Pyridinium cationic lipids in gene delivery: an in vitro and in vivo comparison of transfection efficiency versus a tetraalkylammonium congener

A systematic study of the effect of lipid architecture on cytotoxicity and cellular uptake of cationic cubosomes

HYPOTHESIS

Lipid nanoparticles containing a cationic lipid are increasingly used in drug and gene delivery as they can display improved cellular uptake, enhanced loading for anionic cargo such as siRNA and mRNA or exhibit additional functionality such as cytotoxicity against cancer cells. This research study tests the hypothesis that the molecular structure of the cationic lipid influences the structure of the lipid nanoparticle, the cellular uptake, and the resultant cytotoxicity.

EXPERIMENTS

Three potentially cytotoxic cationic lipids, with systematic variations to the hydrophobic moiety, were designed and synthesised. All the three cationic lipids synthesised contain pharmacophores such as the bicyclic coumarin group (CCA12), the tricyclic etodolac moiety (ETD12), or the large pentacyclic triterpenoid "ursolic" group (U12) conjugated to a quaternary ammonium cationic lipid containing twin C12 chains. The cationic lipids were doped into monoolein cubosomes at a range of concentrations from 0.1 mol% to 5 mol% and the effect of the lipid molecular architecture on the cubosome phase behaviour was assessed using a combination of Small Angle X-Ray Scattering (SAXS), Dynamic Light Scattering (DLS), zeta-potential and cryo-Transmission Electron Microscopy (Cryo-TEM). The resulting cytotoxicity of these particles against a range of cancerous and non-cancerous cell-lines was assessed, along with their cellular uptake.

FINDINGS

The molecular architecture of the cationic lipid was linked to the internal nanostructure of the resulting cationic cubosomes with a transition to more curved cubic and hexagonal phases generally observed. Cubosomes formed from the cationic lipid CCA12 were found to have improved cellular uptake and significantly higher cytotoxicity than the cationic lipids ETD12 and U12 against the gastric cancer cell-line (AGS) at lipid concentrations ≥ 75 µg/mL. CCA12 cationic cubosomes also displayed reasonable cytotoxicity against the prostate cancer PC-3 cell-line at lipid concentrations ≥ 100 µg/mL. In contrast, 2.5 mol% ETD12 and 2.5 mol% U12 cubosomes were generally non-toxic against both cancerous and non-cancerous cell lines over the entire concentration range tested. The molecular architecture of the cationic lipid was found to influence the cubosome phase behaviour, the cellular uptake and the toxicity although further studies are necessary to determine the exact relationship between structure and cellular uptake across a range of cell lines.

Recent Advances in Engineering Carriers for siRNA Delivery

RNA interference (RNAi) technology has been a promising treatment strategy for combating intractable diseases. However, the applications of RNAi in clinical are hampered by extracellular and intracellular barriers. To overcome these barriers, various siRNA delivery systems have been developed in the past two decades. The first approved RNAi therapeutic, Patisiran (ONPATTRO) using lipids as the carrier, for the treatment of amyloidosis is one of the most important milestones. This has greatly encouraged researchers to work on creating new functional siRNA carriers. In this review, the recent advances in siRNA carriers consisting of lipids, polymers, and polymer-modified inorganic particles for cancer therapy are summarized. Representative examples are presented to show the structural design of the carriers in order to overcome the delivery hurdles associated with RNAi therapies. Finally, the existing challenges and future perspective for developing RNAi as a clinical modality will be discussed and proposed. It is believed that the addressed contributions in this review will promote the development of siRNA delivery systems for future clinical applications.

Lipid-based nucleic acid therapeutics with in vivo efficacy

Synthetic vectors for therapeutic nucleic acid delivery are currently competing significantly with their viral counter parts due to their reduced immunogenicity, large payload capacity, and ease of manufacture under GMP-compliant norms. The approval of Onpattro, a lipid-based siRNA therapeutic, and the proven clinical success of two lipid-based COVID-19 vaccines from Pfizer-BioNTech, and Moderna heralded the specific advantages of lipid-based systems among all other synthetic nucleic acid carriers. Lipid-based systems with diverse payloads-plasmid DNA (pDNA), antisense oligonucleotide (ASO), small interfering RNA (siRNA), microRNA (miRNA), small activating RNA (saRNA), and messenger RNA (mRNA)-are now becoming a mature technology, with growing impact in the clinic. Research over four decades identified the key factors determining the therapeutic success of these multi-component systems. Here, we discuss the main nucleic acid-based technologies, presenting their mechanism of action, delivery barriers facing them, the structural properties of the payload as well as the component lipids that regulate physicochemical properties, pharmacokinetics and biodistribution, efficacy, and toxicity of the resultant nanoparticles. We further detail on the formulation parameters, evolution of the manufacturing techniques that generate reproducible and scalable outputs, and key manufacturing aspects that enable control over physicochemical properties of the resultant particles. Preclinical applications of some of these formulations that were successfully translated from in vitro studies to animal models are subsequently discussed. Finally, clinical success and failure of these systems starting from 1993 to present are highlighted, in a holistic literature review focused on lipid-based nucleic acid delivery systems. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

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.

Evaluation of Physicochemical Properties of Amphiphilic 1,4-Dihydropyridines and Preparation of Magnetoliposomes

This study was focused on the estimation of the targeted modification of 1,4-DHP core with (1) different alkyl chain lengths at 3,5-ester moieties of 1,4-DHP (C₁₂, C₁₄ and C₁₆); (2) N-substituent at position 1 of 1,4-DHP (N-H or N-CH₃); (3) substituents of pyridinium moieties at positions 2 and 6 of 1,4-DHP (H, 4-CN and 3-Ph); (4) substituent at position 4 of 1,4-DHP (phenyl and napthyl) on physicochemical properties of the entire molecules and on the characteristics of the obtained magnetoliposomes formed by them. It was shown that thermal behavior of the tested 1,4-DHP amphiphiles was related to the alkyl chains length, the elongation of which decreased their transition temperatures. The properties of 1,4-DHP amphiphile monolayers and their polar head areas were determined. The packing parameters of amphiphiles were in the 0.43–0.55 range. It was demonstrated that the structure of 1,4-DHPs affected the physicochemical properties of compounds. “Empty” liposomes and magnetoliposomes were prepared from selected 1,4-DHP amphiphiles. It was shown that the variation of alkyl chains length or the change of substituents at positions 4 of 1,4-DHP did not show a significant influence on properties of liposomes.

Improvement of DNA Vector Delivery of DOTAP Lipoplexes by Short-Chain Aminolipids

Cellular delivery of DNA vectors for the expression of therapeutic proteins is a promising approach to treat monogenic disorders or cancer. Significant efforts in a preclinical and clinical setting have been made to develop potent nonviral gene delivery systems based on lipoplexes composed of permanently cationic lipids. However, transfection efficiency and tolerability of such systems are in most cases not satisfactory. Here, we present a one-pot combinatorial method based on double-reductive amination for the synthesis of short-chain aminolipids. These lipids can be used to maximize the DNA vector delivery when combined with the cationic lipid 1,2-dioleoyl-3-trimethylammonium propane (DOTAP). We incorporated various aminolipids into such lipoplexes to complex minicircle DNA and screened these systems in a human liver-derived cell line (HuH7) for gene expression and cytotoxicity. The lead aminolipid AL-A12 showed twofold enhanced gene delivery and reduced toxicity compared to the native DOTAP:cholesterol lipoplexes. Moreover, AL-A12-containing lipoplexes enabled enhanced transgene expression in vivo in the zebrafish embryo model.

Structure-function relationships of nonviral gene vectors: Lessons from antimicrobial polymers

In recent years, substantial advances have been achieved in the design and synthesis of nonviral gene vectors. However, lack of effective and biocompatible vectors still remains a major challenge that hinders their application in clinical settings. In the past decade, there has been a rapid expansion of cationic antimicrobial polymers, due to their potent, rapid, and broad-spectrum biocidal activity against resistant microbes, and biocompatible features. Given that antimicrobial polymers share common features with nonviral gene vectors in various aspects, such as membrane affinity, functional groups, physicochemical characteristics, and unique macromolecular architectures, these polymers may provide us with inspirations to overcome challenges in the design of novel vectors toward more safe and efficient gene delivery in clinic. Building off these observations, we provide here an overview of the structure-function relationships of polymers for both antimicrobial applications and gene delivery by elaborating some key structural parameters, including functional groups, charge density, hydrophobic/hydrophilic balance, MW, and macromolecular architectures. By borrowing a leaf from antimicrobial agents, great advancement in the development of newer nonviral gene vectors with high transfection efficiency and biocompatibility will be more promising. STATEMENT OF SIGNIFICANCE: The development of gene delivery is still in the preclinical stage for the lack of effective and biocompatible vectors. Given that antimicrobial polymers share common features with gene vectors in various aspects, such as membrane affinity, functional groups, physicochemical characteristics, and unique macromolecular architectures, these polymers may provide us with inspirations to overcome challenges in the design of novel vectors toward more safe and efficient gene delivery in clinic. In this review, we systematically summarized the structure-function relationships of antimicrobial polymers and gene vectors, with which the design of more advanced nonviral gene vectors is anticipated to be further boosted in the future.

Transfection by cationic gemini lipids and surfactants

Diseases that are linked to defective genes or mutations can in principle be cured by gene therapy, in which damaged or absent genes are either repaired or replaced by new DNA in the nucleus of the cell. Related to this, disorders associated with elevated protein expression levels can be treated by RNA interference via the delivery of siRNA to the cytoplasm of cells. Polynucleotides can be brought into cells by viruses, but this is not without risk for the patient. Alternatively, DNA and RNA can be delivered by transfection, i.e. by non-viral vector systems such as cationic surfactants, which are also referred to as cationic lipids. In this review, recent progress on cationic lipids as transfection vectors will be discussed, with special emphasis on geminis, surfactants with 2 head groups and 2 tails connected by a spacer.

Pyridinium salts: from synthesis to reactivity and applications

This review highlights the pyridinium salts in terms of their natural occurrence, synthesis, reactivity, biological properties, and diverse applications.

Next-Generation Lipids in RNA Interference Therapeutics

RNA is emerging as a potential therapeutic modality for the treatment of incurable diseases. Despite intense research, the advent to clinical utility remains compromised by numerous biological barriers, hence, there is a need for sophisticated delivery vehicles. In this aspect, lipid nanoparticles (LNPs) are the most advanced platform among nonviral vectors for gene delivery. In this review, we critically review the literature and the reasons for ineffective delivery beyond the liver. We discuss the toxicity issues associated with permanently charged cationic lipids and then turn our attention to next-generation ionizable cationic lipids. These lipids exhibit reduced toxicity and immunogenicity and undergo ionization under the acidic environment of the endosome to release the encapsulated payload to their site of action in the cytosol. Finally, we summarize recent achievements in therapeutic nucleic acid delivery and report on the current status of clinical trials using LNP and the obstacles to clinical translation.

Bridging small interfering RNA with giant therapeutic outcomes using nanometric liposomes

The scope of RNAi based therapeutics is unquestionable. However, if we dissect the current trend of clinical trials for afore mentioned drug class, some stark trends appear: 1) naked siRNA only exerts influence in topical mode whilst systemic delivery requires a carrier and 2) even after two decades of extensive efforts, not even a single siRNA containing product is commercially available. It was therefore felt that a perspective simplifying the unique intricacies of working with a merger of siRNA and liposomes from a pharmaceutical viewpoint could draw the attention of a wider array of interested researchers. We begin from the beginning and attempt to conduit the gap between theoretical logic and experimental/actual constraints. This, in turn could stimulate the next generation of investigators, gearing them to tackle the conundrum, which is siRNA delivery.

Heterocyclic amine-modified polyethylenimine as gene carriers for transfection of mammalian cells

Branched polyethylenimine (PEI) is extensively used as a polycationic non-viral vector for gene delivery. Polyplexes formed with PEI are believed to be released from endocytotic vesicles by the osmotic burst mechanism in the rate-limiting step in transfection. Increasing the buffering capacity of PEI derivatives in the endosomal pH range of 4.5-7.5 should enhance transfection efficiency. In this study, PEI was derivatized by covalently attaching heterocyclic amine moieties (piperazine, pyridine and imidazole rings with pKa values from 5.23 to 6.04) through amide bonds. PEI derivatives with 50% of the primary amines on PEI exhibited increased buffering capacity, increased transfection activity and decreased cytotoxicity in murine neuroblastoma (Neuro-2a) cells. The relative effectiveness in enhancing transfection efficiency was piperazine>pyridine>histidine, but each type of amine was the most effective under a particular set of conditions. Modified vectors could significantly improve transfection efficiency in murine mesenchymal stem cells. PEI25 derivatized at 50% with histidine administered as polyplexes in the tail veins of mice resulted in remarkably enhanced luciferase gene expression in the expected organ distribution and much lower toxicity than underivatized PEI25.

Structure-transfection activity relationships in a series of novel cationic lipids with heterocyclic head-groups

Cationic liposomes are promising candidates for the delivery of various therapeutic nucleic acids. Here, we report a convenient synthesis of carbamate-type cationic lipids with various hydrophobic domains (tetradecanol, dialkylglycerol, cholesterol) and positively charged head-groups (pyridinium, N-methylimidazolium, N-methylmorpholinium) and data on the structure-transfection activity relationships. It was found that single-chain lipids possess high surface activity, which correlates with high cytotoxicity due to their ability to disrupt the cellular membrane by combined hydrophobic and electrostatic interactions. Liposomes containing these lipids also display high cytotoxicity with respect to all cell lines. Irrespective of chemical structures, all cationic lipids form liposomes with similar sizes and surface potentials. The characteristics of complexes composed of cationic liposomes and nucleic acids depend mostly on the type of nucleic acid and P/N ratios. In the case of oligodeoxyribonucleotide delivery, the transfection activity depends on the type of cationic head-group regardless of the type of hydrophobic domain: all types of cationic liposomes mediate efficient oligonucleotide transfer into 80-90% of the eukaryotic cells, and liposomes based on lipids with N-methylmorpholinium cationic head-group display the highest transfection activity. In the case of plasmid DNA and siRNA, the type of hydrophobic domain determines the transfection activity: liposomes composed of cholesterol-based lipids were the most efficient in DNA transfer, while liposomes containing glycerol-based lipids exhibited reasonable activity in siRNA delivery under serum-free conditions.

Modulation of pyridinium cationic lipid-DNA complex properties by pyridinium gemini surfactants and its impact on lipoplex transfection properties

The study presents the effects of blending a cationic gemini surfactant into cationic lipid bilayers and its impact on the plasmid DNA compaction and delivery process. Using nanoDSC, dynamic light scattering, zeta potential, and electrophoretic mobility measurements, together with transfection (2D- and 3D-) and viability assays, we identified the main physicochemical parameters of the lipid bilayers, liposomes, and lipoplexes that are affected by the gemini surfactant addition. We also correlated the cationic bilayer composition with the dynamics of the DNA compaction process and with transfection efficiency, cytotoxicity, and the internalization mechanism of the resultant nucleic acid complexes. We found that the blending of gemini surfactant into the cationic bilayers fluidized the supramolecular assemblies, reduced the amount of positive charge required to fully compact the plasmid DNA and, in certain cases, changed the internalization mechanism of the lipoplexes. The transfection efficiency of select ternary lipoplexes derived from cationic gemini surfactants and lipids was several times superior to the transfection efficiency of corresponding binary lipoplexes, also surpassing standard transfection systems. The overall impact of gemini surfactants into the formation and dynamic of cationic bilayers was found to depend heavily on the presence of colipids, their nature, and amount present in lipoplexes. The study confirmed the possibility of combining the specific properties of pyridinium gemini surfactants and cationic lipids synergistically to obtain efficient synthetic transfection systems with negligible cytotoxicity useful for therapeutic gene delivery.

Aspects of nonviral gene therapy: correlation of molecular parameters with lipoplex structure and transfection efficacy in pyridinium-based cationic lipids

This study seeks correlations between the molecular structures of cationic and neutral lipids, the lipid phase behavior of the mixed-lipid lipoplexes they form with plasmid DNA, and the transfection efficacy of the lipoplexes. Synthetic cationic pyridinium lipids were co-formulated (1:1) with the cationic lipid 1,2-dimyristoyl-sn-glycero-3-ethylphosphocholine (EPC), and these lipids were co-formulated (3:2) with the neutral lipids 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) or cholesterol. All lipoplex formulations exhibited plasmid DNA binding and a level of protection from DNase I degradation. Composition-dependent transfection (beta-galactosidase and GFP) and cytotoxicity was observed in Chinese hamster ovarian-K1 cells. The most active formulations containing the pyridinium lipids were less cytotoxic but of comparable activity to a Lipofectamine 2000™ control. Molecular structure parameters and partition coefficients were calculated for all lipids using fragment additive methods. The derived shape parameter values correctly correlated with observed hexagonal lipid phase behavior of lipoplexes as derived from small-angle X-ray scattering experiments. A transfection index applicable to hexagonal phase lipoplexes derived from calculated parameters of the lipid mixture (partition coefficient, shape parameter, lipoplex packing) produced a direct correlation with transfection efficiency.

Overcoming nonviral gene delivery barriers: perspective and future

A key end goal of gene delivery research is to develop clinically relevant vectors that can be used to combat elusive diseases such as AIDS. Despite promising engineering strategies, efficiency and ultimately gene modulation efficacy of nonviral vectors have been hindered by numerous in vitro and in vivo barriers that have resulted in subviral performance. In this perspective, we concentrate on the gene delivery barriers associated with the two most common classes of nonviral vectors, cationic-based lipids and polymers. We present the existing delivery barriers and summarize current vector-specific strategies to overcome said barriers.

Benzothiazole head group based cationic lipids: synthesis and application for gene delivery

A series of benzothiazole based lipids (1-10) containing different derivatives of benzothiazole in the head group region were synthesized to determine the structure-activity relationship for gene delivery. The liposomes formulated were mixed with plasmid DNA encoding green fluorescent protein (α5GFP) or β-galactosidase (pCMV-SPORT-β-gal) and transfected into B16F10 (Human melanoma cancer cells), CHO (Chinese hamster ovary), A-549 (Human lung carcinoma cells) and MCF-7 (Human breast carcinoma cells) types of cell lines. The efficiencies of lipids 9 and 10 in particular, were found to be comparable and even more when compared to that of LipofectAmine-2000. The transfection profiles of the efficient lipids are proved to be maintained even in the presence of serum. Thus, the benzothiazole head group based lipids developed have the potential to be used as transfection reagents in vitro and in vivo.

Tuning the self-assembling of pyridinium cationic lipids for efficient gene delivery into neuronal cells

We are reporting a new set of biocompatible, low-toxicity pyridinium cationic lipids based on a dopamine backbone on which hydrophobic alkyl tails are attached via an ether linkage. Due to their optimized hydrophilic/hydrophobic interface and packing parameter, the new lipids are able to strongly self-assemble either alone or when coformulated with colipids DOPE or cholesterol. The supra-molecular assemblies generated with the novel pyridinium amphiphiles were characterized in bulk and in solution via a combination of techniques including DSC, nanoDSC, SAXS, TOPM, TEM, DLS, zeta potential, and electrophoretic mobility measurements. These cationic bilayers can efficiently condense and deliver DNA to a large variety of cell lines, as proven by our self-assembling/physicochemical/biological correlation study. Using the luciferase reporter gene plasmid, we have also conducted a comprehensive structure-activity relationship study, which identified the best structural parameters and formulations for efficient and nontoxic gene delivery. Several formulations greatly surpassed established transfection systems with proved in vitro and in vivo efficiency, being able to transfect a large variety of malignant cells even in the presence of elevated levels of serum. The most efficient formulation was able to transfect selectively primary rat dopaminergic neurons harvested from nucleus accumbens, and neurons from the frontal cortex, a premise that recommends these synthetic vectors for future in vivo delivery studies for neuronal reprogramming.

Effects of molecular weight and pyridinium moiety on water-soluble chitosan derivatives for mediated gene delivery

The aim of this study is to investigate the effects of molecular weight, the pyridinium/trimethyl ammonium (Py/Tr) ratio, the nitrogen atoms (N) in the methylated N-(3-pyridylmethyl) chitosan chloride (M3-PyMeChC)/the phosphorus atoms (P) in DNA (N/P) ratio, and the physicochemical properties of nanopolyplexes on transfection efficiency. The water-soluble chitosan derivative, M3-PyMeChC, was used as a non-viral vector to deliver pEGFP-C2 into human hepatoma (Huh7) cell lines. The results revealed that higher molecular weight M3-PyMeChC was able to form complexes completely with DNA at lower N/P ratios than that with lower molecular weights, which led to higher transfection efficiency. Moreover, the M3-PyMeChC with higher Py/Tr ratios showed superior transfection efficiency at lower Py/Tr ratios at all N/P ratios studied. The highest transfection efficiency for the nanopolyplexes occurred for a molecular weight of 82kDa at a N/P ratio of 5. The results indicated that the hydrophobic effect of pyridinium moiety could enhance gene transfection efficiency, which can be attributed to the dissociation of DNA from nanopolyplexes. High Py/Tr ratios in nanopolyplexes tended to decrease cytotoxicity due to delocalization of positive charge into a pyridine ring while high N/P ratios and molecular weight increased cytotoxicity. Our results showed that the vector was able to spread the positive charge by delocalizing it into a heterocyclic ring, suggesting to a promising approach to mediate higher levels of gene transfection.

High transfection efficiency of cationic lipids with asymmetric acyl-cholesteryl hydrophobic tails

The ability of a nonviral gene delivery system to overcome extra- and intracellular barriers is a critical issue for the future clinical applications of gene therapy. In recent years much effort has been focused on the development of a variety of DNA carriers, and cationic liposomes have become the most common nonviral gene delivery system. One hundred and eighty novel cationic lipids with asymmetric acyl-cholesteryl hydrophobic tails were synthesized by parallel solid-phase chemistry. The liposomes were prepared and gel retardation assays were used to study the binding efficiency between the prepared liposome and the DNA. Transfection efficiencies of the lipids were evaluated against various mammalian cells, such as human embryonic kidney (HEK293), human cervical adenocarcinoma (HeLa), canine osteosarcoma (D17), colorectal adenocarcinoma (COLO 205), and human prostate adenocarcinoma (PC3) cells. The lipids with an acyl portion at the terminal part of the polyamine backbone exhibited higher transfection efficiency than those with the acyl portion as an internal part of the backbone. These compounds also showed higher transfection efficiency and lower cytotoxicity than the commercially available agents, Effectene, DOTAP, and DC-Chol.

Cationic liposome-nucleic acid complexes for gene delivery and silencing: pathways and mechanisms for plasmid DNA and siRNA

Motivated by the promises of gene therapy, there is great interest in developing non-viral lipid-based vectors for therapeutic applications due to their low immunogenicity, low toxicity, ease of production, and the potential of transferring large pieces of DNA into cells. In fact, cationic liposome (CL) based vectors are among the prevalent synthetic carriers of nucleic acids (NAs) currently used in gene therapy clinical trials worldwide. These vectors are studied both for gene delivery with CL-DNA complexes and gene silencing with CL-siRNA (short interfering RNA) complexes. However, their transfection efficiencies and silencing efficiencies remain low compared to those of engineered viral vectors. This reflects the currently poor understanding of transfection-related mechanisms at the molecular and self-assembled levels, including a lack of knowledge about interactions between membranes and double stranded NAs and between CL-NA complexes and cellular components. In this review we describe our recent efforts to improve the mechanistic understanding of transfection by CL-NA complexes, which will help to design optimal lipid-based carriers of DNA and siRNA for therapeutic gene delivery and gene silencing.

Novel cholesterol-based cationic lipids for gene delivery

Gene therapy based on gene delivery is a promising strategy for the treatment of human disease. Here we present data on structure/biological activity of new biodegradable cholesterol-based cationic lipids with various heterocyclic cationic head groups and linker types. Enhanced accumulation of nucleic acids in the cells mediated by the lipids was demonstrated by fluorescent microscopy and flow cytometry. Light scattering and atomic force microscopy were used to find structure/transfection activity correlations for the lipids. We found that the ability of the lipids to stimulate intracellular accumulation of the oligodeoxyribonucleotides and plasmid DNA correlates well with their ability to form in solution lipid/NA complexes of sizes that do not exceed 100 nm. Screening of the lipids revealed the most promising transfection agents both in terms of low toxicity and efficient delivery: cholesterol-based lipids with positively charged pyridine and methyl imidazole head groups and either the ester or carbamate linker.

The role of cholesterol and structurally related molecules in enhancing transfection of cationic liposome-DNA complexes

Motivated by its important role in gene delivery, we have studied the effect of cholesterol and analogs on the transfection efficiency (TE) of lamellar cationic liposome-DNA (CL-DNA) complexes in vitro. Addition of cholesterol to low-transfecting DOTAP/DOPC-DNA complexes increases TE, with 15 mol % cholesterol already yielding 10-fold improvement. Steroids lacking the alkyl tail only modestly enhance TE, while molecules retaining it strongly enhance TE. All steroid-containing CL-DNA complexes exhibit the lamellar structure. The increase in experimentally determined membrane charge density (a universal parameter governing the TE of lamellar CL-DNA complexes) with cholesterol content alone cannot account for the rapid increase of TE. Instead, the reduction of the hydration repulsion layer of the membrane, caused by replacement of DOPC by cholesterol, promotes fusion between cationic membranes of CL-DNA complexes and anionic endosomal membranes, thus facilitating release of complexes and enhancing TE.

Structural and formulation factors influencing pyridinium lipid-based gene transfer

A series of pyridinium lipids containing a heterocyclic ring and a nitrogen atom were synthesized to determine the structure-activity relationship for gene delivery. Pyrylium chloroaluminate was synthesized by monoacylation of mesityl oxide and converted into pyrylium hexafluorophosphate, which was used as the key intermediate for reaction with different primary amines, to yield hydroxyethylpyridinium hexafluorophosphate and aminoethylpyridinium hexafluorophosphate. Acylation of these pyridinium salts with different types of fatty acid chlorides afforded the final pyridinium lipids, which were mixed with a co-lipid, such as L-alpha-dioleoylphosphatidylethanolamine (DOPE) and cholesterol (Chol) to prepare cationic liposomes by sonication. These liposomes were mixed with plasmid DNA encoding enhanced green fluorescent protein (pCMS-EGFP) or luciferase (pcDNA3-Luc) and transfected into Chinese hamster ovary (CHO) cells. Several factors including hydrophobic anchor chain length, anchor chain type, configuration of double bond, linker type, co-lipid type, cationic lipid/co-lipid molar ratio, charge ratio (N/P), and cell type had significant influence on transfection efficiency and cytotoxicity. Pyridinium lipids with amide linker showed significantly higher transfection efficiency compared to their ester counterparts. Liposomes prepared at a 1:1 molar ratio of pyridinium lipid and co-lipid showed higher transfection efficiency when either DOPE or cholesterol was used as a co-lipid to prepare cationic liposomes for complex formation with plasmid DNA at 3:1(+/-) charge ratio. Pyridinium liposomes based on a hydrophobic anchor chain length of 16 showed higher transfection efficiency and lower cytotoxicity. The pyridinium lipid with a trans-configuration of the double bond in the fatty acid chain showed higher transfection efficiency than its counterpart with cis-configuration at the same fatty acid chain length. In the presence of serum, C16:0 and Lipofectamine significantly decreased their transfection efficiencies, which were completely lost at a serum concentration of 30% and higher, while C16:1 trans-isomer still had high transfection efficiency under these conditions. In conclusion, pyridinium lipids showed high transfection efficiency and have the potential to be used as transfection reagents in vitro and in vivo.

In vivotransfection rat small intestine K-cell with pGIP/Ins plasmid by DOTAP liposome

Gene therapies to produce insulin in diabetic patients have been considered for several years. Genetic engineering of ectopic insulin production and secretion in autologous non-beta-cells has been tested in different tissues. Recently, gut K-cells have been shown to express glucokinase, the glucose sensor of pancreatic beta-cells. K-cells are responsible for the secretion of the glucose-dependent insulinotropic peptide (GIP). Transfection of K-cells by a specific plasmid to produce insulin correlated to glucose level is being considered. Cationic liposomes are non-viral gene delivery to lung, spleen, liver and intestinal cells. DOTAP-GIP/Ins plasmid complex was used for transfection of K-cells in vivo. RT-PCR assay of human insulin mRNA revealed that the transfection of insulin gene by DOTAP liposome is an efficient tool. The genetic engineering of ectopic insulin production and secretion in autologous non-beta-cells is an appropriate method. The potential of the transmission of a constructed plasmid, which contains human insulin gene under the control of GIP promoter, to gut K-cells could be considered for treatment of diabetes.

Effect of the hydrocarbon chain and polymethylene spacer lengths on gene transfection efficacies of gemini lipids based on aromatic backbone

Design, syntheses, and gene delivery efficacies of fifteen novel gemini (dimeric) and three monomeric cationic lipids anchored on an aromatic backbone have been described. Each new lipid has been used for liposome formation, and optimal formulations were used to determine the structure-activity correlation of the gene transfection efficacies of these lipids in HeLa and HT1080 cells. The results of the present investigation bring out the effect of hydrocarbon chain lengths and the length of the spacer between the headgroups on gene transfection efficiencies of the cationic gemini lipids based on aromatic backbone. The lipids bearing n-C 14H 29 hydrocarbon chain lengths have been found to be the best transfecting agents compared to their counterparts with n-C 16H 33 and n-C 12H 25 chains in HeLa cells. On the other hand, in HT1080 cells, the lipids based on n-C 12H 25 and n-C 14H 29 chains were found to be more potent transfecting agents than lipids possessing n-C 16H 33 chains. Transmission electron microscopy examination revealed the existence of spherical lipid-DNA complexes.

Design, Synthesis, and in Vitro Gene Delivery Efficacies of Novel Cholesterol-Based Gemini Cationic Lipids and Their Serum Compatibility: A Structure−Activity Investigation

Five cholesterol-based gemini cationic lipids, which differ in the length of the spacer [-(CH2)n-] chain between the head groups, have been synthesized. These lipids are useful as nonviral gene delivery agents, and all cholesterol-based gemini lipids (2a-2e) are better transfecting agents than their monomeric lipid counterpart 1. Transfection efficiency of all the gemini lipids except lipid 2a [-(CH2)3-] was maintained even when the serum was present during the transfection conditions as compared to the monomeric lipid 1, with which a dramatic decrease in transfection efficiency was observed. With the increase in spacer chain length from propanediyl [-(CH2)3-] to pentanediyl [-(CH2)5-], transfection efficiency increased both in the absence and presence of serum. However, transfection efficiency decreased with further increase in the length from the pentanediyl [-(CH2)5-] to the dodecanediyl [-(CH2)12-] spacer. Among these gemini lipids 2c showed the highest transfection activity, which was also greater than that of the commercially available formulation.

RETRACTED ARTICLE: Engineered Polyallylamine Nanoparticles for Efficient In Vitro Transfection

PURPOSE

Cationic polymers (i.e. polyallylamine, poly-L-lysine) having primary amino groups are poor transfection agents and possess high cytotoxicity index when used without any chemical modification and usually entail specific receptor mediated endocytosis or lysosomotropic agents to execute efficient gene delivery. In this report, primary amino groups of polyallylamine (PAA, 17 kDa) were substituted with imidazolyl functions, which are presumed to enhance endosomal release, and thus enhance its gene delivery efficiency and eliminate the requirement of external lysosomotropic agents. Further, systems were cross-linked with polyethylene glycol (PEG) to prepare PAA-IAA-PEG (PIP) nanoparticles and evaluated them in various model cell lines.

MATERIALS AND METHODS

The efficacy of PIP nanoparticles in delivering a plasmid encoding enhanced green fluorescent protein (EGFP) gene was assessed in COS-1, N2a and HEK293 cell lines, while their cytotoxicity was investigated in COS-1 and HEK293 cell lines. The PAA was chemically modified using imidazolyl moieties and ionically cross-linked with PEG to engineer nanoparticles. The extent of substitution was determined by ninhydrin method. The PIP nanoparticles were further characterized by measuring the particle size (dynamic light scattering and transmission electron microscopy), surface charge (zeta potential), DNA accessibility and buffering capacity. The cytotoxicity was examined using the MTT method.

RESULTS

In vitro transfection efficiency of synthesized nanoparticles is increased up to several folds compared to native polymer even in the presence of serum, while maintaining the cell viability over 100% in COS-1 cells. Nanoparticles possess positive zeta potential between 5.6-13 mV and size range of 185-230 nm in water. The accessibility experiment demonstrated that nanoparticles with higher degree of imidazolyl substitution formed relatively loose complexes with DNA. An acid-base titration showed enhanced buffering capacity of modified PAA.

CONCLUSIONS

The PIP nanoparticles reveal tremendous potential as novel delivery system for achieving improved transfection efficiency, while keeping the cells at ease.

Membrane-Forming Properties of Pseudoglyceryl Backbone Based Gemini Lipids Possessing Oxyethylene Spacers

Five pseudoglyceryl backbone based gemini lipids possessing varying lengths of oxyethylene [(-CH2-O-CH2-)n] spacers between cationic ammonium head groups have been synthesized, where n varies from 1 to 5. The membrane-forming properties of these gemini cationic lipids have been investigated. All the gemini lipids formed stable suspensions in water. The presence of membranous aggregates in such lipid suspensions was evidenced by transmission electron microscopy. The membrane-forming characteristics of these gemini lipids were compared with those of the corresponding monomeric lipid with one head group to understand the effect of lipid dimerization. The lipid suspensions were further characterized by dynamic light scattering and zeta potential measurements. Except for the gemini lipid with -CH2-CH2-O-CH2-CH2- spacer (2a), zeta potential of aggregates of all other gemini lipids were significantly greater than that of monomeric lipid suspensions. X-ray diffraction studies with lipid cast films revealed the increase in membrane bilayer width with increase in the length of the spacer (-CH2-O-CH2-)n. Clear thermotropic phase transitions typical of membranous assemblies were observed for all the lipid suspensions by high sensitivity differential scanning calorimetry. Aggregates of gemini lipid 2a bearing one oxyethylene [-(CH2-CH2-O-CH2-CH2)-] unit between headgroups manifested the highest phase transition temperature as compared to other gemini analogues as well as that of monomeric lipid 1. The phase transitions were reversible and exhibited large hysteresis, indicating that the observed phase transitions were of first order. To probe the surface hydration of these membranous aggregates, Paldan fluorescence studies were performed. These studies indicated the high polarity of the vesicular surface of gemini lipid 2a both in the gel and fluid melted phase as compared to vesicles of other gemini lipids.