-encapsulated LNP formulations were prepared using a microfluidic mixer based on H-series and MC3 lipids. These formulations exhibited spherical structures with an average diameter ranging from 90-140 nm, as characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The safety of these formulations was confirmed in vitro by the cytotoxicity assay. Moreover, transfection assay, lysosomal escape test, and western blot, and in vivo biodistribution analyses collectively demonstrated that lipids H03 and MC3 exhibited superior in vitro and in vivo delivery efficacy in comparison to other H-series lipids. Notably, H03-Fluc mRNA exhibited an approximately 2.2-fold higher in vivo bioluminescence signal intensity than MC3-Fluc mRNA. Additionally, evaluation of humoral immunity demonstrated that homologous H03-mRNA vaccination elicited an immune response that was approximately 3-fold higher than that of homologous MC3-mRNA vaccination. More significantly, the heterologous H03-mRNA/MC3-mRNA vaccination elicited an immune response that was approximately 2-3-fold higher than that of homologous H03-mRNA vaccination and 6-9-fold higher than that of homologous MC3-mRNA vaccination, without any observable adverse effects. These results suggest that heterologous mRNA vaccination is superior to homologous mRNA vaccination and may be attributed to differences in LNP carriers. Therefore, our research may inspire further exploration of different delivery systems to enhance mRNA-based therapeutics.

Recent Advances in Lipid Nanoparticles for Delivery of mRNA

Messenger RNA (mRNA), which is composed of ribonucleotides that carry genetic information and direct protein synthesis, is transcribed from a strand of DNA as a template. On this basis, mRNA technology can take advantage of the body's own translation system to express proteins with multiple functions for the treatment of various diseases. Due to the advancement of mRNA synthesis and purification, modification and sequence optimization technologies, and the emerging lipid nanomaterials and other delivery systems, mRNA therapeutic regimens are becoming clinically feasible and exhibit significant reliability in mRNA stability, translation efficiency, and controlled immunogenicity. Lipid nanoparticles (LNPs), currently the leading non-viral delivery vehicles, have made many exciting advances in clinical translation as part of the COVID-19 vaccines and therefore have the potential to accelerate the clinical translation of gene drugs. Additionally, due to their small size, biocompatibility, and biodegradability, LNPs can effectively deliver nucleic acids into cells, which is particularly important for the current mRNA regimens. Therefore, the cutting-edge LNP@mRNA regimens hold great promise for cancer vaccines, infectious disease prevention, protein replacement therapy, gene editing, and rare disease treatment. To shed more lights on LNP@mRNA, this paper mainly discusses the rational of choosing LNPs as the non-viral vectors to deliver mRNA, the general rules for mRNA optimization and LNP preparation, and the various parameters affecting the delivery efficiency of LNP@mRNA, and finally summarizes the current research status as well as the current challenges. The latest research progress of LNPs in the treatment of other diseases such as oncological, cardiovascular, and infectious diseases is also given. Finally, the future applications and perspectives for LNP@mRNA are generally introduced.

Temperature and oxidation-sensitive dioleoylphophatidylethanolamine liposome stabilized with poly(ethyleneimine)/(phenylthio)acetic acid ion pair

Temperature and oxidation-sensitive liposomes were prepared by stabilizing dioleoylphosphatidylethanolamine (DOPE) bilayers with the ion pair of poly(ethyleneimine)/(phenylthio)acetic acid (PEI/PTA). An upper critical solution temperature (UCST) behavior was observed when PEI/PTA ion pair was suspended in an aqueous solution. It was observed that the UCST increased with increasing PTA content. The ion pair was self-assembled into nanospheres owing to its amphiphilic property which was confirmed by transmission electron microscopy. The FT-IR spectroscopic spectrum showed that the ion pair formed a salt bridge between the amino group and the carboxyl group and the PTA content in the ion pair was readily oxidized by H₂O₂. Further, DOPE liposomal membranes could be stabilized with PEI/PTA ion pair. Due to the amphiphilic property, the ion pair played a role as a stabilizer for the formation of DOPE liposomes. The liposome released its payload in a temperature-responsive manner, possibly because when the temperature is raised, the ion pair loses its amphiphilic property and can be detached from the liposomal membrane. The liposome was also oxidation-responsive in terms of release, possibly because the amphiphilic property of the ion pair disappears when the PTA is oxidized.

The role of lipid components in lipid nanoparticles for vaccines and gene therapy

Lipid nanoparticles (LNPs) play an important role in mRNA vaccines against COVID-19. In addition, many preclinical and clinical studies, including the siRNA-LNP product, Onpattro®, highlight that LNPs unlock the potential of nucleic acid-based therapies and vaccines. To understand what is key to the success of LNPs, we need to understand the role of the building blocks that constitute them.

In this Review, we discuss what each lipid component adds to the LNP delivery platform in terms of size, structure, stability, apparent pK_a, nucleic acid encapsulation efficiency, cellular uptake, and endosomal escape. To explore this, we present findings from the liposome field as well as from landmark and recent articles in the LNP literature. We also discuss challenges and strategies related to in vitro/in vivo studies of LNPs based on fluorescence readouts, immunogenicity/reactogenicity, and LNP delivery beyond the liver. How these fundamental challenges are pursued, including what lipid components are added and combined, will likely determine the scope of LNP-based gene therapies and vaccines for treating various diseases.

Lipids and Lipid Derivatives for RNA Delivery

RNA-based therapeutics have shown great promise in treating a broad spectrum of diseases through various mechanisms including knockdown of pathological genes, expression of therapeutic proteins, and programmed gene editing. Due to the inherent instability and negative-charges of RNA molecules, RNA-based therapeutics can make the most use of delivery systems to overcome biological barriers and to release the RNA payload into the cytosol. Among different types of delivery systems, lipid-based RNA delivery systems, particularly lipid nanoparticles (LNPs), have been extensively studied due to their unique properties, such as simple chemical synthesis of lipid components, scalable manufacturing processes of LNPs, and wide packaging capability. LNPs represent the most widely used delivery systems for RNA-based therapeutics, as evidenced by the clinical approvals of three LNP-RNA formulations, patisiran, BNT162b2, and mRNA-1273. This review covers recent advances of lipids, lipid derivatives, and lipid-derived macromolecules used in RNA delivery over the past several decades. We focus mainly on their chemical structures, synthetic routes, characterization, formulation methods, and structure-activity relationships. We also briefly describe the current status of representative preclinical studies and clinical trials and highlight future opportunities and challenges.

Ionization and structural properties of mRNA lipid nanoparticles influence expression in intramuscular and intravascular administration

Lipid Nanoparticles (LNPs) are used to deliver siRNA and COVID-19 mRNA vaccines. The main factor known to determine their delivery efficiency is the pKa of the LNP containing an ionizable lipid. Herein, we report a method that can predict the LNP pKa from the structure of the ionizable lipid. We used theoretical, NMR, fluorescent-dye binding, and electrophoretic mobility methods to comprehensively measure protonation of both the ionizable lipid and the formulated LNP. The pKa of the ionizable lipid was 2-3 units higher than the pKa of the LNP primarily due to proton solvation energy differences between the LNP and aqueous medium. We exploited these results to explain a wide range of delivery efficiencies in vitro and in vivo for intramuscular (IM) and intravascular (IV) administration of different ionizable lipids at escalating ionizable lipid-to-mRNA ratios in the LNP. In addition, we determined that more negatively charged LNPs exhibit higher off-target systemic expression of mRNA in the liver following IM administration. This undesirable systemic off-target expression of mRNA-LNP vaccines could be minimized through appropriate design of the ionizable lipid and LNP.

Carrasco et al. report a method that can predict the lipid nanoparticles (LNP) pKa from the structure of the ionizable lipid. They investigate the delivery efficiency for intramuscular and intravascular administration and propose design principles to limit off-target systemic distribution and expression for mRNA LNP vaccines.

Characterisation of a synthetic Archeal membrane reveals a possible new adaptation route to extreme conditions

It has been proposed that adaptation to high temperature involved the synthesis of monolayer-forming ether phospholipids. Recently, a novel membrane architecture was proposed to explain the membrane stability in polyextremophiles unable to synthesize such lipids, in which apolar polyisoprenoids populate the bilayer midplane and modify its physico-chemistry, extending its stability domain. Here, we have studied the effect of the apolar polyisoprenoid squalane on a model membrane analogue using neutron diffraction, SAXS and fluorescence spectroscopy. We show that squalane resides inside the bilayer midplane, extends its stability domain, reduces its permeability to protons but increases that of water, and induces a negative curvature in the membrane, allowing the transition to novel non-lamellar phases. This membrane architecture can be transposed to early membranes and could help explain their emergence and temperature tolerance if life originated near hydrothermal vents. Transposed to the archaeal bilayer, this membrane architecture could explain the tolerance to high temperature in hyperthermophiles which grow at temperatures over 100 °C while having a membrane bilayer. The induction of a negative curvature to the membrane could also facilitate crucial cell functions that require high bending membranes.

Cytosolic delivery of nucleic acids: The case of ionizable lipid nanoparticles

Ionizable lipid nanoparticles (LNPs) are the most clinically advanced nano-delivery system for therapeutic nucleic acids. The great effort put in the development of ionizable lipids with increased in vivo potency brought LNPs from the laboratory benches to the FDA approval of patisiran in 2018 and the ongoing clinical trials for mRNA-based vaccines against SARS-CoV-2. Despite these success stories, several challenges remain in RNA delivery, including what is known as "endosomal escape." Reaching the cytosol is mandatory for unleashing the therapeutic activity of RNA molecules, as their accumulation in other intracellular compartments would simply result in efficacy loss. In LNPs, the ability of ionizable lipids to form destabilizing non-bilayer structures at acidic pH is recognized as the key for endosomal escape and RNA cytosolic delivery. This is motivating a surge in studies aiming at designing novel ionizable lipids with improved biodegradation and safety profiles. In this work, we describe the journey of RNA-loaded LNPs across multiple intracellular barriers, from the extracellular space to the cytosol. In silico molecular dynamics modeling, in vitro high-resolution microscopy analyses, and in vivo imaging data are systematically reviewed to distill out the regulating mechanisms underlying the endosomal escape of RNA. Finally, a comparison with strategies employed by enveloped viruses to deliver their genetic material into cells is also presented. The combination of a multidisciplinary analytical toolkit for endosomal escape quantification and a nature-inspired design could foster the development of future LNPs with improved cytosolic delivery of nucleic acids.

Solid-Binding Proteins: Bridging Synthesis, Assembly, and Function in Hybrid and Hierarchical Materials Fabrication

There is considerable interest in the development of hybrid organic-inorganic materials because of the potential for harvesting the unique capabilities that each system has to offer. Proteins are an especially attractive organic component owing to the high amount of chemical information encoded in their amino acid sequence, their amenability to molecular and computational (re)design, and the many structures and functions they specify. Genetic installation of solid-binding peptides (SBPs) within protein frameworks affords control over the position and orientation of adhesive and morphogenetic segments, and a path toward predictive synthesis and assembly of functional materials and devices, all while harnessing the built-in properties of the host scaffold. Here, we review the current understanding of the mechanisms through which SBPs bind to technologically relevant interfaces, with an emphasis on the variables that influence the process, and highlight the last decade of progress in the use of solid-binding proteins for hybrid and hierarchical materials synthesis.

Lipid membrane-based therapeutics and diagnostics

Success rates in drug discovery are extremely low, and the imbalance between new drugs entering clinical research and their approval is steadily widening. Among the causes of the failure of new therapeutic agents are the lack of safety and insufficient efficacy. On the other hand, timely disease diagnosis may enable an early management of the disease, generally leading to better and less costly outcomes. Several strategies have been explored to overcome the barriers for drug development and facilitate diagnosis. Using lipid membranes as platforms for drug delivery or as biosensors are promising strategies, due to their biocompatibility and unique physicochemical properties. We examine some of the lipid membrane-based strategies for drug delivery and diagnostics, including their advantages and shortcomings. Regarding synthetic lipid membrane-based strategies for drug delivery, liposomes are the archetypic example of a successful approach, already with a long period of well-succeeded clinical application. The use of lipid membrane-based structures from biological sources as drug carriers, currently under clinical evaluation, is also discussed. These biomimetic strategies can enhance the in vivo lifetime of drug and delivery system by avoiding fast clearance, consequently increasing their therapeutic window. The strategies under development using lipid membranes for diagnostic purposes are also reviewed.

Liposomal Encapsulation of Carvacrol to Obtain Active Poly (Vinyl Alcohol) Films

Lecithins of different origins and compositions were used for the liposomal encapsulation of carvacrol within the framework of the development of active films for food packaging. Liposomes were incorporated into aqueous polymeric solutions from fully (F) and partially (P) hydrolysed Poly (vinyl alcohol) (PVA) to obtain the films by casting. The particle size distribution and ζ-potential of the liposomal suspensions, as well as their stability over time, were evaluated. Liposomal stability during film formation was analysed through the carvacrol retention in the dried film and the film microstructure. Subtle variations in the size distributions of liposomes from different lecithins were observed. However, the absolute values of the ζ-potential were higher (−52, −57 mV) for soy lecithin (SL) liposomes, followed by those of soy lecithin enriched with phosphatidylcholine (SL-PC) (−43, −50 mV) and sunflower lecithin (SFL) (−33, −38 mV). No significant changes in the liposomal properties were observed during the study period. Lyotropic mesomorphism of lipid associations and carvacrol leakage occurred to differing extents during the film drying step, depending on the membrane lipid composition and surface charge. Liposomes obtained with SL-PC were the most effective at maintaining the stability of carvacrol emulsion during film formation, which led to the greatest carvacrol retention in the films, whereas SFL gave rise to the least stable system and the highest carvacrol losses. P-PVA was less sensitive to the emulsion destabilisation due to its greater bonding capacity with carvacrol. Therefore, P-PVA with carvacrol-loaded SL-PC liposomes has great potential to produce active films for food packaging applications.

Nanomaterial Delivery Systems for mRNA Vaccines

The recent success of mRNA vaccines in SARS-CoV-2 clinical trials is in part due to the development of lipid nanoparticle delivery systems that not only efficiently express the mRNA-encoded immunogen after intramuscular injection, but also play roles as adjuvants and in vaccine reactogenicity. We present an overview of mRNA delivery systems and then focus on the lipid nanoparticles used in the current SARS-CoV-2 vaccine clinical trials. The review concludes with an analysis of the determinants of the performance of lipid nanoparticles in mRNA vaccines.

Strategies for altering lipid self-assembly to trigger liposome cargo release

While liposomes have proven to be effective drug delivery nanocarriers, their therapeutic attributes could be improved through the development of clinically viable triggered release strategies in which encapsulated drug contents could be selectively released at the sites of diseased cells. As such, a significant amount of research has been reported involving the development of stimuli-responsive liposomes and a broad range of strategies have been explored for driving content release. These have included the introduction of trigger groups at either the lipid headgroup or within the acyl chains that alter lipid self-assembly properties of known lipids as well as the rational design of lipid analogs programed to undergo conformational changes induced by events such as binding interactions. This review article describes advances in the design of stimuli-responsive liposome strategies with an eye towards emerging trends in the field.

NMR structural studies and mechanism of action of Lactophoricin analogs as antimicrobial peptides

Antimicrobial peptides (AMPs) are effective alternatives to conventional antibiotics. They protect the host from the constant invasion of a broad range of infectious microorganisms. AMPs have been at the forefront of the response to multidrug-resistant microbial strains and appear to be ideal drug candidates. Lactophoricin (LPcin), naturally produced from bovine milk, is a typical cationic antimicrobial peptide. Three analog peptides, including LPcin-YK5, LPcin-YK8, and LPcin-YK11, with enhanced antimicrobial activity compared to the wild-type LPcin, were designed and expressed in our laboratory. We investigated the structure and antimicrobial mechanisms of action of the three novel antimicrobial peptide analogs derived from LPcin using solution NMR and solid-state NMR spectroscopy in membrane environments. Our results revealed that the three LPcin analogs exhibited helical structures with different tilt angles on the phospholipid membrane surface. We proposed three-dimensional conformations and antibacterial mechanisms of action of the three peptide analogs in the phospholipid bilayers using two-dimensional solid-state separated local field NMR experiments.

Membrane Lipids Assist Catalysis by CTP: Phosphocholine Cytidylyltransferase

While most of the articles in this issue review the workings of integral membrane enzymes, in this review, we describe the catalytic mechanism of an enzyme that contains a soluble catalytic domain but appears to catalyze its reaction on the membrane surface, anchored and assisted by a separate regulatory amphipathic helical domain and inter-domain linker. Membrane partitioning of CTP: phosphocholine cytidylyltransferase (CCT), a key regulatory enzyme of phosphatidylcholine metabolism, is regulated chiefly by changes in membrane phospholipid composition, and boosts the enzyme's catalytic efficiency >200-fold. Catalytic enhancement by membrane binding involves the displacement of an auto-inhibitory helix from the active site entrance-way and promotion of a new conformational ensemble for the inter-domain, allosteric linker that has an active role in the catalytic cycle. We describe the evidence for close contact between membrane lipid, a compact allosteric linker, and the CCT active site, and discuss potential ways that this interaction enhances catalysis.

Lipid nanoparticle technology for therapeutic gene regulation in the liver

Hereditary genetic disorders, cancer, and infectious diseases of the liver affect millions of people around the globe and are a major public health burden. Most contemporary treatments offer limited relief as they generally aim to alleviate disease symptoms. Targeting the root cause of diseases originating in the liver by regulating malfunctioning genes with nucleic acid-based drugs holds great promise as a therapeutic approach. However, employing nucleic acid therapeutics in vivo is challenging due to their unfavorable characteristics. Lipid nanoparticle (LNP) delivery technology is a revolutionary development that has enabled clinical translation of gene therapies. LNPs can deliver siRNA, mRNA, DNA, or gene-editing complexes, providing opportunities to treat hepatic diseases by silencing pathogenic genes, expressing therapeutic proteins, or correcting genetic defects. Here we discuss the state-of-the-art LNP technology for hepatic gene therapy including formulation design parameters, production methods, preclinical development and clinical translation.

Concepts and Methods of Solid-State NMR Spectroscopy Applied to Biomembranes

Concepts of solid-state NMR spectroscopy and applications to fluid membranes are reviewed in this paper. Membrane lipids with ²H-labeled acyl chains or polar head groups are studied using ²H NMR to yield knowledge of their atomistic structures in relation to equilibrium properties. This review demonstrates the principles and applications of solid-state NMR by unifying dipolar and quadrupolar interactions and highlights the unique features offered by solid-state ²H NMR with experimental illustrations. For randomly oriented multilamellar lipids or aligned membranes, solid-state ²H NMR enables direct measurement of residual quadrupolar couplings (RQCs) due to individual C-²H-labeled segments. The distribution of RQC values gives nearly complete profiles of the segmental order parameters S_CD⁽ⁱ⁾ as a function of acyl segment position (i). Alternatively, one can measure residual dipolar couplings (RDCs) for natural abundance lipid samples to obtain segmental S_CH order parameters. A theoretical mean-torque model provides acyl-packing profiles representing the cumulative chain extension along the normal to the aqueous interface. Equilibrium structural properties of fluid bilayers and various thermodynamic quantities can then be calculated, which describe the interactions with cholesterol, detergents, peptides, and integral membrane proteins and formation of lipid rafts. One can also obtain direct information for membrane-bound peptides or proteins by measuring RDCs using magic-angle spinning (MAS) in combination with dipolar recoupling methods. Solid-state NMR methods have been extensively applied to characterize model membranes and membrane-bound peptides and proteins, giving unique information on their conformations, orientations, and interactions in the natural liquid-crystalline state.

Super-Resolution Microscopy: Shedding Light on the Cellular Plasma Membrane

Lipids and the membranes they form are fundamental building blocks of cellular life, and their geometry and chemical properties distinguish membranes from other cellular environments. Collective processes occurring within membranes strongly impact cellular behavior and biochemistry, and understanding these processes presents unique challenges due to the often complex and myriad interactions between membrane components. Super-resolution microscopy offers a significant gain in resolution over traditional optical microscopy, enabling the localization of individual molecules even in densely labeled samples and in cellular and tissue environments. These microscopy techniques have been used to examine the organization and dynamics of plasma membrane components, providing insight into the fundamental interactions that determine membrane functions. Here, we broadly introduce the structure and organization of the mammalian plasma membrane and review recent applications of super-resolution microscopy to the study of membranes. We then highlight some inherent challenges faced when using super-resolution microscopy to study membranes, and we discuss recent technical advancements that promise further improvements to super-resolution microscopy and its application to the plasma membrane.

CHARMM-GUI 10 years for biomolecular modeling and simulation

CHARMM-GUI, http://www.charmm-gui.org, is a web-based graphical user interface that prepares complex biomolecular systems for molecular simulations. CHARMM-GUI creates input files for a number of programs including CHARMM, NAMD, GROMACS, AMBER, GENESIS, LAMMPS, Desmond, OpenMM, and CHARMM/OpenMM. Since its original development in 2006, CHARMM-GUI has been widely adopted for various purposes and now contains a number of different modules designed to set up a broad range of simulations: (1) PDB Reader & Manipulator, Glycan Reader, and Ligand Reader & Modeler for reading and modifying molecules; (2) Quick MD Simulator, Membrane Builder, Nanodisc Builder, HMMM Builder, Monolayer Builder, Micelle Builder, and Hex Phase Builder for building all-atom simulation systems in various environments; (3) PACE CG Builder and Martini Maker for building coarse-grained simulation systems; (4) DEER Facilitator and MDFF/xMDFF Utilizer for experimentally guided simulations; (5) Implicit Solvent Modeler, PBEQ-Solver, and GCMC/BD Ion Simulator for implicit solvent related calculations; (6) Ligand Binder for ligand solvation and binding free energy simulations; and (7) Drude Prepper for preparation of simulations with the CHARMM Drude polarizable force field. Recently, new modules have been integrated into CHARMM-GUI, such as Glycolipid Modeler for generation of various glycolipid structures, and LPS Modeler for generation of lipopolysaccharide structures from various Gram-negative bacteria. These new features together with existing modules are expected to facilitate advanced molecular modeling and simulation thereby leading to an improved understanding of the structure and dynamics of complex biomolecular systems. Here, we briefly review these capabilities and discuss potential future directions in the CHARMM-GUI development project. © 2016 Wiley Periodicals, Inc.

Adaptations of archaeal and bacterial membranes to variations in temperature, pH and pressure

The cytoplasmic membrane of a prokaryotic cell consists of a lipid bilayer or a monolayer that shields the cellular content from the environment. In addition, the membrane contains proteins that are responsible for transport of proteins and metabolites as well as for signalling and energy transduction. Maintenance of the functionality of the membrane during changing environmental conditions relies on the cell's potential to rapidly adjust the lipid composition of its membrane. Despite the fundamental chemical differences between bacterial ester lipids and archaeal ether lipids, both types are functional under a wide range of environmental conditions. We here provide an overview of archaeal and bacterial strategies of changing the lipid compositions of their membranes. Some molecular adjustments are unique for archaea or bacteria, whereas others are shared between the two domains. Strikingly, shared adjustments were predominantly observed near the growth boundaries of bacteria. Here, we demonstrate that the presence of membrane spanning ether-lipids and methyl branches shows a striking relationship with the growth boundaries of archaea and bacteria.

Liposomal adjuvants for human vaccines

INTRODUCTION

Liposomes are well-known as drug carriers, and are now critical components of two of six types of adjuvants present in licensed vaccines. The liposomal vaccine adjuvant field has long been dynamic and innovative, and research in this area is further examined as new commercial products appear in parallel with new vaccines. In an arena where successful products exist the potential for new types of vaccines with liposomal adjuvants, and alternative liposomal adjuvants that could emerge for new types of vaccines, are discussed.

AREAS COVERED

Major areas include: virosomes, constructed from phospholipids and proteins from influenza virus particles; liposomes containing natural and synthetic neutral or anionic phospholipids, cholesterol, natural or synthetic monophosphoryl lipid A, and QS21 saponin; non-phospholipid cationic liposomes; and combinations and mixtures of liposomes and immunostimulating ingredients as adjuvants for experimental vaccines.

EXPERT OPINION

Liposomes containing monophosphoryl lipid A and QS21 have considerable momentum that will result soon in emergence of prophylactic vaccines to malaria and shingles, and possible novel cancer vaccines. The licensed virosome vaccines to influenza and hepatitis A will be replaced with virosome vaccines to other infectious diseases. Alternative liposomal formulations are likely to emerge for difficult diseases such as tuberculosis or HIV-1 infection.

Structural Diversity of Arthropod Biophotonic Nanostructures Spans Amphiphilic Phase-Space

Many organisms, especially arthropods, produce vivid interference colors using diverse mesoscopic (100-350 nm) integumentary biophotonic nanostructures that are increasingly being investigated for technological applications. Despite a century of interest, precise structural knowledge of many biophotonic nanostructures and the mechanisms controlling their development remain tentative, when such knowledge can open novel biomimetic routes to facilely self-assemble tunable, multifunctional materials. Here, we use synchrotron small-angle X-ray scattering and electron microscopy to characterize the photonic nanostructure of 140 integumentary scales and setae from ∼127 species of terrestrial arthropods in 85 genera from 5 orders. We report a rich nanostructural diversity, including triply periodic bicontinuous networks, close-packed spheres, inverse columnar, perforated lamellar, and disordered spongelike morphologies, commonly observed as stable phases of amphiphilic surfactants, block copolymer, and lyotropic lipid-water systems. Diverse arthropod lineages appear to have independently evolved to utilize the self-assembly of infolding lipid-bilayer membranes to develop biophotonic nanostructures that span the phase-space of amphiphilic morphologies, but at optical length scales.

Isolation of mitochondria with cubic membrane morphology reveals specific ionic requirements for the preservation of membrane structure

Biological membranes with cubic symmetry are a hallmark of virus-infected or diseased cells. The mechanisms of formation and specific cellular functions of cubic membranes, however, are unclear. The best-documented cubic membrane formation occurs in the free-living giant amoeba Chaos carolinense. In that system, mitochondrial inner membranes undergo a reversible structural change from tubular to cubic membrane organization upon starvation of the organism. As a prerequisite to further analyze the structural and functional features of cubic membranes, we adapted protocols for the isolation of mitochondria from starved amoeba and have identified buffer conditions that preserve cubic membrane morphology in vitro. The requirement for high concentration of ion-chelating agents in the isolation media supports the importance of a balanced ion milieu in establishing and maintaining cubic membranes in vivo.

Ursolic acid incorporation does not prevent the formation of a non-lamellar phase in pH-sensitive and long-circulating liposomes

Ursolic acid (UA) is a triterpene found in different plant species that has been shown to possess significant antitumor activity. However, UA presents a low water solubility, which limits its biological applications. In this context, our research group has proposed the incorporation of UA in long-circulating and pH-sensitive liposomes (SpHL-UA).These liposomes, composed of dioleylphosphatidylethanolamine (DOPE), cholesteryl hemisuccinate (CHEMS), and distearoylphosphatidylethanolamine-polyethylene glycol2000 (DSPE-PEG2000), were shown to be very promising carriers for UA. Considering that the release of UA from SpHL-UA and its antitumor activity depend upon the occurrence of the lamellar to non-lamellar phase transition of DOPE, in the present work, the interactions of UA with the components of the liposomes were evaluated, aiming to clarify their role in the structural organization of DOPE. The study was carried out by differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) under low hydration conditions. DSC studies revealed that DOPE phase transition temperatures did not shift significantly upon UA addition. On the other hand, in SAXS studies, a different pattern of DOPE phase organization was observed in the presence of UA, with the occurrence of the cubic phase Im3m at 20 °C and the cubic phase Pn3m at 60 °C. These findings suggest that UA interacts with the lipids and changes their self-assembly. However, these interactions between the lipids and UA were unable to eliminate the lamellar to non-lamellar phase transition, which is essential for the cytoplasmic delivery of UA molecules from SpHL-UA.

Role of lipid polymorphism in acoustically sensitive liposomes

Ultrasound (US) triggered drug release is a promising drug delivery method that allows ex vivo modulation of treatment intensity and duration. This method relies on the synergistic interaction between the rupture of sonosensitive particles and enhanced plasma membrane permeability. Conventional liposomal systems where the drug passively diffuses through the membrane show virtually no response to acoustic energy. One method to activate drug transport is to induce a topological restructuring of the lipid membrane (zero intrinsic curvature, H = 0) by puncturing pores (H < 0) through which the drug can readily leak out from the interior of the liposomes. In this work we demonstrate strategies to lower the energy cost of creating such membrane defects by introducing lipid molecules with molecular shapes prone to self-assemble into non-lamellar (negative intrinsic curvature, H < 0) structures. All formulations investigated comprise the relevant components typically required for delivery applications such as stealth moieties, cholesterol, and phospholipids. Small angle X-ray scattering studies of a number of lipid systems at increasing amounts of phosphatidylethanolamine (PE) phospholipids reveal that membranes without PE respond to ultrasound by thinning ca. 10 Å, which concomitantly lowers the bending rigidity quadratically in addition to increasing the passive drug permeability. However, at the appropriate PE content the lipid systems display a classic lamellar structure (H = 0) that undergoes a topological transformation after ultrasound exposure into lipid tubes of the reversed type (H < 0) packed in a 2D hexagonal array. At the dilute regime, Fluorescence Microscopy of giant unilamellar vesicles (GUVs) comprising DOPE also experience ultrasound induced restructuring that can be modulated by DOPE content. In general, smaller vesicles of diverse shape connect and form into a "pearl-necklace" configuration. We argue that the inclusion of DOPE within the GUV membrane may result in curvature-driven lipid sorting, providing the system with local membrane instabilities that drive vesicle pearling when exposed to ultrasound.

Membrane-forming lipids of wild halophytes growing under the conditions of Prieltonie of South Russia

The composition of membrane-forming lipids has been examined for 10 wild halophyte species growing in southern Russian on alkaline soil. The plants belong to seven taxa of family rank: by their life form, which are semi-shrubs, herbaceous annuals, and perennial plants; their salt tolerance, which are classified as the euhalophytes, crynohalophytes, and glycohalophytes; and by their sensitivity to water, classifications of mesoxerophytes and xeromesophytes. Parallels have been found between the lipid composition and the ecological status of the plants. It has also been revealed that the similarity in the glyco- and phospholipid composition of different plant groups relates to the water factor and the type of salt accumulation, respectively. The fatty acid compositions of the examined plants is determined at the species level.

Biophysics of cell membrane lipids in cancer drug resistance: Implications for drug transport and drug delivery with nanoparticles

In this review, we focus on the biophysics of cell membrane lipids, particularly when cancers develop acquired drug resistance, and how biophysical changes in resistant cell membrane influence drug transport and nanoparticle-mediated drug delivery. Recent advances in membrane lipid research show the varied roles of lipids in regulating membrane P-glycoprotein function, membrane trafficking, apoptotic pathways, drug transport, and endocytic functions, particularly endocytosis, the primary mechanism of cellular uptake of nanoparticle-based drug delivery systems. Since acquired drug resistance alters lipid biosynthesis, understanding the role of lipids in cell membrane biophysics and its effect on drug transport is critical for developing effective therapeutic and drug delivery approaches to overcome drug resistance. Here we discuss novel strategies for (a) modulating the biophysical properties of membrane lipids of resistant cells to facilitate drug transport and regain endocytic function and (b) developing effective nanoparticles based on their biophysical interactions with membrane lipids to enhance drug delivery and overcome drug resistance.

Design and evaluation of new pH-sensitive amphiphilic cationic lipids for siRNA delivery

Synthetic small interfering RNA (siRNA) has become the basis of a new generation of gene-silencing cancer therapeutics. However, successful implementation of this novel therapy relies on the ability to effectively deliver siRNA into target cells and to prevent degradation of siRNA in lysosomes after endocytosis. In this study, our goal was to design and optimize new amphiphilic cationic lipid carriers that exhibit selective pH-sensitive endosomal membrane disruptive capabilities to allow for the efficient release of their siRNA payload into the cytosol. The pH sensitive siRNA carriers consist of three domains (cationic head, hydrophobic tail, amino acid-based linker). A library of eight lipid carriers were synthesized using solid phase chemistry, and then studied to determine the role of (1) the number of protonable amines and overall pKa of the cationic head group, (2) the degree of unsaturation of the hydrophobic tail, and (3) the presence of histidine residues in the amino acid linker for transfection and silencing efficacy. In vitro screening evaluation of the new carriers demonstrated at least 80% knockdown of a GFP reporter in CHO cells after 72h. The carriers ECO and ECLn performed the best in a luciferase knockdown study in HT29 human colon cancer cells, which were found to be more difficult to transfect. They significantly reduced expression of this reporter to 22.7±3.31% and 23.5±5.11% after 72h post-transfection, better than Lipofectamine RNAiMax. Both ECO and ECLn carriers caused minimal cytotoxicity, preserving relative cell viabilities at 87.3±2.72% and 88.9±6.84%, respectively. A series of hemolysis assays at various pHs revealed that increasing the number of amines in the protonable head group, and removing the histidine residue from the linker, both resulted in improved membrane disruptive activity at the endosomal pH of 6.5. Meanwhile, the cellular uptake into HT29 cancer cells was improved, not only by increasing the amines of the head group, but also by increasing the degree of unsaturation in the lipid tails. Due to flexibility of the synthetic procedure, the delivery system could be modified further for different applications. The success of ECO and ECLn for in vitro siRNA delivery potentially makes them promising candidates for future in vivo studies.

Lipid nature and their influence on opening of redox-active liposomes

The pathway for content release from reduction-sensitive liposomes based on a quinone-dioleoylphosphatidylethanolamine lipid conjugate (Q-DOPE) is outlined using results from fluorescent dye content release assays as well as single- and multiple-angle light scattering. Experimental observations are consistent with a shape/size change of the reduced liposomes prior to their aggregation, with subsequent near-quantitative content release achieved only when the lipid membrane experiences conditions favorable to a lamellar to an inverted hexagonal phase transition. Addition of poly(ethyleneglycol)-modified DOPE (PEG-DOPE) to the Q-DOPE liposomal formulation results in stabilization of the lipid bilayer, whereas incorporation of DOPE yields faster content release. At high DOPE concentrations, DOPE/PEG-DOPE/Q-DOPE liposomes exhibit larger content release, indicating a change in pathway for content release. The outcomes here provide a better understanding of the underlying principles of triggered liposomal content release and the potential utility of specific lipid properties for the rational design of drug delivery systems based on the novel Q-DOPE lipid.

Lipid crystallization: from self-assembly to hierarchical and biological ordering

Lipid crystallization is ubiquitous in nature, observed in biological structures as well as in commercial products and applications. In a dehydrated state most of the lipids form well ordered crystals, whereas in an aqueous environment they self-assemble into various crystalline, liquid crystalline or sometimes macroscopically disordered phases. Lipid self-organization extends further to hierarchical levels including structured emulsions and nanostructured particles. Many consumer products including cosmetics, foods and medicines account for such lipid architectures. Cell membranes primarily consist of planar lipid bilayers; however sub-cellular biomembranes are more of a convoluted type. Some of the biological entities have lipids in truly crystalline form; yet liquid crystalline lipid phases are prevalent, in general. Crystallization of fats - triglyceride lipids - has been relatively well documented and reviewed more often, but this review features other areas where lipid organization is crucial and diverse. Some recent advances along with a few explicit examples of model lipid phases and biological evidences are also reported.

Constant pressure-controlled extrusion method for the preparation of Nano-sized lipid vesicles

Liposomes are artificially prepared vesicles consisting of natural and synthetic phospholipids that are widely used as a cell membrane mimicking platform to study protein-protein and protein-lipid interactions, monitor drug delivery, and encapsulation. Phospholipids naturally create curved lipid bilayers, distinguishing itself from a micelle. Liposomes are traditionally classified by size and number of bilayers, i.e. large unilamellar vesicles (LUVs), small unilamellar vesicles (SUVs) and multilamellar vesicles (MLVs). In particular, the preparation of homogeneous liposomes of various sizes is important for studying membrane curvature that plays a vital role in cell signaling, endo- and exocytosis, membrane fusion, and protein trafficking. Several groups analyze how proteins are used to modulate processes that involve membrane curvature and thus prepare liposomes of diameters <100 - 400 nm to study their behavior on cell functions. Others focus on liposome-drug encapsulation, studying liposomes as vehicles to carry and deliver a drug of interest. Drug encapsulation can be achieved as reported during liposome formation. Our extrusion step should not affect the encapsulated drug for two reasons, i.e. (1) drug encapsulation should be achieved prior to this step and liposomes should retain their natural biophysical stability, securely carrying the drug in the aqueous core. These research goals further suggest the need for an optimized method to design stable sub-micron lipid vesicles. Nonetheless, the current liposome preparation technologies (sonication, freeze-and-thaw, sedimentation) do not allow preparation of liposomes with highly curved surface (i.e. diameter <100 nm) with high consistency and efficiency, which limits the biophysical studies of an emerging field of membrane curvature sensing. Herein, we present a robust preparation method for a variety of biologically relevant liposomes. Manual extrusion using gas-tight syringes and polycarbonate membranes, is a common practice but heterogeneity is often observed when using pore sizes <100 nm due to due to variability of manual pressure applied. We employed a constant pressure-controlled extrusion apparatus to prepare synthetic liposomes whose diameters range between 30 and 400 nm. Dynamic light scattering (DLS), electron microscopy and nanoparticle tracking analysis (NTA) were used to quantify the liposome sizes as described in our protocol, with commercial polystyrene (PS) beads used as a calibration standard. A near linear correlation was observed between the employed pore sizes and the experimentally determined liposomes, indicating high fidelity of our pressure-controlled liposome preparation method. Further, we have shown that this lipid vesicle preparation method is generally applicable, independent of various liposome sizes. Lastly, we have also demonstrated in a time course study that these prepared liposomes were stable for up to 16 hours. A representative nano-sized liposome preparation protocol is demonstrated below.

In vivo delivery of RNAi with lipid-based nanoparticles

RNA interference (RNAi) technology represents a fundamentally new category of treatments for human disease by addressing targets that are traditionally considered undruggable with existing medicines. The major challenge for RNAi-based therapy is the delivery system that meets human therapeutic needs. Therefore, engineering vectors with good delivery efficiency and safety profile is an intense area of research. Lipid-based nanoparticles for RNAi have yielded successful advances in vivo and to an extent in clinical trials. In this review, we discuss the barriers in developing lipid-based nanoparticles for in vivo RNAi and different strategies to overcome them. Rational designs that address safety concerns and ensure effective delivery will aid the translation of engineered lipid-based nanoparticles toward the clinic in the foreseeable future.

Aggregation behavior of aqueous dioctadecyldimethylammonium bromide/monoolein mixtures: a multitechnique investigation on the influence of composition and temperature

A recently described non-viral gene delivery system [dioctadecyldimethylammonium bromide (DODAB)/monoolein (MO)] has been studied in detail to improve knowledge on the interactions between lamellar (DODAB) and non-lamellar-forming (MO) lipids, as a means to enhance their final cell transfection efficiency. Indeed, the morphology, fluidity, and size of these cationic surfactant/neutral lipid mixtures play an important role in the ability of these systems to complex nucleic acids. The different techniques used in this work, namely dynamic light scattering (DLS), fluorescence spectroscopy, differential scanning calorimetry (DSC), cryogenic transmission electron microscopy (cryo-TEM), light microscopy (LM), and surface pressure-area isotherms, allowed fully characterization of the phase behavior and aggregate morphology of DODAB/MO mixtures at different molar ratios. Overall, the results indicate that the final morphology of DODAB/MO aggregates depends on the balance between the tendency of DODAB to form zero-curvature bilayer structures and the propensity of MO to form non-bilayer structures with negative curvature. These results also show that in the MO-rich region, an increase in temperature has a similar effect on aggregate morphology as an increase in MO concentration.

Real-time imaging of lipid domains and distinct coexisting membrane protein clusters

A detailed understanding of biomembrane architecture is still a challenging task. Many in vitro studies have shown lipid domains but much less information is known about the lateral organization of membrane proteins because their hydrophobic nature limits the use of many experimental methods. We examined lipid domain formation in biomimetic Escherichia coli membranes composed of phosphatidylethanolamine and phosphatidylglycerol in the absence and presence of 1% and 5% (mol/mol) membrane multidrug resistance protein, EmrE. Monolayer isotherms demonstrated protein insertion into the lipid monolayer. Subsequently, Brewster angle microscopy was applied to image domains in lipid matrices and lipid-protein mixtures. The images showed a concentration dependent impact of the protein on lipid domain size and shape and more interestingly distinct coexisting protein clusters. Whereas lipid domains varied in size (14-47μm), protein clusters exhibited a narrow size distribution (2.6-4.8μm) suggesting a non-random process of cluster formation. A 3-D display clearly indicates that these proteins clusters protrude from the membrane plane. These data demonstrate distinct co-existing lipid domains and membrane protein clusters as the monofilm is being compressed and illustrate the significant mutual impact of lipid-protein interactions on lateral membrane architecture.

Effect of lipid molecule headgroup mismatch on non steroidal anti-inflammatory drugs induced membrane fusion

Membrane fusion is an essential process guiding many important biological events, which most commonly requires the aid of proteins and peptides as fusogenic agents. Small drug induced fusion at low drug concentration is a rare event. Only three drugs, namely, meloxicam (Mx), piroxicam (Px), and tenoxicam (Tx), belonging to the oxicam group of non steroidal anti-inflammatory drugs (NSAIDs) have been shown by us to induce membrane fusion successfully at low drug concentration. A better elucidation of the mechanism and the effect of different parameters in modulating the fusion process will allow the use of these common drugs to induce and control membrane fusion in various biochemical processes. In this study, we monitor the effect of lipid headgroup size mismatch in the bilayer on oxicam NSAIDs induced membrane fusion, by introducing dimyristoylphosphatidylethanolamine (DMPE) in dimyristoylphosphatidylcholine (DMPC) small unilamellar vesicles (SUVs). Such headgroup mismatch affects various lipid parameters which includes inhibition of trans-bilayer motion, domain formation, decrease in curvature, etc. Changes in various lipidic parameters introduce defects in the membrane bilayer and thereby modulate membrane fusion. SUVs formed by DMPC with increasing DMPE content (10, 20, and 30 mol %) were used as simple model membranes. Transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) were used to characterize the DMPC-DMPE mixed vesicles. Fluorescence assays were used to probe the time dependence of lipid mixing, content mixing, and leakage and also used to determine the partitioning of the drugs in the membrane bilayer. How the inhibition of trans-bilayer motion, heterogeneous distribution of lipids, decrease in vesicle curvature, etc., arising due to headgroup mismatch affect the fusion process has been isolated and identified here. Mx amplifies these effects maximally followed by Px and Tx. This has been correlated to the enhanced partitioning of the hydrophobic Mx compared to the more hydrophilic Px and Tx in the mixed bilayer.

Identification of gene encoding Plasmodium knowlesi phosphatidylserine decarboxylase by genetic complementation in yeast and characterization of in vitro maturation of encoded enzyme

The 23-megabase genome of Plasmodium falciparum, the causative agent of severe human malaria, contains ∼5300 genes, most of unknown function or lacking homologs in other organisms. Identification of these gene functions will help in the discovery of novel targets for the development of antimalarial drugs and vaccines. The P. falciparum genome is unusually A+T-rich, which hampers cloning and expressing these genes in heterologous systems for functional analysis. The large repertoire of genetic tools available for Saccharomyces cerevisiae makes this yeast an ideal system for large scale functional complementation analyses of parasite genes. Here, we report the construction of a cDNA library from P. knowlesi, which has a lower A+T content compared with P. falciparum. This library was applied in a yeast complementation assay to identify malaria genes involved in the decarboxylation of phosphatidylserine. Transformation of a psd1Δpsd2Δdpl1Δ yeast strain, defective in phosphatidylethanolamine synthesis, with the P. knowlesi library led to identification of a new parasite phosphatidylserine decarboxylase (PkPSD). Unlike phosphatidylserine decarboxylase enzymes from other eukaryotes that are tightly associated with membranes, the PkPSD enzyme expressed in yeast was equally distributed between membrane and soluble fractions. In vitro studies reveal that truncated forms of PkPSD are soluble and undergo auto-endoproteolytic maturation in a phosphatidylserine-dependent reaction that is inhibited by other anionic phospholipids. This study defines a new system for probing the function of Plasmodium genes by library-based genetic complementation and its usefulness in revealing new biochemical properties of encoded proteins.

Interaction of cholesterol-conjugated ionizable amino lipids with biomembranes: lipid polymorphism, structure-activity relationship, and implications for siRNA delivery

Delivery of siRNA is a major obstacle to the advancement of RNAi as a novel therapeutic modality. Lipid nanoparticles (LNP) consisting of ionizable amino lipids are being developed as an important delivery platform for siRNAs, and significant efforts are being made to understand the structure-activity relationship (SAR) of the lipids. This article uses a combination of small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) to evaluate the interaction between cholesterol-conjugated ionizable amino lipids and biomembranes, focusing on an important area of lipid SAR--the ability of lipids to destabilize membrane bilayer structures and facilitate endosomal escape. In this study, cholesterol-conjugated amino lipids were found to be effective in increasing the order of biomembranes and also highly effective in inducing phase changes in biological membranes in vitro (i.e., the lamellar to inverted hexagonal phase transition). The phase transition temperatures, determined using SAXS and DSC, serve as an indicator for ranking the potency of lipids to destabilize endosomal membranes. It was found that the bilayer disruption ability of amino lipids depends strongly on the amino lipid concentration in membranes. Amino lipids with systematic variations in headgroups, the extent of ionization, tail length, the degree of unsaturation, and tail asymmetry were evaluated for their bilayer disruption ability to establish SAR. Overall, it was found that the impact of these lipid structure changes on their bilayer disruption ability agrees well with the results from a conceptual molecular "shape" analysis. Implications of the findings from this study for siRNA delivery are discussed. The methods reported here can be used to support the SAR screening of cationic lipids for siRNA delivery, and the information revealed through the study of the interaction between cationic lipids and biomembranes will contribute significantly to the design of more efficient siRNA delivery vehicles.

Ultrasound-mediated destabilization and drug release from liposomes comprising dioleoylphosphatidylethanolamine

Novel sonosensitive doxorubicin-containing liposomes comprising dioleoylphosphatidylethanolamine (DOPE) as the main lipid constituent were developed and characterized in terms of ultrasound-mediated drug release in vitro. The liposome formulation showed high sonosensitivity; where approximately 95% doxorubicin was released from liposomes after 6min of 40kHz US exposure in buffered sucrose solution. This represented a 30% increase in release extent in absolute terms compared to liposomes comprising the saturated lipid analogue distearoylphosphatidylethanolamine (DSPE), and a 9-fold improvement in release extent when compared to standard pegylated liposomal doxorubicin, respectively. Ultrasound release experiments in the presence of serum showed a significantly reduction in sonosensitivity of DSPE-based liposomes, whilst the release properties of DOPE-based liposomes were essentially maintained. Dynamic light scattering measurements and cryo-transmission electron microscopy of DOPE-based liposomes after ultrasound treatment indicated liposome disruption and formation of various lipid structures, corroborating the high release extent. The results point to the potential of DOPE-based liposomes as a new class of drug carriers for ultrasound-mediated drug delivery.