Amphiphilic Cationic Polymers Research Articles

Controlled synthesis of amino-acid based tadpole-shaped organic/inorganic hybrid polymers and their self-assembly in aqueous media

Synthesis, characterization and solution behavior of tadpole-shaped amphiphilic polymers with hydrophobic polyhedral oligomeric silsesquioxane (POSS) chain-end and hydrophilic main-chain having leucine pendants were investigated. Reversible addition-fragmentation chain transfer (RAFT) polymerization technique was employed to polymerize tert-butyloxycarbonyl-l-leucine methacryloyloxyethyl ester (Boc-Leu-HEMA) in the presence of POSS based RAFT agent. The POSS content and molecular weight of polymers could be controlled while maintaining a narrow molecular weight distribution (<1.3). Glass transition temperature (Tg) of tadpole shaped polymers (TSP) increased with increasing content of POSS moiety in the polymer matrix. Circular dichroism (CD) spectroscopy confirmed that the POSS moiety did not perturb the higher ordered secondary conformation of TSP, attained due to the presence of pendent chiral leucine moiety. Expulsion of side chain Boc groups produced pH responsive amphiphilic cationic polymers, which exhibited self-assembly in aqueous medium, confirmed by dynamic light scattering (DLS) and field-emission scanning electron microscopy (FE-SEM). The aggregation behavior of POSS end-capped polymeric nanoparticles was further investigated through nile red encapsulation as a hydrophobic probe in aqueous medium.

A self-assembled polymeric micellar immunomodulator for cancer treatment based on cationic amphiphilic polymers

Here, we report a self-assembled polymeric micellar immunomodulator (SPI) for enhanced cancer treatment based on cationic amphiphilic polymers. To obtain the cationic amphiphilic polymer, the hydrophobic all-trans-retinoic acid (ATRA) was conjugated with a hydrophilic low-molecular-weight PEI (LowPEI, Mn = 1.8 kDa). The ATRA–LowPEI conjugates could self-assemble in aqueous media, forming micelles with a strong positive charge (∼+40 mV) and particle sizes of ∼70 nm. Compared to conventional therapeutic agents (e.g., cisplatin), the SPI exhibited enhanced anti-cancer activity regardless of drug resistance. After mechanistic in vitro cell death studies, we revealed that the mechanical disruptive force generated by the cationic charge of SPI primarily induced necrotic cell death. Furthermore, the organelle fragments induced by the necrotic cell death triggered antitumoral immune responses. Therefore, SPI induced synergistic effects of the cationic charge-induced necrosis and antitumoral immune responses could produce an effective cancer treatment. In addition, the SPI was shielded by hyaluronic acid (HA/SPI complex) to enhance its tumor selectivity in vivo. Finally, the HA/SPI complex accumulated selectively into tumor sites after systemic administration into tumor-bearing mice, exhibiting effective antitumoral effects without systemic toxicity. Therefore, this technology holds great potential for translation into a clinical cancer treatment.

Nature-inspired antimicrobial polymers--assessment of their potential for biomedical applications.

We explored the potential of poly(oxonorbornene)-based synthetic mimics of antimicrobial peptides (SMAMPs), a promising new class of antimicrobial polymers with cell-selectivity and low resistance development potential, for clinical applications. We evaluated their antimicrobial activity against a panel of seven clinical and regulatory relevant bacteria strains, and tested their toxicity with two different kinds of primary human cells. For the antimicrobial activity, we performed the minimum inhibitory concentration (MIC) assay and determined the minimum bactericidal concentration (MBC) according to the NCCLS guidelines. The results revealed specific problems that may occur when testing the antimicrobial activity of amphiphilic cationic polymers, and confirmed the working hypothesis that the more hydrophilic SMAMP polymers in our portfolio were ‘doubly selective’, i.e. they are not only selective for bacteria over mammalian cells, but also for Gram-positive over Gram-negative bacteria. The data also showed that we could improve the broad-band activity of one SMAMP, and in combination with the results from the cell toxicity experiments, identified this polymer as a promising candidate for further in-vitro and in-vivo testing. Transmission electron studies revealed that the cellular envelopes of both E. coli and S. aureus were severely damaged due to SMAMP action on the bacterial membrane, which strengthened the argument that SMAMPs closely resemble antimicrobial peptides. To test cell toxicity, we used the traditional hemolysis assay with human red blood cells, and the novel xCelligence assay with primary human fibroblasts. The data reported here is the first example in which a hemolysis assay is benchmarked against the xCelligence assay. It revealed that the same trends were obtained using these complementary methods. This establishes the xCelligence assay with primary human cells as a useful tool for SMAMP characterization.

Cationic antimicrobial polymers and their assemblies.

Cationic compounds are promising candidates for development of antimicrobial agents. Positive charges attached to surfaces, particles, polymers, peptides or bilayers have been used as antimicrobial agents by themselves or in sophisticated formulations. The main positively charged moieties in these natural or synthetic structures are quaternary ammonium groups, resulting in quaternary ammonium compounds (QACs). The advantage of amphiphilic cationic polymers when compared to small amphiphilic molecules is their enhanced microbicidal activity. Besides, many of these polymeric structures also show low toxicity to human cells; a major requirement for biomedical applications. Determination of the specific elements in polymers, which affect their antimicrobial activity, has been previously difficult due to broad molecular weight distributions and random sequences characteristic of radical polymerization. With the advances in polymerization control, selection of well defined polymers and structures are allowing greater insight into their structure-antimicrobial activity relationship. On the other hand, antimicrobial polymers grafted or self-assembled to inert or non inert vehicles can yield hybrid antimicrobial nanostructures or films, which can act as antimicrobials by themselves or deliver bioactive molecules for a variety of applications, such as wound dressing, photodynamic antimicrobial therapy, food packing and preservation and antifouling applications.

Hydrophobic poly (amino acid) modified PEI mediated delivery of rev-casp-3 for cancer therapy

Recent studies in amphiphilic cationic polymers have demonstrated their potential as gene carriers with high transfection efficiency and low cytotoxicity in the in vitro settings to deliver drug, siRNA and plasmid DNA. Yet their safety and efficacy in vivo remain to be a challenge, and require further investigation. In our previous work, PP80 was synthesized as a novel amphiphilic cationic polymer by grafting hydrophobic polyphenylalanine segment on PEI, which displayed higher transfection efficiency than PEI in a number of cell lines in vitro. Here, we reported the favorable biocompatibility displayed by PP80/pDNA complex both in vitro and in vivo. Furthermore, when therapeutic gene rev-casp-3 was conjugated to PP80 and administered intratumorally to a HeLa xenograft model, significant tumor apoptosis was induced with concurrent tumor growth inhibition, indicating that PP80 mediated expression of rev-casp-3 gene in solid tumors with not detectable side effects on the tumor-bearing mice. These data demonstrated that PP80 warrants further investigation as a promising cancer gene delivery vehicle.

Structural contributions of blocked or grafted poly(2-dimethylaminoethyl methacrylate) on PEGylated polycaprolactone nanoparticles in siRNA delivery

The multiformity in polymer structure and conformation design provides a great potential in improving the gene silencing efficiency of siRNA by polymer vectors. In order to provide information on the polymer design for siRNA delivery, the structural contributions of blocked or grafted poly(2-dimethylaminoethyl methacrylate) on PEGylated polycaprolactone nanoparticles (NPs) in siRNA delivery were studied. Herein, two kinds of self-assembly nanoparticles (NPs) formed by amphiphilic cationic polymers, methoxy poly(ethylene glycol)-block-polycaprolactone-block-poly(2-dimethylaminoethyl methacrylate) (mPEG-PCL- b-PDMAEMA, PEC bD) and methoxy poly(ethylene glycol)-block-(polycaprolactone-graft-poly(2-dimethylaminoethyl methacrylate)) (mPEG-PCL- g-PDMAEMA, PEC gD), were used to deliver siRNA for in vitro and in vivo studies. The physiochemical properties including size and zeta potential of PEC bD NPs/siRNA and PEC gD NPs/siRNA complexes were characterized. In vitro cytotoxicity, cellular uptake and siRNA knockdown efficiency were evaluated in HeLa-Luc cells. The endosome escape and intracellular distribution of PEC bD NPs/siRNA and PEC gD NPs/siRNA in HeLa-Luc cells were also observed. In vivo polymer mediated siRNA delivery and the complexes distribution in isolated organs were studied using mice and tumor-bearing mice. At the same total degree of polymerization (DP) of DMAEMA, PEC gD NPs/siRNA complexes possessed higher zeta potentials than PEC bD NPs/siRNA complexes (at the same N/P ratio), which may be the reason that PEC gD NPs/siRNA complexes can deliver more siRNA into the cytoplasm and lead to higher in vitro luciferase and lamin A/C silencing efficiency than PEC bD NPs/siRNA complexes. The in vivo imaging measurement and histochemical analysis also confirmed that siRNA could be delivered to lungs, livers, pancreas and HeLa-Luc tumors more efficiently by PEC gD NPs than PEC bD NPs. Meanwhile, the PDMAEMA chains of PEC gD could be shortened which provides benefits for clearing. Therefore, PEC gD NPs have great potential to be used as efficient non-viral carriers for in vivo siRNA delivery.

Theranostic Nanoparticles Engineered for Clinic and Pharmaceutics

Nanomedicine is the manipulation of human biological systems at the molecular level using nanoscale or nanostructured materials. Because nanoscale materials interact effectively with biological systems, the use of nanodiagnostics and nanotherapeutics may overcome many intractable health challenges. A variety of nanoparticles have been designed with modifiable functional surfaces and bioactive cores. The engineering of nanoparticles can result in several advantageous therapeutic and diagnostic properties including enhanced permeation and retention in the circulatory system, specific delivery of drugs to target sites, highly-efficient gene transfection, and enhanced medical imaging. These nanoscale materials offer the opportunity to detect chronic diseases early and to monitor the therapeutic effects of nanoformulated drugs used in the clinic. Many of these novel nanoparticles contain both drug(s) and imaging agent(s) within an individual nanoparticle for simultaneous disease diagnosis and therapy. Further integration of therapeutic compounds with diagnostic agents into theranostic nanoparticles would be highly beneficial. However, the unique physiochemical properties that make nanomaterials attractive for therapy and diagnosis may be also associated with potential health hazards. Our research has demonstrated that the biological response to nanomaterials is related to many factors including exposure levels, systemic accumulation and excretion profiles, tissue and organ distribution, and the age of the test subject. Therefore, when engineering new nanomaterials for clinical use, researchers need to consider these factors to minimize toxicity of nanoparticles in these applications. We have fabricated and evaluated nanomaterials such as cationic amphiphilic polymers and metallofullerenes that demonstrate both high efficiency and low toxicity in gene therapy and/or chemotherapy. In this Account, we describe the development of theranostic nanomaterials with low toxicity and illustrate their potential use as novel nanomedicines in translational research.

Novel poly(glycidyl methacrylate-b-propylene oxide-b-glycidyl methacrylate) derivatives with low cytotoxicity and efficient gene delivery

Gene therapy has been developed for decades, but is still hampered for general clinical treatment by lack of gene delivery vectors with high transfection efficiency and low cytotoxicity. In this study, well-defined BAB triblock copolymer, poly(glycidyl methacrylate-b-propylene oxide-b-glycidyl methacrylate), P(GMA-b-PO-b-GMA), was prepared via atom transfer radical polymerization and modified by different ratios of ethylenediamine (EDA) and 1-(3-aminopropyl) imidazole (API) to obtain cationic amphiphilic polymers. The difference in the ratio of EDA and API had an influence on pDNA-binding capability, size, and zeta potential of P(GMA-b-PO-b-GMA) derivatives. All the cationic amphiphilic polymers exhibited low cytotoxicity and good transfection activity in comparison with 25 kDa polyethylenimine (PEI) due to their special architecture. The optimal polymer, with 89% API and 11% EDA, showed the highest transfection efficiency among these polymers. Its luciferase expression at N/P ratio of 30 was comparable to that of 25 kDa PEI in a serum-free medium and higher than that of 25 kDa PEI by roughly an order of magnitude in a medium with serum.

Amphiphilic and biodegradable methoxy polyethylene glycol-block-(polycaprolactone-graft-poly(2-(dimethylamino)ethyl methacrylate)) as an effective gene carrier

A group of amphiphilic cationic polymers, methoxy polyethylene glycol- block-(polycaprolactone- graft-poly(2-(dimethylamino)ethyl methacrylate)) (PECD), were synthesized by combining ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP) methods to form nanoparticles (NPs). The structures of these amphiphilic cationic polymers were characterized by 1H NMR measurement. The PECD NPs have hydrophobic cores covered with hydrophilic PEG and cationic PDMAEMA chains. These self-assembly nanoparticles were characterized by dynamic light scattering (DLS) technique. PECD NPs can effectively condense DNA to form compact complexes of the size 65–160 nm suitable for gene delivery. The in vitro gene transfection studies of HeLa and HepG2 cells show that PECD NPs have better transfection efficiency compared to polyethylenimine (PEI) and Lipofectamine 2000 at low dose ( N/P = 5). The cytotoxicity result shows that PECD NPs/DNA complexes at the optimal N/P ratio for transfection have comparable toxicity with PEI and Lipofectamine. These results indicate that PECD NPs have a great potential to be used as efficient polymeric carriers for gene transfection.

Properties of new cationic amphiphilic polymers in hydro-alcoholic media

BACKGROUND: Following our recent synthesis and characterization of three new families of cationic amphiphilic polymers with great structural variability, this paper reports their physical chemical properties in aqueous media in relation to their chemical structure. These amphiphilic polymers are comb poly(meth)acrylamides laterally substituted by groups containing a quaternary ammonium site and hydrophobic n-alkyl side chains with variable lengths. RESULTS: Viscometry first showed that these polymers display typical polysoap behaviour in hydro-alcoholic mixtures. Fluorescence spectrometry was then used to characterize the corresponding intramolecular association with two complementary fluorescent probes. In addition to confirming macromolecular folding, pyrene provided information about the probe local environment polarity whereas a molecular rotor gave interesting complementary information about the compactness of the corresponding nano-domains. CONCLUSION: It was shown that increasing the length of the n-alkyl side chain induced much better polysoap properties whereas increasing the size of the spacer between the two polar amide and ammonium groups and the presence of a methyl side group had the greatest impact on the nano-domain characteristics. Copyright © 2009 Society of Chemical Industry

Amphiphilic Branched Polymers as Antimicrobial Agents

Cationic amphiphilic polymers were prepared from PEI and functional ethylene carbonates bearing cationic, hydrophobic or amphiphilic groups. The polymers are designed to exhibit antimicrobial properties. In a one-step addition, different functional ethylene carbonates were added to react with the primary amine groups of PEI. The water soluble polymers were studied regarding their ability to form soluble aggregates. Their hydrodynamic radii, their inhibition potential against proliferation of E. coli and their hemolytic potential were determined. A structure-property relationship was established by analyzing the antimicrobial activity as a function of the ratio of alkyl to cationic groups, length of the alkyl chains, and molecular weight of the PEI.

New amphiphilic polyacrylamides: Synthesis and characterisation of pseudo-micellar organisation in aqueous media

In order to offer new tools for developing structure–property relationships for intramolecular associative polymers (polysoaps), the synthesis of three families of comb-like amphiphilic cationic polymers with great structure variability is described. These polymers with amphiphilic repeating units are polyacryl or methacrylamides laterally substituted by a group containing a quaternary ammonium site and a hydrophobic alkyl side chain with 10–16 carbon atoms. Two complementary synthesis methods were developed successfully. In the first method, the tertiary amine groups of neutral polymer precursors were quaternised with various n-alkyl bromides. Five polymers were obtained in this way. On the contrary, the second method consisted of synthesizing first amphiphilic cationic acryl or methacrylamide monomers. The 11 monomers thus obtained were then polymerised by conventional free radical polymerisation in solution. The polymers obtained by both methods only differed in their molecular weights, the second method leading to much higher molecular weights (up to 2 × 10 6 g/mol). A preliminary investigation of the properties of a few of these polymers in solution showed interesting amphiphilic behaviour. The variation of the reduced viscosity of hydro-methanolic polymer solutions with polymer concentration revealed a strong intramolecular macromolecular folding. The microdomains corresponding to the intramolecular association of the hydrophobic alkyl side chains were eventually characterised by pyrene fluorescence spectroscopy. The local polarity of the pyrene probe was considerably lowered with respect to that of the surrounding aqueous phase and was dependent upon the macromolecular structure of the amphiphilic cationic polymers.

Self-assembled polyethylenimine-graft-poly(ε-caprolactone) micelles as potential dual carriers of genes and anticancer drugs

A series of amphiphilic cationic graft polymers (PEC) were synthesized by coupling poly(ε-caprolactone) of differing molecular weights (MW) to low MW branched polyethylenimine via an amide group. IR, 1H-NMR and GPC were employed to characterize the graft copolymers. The self-assembly characteristics of these copolymers in an aqueous solution were studied by fluorescence techniques. The critical micelle concentration (CMC) varied from 0.044 to 0.032g/L when the MW of poly(ε-caprolactone) increased from 1800 to 5500. The micelles formed electrostatic complexes with a reporter gene (pCMV-Luc) after an anticancer drug, Doxorubicin (DOX), was loaded by dialysis method. Gel retardation studies proved that micelles with or without DOX were able to complex with DNA completely at an equivalent N/P ratio of around 2.0, indicating that drug loading did not interfere in the interaction between the PEI shell and DNA. Particle size slightly decreased at higher N/P ratios of polyplexes, but increased with drug encapsulation. It was also noted that DNA/micelle complexes were significantly less toxic to HepG2 cells than blank PEC micelles, and improved gene transfection efficiency (about 3 orders of magnitude greater than PEI 25K alone at most) whether DOX was present in the system or not. These results suggest that this group of cationic graft polymers may be a potential candidate for the development of a drug delivery system that can examine the synergistic effects of combined drug and gene therapy.

Effect of cationic surfactant and block copolymer on carbon black particle surface charge and size

In this paper, the size reduction and surface charge modification of carbon black particles aqueous dispersions by cationic surfactant, cetyltrimethylammonium chloride (CTAC), and amphiphilic polymer, polystyrene-polyethylene oxide (PS-PEO) are described. Aqueous and vacuum dried carbon black dispersions containing various amounts of CTAC surfactant or PS-PEO copolymer were analysed by dynamic light scattering, microelectrophoresis and by transmission electron microscopy. In presence of CTAC and PS-PEO additives, the final carbon particle sizes in aqueous dispersions were in the range 170–230 nm, whereas in vacuum dried dispersions, the achieved particle sizes were in the range 327–372 nm. Blank experiments made in absence of surfactant and copolymer gave carbon black particles mean sizes of 330 and 470 nm, respectively, in aqueous and vacuum dried dispersions. Further, in presence of PS-PEO copolymer, the magnitude of zeta potential was reduced from −50 to −18 mV, whereas in presence of CTAC surfactant, the sign of zeta potential was reversed from negative to positive and its magnitude decreased from −50 to +35 mV. Beyond the size reduction and the surface charge modification of carbon particles by CTAC surfactant and PS-PEO copolymer, the preparation mode of carbon dispersions was also found to affect the carbon particle properties. The overall data are explained in term of the nature of interactions occurring at carbon-aqueous solution interface. The knowledge of such interactions is the prerequisite to prevent the aggregation of carbon particles either in solution or in polymeric matrix.

Controlled Polymerization of Functional Monomers and Synthesis of Block Copolymers Using a β-Phosphonylated Nitroxide

4-Vinylpyridine (4VP) and N,N-dimethylacrylamide (DMAA) were polymerized in a controlled manner using a β-phosphonylated nitroxide (N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide, commonly designated as DEPN) as a control agent. Compared to the results that had previously been reported for the nitroxide-mediated radical polymerization (NMRP) with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), the polymerization of 4VP was much faster and very well controlled up to higher monomer conversions. Unlike 4VP, the controlled radical polymerization of DMAA using different types of nitroxides had so far remained limited to a very low conversion range (typically inferior to 10%). The use of DEPN gave rise to a very significant improvement of the NMRP of DMAA by providing a good reaction control up to high conversion (approximately 60%). For the first time, the ability of DEPN to control the homopolymerization of DMAA even at high conversion allowed the synthesis of poly(DMAA-b-4VP) block copolymers with a hydrophilic poly(DMAA) block which was longer than the poly(4VP) block. This particular feature should fairly improve the hydrosolubility of the derived amphiphilic cationic polymers, which can be obtained by simple quaternization of the former block copolymers, and extend the scope of their applications.

AMINE FUNCTIONALIZED POLYETHERS AS BILE ACID SEQUESTRANTS: SYNTHESIS AND BIOLOGICAL EVALUATION

A series of amine functionalized polymers based on polyether backbones was prepared by the chemical modification of poly(epichlorohydrin) and poly(2-chloroethylvinyl ether). Nucleophilic substitution of pendant chloroalkyl groups offers a versatile route to prepare hydrophilic, cationic polymers. Through the choice of appropriate experimental conditions, including solvent, temperature, and amine reagent, a high degree of substitution at the chloromethyl groups can be achieved. Depending on the nature of the amine used, both water-soluble and amphiphilic cationic polymers were obtained. Crosslinked hydrogels were prepared by either subsequent crosslinking of the amine functional polyethers or by reaction of chloroalkyl polyethers with multifunctional amines. These amine functional polyethers exhibited promising bile acid sequestration properties during in vivo experiments using hamsters as animal models, providing a novel approach for treating hypercholesterolemia. Some of these polymers show efficacy superior to commercially available bile acid sequestrants. The results suggest that these novel polyammonium gels may be useful as cholesterol lowering agents.

Fluorescent molecular rotors as probes for polymers

AbstractThe use of a molecular rotor (1,1‐dicyano‐4‐(4'‐dimethylaminophenyl)‐1,3‐butadiene) as a fluorescent probe was proved to be of great interest for the study of polymers. First, the rotor can detect the critical time of the glass effect in the bulk polymerization of MMA into PMMA due to viscosity change, this will allow a better control of the process and is complementary to the information issued from the use of the fluorescent pyrene probe which is sensitive to the gel effect. Second, the cinnamylidene rotor was able to detect the formation of hydrophobic microdomains for cationic amphiphilic polymers in their aggregation modes when they were solubilized in water, both polarity and viscosity changes are playing a role. The possibility of incorporation of various molecular fluorescent rotors in polymers beads was also studied.

Fluorescent probes for detection of amphiphilic polymer hydrophobic microdomains: A comparative study between pyrene and molecular rotors

Cationic amphiphilic polymers (e.g. polyvinylpyridinium bromides and polyvinylimidazolium bromides) adopt a compact coiled form in aqueous solutions. In the case of former polymers, the resulting hydrophobic microdomains are evidenced only by fluorescence spectroscopy if a molecular rotor (DMAC) is used as a fluorescent probe, while the behaviour of the latter can be studied in aqueous solution by using both types of fluorescent probes, i.e., pyrene and the molecular rotor. The purpose of the present investigation deals with a comparative study between the magnitude of the local viscosity and the polarity of the hydrophobic microdomains generated by poly(3-hexadecyl-1-vinylimidazolium bromide) in an aqueous medium using pyrene and DMAC as fluorescent probes. Moreover, the results are compared with the data obtained with micelles of conventional surfactants such as the homopolymer repetitive unit model and CTAB.