On the disulfide-linker strategy for designing efficacious cationic transfection lipids: an unexpected transfection profile

AbstractHerein, employing a previously reported disulfide-linker strategy, we have designed and synthesized a novel cationic lipid 2 with a disulfide-linker and its non-disulfide control analog lipid 1. The relative efficacies of lipids 1 and 2 in transfecting CHO, COS-1 and MCF-7 cells were measured using both reporter gene and whole cell histochemical staining assays. In stark contrast to the expectation based on the disulfide-linker strategy, the control non-disulfide cationic lipid 1 showed phenomenally superior in vitro transfection efficacies to its essentially transfection incompetent disulfide counterpart lipid 2. Results in DNase I protection experiments and the electrophoretic gel patterns in the presence of glutathione, taken together, are consistent with the notion that the success of the disulfide-linker strategy may depend more critically on the DNase I sensitivity of the lipoplexes than on the efficient DNA release induced by intracellular glutathione pool

Single additional methylene group in the head-group region imparts high gene transfer efficacy to a transfection-incompetent cationic lipid

In combination with equimolar 1,2-dioleoyl-L-α-glycero-3-phosphatidyl ethanolamine, a novel cholesterol-based cationic lipid with β-alanine head-group (2) has been demonstrated to be strikingly more efficacious (10-24-fold) in transfecting CHO, COS-1 and HepG2 cells than its glycine analog (1) containing just one less methylene unit in its head-group region. Syntheses, characterizations and in vitro transfection biology of lipids 1 and 2 are described. Present findings demonstrate that even truly minor structural alterations, such as inclusion of just one additional methylene functionality in the polar head-group region, can convert an essentially transfection-incompetent cholesterol-based cationic amphiphile to a remarkably efficient cationic transfection lipid

Crossing Blood-Brain Barrier with Nano-drug Carriers for Treatment of Brain Tumors: Advances and Unmet Challenges

Blood-brain barrier (BBB), a unique membrane barrier formed by closely stitched brain capillary endothelial cells (BCEC) with tight cellular junctions, separates brain from the circulating blood to protect it from bloodborne pathogens. BBB greatly limits the entry of chemotherapeutics to brain, and in consequence, it is a major obstacle for treating brain tumor. Advances in designing efficient nano-drug carriers are opening new avenues for overcoming this uphill systemic challenge. This book chapter describes current understanding of nanocarriers-mediated noninvasive drug targeting to brain tumor. Design principles behind the construction of the most promising recently designed receptor and transporter selective nano-drug carriers for combating brain tumors have been highlighted

Histidylated lipid-modified sendai viral envelopes mediate enhanced membrane fusion and potentiate targeted gene delivery

Recent studies have demonstrated that covalent grafting of a single histidine residue into a twin-chain aliphatic hydrocarbon compound enhances its endosome-disrupting properties and thereby generates an excellent DNA transfection system. Significant increase in gene delivery efficiencies has thus been obtained by using endosome-disrupting multiple histidine functionalities in the molecular architecture of various cationic polymers. To take advantage of this unique feature, we have incorporated L-histidine (N,N-di-n-hexadecylamine) ethylamide (L(H)) in the membrane of hepatocyte-specific Sendai virosomes containing only the fusion protein (F-virosomes (Process for Producing a Targeted Gene (Sarkar, D. P., Ramani, K., Bora, R. S., Kumar, M., and Tyagi, S. K. (November 4, 1997) U. S. Patent 5,683,866))). Such L(H)-modified virosomal envelopes were four times more (p <0.001) active in terms of fusion with its target cell membrane. On the other hand, the presence of L(H) in reconstituted influenza and vesicular stomatitis virus envelopes failed to enhance spike glycoprotein-induced membrane fusion with host cell membrane. Circular dichroism and limited proteolysis experiments with F-virosomes indicated that the presence of L(H) leads to conformational changes in the F protein. The molecular mechanism associated with the increased membrane fusion induced by L(H) has been addressed in the light of fusion-competent conformational change in F protein. Such enhancement of fusion resulted in a highly efficient gene delivery system specific for liver cells in culture and in whole animals

New histidylated cationic lipids for DNA and mRNA- based lipofection

Plasmid delivery into the cytosol remains one of the limiting factor to achieve efficient transfection. We have previously demonstrated that the presence of endosome-disrupting multiple histidine functionalities in the molecular architecture of cationic polymers significantly enhances their gene delivery efficiencies. We designed and synthesized two novel non-glycerol and a cholesterol based histidylated cationic amphiphiles containing a single histidine head group. Physico-chemical characteristics of all the novel liposomes and lipoplexes including lipid:DNA interactions, global surface charge, sizes, etc. were evaluated. We found that L-histidine-(N,N-di-n-hexadecylamine)ethylamide (lipid 1) and L-Histidine(N,N-di-n-hexadecylamine, N-methyl)ethylamide (lipid 2) in combination with cholesterol and Cholesteryl-L-Histidine-Ethylamide (lipid 3) in combinaison with DOPE gave efficient DNA and mRNA transfections into various cell lines. DNA transfection efficiency into A549, 293T7 and HeLa cells of Chol/lipid 1 lipoplexes was similar with that of FuGENE6 and DC-Chol lipoplexes but was two order of magnitude higher in HepG2 cells. Membrane fusion activity measurements using FRET technique showed that the histidine head-groups of Chol/lipid 1 liposomes mediated membrane fusion in the pH range 5-7. By using the cytosolic luciferase expression vector (pT7Luc) under the control of the bacterial T7 promoter, we showed that the release of DNA from the endosomally trapped lipoplexes to the cytosol is acidic dependent and presumably mediated by the imidazole ring protonation of histidine head group of these cationic amphiphiles. A better efficiency was obtained with Chol/lipid 2 lipoplexes than with Chol/lipid 1 lipoplexes when using the cytosolic luciferase expression vector. As anticipated, transfection efficiency of Lipid 3 was greatly inhibited in the presence of Bafilomycin A1. By contrast, endosome escape of DNA with a new cholesterol based cationic lipid containing no histidine head-group (Alanine-Cholesteryl-Ethylamide; lipid 4) seemed to be independent of endosome acidification. However, transfection efficacy of lipids 3 & 4 was similar. In conclusion, we show that covalent grafting of a single histidine amino acid residue to suitable twin-chain hydrophobic compounds or cholesterol is sufficient to impart remarkable transfection properties on the resulting cationic amphiphile via endosome-disrupting characteristics of the histidine functionalities Figure 1

Long-term reduction of jaundice in gunn rats by nonviral liver-targeted delivery of sleeping beauty transposon

Asialoglycoprotein receptor (ASGPR)-mediated endocytosis has been used to target genes to hepatocytes in vivo. However, the level and duration of transgene expression have been low because of lysosomal translocation and degradation of the DNA and lack of its integration into the host genome. In this study we packaged the DNA of interest in proteoliposomes containing the fusogenic galactose-terminated F-glycoprotein of the Sendai virus (FPL) for targeted delivery to hepatocytes. After the FPL binds to ASGPR on the hepatocyte surface, fusogenic activity of the F-protein delivers the DNA into the cytosol, bypassing the endosomal pathway. For transgene integration we designed plasmids containing one transcription unit expressing the Sleeping Beauty transposase (SB) and another expressing human uridinediphosphoglucuronate glucuronosyltransferase-1A1 (pSB-hUGT1A1). The latter was flanked by inverted/direct repeats that are substrates of SB. In cell culture, FPL-mediated delivery of the E. coli β-galactosidase gene (LacZ) resulted in transduction of ASGPR-positive cells (rat hepatocytes or Hepa1 cell line), but not of ASGPR-negative 293 cells. Intravenous injection of the FPL-entrapped pSB-hUGT1A1 (4-8 μg/day, 1-4 doses) into UGT1A1-deficient hyperbilirubinemic Gunn rats (model of Crigler-Najjar syndrome type 1) resulted in hUGT1A1 expression in 5%-10% of hepatocytes, but not in other cell types. Serum bilirubin levels declined by 30% ± 4% in 2 weeks and remained at that level throughout the 7-month study duration. With histidine containing FPL, serum bilirubin was reduced by 40% ± 5%, and bilirubin glucuronides were excreted into bile. No antibodies were detectable in the recipient rats against the F-protein or human UGT1A1. Conclusion: FPL is an efficient hepatocyte-targeted gene delivery platform in vivo that warrants further exploration toward clinical application

Design, syntheses, and transfection biology of novel non-cholesterol-based guanidinylated cationic lipids

The design of efficacious cationic transfection lipids with guanidinium headgroups is an actively pursued area of research in nonviral gene delivery. Herein, we report on the design, syntheses, and gene transfection properties of six novel non-cholesterol-based cationic amphiphiles (1-6) with a single guanidinium headgroup in transfecting CHO, COS-1, MCF-7, A549, and HepG2 cells. The in vitro gene transfer efficiencies of lipids 1-6 were evaluated using both the reporter gene and the whole cell histochemical X-gal staining assays. The efficiencies of lipids 1-3, in particular, were found to be about 2- to 4-fold higher than that of commercially available LipofectAmine in transfecting COS-1, CHO, A-549, and MCF-7 cells. However, the relative transfection efficiencies of lipids 1-3 and LipofectAmine were found to be comparable in HepG2 cells. Cholesterol was found to be a more efficacious co-lipid than dioleoyllphosphatidyl ethanolamine (DOPE). In general, lipids 1-3 containing the additional quaternized centers were observed to be more transfection efficient than lipids 4-6 with less positive headgroups. MTT-assay-based cell viability measurements in representative CHO cells revealed high (>75%) cell viabilities of lipids 1-6 across the lipid/DNA charge ratios 0.1:1 to 3:1. Electrophoretic gel patterns observed in DNase I protection experiments support the notion that enhanced degradation of DNA associated with lipoplexes of lipids 4-6 might play some role in diminishing their in vitro gene transfer efficacies. Size and global surface charge measurement by a dynamic laser light scattering instrument equipped with ζ-sizing capacity revealed the nanosizes and surface potentials of both the transfection efficient and the incompetent lipoplexes to be within the range of 200-600 nm and +3.4 to -34 mV, respectively. To summarize, given the feasibility of a wide range of structural manipulations in the headgroup regions of non-cholesterol-based cationic amphiphiles, our present findings are expected to broaden the potential of cationic amphiphiles with guanidinium headgroups for use in nonviral gene therapy

Gene transfer efficacies of novel cationic amphiphiles with alanine, β-alanine, and serine headgroups: a structure-activity investigation

Herein, we report on the relative in vitro efficacies of nine novel nonglycerol based cationic amphiphiles with increasing hydrophobic tails and the amino acids serine, alanine and β-alanine as the headgroup functionalities (lipids 1-9, Scheme 1) in transfecting multiple cultured cells including CHO, COS-1, MCF-7, and HepG2. The gene transfer efficiencies of lipids 1-9 were evaluated using the reporter gene assays in all the four cell lines and the whole cell histochemical X-gal staining assays in representative CHO cells. In CHO, HepG2, and MCF-7 cells, cationic lipids with alanine (4-6) and β-alanine (7-9) headgroups were found to be remarkably more transfection efficient than their serine headgroup counterparts (1-3). Most notably, in CHO, HepG2, and MCF-7 cells, in combination with cholesterol as auxiliary lipid, the transfection efficiencies of the cationic lipids with alanine and β-alanine headgroups and myristyl and palmityl tails (lipids 4, 5, 7 and 8) were significantly higher (2-3-fold) than that of LipofectAmine-2000, a widely used commercially available liposomal tranfection vectors. Surprisingly, in COS-1 cells, although cationic lipids with β-alanine headgroups (7-9) were strikingly transfection efficient (3-4-fold more efficacious than LipofectAmine-2000), the gene transfer properties of both their structural isomers (4-6) and their serine headgroup counterparts (1-3) were adversely affected. In summary, the present structure-activity investigation demonstrate that high gene delivery efficacies of cationic amphiphiles containing alanine or β-alanine headgroups can get seriously compromised by substituting the alanine or β-alanine with serine presumably due to the enhanced sensitivity of DNA associated with such serine-head-containing cationic lipids

Cationic liposomes as non-viral carriers of gene medicines: resolved issues, open questions, and future promises

The clinical success of gene therapy is critically dependent on the development of efficient and safe gene delivery reagents, popularly known as "transfection vectors." The transfection vectors commonly used in gene therapy are mainly of two types: viral and non-viral. The efficiencies of viral transfection vectors are, in general, superior to their non-viral counterparts. However, the myriads of potentially adverse immunogenic aftermaths associated with the use of viral vectors are increasingly making the non-viral gene delivery reagents as the vectors of choice. Among the existing arsenal of non-viral gene delivery reagents, the distinct advantages associated with the use of cationic transfection lipids include their: (a) robust manufacture; (b) ease in handling and preparation techniques; (c) ability to inject large lipid:DNA complexes; and (d) low immunogenic response. The present review highlights the major achievements in the area of designing efficacious cationic transfection lipids, some of the more recent advances in the field of cationic liposomes-mediated gene transfer and targeted gene delivery, some unresolved issues and challenges in liposomal gene delivery, and future promises of cationic liposomes as gene-carriers in non-viral gene therapy