Evaluation of lipophosphoramidates-based amphiphilic compounds on the formation of biofilms of marine bacteria.

The bacteriostatic and/or bactericidal properties of few phosphoramide-based amphiphilic compounds on human pathogenic bacteria were previously reported. In this study, the potential of two cationic (BSV36 and KLN47) and two zwitterionic (3 and 4) amphiphiles as inhibitors of marine bacterial growth and biofilm formation were investigated. Results showed that the four compounds have little impact on the growth of a panel of 18 selected marine bacteria at a concentration of 200 µM, and up to 700 µM for some bacterial strains. Interestingly, cationic lipid BSV36 and zwitterionic lipids 3 and 4 effectively disrupt biofilm formation of Paracoccus sp. 4M6 and Vibrio sp. D02 at 200 µM and to a lesser extent of seven other bacterial strains tested. Moreover, ecotoxicological assays on four species of microalgae highlighted that compounds 3 and 4 have little impact on microalgae growth with EC50 values of 51 µM for the more sensitive species and up to 200 µM for most of the others. Amphiphilic compounds, especially zwitterionic amphiphiles 3 and 4 seem to be promising candidates against biofilm formation by marine bacteria.

Synthesis of ether lipids: natural compounds and analogues.

Ether lipids are compounds present in many living organisms including humans that feature an ether bond linkage at the sn-1 position of the glycerol. This class of lipids features singular structural roles and biological functions. Alkyl ether lipids and alkenyl ether lipids (also identified as plasmalogens) correspond to the two sub-classes of naturally occurring ether lipids. In 1979 the discovery of the structure of the platelet-activating factor (PAF) that belongs to the alkyl ether class of lipids increased the interest in these bioactive lipids and further promoted the synthesis of non-natural ether lipids that was initiated in the late 60's with the development of edelfosine (an anticancer drug). More recently, ohmline, a glyco glycero ether lipid that modulates selectively SK3 ion channels and reduces in vivo the occurrence of bone metastases, and other glyco glycero ether also identified as GAEL (glycosylated antitumor ether lipids) that exhibit promising anticancer properties renew the interest in this class of compounds. Indeed, ether lipid represent a new and promising class of compounds featuring the capacity to modulate selectively the activity of some membrane proteins or, for other compounds, feature antiproliferative properties via an original mechanism of action. The increasing interest in studying ether lipids for fundamental and applied researches invited to review the methodologies developed to prepare ether lipids. In this review we focus on the synthetic method used for the preparation of alkyl ether lipids either naturally occurring ether lipids (e.g., PAF) or synthetic derivatives that were developed to study their biological properties. The synthesis of neutral or charged ether lipids are reported with the aim to assemble in this review the most frequently used methodologies to prepare this specific class of compounds.

Phosphonodithioester-amine coupling in water: a fast reaction to modify the surface of liposomes.

The incorporation of lipophilic phosphonodithioesters in phospholipid formulations generates clickable liposomes that react with amines. The kinetics of this metal free phosphonodithioester-amine coupling (PAC) on liposomes in water is reported and can be classified as a fast reaction with a second order rate constant of k ≈ 8 × 102 M-1 s-1. The PAC reaction represents a versatile strategy to functionalize liposomes.

Phosphonodithioester-Amine Coupling as a Key Reaction Step for the Design of Cationic Amphiphiles Used for Gene Delivery.

A convergent synthesis of cationic amphiphilic compounds is reported here with the use of the phosphonodithioester-amine coupling (PAC) reaction. This versatile reaction occurs at room temperature without any catalyst, allowing binding of the lipid moiety to a polar head group. This strategy is illustrated with the use of two lipid units featuring either two oleyl chains or two-branched saturated lipid chains. The final cationic amphiphiles were evaluated as carriers for plasmid DNA delivery in four cell lines (A549, Calu3, CFBE and 16HBE) and were compared to standards (BSV36 and KLN47). These new amphiphilic derivatives, which were formulated with DOPE or DOPE-cholesterol as helper lipids, feature high transfection efficacies when associated with DOPE. The highest transfection efficacies were observed in the four cell lines at low charge ratios (CR = 0.7, 1 or 2). At these CRs, no toxic effects were detected. Altogether, this new synthesis scheme using the PAC reaction opens up new possibilities for investigating the effects of lipid or polar head groups on transfection efficacies.

Branched lipid chains to prepare cationic amphiphiles producing hexagonal aggregates: supramolecular behavior and application to gene delivery.

A ramified lipid alcohol, 2-hexyldecanol, was used as a hydrophobic moiety to prepare cationic amphiphiles on a gram scale in 3 to 4 steps, featuring either a trimethylammonium 5, dimethylhydroxyethylammonium 6 or N-methylimidazolium 7 polar head group. Compression isotherms at the air-water interface reveal that all these cationic amphiphiles collapse at a relatively low pressure indicating a weak stabilization of the monolayer via hydrophobic interactions. Ellipsometry measurements point out the presence of a thin monolayer at low lateral pressure whereas thickening of the monolayer occurs at higher pressure with a high percentage of variation of the thickness, thus demonstrating an adaptability to the constraints. 31P NMR spectroscopy of the hydrated cationic amphiphiles clearly shows that these cationic amphiphiles self-assemble in water to form hexagonal phases, irrespective of the nature of their polar head group. Furthermore, a comparison of molecular structures suggests that compounds 5-7 self-organize into an inverted hexagonal phase (HII). These cationic amphiphiles, alone or in the presence of DOPE, were evaluated for the transfection of three human-derived cell lines (i.e. A549, 16HBE and HeLa). The three compounds demonstrated high transfection efficacies in every cell line tested, 7/DOPE being the most efficient.

Bis-Thioether-Containing Lipid Chains in Cationic Amphiphiles: Physicochemical Properties and Applications in Gene Delivery.

Cationic amphiphiles featuring two thioether functions in each lipid chain of bicatenar cationic amphiphiles are reported here for the first time. The physicochemical properties and transfection abilities of these new amphiphiles were compared with those of already reported analogues featuring either (i) saturated, (ii) unsaturated or (iii) mono-thioether containing lipid chains. The homogeneity of the series of new compounds allowed to clearly underscore the effect of bis-thioether containing lipid chains. This study shows that besides previous strategies based on unsaturation or ramification, the incorporation of two thioether functions per lipid chain constitutes an original complementary alternative to tune the supramolecular properties of amphiphilic compounds. The potential of this strategy was evaluated in the context of gene delivery and report that two cationic amphiphiles (i. e. 4 a and 4 b) can be proposed as new efficient transfection reagents.

Substitution of unsaturated lipid chains by thioether-containing lipid chains in cationic amphiphiles: physicochemical consequences and application for gene delivery.

The hydrophobic moiety of cationic amphiphiles plays an important role in the transfection process because its structure has an impact on both the type of the supramolecular assembly and the dynamic properties of these assemblies. The latter have to exhibit a compromise between stability and instability to efficiently compact then deliver DNA into target cells. In the present work, we report the synthesis of new cationic amphiphiles featuring a thioether function at different positions of two 18-atom length lipid chains and we study their physicochemical properties (anisotropy of fluorescence and compression isotherms) with analogues possessing either oleyl (C18:1) or stearyl (C18:0) chains. We show that the fluidity of cationic lipids featuring a thioether function located close to the middle of each lipid chain is intermediate between that of oleyl- and stearyl-containing analogues. These properties are also supported by the compression isotherm assays. When used as carriers to deliver a plasmid DNA, thioether-containing cationic amphiphiles demonstrate a good ability to transfect human-derived cell lines, with those incorporating such a moiety in the middle of the chain being the most efficient. This work supports the use of a thioether function as a possible alternative to unsaturation in aliphatic lipid chains of cationic amphiphiles to modulate physicochemical behaviours and in turn biological activities such as gene delivery ability.

Phosphonic acid: preparation and applications.

The phosphonic acid functional group, which is characterized by a phosphorus atom bonded to three oxygen atoms (two hydroxy groups and one P=O double bond) and one carbon atom, is employed for many applications due to its structural analogy with the phosphate moiety or to its coordination or supramolecular properties. Phosphonic acids were used for their bioactive properties (drug, pro-drug), for bone targeting, for the design of supramolecular or hybrid materials, for the functionalization of surfaces, for analytical purposes, for medical imaging or as phosphoantigen. These applications are covering a large panel of research fields including chemistry, biology and physics thus making the synthesis of phosphonic acids a determinant question for numerous research projects. This review gives, first, an overview of the different fields of application of phosphonic acids that are illustrated with studies mainly selected over the last 20 years. Further, this review reports the different methods that can be used for the synthesis of phosphonic acids from dialkyl or diaryl phosphonate, from dichlorophosphine or dichlorophosphine oxide, from phosphonodiamide, or by oxidation of phosphinic acid. Direct methods that make use of phosphorous acid (H3PO3) and that produce a phosphonic acid functional group simultaneously to the formation of the P-C bond, are also surveyed. Among all these methods, the dealkylation of dialkyl phosphonates under either acidic conditions (HCl) or using the McKenna procedure (a two-step reaction that makes use of bromotrimethylsilane followed by methanolysis) constitute the best methods to prepare phosphonic acids.

Important role of phosphoramido linkage in imidazole-based dioleyl helper lipids for liposome stability and primary cell transfection.

BACKGROUND: To optimize synthetic gene delivery systems, there is a need to develop more efficient lipid formulations. Most cationic lipid formulations contain 'helper' neutral lipids because of their ability to increase DNA delivery, in particular by improving endosomal escape of DNA molecules via the pH-buffering effect of protonatable groups and/or fusion with the lipid bilayer of endosomes. METHODS: We evaluated the influence of the linker structure between the two oleyl chains in the helper lipid on transfection efficiency in cell lines, as well as in primary cells (hepatocytes/cardiomyocytes). We reported the synthesis of two new pH-buffering imidazole helper lipids characterized by a polar headgroup containing one (compound 6) or two (compound 5) imidazole groups and two oleyl chains linked by an amide group. We studied their association with the aminoglycoside lipidic derivative dioleylsuccinylparomomycin (DOSP), which contains two oleyl chains linked to the aminoglycoside polar headgroup via an amide function. We compared the morphology and transfection properties of such binary liposomes of DOSP/5 and DOSP/6 with those of liposomes combining DOSP with another imidazole-based dioleyl helper lipid (MM27) in which a phosphoramido group acts as a linker between the two oleyl chains and imidazole function. RESULTS: The phosphoramido linker in the helper lipid induces a major difference in terms of morphology and resistance to decomplexation at physical pH for DOSP/helper lipid complexes. CONCLUSIONS: This hybrid dioleyl linker composition of DOSP/MM27 led to higher transfection efficiency in cell lines and in primary cells compared to complexes with homogeneous dioleyl linker.

Triggering bilayer to inverted-hexagonal nanostructure formation by thiol-ene click chemistry on cationic lipids: consequences on gene transfection.

The ramification of cationic amphiphiles on their unsaturated lipid chains is readily achieved by using the thiol-ene click reaction triggering the formation of an inverted hexagonal phase (HII). The new ramified cationic lipids exhibit different bio-activities (transfection, toxicity) including higher transfection efficacies on 16HBE 14o-cell lines.

Lipophosphoramidate-based bipolar amphiphiles: their syntheses and transfection properties.

Six new cationic bolaamphiphiles (also called bipolar amphiphiles, bolaform amphiphiles, or bolalipids) were readily prepared by a thiol-ene click reaction that engaged a mercapto-alcohol (mercapto-ethanol or mercapto-hexanol) and a cationic based lipophosphoramidate. The cationic lipophosphoramidates contain two lipid chains that end in an alkene group and a selected cationic polar head group (trimethylammonium, dimethyl hydroxyethyl ammonium, or methylimidazolium). These compounds were formulated in water (with or without DOPE as a colipid) to produce supramolecular aggregates. These aggregates, before (i.e. bolasomes) and after (i.e. bolaplexes) mixing with plasmid DNA (pDNA) at various charge ratios, were characterized with regard to their sizes and zeta potentials. In the case of bolasomes, the suspensions were unstable since precipitation occurred after only a few hours at room temperature. On the other hand, bolaplex formulations exhibited clearly a better colloidal stability. Then, the gene delivery properties of the cationic bolasomes were investigated using two human-derived epithelial cell lines (A549 and 16HBE). Compared to the commercially available lipofection reagent (Lipofectamine), most of the cationic bolaamphiphiles were able to efficiently transfect these cells when they were formulated with DOPE in a 1 : 1 molar ratio. We report herein that bolaamphiphiles possessing a trimethylammonium or a dimethyl hydroxyethyl ammonium head group were the most efficient in terms of transfection efficiency while exhibiting no significant cytotoxicity.

Cationic lipophosphoramidates containing a hydroxylated polar headgroup for improving gene delivery.

The structure of the cationic moiety of amphiphiles is a key factor which directly influences their transfection efficacy. Accordingly, in the present work, we have synthesized three new lipophosphoramide-based amphiphilic compounds incorporating a methoxy 5, hydroxyl 6, or dihydroxyl 7 functional group in their cationic part. Gene delivery efficacies of these novel vectors were compared to our benchmark compound, the arsenolipophosphoramidate KLN47, and to its trimethylammonium (TMA) analogue 4. We next studied the characteristics (size, ζ potential) of the nanometric assemblies formed (liposomes and lipid/DNA complexes), and the DNA binding ability of the cationic liposomes was characterized at the physicochemical level. In vitro, all of the cationic lipids evaluated were efficient not only to condense plasmids but also to transfect two types of human airway epithelial cells. Interestingly, in vivo administration to mice (via simple tail vein injection) showed that compound 6 was the most efficient in transfecting the lungs when compared to that of the other cationic lipids studied, including compound KLN47. All of these results suggest that a hydroxyethyldimethylammonium (HE-DMA) polar head could be a valuable alternative to a trimethylarsonium (TMAs) polar head and that they also invite further evaluation of the in vivo potential of compound 6 using more clinically relevant delivery procedures.

Silver-based hybrid materials from meta- or para-phosphonobenzoic acid: influence of the topology on silver release in water.

Three novel silver-based metal-organic frameworks materials, which were synthesized from either 3-phosphono or 4-phosphonobenzoic acid and silver nitrate, are reported. The novel hybrids were synthesized under hydrothermal conditions; the pH of the reaction media was controlled by adding different quantities of urea thereby producing different topologies. Compound 1 (Ag3(4-PO3-C6H4-COO)), synthesized in the presence of urea, exhibits a compact 3D structure in which both phosphonic acid and carboxylic acid functional groups are linked to the silver-based inorganic network. Compound 2 (Ag(4-PO3H-C6H4-COOH)), which was synthesized at lower pH (without urea), has a layered structure in which only the phosphonic acid functional groups from 4-phosphonobenzoic acid moieties are linked to the silver inorganic network; the carboxylic acid groups being engaged in hydrogen bonds. Finally, material 3 (Ag(3-PO3H-C6H4-COOH)) was synthesized from 3-phosphonobenzoic acid and silver nitrate without urea. This material 3 features a layered structure exhibiting carboxylic acid functional groups linked via hydrogen bonds in the interlayer space. After the full characterization of these materials (single X-ray structure, IR, TGA), their ability to release silver salts in aqueous environment was measured. Silver release, determined in aqueous solution by cathodic stripping voltammetry, shows that the silver release capacity of these materials is dependent on the topology of the hybrids. The more compact structure 1 is extremely stable in water with only trace levels of silver ions being detected. On the other hand, compounds 2 and 3, in which only the phosphonic acid functional groups were bonded to the inorganic network, released larger quantities of silver ions into aqueous solution. These results which were compared with the silver release of the previously described compound 4 (Ag6(3-PO3-C6H4-COO)2). The results clearly show that the release capacity of silver-based metal organic framework can be tuned by modifying their topology which, in the present study, is governed by the regio-isomer of the organic precursor and the synthetic conditions under which the hybrids are prepared.

Cationic dialkylarylphosphates: a new family of bio-inspired cationic lipids for gene delivery.

In this work that aims to synthesize and evaluate new cationic lipids as vectors for gene delivery, we report the synthesis of a series of cationic lipids in which a phosphate functional group acts as a linker to assemble on a molecular scale, two lipid chains and one cationic polar head. The mono or dicationic moiety is connected to the phosphate group by an aryl spacer. In this work, two synthesis strategies were evaluated. The first used the Atherton-Todd coupling reaction to introduce a phenolic derivative to dioleylphosphite. The second strategy used a sequential addition of lipid alcohol and a phenolic derivative on POCl3. The two methods are efficient, but the latter allows larger yields. Different polar head groups were introduced, thus producing amphiphilic compounds possessing either one permanent (N-methyl-imidazolium, pyridinium, trimethylammonium) or two permanent cationic charges. All these cationic lipids were formulated as liposomal solutions and characterized (size and zeta potential). They formed stable liposomal solutions both in water (at pH 7.0) and in a weakly acidic medium (at pH 5.5). Finally, this new generation of cationic lipids was used to deliver DNA into various human-derived epithelial cells cultured in vitro. Compared with Lipofectamine used as a reference commercial lipofection reagent, some cationic dialkylarylphosphates were able to demonstrate potent gene transfer abilities, and noteworthily, monocationic derivatives were much more efficient than dicationic analogues.

Enhanced Achilles tendon healing by fibromodulin gene transfer.

Tendon injury is a major musculoskeletal disorder with a high public health impact. We propose a non-viral based strategy of gene therapy for the treatment of tendon injuries using histidylated vectors. Gene delivery of fibromodulin, a proteoglycan involved in collagen assembly was found to promote rat Achilles tendon repair in vivo and in vitro. In vivo liposome-based transfection of fibromodulin led to a better healing after surgical injury, biomechanical properties were better restored compared to untransfected control. These measures were confirmed by histological observations and scoring. To get better understandings of the mechanisms underlying fibromodulin transfection, an in vitro tendon healing model was developed. In vitro, polymer-based transfection of fibromodulin led to the best wound enclosure speed and a pronounced migration of tenocytes primary cultures was observed. These results suggest that fibromodulin non-viral gene therapy could be proposed as a new therapeutic strategy to accelerate tendon healing. FROM THE CLINICAL EDITOR: Tendon injury is relatively common and healing remains unsatisfactory. In this study, the effects of liposomal-based delivery of fibromodulin gene were investigated in a rat Achilles tendon injury model. The positive results observed would provide a new therapeutic strategy in clinical setting in the future.

Evaluation of New Fluorescent Lipophosphoramidates for Gene Transfer and Biodistribution Studies after Systemic Administration.

The objective of lung gene therapy is to reach the respiratory epithelial cells in order to deliver a functional nucleic acid sequence. To improve the synthetic carrier's efficacy, knowledge of their biodistribution and elimination pathways, as well as cellular barriers faced, depending on the administration route, is necessary. Indeed, the in vivo fate guides the adaptation of their chemical structure and formulation to increase their transfection capacity while maintaining their tolerance. With this goal, lipidic fluorescent probes were synthesized and formulated with cationic lipophosphoramidate KLN47 (KLN: Karine Le Ny). We found that such formulations present constant compaction properties and similar transfection results without inducing additional cytotoxicity. Next, biodistribution profiles of pegylated and unpegylated lipoplexes were compared after systemic injection in mice. Pegylation of complexes led to a prolonged circulation in the bloodstream, whereas their in vivo bioluminescent expression profiles were similar. Moreover, systemic administration of pegylated lipoplexes resulted in a transient liver toxicity. These results indicate that these new fluorescent compounds could be added into lipoplexes in small amounts without perturbing the transfection capacities of the formulations. Such additional properties allow exploration of the in vivo biodistribution profiles of synthetic carriers as well as the expression intensity of the reporter gene.

Effects of a novel archaeal tetraether-based colipid on the in vivo gene transfer activity of two cationic amphiphiles.

Gene therapy for treating inherited diseases like cystic fibrosis might be achieved using multimodular nonviral lipid-based systems. To date, most optimizations have concerned cationic lipids rather than colipids. In this study, an original archaeal tetraether derivative was used as a colipid in combination with one or the other of two monocationic amphiphiles. The liposomes obtained, termed archaeosomes, were characterized regarding lipid self-assembling properties, macroscopic/microscopic structures, DNA condensation/neutralization/relaxation abilities, and colloidal stability in the presence of serum. In addition, gene transfer experiments were conducted in mice with lipid/DNA complexes being administered via systemic or local delivery routes. Altogether, the results showed that the tetraether colipid can provide complexes with different in vivo transfection abilities depending on the lipid combination, the lipid/colipid molar ratio, and the administration route. This original colipid appears thus as an innovative modular platform endowed with properties possibly beneficial for fine-tuning of in vivo lipofection and other biomedical applications.

Cationic lipophosphoramidates with two different lipid chains: synthesis and evaluation as gene carriers.

Cationic lipids constitute a family of synthetic vectors commonly used for nucleic acids delivery. We herein report the results of a systematic study that aimed to compare the transfection efficacies of cationic lipophosphoramidates possessing either two identical lipid chains (termed symmetric cationic lipids) or two different lipid chains (non-symmetric cationic lipids). In addition, we also compared the transfection results of such a 'molecular approach' (the two different lipid chains being included in the same molecule) with those of a 'supramolecular approach' in which two types of symmetrical cationic lipids were mixed in one liposomal formulation. Thus, the present work allowed us first to optimize the methods used to synthesize non-symmetric cationic lipophosphoramidates. In addition, we could also identify two non-symmetric cationic lipids exhibiting high transfection efficiencies with a series of mammalian cell lines, both vectors being characterized by a single phytanyl chain and either an oleyl or a lauryl lipid chain.

Atherton-Todd reaction: mechanism, scope and applications.

Initially, the Atherton-Todd (AT) reaction was applied for the synthesis of phosphoramidates by reacting dialkyl phosphite with a primary amine in the presence of carbon tetrachloride. These reaction conditions were subsequently modified with the aim to optimize them and the reaction was extended to different nucleophiles. The mechanism of this reaction led to controversial reports over the past years and is adequately discussed. We also present the scope of the AT reaction. Finally, we investigate the AT reaction by means of exemplary applications, which mainly concern three topics. First, we discuss the activation of a phenol group as a phosphate which allows for subsequent transformations such as cross coupling and reduction. Next, we examine the AT reaction applied to produce fire retardant compounds. In the last section, we investigate the use of the AT reaction for the production of compounds employed for biological applications. The selected examples to illustrate the applications of the Atherton-Todd reaction mainly cover the past 15 years.

BSV163/DOPE-mediated TRAIL gene transfection acts synergistically with chemotherapy against cisplatin-resistant ovarian cancer.

Ovarian cancer is the seventh most frequently diagnosed cancer among women worldwide. Most patients experience recurrence and succumb eventually to resistant disease, underscoring the need for an alternative treatment option. In the presented manuscript, we investigated the effect of the TRAIL-gene, transfected by an innovative bioinspired lipid vector BSV163/DOPE in the presence or absence of cisplatin, to fight against sensitive and resistant ovarian cancer. We showed that BSV163/DOPE can transfect ovarian cancer cell lines (Caov3, OVCAR3, and our new cisplatin-resistant, CR-Caov3) safely and efficiently. In addition, TRAIL-gene transfection in association with cisplatin inhibited cellular growth more efficiently (nearly 50% in Caov3 cells after the combined treatment, and 15% or 25% by each treatment alone, respectively) owing to an increase in apoptosis rate, caspases activity and TRAIL's death receptors expression. Most importantly, such synergistic effect was also observed in CR-Caov3 cells demonstrated by an apoptosis rate of 35% following the combined treatment in comparison with 17% after TRAIL-gene transfection or 6% after cisplatin exposition. These results suggest this combination may have potential application for sensitive as well as refractory ovarian cancer patients.