The phototumorigenic fluoroquinolone, lomefloxacin, photosensitises p53 accumulation and transcriptional activity in human skin cells

An Observed Effect of p53 Status on the Bystander Response to Radiation-Induced Cellular Photon Emission

In this study, we investigated the potential influence of p53 on ultraviolet (UV) signal generation and response of bystander cells to the UV signals generated by beta-irradiated cells. Five cell lines of various p53 status (HaCaT, mutated; SW48, wild-type; HT29, mutated; HCT116^+/+, wild-type; HCT116^-/-, null) were irradiated with beta particles from tritium. Signal generation (photon emission at 340 ± 5 nm) was quantified from irradiated cells using a photomultiplier tube. Bystander response (clonogenic survival) was assessed by placing reporter cell flasks directly superior to irradiated signal-emitting cells. All cell lines emitted significant quantities of UV after tritium exposure. The magnitudes of HaCaT and HT29 photon emission at 340 nm were similar to each other while they were significantly different from the stronger signals emitted from SW48, HCT116^+/+ and HCT116^-/- cells. In regard to the bystander responses, HaCaT, HCT116^+/+ and SW48 cells demonstrated significant reductions in survival as a result of exposure to emission signals. HCT116^-/- and HT29 cells did not exhibit any changes in survival and thus were considered to be lacking the mechanisms or functions required to elicit a response. The survival response was found not to correlate with the observed signal strength for all experimental permutations; this may be attributed to varying emission spectra from cell line to cell line or differences in response sensitivity. Overall, these results suggest that the UV-mediated bystander response is influenced by the p53 status of the cell line. Wild-type p53 cells (HCT116^+/+ and SW48) demonstrated significant responses to UV signals whereas the p53-null cell line (HCT116^-/-) lacked any response. The two mutated p53 cell lines exhibited contrasting responses, which may be explained by unique modulation of functions by different point mutations. The reduced response (cell death) exhibited by p53-mutated cells compared to p53 wild-type cells suggests a possible role of the assessed p53 mutations in radiation-induced cancer susceptibility and reduced efficacy of radiation-directed therapy.

Exposure to phototoxic NSAIDs and quinolones is associated with an increased risk of melanoma

PURPOSE

Ultraviolet radiation exposure is the most important exogenous risk factor for cutaneous malignancies. It is possible that phototoxic drugs promote the development of cutaneous melanoma (CM) by intensifying the effect of ultraviolet light on the skin. We investigated the association between the use of common systemic phototoxic drugs and development of CM.

METHODS

This study was a case-control study in a Dutch population-based cohort. The drug dispensing data was obtained from PHARMO, a Dutch drug dispensing and hospital admissions registry, and linked to PALGA, the nationwide pathology network of the Netherlands. The cases were patients diagnosed with pathologically confirmed primary CM between 1991 and 2004. Controls were sampled from the PHARMO population. Exposure to systemic phototoxic drugs was measured and included antimicrobial agents, diuretics, antipsychotic drugs, antidiabetic drugs, cardiac drugs, antimalarials and nonsteroidal anti-inflammatory drugs (NSAIDs). A multivariate conditional logistic regression analysis was performed to study the association between exposure to phototoxic drugs and CM.

RESULTS

The study population included 1,318 cases and 6,786 controls. Any phototoxic drug during the study period was dispensed for 46 % of the cases and 43 % of the controls (p = 0.012). The use of quinolones [odds ratio (OR) 1.33, 95 % confidence interval (CI) 1.01-1.76] and propionic acid derivative NSAIDs (OR 1.33, 95 % CI 1.14-1.54) had a positive association with CM.

CONCLUSIONS

Our study shows that the use of phototoxic drugs is associated with an increased risk of developing CM. Even a short-term use of phototoxic quinolones and propionic acid derivative NSAIDs may increase the risk for CM. Patient education to promote sun-protective behaviour is essential to avoid immediate adverse effects and possible long-term effects of phototoxic drugs.

The photo comet assay—A fast screening assay for the determination of photogenotoxicity in vitro

Different classes of chemicals can induce a phototoxic effect by absorbing light energy within the wavelength range of sunlight. The assessment of photo-safety is therefore an obligatory part of the development of new drugs. Ten UV-vis (280-800nm)-absorbing compounds (ketoprofen, promazine, chlorpromazine, dacarbazine, acridine, lomefloxacin, 8-methoxypsoralen, chlorhexidine, titanium dioxide, octylmethoxycinnamate) were tested for their photogenotoxic potential in the alkaline comet assay in the presence and absence of UV-vis. In order to establish an easy and timesaving protocol for a photo comet assay screening test, the application of 96-well plates was essential. The use of mouse lymphoma L5178Y cells, a cell line growing in suspension, allowed the determination of photocytotoxicity with the Alamar Blue assay and of photogenotoxicity with the alkaline comet assay in parallel. L5178Y cells were incubated with the test compounds for 20min and irradiated with simulated sunlight in the wavelength range from 280 to 800nm. The applied UV dose was 600mJ/cm(2) UV-A and 30mJ/cm(2) UV-B. After a post-incubation of 10min, the Alamar Blue assay and the alkaline comet assay were performed. All of the compounds which are known to be photogenotoxic (8-methoxypsoralen, acridine, chlorpromazine, dacarbazine, ketoprofen, lomefloxacin) showed a positive effect under our assay conditions. Furthermore, four UV-vis absorbing chemicals which are known to be not photogenotoxic (promazine, chlorhexidine, titanium dioxide, octylmethoxycinnamate) were analysed. For none of them an increase of the DNA damage following irradiation was observed in this study. In conclusion, all of the chemical compounds tested were classified in agreement with published data. From the data presented it is concluded that the photo comet assay with L5178Y mouse lymphoma cells is a reliable model to assess photochemical genotoxicity in vitro.

Rufloxacin-induced photosensitization in yeast

The fluoroquinolone Rufloxacin (RFX) is active as specific inhibitor of bacterial gyrase. The adverse effects of the photosensitization induced by fluoroquinolones are well known. A predominant type II photosensitizing activity of Rufloxacin has already been demonstrated on simpler models (free nucleosides, calf thymus DNA), whereas a cooperative mechanism was corroborated on more complex ones (plasmid and fibroblast). The purpose of this study is to examine the drug photocytoxicity in another complex cellular model, a wild-type eukaryotic fast-growing microorganism whose cultivation is cheap and easily managed, Saccharomyces cerevisiae. This work represents the first report of the potential photogenotoxicity of Rufloxacin. Particular emphasis was given to DNA modifications caused in yeast by the formation of Rufloxacin photomediated toxic species, such as hydrogen peroxide and formaldehyde. Drug phototoxicity on yeast was evaluated by measuring DNA fragmentation (single/double strand breaks) using single cell gel electrophoresis assay and 8-OH-dGuo, a DNA photooxidation biomarker, by HPLC-ECD. Cellular sensitivity was also assessed by cell viability test. The extra- and intracellular RFX concentration (as well as its main photoproduct) was verified by HPLC-MS, whereas the cytotoxic species were evaluated by colorimetric assays. The results confirm the phototoxicity of Rufloxacin on yeast cell and are in agreement with those previously obtained with human fibroblast and with simpler models used recently, and provide a clear link between DNA photosensitization and overall phototoxicity.

Development of genotoxicity test procedures with Episkin®, a reconstructed human skin model: Towards new tools for in vitro risk assessment of dermally applied compounds?

Today reconstructed skin models that simulate human skin, such as Episkin, are widely used for safety or efficacy pre-screening. Moreover, they are of growing interest for regulatory purposes in the framework of alternatives to animal testing. In order to reduce and eventually replace results of in vivo genotoxicity testing with in vitro data, there is a need to develop new complementary biological models and methods with improved ability to predict genotoxic risk. This can be achieved if these new assays do take into account exposure conditions that are more relevant than in the current test systems. In an attempt to meet this challenge, two new applications using a human reconstructed skin model for in vitro genotoxicity assessment are proposed. The skin is the target organ for dermally exposed compounds or environmental stress. Although attempts have been made to develop genotoxicity test procedures in vivo on mouse skin, human reconstructed skin models have not been used for in vitro genotoxicity testing so far, although they present clear advantages over mouse skin for human risk prediction. This paper presents the results of the development of a specific protocol allowing to perform the comet assay, a genotoxicity test procedure, on reconstructed skin. The comet assay was conducted after treatment of Episkin with UV, Lomefloxacin and UV or 4-nitroquinoline-N-oxide (4NQO). Treatment with the sunscreen Mexoryl was able to reduce the extent of comet signal. A second approach to use reconstructed epidermis in genotoxicity assays is also proposed. Indeed, the skin is a biologically active barrier driving the response to exposure to chemical agents and their possible metabolites. A specific co-culture system (Figure 1) using Episkin to perform the regular micronucleus assay is presented. Micronucleus induction in L5178Y cells cultured underneath Episkin was assessed after treatment of the reconstructed epidermis with mitomycin C, cyclophosphamide or apigenin. This second way of using human reconstructed skin for genotoxicity testing aims at improving the relevance of exposure conditions in in vitro genotoxicity assays for dermally applied compounds.

Rufloxacin induced photosensitization in bio-models of increasing complexity

Rufloxacin belongs to the class of fluoroquinolones that act mainly as specific inhibitors of bacterial Topoisomerase II. These drugs are widely known to be involved in various diseases ranging from cutaneous reactions to aging. The type II photosensitizing activity of Rufloxacin has been already demonstrated on calf thymus DNA and free nucleosides. The aim of this study is to examine in control untreated and UVA irradiated human fibroblasts the modifications on DNA status induced by Rufloxacin added in the culture medium. This allows to investigate the photosensitizing activity of Rufloxacin in a more complex cell model. Fibroblasts, either in the presence or in the absence of Rufloxacin, were exposed to UVA irradiation for different times. An experimental protocol was followed in order to evaluate the amount of single-strand breaks (SSB) and double-strand breaks (DSB) DNA fragmentation by comet assay, and plasmid photocleavage. The presence of oxidized bases was also evaluated using the 8-OH-dGuo test. The comet assay test was also employed to assess cellular repair capacity. The intracellular drug concentration was verified by HPLC-MS. The results confirming the role of Rufloxacin as photosensitizer were: (i) a time-dependent increase in DNA fragmentation when fibroblasts were irradiated in the presence of Rufloxacin; (ii) the efficiency of the cellular repair machinery to be exhaustive after 2 h (whereas no correlation between irradiation time and DNA damage repair was observed with a higher level of DNA fragmentation after shorter irradiation times); (iii) the increased number of cells exhibiting high DNA fragmentation, seen as comets with long tails, was not accompanied by a similar large extent of oxidised DNA base formation, as measured by 8-OH-dGuo analysis; (iv) the double helix SSB, formed in plasmid photosensitization, agreed with the comet assay results, pointing out a good correlation among the cell system and the simpler models used.

UV-B induced keratinocyte apoptosis is blocked by 2-selenium-bridged beta-cyclodextrin, a GPX mimic

Cell proliferation and cell death of keratinocytes are tightly regulated to ensure epidermal homeostasis. UV-B induces keratinocyte apoptosis. UV-B also induces lipid peroxidation of keratinocytes to increase their amount of malondialdehyde (MDA). These phenomena can be explained by the production of reactive oxygen species (ROS) induced by UV-B radiation. We synthesized 2-selenium-bridged beta-cyclodextrin (2-SeCD) to imitate glutathione peroxidase (GPX), an important antioxidant and established a damage system, in which keratinocytes can be damaged by Ultraviolet B (UV-B) radiation. Using this damage system we studied 2-SeCD protection of keratinocytes against injury induced by UV-B. Experimental results showed that 2-SeCD could protect keratinocytes from apoptosis. Moreover, 2-SeCD inhibits lipid peroxidation of keratinocytes and scavenges ROS. 2-SeCD inhibits the UV-B induced apoptotic signal transduction. This antiapoptotic mechanism may be partly related to the elimination of hydrogen peroxide.

Photogenotoxicity of mammalian cells: a review of the different assays for in vitro testing

During the past several years, phototoxicity has been studied at the molecular level, and these studies have provided new insights in the field of DNA lesion characterization, DNA repair and cell response to ultraviolet (UV)-induced stress. The development of new antibiotics and antiinflammatory drugs has highlighted the necessity to develop the assessment of phototoxicity in the safety evaluation of new chemical compounds. This paper aims at reviewing the known molecular mechanisms of the cellular response to UV-induced stress, the in vitro methods that can be proposed and used to screen for toxicity of sunlight and the photosensitization process resulting from the activation of drugs by light. UV sources, biological systems and endpoints of interest in that particular objective are listed. Phototoxic effects span from the cytotoxic-apoptotic effect to the induction of primary DNA damage, DNA repair and a variety of stress genes acting on the cell cycle and the fate of the cell. Ultimately, it can lead to the induction of hereditary DNA modification. A variety of assays are proposed to specifically address all these particular consequences of UV-induced toxicity.