Water insoluble and soluble lipids for gene delivery

The clinical progress and challenges of mRNA vaccines

Owing to the breakthroughs in the prevention and control of the COVID-19 pandemic, messenger RNA (mRNA)-based vaccines have emerged as promising alternatives to conventional vaccine approaches for infectious disease prevention and anticancer treatments. Advantages of mRNA vaccines include flexibility in designing and manipulating antigens of interest, scalability in rapid response to new variants, ability to induce both humoral and cell-mediated immune responses, and ease of industrialization. This review article presents the latest advances and innovations in mRNA-based vaccines and their clinical translations in the prevention and treatment of infectious diseases or cancers. We also highlight various nanoparticle delivery platforms that contribute to their success in clinical translation. Current challenges related to mRNA immunogenicity, stability, and in vivo delivery and the strategies for addressing them are also discussed. Finally, we provide our perspectives on future considerations and opportunities for applying mRNA vaccines to fight against major infectious diseases and cancers. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Biology-Inspired Nanomaterials > Lipid-Based Structures.

Development of a novel oral complex lipid emulsion containing triptolide for targeting pancreatic cancer

Triptolide (TP), a diterpenoid triepoxide, exhibits strong anti-cancer activities, especially against pancreatic cancer, but its clinical application is limited by organ toxicity. TP was combined with diammonium glycyrrhizinate (DG), as a cytoprotective agent, in a novel oral complex lipid emulsion (TP/DG-CLE) to increase the therapeutic index of TP against pancreatic cancer. The emulsion was produced by subjecting phospholipid and active components to high shear conditions using high-pressure homogenization resulting in droplets of essentially neutral or small positive charge and consistent size below 200nm. Pharmacokinetic studies in Sprague Dawley rats revealed an AUC _(0-8h) of TP following oral dosing of TP/DG-CLE that was 4-fold higher than that achieved for triptolide/diammonium glycyrrhizinate suspension, demonstrating significantly higher TP bioavailability and longer residence time in the bloodstream. Tissue distribution data obtained in mice demonstrated that TP/DG-CLE having a TP/DG weight ratio of 1:22.5 preferentially accumulated in the pancreas. Moreover, toxicology assays in rats provided indications of minor liver damage following daily administration of the emulsion for two weeks. Together these studies establish complex lipid emulsions containing triptolide and DG as a promising oral formulation for treatment of pancreatic cancer and establish a platform for developing new chemotherapeutic treatments.

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.

Delivery of small interfering RNAs by nanovesicles for cancer therapy

Small interfering ribonucleic acids (siRNAs) are originally recognized as an intermediate of the RNA interference (RNAi) pathway. They can inhibit or silence various cellular pathways by knocking down specific messenger RNA molecules. In cancer cells, siRNAs can suppress the expression of several multidrug-resistant genes, leading to the increased deposition of chemotherapeutic drugs at the tumor site. siRNA therapy can be used to selectively increase apoptosis of cancer cells or activate an immune response to the cancer. However, delivering siRNAs to the targeted location is the main limitation in achieving safe and effective delivery of siRNAs. This review highlights some representative examples of nonviral delivery systems, especially nanovesicles such as exosomes, liposomes, and niosomes. Nanovesicles can improve the delivery of siRNAs by increasing their intracellular delivery, and they have demonstrated excellent potential for cancer therapy. This review focuses on recent discoveries of siRNA targets for cancer therapy and the use of siRNAs to successfully silence these targets. In addition, this review summarizes the recent progress in designing nanovesicles (liposomes or niosomes) for siRNA delivery to cancer cells and the effects of a combination of anticancer drugs and siRNA therapy in cancer therapy.

Emerging Approaches to Functionalizing Cell Membrane-Coated Nanoparticles

There has been significant interest in developing cell membrane-coated nanoparticles due to their unique abilities of biomimicry and biointerfacing. As the technology progresses, it becomes clear that the application of these nanoparticles can be drastically broadened if additional functions beyond those derived from the natural cell membranes can be integrated. Herein, we summarize the most recent advances in the functionalization of cell membrane-coated nanoparticles. In particular, we focus on emerging methods, including (1) lipid insertion, (2) membrane hybridization, (3) metabolic engineering, and (4) genetic modification. These approaches contribute diverse functions in a nondisruptive fashion while preserving the natural function of the cell membranes. They also improve on the multifunctional and multitasking ability of cell membrane-coated nanoparticles, making them more adaptive to the complexity of biological systems. We hope that these approaches will serve as inspiration for more strategies and innovations to advance cell membrane coating technology.

Gene delivery to the rat retina by non-viral vectors based on chloroquine-containing cationic niosomes

The incorporation of chloroquine within nano formulations, rather than as a co-treatment of the cells, could open a new avenue for in vivo retinal gene delivery. In this manuscript, we evaluated the incorporation of chloroquine diphosphate into the cationic niosome formulation composed of poloxamer 188, polysorbate 80 non-ionic surfactants, and 2,3-di (tetradecyloxy) propan-1-amine (hydrochloride salt) cationic lipid, to transfect rat retina. Niosome formulations without and with chloroquine diphosphate (DPP80, and DPP80-CQ, respectively) were prepared by the reverse phase evaporation technique and characterized in terms of size, PDI, zeta potential, and morphology. After the incorporation of the pCMS-EGFP plasmid, the resultant nioplexes -at different cationic lipid/DNA mass ratios- were further evaluated to compact, liberate, and secure the DNA against enzymatic digestion. In vitro procedures were achieved in ARPE-19 cells to assess transfection efficacy and intracellular transportation. Both nioplexes formulations transfected efficiently ARPE-19 cells, although the cell viability was clearly better in the case of DPP80-CQ nioplexes. After subretinal and intravitreal injections, DPP80 nioplexes were not able to transfect the rat retina. However, chloroquine containing vector showed protein expression in many retinal cells, depending on the administration route. These data provide new insights for retinal gene delivery based on chloroquine-containing niosome non-viral vectors.

Efficient Cytosolic Delivery Using Crystalline Nanoflowers Assembled from Fluorinated Peptoids

The design and synthesis of biocompatible nanomaterials as cargoes for the intracellular delivery of therapeutic proteins or genes have attracted intense attention because of their potential for use in therapeutics. Despite the advances in this area, very few nanomaterials can be efficiently delivered to the cytosol. To address these challenges, crystalline nanoflower-like particles are designed and synthesized from fluorinated sequence-defined peptoids; the crystallinity and fluorination of these particles enable highly efficient cytosolic delivery with minimal cytotoxicity. A cytosol delivery rate of 80% has been achieved for the fluorinated peptoid nanoflowers. Furthermore, these nanocrystals can carry therapeutic genes, such as mRNA and effectively deliver the payload into the cytosol, demonstrating the universal delivery capability of the nanocrystals. The results indicate that self-assembly of crystalline nanomaterials from fluorinated peptoids paves a new way toward development of nanocargoes with efficient cytosolic gene delivery capability.

Non-viral vectors based on cationic niosomes as efficient gene delivery vehicles to central nervous system cells into the brain

Development of safe and efficient non-viral vectors to deliver DNA into the CNS represents a huge challenge to face many neurological disorders. We elaborated niosomes based on DOTMA cationic lipid, lycopene "helper" lipid and polysorbate 60 as non-ionic surfactants for gene delivery to the CNS. Niosomes, and their corresponding nioplexes obtained after the addition of the pCMS-EGFP plasmid, were characterized in terms of size, charge, morphology and capacity to condense, release and protect DNA. In vitro experiments were performed in NT2 cells to evaluate transfection efficiency, viability, cellular uptake and intracellular distribution. Additionally, transfection in primary cortex cells were performed prior to brain administration into rat cerebral cortex. Data obtained showed that nioplexes exhibited not only adequate physicochemical properties for gene delivery applications, but also relevant transfection efficiencies (17%), without hampering viability (90%). Interestingly, In vivo experiments depicted promising protein expression in both cortical glial cells and blood vessels.

WITHDRAWN: Non-viral vectors based on cationic niosomes as efficient gene delivery vehicles to central nervous system cells into the brain

This article has been withdrawn: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been withdrawn at the request of the editor and publisher. The publisher regrets that an error occurred which led to the premature publication of this paper. This error bears no reflection on the article or its authors. The publisher apologizes to the authors and the readers for this unfortunate error.

Fliposomes: trans-2-aminocyclohexanol-based amphiphiles as pH-sensitive conformational switches of liposome membrane - a structure-activity relationship study

Recently developed lipids with the trans-2-aminocyclohexanol (TACH) moiety represent unique pH-sensitive conformational switches ("flipids") that can trigger the membrane of liposome-based drug delivery systems at lowered pH as seen in many pathological scenarios. A library of flipids with various TACH-based headgroups and hydrocarbon tails were designed, prepared, and characterized to systematically elucidate the relationship between their chemical structures and their ability to form and to trigger liposomes. Liposomes (fliposomes) consisting of a flipid, POPC and PEG-ceramide were stable at 4°C, pH 7.4 for up to several months and yet released the encapsulated fluorophore in seconds upon acidification. The colloidal properties and encapsulation efficiencies of the fliposomes depended on the structure features of the flipids such as the polarity of the headgroups and the shape and fluidity of the lipid tails. The pH-triggered release also depended on the flipid structure, where shorter linear tails yielded more efficient release. The release of fliposomes was enhanced at different narrow pH ranges, depending on the basicity of the flipid headgroup, which can be estimated either by calculated pKa or by acid/base titration of the flipids while its conformation is monitored by ¹H NMR. The structure-activity relationship of the flipids supports "lipid tail conformational shortening" as the mechanism to disrupt lipid membranes and would provide great flexibility in the design of pH-sensitive drug delivery systems.

Bioreducible Fluorinated Peptide Dendrimers Capable of Circumventing Various Physiological Barriers for Highly Efficient and Safe Gene Delivery

Polymeric vectors have shown great promise in the development of safe and efficient gene delivery systems; however, only a few have been developed in clinical settings due to poor transport across multiple physiological barriers. To address this issue and promote clinical translocation of polymeric vectors, a new type of polymeric vector, bioreducible fluorinated peptide dendrimers (BFPDs), was designed and synthesized by reversible cross-linking of fluorinated low generation peptide dendrimers. Through masterly integration all of the features of reversible cross-linking, fluorination, and polyhedral oligomeric silsesquioxane (POSS) core-based peptide dendrimers, this novel vector exhibited lots of unique features, including (i) inactive surface to resist protein interactions; (ii) virus-mimicking surface topography to augment cellular uptake; (iii) fluorination-mediated efficient cellular uptake, endosome escape, cytoplasm trafficking, and nuclear entry, and (iv) disulfide-cleavage-mediated polyplex disassembly and DNA release that allows efficient DNA transcription. Noteworthy, all of these features are functionally important and can synergistically facilitate DNA transport from solution to the nucleus. As a consequences, BFPDs showed excellent gene transfection efficiency in several cell lines (∼95% in HEK293 cells) and superior biocompatibility compared with polyethylenimine (PEI). Meanwhile BFPDs provided excellent serum resistance in gene delivery. More importantly, BFPDs offer considerable in vivo gene transfection efficiency (in muscular tissues and in HepG2 tumor xenografts), which was approximately 77-fold higher than that of PEI in luciferase activity. These results suggest bioreducible fluorinated peptide dendrimers are a new class of highly efficient and safe gene delivery vectors and should be used in clinical settings.

Cationic niosomes an effective gene carrier composed of novel spermine-derivative cationic lipids: effect of central core structures

CONTEXT

Cationic niosomes formulated from Span 20, cholesterol (Chol) and novel spermine-based cationic lipids of multiple central core structures (di(oxyethyl)amino, di(oxyethyl)amino carboxy, 3-amino-1,2-dioxypropyl and 2-amino-1,3-dioxypropyl) were successfully prepared for improving transfection efficiency in vitro. The niosomes composed of spermine cationic lipid with central core structure of di(oxyethyl)amino revealed the highest gene transfection efficiency.

OBJECTIVES

To investigate the factors affecting gene transfection and cell viability including differences in the central core structures of cationic lipids, the composition of vesicles, molar ratio of cationic lipids in formulations and the weight ratio of niosomes to DNA.

METHODS

Cationic niosomes composed of nonionic surfactants (Span20), cholesterol and spermine-based cationic lipids of multiple central core structures were formulated. Gene transfection and cell viability were evaluated on a human cervical carcinoma cell line (HeLa cells) using pDNA encoding green fluorescent protein (pEGFP-C2). The morphology, size and charge were also characterized.

RESULTS AND DISCUSSION

High transfection efficiency was obtained from cationic niosomes composed of Span20:Chol:cationic lipid at the molar ratio of 2.5:2.5:0.5 mM. Cationic lipids with di(oxyethyl)amino as a central core structure exhibited highest transfection efficiency. In addition, there was also no serum effect on transfection efficiency.

CONCLUSIONS

These novel cationic niosomes may constitute a good alternative carrier for gene transfection.

Supramolecular Organization and siRNA Binding of Hyaluronic Acid-Coated Lipoplexes for Targeted Delivery to the CD44 Receptor

The dynamics of the formation of siRNA-lipoplexes coated with hyaluronic acid (HA) and the parameters influencing their supramolecular organization were studied. The insertion of a HA-dioleylphosphatidylethanolamine (DOPE) conjugate in the liposome structure as well as subsequent complexation with siRNA increased the liposome size. Lipoplexes were around 110 nm at high ± charge ratios with a zeta potential around +50 mV and around 230 nm at low ± ratios, with a zeta potential that decreased to negative values, reaching -45 mV. The addition of the conjugate did not compromise siRNA binding to liposomes, although these nucleic acids induced a displacement of part of the HA-DOPE conjugate upon lipoplex formation, as confirmed by capillary electrophoresis. Isothermal titration calorimetry, X-ray diffraction studies, and cryo-TEM microscopy demonstrated that in addition to electrostatic interactions with siRNA a rearrangement of the lipid bilayers takes place, resulting in condensed oligolamellar vesicles. This phenomenon is dependent on the number of siRNA molecules and the degree of modification with HA. Finally, the suitable positioning of HA on the lipoplex surface and its ability to bind specifically to the CD44 receptors in a concentration-dependent manner was demonstrated by surface plasmon resonance analysis.

Rapid endosomal escape of prickly nanodiamonds: implications for gene delivery

The prickly nanodiamonds easily entered cells via endocytosis followed by unique intracellular translocation characteristics—quick endosomal escape followed by stable residence in cytoplasm. Endosomal membrane rupturing is identified as the major route of nanodiamonds’ escaping the vesicle confinement and to the cytoplasm. Little cytotoxicity is observed to associate with the nanodiamonds’ cytosolic release. Such features enable its application for gene delivery, which requires both effective cellular uptake and cytosolic release of the gene. Taking green fluorescent protein gene as an example, we demonstrate the successful cytosolic delivery and expression of such a gene using the prickly nanodiamonds as carrier.

Nonionic surfactant vesicles composed of novel spermine-derivative cationic lipids as an effective gene carrier in vitro

In the present study, nonionic surfactant vesicles (niosomes) formulated with Span 20, cholesterol, and novel synthesized spermine-based cationic lipids with four hydrocarbon tails in a molar ratio of 2.5:2.5:1 were investigated as a gene carrier. The effects of the structure of the cationic lipids, such as differences in the acyl chain length (C14, C16, and C18) of the hydrophobic tails, as well as the weight ratio of niosomes to DNA on transfection efficiency and cell viability were evaluated in a human cervical carcinoma cell line (HeLa cells) using pDNA encoding green fluorescent protein (pEGFP-C2). The niosomes were characterized both in terms of morphology and of size and charge measurement. The formation of complexes between niosomes and DNA was verified with a gel retardation assay. The transfection efficiency of these cationic niosomes was in the following order: spermine-C18 > spermine-C16 > spermine-C14. The highest transfection efficiency was obtained for transfection with spermine-C18 niosomes at a weight ratio of 10. Additionally, no serum effect on transfection efficiency was observed. The results from a cytotoxicity and hemolytic study showed that the cationic niosomes were safe in vitro. In addition, the cationic niosomes showed good physical stability for at least 1 month at 4°C. Therefore, the cationic niosomes offer an excellent prospect as an alternative gene carrier.

Current progress in gene delivery technology based on chemical methods and nano-carriers

Gene transfer methods are promising in the field of gene therapy. Current methods for gene transfer include three major groups: viral, physical and chemical methods. This review mainly summarizes development of several types of chemical methods for gene transfer in vitro and in vivo by means of nano-carriers like; calcium phosphates, lipids, and cationic polymers including chitosan, polyethylenimine, polyamidoamine dendrimers, and poly(lactide-co-glycolide). This review also briefly introduces applications of these chemical methods for gene delivery.

Structure relationship of cationic lipids on gene transfection mediated by cationic liposomes

The aim of this study was to investigate the transfection efficiency of cationic liposomes formulated with phosphatidylcholine (PC) and novel synthesized diethanolamine-based cationic lipids at a molar ratio of 5:1 in comparison with Lipofectamine™ 2000. Factors affecting transfection efficiency and cell viability, including the chemical structure of the cationic lipids, such as different amine head group (diamine and polyamine; and non-spermine and spermine) and acyl chain lengths (C14, C16, and C18) and the weight ratio of liposomes to DNA were evaluated on a human cervical carcinoma cell line (HeLa cells) using the pDNA encoding green fluorescent protein (pEGFP-C2). Characterizations of these lipoplexes in terms of size and charge measurement and agarose gel electrophoresis were performed. The results from this study revealed that almost no transfection was observed in the liposome formulations composed of cationic lipids with a non-spermine head group. In addition, the transfection efficiency of these cationic liposomes was in the following order: spermine-C14 > spermine-C16 > spermine-C18. The highest transfection efficiency was observed in the formulation of spermine-C14 liposomes at a weight ratio of 25; furthermore, this formulation was safe for use in vitro. In conclusion, cationic liposomes containing spermine head groups demonstrated promising potential as gene carriers.

Crosslinked self-assemblies of lipoid acid-substituted low molecular weight (1800 Da) polyethylenimine as reductive-sensitive non-viral gene vectors

In this study, amphiphilic polyethylenimine-graft-thioctic acid (PEI-TA) and polyethylenimine-graft-lauric acid (PEI-LA) were synthesized. Both PEI-TA and PEI-LA could self-assemble into micelles. Due to the existence of disulfide-linked rings at the end of hydrophobic moieties, PEI-TA could form stable micelles with disulfide crosslinked cores (PEI-TA-SS). In comparison with the PEI-LA micelle, PEI-TA-SS possessed higher DNA binding ability according to the gel retardation assay and heparin replacement assay. In vitro transfection experiments indicated that PEI-TA-SS showed comparably high transfection efficiency as compared to 25 kDa PEI. More interestingly, the luciferase expression of PEI-TA-SS was superior to that of PEI-LA at low N/P ratio, which might be ascribed to the stronger binding capacity of PEI-TA-SS facilitating the entering of PEI-TA-SS/pDNA complexes into cells.

The delineation of the morphology of charged liposomal vectors via a fractal analysis in aqueous and biological media: physicochemical and self-assembly studies

The present study deals with the physicochemical characterization of DPPC:DPPG (9:1 molar ratio) and DPPC:DODAP (9:1 molar ratio) liposomes, and the determination of their fractal dimension in HPLC-grade water, PBS and in FBS. Light scattering techniques were used in order to extract information on the structure, morphology, size and surface charge of liposomes in an ageing study and their structural response to changes in concentration and temperature. Fluorescence spectroscopy showed that the microviscosity of cationic liposomes changed by an increase of temperature. The fractal dimension, d(f), was found equal to 1.8 for reconstituted DPPC:DPPG (9:1) and DPPC:DODAP (9:1) liposomes in aqueous media. Aggregation of reconstituted DPPC:DPPG (9:1) and DPPC:DODAP (9:1) liposomes in FBS was observed. Their fractal dimensions were 1.46 and 2.45, respectively. The first order aggregation kinetics of DPPC:DODAP (9:1) liposomes in the presence of serum proteins was determined; the aggregates of cationic liposomes with serum components remained stable during 20 days with fractal dimension 2.5. The responsiveness of cationic liposomes to changes in temperature in the three dispersion media has revealed the self-assembly and the morphological complexity of cationic vectors. Finally, we suggest that these studies could be used for developing effective advanced drug delivery nano-systems (aDDnSs) based on their fractal characteristics which effectively draw their morphological profile.

Mucosal vaccine design and delivery

Mucosal surfaces are a major portal of entry for many human pathogens that are the cause of infectious diseases worldwide. Vaccines capable of eliciting mucosal immune responses can fortify defenses at mucosal front lines and protect against infection. However, most licensed vaccines are administered parenterally and fail to elicit protective mucosal immunity. Immunization by mucosal routes may be more effective at inducing protective immunity against mucosal pathogens at their sites of entry. Recent advances in our understanding of mucosal immunity and identification of correlates of protective immunity against specific mucosal pathogens have renewed interest in the development of mucosal vaccines. Efforts have focused on efficient delivery of vaccine antigens to mucosal sites that facilitate uptake by local antigen-presenting cells to generate protective mucosal immune responses. Discovery of safe and effective mucosal adjuvants are also being sought to enhance the magnitude and quality of the protective immune response.

2011 Rita Schaffer lecture: nanoparticles for intracellular nucleic acid delivery

Nanoparticles are a promising technology for delivery of new types of therapeutics. A polymer library approach has allowed engineering of polymeric particles that are particularly effective for the delivery of DNA and siRNA to human cells. Certain chemical structural motifs, degradable linkages, hydrophobicity, and biophysical properties are key for successful intracellular delivery. Small differences to biomaterial structure, and especially the type of degradable linkage in the polymers, can be critical for successful delivery of siRNA vs. DNA. Furthermore, subtle changes to biomaterial structure can facilitate cell-type gene delivery specificity between human brain cancer cells and healthy cells as well as between human retinal endothelial cells and epithelial cells. These polymeric nanoparticles are effective for nucleic acid delivery in a broad range of human cell types and have applications to regenerative medicine, ophthalmology, and cancer among many other biomedical research areas.

Fliposomes: pH-controlled Release from Liposomes Containing New trans-2-Morpholinocyclohexanol-based Amphiphiles that Perform a Conformational Flip and Trigger an Instant Cargo Release upon Acidification

A new type of pH-sensitive liposome (fliposomes) was designed based on the amphiphiles that are able to perform a pH-triggered conformational flip (flipids). This flip disrupts the liposome membrane and causes rapid release of the liposome cargo, specifically in the areas of increased acidity. The flipids (1-3) are equipped with a trans-2-morpholinocyclohexanol conformational switch. pH-Sensitive fliposomes containing one of these flipids, POPC and PEG-ceramide (molar ratio 50/45/5) were constructed and characterized. These compositions were stable at 4oC and pH 7.4 for several months. Fliposomes loaded with ANTS/DPX demonstrated an unusually quick content release (in a few seconds) at pH below 5.5, which was more efficient in the case of flipid 1 with the shorter linear C12-tails. The pH-titration curve for the fliposome leakage paralleled the curve for the acid-induced conformational flip of 1-3 studied by 1H NMR. A plausible mechanism of the pH-sensitivity starts with an acid-triggered conformational flip of 1, 2 or 3, which changes the molecular size and shape, shortens the lipid tails, and perturbs the liposome membrane resulting in the content leakage.

A novel dendrimer based on poly (L-glutamic acid) derivatives as an efficient and biocompatible gene delivery vector

Non-viral gene delivery systems based on cationic polymers have faced limitations related to their relative low gene transfer efficiency, cytotoxicity and system instability in vivo. In this paper, a flexible and pompon-like dendrimer composed of poly (amidoamine) (PAMAM) G4.0 as the inner core and poly (L-glutamic acid) grafted low-molecular-weight polyethylenimine (PLGE) as the surrounding multiple arms was synthesized (MGI dendrimer). The novel MGI dendrimer was designed to combine the merits of size-controlled PAMAM G4.0 and the low toxicity and flexible chains of PLGE. In phosphate-buffered saline dispersions the well-defined DNA/MGI complex above a N/P ratio of 30 showed good stability with particle sizes of approximately 200 nm and a comparatively low polydispersity index. However, the particle size of the DNA/25 kDa polyethylenimine (DNA/PEI 25K) complex was larger than 700 nm under the same salt conditions. The shielding of the compact amino groups at the periphery of flexible PAMAM and biocompatible PLGE chains in MGI resulted in a dramatic decrease of the cytotoxicity compared to native PAMAM G4.0 dendrimer. The in vitro transfection efficiency of DNA/MGI dendrimer complex was higher than that of PAMAM G4.0 dendrimer. Importantly, in serum-containing medium, DNA/MGI complexes at their optimal N/P ratio maintained the same high levels of transfection efficiency as in serum-free medium, while the transfection efficiency of native PAMAM G4.0, PEI 25K and Lipofectamine 2000 were sharply decreased. In vivo gene delivery of pVEGF165/MGI complex into balloon-injured rabbit carotid arteries resulted in significant inhibition of restenosis by increasing VEGF165 expression in local vessels. Therefore, the pompon-like MGI dendrimer may be a promising vector candidate for efficient gene delivery in vivo.

Study of relaxation process of dipalmitoyl phosphatidylcholine monolayers at air-water interface: effect of electrostatic energy

The instability of organic monolayer composed of polar molecules at the air-water interface has been a spotlight in interface science for many decades. However, the effect of electrostatic energy contribution to the free energy in the system is still not understood. Herein, we investigate the mechanical and electrical properties by studying the isobaric relaxation process of a dipalmitoyl phosphatidylcholine monolayer on water subphase with various concentrations of divalent ions to reveal the effect of electrostatic energy on thermodynamics and kinetics of the collapse mechanism. Our results demonstrate that electrical energy among the dipolar molecules plays an important role in the stability of monolayer and enhances the formation of micelles into subphase under high pressure. In addition, to confirm the electrostatic energy contribution, the well-known thermal effect on the stability of the film is compared. Hence, the general description of the monolayer free energy with contribution of electrostatic energy is suggested to describe the phase transition.

Liposomal nanomedicine for breast cancer therapy

Liposomes are well-established nanocarriers for improving the therapeutic index of anticancer agents. A remarkable understanding in the pathophysiology of breast cancer progression has emerged with information on the involved specific biomolecules, which may serve as molecular targets for its therapy. Hormonal and nonhormonal receptors can both be exploited for targeting to breast cancer cells. Targeted delivery of cytotoxic drugs using liposomes is a novel approach for breast cancer therapy. In the present article, we summarize molecular targets present on the breast cancer cells. Recent developments in liposome-based delivery of bioactives for selective treatments of breast cancer are discussed. In addition, utilization of bioenvironmental conditions of tumor for liposome-based targeted delivery is also summed up.

Fliposomes: pH-Sensitive Liposomes Containing a trans-2-morpholinocyclohexanol-Based Lipid That Performs a Conformational Flip and Triggers an Instant Cargo Release in Acidic Medium

Incorporation of a pH-sensitive conformational switch into a lipid structure enables a drastic conformational flip upon protonation that disrupts the liposome membrane and causes rapid release of cargo specifically in areas of increased acidity. pH-sensitive liposomes containing the amphiphile (1) with trans-2-morpholinocyclohexanol conformational switch, a phospholipid, and a PEG-lipid conjugate were constructed and characterized. The optimized composition—1/POPC/PEG-ceramide (50/4/5)—could be stored at 4 °C and pH 7.4 for up to 1.5 years, and was stable in blood serum in vitro after 48 h at 37 °C. Liposomes loaded with ANTS/DPX or methotrexate demonstrated an unusually quick content release (in a few seconds) at pH below 5.5, which was independent of inter-liposome contact. The pH-titration curve for the liposome leakage paralleled the curve for the acid-induced conformational flip of 1 studied by ¹H-NMR. Freeze-fracture electron microscopy images showed budding and division of the bilayer at pH 5.5. A plausible mechanism of pH-sensitivity involves an acid-triggered conformational flip of 1, shortening of lipid tails, and membrane perturbations, which cause the content leakage. The methotrexate-loaded liposomes demonstrated much higher cytotoxicity in HeLa cells than the free drug indicating that they can serve as viable drug delivery systems.

Poly(β-amino ester)-DNA complexes: time-resolved fluorescence and cellular transfection studies

A large number of different polymers have been developed and studied for application as DNA carriers for non-viral gene delivery, but the DNA binding properties are not understood. This study describes the efficiency of nanoparticle formation by time-resolved fluorescence measurements for poly(β-amino esters), cationic biodegradable polymers with DNA complexation and transfection capability. From the large library of poly(β-amino esters) ten polymers with different transfection efficacies were chosen for this study. The binding constants for nanoparticle formation were determined and compared to with the same method. Although the DNA binding efficiency of the amine groups are similar for both types of polymers, the overall binding constants are an order of magnitude smaller for poly(β-amino esters) than for 25 kDa polyethylenimines, yet poly(β-amino esters) show comparable DNA transfection efficacy with polyethylenimines. Within this series of polymers the transfection efficacy showed increasing trend in association with relative efficiency of nanoparticle formation.

Lipid substitution on low molecular weight (0.6-2.0 kDa) polyethylenimine leads to a higher zeta potential of plasmid DNA and enhances transgene expression

Cationic polymers are desirable gene carriers because of their better safety profiles than viral delivery systems. Low molecular weight (MW) polymers are particularly attractive, since they display little cytotoxicity, but they are also ineffective for gene delivery. To create effective carriers from low MW polymers palmitic acid (PA) was substituted on 0.6-2.0 kDa polyethylenimines (PEIs) and their efficiency for plasmid DNA (pDNA) delivery was evaluated. The extent of lipid substitution was dependent on the lipid/PEI feed ratio and the polymer MW. While the hydrodynamic size of the polymer/pDNA complexes (polyplexes) increased or decreased depending on the extent of lipid substitution, the ζ potential of the assembled complexes was consistently higher as a result of lipid substitution. Lipid substitution generally increased the in vitro toxicity of the PEIs, but it was significantly lower than that of the 25 kDa branched PEI. The in vitro transfection efficiency of the lipid-substituted polymers was higher than that of native PEIs, which were not at all effective. The delivery efficiency was proportional to the extent of lipid substitution as well as the polymer MW. This correlated with the increased uptake of lipid-substituted polyplexes, based on confocal microscopic investigations with FITC-labeled pDNA. The addition of chloroquine further increased the transfection efficiency of lipid-substituted PEIs, indicating that endosomal release was a limiting factor affecting the efficiency of these carriers. This study indicates that lipid substitution on low MW PEIs makes their assembly more effective, resulting in better delivery of pDNA into mammalian cells.

A review on composite liposomal technologies for specialized drug delivery

The combination of liposomes with polymeric scaffolds could revolutionize the current state of drug delivery technology. Although liposomes have been extensively studied as a promising drug delivery model for bioactive compounds, there still remain major drawbacks for widespread pharmaceutical application. Two approaches for overcoming the factors related to the suboptimal efficacy of liposomes in drug delivery have been suggested. The first entails modifying the liposome surface with functional moieties, while the second involves integration of pre-encapsulated drug-loaded liposomes within depot polymeric scaffolds. This attempts to provide ingenious solutions to the limitations of conventional liposomes such as short plasma half-lives, toxicity, stability, and poor control of drug release over prolonged periods. This review delineates the key advances in composite technologies that merge the concepts of depot polymeric scaffolds with liposome technology to overcome the limitations of conventional liposomes for pharmaceutical applications.

Gene therapy in HIV-infected cells to decrease viral impact by using an alternative delivery method

The ability of dendrimer 2G-[Si{O(CH(2))(2)N(Me)(2) (+)(CH(2))(2)NMe(3) (+)(I(-))(2)}](8) (NN16) to transfect a wide range of cell types, as well as the possible biomedical application in direct or indirect inhibition of HIV replication, was investigated. Cells implicated in HIV infection such as primary peripheral blood mononuclear cells (PBMC) and immortalized suspension cells (lymphocytes), primary macrophages and dendritic cells, and immortalized adherent cells (astrocytes and trophoblasts) were analyzed. Dendrimer toxicity was evaluated by mitochondrial activity, cell membrane rupture, release of lactate dehydrogenase, erythrocyte hemolysis, and the effect on global gene expression profiles using whole-genome human microarrays. Cellular uptake of genetic material was determined using flow cytometry and confocal microscopy. Transfection efficiency and gene knockdown was investigated using dendrimer-delivered antisense oligonucleotides and small interfering RNA (siRNA). Very little cytotoxicity was detected in a variety of cells relevant to HIV infection and erythrocytes after NN16 dendrimer treatment. Imaging of cellular uptake showed high transfection efficiency of genetic material in all cells tested. Interestingly, NN16 further enhanced the reduction of HIV protein 24 antigen release by antisense oligonucleotides due to improved transfection efficiency. Finally, the dendrimer complexed with siRNA exhibited therapeutic potential by specifically inhibiting cyclooxygenase-2 gene expression in HIV-infected nervous system cells. NN16 dendrimers demonstrated the ability to transfect genetic material into a vast array of cells relevant to HIV pathology, combining high efficacy with low toxicity. These results suggest that NN16 dendrimers have the potential to be used as a versatile non-viral vector for gene therapy against HIV infection.

Poly(α-glutamic acid) combined with polycation as serum-resistant carriers for gene delivery

The transfection efficiency of cationic polymers decreases dramatically in the presence of serum, which hampers the in vivo application of these polymers for gene delivery. Due to its shielding effect of poly(alpha-glutamic acid) (PGA) from negatively charged serum proteins, it was introduced into DNA polyplexes to overcome the serum inhibitory effect. In the present studies, the transfection efficiency of DNA/PEI/PGA terplex system was compared to PEI 25 kDa and Lipofectamine 2000 in the presence of serum. The successful formation of DNA/PEI/PGA terplexes was confirmed by their near-neutral surface charge. Interaction between components in the terplex system demonstrated that PGA was competing with DNA to combine with PEI. PEI/PGA combined carriers were not cytotoxic at a C/N ratio higher than 0.3. The in vitro transfection efficiency of DNA/PEI/PGA terplexes was not significantly different from those of DNA/PEI25kDa in serum-free medium. Importantly, in serum-containing medium, the DNA terplexes at their optimal C/N ratios maintained the same level of transfection efficiency as that of serum-free medium, even though the transfection efficiency of PEI 25 kDa and Lipofectamine 2000 was significantly decreased under serum-containing conditions. CLSM results confirmed that the cellular import of pDNA delivered by PEI/PGA combined carriers was more efficient than PEI 25 kDa alone under serum-containing conditions. Therefore, PGA could be used as a versatile serum-resistant reagent to overcome the serum inhibitory effect of polycations for gene delivery.

Interaction of DNA/nuclear protein/polycation and the terplexes for gene delivery

Nuclear transport of exogenous DNA is a major barrier to nonviral gene delivery that needs to be addressed in the design of new vectors. In this study, we prepared pDNA/HMGB1/PEG-PEI terplexes to promote nuclear import. HMGB1 in the terplexes was used to assist the transportation of pDNA into the nucleus of cells, since it contained nuclear localization signal (NLS); PEG chains were introduced to stabilize pDNA/vector terplexes and reduce the cytotoxicity. HMGB1/PEG-PEI combined vectors have been investigated specifically for their structure interaction by atomic force microscopy and circular dichroic spectroscopy. The results demonstrated that the HMGB1 molecule could bind with the pDNA chains, but not condense pDNA well. The PEG-PEI further compacted pDNA/HMGB1 complexes into nanosized spherical terplexes. The pDNA delivered by HMGB1/PEG-PEI combined vectors was significantly accumulated in the nucleus of cells, as observed by confocal laser scanning microscopy. The percentage of GFP-transfected cells and VEGF protein expression level induced by HMGB1/PEG-PEI were 2.6-4.9-fold and 1.4-2.8-fold higher, respectively, than that of a common cationic polymer PEI 25 kDa. Therefore, the HMGB1/PEG-PEI combined vector could be used as a versatile vector for promoting exogenous DNA nuclear localization, thereby enhancing its expression.

Dendritic poly(L-lysine)-b-Poly(L-lactide)-b-dendritic poly(L-lysine) amphiphilic gene delivery vectors: roles of PLL dendritic generation and enhanced transgene efficacies via termini modification

As an effort to prepare new efficient gene delivery vectors, we have recently developed and reported an amphiphilic dendritic poly(L-lysine)-b-poly(L-lactide)-b-dendritic poly(L-lysine) D(2)-PLLA-D(2) with two-generation PLL dendrons and a PLLA block. In this work, we continued to explore the roles of dendritic PLL generation in DNA binding and intracellular delivery of gene, and a new series of amphiphilic dendritic poly(L-lysine)-b-poly(L-lactide)-b-dendritic poly(L-lysine)s D(n)-PLLA-D(n) (n = 3-5) were synthesized and were structurally characterized. Furthermore, plasmid DNA binding affinity for these cationic amphiphiles was examined by agarose gel electrophoresis and fluorescence titration assay in pure water and PBS buffer solution containing 150 mM NaCl (pH = 7.4), respectively. By dynamic light scattering (DLS) and transmission electronic microscopy (TEM), the interaction and complexation in between were investigated, concerning the DNA/vector polyplex particle morphologies and zeta potentials. Utilizing a human hepatocellular carcinoma cell-line SMMC-7721, cell toxicity, and gene transfection in vitro were explored. To further improve transgene efficiency for these synthetic cationic amphiphiles as gene delivery vectors, new structural DE(n)-PLLA-DE(n) (n = 2-3) were prepared through an amino termini modification of the D(n)-PLLA-D(n) (n = 2-3) with less toxic 4,7,10,13-tetraazatridecanoic acids, and gene transfection with these DE(n)-PLLA-DE(n) (n = 2-3) was examined with an alternative human gastric carcinoma cell-line HGC-27. As a result, the high plasmid DNA binding affinity, low cytotoxicity, and much enhanced transgene efficacy suggest a new possible clue to design effective synthetic gene delivery vectors with amphiphilic skeleton and less toxic polyamine building blocks.

Layered double hydroxide nanoparticles in gene and drug delivery

Layered double hydroxides (LDHs) have been known for many decades as catalyst and ceramic precursors, traps for anionic pollutants, catalysts and additives for polymers, but their successful synthesis on the nanometer scale a few years ago opened up a whole new field for their application in nanomedicine. The delivery of drugs and other therapeutic/bioactive molecules (e.g., peptides, proteins, nucleic acids) to mammalian cells is an area of research that is of tremendous importance to medicine and provides manifold applications for any new developments in the area of nanotechnology. Among the many different nanoparticles that have been shown to facilitate gene and/or drug delivery, LDH nanoparticles have attracted particular attention owing to their many desirable properties. This review aims to report recent progress in gene and drug delivery using LDH nanoparticles. It summarizes the advantages and disadvantages of using LDH nanoparticles as carriers for nucleic acids and drugs against the general background of bottlenecks that are encountered by cellular delivery systems. It describes further the models that have been proposed for the internalization of LDH nanoparticles into cells so far and discusses the intracellular fate of the particles and their cargo. The authors offer some remarks on how this field of research will progress in the near future and which challenges need to be overcome before LDH nanoparticles can be used in a clinical setting.

Antisense applications for biological control

Although Nature's antisense approaches are clearly impressive, this Perspectives article focuses on the experimental uses of antisense reagents (ASRs) for control of biological processes. ASRs comprise antisense oligonucleotides (ASOs), and their catalytically active counterparts ribozymes and DNAzymes, as well as small interfering RNAs (siRNAs). ASOs and ribozymes/DNAzymes target RNA molecules on the basis of Watson-Crick base pairing in sequence-specific manner. ASOs generally result in destruction of the target RNA by RNase-H mediated mechanisms, although they may also sterically block translation, also resulting in loss of protein production. Ribozymes and DNAzymes cleave target RNAs after base pairing via their antisense flanking arms. siRNAs, which contain both sense and antisense regions from a target RNA, can mediate target RNA destruction via RNAi and the RISC, although they can also function at the transcriptional level. A considerable number of ASRs (mostly ASOs) have progressed into clinical trials, although most have relatively long histories in Phase I/II settings. Clinical trial results are surprisingly difficult to find, although few ASRs appear to have yet established efficacy in Phase III levels. Evolution of ASRs has included: (a) Modifications to ASOs to render them nuclease resistant, with analogous modifications to siRNAs being developed; and (b) Development of strategies to select optimal sites for targeting. Perhaps the biggest barrier to effective therapies with ASRs is the "Delivery Problem." Various liposomal vehicles have been used for systemic delivery with some success, and recent modifications appear to enhance systemic delivery, at least to liver. Various nanoparticle formulations are now being developed which may also enhance delivery. Going forward, topical applications of ASRs would seem to have the best chances for success. In summary, modifications to ASRs to enhance stability, improve targeting, and incremental improvements in delivery vehicles continue to make ASRs attractive as molecular therapeutics, but their advance toward the bedside has been agonizingly slow.

Facile approach for DNA encapsulation in functional polyion complex for triggered intracellular gene delivery: design, synthesis, and mechanism

A facile route for DNA encapsulation in triggered intracellular degradable polymer microcapsules has been achieved via electrostatic interaction, using a polycation, that is, poly[(dimethylamino)ethyl methacrylate] end-capped with cholesterol moiety (Chol-PDMAEMA(30)), along with a polyanion named MePEG2000-block-poly(methacrylic acid) carring partial thiol groups (MePEG2000-b-PMAA(SH)). The encapsulation procedure involves three steps: (i) DNA was first complexed with the polycation (Chol-PDMAEMA(30)); (ii) the complex was then further set into interaction with the anion-containing MePEG2000-b-PMAA(SH); and (iii) the compound carrier was subsequently obtained by cross-linking the thiol groups of the MePEG2000-b-PMAA(SH) to form disulfide linkages. The interactions between every pair among calf thymus DNA, Chol-PDMAEMA(30), and MePEG2000-b-PMAA(SH) were studied by agarose gel retardation assay and ethidium bromide displacement assay. The results indicate that the prepared microcapsules may remain stable during systemic circulation, but degrade and release the carried DNA in a cellular reducing environment. Furthermore, the biophysical properties of the microcapsule have been investigated by zeta-potential, laser light scattering, and transmission electron microscopy (TEM) measurements.