Cationic facial amphiphiles: a promising class of transfection agents

Liposomal nanoparticles based on steroids and isoprenoids for nonviral gene delivery

Natural lipid molecules are an essential part of life as they constitute the membrane of cells and organelle. In most of these cases, the hydrophobicity of natural lipids is contributed by alkyl chains. Although natural lipids with a nonfatty acid hydrophobic backbone are quite rare, steroids and isoprenoids have been strong candidates as part of a lipid. Over the years, these natural molecules (steroid and isoprenoids) have been used to make either lipid-based nanoparticle or functionalize in such a way that it could form nano assembly alone for therapeutic delivery. Here we mainly focus on the synthetic functionalized version of these natural molecules which forms cationic liposomal nanoparticles (LipoNPs). These cationic LipoNPs were further used to deliver various negatively charged genetic materials in the form of pDNA, siRNA, mRNA (nucleic acids), and so on. This article is categorized under: Biology-Inspired Nanomaterials > Lipid-Based Structures.

Cationic lipids for gene delivery: many players, one goal

Lipid-based carriers represent the most widely used alternative to viral vectors for gene expression and gene silencing purposes. This class of non-viral vectors is particularly attractive for their ease of synthesis and chemical modifications to endow them with desirable properties. Despite combinatorial approaches have led to the generation of a large number of cationic lipids displaying different supramolecular structures and improved behavior, additional effort is needed towards the development of more and more effective cationic lipids for transfection purposes. With this review, we seek to highlight the great progress made in the design of each and every constituent domain of cationic lipids, that is, the chemical structure of the headgroup, linker and hydrophobic moieties, and on the specific effect on the assembly with nucleic acids. Since the complexity of such systems is known to affect their performances, the role of formulation, stability and phase behavior on the transfection efficiency of such assemblies will be thoroughly discussed. Our objective is to provide a conceptual framework for the development of ever more performing lipid gene delivery vectors.

Facially amphiphilic polyionene biocidal polymers derived from lithocholic acid

Bacterial infections have become a global issue that requires urgent attention, particularly regarding to emergence of multidrug resistant bacteria. We developed quaternary amine-containing antimicrobial poly(bile acid)s that contain a hydrophobic core of lithocholic acid in the main-chain. Interestingly, by choosing appropriate monomers, these cationic polymers can form core-shell micelles. These polymers exhibited biocidal activity against both Gram-positive and Gram-negative bacterial species. It is demonstrated that the micelles can deliver hydrophobic antibiotics that functionally have dual antimicrobial activities. Cytotoxicity assays against HeLa cells showed dosage-dependent toxicity for polymers with longer linkers.

One-Pot Parallel Synthesis of Lipid Library via Thiolactone Ring Opening and Screening for Gene Delivery

Efficient delivery of nucleic acids into cells is of great interest in the field of cell biology and gene therapy. Despite a lot of research, transfection efficiency and structural diversity of gene-delivery vectors are still limited. A better understanding of the structure-function relationship of gene delivery vectors is also essential for the design of novel and intelligent delivery vectors, efficient in "difficult-to-transfect" cells and in vivo clinical applications. Most of the existing strategies for the synthesis of gene-delivery vectors require multiple steps and lengthy procedures. Here, we demonstrate a facile, three-component one-pot synthesis of a combinatorial library of 288 structurally diverse lipid-like molecules termed "lipidoids" via a thiolactone ring opening reaction. This strategy introduces the possibility to synthesize lipidoids with hydrophobic tails containing both unsaturated bonds and reducible disulfide groups. The whole synthesis and purification are convenient, extremely fast, and can be accomplished within a few hours. Screening of the produced lipidoids using HEK293T cells without addition of helper lipids resulted in identification of highly stable liposomes demonstrating ∼95% transfection efficiency with low toxicity.

Antibacterial activity and safety of commercial veterinary cationic steroid antibiotics and neutral superoxidized water

Antibiotic resistance of bacteria common to the ocular surface is an evolving problem. Thus, novel treatment options with new modes of action are required. We investigated the antibacterial activity and safety of three commercially available topical veterinary ophthalmic products (cationic steroid antibiotics, products A and B, and a neutral superoxidized water, product C) to determine their potential use as antimicrobial alternatives. The minimum inhibitory concentrations (MIC) of the three products were determined against 17 antibiotic resistant bacterial clinical isolates from the ocular surface. Using a standard cytotoxicity assay, the products at varying concentrations were evaluated with a corneal fibroblast cell line and a macrophage-like cell line to determine their potential toxic effect in vitro. The commercial ophthalmic solutions, ofloxacin 0.3%, tobramycin 0.3% and gentamicin 0.3% were used as positive controls for the MIC and tobramycin 0.3% was used as positive control for the cytotoxicity assays. For the MIC, Product C showed no inhibition of growth for any organisms, while Products A and B showed inhibition of growth similar to slightly less than the positive controls. For the cytotoxicity assays, Product C exhibited minimal toxicity while Products A and B exhibited toxicity similar to the controls. In conclusion, Product C had no antibacterial activity in these assays, while Products A and B had antibacterial profiles similar to slightly less than common topical ophthalmic antibiotics and cytotoxicity profiles similar to common topical ophthalmic antibiotics. To our knowledge, this is the first report on the antibacterial activity and safety of the cationic steroid antibiotics and superoxidized water.

Self-Assembly of Lecithin and Bile Salt in the Presence of Inorganic Salt in Water: Mesoscale Computer Simulation

The influence of inorganic salt on the structure of lecithin/bile salt mixtures in aqueous solution is studied by means of dissipative particle dynamics simulations. We propose a coarse-grained model of phosphatidylcholine and two types of bile salts (sodium cholate and sodium deoxycholate) and also take into account the presence of low molecular weight salt. This model allows us to study the system on rather large time and length scales (up to about ∼20 μs and 50 nm) and to reveal mechanisms of experimentally observed increasing viscosity upon increasing the low molecular weight salt concentration in this system. We show that increasing the low molecular weight salt concentration induces the growth of cylinder-like micelles formed in lecithin/bile salt mixtures in water. These wormlike micelles can entangle into transient networks displaying perceptible viscoelastic properties. Computer simulation results are in good qualitative agreement with experimental observations.

Unraveling the impact of hydroxylation on interactions of bile acid cationic lipids with model membranes by in-depth calorimetry studies

We used eight bile acid cationic lipids differing in the number of hydroxyl groups and performed in-depth differential scanning calorimetry studies on model membranes doped with different percentages of these cationic bile acids. These studies revealed that the number and positioning of free hydroxyl groups on bile acids modulate the phase transition and co-operativity of membranes. Lithocholic acid based cationic lipids having no free hydroxyl groups gel well with dipalmitoylphosphatidylcholine (DPPC) membranes. Chenodeoxycholic acid lipids having one free hydroxyl group at the 7'-carbon position disrupt the membranes and lower their co-operativity. Deoxycholic acid and cholic acid based cationic lipids have free hydroxyl groups at the 12'-carbon position, and at 7'- and 12'-carbon positions respectively. Doping of these lipids at high concentrations increases the co-operativity of membranes suggesting that these lipids might induce self-assembly in DPPC membranes. These different modes of interactions between cationic lipids and model membranes would help in future for exploring their use in DNA/drug delivery.

Conformationally switchable water-soluble fluorescent bischolate foldamers as membrane-curvature sensors

Membrane curvature is an important parameter in biological processes such as cellular movement, division, and vesicle fusion and budding. Traditionally, only proteins and protein-derived peptides have been used as sensors for membrane curvature. Three water-soluble bischolate foldamers were synthesized, all labeled with an environmentally sensitive fluorophore to report their binding with lipid membranes. The orientation and ionic nature of the fluorescent label were found to be particularly important in their performance as membrane-curvature sensors. The bischolate with an NBD group in the hydrophilic α-face of the cholate outperformed the other two analogues as a membrane-curvature sensor and responded additionally to the lipid composition including the amounts of cholesterol and anionic lipids in the membranes.

Cholate-based synthesis of size-tunable cage compounds

We describe cholate-based cage amphiphiles with a unique architecture that combines elements of structural rigidity and flexibility. The cage compounds are built by extending and bridging three polar chains underneath the concave steroid rings of cholate and capping with another rigid, symmetrically trifunctionalized cyanuric acid moiety. The connecting chains are varied to include, for instance, oligo(ethylene glycol) or chains containing 1,2,3-triazole units to present flexibility in the chemical and structural space and potentially deliver functional molecules for molecular recognition applications.

Supramolecular disassembly of facially amphiphilic dendrimer assemblies in response to physical, chemical, and biological stimuli

Supramolecular assemblies formed from spontaneous self-assembly of amphiphilic macromolecules are explored as biomimetic architectures and for applications in areas such as sensing, drug delivery, and diagnostics. Macromolecular assemblies are usually preferred, compared with their simpler small molecule counterparts, due to their low critical aggregate concentrations (CAC) and high thermodynamic stability. This Account focuses on the structural and functional aspects of assemblies formed from dendrimers, specifically facially amphiphilic dendrons that form micelle or inverse micelle type supramolecular assemblies depending on the nature of the solvent medium.

The micelle type assemblies formed from facially amphiphilic dendrons sequester hydrophobic guest molecules in their interiors. The stability of these assemblies is dependent on the relative compatibility of the hydrophilic and hydrophobic functionalities with water, often referred to as hydrophilic–lipophilic balance (HLB). Disruption of the HLB, using an external stimulus, could lead to disassembly of the aggregates, which can then be utilized to cause an actuation event, such as guest molecule release. Studying these possibilities has led to (i) a robust and general strategy for stimulus-induced disassembly and molecular release and (ii) the introduction of a new approach to protein-responsive supramolecular disassembly. The latter strategy provides a particularly novel avenue for impacting biomedical applications. Most of the stimuli-sensitive supramolecular assemblies have been designed to be responsive to factors such pH, temperature, and redox conditions. The reason for this interest stems from the fact that certain disease microenvironments have aberrations in these factors. However, these variations are the secondary imbalances in biology. Imbalances in protein activity are the primary reasons for most, if not all, human pathology. There have been no robust strategies in stimulus-responsive assemblies that respond to these variations. The facially amphiphilic dendrimers provide a unique opportunity to explore this possibility.

Similarly, the propensity of these molecules to form inverse micelles in apolar solvents and thus bind polar guest molecules, combined with the fact that these assemblies do not thermodynamically equilibrate in biphasic mixtures, was used to predictably simplify peptide mixtures. The structure–property relationships developed from these studies have led to a selective and highly sensitive detection of peptides in complex mixtures. Selectivity in peptide extraction was achieved using charge complementarity between the peptides and the hydrophilic components present in inverse micellar interiors. These findings will have implications in areas such as proteomics and biomarker detection.

MSC-based VEGF gene therapy in rat myocardial infarction model using facial amphipathic bile acid-conjugated polyethyleneimine

Mesenchymal stem cells (MSCs) have attracted much attention in regenerative medicine owing to their apparent usefulness as multi-potent replacement cells. The potential of MSC therapy can be further improved by transforming MSCs with therapeutic genes that maximize the efficacy of gene therapy and their own therapeutic ability. Since most conventional transfection methodologies have shown marginal success in delivering exogenous genes into primary cultured cells, efficient gene transfer into primary MSCs is a prerequisite for the development of MSC-based gene therapy strategies to achieve repair and regeneration of damaged tissues. Herein, facially amphipathic bile acid-modified polyethyleneimine (BA-PEI) conjugates were synthesized and used to transfer hypoxia-inducible vascular endothelial growth factor gene (pHI-VEGF) in MSCs for the treatment of rat myocardial infarction. Under the optimized transfection conditions, the BA-PEI conjugates significantly increased the VEGF protein expression levels in rat MSCs, compared with traditional transfection methods such as Lipofectamine™ and branched-PEI (25 kDa). Furthermore, the prepared pHI-VEGF-engineered MSCs (VEGF-MSCs) resulted in improved cell viability, particularly during severe hypoxic exposure in vitro. The transplantation of MSCs genetically modified to overexpress VEGF by BA-PEI enhanced the capillary formation in the infarction region and eventually attenuated left ventricular remodeling after myocardial infarction in rats. This study demonstrates the applicability of the BA-PEI conjugates for the efficient transfection of therapeutic genes into MSCs and the feasibility of using the genetically engineered MSCs in regenerative medicine for myocardial infarction.

Cyclodextrin-scaffolded glycotransporters for gene delivery

Conventional drugs consist of a formulation of a bioactive species and a carrier, the former accounting for most of the sophistication of the design. In the case of biomolecular drugs, however, the role of the carrier becomes decisive in enabling the load to reach its target to carry out its designed therapeutic function. Thus, the clinical success of gene therapy, where the active principles are nucleic acids, critically depends on the use of efficient and safe delivery systems. Carbohydrates have proven particularly useful in this regard. Glycocoating, similarly to poly(ethylene)glycol (PEG)-coating (pegylation), can stabilize colloidal aggregates by improving solvation and preventing nonspecific interactions, for example, with serum proteins. Moreover, glycoconjugates can drive specific recognition and receptor-mediated internalization in target cells. Actually, the inherent flexibility of carbohydrate and glycoconjugate chemistry has greatly contributed to enlarging the range of functional materials that can be rationally conceived for gene delivery. Herein, this is illustrated with selected examples that focus on controlling the architectural parameters of the vectors to make them suitable for structure–activity relationship (SAR) and optimization studies. The members of the cyclomaltooligosaccharide (cyclodextrin, CD) family will be the central actors of the story.

A biomimetic lipid library for gene delivery through thiol-yne click chemistry

The delivery of nucleic acids such as plasmid DNA and siRNA into cells is a cornerstone of biological research and is of fundamental importance for medical therapeutics. Although most gene delivery therapeutics in clinical trials are based on viral vectors, safety issues remain a major concern. Non-viral vectors, such as cationic lipids and polymers, offer safer alternatives but their gene delivery efficiencies are usually not high enough for clinical applications. Thus, there is a high demand for more efficient and safe non-viral vectors. Here, we present a facile two-step method based on thiol-yne click chemistry for parallel synthesis of libraries of new biomimetic cationic thioether lipids. A library of novel lipids was synthesized using the developed method and more than 10% of the lipids showed highly efficient transfection in different cell types, surpassing the efficiency of several popular commercial transfection reagents. One of the new lipids showed highly efficient siRNA delivery to multiple cell types and could successfully deliver DNA plasmid to difficult-to-transfect mouse embryonic stem cells (mESC). Analysis of structure-activity relationship revealed that the length of the hydrophobic alkyl groups was a key parameter for efficient cell transfection and was more important for transfection efficiency than the nature of cationic head groups. The correlation of the size and surface charge of liposomes with transfection efficiency is described.

Facial amphipathic deoxycholic acid-modified polyethyleneimine for efficient MMP-2 siRNA delivery in vascular smooth muscle cells

Clinical applications of RNA interference-based therapeutics such as small interfering RNAs (siRNAs) have been limited mainly due to low intracellular delivery efficiency in vitro and in vivo. In this study, facially amphipathic deoxycholic acid (DA)-modified polyethyleneimine (PEI(1.8)) (DA-PEI(1.8)) was synthesized and used as a potent carrier system for siRNA targeted against matrix metalloproteinase-2 (MMP-2) to inhibit the migration of vascular smooth muscle cells (SMCs), which is the major pathomechanism in the development of atherosclerosis and restenosis after arterial injury. A representative facial amphipathic bile acid DA having a high membrane permeability was conjugated to the terminal amine groups of the low molecular weight PEI(1.8) via amide bonds. The DA-PEI(1.8) conjugates formed self-assembled nanoparticles with siRNA molecules in an aqueous phase and the DA-PEI(1.8)/siRNA polyplexes became stabilized and condensed as particle incubation time increased from 0 to 4h. Both cellular internalization and target gene silencing were enhanced as the DA-PEI(1.8)/siRNA polyplexes stabilized. When vascular SMCs were transfected with MMP-2 siRNA, the DA-PEI(1.8)/siRNA polyplex formulation led to a significant decrease in MMP-2 gene expression, resulting in the suppression of cell migration. These results suggest that the DA-PEI(1.8)/MMP-2 siRNA delivery system may be useful in anti-restenotic treatment for various vasculoproliferative disorders such as atherosclerosis, in-stent restenosis, and vein graft failure.

Slow release and delivery of antisense oligonucleotide drug by self-assembled peptide amphiphile nanofibers

Antisense oligonucleotides provide a promising therapeutic approach for several disorders including cancer. Chemical stability, controlled release, and intracellular delivery are crucial factors determining their efficacy. Gels composed of nanofibrous peptide network have been previously suggested as carriers for controlled delivery of drugs to improve stability and to provide controlled release, but have not been used for oligonucleotide delivery. In this work, a self-assembled peptide nanofibrous system is formed by mixing a cationic peptide amphiphile (PA) with Bcl-2 antisense oligodeoxynucleotide (ODN), G3139, through electrostatic interactions. The self-assembly of PA-ODN gel was characterized by circular dichroism, rheology, atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM and SEM images revealed establishment of the nanofibrous PA-ODN network. Due to the electrostatic interactions between PA and ODN, ODN release can be controlled by changing PA and ODN concentrations in the PA-ODN gel. Cellular delivery of the ODN by PA-ODN nanofiber complex was observed by using fluorescently labeled ODN molecule. Cells incubated with PA-ODN complex had enhanced cellular uptake compared to cells incubated with naked ODN. Furthermore, Bcl-2 mRNA amounts were lower in MCF-7 human breast cancer cells in the presence of PA-ODN complex compared to naked ODN and mismatch ODN evidenced by quantitative RT-PCR studies. These results suggest that PA molecules can control ODN release, enhance cellular uptake and present a novel efficient approach for gene therapy studies and oligonucleotide based drug delivery.

Efficient preparation and labeling of human induced pluripotent stem cells by nanotechnology

Efficient preparation and labeling of human induced pluripotent stem (iPS) cells is a great challenge in stem cell research and development. With the aim of investigating the feasibility of using nanotechnology to enhance the preparation efficiency of iPS cells and to label iPS cells for long-term tracing and imaging, in this paper, four transcription factor genes, ie, Oct4, Sox2, LIN28, and Nanog, and packaging plasmids such as PSPAX2 and PMD2.G were cotransfected into 293T cells using Generation 5.0 polyamidoamine dendrimer-modified magnetic nanoparticles (dMNPs) as a delivery system. The resultant supernatant liquids were incubated with human fibroblast cells at 37°C for 21 days, then the embryonic stem (ES) cell-like clones were screened, cultured, and identified. Finally, the prepared iPS cells were labeled with fluorescent magnetic nanoparticles (FMNPs). The results showed that dMNPs can efficiently deliver all vectors into 293T cells. The resultant lentiviruses’ titers were 10-fold more than those based on Lipofectamine™ 2000. Reverse transcription polymerase chain reaction analysis showed that four genes (Oct4, Sox2, LIN28, and Nanog) exhibited different expressions in iPS cells. Immunostaining analysis showed that specific surface markers of ES cells such as SSEA-3, SSEA-4, Tra-1-60, and Tra-1-81 were positive in iPS cells, and the terotomas were formed in NOD-SCID mice that were implanted with iPS cells. Red fluorescent signals could be observed in iPS cells labeled with FMNPs by fluorescent microscopy, and the magnetic signals were detected in labeled iPS cells by magnetic resonance imaging. In conclusion, human iPS cells can be efficiently generated using polyamidoamine dMNPs and lentivirus and labeled with FMNPs for long-term observation and tracking, which has great potential application in the research and development of stem cells in the near future.

Cyclodextrin-based gene delivery systems

Cyclodextrin (CD) history has been largely dominated by their unique ability to form inclusion complexes with guests fitting in their hydrophobic cavity. Chemical funcionalization was soon recognized as a powerful mean for improving CD applications in a wide range of fields, including drug delivery, sensing or enzyme mimicking. However, 100 years after their discovery, CDs are still perceived as novel nanoobjects of undeveloped potential. This critical review provides an overview of different strategies to promote interactions between CD conjugates and genetic material by fully exploiting the inside-outside/upper-lower face anisotropy of the CD nanometric platform. Covalent modification, self-assembling and supramolecular ligation can be put forward with the ultimate goal to build artificial viruses for programmed and efficient gene therapy (222 references).

Altered activity and physicochemical properties of short cationic antimicrobial peptides by incorporation of arginine analogues

The incorporation of nongenetically encoded amino acids is a well established strategy to alter the behavior of several types of promising cationic antimicrobial peptides. Generally, these elements have been improved mimics of the hydrophobic amino acids yielding peptides with increased stability and potency. In this initial study, the effect of systematic replacement of Arg in a well-defined moderately antimicrobial tripeptide library is described. It is shown that the arginine analogues need to display a strong basicity to produce active peptides. It is further revealed that the hydrophobic units needed for activity in these peptides can be effectively incorporated in the direct vicinity of the cationic charge to produce compounds with improved antibacterial properties. A well-defined facial amphiphilic structure, which remains intact upon introduction of hydrophobic elements in the cationic side chains, is seen for the majority of the tested peptides. Microcalorimetric studies revealed a peptide binding to large anionic unilamellar vesicles (LUVs) mimicking the Gram-positive bacterial membrane as well as a potentially competitive binding to human serum albumin in the low- to mid-micromolar range. No considerable alterations in binding to either albumin or the LUVs were seen for the analogue containing peptides. A neutral LUV mimicking the eukaryotic cell membrane showed no significant binding to any of the peptides. The oral absorption of this class of short lactoferricin based peptides was investigated for the first time and revealed that incorporation of weaker bases than Arg produced peptides with much improved permeability in a recently developed permeation model, the phospholipid vesicle based barrier assay. Collectively, the results presented here show that there is ample room to toggle the activity and physical properties of short cationic antimicrobial peptides by incorporation of arginine analogues.

Chitosan nanoparticles for drug delivery to the eye

The purpose of this review is to provide the reader with an overview of the advances made in ocular delivery of bioactive molecules by means of chitosan-based nanosystems, and their potential relevance in clinical use. The studies described clearly emphasise that chitosan-based nanostructures are versatile systems that can be tailor-made according to required compositions, surface characteristics and particle size. Such parameters, which are known to influence their in vivo performance, can be modulated by adjusting the formulation conditions of the nanotechnologies responsible for their formation, by incorporating additional materials in the preparation steps, and/or by using synthetically modified chitosan. Moreover, this review illustrates how the advances achieved in the understanding of the interaction of nanosystems with the ocular structures should result in the coming years, logically, into challenging innovations in ocular nanomedicines with significant impact on clinical practice.

Nanoparticles as protein and gene carriers to mucosal surfaces

One of the most exciting and challenging applications of nanotechnology in medicine is the development of nanocarriers for the intraepithelial delivery of biomacromolecules through mucosal surfaces. These biomacromolecules represent an increasingly important segment of the therapeutic arsenal; however, their potential is still limited by their instability and inability to cross biological barriers. Nanoparticle carriers have emerged as one of the most promising technologies to overcome this limitation, owing mainly to their demonstrated capacity to interact with biological barriers. In this review, we summarize the current advances made on nanoparticles designed for transmucosal delivery. Supported by the examples of a variety of therapeutic macromolecules – peptides and proteins, gene medicines and vaccines – we review the lessons learned from the past and we offer a future perspective for this field.

Tumour gene expression from C12 spermine amphiphile gene delivery systems

Gene therapy requires safe and efficient gene delivery systems. Towards this aim both the gene formulation and tumour transfection ability of C12 spermine amphiphiles were tested. Five amphiphiles were synthesised and characterised: 1-[N,N-bis(3-aminopropyl)-1,4-butane diamine] dodecane (12G0--a C12 spermine amphiphile), a poly(ethylene glycol) (PEG, MW = 2 kDa) derivative of 12G0, 1,12-[N,N-bis(3-aminopropyl)-1,4-butane diamine] dodecane (12G1--a C12 spermine bolaamphiphile) and N-methyl quaternary ammonium derivatives of both 12G0 (12QG0) and 12G1 (12QG1). All amphiphiles except 12G0, which precipitates, yield nanoparticles in aqueous media with and without DNA. Thus when 12G0 is substituted with either quaternary ammonium or PEG groups it forms nanoparticles both with and without DNA. The minimum nitrogen, phosphate ratio required to completely condense DNA (NP) was inversely proportional to the particles' zeta potential (zeta), NP = 1626/zeta(0.98). Biological testing showed that both PEG and quaternary ammonium groups diminished the membrane lytic ability of these C12 amphiphiles. On intratumoural injection, while PEG groups hamper gene transfer, the quaternary ammonium amphiphile (12QG0) produces tumour confined gene expression that is 80% of that produced by linear poly(ethylenimine) (LPEI, MW = 22 kDa); while the intratumoural injection of LPEI produced significant gene expression in the liver and lung, making 12QG0 suitable for the administration of cytotoxic tumouricidal genes.

Ceragenins: cholic acid-based mimics of antimicrobial peptides

The prevalence of drug-resistant bacteria drives the quest for new antimicrobials, including those that are not expected to readily engender resistance. One option is to mimic Nature's most ubiquitous means of controlling bacterial growth, antimicrobial peptides, which have evolved over eons. In general, bacteria remain susceptible to these peptides. Human antimicrobial peptides play a central role in innate immunity, and deficiencies in these peptides have been tied to increased rates of infection. However, clinical use of antimicrobial peptides is hampered by issues of cost and stability. The development of nonpeptide mimics of antimicrobial peptides may provide the best of both worlds: a means of using the same mechanism chosen by Nature to control bacterial growth without the problems associated with peptide therapeutics. The ceragenins were developed to mimic the cationic, facially amphiphilic structures of most antimicrobial peptides. These compounds reproduce the required morphology using a bile-acid scaffolding and appended amine groups. The resulting compounds are actively bactericidal against both gram-positive and gram-negative organisms, including drug-resistant bacteria. This antimicrobial activity originates from selective association of the ceragenins with negatively charged bacterial membrane components. Association has been studied with synthetic models of bacterial membrane components, with bacterial lipopolysaccharide, with vesicles derived from bacterial phospholipids, and with whole cells. Comparisons of the antimicrobial activities of ceragenins and representative antimicrobial peptides suggest that these classes of compounds share a mechanism of action. Rapid membrane depolarization is caused by both classes as well as blebbing of bacterial membranes. Bacteria express the same genes in response to both classes of compounds. On the basis of the antibacterial activities of ceragenins and preliminary in vivo studies, we expect these compounds to find use in augmenting or replacing antimicrobial peptides in treating human disease.

Cationic cyclocholamides; toroidal facial amphiphiles with potential for anion transport

Cholic acid has been transformed into cyclotrimeric and cyclotetrameric toroidal amphiphiles with inward-directed ammonium substituents; the cyclotrimer effects the transport of chloride anions across vesicle bilayer membranes.

Structure-function relationship research of glycerol backbone-based cationic lipids for gene delivery

Transfection activities of two series of synthetic glycerol backbone-based cationic lipids were studied as gene delivery carriers. The variable length of hydrocarbon chains, diverse quaternary ammonium heads, different linkage, as well as alternative anion combined with them allowed to find how these factors affect cationic lipids on their gene delivery performance. The structure-function relationship of the synthetic glycerol backbone-based cationic lipids was discussed, and the transfection efficiency of some of the cationic liposomes was superior or parallel to that of two commercial transfection agents.

Bile acid-oligopeptide conjugates interact with DNA and facilitate transfection

Bile acids conjugated to oligoarginine-containing peptides (BACs) form complexes with DNA based on the electrostatic interactions between negatively charged phosphate groups of the nucleic acid and the positively charged side chain guanidinium groups of the oligoarginine in the BACs. Charge neutralization of both components and subsequent increases of the net positive charge of the complex combined with the water-soluble lipophilic nature of the bile acid results in changes in the physicochemistry and biological properties of the complexes. We have examined the relationship of a series of 13 BACs on their interaction with circular plasmid DNA (pDNA). The formation of soluble, low-density and insoluble, high-density complexes was analyzed using several methods. The formation of high-density complexes was dependent on the DNA concentration, and was enhanced by increasing the BAC to pDNA charge ratio. Several of the BAC:pDNA complexes demonstrated exclusion of the DNA-intercalator Hoechst 33258 from pDNA, and were also protected from DNase activity. Several BAC conjugates interacted with pDNA to form nanometer-sized particles suitable for cell transfection in vitro. Five of the 13 BACs were transfection competent as single agents, and 11 of the 13 BACs showed enhancement of transfection in combination with DOPE containing liposomes or silica nanoparticles.

Synthetic diether-linked cationic lipids for gene delivery

Quaternary ammonium lipids 2a-p, with diether linkages between hydrocarbon chains and their ammonium headgroups, were synthesized as potential vectors for cationic liposome-mediated gene delivery. Varying the length of carbon chains and quaternary ammonium heads as well as different anionic complexes will enable the study of the structure-function relationships of these cationic lipids in terms of gene delivery properties.

Cell Biological and Biophysical Aspects of Lipid-mediated Gene Delivery

Cationic lipids are conceptually and methodologically simple tools to deliver nucleic acids into the cells. Strategies based on cationic lipids are viable alternatives to viral vectors and are becoming increasingly popular owing to their minimal toxicity. The first-generation cationic lipids were built around the quaternary nitrogen primarily for binding and condensing DNA. A large number of lipids with variations in the hydrophobic and hydrophilic region were generated with excellent transfection efficiencies in vitro. These cationic lipids had reduced efficiencies when tested for gene delivery in vivo. Efforts in the last decade delineated the cell biological basis of the cationic lipid gene delivery to a significant detail. The application of techniques such as small angle X-ray spectroscopy (SAXS) and fluorescence microscopy, helped in linking the physical properties of lipid:DNA complex (lipoplex) with its intracellular fate. This biological knowledge has been incorporated in the design of the second-generation cationic lipids. Lipid-peptide conjugates (peptoids) are effective strategies to overcome the various cellular barriers along with the lipoplex formulations methodologies. In this context, cationic lipid-mediated gene delivery is considerably benefited by the methodologies of liposome-mediated drug delivery. Lipid mediated gene delivery has an intrinsic advantage of being a biomimetic platform on which considerable variations could be built to develop efficient in vivo gene delivery protocols.