Modulation of photo-oxidative DNA damage by cationic surfactant complexation

Arginine-phenylalanine and arginine-tryptophan-based surfactants as new biocompatible antifungal agents and their synergistic effect with Amphotericin B against fluconazole-resistant Candida strains

In the past two decades, the increase in microbial resistance to conventional antimicrobials has spurred scientists around the world to search tirelessly for new treatments. Synthetic amino acid-based surfactants constitute a promising alternative to conventional antimicrobial compounds. In this work, two new cationic amino acid-based surfactants were synthesized and their physicochemical, antifungal and antibiofilm properties evaluated. The surfactants were based on phenylalanine-arginine (LPAM) and tryptophan-arginine (LTAM) and prepared from renewable raw materials using a simple chemical procedure. The critical micelle concentrations of the new surfactants were determined by conductivity and fluorescence. Micellization of LPAM and LTAM took place at 1.05 and 0.54 mM, respectively. Both exhibited good antifungal activity against fluconazole-resistant Candida spp. strains, with a low minimum inhibitory concentration (8.2 μg/mL). Their mechanism of action involves alterations in cell membrane permeability and mitochondrial damage, leading to death by apoptosis. Furthermore, when LPAM and LTAM were applied with Amphotericin B, a significant synergistic effect was observed against all the studied Candida strains. These new cationic surfactants are also able to disperse biofilms of Candida spp. at low concentrations. The results indicate that LPAM and LTAM have potential application to combat the advance of fungal resistance as well as microbial biofilms.

Reversible Supra-Folding of User-Programmed Functional DNA Nanostructures on Fuzzy Cationic Substrates

We report that user-defined DNA nanostructures, such as two-dimensional (2D) origamis and nanogrids, undergo a rapid higher-order folding transition, referred to as supra-folding, into three-dimensional (3D) compact structures (origamis) or well-defined μm-long ribbons (nanogrids), when they adsorb on a soft cationic substrate prepared by layer-by-layer deposition of polyelectrolytes. Once supra-folded, origamis can be switched back on the surface into their 2D original shape through addition of heparin, a highly charged anionic polyelectrolyte known as an efficient competitor of DNA-polyelectrolyte complexation. Orthogonal to DNA base-pairing principles, this reversible structural reconfiguration is also versatile; we show in particular that 1) it is compatible with various origami shapes, 2) it perfectly preserves fine structural details as well as site-specific functionality, and 3) it can be applied to dynamically address the spatial distribution of origami-tethered proteins.

Light-Controlled in Vitro Gene Delivery Using Polymer-Tethered Spiropyran as a Photoswitchable Photosensitizer

A gene delivery system using spiropyran as a photoswitchable photosensitizer for the controlled photochemical internalization effect was developed by engineering the outer coating of a polyethylenimine/DNA complex with a small amount of spiropyran-containing cationic copolymers. The successful binding of cationic polymers by the polyethylenimine coating was detected by the distance-sensitive fluorescence resonance energy-transfer technique that evidenced the occurrence of energy transfer between fluorescein-labeled cationic copolymers and polyethylenimine-condensed rhodamine-labeled DNA. The ternary polyplexes feature reversible controllability of singlet oxygen generation based on the dual effect of spiropyrans in photochromism and aggregation-induced enhanced photosensitization, allowing significant light-induced amplification of bPEI-mediated in vitro transgene efficiency (from original 15% to final 91%) at a low DNA dose, with the integrity of supercoiled DNA structure unaffected. The use of spiropyran without the need of other photosensitizers circumvents the issue of uncontrolled long-lasting photocytotoxicity in gene delivery.

ortho-Fluoroazobenzene derivatives as DNA intercalators for photocontrol of DNA and nucleosome binding by visible light

We report a high-affinity photoswitchable DNA binder, which displays different nucleosome-binding capacities upon visible-light irradiation. Both photochemical and DNA-recognition properties were examined by UV-Vis, HPLC, CD spectroscopy, NMR, FID assays, EMSA and DLS. Our probe sets the basis for developing new optoepigenetic tools for conditional modulation of nucleosomal DNA accessibility.

Remarkable Amplification of Polyethylenimine-Mediated Gene Delivery Using Cationic Poly(phenylene ethynylene)s as Photosensitizers

Conjugated polymers can serve as good photosensitizers in biomedical applications. However, it remains unknown whether they are phototoxic to the supercoiled structure of DNA in improving gene delivery by the photochemical internalization (PCI) strategy, which complicates the application of conjugated polymers in gene delivery. In this work, we introduced a trace amount of cationic poly(phenylene ethynylene)s (cPPEs) into the polymeric shell of branched polyethylenimine (BPEI)/DNA complexes, studied the photosensitization of singlet oxygen by cPPEs, and confirmed that the supercoiled DNA is undamaged by the singlet oxygen generated by the photoexcitation of cPPEs. By taking advantage of the cPPE-mediated PCI effect, we report that the addition of the trace amount of cPPEs to the outer shell of the BPEI/DNA polyplexes could greatly amplify the transfection of gene green fluorescent protein on tumor cells with the efficiency from 14 to 86% without decreasing the cell viabilities, well solving the problem with a poor transfection capability of BPEI under low DNA-loading conditions. Our strategy to employ conjugated polymers as photosensitizing agents in gene delivery systems is simple, safe, efficient, and promising for broad applications in gene delivery areas.

Benzophenone photosensitized DNA damage

Although the carcinogenic potential of ultraviolet radiation is well-known, UV light may interact with DNA by direct absorption or through photosensitization by endogenous or exogenous chromophores. These chromophores can extend the "active" fraction of the solar spectrum to the UVA region and beyond, which means that photosensitizers increase the probability of developing skin cancer upon exposure to sunlight. Therefore researchers would like to understand the mechanisms involved in photosensitized DNA damage both to anticipate possible photobiological risks and to design tailor-made photoprotection strategies. In this context, photosensitized DNA damage can occur through a variety of processes including electron transfer, hydrogen abstraction, triplet-triplet energy transfer, or generation of reactive oxygen species. In this Account, we have chosen benzophenone (BP) as a classical and paradigmatic chromophore to illustrate the different lesions that photosensitization may prompt in nucleosides, in oligonucleotides, or in DNA. Thus, we discuss in detail the accumulated mechanistic evidence of the BP-photosensitized reactions of DNA or its building blocks obtained by our group and others. We also include ketoprofen (KP), a BP-derivative that possesses a chiral center, to highlight the stereodifferentiation in the key photochemical events, revealed through the dynamics of the reactive triplet excited state ((3)KP*). Our results show that irradiation of the BP chromophore in the presence of DNA or its components leads to nucleobase oxidations, cyclobutane pyrimidine dimer formation, single strand breaks, DNA-protein cross-links, or abasic sites. We attribute the manifold photoreactivity of BP to its well established photophysical properties: (i) it absorbs UV light, up to 360 nm; (ii) its intersystem crossing quantum yield (ϕ(ISC)) is almost 1; (iii) the energy of its nπ* lowest triplet excited state (E(T)) is ca. 290 kJ mol(-1); (iv) it produces singlet oxygen ((1)O(2)) with a quantum yield (ϕ(Δ)) of ca. 0.3. For electron transfer and singlet oxygen reactions, we focused on guanine, the nucleobase with the lowest oxidation potential. Among the possible oxidative processes, electron transfer predominates. Conversely, triplet-triplet energy transfer occurs mainly from (3)BP* to thymine, the base with the lowest lying triplet state in DNA. This process results in the formation of cyclobutane pyrimidine dimers, but it also competes with the Paternò-Büchi reaction in nucleobases or nucleosides, giving rise to oxetanes as a result of crossed cycloadditions. Interestingly, we have found significant stereodifferentiation in the quenching of the KP triplet excited state by both 2'-deoxyguanosine and thymidine. Based on these results, this chromophore shows potential as a (chiral) probe for the investigation of electron and triplet energy transport in DNA.

Enhancement of DNA compaction by negatively charged nanoparticles: effect of nanoparticle size and surfactant chain length

We study the compaction of genomic DNA by a series of alkyltrimethylammonium bromide surfactants having different hydrocarbon chain lengths n: dodecyl-(DTAB, n=12), tetradecyl-(TTAB, n=14) and hexadecyl-(CTAB, n=16), in the absence and in the presence of negatively charged silica nanoparticles (NPs) with a diameter in the range 15-100 nm. We show that NPs greatly enhance the ability of all cationic surfactants to induce DNA compaction and that this enhancement increases with an increase in NP diameter. In the absence of NP, the ability of cationic surfactants to induce DNA compaction increases with an increase in n. Conversely, in the presence of NPs, the enhancement of DNA compaction increases with a decrease in n. Therefore, although CTAB is the most efficient surfactant to compact DNA, maximal enhancement by NPs is obtained for the largest NP diameter (here, 100 nm) and the smallest surfactant chain length (here, DTAB). We suggest a mechanism where the preaggregation of surfactants on NP surface mediated by electrostatic interactions promotes cooperative binding to DNA and thus enhances the ability of surfactants to compact DNA. We show that the amplitude of enhancement is correlated with the difference between the surfactant concentration corresponding to aggregation on DNA alone and that corresponding to the onset of adsorption on nanoparticles.

Interaction of DNA and a series of aromatic donor-viologen acceptor molecules with and without the presence of CB[8]

A series of 1-ethyl-1'-arylmethyl-4,4'-bipyridinium compounds is synthesized, where the aryl is phenyl (BEV), 2-naphthyl (NEV), 2-anthracenyl (AEV) or 1-pyrenyl (PEV). Among them, PEV and AEV can bind with calf thymus DNA mainly through intercalation and groove-binding modes, and both of them can be observed to photocleave plasmid pBR 322 DNA significantly under irradiation with a xenon arc lamp. After inclusion of cucurbit[8]uril (CB[8]), all of the aromatic donor-viologen acceptor compounds exhibit efficient DNA photocleavage ability. The reason is that CB[8] can inhibit the intramolecular backwards electron transfer in the aromatic donor-viologen acceptor molecule, prolonging the lifetime of the charge separated excited state to some extent. These studies bring a new subject in DNA photocleavage research and a potential application of the host-guest supramolecular system.

Electrochemical and spectroscopic study of octadecyltrimethylammonium bromide/DNA surfoplexes

The use of cationic micelles consisting of octadecyltrimethylammonium bromide (C18TAB) to compact calf thymus DNA has been investigated in aqueous buffered solution at 310.15 K by means of conductometry, electrophoretic mobility, and several fluorescence spectroscopy methods. The results indicate that C18TAB micelles, consisting of 44 monomers on average, may compact DNA molecule by an electrostatic interaction that takes place at the cationic spherical micelle surface. The surfoplexes thus formed show a surface density charge that goes from negative to positive values at a Lmic/D mass ratio of around 1.0 (where Lmic and D are the masses of micellized cationic surfactant and DNA), called the isoneutrality ratio (Lmic/D)phi. Values of this characteristic parameter, determined in this work not only from the electrochemical experimental data but also from spectroscopic measurements, are in very good agreement with those ones calculated from molecular parameters and some other properties also obtained in this work. The electrostatic character of the DNA-micelle interaction has been confirmed by analyzing the decrease in fluorescence emission of the fluorophore ethidium bromide, EtBr, initially intercalated between DNA base pairs, as long as the surfoplexes are formed. Fluorescence anisotropy experiments have revealed that micelle packing becomes more rigid in the presence of DNA, but once the surfoplex is formed, the fluidity increases with the Lmic/D mass ratio, attaining its maximum when the isoneutrality ratio is exceeded. This fact, together with the net positive charge of the surfoplexes with the Lmic/D mass ratio over the isoneutrality ratio, makes this regimen of lipid and DNA content the optimum for efficiency in the transfection process.