Phase behavior of cationic amphiphiles and their mixtures with helper lipid influences lipoplex shape, DNA translocation, and transfection efficiency

Recent advances in polymeric and lipid stimuli-responsive nanocarriers for cell-based cancer immunotherapy

Conventional cancer therapy has major limitations, including non-specificity, unavoidable side effects, low specific tumor accumulation and systemic toxicity. In recent years, more effective and precise treatment methods have been developed, including cell-based immunotherapy. Carriers that can accurately and specifically target cells and equip them to combat cancer cells are particularly important for developing this therapy. As a result, attention has been drawn to smart nanocarriers that can react to specific stimuli. Thus, stimuli-responsive nanocarriers have attracted increasing attention because they can change their physicochemical properties in response to stimulus conditions, such as pH, enzymes, redox agents, hypoxia, light and temperature. This review highlights recent advances in various stimuli-responsive nanocarriers, discussing loading, targeted delivery, cellular uptake, biocompatibility and immunomodulation in cell-based immunotherapy. Finally, future challenges and perspectives regarding the possible clinical translation of nanocarriers are discussed.

Ionizable lipids based on branched fatty acids - An explorative study on Langmuir monolayers

Ionizable lipids are a class of pharmaceutical excipients with a main application in lipid nanoparticles for nucleic acid delivery. New ionizable lipids are needed to tune characteristics of lipid-based nucleic acid delivery systems, e.g. stability, nucleic acid loading capacity and binding strength, as well as bio-distribution. Herein, we present the synthesis of three novel ionizable lipids as putative excipients for lipid-based nucleic acid delivery systems. Langmuir monolayer experiments with classical surface pressure/area isotherm evaluation were used to understand the self-assembly behavior of the lipids. Additional experiments with surface sensitive techniques, namely grazing incidence x-ray scattering and infrared reflection-absorption spectroscopy (IRRAS), were performed to understand structural characteristics of lipid associates. The latter technique was also used to investigate the nucleic acid binding process between DNA and the ionizable lipids. Finally, first transfection experiments with the novel lipids formulated as cationic liposomes were performed providing first efficacy data. Although the alkyl chain pattern was comparable for all three ionizable lipids, the results demonstrated that with increasing head-group size the DNA binding capacity changed and the alkyl chain fluidity was increased. The lipid with the lowest phase transition temperature and the smallest packing parameter showed the highest DNA transfer efficiency.

Optimizing Transfection Efficiency in CAR-T Cell Manufacturing through Multiple Administrations of Lipid-Based Nanoparticles

The existing manufacturing protocols for CAR-T cell therapies pose notable challenges, particularly in attaining a transient transfection that endures for a significant duration. To address this gap, this study aims to formulate a transfection protocol utilizing multiple lipid-based nanoparticles (LNPs) administrations to enhance transfection efficiency (TE) to clinically relevant levels. By systematically fine-tuning and optimizing our transfection protocol through a series of iterative refinements, we have accomplished a remarkable one-order-of-magnitude augmentation in TE within the immortalized T-lymphocyte Jurkat cell line. This enhancement has been consistently observed over 2 weeks, and importantly, it has been achieved without any detrimental impact on cell viability. In the subsequent phase of our study, we aimed to optimize the gene delivery system by evaluating three lipid-based formulations tailored for DNA encapsulation using our refined protocol. These formulations encompassed two LNPs constructed from ionizable lipids and featuring systematic variations in lipid composition (iLNPs) and a cationic lipoplex (cLNP). Our findings showcased a notable standout among the three formulations, with cLNP emerging as a frontrunner for further refinement and integration into the production pipeline of CAR-T therapies. Consequently, cLNP was scrutinized for its potential to deliver CAR-encoding plasmid DNA to the HEK-293 cell line. Confocal microscopy experiments demonstrated its efficiency, revealing substantial internalization compared to iLNPs. By employing a recently developed confocal image analysis method, we substantiated that cellular entry of cLNP predominantly occurs through macropinocytosis. This mechanism leads to heightened intracellular endosomal escape and mitigates lysosomal accumulation. The successful expression of anti-CD19-CD28-CD3z, a CAR engineered to target CD19, a protein often expressed on the surface of B cells, was confirmed using a fluorescence-based assay. Overall, our results indicated the effectiveness of cLNP in gene delivery and suggested the potential of multiple administration transfection as a practical approach for refining T-cell engineering protocols in CAR therapies. Future investigations may focus on refining outcomes by adjusting transfection parameters like nucleic acid concentration, lipid-to-DNA ratio, and incubation time to achieve improved TE and increased gene expression levels.

Messenger RNA Lipid-Based Nanoparticles: Optimization of Formulations in the Lab

Among the large variety of messenger RNA (mRNA) delivery systems, those developed with lipid-based formulations were the most widely used and efficient. In our lab, we produced different mRNA formulations made with liposomes, hybrid lipid polymer, and lipid nanoparticles. Our formulations were made with lipids bearing imidazole groups that trigger the endosomal escape of nanoparticles once protonated inside the mild acidic milieu of endosomes upon their cell uptake. Herein, we describe protocols that we used to produce, optimize, and characterize those formulations. The transfection efficiency is influenced by various factors including the physicochemical parameters of the nanoparticles, their efficiency to be internalized in cells, and their intracellular routing as well as their capacity to induce immune system sensors. We provide details on how to quantify the amount of mRNA nanoparticles uptake by cells and evaluate the acidity of the intracellular compartments where they are located, to investigate the endosomal escape, and to assess the activation of innate immune sensors as phosphorylation of PKR hampering mRNA translation.

Looking Back, Moving Forward: Lipid Nanoparticles as a Promising Frontier in Gene Delivery

Lipid nanoparticles (LNPs) have shown remarkable success in delivering genetic materials like COVID-19 LNP vaccines, such as mRNA-1273/SpikeVax by Moderna and BNT162b2/Comirnaty by BioNTech/Pfizer, as well as siRNA for rare inherited diseases, such as Onpattro from Alnylam Pharmaceuticals. These LNPs are advantageous since they minimize side effects, target specific cells, and regulate payload delivery. There has been a surge of interest in these particles due to their success stories; however, we still do not know much about how they work. This perspective will recapitulate the evolution of lipid-based gene delivery, starting with Felgner's pioneering 1987 PNAS paper, which introduced the initial DNA-transfection method utilizing a synthetic cationic lipid. Our journey takes us to the early 2020s, a time when advancements in bionano interactions enabled us to create biomimetic lipoplexes characterized by a remarkable ability to evade capture by immune cells in vivo. Through this overview, we propose leveraging previous achievements to assist us in formulating improved research goals when optimizing LNPs for medical conditions such as infectious diseases, cancer, and heritable disorders.

A cationic lipid with advanced membrane fusion performance for pDNA and mRNA delivery

The success of mRNA vaccines for COVID-19 prevention raised global awareness of the importance of nucleic acid drugs. The approved systems for nucleic acid delivery were mainly formulations of different lipids, yielding lipid nanoparticles (LNPs) with complex internal structures. Due to the multiple components, the relationship between the structure of each component and the overall biological activity of LNPs is hard to study. However, ionizable lipids have been extensively explored. In contrast to former studies on the optimization of hydrophilic parts in single-component self-assemblies, we report in this study on structural alterations of the hydrophobic segment. We synthesize a library of amphiphilic cationic lipids by varying the lengths (C = 8-18), numbers (N = 2, 4), and unsaturation degrees (Ω = 0, 1) of hydrophobic tails. Notably, all self-assemblies with nucleic acid have significant differences in particle size, stability in serum, membrane fusion, and fluidity. Moreover, the novel mRNA/pDNA formulations are characterized by overall low cytotoxicity, efficient compaction, protection, and release of nucleic acids. We find that the length of hydrophobic tails dominates the formation and stability of the assembly. And at a certain length, the unsaturated hydrophobic tails enhance the membrane fusion and fluidity of assemblies and thus significantly affect the transgene expression, followed by the number of hydrophobic tails.

mRNA Lipoplexes with Cationic and Ionizable α-Amino-lipophosphonates: Membrane Fusion, Transfection, mRNA Translation and Conformation

Cationic liposomes are attractive carriers for mRNA delivery. Here, mRNA lipoplexes (LX) were prepared with the cationic lipids α-aminolipophosphonate (3b) or imidazolium lipophosphoramidate (2) associated with various α-aminolipophosphonates co-lipids comprising protonable groups (imidazole or pyridine) and DOPE. Physicochemical parameters of liposomes and their membrane fusion activity were measured. LXs comprising either 3b- or 2- allowed transfection of ~25% and 40% of dendritic cells with low cytotoxicity, respectively; the efficiency increased up to 80% when 2 was combined with the imidazole-based co-lipid 1. The transfections were high with 3b/1, 3b/DOPE, 2/1 and 2/DOPE LXs. We observed that the transfection level was not well correlated with the acid-mediated membrane fusion activity of liposomes supposed to destabilize endosomes. The mRNA release from LXs and its translation capacity after release were studied for the most efficient LXs. The results showed that the more mRNA was condensed, the poorer the translation efficiency after release was. In contrast to DNA, circular dichroism performed on mRNA complexed with 2/DOPE revealed the presence of denatured mRNA in LXs explaining this lack of translation efficiency. This is an important parameter that should be stressed for the preparation of mRNA LXs with a conserved mRNA translation activity.

Aerosol-Mediated Non-Viral Lung Gene Therapy: The Potential of Aminoglycoside-Based Cationic Liposomes

Aerosol lung gene therapy using non-viral delivery systems represents a credible therapeutic strategy for chronic respiratory diseases, such as cystic fibrosis (CF). Progress in CF clinical setting using the lipidic formulation GL67A has demonstrated the relevance of such a strategy while emphasizing the need for more potent gene transfer agents. In recent years, many novel non-viral gene delivery vehicles were proposed as potential alternatives to GL67 cationic lipid. However, they were usually evaluated using procedures difficult or even impossible to implement in clinical practice. In this study, a clinically-relevant administration protocol via aerosol in murine lungs was used to conduct a comparative study with GL67A. Diverse lipidic compounds were used to prepare a series of formulations inspired by the composition of GL67A. While some of these formulations were ineffective at transfecting murine lungs, others demonstrated modest-to-very-efficient activities and a series of structure-activity relationships were unveiled. Lipidic aminoglycoside derivative-based formulations were found to be at least as efficient as GL67A following aerosol delivery of a luciferase-encoding plasmid DNA. A single aerosol treatment with one such formulation was found to mediate long-term lung transgene expression, exceeding half the animal's lifetime. This study clearly supports the potential of aminoglycoside-based cationic lipids as potent GL67-alternative scaffolds for further enhanced aerosol non-viral lung gene therapy for diseases such as CF.

Aliphatic Quaternary Ammonium Functionalized Nanogels for Gene Delivery

Gene therapy is a promising treatment for hereditary diseases, as well as acquired genetic diseases, including cancer. Facing the complicated physiological and pathological environment in vivo, developing efficient non-viral gene vectors is needed for their clinical application. Here, poly(N-isopropylacrylamide) (p(NIPAM)) nanogels are presented with either protonatable tertiary amine groups or permanently charged quaternized ammonium groups to achieve DNA complexation ability. In addition, a quaternary ammonium-functionalized nanogel was further provided with an aliphatic moiety using 1-bromododecane to add a membrane-interacting structure to ultimately facilitate intracellular release of the genetic material. The ability of the tertiary amine-, quaternized ammonium-, and aliphatic quaternized ammonium-functionalized p(NIPAM) nanogels (i.e., NGs, NGs-MI, and NGs-BDD, respectively) to mediate gene transfection was evaluated by fluorescence microscopy and flow cytometry. It is observed that NGs-BDD/pDNA complexes exhibit efficient gene loading, gene protection ability, and intracellular uptake similar to that of NGs-MI/pDNA complexes. However, only the NGs-BDD/pDNA complexes show a notable gene transfer efficiency, which can be ascribed to their ability to mediate DNA escape from endosomes. We conclude that NGs-BDD displays a cationic lipid-like behavior that facilitates endosomal escape by perturbing the endosomal/lysosomal membrane. These findings demonstrate that the presence of aliphatic chains within the nanogel is instrumental in accomplishing gene delivery, which provides a rationale for the further development of nanogel-based gene delivery systems.

Cationic lipids for gene delivery: many players, one goal

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

Lipofection-Based Delivery of DNA Vaccines

The preventive and therapeutic potential of DNA vaccines combined with benefits of lipid-based delivery (lipofection) allow efficient nucleic acid transfer and immunization applicable in treatment of infections, cancer or autoimmune disorders. Lipofecting compositions consisting of cationic and neutral lipids can be used for both in vitro and in vivo applications and may also play the role of adjuvants. Here we describe a simple protocol of DNA vaccine carrier preparation based on cationic polyprenyl derivatives (PTAI-trimethylpolyprenylammonium iodides) and commonly used helper lipids with use of basic laboratory equipment. Such formulas have proven effective for immunization of animals as well as for cell transfection.

Boost of serum resistance and storage stability in cationic polyprenyl-based lipofection by helper lipids compositions

Lipofection is a widely used molecular biology technique and one of the most promising non-viral gene therapy strategies. However, one of the main drawbacks of using cationic lipids-based lipoplexes in DNA/RNA delivery is serum-associated inhibition of transfection. We have addressed this issue using PTAI (trimethylpolyprenylammonium iodides)-based lipofection model. To overcome serum-sensitivity we used 100 different formulations based on different PTAI, various helper lipids compositions, lipoplex surface modifications with polyethylene glycol (PEG), and precondensation of DNA with poly-L-lysine (PLL). Multicomponent helper lipids compositions boosted serum resistance and largely improved long-term storage of PTAI-based reagents. This was observed, in particular, for PTAI with longer isoprenoid chains. Additionally, our PTAI-based carriers were efficient for DNA and RNA delivery and safe for human red blood cells (RBC). Moreover, a broad array of the modifications used resulted in an important observation - a diverse susceptibility of various cell types to different compositions was noted. Overall, our results show that helper lipids composition mediates efficient serum-resistant DNA/RNA lipofection. Additionally, multicomponent PTAI-based reagents are promising gene delivery carriers both, at the cellular and organismal level.

siRNA based drug design, quality, delivery and clinical translation

Gene silencing by RNA interference represents a promising therapeutic approach. The development of carriers, e.g., polymers, lipids, peptides, antibodies, aptamers, small molecules, exosome and red blood cells, is crucial for the systemic delivery of siRNA. Cell-specific targeting ligands in the nano-carriers can improve the pharmacokinetics, biodistribution, and selectivity of siRNA therapeutics. The safety, effectiveness, quality and prosperity of production and manufacturing are important considerations for selecting the appropriate siRNA carriers. Efficacy of systemic delivery of siRNA requires considerations of trafficking through the blood, off-target effects, innate immune response and endosomal escape avoiding lysosomal degradation for entering into RNAi process. Multifunctional nanocarriers with stimuli-responsive properties such as pH, magnetic and photo-sensitive segments can enhance the efficacy of siRNA delivery. The improved preclinical characterization of suitable siRNA drugs, good laboratory practice, that reduce the differences between in vitro and in vivo results may increase the success of siRNA drugs in clinical settings.

The effect of polar headgroups and spacer length on the DNA transfection of cholesterol-based cationic lipids

This article is related to the effects of the headgroups and spacer length of cationic lipids on transfection efficiency. To develop highly potent cationic lipids, a series of divalent lysine-diamine conjugated cholesterol-based cationic lipids with three different headgroups (ammonium, trimethyl ammonium, and guanidinium) were synthesized. The newly synthesized cationic lipids (1-6)A formed cationic liposomes in the presence and absence of a zwitterionic helper lipid, DOPE (dioleoylphosphatidylethanolamine). A gel retardation assay showed that most of the prepared lipoplexes could retard DNA migration in the presence of DOPE. We attempted to modify the diverse cationic headgroups to improve the transfection efficiency. However, the lysine-1,3-diaminopropane-conjugated cholesterol-based lipid 4A, having divalent ammonium of unmodified lysine headgroup, exhibited high relative transfection efficiency in HEK293. When the transfection efficiency of 4A was formulated with DOPE (1 : 1 weight ratio), it produced the same range in comparison with that of a commercially available transfection agent, Lipofectamine™ 2000 (L2k). The lipid 4A was studied to optimize the conditions with respect to the lipid/DOPE and DNA/lipid ratios and the amount of DNA. The transfection efficiency of the highly potent lipid 4A was also studied to determine the transfection efficiency of HeLa, PC3, and HC-04 cell lines. This lipid also protected the DNA from a serum and had low toxicity. Lipoplexes 4A with DOPE had the particle size of around 300-600 nm and the zeta potential of around 0-45 mV. In summary, cationic liposomes 4A demonstrated a high performance as DNA carriers.

Efficient nanocarriers of siRNA therapeutics for cancer treatment

Nanocarriers as drug delivery systems are promising and becoming popular, especially for cancer treatment. In addition to improving the pharmacokinetics of poorly soluble hydrophobic drugs by solubilizing them in a hydrophobic core, nanocarriers allow cancer-specific combination drug deliveries by inherent passive targeting phenomena and adoption of active targeting strategies. Nanoparticle-drug formulations can enhance the safety, pharmacokinetic profiles, and bioavailability of locally or systemically administered drugs, leading to improved therapeutic efficacy. Gene silencing by RNA interference (RNAi) is rapidly developing as a personalized field of cancer treatment. Small interfering RNAs (siRNAs) can be used to switch off specific cancer genes, in effect, "silence the gene, silence the cancer." siRNA can be used to silence specific genes that produce harmful or abnormal proteins. The activity of siRNA can be used to harness cellular machinery to destroy a corresponding sequence of mRNA that encodes a disease-causing protein. At present, the main barrier to implementing siRNA therapies in clinical practice is the lack of an effective delivery system that protects the siRNA from nuclease degradation, delivers to it to cancer cells, and releases it into the cytoplasm of targeted cancer cells, without creating adverse effects. This review provides an overview of various nanocarrier formulations in both research and clinical applications with a focus on combinations of siRNA and chemotherapeutic drug delivery systems for the treatment of multidrug resistant cancer. The use of various nanoparticles for siRNA-drug delivery, including liposomes, polymeric nanoparticles, dendrimers, inorganic nanoparticles, exosomes, and red blood cells for targeted drug delivery in cancer is discussed.

Carriers Break Barriers in Drug Delivery: Endocytosis and Endosomal Escape of Gene Delivery Vectors

Over the past decades, major efforts were undertaken to develop devices on a nanoscale level for the efficient and nontoxic delivery of molecules to tissues and cells, for the purpose of either diagnosis or treatment of disease. The application of such devices in drug delivery has proven to be beneficial for matters as diverse as drug solubility, drug targeting, controlled drug release, and transport of drugs across cellular barriers. Multiple nanotherapeutics have been approved for clinical treatment, and more products are being evaluated in preclinical and clinical trials. However, many biological barriers hinder the medical application of nanocarriers. There are two main classes of barriers that need to be overcome by drug nanocarriers: extracellular and intracellular barriers, both of which may capture and/or destroy therapeutics before they reach their target site. This Account discusses major biological barriers that are confronted by nanotherapeutics, following their systemic administration, focusing on cellular entry and endosomal escape of gene delivery vectors. The use of pH-responsive materials to overcome the endosomal barrier is addressed. Historically, cell biologists have studied the interaction between cells and pathogens in order to unveil the mechanisms of endocytosis and cell signaling. Meanwhile, it is becoming clear that cells may respond in similar ways to artificial drug delivery systems and, consequently, that knowledge on the cellular response against both pathogens and nanoparticulate systems will aid in the design of improved nanomedicine. A close collaboration between bioengineers and cell biologists will promote this development. At the same time, we have come to realize that tools that we use to study fundamental cellular processes, including metabolic inhibitors of endocytosis and overexpression/downregulation of proteins, may cause changes in cellular physiology. This calls for the implementation of refined methods to study nanocarrier-cell interactions, as is discussed in this Account. Finally, recent papers on the dynamics of cargo release from endosomes by means of live cell imaging have significantly advanced our understanding of the transfection process. They have initiated discussion (among others) on the limited number of endosomal escape events in transfection, and on the endosomal stage at which genetic cargo is most efficiently released. Advancements in imaging techniques, including super-resolution microscopy, in concert with techniques to label endogenous proteins and/or label proteins with synthetic fluorophores, will contribute to a more detailed understanding of nanocarrier-cell dynamics, which is imperative for the development of safe and efficient nanomedicine.

Probing relaxation dynamics of a cationic lipid based non-viral carrier: a time-resolved fluorescence study

Lipid vesicles composed of cationic dioctadecyldimethylammonium bromide (DODAB) and neutral 1-monooleoyl-rac-glycerol (MO) are promising non-viral carriers of nucleic acids for delivery into cells. Among them, higher cell transfection efficiency was displayed by DODAB-rich vesicles than those enriched with MO. Structural relaxation of these mixed lipid vesicles plays a key role in their cell transfection efficiency because structural organization of the DODAB-rich vesicles are different from that of the MO-rich vesicles. Polarization-gated anisotropy in conjunction with picosecond resolved emission transients of a novel fluorophore 6-acetyl-(2-((4-hydroxycyclohexyl)(methyl)amino)naphthalene) (ACYMAN) has been employed to probe relaxation dynamics in pure DODAB vesicles, and in mixed vesicles of DODAB with varying content of MO. Both orientational relaxation of ACYMAN and relaxation dynamics of its local environment are retarded significantly in mixed lipid vesicles with increasing MO content, from a mole fraction (χ_MO) of 0.2 to that of 0.8 which is consistent with increased rigidity of the MO-rich (χ_MO > 0.5) vesicles relative to the DODAB-rich (χ_MO < 0.5) vesicles. Therefore, higher structural rigidity of the MO-rich vesicles (χ_MO > 0.5) gives rise to their lower cell transfection efficiency than the more flexible DODAB-rich (χ_MO < 0.5) vesicles as observed in previous in vivo studies (Biochim. Biophys. Acta, Biomembr., 2014, 1838, 2555–2567).

Lipid vesicles composed of cationic dioctadecyldimethylammonium bromide (DODAB) and neutral 1-monooleoyl-rac-glycerol (MO) are promising non-viral carriers of nucleic acids for delivery into cells.

Interactions of Cationic Lipids with DNA: A Structural Approach

Colloidal nucleic acid carrier systems based on cationic lipids are a promising pharmaceutical tool in the implementation of gene therapeutic strategies. This study demonstrates the complex behavior of DNA at the lipid-solvent interface facilitating structural changes of the lyotropic liquid-crystalline phases. For this study, the structural properties of six malonic acid based cationic lipids were determined using small- and wide-angle X-ray scattering (SAXS and WAXS) as well as differential scanning calorimetry (DSC). Selected lipids (lipid 3 and lipid 6) with high nucleic acid transfer activity have been investigated in detail because of the strong influence of the zwitterionic helper lipid 1,2-di(9 Z-octadecenoyl)- sn-glycero-3-phosphoethanolamine (DOPE) on the structural properties as well as of the complex formation of lipid-DNA complexes (lipoplexes). In the case of lipid 3, DNA stabilizes a metastable cubic mesophase with Im3 m symmetry and an Im3 m Q_α^c lipoplex is formed, which is rarely described for DNA lipoplexes in literature. In the case of lipid 6, a cubic mesophase with Im3 m symmetry turns into a fluid lamellar phase while mixing with DOPE and complexing DNA.

Lipoplex-Mediated Single-Cell Transfection via Droplet Microfluidics

While lipoplex (cationic lipid-nucleic acid complex)-mediated intracellular delivery is widely adopted in mammalian cell transfection, its transfection efficiency for suspension cells, e.g., lymphatic and hematopoietic cells, is reported at only ≈5% or even lower. Here, efficient and consistent lipoplex-mediated transfection is demonstrated for hard-to-transfect suspension cells via a single-cell, droplet-microfluidics approach. In these microdroplets, monodisperse lipoplexes for effective gene delivery are generated via chaotic mixing induced by the serpentine microchannel and co-confined with single cells. Moreover, the cell membrane permeability increases due to the shear stress exerted on the single cells when they pass through the droplet pinch-off junction. The transfection efficiency, examined by the delivery of the pcDNA3-EGFP plasmid, improves from ≈5% to ≈50% for all three tested suspension cell lines, i.e., K562, THP-1, Jurkat, and with significantly reduced cell-to-cell variation, compared to the bulk method. Efficient targeted knockout of the TP53BP1 gene for K562 cells via the CRISPR (clustered regularly interspaced short palindromic repeats)-CAS9 (CRISPR-associated nuclease 9) mechanism is also achieved using this platform. Lipoplex-mediated single-cell transfection via droplet microfluidics is expected to have broad applications in gene therapy and regenerative medicine by providing high transfection efficiency and low cell-to-cell variation for hard-to-transfect suspension cells.

Efficient and non-toxic gene delivery by anionic lipoplexes based on polyprenyl ammonium salts and their effects on cell physiology

BACKGROUND

One of the major challenges limiting the development of gene therapy is an absence of efficient and safe gene carriers. Among the nonviral gene delivery methods, lipofection is considered as one of the most promising. In the present study, a set of cationic polyprenyl derivatives [trimethylpolyprenylammonium iodides (PTAI)] with different lengths of polyprenyl chains (from 7, 8 and 11 to 15 isoprene units) was suggested as a component of efficient DNA vehicles.

METHODS

Optimization studies were conducted for PTAI in combination with co-lipid dioleoylphosphatidylethanolamine on DU145 human prostate cancer cells using: size and zeta potential measurements, confocal microscopy, the fluorescein diacetate/ethidium bromide test, cell counting, time-lapse monitoring of cell movement, gap junctional intercellular coupling analysis, antimicrobial activity assay and a red blood cell hemolysis test.

RESULTS

The results obtained show that the lipofecting activity of PTAI allows effective transfection of plasmid DNA complexed in negatively-charged lipoplexes of 200-500 nm size into cells without significant side effects on cell physiology (viability, proliferation, morphology, migration and gap junctional intercellular coupling). Moreover, PTAI-based vehicles exhibit a potent bactericidal activity against Staphylococcus aureus and Escherichia coli. The developed anionic lipoplexes are safe towards human red blood cell membranes, which are not disrupted in their presence.

CONCLUSIONS

The developed carriers constitute a group of promising lipofecting agents of a new type that can be utilized as effective lipofecting agents in vitro and they are also an encouraging basis for in vivo applications.

Malonic acid based cationic lipids - The way to highly efficient DNA-carriers

Cationic lipids play an important role as non-viral nucleic acid carriers in gene therapy since 3 decades. This review will introduce malonic acid derived cationic lipids as nucleic acid carriers which appeared in the literature dealing with lipofection 10years ago. The family of amino-functionalized branched fatty acid amides will be presented as well as different generations of malonic acid diamides. Both groups of cationic lipids yield lipid mixtures with highly efficient nucleic acid transfer activities in in-vitro cell culture models. The DNA transfer screening of lipid libraries with directed structural variations in the lipophilic as well as in the hydrophilic part of the amphiphiles yields structure/activity relationships. Furthermore, the detailed characterizations of selected lipid composites at the air/water interface and in bulk systems are summarized with regard to transfection determining physical-chemical properties. The findings are also discussed in comparison to results obtained with other families of cationic lipids.

Tumor-targeted delivery of siRNA using fatty acyl-CGKRK peptide conjugates

Tumor-targeted carriers provide efficient delivery of chemotherapeutic agents to tumor tissue. CGKRK is one of the well-known tumor targeting peptides with significant specificity for angiogenic blood vessels and tumor cells. Here, we designed fatty acyl conjugated CGKRK peptides, based on the hypothesis that hydrophobically-modified CGKRK peptide could enhance cellular permeation and delivery of siRNA targeted to tumor cells for effective silencing of selected proteins. We synthesized six fatty acyl-peptide conjugates, using a diverse chain of saturated and unsaturated fatty acids to study the efficiency of this approach. At peptide:siRNA weight/weight ratio of 10:1 (N/P ≈ 13.6), almost all the peptides showed complete binding with siRNA, and at a w/w ratio of 20:1 (N/P ≈ 27.3), complete protection of siRNA from early enzymatic degradation was observed. Conjugated peptides and peptide/siRNA complexes did not show significant cytotoxicity in selected cell lines. The oleic acid-conjugated peptide showed the highest efficiency in siRNA uptake and silencing of kinesin spindle protein at peptide:siRNA w/w ratio of 80:1 (N/P ≈ 109). The siRNA internalization into non-tumorigenic kidney cells was negligible with all fatty acyl-peptide conjugates. These results indicate that conjugation of fatty acids to CGKRK could create an efficient delivery system for siRNA silencing specifically in tumor cells.

Atomic force microscopy as a tool to study the adsorption of DNA onto lipid interfaces

The Atomic Force Microscopy (AFM) technique appears as a central tool for the characterization of DNA adsorption onto lipid interfaces. Regardless of the huge number of surveys devoted to this issue, there are still fascinating phenomena in this field that have not been explored in detail by AFM. For instance, adsorption of DNA onto like-charged lipid surfaces mediated by cations is still not fully understood even though it is gaining popularity nowadays in gene therapy and nanotechnology. Studies related to the complexation of DNA with anionic lipids as a non-viral gene delivery vehicle as well as the formation of self-assembled nanoscale DNA constructs (DNA origami) are two of the most attractive systems. Unfortunately, molecular mechanisms underlying the adsorption of DNA onto anionic lipid interfaces remain unclear so far. In view of that, AFM becomes an appropriate technique to provide valuable information to understand the adsorption of DNA to anionic lipid surfaces. As a second part of this review we provide an illustrative example of application of the AFM technique to probe the DNA adsorption onto a model lipid monolayer negatively charged. Microsc. Res. Tech. 80:11-17, 2017. © 2016 Wiley Periodicals, Inc.

Stimuli responsive charge-switchable lipids: Capture and release of nucleic acids

Stimuli responsive lipids, which enable control over the formation, transformation, and disruption of supramolecular assemblies, are of interest for biosensing, diagnostics, drug delivery, and basic transmembrane protein studies. In particular, spatiotemporal control over a supramolecular structure can be achieved using light activated compounds to induce significant supramolecular rearrangements. As such, a family of cationic lipids are described which undergo a permanent switch in charge upon exposure to 365 nm ultraviolet (UV) light to enable the capture of negatively charged nucleic acids within the self-assembled supramolecular structure of the lipids and subsequent release of these macromolecules upon exposure to UV light and disruption of the assemblies. The lipids are composed of either two different tripeptide head groups, Lysine-Glycine-Glycine (KGG) and Glycine-Glycine-Glycine (GGG) and three different hydrocarbon chain lengths (C6, C10, or C14) terminated by a UV light responsive 1-(2-nitrophenyl)ethanol (NPE) protected carboxylic acid. The photolysis of the NPE protected lipid is measured as a function of time, and the resulting changes in net molecular charge are observed using zeta potential analysis for each head group and chain length combination. A proof of concept study for the capture and release of both linear DNA (calf thymus) and siRNA is presented using an ethidium bromide quenching assay where a balance between binding affinity and supramolecular stability are found to be the key to optimal nucleic acid capture and release.

Next generation macrocyclic and acyclic cationic lipids for gene transfer: Synthesis and in vitro evaluation

Previously we reported the synthesis and in vitro evaluation of four novel, short-chain cationic lipid gene delivery vectors, characterized by acyclic or macrocyclic hydrophobic regions composed of, or derived from, two 7-carbon chains. Herein we describe a revised synthesis of an expanded library of related cationic lipids to include extended chain analogues, their formulation with plasmid DNA (pDNA) and in vitro delivery into Chinese hamster ovarian (CHO-K1) cells. The formulations were evaluated against each other based on structural differences in the hydrophobic domain and headgroup. Structurally the library is divided into four sets based on lipids derived from two 7- or two 11-carbon hydrophobic chains, C7 and C11 respectively, which possess either a dimethylamine or a trimethylamine derived headgroup. Each set includes four cationic lipids based on an acyclic or macrocyclic, saturated or unsaturated hydrophobic domain. All lipids were co-formulated with the commercial cationic lipid 1,2-dimyristoyl-sn-glycero-3-ethylphosphocholine (EPC) in a 1:1 molar ratio, along with one of two distinct neutral co-lipids, cholesterol or 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) in an overall cationic-to-neutral lipid molar ratio of 3:2. Binding of lipid formulations with DNA, and packing morphology associated with the individual lipid-DNA complexes were characterized by gel electrophoresis and small angle X-ray diffraction (SAXD), respectively. As a general trend, lipoplex formulations based on mismatched binary cationic lipids, composed of a shorter C7 lipid and the longer lipid EPC (C14), were generally associated with higher transfection efficiency and lower cytotoxicity than their more closely matched C11/EPC binary lipid formulation counterparts. Furthermore, the cyclic lipids gave transfection levels as high as or greater than their acyclic counterparts, and formulations with cholesterol exhibited higher transfection and lower cytotoxicity than those formulated with DOPE. A number of the lipid formulations with cholesterol as co-lipid performed as well as, or better than Lipofectamine 2000™ and EPC, the two positive controls employed in these studies. These results suggest that our novel cyclic and acyclic cationic lipid vectors are effective nonviral gene transfer agents that warrant further investigation.

Cyclen-based cationic lipids containing a pH-sensitive moiety as gene delivery vectors

Imidazole-functionalized cationic lipids with a cyclen headgroup were synthesized, and the structure–activity relationship in gene delivery mediated by these lipids was discussed.

SAINT-liposome-polycation particles, a new carrier for improved delivery of siRNAs to inflamed endothelial cells

Interference with acute and chronic inflammatory processes by means of delivery of siRNAs into microvascular endothelial cells at a site of inflammation demands specific, non-toxic and effective siRNA delivery system. In the current work we describe the design and characterization of siRNA carriers based on cationic pyridinium-derived lipid 1-methyl-4-(cis-9-dioleyl)methyl-pyridinium-chloride) (SAINT-C18) and the transfection enhancer protamine, complexed with siRNA/carrier DNA or siRNA only. These carriers, called SAINT-liposome-polycation-DNA (S-LPD) and SAINT-liposome-polycation (S-LP), have a high efficiency of siRNA encapsulation, low cellular toxicity, and superior efficacy of gene downregulation in endothelial cells in vitro as compared to DOTAP-LPD. Incorporation of 10 mol% PEG and anti-E-selectin antibody in these formulations resulted in selective siRNA delivery into activated endothelial cells. Furthermore, we showed that the physicochemical characteristics of S-LPD and S-LP, including size-stability and maintenance of the siRNA integrity in the presence of serum at 37 °C, comply with requirements for in vivo application.

Structure-delivery relationships of lysine-based gemini surfactants and their lipoplexes

The synthesis and properties of gemini surfactants of the type (R(1)(CO)-Lys(H)-NH)2(CH2)n are reported. For a spacer length of n = 6, the hydrophobic acyl tail was varied in length (R(1) = C8, C10, C12, C14, C16, and C18) and, for R(1) = C18, the degree of unsaturation. For R(1)(CO) = oleoyl (C18:1 Z) the spacer length (n = 2-8) and the stereochemistry of the lysine building block were varied; a 'half-gemini' derivative with a single oleoyl tail and head group was also prepared. The potential of the gemini surfactants to transfer polynucleotides across a cell membrane was investigated by transfection of HeLa cells with beta-galactosidase, both in the presence and absence of the helper lipid DOPE. Oleoyl was found to be by far the best hydrophobic tail for this biological activity, whereas the effect of the lysine stereochemistry was less pronounced. The effect of an optimum spacer length (n = 6) was observed only in the absence of helper lipid. The most active surfactant, i.e. the one with oleoyl chains and n = 6, formed liposomes with sizes in the range of 60-350 nm, and its lipoplex underwent a transition from a lamellar to a hexagonal morphology upon lowering the pH from 7 to 3.

Bis-quaternary gemini surfactants as components of nonviral gene delivery systems: a comprehensive study from physicochemical properties to membrane interactions

Gemini surfactants have been successfully used as components of gene delivery systems. In the present work, a family of gemini surfactants, represented by the general structure [CmH2m+1(CH3)2N(+)(CH2)sN(+)(CH3)2CmH2m+1]2Br(-), or simply m-s-m, was used to prepare cationic gene carriers, aiming at their application in transfection studies. An extensive characterization of the gemini surfactant-based complexes, produced with and without the helper lipids cholesterol and DOPE, was carried out in order to correlate their physico-chemical properties with transfection efficiency. The most efficient complexes were those containing helper lipids, which, combining amphiphiles with propensity to form structures with different intrinsic curvatures, displayed a morphologically labile architecture, putatively implicated in the efficient DNA release upon complex interaction with membranes. While complexes lacking helper lipids were translocated directly across the lipid bilayer, complexes containing helper lipids were taken up by cells also by macropinocytosis. This study contributes to shed light on the relationship between important physico-chemical properties of surfactant-based DNA vectors and their efficiency to promote gene transfer, which may represent a step forward to the rational design of gene delivery systems.

Structural dynamics and physicochemical properties of pDNA/DODAB:MO lipoplexes: effect of pH and anionic lipids in inverted non-lamellar phases versus lamellar phases

Dioctadecyldimethylammonium bromide (DODAB):Monoolein (MO) lipoplexes have mainly been studied within the range of high molar ratios of DODAB, with noticeable transfection efficiencies in the Human Embryonic Kidney (HEK, a.k.a. 293T) cell line. In this work, we intend to study the effect of high MO content on the structure and physicochemical properties of pDNA/DODAB:MO lipoplexes to achieve some correlation with their transfection efficiency. Static/Dynamic Light Scattering and Cryo-TEM imaging were used to characterize the size/morphology of DNA/DODAB:MO lipoplexes at different DODAB:MO contents (2:1, 1:1, 1:2) and charge ratios (CRs) (+/-). Nile Red fluorescence emission was performed to detect changes in microviscosity, hydration and polarity of DNA/DODAB:MO systems. Lipoplexes stability at physiological pH values and in the presence of anionic lipids was evaluated by Förster Resonance Energy Transfer (FRET). Physicochemical/structural data were complemented with transfection studies in HEK cells using the β-galactosidase reporter gene activity assay. This work reports the coexistence of multilamellar and non-lamellar inverted phases in MO-richer lipoplexes (DODAB:MO 1:2 and 1:4), leading to transfection efficiencies comparable to those of multilamellar (DODAB-richer) lipoplexes, but at higher charge ratios [CR (+/-)=6.0] and without dose-effect response. These results may be related to the structural changes of lipoplexes promoted by high MO content.

Demixing and crystallization of DODAB in DPPC-DODAB binary mixtures

The crystallization mechanism of one lipid component within multicomponent lipid mixtures remains unclear. To shed light on this issue, we studied the demixing and crystallization behaviors of a binary lipid system using neutral dipalmitoylphosphatidylcholine (DPPC) and cationic dioctadecyldimethylammonium bromide (DODAB) as model molecules. The results indicate that when DODAB is no more than equimolar (e.g., DPPC/DODAB = 2/1 and 1/1), DPPC is miscible with DODAB and hinders the crystallization of DODAB, and the samples undergo reversible gel-fluid phase transitions upon heating and cooling. However, when DODAB is dominant in the mixture (DPPC/DODAB = 1/2), cooling of the mixed fluid phase results in the formation of a DODAB-rich gel domain and a DPPC-DODAB mixed gel domain. Such phase-separated mixed gels can undergo further demixing and crystallization, producing a DODAB-rich crystalline domain and a DPPC-rich tilted gel domain upon prolonged (or plus low-temperature) incubation. Besides, evidence has been given that the crystallized DODAB-rich domain remains in the same lipid bilayer as the DPPC-rich domain. All the three binary lipid mixtures can hold large amounts of water in the lipid interlamellar regions, allowing the incorporation of a large number of water-soluble substances such as DNA or proteins, which can be used for the fabrication of functional biofilms and biomaterials. Influences of water content and salt concentration on the phase structures (e.g., repeat distances) of the binary mixtures have also been studied.

Tunable pDNA/DODAB:MO lipoplexes: the effect of incubation temperature on pDNA/DODAB:MO lipoplexes structure and transfection efficiency

Dioctadecyldimethylammonium bromide (DODAB):1-monooleoyl-rac-glycerol (MO) cationic liposomes were reported as a promising alternative to common transfection agents, showing superior effectiveness on the transfection of the 293T mammalian cell line with pSV-β-gal plasmid DNA. The study of DODAB:MO aggregates in the absence of DNA has indicated that their morphology depends on the balance between DODAB's tendency to form bilayer structures and MO's propensity to form inverted non-lamellar structures. Other parameters, such as the temperature have proved to be crucial in the definition of the morphology of the developed nanocarrier. Therefore, in this work, a step forward to the current gene carrier system will be given by studying the effect of the tunable parameters (incubation temperature and MO content) on the structure of pDNA:DODAB:MO lipoplexes. More importantly, the implications that these tunable parameters could have in terms of lipoplex transfection efficiency will be investigated. Dynamic light scattering (DLS), zeta (ζ) potential, cryo-transmission electron microscopy (cryo-TEM) and ethidium bromide (EtBr) exclusion were used to assess the formation, structure and destabilization of pDNA:DODAB:MO lipoplexes at DODAB molar fractions of (1:1) and above equimolarity (2:1, 4:1) prepared at incubation temperatures from 25 to 50°C. Experimental results indicate that pDNA:DODAB:MO's structure is sensitive to the lipoplex incubation temperature, resulting in particles of distinct size, superficial charge and structure. These variations are also visible on the complexation dynamics of pDNA, and subsequent release upon incubation with the model proteoglycan heparin (HEP), at 25 and 50°C. Increase in temperature leads to re-organization of DODAB and MO molecules within the liposomal formulation, causing a positive charge re-localization in the lipoplex surface, which not only alters its structure but also its transfection efficiency. Altogether, these results confirm that in the DODAB:MO carriers, an increase in the incubation temperature has a similar effect on aggregate morphology as the observed with an increase in MO content. This conclusion is extended to the pDNA:DODAB:MO lipoplexes morphology and subsequent transfection efficiency defining new strategies in lipoplexes preparation that could be used to modulate the properties of other lipid formulations for nonviral gene delivery applications.

The development of an in vitro assay to screen lipid based nanoparticles for siRNA delivery

In order to rapidly screen and select lead candidates for in vivo evaluation of lipid nanoparticles (LNPs) for systemic small interfering RNA (siRNA) delivery, an in vitro assay amenable to high-throughput screening (HTS) is developed. The strategy is to mimic the in vivo experience of LNPs after systemic administration, such as interactions with serum components, exposure to endosomal pH environments, and interactions with endosomal membrane lipids. It is postulated that the amount of siRNA released from LNPs after going through these treatments can be used as a screening tool to rank order the effectiveness of siRNA delivery by lipid nanoparticles in vivo. LNPs were incubated with 50% serum from different species (i.e. mouse, rat, or rhesus) at 37°C. The resulting samples were then reacted with anionic, endosomal-mimicking lipids at different pHs. The amount of siRNA released from LNPs was determined using spectrophotometry employing the fluorescent indicator SYBR Gold. Our results indicated that the amount of siRNA liberated was highly dependent upon the species of serum used and the pH to which it was exposed. LNPs treated with mouse serum showed higher levels of siRNA release, as did those subjected to endosomal pH (6.0), compared to physiological pH. Most interestingly, a good correlation between the amount of siRNA released and the in vivo efficacy was observed. In conclusion, an in vitro siRNA release assay was developed to screen and rank order LNPs for in vivo evaluation.

A combinatorial library of unsaturated lipidoids for efficient intracellular gene delivery

A combinatorial library of unsaturated lipidoids was synthesized through the Michael addition of amines to oleyl acrylamide. Their capability in facilitating in vitro gene delivery was evaluated by transfecting HeLa cells with EGFP-encoding plasmid DNA and mRNA. The preliminary screening results indicated that lipidoids with unsaturated oleyl tails are superior transfection agents compared to saturated lipidoids with n-octadecyl tails under the same conditions. The different transfection abilities of the unsaturated and saturated lipidioids were ascribed to the large, tightly packed lipoplexes of saturated lipidoids. The potential applications of the library of lipidoids were further expanded by looking at their ability to transfect fibroblasts as well as different cancerous cell lines.