Solid phase synthesis of novel asymmetric hydrophilic head cholesterol-based cationic lipids with potential DNA delivery

Design, synthesis, and in vitro gene transfer efficacy of novel ionizable cholesterol derivatives

ABSTACTThe medicinal properties of genetic drugs are highly dependent on the design of delivery systems. Ionizable cationic lipids are considered core materials in delivery systems. However, there has not yet been a widespread consensus on the relationship between the wide diversity of lipid structure design and gene delivery efficiency. The aims of the research work were to synthesize ionizable cholesterol derivatives (iChol-lipids) and to evaluate their potential applications as gene delivery vector. A series of iChol-lipids with different head groups were synthesized with carbamate bond spacer. The chemical structures were characterized by 1H NMR, MS, melting range, and pKa. The interactions between iChol-lipids and MALAT1-siRNA were studied by molecular dynamics simulations and compared with market available DC-Chol, which revealed that hydrogen bonds, salt-bridge, and electrostatic interaction were probably involved. The self-assemble behaviors of these lipids were intensively investigated and evaluated by dynamic laser scattering in the presence of different helper lipids and PEGylated lipids. Their plasmid binding ability, transfection efficiency, hemolytic toxicity, and cytotoxicity were fully studied. IZ-Chol-LNPs was proved to be highly potential to effectively complex with DNA, and endosome escape mechanisms mediated by proton sponge effect was verified by pH-sensitive fluorescence probe BCFL.

In vitro transfection efficiencies of T-shaped spermine-based cationic lipids with identical and nonidentical tails under high serum conditions

T-shaped spermine-based cationic lipids with identical and nonidentical hydrophobic tails having variable carbon lengths (from C10 to C18) were designed and synthesized. These lipids were characterized, and their structure-activity relationships were determined for DNA binding and transfection ability of these compounds when formulated as cationic liposomes. These liposomes were then applied as non-viral vectors to transfect HEK293T, HeLa, PC3, H460, HepG2, and Calu'3 cell lines with plasmid DNA encoding the green fluorescent protein. ST9, ST12 and ST13 with nonidentical tails could deliver DNA into HEK293T cells up to 60% under serum-free conditions. The lipid ST15 bearing nonidentical tails was found to be a potent gene transfer agent under 40% serum conditions in HEK293T and HeLa cells. Besides their low cytotoxicity, these lipoplexes also exhibited greater transfection efficiency than the commercially available transfection agent, Lipofectamine 3000.

Binding affinity and conformation of a conjugated AS1411 aptamer at a cationic lipid bilayer interface

Aptamers have been widely used in the detection, diagnosis, and treatment of cancer. Owing to their special binding affinity toward cancer-related biomarkers, aptamers can be used for targeted drug delivery or bio-sensing/bio-imaging in various scenarios. The interfacial properties of aptamers play important roles in controlling the surface charge, recognition efficiency, and binding affinity of drug-delivering lipid-based carriers. In this research, the interfacial behaviors, such as surface orientation, molecular conformation, and adsorption kinetics of conjugated AS1411 molecules at different cationic lipid bilayer interfaces were investigated by sum frequency generation vibrational spectroscopy (SFG-VS) in situ and in real-time. It is shown that the conjugated AS1411 molecules at the DMTAP bilayer interface show a higher binding affinity but with slower binding kinetics compared to the DMDAP bilayer interface. The analysis results also reveal that the thymine residues of cholesteryl conjugated AS1411 molecules show higher conformational ordering compared to the thymine residues of the alkyl chain conjugated AS1411 molecules. These understandings provide unique molecular insight into the aptamer-lipid membrane interactions, which may help researchers to improve the efficiency and safety of aptamer-related drug delivery systems.

Serum Compatible Spermine-based Cationic Lipids with Non-identical Hydrocarbon Tails Mediate High Transfection Efficiency

Cationic lipids are widely used as non-viral synthetic vectors for gene delivery as a safer alternative to viral vectors. In this work, a library of L-shaped spermine-based cationic lipids with identical and non-identical hydrophobic chains having variable carbon length (from C10 to C18) was designed and synthesized. These lipids were characterized and the structure-activity relationships of these compounds were determined for DNA binding and transfection ability when formulated as cationic liposomes. The liposomes were then used successfully for the transfection of HEK293T, HeLa, PC3, H460, HepG2, SH-SY5Y and Calu'3 cell lines. The transfection efficiency of lipids with non-identical hydrocarbon chains was greater than the identical analog. These reagents exhibited superior efficiency to the commercial reagent, Lipofectamine3000, under both serum-free and 10-40% serum conditions in HEK293T, HeLa and H460 cell lines. The lipids were also not toxic to the tested cells. The results suggested that L-shaped spermine-based cationic lipids with non-identical hydrocarbon tails could serve as an efficient and safe non-viral vector gene carrier for further in vivo studies.

Liposomal nanoparticles based on steroids and isoprenoids for nonviral gene delivery

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

Updates in bile acid-bioactive molecule conjugates and their applications

Bile acid conjugates are emerging as important chemical resources due to their low cost and wide availability of bile acids, making them privileged molecules in drug carrier systems and building blocks for derivatization and chiral template introduction into bioactive molecules. In recent years, bile acids as scaffolds in supramolecular, medicinal, and material chemistry attracted prime focus of researchers as an area of research to be followed with passion. Due to peculiar physicochemical and biological properties, bile acid exhibited various applications in biomedical and pharmaceutical fields. In this review, the bile acid conjugations with different bioactive compounds have been discussed to understand their influence on the bioavailability of bioactive compounds.

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.

A review on cationic lipids with different linkers for gene delivery

Cationic lipids have become known as one of the most versatile tools for the delivery of DNA, RNA and many other therapeutic molecules, and are especially attractive because they can be easily designed, synthesized and characterized. Most of cationic lipids share the common structure of cationic head groups and hydrophobic portions with linker bonds between both domains. The linker bond is an important determinant of the chemical stability and biodegradability of cationic lipid, and further governs its transfection efficiency and cytotoxicity. Based on the structures of linker bonds, they can be grouped into many types, such as ether, ester, amide, carbamate, disulfide, urea, acylhydrazone, phosphate, and other unusual types (carnitine, vinyl ether, ketal, glutamic acid, aspartic acid, malonic acid diamide and dihydroxybenzene). This review summarizes some research results concerning the nature (such as the structure and orientation of linker groups) and density (such as the spacing and the number of linker groups) of linker bond for improving the chemical stability, biodegradability, transfection efficiency and cytotoxicity of cationic lipid to overcome the critical barriers of in vitro and in vivo transfection.

Combinatorial library strategies for synthesis of cationic lipid-like nanoparticles and their potential medical applications

The past two decades have witnessed the high efficiency and efficacy of cationic lipids and liposomal formations for drug delivery. The tedious synthesis of conventional lipids and the inefficiency in studying structure-activity relationships, however, have hindered the clinical translation of lipid nanoparticle delivery systems. Combinatorial synthesis of lipid-like nanoparticles ('lipidoids') has recently emerged as an approach to accelerate the development of these delivery platforms. Utilizing a high-throughput screening strategy, the libraries of lipidoids are sorted and prime candidates for the delivery in the intended application can be identified and optimized for the next generation. In this review, we outline methods used for combinatorial lipidoid synthesis, the application of high-throughput screening, and the current medical applications of candidate lipidoids.

The chemistry and biology of organic guanidine derivatives

The chemistry and biology of organic natural guanidines are reviewed, including the isolation, structure determination, synthesis, biosynthesis and biological activities of alkaloids, non-ribosomal peptides, guanidine-bearing terpenes, polyketides and shikimic acid derivatives from natural sources.

Improvement in the colloidal stability of protein kinase-responsive polyplexes by PEG modification

We have reported a disease-cell specific gene expression system that is responsive to intracellular signaling proteins (e.g., protein kinases and proteases) hyperactivated in diseased cells. For this system, cationic peptide-grafted polymers were synthesized for polyplex formation with genes. Here, we modified poly(ethylene glycol) (PEG) to a protein kinase A (PKA)-responsive polymer to improve polyplex stability. PEG modification neutralized the surface charge of the polyplex and successfully increased polyplex stability at physiological conditions. However, PEG modification (PEG contents, 0.6 and 3.3 mol %) showed almost negligible effects on the reactivity of grafted peptides to PKA and the promotion of gene expression responding to PKA activity. Excessive modification of PEG (PEG contents, 6.8 mol %) inhibited polyplex formation. These results indicate that moderate modification of PEG to the enzyme-responsive polymer improves polyplex stability without inhibiting the reaction with enzymes.

Self-Assembled Lipoplexes of Short Interfering RNA (siRNA) Using Spermine-Based Fatty Acid Amide Guanidines: Effect on Gene Silencing Efficiency

Four guanidine derivatives of N4,N9-diacylated spermine have been designed, synthesized, and characterized. These guanidine-containing cationic lipids bound siRNA and formed nanoparticles. Two cationic lipids with C18 unsaturated chains, N1,N12-diamidino-N4,N9-dioleoylspermine and N1,N12-diamidino-N4-linoleoyl-N9-oleoylspermine, were more efficient in terms of GFP expression reduction compared to the other cationic lipids with shorter C12 (12:0) and very long C22 (22:1) chains. N1,N12-Diamidino-N4-linoleoyl-N9-oleoylspermine siRNA lipoplexes resulted in GFP reduction (26%) in the presence of serum, and cell viability (64%). These data are comparable to those obtained with TransIT TKO. Thus, cationic lipid guanidines based on N4,N9-diacylated spermines are good candidates for non-viral delivery of siRNA to HeLa cells using self-assembled lipoplexes.

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.

Synthesis and characterization of new aromatic esters based on 4,16-pregnadiene-6,20-dione skeleton

A series of new aromatic esters based on 4,16-pregnadiene-6,20-dione skeleton, namely 3β-benzoyloxy-4,16-pregnadiene-6,20-dione and 3β-furoyloxy-4,16-pregnadiene- 6,20-dione, which may be good inhibitors for the 5α-reductase enzyme and show high antiandrogenic activity, were synthesized starting from diosgenin. The structures of the steroids were characterized by elemental analysis, ¹H NMR, ¹³C NMR, IR and mass spectrum. Single crystal X-ray diffraction measurement on one of the new compounds, 3β-(p-methoxybenzoyloxy)-4,16-pregnadiene-6,20-dione revealed that the A, B, C, and D ring adopted half chair, distorted chair, distorted chair, and distorted envelope conformation, respectively. The molecules in the crystal were packed face-to-face at the normal van der Waals distances.