Coumarin-poly(2-oxazoline)s as synergetic and protein-undetected nanovectors for photodynamic therapy

Because of the difficult challenges of nanopharmaceutics, the development of a variety of nanovectors is still highly desired. Photodynamic therapy, which uses a photosensitizer to locally produce reactive oxygen species to kill the undesired cells, is a typical example for which encapsulation has been shown to be beneficial. The present work describes the use of coumarin-functionalized polymeric nanovectors based on the self-assembly of amphiphilic poly(2-oxazoline)s. Encapsulation of pheophorbide a, a known PDT photosensitizer, is shown to lead to an increased efficiency compared to the un-encapsulated version. Interestingly, the presence of coumarin both enhances the desired photocytotoxicity and enables the crosslinking of the vectors. Various nanovectors are examined, differing by their size, shape and hydrophilicity. Their behaviour in PDT protocols on HCT-116 cells monolayers is described, the influence of their crosslinking commented. Furthermore, the formation of a protein corona is assessed.

Terahertz Spectroscopy Sheds Light on Real-Time Exchange Kinetics Occurring through Plasma Membrane during Photodynamic Therapy Treatment

Methods to follow in real time complex processes occurring along living cell membranes such as cell permeabilization are rare. Here, the terahertz spectroscopy reveals early events in plasma membrane alteration generated during photodynamic therapy (PDT) protocol, events which are not observable in any other conventional biological techniques performed in parallel as comparison. Photodynamic process is examined in Madin-Darby canine kidney cells using Pheophorbide (Pheo) photosensitizer alone or alternatively encapsulated in poly(ethylene oxide)-block-poly(ε-caprolactone) micelles for drug delivery purpose. Terahertz spectroscopy (THz) reveals that plasma membrane permeabilization starts simultaneously with illumination and is stronger when photosensitizer is encapsulated. In parallel, the exchange of biological species is assessed. Over several hours, this conventional approach demonstrates significant differences between free and encapsulated Pheo, the latter leading to high penetration of propidium iodide, Na+ and Ca2+ ions, and a high level of leakage of K+ , ATP, and lactate dehydrogenase. THz spectroscopy provides, in a single measurement, the relative number of defects per membrane surface created after PDT, which is not achieved by any other method, providing early, sensitive real-time information. THz spectroscopy is therefore a promising technique and can be applied to any biological topic requiring the examination of short-term plasma membrane permeabilization.

Synthesis and Self-Assembly of UV-Cross-Linkable Amphiphilic Polyoxazoline Block Copolymers: Importance of Multitechnique Characterization

In the nanomedicine field, there is a need to widen the availability of nanovectors to compensate for the increasingly reported side effects of poly(ethene glycol). Nanovectors enabling cross-linking can further optimize drug delivery. Cross-linkable polyoxazolines are therefore relevant candidates to address these two points. Here we present the synthesis of coumarin-functionalized poly(2-alkyl-2-oxazoline) block copolymers, namely, poly(2-methyl-2-oxazoline)-block-poly(2-phenyl-2-oxazoline) and poly(2-methyl-2-oxazoline)-block-poly(2-butyl-2-oxazoline). The hydrophilic ratio and molecular weights were varied in order to obtain a range of possible behaviors. Their self-assembly after nanoprecipitation or film rehydration was examined. The resulting nano-objects were fully characterized by transmission electron microscopy (TEM), cryo-TEM, multiple-angle dynamic and static light scattering. In most cases, the formation of polymer micelles was observed, as well as, in some cases, aggregates, which made characterization more difficult. Cross-linking was performed under UV illumination in the presence of a coumarin-bearing cross-linker based on polymethacrylate derivatives. Addition of the photo-cross-linker and cross-linking resulted in better-defined objects with improved stability in most cases.

Cold helium plasma jet does not stimulate collagen remodeling in a 3D human dermal substitute

Cold Atmospheric Plasma (CAP) is an emerging physical approach displaying encouraging antitumor and wound healing effects both in vitro and in vivo. In this study, we assessed the potential of direct CAP to remodel skin collagens using an original tissue-engineered human dermal substitute model rich in endogenous extracellular matrix (ECM) covered with 600 µl of culture medium and treated with CAP for 30 and 120 s. Our results indicated that Reactive Oxygen and Nitrogen Species (RONS) such as H₂O₂, NO₃^- and NO₂^- were produced in the medium during treatment. It appeared that in the CAP-treated dermal substitutes 1) cell viability was not altered, 2) pro-collagen I secretion was not modified over 48 h of culture after treatment, 3) global activity of matrix metalloproteinases MMPs was not modulated over 48 h after treatment, and 4) no change in hydroxyproline content was observed over 5 days after treatment. In order to confirm the efficiency of our device, we showed that the plasma-activated culture medium induced cell apoptosis and growth delay using a 3D human tumor spheroid model. In conclusion, no effect of direct CAP treatment was monitored on dermal ECM production and degradation, indicating that CAP does not stimulate collagen remodeling at the tissue scale.

Vascular and extracellular matrix remodeling by physical approaches to improve drug delivery at the tumor site

INTRODUCTION

Modern comprehensive studies of tumor microenvironment changes allowed scientists to develop new and more efficient strategies that will improve anticancer drug delivery on site. The tumor microenvironment, especially the dense extracellular matrix, has a recognized capability to hamper the penetration of conventional drugs. Development and co-applications of strategies aiming at remodeling the tumor microenvironment are highly demanded to improve drug delivery at the tumor site in a therapeutic prospect.

AREAS COVERED

Increasing indications suggest that classical physical approaches such as exposure to ionizing radiations, hyperthermia or light irradiation, and emerging ones as sonoporation, electric field or cold plasma technology can be applied as standalone or associated strategies to remodel the tumor microenvironment. The impacts on vasculature and extracellular matrix remodeling of these physical approaches will be discussed with the goal to improve nanotherapeutics delivery at the tumor site.

EXPERT OPINION

Physical approaches to modulate vascular properties and remodel the extracellular matrix are of particular interest to locally control and improve drug delivery and thus increase its therapeutic index. They are particularly powerful as adjuvant to nanomedicine delivery; the development of these technologies could have extremely widespread implications for cancer treatment.[Figure: see text].

Electroporation does not affect human dermal fibroblast proliferation and migration properties directly but indirectly via the secretome

Aesthetic wound healing is often experienced by patients after electrochemotherapy. We hypothesized that pulsed electric fields applied during electrochemotherapy (ECT) or gene electrotransfer (GET) protocols could stimulate proliferation and migration of human cutaneous cells, as described in protocols for electrostimulation of wound healing. We used videomicroscopy to monitor and quantify in real time primary human dermal fibroblast behavior when exposed in vitro to ECT and GET electric parameters, in terms of survival, proliferation and migration in a calibrated scratch wound assay. Distinct electric field intensities were applied to allow gradient in cell electropermeabilization while maintaining reversible permeabilization conditions, in order to mimic in vivo heterogeneous electric field distribution of complex tissues. Neither galvanotaxis nor statistical modification of fibroblast migration were observed in a calibrated scratch wound assay after application of ECT and GET parameters. The only effect on proliferation was observed under the strongest GET conditions, which drastically reduced the number of fibroblasts through induction of mitochondrial stress and apoptosis. Finally, we found that 24 h-conditioned cell culture medium by electrically stressed fibroblasts tended to increase the migration properties of cells that were not exposed to electric field. RT-qPCR array indicated that several growth factor transcripts were strongly modified after electroporation.

Role of Polymer Micelles in the Delivery of Photodynamic Therapy Agent to Liposomes and Cells

The use of nanocarriers for hydrophobic photosensitizers, in the context of photodynamic therapy (PDT) to improve pharmacokinetics and bio-distribution, is well-established. However, the mechanisms at play in the internalization of nanocarriers are not well-elucidated, despite its importance in nanocarrier design. In this study, we focus on the mechanisms involved in copolymer poly(ethylene oxide)-block-poly(-caprolactone) PEO-PCL and poly(ethylene oxide)-block-poly styrene PEO-PS micelles - membrane interactions through complementary physico-chemical studies on biomimetic membranes, and biological experiments on two-dimensional (2D) and three-dimensional (3D) cell cultures. Förster Resonance Energy Transfer measurements on fluorescently-labelled lipid vesicles, and flow cytometry on two cancerous cell lines enabled the evaluation in the uptake of a photosensitizer, Pheophorbide a (Pheo), and copolymer chains towards model membranes, and cells, respectively. The effects of calibrated light illumination for PDT treatment on lipid vesicle membranes, i.e., leakage and formation of oxidized lipids, and cell viability, were assessed. No significant differences were observed between the ability of PEO-PCL and PEO-PS micelles in delivering Pheo to model membranes, but Pheo was found in higher concentrations in cells in the case of PEO-PCL. These higher Pheo concentrations did not correspond to better performances in PDT treatment. We demonstrated that there are subtle differences in PEO-PCL and PEO-PS micelles for the delivery of Pheo.

Rational design of block copolymer self-assemblies in photodynamic therapy

Photodynamic therapy is a technique already used in ophthalmology or oncology. It is based on the local production of reactive oxygen species through an energy transfer from an excited photosensitizer to oxygen present in the biological tissue. This review first presents an update, mainly covering the last five years, regarding the block copolymers used as nanovectors for the delivery of the photosensitizer. In particular, we describe the chemical nature and structure of the block copolymers showing a very large range of existing systems, spanning from natural polymers such as proteins or polysaccharides to synthetic ones such as polyesters or polyacrylates. A second part focuses on important parameters for their design and the improvement of their efficiency. Finally, particular attention has been paid to the question of nanocarrier internalization and interaction with membranes (both biomimetic and cellular), and the importance of intracellular targeting has been addressed.

Effects of Plasma Activated Medium on Head and Neck FaDu Cancerous Cells: Comparison of 3D and 2D Response

OBJECTIVE

The aim of this work is to investigate the inhibitory effect of Plasma Activated Medium (PAM) on Head and Neck cancerous cells (FaDu). The response of FaDu cells in monolayer cultures and Multi Cellular Tumor Spheroids (MCTS) after treatment with different PAMs will be compared.

BACKGROUND

Head and Neck squamous cell carcinoma is a widespread cancer that responds poorly to anticancer treatments such as chemotherapy and radiotherapy. Nowadays there is a growing interest in cold plasmas and their applications in cancer therapy.

METHODS

A homemade helium plasma jet is used to produce PAM. The effects of PAM and hydrogen peroxide H₂O₂ on FaDu 2D cells cultures and MCTS were characterized by evaluating the cell viability with PrestoBlue test and by measuring the size of MCTS.

RESULTS

One treatment with PAM induce cell detachment from MCTS since the first day in a PAM exposure dependent manner. This is due to the presence of H₂O₂ in PAM. However, a rapid spheroids regrowth is observed attributed to a resistance of FaDu cells to H₂O₂. After multiple treatments of MCTS with PAM we obtained an inhibition of cell growth. MCTS are brought out when comparing PAM effect on 2D versus MCTS. Inversely, PAM induces cell death in the case of 2D cell culture.

CONCLUSION

PAM may be considered as a potentially efficient agent in the therapy of head and neck cancer. We also point out that MCTS is a more valuable model than 2D cell culture for the evaluation of the anti-cancer activity of PAM.

Effect of trans(NO, OH)-[RuFT(Cl)(OH)NO](PF6) ruthenium nitrosyl complex on methicillin-resistant Staphylococcus epidermidis

Antibiotic resistance is becoming a global scourge with 700,000 deaths each year and could cause up to 10 million deaths by 2050. As an example, Staphylococcus epidermidis has emerged as a causative agent of infections often associated with implanted medical devices. S. epidermidis can form biofilms, which contribute to its pathogenicity when present in intravascular devices. These staphylococci, embedded in the biofilm matrix, are resistant to methicillin, which had long been the recommended therapy and which has nowadays been replaced by less toxic and more stable therapeutic agents. Moreover, current reports indicate that 75 to 90% of Staphylococcus epidermidis isolates from nosocomial infections are methicillin-resistant strains. The challenge of successfully combating antibiotics resistance in biofilms requires the use of compounds with a controlled mode of action that can act in combination with antibiotics. Ruthenium nitrosyl complexes are potential systems for NO release triggered by light. The influence of trans(NO, OH)-[RuFT(Cl)(OH)NO](PF₆) on Staphylococcus epidermidis resistant to methicillin is described. The results show a 50% decrease in cell viability in bacteria treated with low concentrations of NO. When combined with methicillin, this low dose of NO dramatically decreases bacterial resistance and makes bacteria 100-fold more sensitive to methicillin.

Amphiphilic polymers based on polyoxazoline as relevant nanovectors for photodynamic therapy

Coumarin crosslinked polyoxazoline-based vectors developed for efficient photodynamic therapy.

Extended photo-induced endosome-like structures in giant vesicles promoted by block-copolymer nanocarriers

Upon irradiation, the photosensitizer pheophorbide-a causes dramatic morphological transitions in giant unilamellar lipid vesicles. This endocytosis-like process occurs only when the photoactive species are encapsulated in a copolymer nanocarrier and strictly depends on the chemical nature of the copolymer. Altogether, these results open up new perspectives in the field of photo-chemical internalization mediated by nanoassemblies.

Testosterone Prevents Cutaneous Ischemia and Necrosis in Males Through Complementary Estrogenic and Androgenic Actions

OBJECTIVE

Chronic nonhealing wounds are a substantial medical concern and are associated with morbidity and mortality; thus, new treatment strategies are required. The first step toward personalized/precision medicine in this field is probably in taking sex differences into account. Impaired wound healing is augmented by ischemia, and we previously demonstrated that 17β-estradiol exerts a major preventive effect against ischemia-induced skin flap necrosis in female mice. However, the equivalent effects of testosterone in male mice have not yet been reported. We then investigated the role of steroid hormones in male mice using a skin flap ischemia model.

APPROACH AND RESULTS

Castrated male mice developed skin necrosis after ischemia, whereas intact or castrated males treated with testosterone were equally protected. Testosterone can (1) activate the estrogen receptor after its aromatization into 17β-estradiol or (2) be reduced into dihydrotestosterone, a nonaromatizable androgen that activates the androgen receptor. We found that dihydrotestosterone protected castrated wild-type mice by promoting skin revascularization, probably through a direct action on resistance arteries, as evidenced using a complementary model of flow-mediated outward remodeling. 17β-estradiol treatment of castrated male mice also strongly protected them from ischemic necrosis through the activation of estrogen receptor-α by increasing skin revascularization and skin survival. Remarkably, 17β-estradiol improved skin survival with a greater efficiency than dihydrotestosterone.

CONCLUSIONS

Testosterone provides males with a strong protection against cutaneous necrosis and acts through both its estrogenic and androgenic derivatives, which have complementary effects on skin survival and revascularization.

Photosensitized oxidation of 2′-deoxyguanosine 5′-monophosphate: mechanism of the competitive reactions and product characterization

We have identified five products containing oxidized guanine and another product containing an intact guanine moiety and a modified one.

Drug Release by Direct Jump from Poly(ethylene-glycol-b-ε-caprolactone) Nano-Vector to Cell Membrane

Drug delivery by nanovectors involves numerous processes, one of the most important being its release from the carrier. This point still remains unclear. The current work focuses on this point using poly(ethyleneglycol-b-ε-caprolactone) micelles containing either pheophorbide-a (Pheo-a) as a fluorescent probe and a phototoxic agent or fluorescent copolymers. This study showed that the cellular uptake and the phototoxicity of loaded Pheo-a are ten times higher than those of the free drug and revealed a very low cellular penetration of the fluorescence-labeled micelles. Neither loaded nor free Pheo-a displayed the same cellular localization as the labeled micelles. These results imply that the drug entered the cells without its carrier and probably without a disruption, as suggested by their stability in cell culture medium. These data allowed us to propose that Pheo-a directly migrates from the micelle to the cell without disruption of the vector. This mechanism will be discussed.

Self-assembled polymeric vectors mixtures: characterization of the polymorphism and existence of synergistic effects in photodynamic therapy

The objective of this work was to assess the relation between the purity of polymeric self-assemblies vectors solution and their photodynamic therapeutic efficiency. For this, several amphiphilic block copolymers of poly(ethyleneoxide-b-ε-caprolactone) have been used to form self-assemblies with different morphologies (micelles, worm-like micelles or vesicles). In a first step, controlled mixtures of preformed micelles and vesicles have been characterized both by dynamic light scattering and asymmetrical flow field flow fractionation (AsFlFFF). For this, a custom-made program, STORMS, was developed to analyze DLS data in a thorough manner by providing a large set of fitting parameters. This showed that DLS only sensed the larger vesicles when the micelles/vesicles ratio was 80/20 w/w. On the other hand, AsFlFFF allowed clear detection of the presence of micelles when this same ratio was as low as 10/90. Subsequently, the photodynamic therapy efficiency of various controlled mixtures was assessed using multicellular spheroids when a photosensitizer, pheophorbide a, was encapsulated in the polymer self-assemblies. Some mixtures were shown to be as efficient as monomorphous systems. In some cases, mixtures were found to exhibit a higher PDT efficiency compared to the individual nano-objects, revealing a synergistic effect for the efficient delivery of the photosensitizer. Polymorphous vectors can therefore be superior in therapeutic applications.

Thymidine radical formation via one-electron transfer oxidation photoinduced by pterin: Mechanism and products characterization

UV-A radiation (320-400nm), recognized as a class I carcinogen, induces damage to the DNA molecule and its components through different mechanisms. Pterin derivatives are involved in various biological functions, including enzymatic processes, and it has been demonstrated that oxidized pterins may act as photosensitizers. In particular, they accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. We have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to photosensitize the degradation of the pyrimidine nucleotide thymidine 5'-monophosphate (dTMP) in aqueous solutions under UV-A irradiation. Although thymine is less reactive than purine nucleobases, our results showed that Ptr is able to photoinduce the degradation of dTMP and that the process is initiated by an electron transfer from the nucleotide to the triplet excited state of Ptr. In the presence of molecular oxygen, the photochemical process leads to the oxidation of dTMP, whereas Ptr is not consumed. In the absence of oxygen, both compounds are consumed to yield a product in which the pterin moiety is covalently linked to the thymine. This compound retains some of the spectroscopic properties of Ptr, such as absorbance in the UV-A region and fluorescence properties.

Crosslinked polymeric self-assemblies as an efficient strategy for photodynamic therapy on a 3D cell culture

Polymeric crosslinked self-assemblies based on poly(ethyleneoxide-b-ε-caprolactone) have been synthesized. They are shown to be more efficient vectors for photodynamic therapy compared to uncrosslinked systems.

trans- and cis-(Cl,Cl)-[RuII(FT)Cl2(NO)](PF6): promising candidates for NO release in the NIR region

Efficient NO photodelivery from cis- and trans-(Cl,Cl)-[Ru^II(FT)Cl₂(NO)](PF₆) complexes upon two-photon excitation in the NIR region.

Comparative photo-release of nitric oxide from isomers of substituted terpyridinenitrosylruthenium(II) complexes: experimental and computational investigations

The 4'-(2-fluorenyl)-2,2':6',2''-terpyridine (FT) ligand and its cis(Cl,Cl)- and trans(Cl,Cl)-[Ru(II)(FT)Cl2(NO)](PF6) complexes have been synthesized. Both isomers were separated by HPLC and fully characterized by (1)H and (13)C NMR. The X-ray diffraction crystal structures were solved for FT (Pna21 space group, a = 34.960(4), b = 5.9306(7), c = 9.5911(10) Å), and trans(Cl,Cl)-[Ru(II)(FT)Cl2(NO)](PF6)·MeOH (P1[combining macron] space group, a = 10.3340(5), b = 13.0961(6), c = 13.2279(6) Å, α = 72.680(2), β = 70.488(2), γ = 67.090(2)°). Photo-release of NO˙ radicals occurs under irradiation at 405 nm, with a quantum yield of 0.31 and 0.10 for cis(Cl,Cl)-[Ru(II)(FT)Cl2(NO)](PF6) and trans(Cl,Cl)-[Ru(II)(FT)Cl2(NO)](PF6), respectively. This significant difference is likely due to the trans effect of Cl(-), which favors the photo-release. UV-visible spectroscopy and cyclic voltammetry indicate the formation of ruthenium(iii) species as photoproducts. A density functional theory (DFT) analysis provides a rationale for the understanding of the photo-physical properties, and allows relating the weakening of the Ru-NO bond, and finally the photo-dissociation, to HOMO → LUMO excitations.

Polymeric micelles encapsulating photosensitizer: structure/photodynamic therapy efficiency relation

Various polymeric micelles were formed from amphiphilic block copolymers, namely, poly(ethyleneoxide-b-ε-caprolactone), poly(ethyleneoxide-b-d,l-lactide), and poly(ethyleneoxide-b-styrene). The micelles were characterized by static and dynamic light scattering, electron microscopy, and asymmetrical flow field-flow fractionation. They all displayed a similar size close to 20 nm. The influence of the chemical structure of the block copolymers on the stability upon dilution of the polymeric micelles was investigated to assess their relevance as carriers for nanomedicine. In the same manner, the stability upon aging was assessed by FRET experiments under various experimental conditions (alone or in the presence of blood proteins). In all cases, a good stability over 48 h for all systems was encountered, with PDLLA copolymer-based systems being the first to release their load slowly. The cytotoxicity and photocytotoxicity of the carriers were examined with or without their load. Lastly, the photodynamic activity was assessed in the presence of pheophorbide a as photosensitizer on 2D and 3D tumor cell culture models, which revealed activity differences between the 2D and 3D systems.

Role of intercalation and redox potential in DNA photosensitization by ruthenium(II) polypyridyl complexes: assessment using DNA repair protein tests

Here we report that the photoreactivity of ruthenium(II) complexes with nucleobases may not only be modulated by their photoredox properties but also by their DNA binding mode. The damage resulting from photolysis of synthetic oligonucleotides and plasmid DNA by [Ru(bpz)3](2+), [Ru(bipy)3](2+) and the two DNA intercalating agents [Ru(bpz)2dppz](2+) and [Ru(bipy)2dppz](2+) has been monitored by polyacrylamide gel electrophoresis and by tests using proteins involved in DNA repair processes (DNA-PKCs, Ku80, Ku70, and PARP-1). The data show that intercalation controls the nature of the DNA damage photo-induced by ruthenium(II) complexes reacting with DNA via an electron transfer process. The intercalating agent [Ru(bpz)2dppz](2+) is a powerful DNA breaker inducing the formation of both single and double (DSBs) strand breaks which are recognized by the PARP-1 and DNA-PKCs proteins respectively. [Ru(bpz)2dppz](2+) is the first ruthenium(II) complex described in the literature that is able to induce DSBs by an electron transfer process. In contrast, its non-intercalating parent compound, [Ru(bpz)3](2+), is mostly an efficient DNA alkylating agent. Photoadducts are recognized by the proteins Ku70 and Ku80 as with cisplatin adducts. This result suggests that photoaddition of [Ru(bpz)2dppz](2+) is strongly affected by its DNA intercalation whereas its photonuclease activity is exalted. The data clearly show that DNA intercalation decreases drastically the photonuclease activity of ruthenium(II) complexes oxidizing guanine via the production of singlet oxygen. Interestingly, the DNA sequencing data revealed that the ligand dipyridophenazine exhibits on single-stranded oligonucleotides a preference for the 5'-TGCGT-3' sequence. Moreover the use of proteins involved in DNA repair processes to detect DNA damage was a powerful tool to examine the photoreactivity of ruthenium(II) complexes with nucleic acids.

Tryptophan oxidation photosensitized by pterin

Pterins are normal components of cells and they have been previously identified as good photosensitizers under UV-A irradiation, inducing DNA damage and oxidation of nucleotides. In this work, we have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to photosensitize the oxidation of another class of biomolecules, amino acids, using tryptophan (Trp) as a model compound. Irradiation of Ptr in the UV-A spectral range (350 nm) in aerated aqueous solutions containing Trp led to the consumption of the latter, whereas the Ptr concentration remained unchanged. Concomitantly, hydrogen peroxide (H₂O₂) was produced. Although Ptr is a singlet oxygen ((1)O₂) sensitizer, the degradation of Trp was inhibited in O₂-saturated solutions, indicating that a (1)O₂-mediated process (type II oxidation) was not an important pathway leading to Trp oxidation. By combining different analytical techniques, we could establish that a type I photooxidation was the prevailing mechanism, initiated by an electron transfer from the Trp molecule to the Ptr triplet excited state, yielding the corresponding radical ions (Trp(·+)/Trp(-H)· and Ptr(·-)). The Trp reaction products that could be identified by UPLC-mass spectrometry are in agreement with this conclusion.

Mechanism of electron transfer processes photoinduced by lumazine

UV-A (320-400 nm) and UV-B (280-320 nm) radiation causes damage to DNA and other biomolecules through reactions induced by different endogenous or exogenous photosensitizers. Lumazines are heterocyclic compounds present in biological systems as biosynthetic precursors and/or products of metabolic degradation. The parent and unsubstituted compound called lumazine (pteridine-2,4(1,3H)-dione; Lum) is able to act as photosensitizer through electron transfer-initiated oxidations. To get further insight into the mechanisms involved, we have studied in detail the oxidation of 2'-deoxyadenosine 5'-monophosphate (dAMP) photosensitized by Lum in aqueous solution. After UV-A or UV-B excitation of Lum and formation of its triplet excited state ((3)Lum*), three reaction pathways compete for the deactivation of the latter: intersystem crossing to singlet ground state, energy transfer to O(2), and electron transfer between dAMP and (3)Lum* yielding the corresponding pair of radical ions (Lum˙(-) and dAMP˙(+)). In the following step, the electron transfer from Lum˙(-) to O(2) regenerates Lum and forms the superoxide anion (O(2)˙(-)), which undergoes disproportionation into H(2)O(2) and O(2). Finally dAMP˙(+) participates in subsequent reactions to yield products.

Electron-transfer processes induced by the triplet state of pterins in aqueous solutions

Pterins (Pt) are heterocyclic compounds widespread in living systems. They participate in relevant biological processes, such as metabolic redox reactions, and can photoinduce the oxidation of biomolecules through electron-transfer mechanisms. We have investigated the electron-transfer pathways initiated by excited states of pterin (Ptr) and 6-methylpterin (Mep), selected as model compounds. The experiments were carried out in aqueous solutions under continuous UV-A irradiation, in the presence and in the absence of ethylenediaminetetraacetic acid (EDTA), used as an electron donor. The reactions were followed by UV/Vis spectrophotometry, HPLC, and an enzymatic method for H(2)O(2) determination. The formation of the superoxide anion (O(2)(*-)) was investigated by electron paramagnetic resonance-spin trapping. The triplet excited states of Ptr and Mep are efficient electron acceptors, able to oxidize a Pt molecule in its ground state. The resulting radical anion (Pt(*-)) reacts with dissolved O(2) to yield O(2)(*-), regenerating the pterin. In the presence of EDTA, this reaction competes efficiently with the anaerobic reaction between Pt(*-) and EDTA(*+), yielding the corresponding stable dihydroderivatives H(2)Pt. The effects of EDTA and dissolved O(2) concentrations on the efficiencies of the different competing pathways were analyzed.

Evaluation of new thiadiazoles and benzothiazoles as potential radioprotectors: free radical scavenging activity in vitro and theoretical studies (QSAR, DFT)

Thiol and aminothiol compounds are among the most efficient chemical radioprotectors. To increase their efficiency, we synthesized two new classes of thiol and aminothiol compounds derived from benzothiazole (T1, T2, AM1, AM2) and thiadiazole (T3, T4, AM3) structures. We examined them for their ability to scavenge free radicals (DPPH*, ABTS(*+), *OH). Thiol derivatives with a thiadiazole structure are the most active compounds scavenging DPPH* and ABTS(*+) free radicals, with an IC(50) of 0.053+/-0.006 and 0.023+/-0.002 mM, respectively, for the derivative T3. Moreover, compounds T1, T2, and T3 at 60 microM gave 83% protection against 2-deoxyribose degradation by *OH. The ability of these compounds to protect DNA against *OH produced by a Fenton reaction and gamma-irradiation (15 Gy)-induced strand breaks was also evaluated on pBR322 plasmid DNA. In both tests thiol derivatives were the most efficient compounds. Derivatives T2 and T3 totally inhibit DNA strand breaks at the concentration of 50 microM. The protection afforded by these derivatives was comparatively higher than that of the radioprotectors WR-2721 and WR-1065. Our data indicate that these two compounds are free radical scavengers and potential antioxidant agents. Finally, DFT and QSAR studies were performed to support the experimental observations.

Prevention of skin flap necrosis by estradiol involves reperfusion of a protected vascular network

Although 17beta-estradiol (E2) is protective in experimental models of myocardial and brain ischemia, its effect on skin ischemia remains unknown. Here, we assessed the protective effect of E2 in a mouse model of skin ischemia, mimicking the surgery of skin flaps. Whereas necrosis appeared in the half portion of the skin flap within 1 week after surgery in ovariectomized mice, it was reduced up to 10-fold when mice were pretreated with E2, at least 3 days before the surgery. The beneficial effect of E2 appeared to be attributable to an increase in skin survival, revealed by measuring viability of ex vivo explants and enhancement of the antiapoptotic Bcl-2 protein expression in vivo. This protective effect on the skin contributed to the protection of the vascular network and facilitated reperfusion, which was found to be accelerated in ovariectomized E2-treated mice, whereas hemorrhages were observed in untreated mice. E2 also increased expression of fibroblast growth factor-2 isoforms in the skin and circulating vascular endothelial growth factor in the serum. Finally, this protective effect of E2 was abolished in estrogen receptor-deficient mice (ERalpha(-/-)) but maintained in chimeric mice reconstituted with ERalpha-deficient bone marrow, indicating dispensable action of E2 in bone marrow-derived cells. This protective effect of E2 was mimicked by treatment with tamoxifen, a selective estrogen receptor modulator. In conclusion, we have demonstrated for the first time that E2 exerts a major preventive effect of skin flap necrosis through a prevention of ischemic-induced skin lesions, including those of the vascular network, which contributes to accelerate the reperfusion of the skin flap.

Is the 3MLCT the Only Photoreactive State of Polypyridyl Complexes?

By means of Delta-SCF and time-dependent density functional theory (DFT) calculations on [Ru(LL)3]2+ (LL = bpy = 2,2'-bipyridyl or bpz = 2,2' -bipyrazyl) complexes, we have found that emission of these two complexes could originate from two metal-to-ligand charge-transfer triplet states (3MLCT) that are quasi-degenerate and whose symmetries are D3 and C2. These two states are true minima. Calculated absorption and emission energies are in good agreement with experiment; the largest error is 0.14 eV, which is about the expected accuracy of the DFT calculations. For the first time, an optimized geometry for the metal-centered (MC) state is proposed for both of these complexes, and their energies are found to be almost degenerate with their corresponding 3MLCT states. These [RuII(LL)(eta1-LL)2]2+ MC states have two vacant coordination sites on the metal, so they may react readily with their environment. If these MC states are able to de-excite by luminescence, the associated transition (ca. 1 eV) is found to be quite different from those of the 3MLCT states (ca. 2 eV).

Photoelectron Transfer Processes with Ruthenium(II) Polypyridyl Complexes and Cu/Zn Superoxide Dismutase

The processes that are photoinduced by [Ru(bpz)(3)](2+) (bpz = 2,2'-bipyrazyl) in the presence of Cu/Zn superoxide dismutase (Cu/Zn SOD) are investigated by laser flash photolysis and electron paramagnetic resonance (EPR) spectroscopy; they are compared to those of the system [Ru(bpy)(3)(2+)-Cu/Zn SOD]. Although the mechanism is complicated, primary and secondary reactions can be evidenced. First, the excited [Ru(bpz)(3)](2+) complex is quenched reductively by Cu/Zn SOD with the production of a reduced complex and an oxidized enzyme. The oxidation site of Cu/Zn SOD is proposed to correspond to amino acids located on the surface of the protein. Afterward and only when this reductive electron transfer to the excited complex has produced enough oxidized protein, another electron-transfer process can be evidenced. In this case, however, the charge-transfer process takes place in the other direction, i.e., from the excited complex to the Cu(II) center of the SOD with the formation of Ru(III) and Cu(I) species. This proposed mechanism is supported by the fact that [Ru(bpy)(3)](2+), which is less photo-oxidizing than [Ru(bpz)(3)](2+), exhibits no photoreaction with Cu/Zn SOD. Because Ru(III) species are generated as intermediates with [Ru(bpz)(3)](2+), they are proposed to be responsible for the enhancement of [poly(dG-dC)](2) and [poly(dA-dT)](2) oxidation observed when Cu/Zn SOD is added to the [Ru(bpz)(3)](2+)-DNA system.

Evaluation, in vitro, of the radioprotection of DNA from gamma-rays by naphazoline

Design of compounds that can protect efficiently against gamma-rays irradiation is a great challenge. An ionizing event can cause variety of DNA damage scenarios leading to mutagenesis, cell death. 2-(1-Naphthylmethyl)-2-imidazoline (naphazoline, NP) is a drug belonging to the vasoregulator class, which was shown to be a very interesting compound in radioprotection. In order to highlight the NP radioprotective activity, a comparison of its ability to protect DNA against either gamma-irradiation or radicals generated by Fenton's reaction was made. Results show that NP inhibits efficiently the generation of DNA single-strand breaks and that NP is a potent radioprotector and also an hydroxyl radical scavenger.