Photosensitized DNA damage: the case of fluoroquinolones

Photo-transformation of acetaminophen sensitized by fluoroquinolones in the presence of bromide

Fluoroquinolones (FQs) are a class of antibiotics with emerging concern. This study investigated the photochemical properties of two representative FQs, i.e., norfloxacin (NORF) and ofloxacin (OFLO). Results showed that both FQs could sensitize the photo-transformation of acetaminophen under UV-A irradiation, during which excited triplet state (³FQ*) was the main active species. In the presence of 3 mM Br^‾, the photolysis rate of acetaminophen increased by 56.3% and 113.5% in the solutions with 10 μM NORF and OFLO, respectively. Such an effect was ascribed to the generation of reactive bromine species (RBS), which was verified by 3,5-dimethyl-1H-pyrazole (DMPZ) probing approach. ³FQ* reacts with acetaminophen through one-electron transfer, producing radical intermediates which then couple to each other. Presence of Br^‾ did not lead to the formation of brominated products but the same coupling products, which suggests that radical bromine species, rather than free bromine, were responsible for the accelerated acetaminophen transformation. According to the identified reaction products and assisted with the theoretical computation, the transformation pathways of acetaminophen under UV-A irradiation were proposed. The results reported herein suggest that sunlight-driven reactions of FQs and Br^‾ may influence the transformation of coexisting pollutants in surface water environments.

Photodegradation of phenylurea herbicides sensitized by norfloxacin and the influence of natural organic matter

The photochemical activity of fluoroquinolone antibiotics (FQs) has gained attention due to the discovery of their phototoxicity and photocarcinogenicity in clinics. This study reveals that norfloxacin (NOR) can sensitize the photodegradation of phenylurea (PU) herbicides. This is attributed to the formation of an excited triplet of norfloxacin (³NOR*) by UV-A irradiation of its quinolone chromophore, which can further react with O₂ to form singlet oxygen (¹O₂). The second-order rate of ³NOR* with PU ranges from 1.54 × 10¹⁰ to 2.76 × 10¹⁰ M^-1s^-1. The steady-state concentrations of ³NOR* were calculated as (4.29-31.2)× 10^-16 M at 10 μM NOR under UV_365nm irradiation. Natural organic matter (NOM) inhibited the degradation of PU induced by ³NOR*. In the presence of 10 mg L^-1 NOM, the pseudo-first-order rate constants (k_obs,NOM) of the degradation of diuron (DIU), isoproturon (IPU), monuron (MOU), and chlorotoluron (CLU) decreased by 65%, 19%, 36%, and 62%, respectively. NOM mainly acts as a reductant which reacted with the radical intermediates of the PU generated by ³NOR*oxidation, thus reversing the oxidation. The inhibitory effect increases with increasing NOM concentration. Results of this study underscore the role of NOR as a photosensitizer in accelerating the abatement of PU pesticides in sunlit surface waters. This study significantly advances the understandings of the behavior of NOR in aquatic environments.

Current advances on the photocatalytic degradation of fluoroquinolones: photoreaction mechanism and environmental application

Heterogeneous photocatalysis is one of the most studied and promising techniques for degradation of contaminants of emerging concern, especially pharmaceuticals, and it represents a potential application in wastewater treatment of recalcitrant pollutants, such as fluoroquinolones, which are almost not abated by standard WWTPs. Although photodegradation partially contributes to alleviate their accumulation into the aquatic systems, heterogeneous photocatalysis assures complete sequestration and mineralization of FQs and their photoproducts and offers many advantages with respect to the other advanced oxidation processes (AOPs). The present brief review summarizes the most recent studies regarding the development and application of novel photocatalytic materials to the removal of FQs from contaminated waters. The collected data are arranged relating the mechanistic aspects to specific catalysts' properties, such as adsorption capacity, easy recovery, and reusability, especially under actual conditions.

Ability of the Putative Decomposition Products of 2,3-dioxetanes of Indoles to Photosensitize Cyclobutane Pyrimidine Dimer (CPD) Formation and its Implications for the "Dark" (Chemisensitized) Pathway to CPDs in Melanocytes†

The formation of cyclobutane pyrimidine dimers (CPDs) by a "dark" pathway in melanocytes has been attributed to chemisensitization by dioxetanes produced from peroxynitrite oxidation of melanin or melanin precursors. These dioxetanes are proposed to decompose to triplet state compounds which sensitize CPD formation by triplet-triplet energy transfer. To determine whether such compounds are capable of sensitizing CPD formation, the putative decomposition products of 2,3-dioxetanes of variously substituted indoles were synthesized and their triplet state energies determined at 77 K. Their ability to photosensitize CPD formation was determined by an enzyme-coupled gel electrophoresis assay in comparison with norfloxacin (NFX) which has the lowest triplet energy known to sensitize CPD formation. The decomposition products of 2,3-dioxetanes of 5-hydroxy and 5,6-dimethoxy indoles used as models for melanin precursors had lower triplet energies and were incapable of photosensitizing CPD formation. Theoretical calculations suggest that the decomposition products of the 2,3-dioxetanes of melanin precursors DHI and DHICA will have similarly low triplet energies. Decomposition products of the 2,3-dioxetanes of indoles lacking oxygen substituents had higher triplet energies than NFX and were capable of photosensitizing CPD formation, suggesting that peroxynitrite oxidation of tryptophan could play a hitherto unrecognized role in the dark pathway to CPDs.

Photosensitization Reactions of Biomolecules: Definition, Targets and Mechanisms

Photosensitization reactions have been demonstrated to be largely responsible for the deleterious biological effects of UV and visible radiation, as well as for the curative actions of photomedicine. A large number of endogenous and exogenous photosensitizers, biological targets and mechanisms have been reported in the past few decades. Evolving from the original definitions of the type I and type II photosensitized oxidations, we now provide physicochemical frameworks, classifications and key examples of these mechanisms in order to organize, interpret and understand the vast information available in the literature and the new reports, which are in vigorous growth. This review surveys in an extended manner all identified photosensitization mechanisms of the major biomolecule groups such as nucleic acids, proteins, lipids bridging the gap with the subsequent biological processes. Also described are the effects of photosensitization in cells in which UVA and UVB irradiation triggers enzyme activation with the subsequent delayed generation of superoxide anion radical and nitric oxide. Definitions of photosensitized reactions are identified in biomolecules with key insights into cells and tissues.

Fluoroquinolone antibiotics sensitized photodegradation of isoproturon

Fluoroquinolone (FQ) antibiotics are a group of contaminants of emerging environmental concern. In the present study, we demonstrated that norfloxacin (NORF) and ofloxacin (OFLO), two typical FQs, have photochemical reactivity analogous to chromophoric dissolved natural organic matter (DOM) in surface waters and can sensitize the photodegradation of isoproturon (IPU), a phenylurea herbicide. Such photochemical reactivity is ascribed to the quinolone chromophore that is excited to a triplet state (³FQ*) upon UV-A irradiation. ³FQ* further reacts with dissolved oxygen to give rise to singlet oxygen. ³FQ* steady-state concentrations of 6.72 × 10^-15 and 1.27 × 10^-15 M were measured in 10 μM NORF and OFLO solutions, respectively, under UV_365nm irradiation. The degradation of IPU was due to the reaction with ³FQ*, with bimolecular rate constants of 6.07 × 10⁹ and 1.51 × 10¹⁰ for ³NORF* and ³OFLO*, respectively. Intriguingly, NORF and OFLO per se were unstable and photolyzed during UV-A irradiation, but the photochemical reactivities of the solutions were not lost accordingly. High-resolution mass spectrometry analysis revealed that defluorination and piperazine moiety oxidation were the main photolysis pathways, while the core quinolone structure remained intact. Thus, the photolysis products largely inherited the photochemical reactivity of the parent compounds. Since all FQs share the same quinolone structure, similar photochemical reactivity is expected. The presence of FQs in surface water would affect the transformation and fate of coexisting compounds. To the best of our knowledge, this is the first study examining the environmental behavior of FQs as photosensitizers. The findings greatly advance the understandings of the influence of FQs in aquatic environment.

The effect of flanking bases on direct and triplet sensitized cyclobutane pyrimidine dimer formation in DNA depends on the dipyrimidine, wavelength and the photosensitizer

Cyclobutane pyrimidine dimers (CPDs) are the major products of DNA produced by direct absorption of UV light, and result in C to T mutations linked to human skin cancers. Most recently a new pathway to CPDs in melanocytes has been discovered that has been proposed to arise from a chemisensitized pathway involving a triplet sensitizer that increases mutagenesis by increasing the percentage of C-containing CPDs. To investigate how triplet sensitization may differ from direct UV irradiation, CPD formation was quantified in a 129-mer DNA designed to contain all 64 possible NYYN sequences. CPD formation with UVB light varied about 2-fold between dipyrimidines and 12-fold with flanking sequence and was most frequent at YYYR and least frequent for GYYN sites in accord with a charge transfer quenching mechanism. In contrast, photosensitized CPD formation greatly favored TT over C-containing sites, more so for norfloxacin (NFX) than acetone, in accord with their differing triplet energies. While the sequence dependence for photosensitized TT CPD formation was similar to UVB light, there were significant differences, especially between NFX and acetone that could be largely explained by the ability of NFX to intercalate into DNA.

Ofloxacin adsorptive interaction with rice husk ash: Parametric and exhausted adsorbent disposability study

The present study investigates the adsorptive interaction of rice husk ash (RHA) with Ofloxacin (OFL) antibiotic. The OFL loaded RHA was studied for its disposability by solidification to find its possible use as a building material. Further, toxicity analysis of leachate from the solidified RHA was also studied for probable leaching of OFL. The effects of adsorption parameters such as initial pH, the dosage of RHA (m), initial OFL concentration (C₀), and contact time (t) on the responses % OFL removal (X₁) and adsorption capacity (mg/g) (X₂) were evaluated using the central composite design (CCD) based on response surface method (RSM). Kinetic and thermodynamic studies were performed at optimized parameters, and adsorption equilibrium data were illustrated by using Langmuir, Redlich-Peterson (R-P), and Tempkin isotherm models. Optimum condition was found as m = 7.94 g/L, t = 430 min and pH = 6, and at this actual responses X₁ and X₂ were evaluated as 79.71% and 6.28 mg/g, respectively. Pseudo-first-order kinetic fitted best for the adsorption kinetic data. Toxicity analysis of leachate from solidified RHA indicated that most of the OFL was encapsulated inside the cement and the OFL present in leachate is not sufficient to eradicate the growth of E.coli and Bacillus subtilis.

Assessing physical properties of amphoteric fluoroquinolones using phosphorescence spectroscopy

The self-association of fluoroquinolones (FQ) in water would play a relevant role in their translocations across lipid membranes. Triplet excited states of these drugs have been shown as reporters of FQ self-association using laser flash photolysis technique. A study using low-temperature phosphorescence technique was performed with quinolone derivatives such as enoxacin (ENX), norfloxacin (NFX), pefloxacin (PFX), ciprofloxacin (CPX, ofloxacin (OFX), nalidixic acid (NLA), pipemidic acid (PPA) and piromidic acid (PRA) to explore emission changes associated with self-associations and to shed some light on the triplet excited state energy (E_T) discrepancies described in the literature for most of these drugs. The emissions obtained at 77 K in buffered aqueous medium revealed that the amphoteric nature of the quinolones CPX, NFX, PFX, ENX, OFX and PPA must generate their self-associations because a redshift of their phosphorescence maxima is produced by FQ concentrations increases. Hence, this effect was not observed for NLA and PRA or when all quinolones were analysed using ethanol or ethylene glycol aqueous mixtures as glassed solvents. Interestingly, the presence of these organic mixtures produced a blue-shift in the phosphorescence emission maximum of each FQ. Additionally, laser flash photolysis experiments with PRA and the amphoteric quinolone PPA, compounds with the same skeleton but different peripheral substituent, confirm the expected correlations between the amphoteric nature of compounds and their self-associations in aqueous media because the excimer generation was only detected for PPA. Now, the discrepancies described in the literature for the E_T of FQs can be understood considering that changes of medium polarity or proticity as well as the temperature can considerably modify their E_T values. Thereby, low-temperature phosphorescence technique, is an effective way to detect molecular self-associations and surrounding changes in quinolones that opens the possibility to evaluate these effects in other drug families.

Experimental and theoretical studies on thymine photodimerization mediated by oxidatively generated DNA lesions and epigenetic intermediates

Combined spectroscopic and computational studies reveal that, in spite of their structural similarities, 5-formyluracil and 5-formylcytosine photosensitize cyclobutane thymine dimers through two different types of mechanisms.

Chemical tuning for potential antitumor fluoroquinolones

Phototoxic effects of 6,8 dihalogenated quinolones confers to this type of molecules a potential property as photochemotherapeutic agents. Two photodehalogenation processes seem to be involved in the remarkable photoinduced cellular damage. In this context, a new 6,8 dihalogenated quinolone 1 (1-methyl-6,8-difluoro-4-oxo-7-aminodimethyl-1,4-dihydroquinoline-3-carboxylic acid) was synthetized looking for improving the phototoxic properties of fluoroquinolones (FQ) and to determine the role of the photodegradation pathways in the FQ phototoxicity. With this purpose, fluorescence emissions, laser flash photolysis experiments and photodegradation studies were performed with compound 1 using 1-ethyl-6,8-difluoro-4-oxo-7-aminodimethyl-1,4-dihidroquinoline-3-carboxylic acid (2) and lomefloxacin (LFX) as reference compounds. The shortening of alkyl chain of the N(1) of the quinolone ring revealed a lifetime increase of the reactive aryl cation generated from photolysis of the three FQ and a significant reduction of the FQ photodegradation quantum yield. The fact that these differences were smaller when the same study was done using a hydrogen donor solvent (ethanol-aqueous buffer, 50/50 v/v) evidenced the highest ability of the reactive intermediate arising from 1 to produce intermolecular alkylations. These results were correlated with in vitro 3T3 NRU phototoxicity test. Thus, when Photo-Irritation-Factor (PIF) was determined for 1, 2 and LFX using cytotoxicity profiles of BALB/c 3T3 fibroblasts treated with each compound in the presence and absence of UVA light, a PIF more higher than 30 was obtained for 1 while the values for 2 and LFX were only higher than 8 and 10, respectively. Thereby, the present study illustrates an approach to modulate the photosensitizing properties of FQ with the purpose to improve the chemotherapeutic properties of antitumor quinolones. Moreover, the results obtained in this study also evidence that the key pathway responsible for the phototoxic properties associated with dihalogenated quinolones is the aryl cation generation.

Photophysical Properties Controlled by Substituents with Lone-Pair Electrons at the Ortho- or Para-Positions of Fluoroquinolone Antibiotics

The ortho- or para-substituents of NH₂ or N-alkyl-containing lone-pair electrons were found to change the energy levels and transition configurations of the highest occupied molecular orbital for some fluoroquinolone-based antibiotics (FQs) and can significantly influence the electronic structure, intermolecular hydrogen bonding, internal conversion, and fluorescence and intersystem crossing efficiencies of FQs in acetonitrile or aqueous solution after photoexcitation. These findings provide new insights that can help in the molecular design strategies to regulate the photophysical properties of photosensitive medicines, photodynamic therapy reagents, and energy conversion materials that contain similar aromatic carbonyl structures.

Drug and chemical induced photosensitivity from a clinical perspective

Drug photosensitivity is a relatively common occurrence and a range of mechanisms may be involved. Some of these mechanisms will be discussed, including the most common, that of drug phototoxicity. Different types of photosensitivity are addressed with respect to clinical presentation, mechanisms and additionally the contribution to our understanding through clinically directed investigations and regulatory requirements. Repeated controlled therapeutic use of drug phototoxicity, with psoralen-UVA (PUVA) photochemotherapy and photodynamic therapy (PDT) will also be discussed. Finally, the potential for drug-induced photocarcinogenesis will also be covered.

Triplet photosensitization mechanism of thymine by an oxidized nucleobase: from a dimeric model to DNA environment

Nucleic acids are constantly exposed to external agents that can induce chemical and photochemical damage. In spite of the great advances achieved in the last years, some molecular mechanisms of DNA damage are not completely understood yet. A recent experimental report (I. Aparici-Espert et al., ACS Chem. Biol. 2018, 13, 542) proved the ability of 5-formyluracil (ForU), a common oxidatively generated product of thymine, to act as an intrinsic sensitizer of nucleic acids, causing single strand breaks and cyclobutane pyrimidine dimers in plasmid DNA. In the present contribution, we use theoretical methodologies to study the triplet photosensitization mechanism of thymine exerted by ForU in a model dimer and in DNA environment. The photochemical pathways in the former system are described combining the CASPT2 and TD-DFT methods, whereas molecular dynamics simulations and QM/MM calculations are employed for the DNA duplex. It is unambiguously shown that the 1n,π* state localised in ForU mediates the population of the triplet manifold, most likely the 3π,π* state centred in ForU, whereas the 3π,π* state localized in thymine can be populated via triplet-triplet energy transfer given the small energy barrier of <0.23 eV determined for this pathway.

Natural extracellular nanovesicles and photodynamic molecules: is there a future for drug delivery?

Photodynamic molecules represent an alternative approach for cancer therapy for their property (i) to be photo-reactive; (ii) to be not-toxic for target cells in absence of light; (iii) to accumulate specifically into tumour tissues; (iv) to be activable by a light beam only at the tumour site and (v) to exert cytotoxic activity against tumour cells. However, to date their clinical use is limited by the side effects elicited by systemic administration. Extracellular vesicles are endogenous nanosized-carriers that have been recently introduced as a natural delivery system for therapeutic molecules. We have recently shown the ability of human exosomes to deliver photodynamic molecules. Therefore, this review focussed on extracellular vesicles as a novel strategy for the delivery of photodynamic molecules at cancer sites. This completely new approach may enhance the delivery and decrease the toxicity of photodynamic molecules, therefore, represent the future for photodynamic therapy for cancer treatment.

Oxidative stress induced by UVA photoactivation of the tryptophan UVB photoproduct 6-formylindolo[3,2-b]carbazole (FICZ) inhibits nucleotide excision repair in human cells

Potentially mutagenic DNA lesions induced by UVB (wavelengths 280–320 nm) are important risk factors for solar ultraviolet (UV) radiation-induced skin cancer. The carcinogenicity of the more abundant UVA (320–400 nm) is less well understood but is generally regarded to reflect its interaction with cellular chromophores that act as photosensitisers. The arylhydrocarbon receptor agonist 6-formylindolo[3,2-b] carbazole (FICZ), is a UVB photoproduct of tryptophan and a powerful UVA chromophore. Combined with UVA, FICZ generates reactive oxygen species (ROS) and induces oxidative DNA damage. Here we demonstrate that ROS generated by FICZ/UVA combinations also cause extensive protein damage in HaCaT human keratinocytes. We show that FICZ/UVA-induced oxidation significantly inhibits the removal of potentially mutagenic UVB-induced DNA photolesions by nucleotide excision repair (NER). DNA repair inhibition is due to FICZ/UVA-induced oxidation damage to the NER proteome and DNA excision repair is impaired in extracts prepared from FICZ/UVA-treated cells. NER protects against skin cancer. As a likely UVB photoproduct of intracellular tryptophan, FICZ represents a de facto endogenous UVA photosensitiser in sun-exposed skin. FICZ formation may increase the risk of solar UV-induced skin cancer by promoting photochemical damage to the NER proteome and thereby preventing the removal of UVB-induced DNA lesions.

Photosensitized UVA-Induced Cross-Linking between Human DNA Repair and Replication Proteins and DNA Revealed by Proteomic Analysis

Long wavelength ultraviolet radiation (UVA, 320-400 nm) interacts with chromophores present in human cells to induce reactive oxygen species (ROS) that damage both DNA and proteins. ROS levels are amplified, and the damaging effects of UVA are exacerbated if the cells are irradiated in the presence of UVA photosensitizers such as 6-thioguanine (6-TG), a strong UVA chromophore that is extensively incorporated into the DNA of dividing cells, or the fluoroquinolone antibiotic ciprofloxacin. Both DNA-embedded 6-TG and ciprofloxacin combine synergistically with UVA to generate high levels of ROS. Importantly, the extensive protein damage induced by these photosensitizer+UVA combinations inhibits DNA repair. DNA is maintained in intimate contact with the proteins that effect its replication, transcription, and repair, and DNA-protein cross-links (DPCs) are a recognized reaction product of ROS. Cross-linking of DNA metabolizing proteins would compromise these processes by introducing physical blocks and by depleting active proteins. We describe a sensitive and statistically rigorous method to analyze DPCs in cultured human cells. Application of this proteomics-based analysis to cells treated with 6-TG+UVA and ciprofloxacin+UVA identified proteins involved in DNA repair, replication, and gene expression among those most vulnerable to cross-linking under oxidative conditions.

Protein oxidation, UVA and human DNA repair

Solar UVB is carcinogenic. Nucleotide excision repair (NER) counteracts the carcinogenicity of UVB by excising potentially mutagenic UVB-induced DNA lesions. Despite this capacity for DNA repair, non-melanoma skin cancers and apparently normal sun-exposed skin contain huge numbers of mutations that are mostly attributable to unrepaired UVB-induced DNA lesions. UVA is about 20-times more abundant than UVB in incident sunlight. It does cause some DNA damage but this does not fully account for its biological impact. The effects of solar UVA are mediated by its interactions with cellular photosensitizers that generate reactive oxygen species (ROS) and induce oxidative stress. The proteome is a significant target for damage by UVA-induced ROS. In cultured human cells, UVA-induced oxidation of DNA repair proteins inhibits DNA repair. This article addresses the possible role of oxidative stress and protein oxidation in determining DNA repair efficiency - with particular reference to NER and skin cancer risk.

Oxidative Damage to RPA Limits the Nucleotide Excision Repair Capacity of Human Cells

Nucleotide excision repair (NER) protects against sunlight-induced skin cancer. Defective NER is associated with photosensitivity and a high skin cancer incidence. Some clinical treatments that cause photosensitivity can also increase skin cancer risk. Among these, the immunosuppressant azathioprine and the fluoroquinolone antibiotics ciprofloxacin and ofloxacin interact with UVA radiation to generate reactive oxygen species that diminish NER capacity by causing protein damage. The replication protein A (RPA) DNA-binding protein has a pivotal role in DNA metabolism and is an essential component of NER. The relationship between protein oxidation and NER inhibition was investigated in cultured human cells expressing different levels of RPA. We show here that RPA is limiting for NER and that oxidative damage to RPA compromises NER capability. Our findings reveal that cellular RPA is surprisingly vulnerable to oxidation, and we identify oxidized forms of RPA that are associated with impaired NER. The vulnerability of NER to inhibition by oxidation provides a connection between cutaneous photosensitivity, protein damage, and increased skin cancer risk. Our findings emphasize that damage to DNA repair proteins, as well as to DNA itself, is likely to be an important contributor to skin cancer risk.

DNA repair inhibition by UVA photoactivated fluoroquinolones and vemurafenib

Cutaneous photosensitization is a common side effect of drug treatment and can be associated with an increased skin cancer risk. The immunosuppressant azathioprine, the fluoroquinolone antibiotics and vemurafenib—a BRAF inhibitor used to treat metastatic melanoma—are all recognized clinical photosensitizers. We have compared the effects of UVA radiation on cultured human cells treated with 6-thioguanine (6-TG, a DNA-embedded azathioprine surrogate), the fluoroquinolones ciprofloxacin and ofloxacin and vemurafenib. Despite widely different structures and modes of action, each of these drugs potentiated UVA cytotoxicity. UVA photoactivation of 6-TG, ciprofloxacin and ofloxacin was associated with the generation of singlet oxygen that caused extensive protein oxidation. In particular, these treatments were associated with damage to DNA repair proteins that reduced the efficiency of nucleotide excision repair. Although vemurafenib was also highly phototoxic to cultured cells, its effects were less dependent on singlet oxygen. Highly toxic combinations of vemurafenib and UVA caused little protein carbonylation but were nevertheless inhibitory to nucleotide excision repair. Thus, for three different classes of drugs, photosensitization by at least two distinct mechanisms is associated with reduced protection against potentially mutagenic and carcinogenic DNA damage.

Conformational, spectroscopic, and molecular dynamics DFT study of precursors for new potential antibacterial fluoroquinolone drugs

Biological activity, functionality, and synthesis of (fluoro)quinolones is closely related to their precursors (for instance 3-fluoroanilinoethylene derivatives) (i.e., their functional groups, conformational behavior, and/or electronic structure). Herein, the theoretical study of 3-fluoroanilinoethylene derivatives is presented. Impact of substituents (acetyl, methyl ester, and ethyl ester) on the conformational analysis and the spectral behavior is investigated. The B3LYP/6-311++G** computational protocol is utilized. It is found that the intramolecular hydrogen bond N-H···O is responsible for the energetic preference of anti (a) conformer (anti position of 3-fluoroanilino group with respect to the C═C double bond). The Boltzmann ratios of the conformers are related to the differences of the particular dipole moments and/or their dependence on the solvent polarity. The studied acetyl, ethyl ester, and methyl ester substituted fluoroquinolone precursors prefer in the solvent either EZa, ZZa, or both conformers equally, respectively. In order to understand the degree of freedom of rotation of the trans ethyl ester group, B3LYP/6-311G** molecular dynamic simulations were carried out. Vibrational frequencies, electron transitions, as well as NMR spectra are analyzed with respect to conformational analysis, including the effect of the substituent. X-ray structures of the precursors are presented and compared with the results of the conformational analysis.

Fused-ring derivatives of quinoxalines: spectroscopic characterization and photoinduced processes investigated by EPR spin trapping technique

10-Ethyl-7-oxo-7,10-dihydropyrido[2,3-f]quinoxaline derivatives, synthesized as promising biologically/photobiologically active compounds were characterized by UV/vis, FT-IR and fluorescent spectroscopy. Photoinduced processes of these derivatives were studied by EPR spectroscopy, monitoring in situ the generation of reactive intermediates upon UVA (λmax=365 nm) irradiation. The formation of reactive oxygen species and further oxygen- and carbon-centered radical intermediates was detected and possible reaction routes were suggested. To quantify the investigated processes, the quantum yields of the superoxide radical anion spin-adduct and 4-oxo-2,2,6,6-tetramethylpiperidine N-oxyl generation were determined, reflecting the activation of molecular oxygen by the excited state of the quinoxaline derivative.

Protein oxidation and DNA repair inhibition by 6-thioguanine and UVA radiation

Damage to skin DNA by solar UV is largely unavoidable, and an optimal cellular response to it requires the coordinated operation of proteins in numerous pathways. A fully functional DNA repair proteome for removing harmful DNA lesions is a prerequisite for an appropriate DNA damage response. Genetically determined failure to repair UV-induced DNA damage is associated with skin photosensitivity and increased skin cancer risk. Patients treated with immunosuppressant/anti-inflammatory thiopurines are also photosensitive and have high rates of sun-related skin cancer. Their DNA contains the base analog 6-thioguanine (6-TG), which acts as a UVA photosensitizer to generate reactive oxygen species (ROS), predominantly singlet oxygen ((1)O2). ROS damage both DNA and proteins. Here we show that UVA irradiation of cultured human cells containing DNA 6-TG causes significant protein oxidation and damages components of the DNA repair proteome, including the Ku, OGG-1, MYH, and RPA proteins. Assays of DNA repair in intact cells or in cell extracts indicate that this protein damage compromises DNA break rejoining and base and nucleotide excision repair. As these experimental conditions simulate those in the skin of patients taking thiopurines, our findings suggest a mechanism whereby UVA in sunlight may contribute to skin carcinogenesis in immunosuppressed patients.

Contribution of cytosine-containing cyclobutane dimers to DNA damage produced by photosensitized triplet-triplet energy transfer

Mutagenic cyclobutane pyrimidine dimers (CPDs) can be induced in DNA through either direct excitation or photosensitized triplet-triplet energy transfer (TTET). In the latter pathway, thymines are expected to receive the excitation energy from the photosensitizer and react with adjacent pyrimidines. By using state-of-the art analytical tools, we provide herein additional information on the formation of cytosine-containing CPDs. We thus determined the yield of all possible CPDs upon TTET in a series of natural DNAs with various base compositions. We show that the distribution of CPDs cannot be explained only by excitation of individual thymines. We propose that the mechanism for TTET involves at least dinucleotides as the minimal targets. The observation of the formation of cytosine-cytosine CPDs also suggests that additional pathways are involved in this photosensitized reaction.

Seeking the mechanism responsible for fluoroquinolone photomutagenicity: a pulse radiolysis, steady-state, and laser flash photolysis study

The mechanism responsible for the remarkable photomutagenicity of fluoroquinolone (FQ) antibiotics remains unknown. For this reason, it was considered worthwhile to study in detail the interactions between DNA and a dihalogenated FQ such as lomefloxacin (LFX; one of the most photomutagenic FQs) and its N-acetyl derivative ALFX. Studies of photosensitized DNA damage by (A)LFX, such as formation of DNA single-strand breaks (SSBs), together with pulse radiolysis, laser flash photolysis, and absorption and fluorescence measurements, have shown the important effects of the cationic character of the piperazinyl ring on the affinity of this type of drug for DNA. Hence, the formation of SSBs was detected for LFX, whereas ALFX and ciprofloxacin (a monofluorated FQ) needed a considerably larger dose of light to produce some damage. In this context, it was determined that the association constant (Ka) for the binding of LFX to DNA is ca. 2×10(3)M(-1), whereas in the case of ALFX it is only ca. 0.5×10(3)M(-1). This important difference is attributed to an association between the cationic peripheral ring of LFX and the phosphate moieties of DNA and justifies the DNA SSB results. The analysis of the transient species detected and the photomixtures has allowed us to establish the intermolecular processes involved in the photolysis of FQ in the presence of DNA and 2'-deoxyguanosine (dGuo). Interestingly, although a covalent binding of the dihalogenated FQ to dGuo occurs, the photodegradation of FQ…DNA complexes did not reveal any significant covalent attachment. Another remarkable outcome of this study was that (A)LFX radical anions, intermediates required for the onset of DNA damage, were detected by pulse radiolysis but not by laser flash photolysis.

Supramolecular photochemistry of drugs in biomolecular environments

We illustrate how the interaction of drugs with proteins or DNA in supramolecular complexes can influence the reactions initiated by drug absorbed photons, evidencing the differences with respect to solution.

Photosensitizing medications and photocarcinogenesis

Photosensitivity is an exaggerated or abnormal response to ultraviolet (UV) or visible light exposure. Many current medications are known photosensitizers; however, the effects of the sensitization can be subclinical and go unnoticed by the person affected. While some of these drugs are used for short and defined periods, others are used indefinitely for the treatment of chronic disease. The question of whether either of these practices translates into an increased risk of skin cancer is an important one. Numerous medications have real, distinct and well-elucidated mechanisms that potentiate the development of skin cancer, while with some medications the mechanism for the observed carcinogenesis remains unclear. In this article we will discuss the clinical, mechanistic and epidemiological evidence supporting photochemical genotoxicity and carcinogenesis.

Light-induced catalytic transformation of ofloxacin by solar Fenton in various water matrices at a pilot plant: mineralization and characterization of major intermediate products

This work investigated the application of a solar driven advanced oxidation process (solar Fenton), for the degradation of the antibiotic ofloxacin (OFX) in various environmental matrices at a pilot-scale. All experiments were carried out in a compound parabolic collector pilot plant in the presence of doses of H2O2 (2.5 mg L(-1)) and at an initial Fe(2+) concentration of 2 mg L(-1). The water matrices used for the solar Fenton experiments were: demineralized water (DW), simulated natural freshwater (SW), simulated effluent from municipal wastewater treatment plant (SWW) and pre-treated real effluent from municipal wastewater treatment plant (RE) to which OFX had been spiked at 10 mg L(-1). Dissolved organic carbon removal was found to be dependent on the chemical composition of the water matrix. OFX mineralization was higher in DW (78.1%) than in SW (58.3%) at 12 mg L(-1) of H2O2 consumption, implying the complexation of iron or the scavenging of hydroxyl radicals by the inorganic ions present in SW. On the other hand, the presence of dissolved organic matter (DOM) in SWW and RE, led to lower mineralization per dose of H2O2 compared to DW and SW. The major transformation products (TPs) formed during the solar Fenton treatment of OFX, were elucidated using liquid chromatography-time of flight-mass spectrometry (LC-ToF-MS). The transformation of OFX proceeded through a defluorination reaction, accompanied by some degree of piperazine and quinolone substituent transformation while a hydroxylation mechanism occurred by attack of the hydroxyl radicals generated during the process leading to the formation of TPs in all the water matrices, seven of which were tentatively identified. The results obtained from the toxicity bioassays indicated that the toxicity originates from the DOM present in RE and its oxidation products formed during the photocatalytic treatment and not from the TPs resulted from the oxidation of OFX.

Hydrochlorothiazide enhances UVA-induced DNA damage

The UVA is currently thought to be carcinogenic because, similar to UVB, it induces the formation of cyclobutane pyrimidine dimers (CPDs). Various drugs have been reported to cause photosensitive drug eruptions as an adverse effect. Although the precise mechanism of photosensitive drug eruption remains to be elucidated, it is generally accepted that free radicals and other reactive molecules generated via UV-irradiated drugs play important roles in the pathogenesis of photosensitive drug eruptions. The waveband of concern for photo-reactive drugs is UVA-visible light, but some extend into the UVB region. We tested whether photosensitive drugs could enhance CPD formation after UVA exposure by using isolated DNA in the presence of several reported photosensitive drugs using high-performance liquid chromatography. We found that the diuretic agent hydrochlorothiazide (HCT) significantly enhanced the production of TT dimers over a wide range of UVA. Furthermore, we investigated whether UVA plus HCT could enhance CPD production in xeroderma pigmentosum model mice defective in nucleotide excision repair. Immunofluorescence studies showed that CPD formation in the skin significantly increased after 365 nm narrow-band UVA irradiation in the presence of HCT, compared with that in wild-type mice. HCT could be used with caution because of its enhancement of UVA-induced DNA damage.

Photoinduced damage to cellular DNA: direct and photosensitized reactions

The survey focuses on recent aspects of photochemical reactions to cellular DNA that are implicated through the predominant formation of mostly bipyrimidine photoproducts in deleterious effects of human exposure to sunlight. Recent developments in analytical methods have allowed accurate and quantitative measurements of the main DNA photoproducts in cells and human skin. Highly mutagenic CC and CT bipyrimidine photoproducts, including cyclobutane pyrimidine dimers and pyrimidine (6-4) pyrimidone photoproducts (6-4PPs) are generated in low yields with respect to TT and TC photoproducts. Another striking finding deals with the formation of Dewar valence isomers, the third class of bipyrimidine photoproducts that is accounted for by UVA-mediated isomerization of initially UVB generated 6-4PPs. Cyclobutadithymine (T<>T) has been unambiguously shown to be involved in the genotoxicity of UVA radiation. Thus, T<>T is formed in UVA-irradiated cellular DNA according to a direct excitation mechanism with a higher efficiency than oxidatively generated DNA damage that arises mostly through the Type II photosensitization mechanism. C<>C and C<>T are repaired at rates intermediate between those of T<>T and 6-4TT. Evidence has been also provided for the occurrence of photosensitized reactions mediated by exogenous agents that act either in an independent way or through photodynamic effects.

Potential phototoxicity of rosuvastatin mediated by its dihydrophenanthrene-like photoproduct

In this work, rosuvastatin has been used to gain insight into the molecular basis of statin photosensitization. This lipid-lowering drug, also known as "superstatin", contains a 2-vinylbiphenyl-like moiety and has been previously described to decompose under solar irradiation, yielding stable dihydrophenanthrene analogues. During photophysical characterization of rosuvastatin, only a long-lived transient at ca. 550 nm was observed and assigned to the primary photocyclization intermediate. Thus, the absence of detectable triplet-triplet absorption and the low yield of fluorescence rules out the role of the parent drug as an efficient sensitizer. In this context, the attention has been placed on the rosuvastatin main photoproduct (ppRSV). Indeed, the photobehavior of this dihydrophenanthrene-like compound presents the essential components needed for an efficient biomolecule photosensitizer i.e. (i) a high intersystem crossing quantum yield (Φ(ISC) = 0.8), (ii) a triplet excited state energy of ca. 67 kcal mol(-1), and (iii) a quantum yield of singlet oxygen formation (Φ(Δ)) of 0.3. Furthermore, laser flash photolysis studies revealed a triplet-triplet energy transfer from the triplet excited state of ppRSV to thymidine, leading to the formation of cyclobutane thymidine dimers, an important type of DNA lesion. Finally, tryptophan has been used as a probe to investigate the type I and/or type II character of ppRSV-mediated oxidation. In this way, both an electron transfer process giving rise to the tryptophanyl radical and a singlet oxygen mediated oxidation were observed. On the basis of the obtained results, rosuvastatin, through its major photoproduct ppRSV, should be considered as a potential sensitizer.

Combined use of in vitro phototoxic assessments and cassette dosing pharmacokinetic study for phototoxicity characterization of fluoroquinolones

The present study aimed to develop an effective screening strategy to predict in vivo phototoxicity of multiple compounds by combined use of in vitro phototoxicity assessments and cassette dosing pharmacokinetic (PK) studies. Photochemical properties of six fluoroquinolones (FQs) were evaluated by UV spectral and reactive oxygen species (ROS) assays, and phototoxic potentials of FQs were also assessed using 3T3 neutral red uptake phototoxicity test (3T3 NRU PT) and intercalator-based photogenotoxicity (IBP) assay. Cassette dosing pharmacokinetics on FQs was conducted for calculating PK parameters and dermal distribution. All the FQs exhibited potent UV/VIS absorption and ROS generation under light exposure, suggesting potent photosensitivity of FQs. In vitro phototoxic risks of some FQs were also elucidated by 3T3 NRU PT and IBP assay. Decision matrix for phototoxicity prediction was built upon these in vitro data, taken together with outcomes from cassette dosing PK studies. According to the decision matrix, most FQs were deduced to be phototoxic, although gatifloxacin was found to be less phototoxic. These findings were in agreement with clinical observations. Combined use of in vitro photobiochemical and cassette dosing PK data will be useful for predicting in vivo phototoxic potentials of drug candidates with high productivity and reliability.

Photochemical Properties and Reactions with Biomolecules of 4'-N-Acetyl Derivative of Norfloxacin

The photochemical properties of 4'-N-acetyl derivative of norfloxacin (ANFX) were investigated in different solutions. Both UV-Vis absorption and the quantum yields of excited states are pH-dependent, and pK a value of ground state for the protonation of 3-carboxylic group was determined to be 6.5 ± 0.2. Pulse radiolysis and laser flash photolysis experiments were carried out to characterize transient species of ANFX and to investigate reactions with tryptophan (TrpH) and 2'-seoxyguanosine-5'-monophosphoric acid disodium salt (dGMP). The ANFX undergoes the photoejection of electron by a mixed mechanism of one-photon and two-photon processes. Under moderate laser energy conditions, two-photon process is predominantly. The ANFX radical dianion (ANFX(–H)·2−) formed in reaction with eaq − is characterized by the absorption around 370 nm, and the rate constant was determined to be 1.2 × 1010 dm3 mol−1 s−1. The 3ANFX(–H)−∗ is able to oxidize TrpH and dGMP with bimolecular rate constants of 5.4 × 108 and 9.5 × 106 dm3 mol−1 s−1, respectively. The ANFX(–H)·2− and the oxidized radicals of TrpH and dGMP were observed directly. Under aerobic conditions, the photo-oxidations involve both type I and type II mechanisms.