Efficient photoinduced DNA damage by coralyne

The photoinduced DNA damage by the berberine derivative coralyne is presented. The irradiation of coralyne in the presence of plasmid DNA namely, pBR322, leads to remarkably fast DNA damage by single-strand cleavage, as determined by agarose-gel electrophoresis. Even upon exposure to sunlight, almost all of the supercoiled plasmid is converted to the open circular form in less than a minute [c(pBR322) = 3.5 x 10(-9) M; c(coralyne) = 4.3 x 10(-5) M]. The efficiency of the DNA strand cleavage is not decreased in the presence of radical-trapping reagents such as tert-butanol or DMSO. Moreover, the extent of the DNA damage is the same under aerobic conditions and at reduced oxygen concentration. Thus, the formation of reactive intermediates such as hydroxyl radicals or singlet oxygen is excluded. These results show that the exposure of coralyne and derivatives thereof to light, even with moderate light intensity, needs to be avoided during experiments in which their biological activity is assessed by plasmid unwinding assays.     

DNA damage and repair in Gorlin syndrome and normal fibroblasts after aminolevulinic acid photodynamic therapy: a comet assay study

Using normal, untransformed, human fibroblasts, the effectiveness of aminolevulinic (ALA)-mediated photodynamic therapy (PDT) was investigated in terms of both clonogenic survival and DNA damage. The response of normal fibroblasts was then compared with Gorlin syndrome-derived fibroblasts (basal cell nevus syndrome [BCNS]). In terms of clonogenic survival, no significant differences were observed between the two groups of cells. Using the alkaline comet assay, initial DNA damage after PDT was measured. Some DNA damage was detected at higher doses, but this was fully repaired within 24 h of treatment. The BCNS-derived cells showed levels of initial damage that did not differ significantly from normal lines.     

Detection of DNA damage in yolk-sac larvae of the Japanese Medaka, Oryzias latipes, by the comet assay

This study was set up to determine the suitability of the early life stage (ELS) alkaline comet assay for the detection of DNA strand breaks induced by genotoxicants in whole organism. This assay was performed on cells of medaka 2 days posthatch (dph). An efficient procedure for cell dissociation using enzymatic and mechanical digestion was developed. This protocol ensures 80% viability of cells and low DNA damage background. Cells from 2 dph medaka larvae were exposed in vitro to model genotoxicants, hydrogen peroxide, cadmium, and fluoranthene, followed by comet assay analysis. Results show a significant increase in the percentage of DNA damage of dissociated cells by all the tested compounds when compared to controls. The assay was also performed in vivo on medaka larvae (2 dph) exposed for 24 h to waterborne cadmium or fluoranthene. Significant induction of DNA damage levels were observed following larvae exposure to cadmium and fluoranthene at concentrations of 0.1 and 50 μM, respectively. This study demonstrates that cells of embryo life stage medaka respond to known DNA damaging agents and that the ELS comet assay may be a useful biomarker to detect DNA strand breakage in whole body of pluricellular organism induced by a range of agents. This technique may provide a sensitive, nonspecific endpoint of genotoxicity as part of ELS toxicity test.     

Comparison of DNA damage photoinduced by ketoprofen, fenofibric acid and benzophenone via electron and energy transfer.

Ketoprofen (KP) and fenofibrate, respectively, anti-inflammatory and hypolipidemiant agents, promote anormal photosensitivity in patients and may induce photoallergic cross-reactions correlated to their benzophenone-like structure. Here, their ability to photosensitize the degradation of biological targets was particularly investigated in DNA. The photosensitization of DNA damage by KP and fenofibric acid (FB), the main metabolite of fenofibrate, and their parent compound, benzophenone (BZ), was examined on a 32P-end-labeled synthetic oligonucleotide in phosphate-buffered solution using gel sequencing experiments. Upon irradiation at lambda > 320 nm, piperidine-sensitive lesions were induced in single-stranded oligonucleotides by KP, FB and BZ at all G sites to the same extent. This pattern of damage, enhanced in D2O is characteristic of a Type-II mechanism. Spin trapping experiments using 2,2,6,6-tetramethyl-4-piperidone have confirmed the production of singlet oxygen during drug photolysis. On double-stranded oligonucleotides, highly specific DNA break occurred selectively at 5'-G of a 5'-GG-3' sequence, after alkali treatment. Prolonged irradiation led to the degradation of all G residues, with efficiency decreasing in the order 5'-GG > 5'-GA > 5'-GC > 5'-GT, in good agreement with the calculated lowest ionization potentials of stacked nucleobase models supporting the assumption of a Type-I mechanism involving electron transfer, also observed to a lesser extent with adenine. Cytosine sites were also affected but the action of mannitol which selectively inhibited cytosine lesions suggests, in this case, the involvement of hydroxyl radical, also detected by electronic paramagnetic resonance using 5,5-dimethyl-1-pyrrolidine-1-oxide as spin trap. On a double-stranded 32P-end-labeled 25-mer oligonucleotide containing TT and TTT sequences, the three compounds were found to photosensitize by triplet-triplet energy transfer the formation of cyclobutane thymine dimers detected using T4 endonuclease V.     

Hydrogen peroxide is responsible for UVA-induced DNA damage measured by alkaline comet assay in HaCaT keratinocytes

We investigated the role of different reactive oxygen species (ROS) in ultraviolet A (UVA)-induced DNA damage in a human keratinocyte cell line, HaCaT. UVA irradiation increased the intracellular levels of hydrogen peroxide (H2O2), detected by a fluorescent probe carboxydichlorodihydrofluorescein, and caused oxidative DNA damage, single strand-breaks and alkali-labile sites, measured by alkaline single cell gel electrophoresis (comet assay). Superoxide anion (O2*-) was a likely substrate for H2O2 production since diethyldithiocarbamate (DDC), a superoxide dismutase blocker, decreased the level of intracellular H2O2. Hydrogen peroxide was shown to play a central role in DNA damage. Increasing the intracellular levels of H2O2 with aminotriazole (AT) (a catalase blocker) and buthionine sulfoximine (BSO) (an inhibitor of glutathione synthesis) potentiated the UVA-induced DNA damage. Exogenous H2O2 was also able to induce DNA damage. Since H2O2 alone is not able to damage DNA directly, we investigated the significance of the H2O2-derived hydroxyl radical (*OH). Addition of FeSO4, that stimulates *OH formation from H2O2 (Fenton reaction) resulted in a twofold increase of DNA-damage. Desferrioxamine, an iron chelator that blocks the Fenton reaction, prevented UVA-induced DNA damage. We also employed a panel of less specific antioxidants and enzyme modulators. Sodium selenite (Na-Se) present in glutathione peroxidase and thioredoxin reductase and addition of glutathione (GSH) prevented DNA-damage. Tocopherol potently prevented UVA-and H2O2-induced DNA damage and reduced intracellular H2O2 -levels. Ascorbic acid reduced H2O2 production, but only partly prevented DNA damage. Singlet oxygen (1O2) did not seem to play an important role in the UVA-induced DNA-damage since the specific 1O2 scavenger sodium azide (NaN3) and the less specific 1O2 scavenger beta-carotene did not markedly prevent either DNA-damage or H2O2 production. In conclusion the conversion of H2O2 to *OH appears to be the most important step in UVA-induced generation of strand breaks and alkali-labile sites and the bulk H2O2 appears to originate from O2*- generated by UVA irradiation.     

Assessment of gamma ray-induced DNA damage in Lasioderma serricorne using the comet assay

We attempted a DNA comet assay under alkaline conditions to verify the irradiation treatment of pests. Lasioderma serricorne (Fabricius) were chosen as test insects and irradiated with gamma rays from a ⁶⁰Co source at 1 kGy. We conducted the comet assay immediately after irradiation and over time for 7 day. Severe DNA fragmentation in L. serricorne cells was observed just after irradiation and the damage was repaired during the post-irradiation period in a time-dependent manner. The parameters of the comet image analysis were calculated, and the degree of DNA damage and repair were evaluated. Values for the Ratio (a percentage determined by fluorescence in the damaged area to overall luminance, including intact DNA and the damaged area of a comet image) of individual cells showed that no cells in the irradiated group were included in the Ratio<0.1 category, the lowest grade. This finding was observed consistently throughout the 7-day post-irradiation period. We suggest that the Ratio values of individual cells can be used as an index of irradiation history and conclude that the DNA comet assay under alkaline conditions, combined with comet image analysis, can be used to identify irradiation history.     

Identification of irradiated wheat by germination test, DNA comet assay and electron spin resonance

In several countries, there has been an increase in the use of radiation for food processing thus improving the quality and sanitary conditions, inhibiting pathogenic microorganisms, delaying the natural aging process and so extending product lifetime. The need to develop analytical methods to detect these irradiated products is also increasing. The goal of this research was to identify wheat irradiated using different radiation doses. Seeds were irradiated with a gamma ⁶⁰Co source (Gammacell 220 GC) in the Centro de Energia Nuclear na Agricultura and the Instituto de Pesquisas Energéticas e Nucleares. Dose rate used were 1.6 and 5.8 kGy/h. Applied doses were 0.0, 0.10, 0.25, 0.50, 0.75, 1.0, and 2.0 kGy. After irradiation, seeds were analysed over a 6 month period. Three different detection methods were employed to determine how irradiation had modified the samples. Screening methods consisted of a germination test measuring the inhibition of shooting and rooting and analysis of DNA fragmentation. The method of electron spin resonance spectroscopy allowed a better dosimetric evaluation. These techniques make the identification of irradiated wheat with different doses possible.     

Assessment of electron beam-induced DNA damage in larvae of chestnut weevil,Curculio sikkimensis (Heller) (Coleoptera: Curculionidae) using comet assay

Effect of electron beam treatment on DNA damage in mature larvae of chestnut weevil Curculio sikkimensis (Heller) was assessed using single-cell gel electrophoresis (DNA comet assay). Electrons at acceleration voltages of 0 (control), 300, 750, 1000, and 1500 kV at radiation doses of 1 and 4 kGy were used. Electron beam-treated chestnut larvae showed typical DNA fragmentation, compared with cells from non-treated ones which showed a more intact DNA. Investigations using the comet assay showed that the parameters including tail length, tail moment, olive tail moment as well as the quota of DNA damage at both the doses were significantly larger than the control batch larvae. Thus, this technique could contribute to analytical identification of an effective disinfestation and quarantine treatment.     

Detection of irradiated quail meat by using DNA comet assay and evaluation of comets by image analysis

A simple technique of microgel electrophoresis of single cells (DNA comet assay) was used to detect DNA comets in irradiated quail meat samples. Obtained DNA comets were evaluated by both photomicrographic and image analysis. Quail meat samples were exposed to radiation doses of 0.52, 1.05, 1.45, 2.00, 2.92 and 4.00 kGy in gamma cell (gammacell ⁶⁰Co, dose rate 1.31 kGy/h) covering the permissible limits for enzymatic decay and stored at 2 °C. The cells isolated from muscle (chest, thorax) in cold PBS were analyzed using the DNA comet assay on 1, 2, 3, 4, 7, 8 and 11 day post irradiation. The cells were lysed between 2, 5 and 9 min in 2.5% SDS and electrophorosis was carried out at a voltage of 2 V/cm for 2 min. After propidium iodide staining, the slides were evaluated through a fluorescent microscope. In all irradiated samples, fragmented DNA stretched towards the anode and damaged cells appeared as a comet. All measurement data were analyzed using BS 200 ProP with software image analysis (BS 200 ProP, BAB Imaging System, Ankara, Turkey). The density of DNA in the tails increased with increasing radiation dose. However, in non-irradiated samples, the large molecules of DNA remained relatively intact and there was only minor or no migration of DNA; the cells were round or had very short tails only. The values of tail DNA%, tail length and tail moment were significantly different and identical between 0.9 and 4.0 kGy dose exposure, and also among storage times on day 1, 4 and 8. In conclusion, the DNA Comet Assay EN 13784 standard method may be used not only for screening method for detection of irradiated quail meat depending on storage time and condition but also for the quantification of applied dose if it is combined with image analysis. Image analysis may provide a powerful tool for the evaluation of head and tail of comet intensity related with applied doses.     

Effect of dye aggregation on triarylmethane-mediated photoinduced damage of hexokinase and DNA

The observation that enhanced mitochondrial membrane potential is a prevalent cancer cell phenotype has provided the conceptual basis for the development of mitochondrial targeting as a novel therapeutic strategy for both chemo- and photochemotherapy of neoplastic diseases. Cationic triarylmethane (TAM(+)) dyes represent a series of photosensitizers whose phototoxic effects develop at least in part at the mitochondrial level. In this report we describe how the molecular structure of four representative TAM(+) dyes (Crystal Violet, Ethyl Violet, Victoria blue R, and Victoria pure blue BO) affects their efficiency as mediators of the photoinduced inactivation of two model mitochondrial targets, hexokinase (HK) and DNA. Our results have indicated that TAM(+) dyes efficiently bind to HK and DNA in aqueous media both as dye monomers and aggregates, with the degree of aggregation increasing with increasing the lipophilic character of the photosensitizer. The efficiency with which HK and DNA are damaged upon 532 nm photolysis of biopolymer-TAM(+) complexes was found to decrease upon increasing the degree of dye aggregation over these macromolecular templates. Comparative experiments carried out both in water and in D(2)O, and in air-equilibrated and nitrogen-purged samples have also indicated that, at least when Crystal Violet is used as the photosensitizer, the mechanism of macromolecular damage does not require the involvement of molecular oxygen to operate. This finding makes Crystal Violet a potential candidate for use in photochemotherapy of hypoxic or poorly perfused tumor areas.     

DNA comet assay: A simple screening technique for identification of some irradiated foods

DNA Comet Assay method was carried out to detect irradiation treatment of some foods like meat, spices, beans and lentils. The fresh meat of cow and duck were irradiated up to radiation doses of 3 kGy, the spices (cardamoms and cumin black) were irradiated to radiation doses of 5, 10, 15 and 20 kGy while the beans (black beans and white beans) and lentils (red and green lentils) were irradiated to 0.5 and 1 kGy. All the foods were then analyzed for radiation treatment using simple microgel electrophoresis of single cells or nuclei (DNA Comet Assay). Sedimentation, lysis and staining times were adjusted to get optimized conditions for correct and easy analysis of each food. Using these optimized conditions, it was found out that radiation damaged DNA showed comets in case of irradiated food samples, whereas in non-treated food samples, round or conical spots of stained DNA were visible. Shape, length and intensity of these comets were also radiation dose dependent. Screening of unirradiated and irradiated samples by Comet Assay was successful in the case of all the foods under consideration under the optimized conditions of assay. Therefore, for different kinds of irradiated foods studied in the present study, the DNA Comet Assay can be used as a rapid, simple and inexpensive screening test.     

Separation of fifteen quinolones by high performance liquid chromatography: application to pharmaceuticals and ofloxacin determination in urine

A simple chromatographic method is described for assaying 15 quinolones and fluoroquinolones (pipemidic acid, marbofloxacin, enoxacin, ofloxacin, norfloxacin, ciprofloxacin, danofloxacin, lomefloxacin, enrofloxacin, sarafloxacin, difloxacin, oxolinic acid, nalidixic acid, flumequine and piromidic acid), in urine and pharmaceutical samples. The determination was achieved by LC using an RP C18 analytical column. A mobile phase composed of mixtures of methanol-ACN-10 mM citrate buffer at pH 3.5 and 10 mM citrate buffer at pH 4.5, delivered under an optimum gradient program, at a flow rate of 1.5 mL/min, allows to accomplish the chromatographic separation in 26 min. For detection, diode-array UV-Vis at 280 nm and fluorescence detection set at excitation wavelength/emission wavelength: 280/450, 280/ 495, 280/405 and 320/360 nm were used. Detection and quantification limits were between 0.3-18 and 0.8-61 ng/mL, respectively. The method was validated in terms of interday (n = 6) and intraday (n = 6) precision and accuracy. The procedure was successfully applied to the analysis of human and veterinary pharmaceuticals. Also, ofloxacin was determined in human urine samples belonging to a patient undergoing treatment with this active principle, among others.     

Photohydrolysis of methotrexate produces pteridine,which induces poly-G-specific DNA damage through photoinduced electron transfer

Methotrexate (MTX), an antineoplastic agent, demonstrates phototoxicity. The mechanism of damage to biomacromolecules induced by photoirradiated MTX was examined using 32P-labeled DNA fragments obtained from a human gene. Photoirradiated MTX caused DNA cleavage specifically at the underlined G in 5'-GG and 5'-GGG sequences in double-stranded DNA only when the DNA fragments were treated with piperidine, which suggests that DNA cleavage was caused by base modification with little or no strand breakage. With denatured single-stranded DNA the damage occurred at most guanine residues. The amount of formation of 8-hydroxy-2'-deoxyguanosine (8-oxodGuo), an oxidative product of 2'-deoxyguanosine, in double-stranded DNA exceeded that in single-stranded DNA. These results suggest that photoirradiated MTX participates in 8-oxodGuo formation at the underlined G in 5'-GG and 5'-GGG sequences in double-stranded DNA through electron transfer, and then 8-oxodGuo undergoes further oxidation into piperidine-labile products. Fluorescence measurement, high-pressure liquid chromatography and mass spectrometry have demonstrated that photoexcited MTX is hydrolyzed into 2,4-diamino-6-(hydroxymethyl)pteridine (DHP). DNA damage induced by DHP was observed in a similar manner as was the damage induced by MTX. The extent of DNA damage and the formation of 8-oxodGuo by DHP were much larger than those induced by MTX. The kinetic analysis, based on the time course of DNA oxidation by photoirradiated MTX, suggests that DNA damage is caused by photoexcited DHP rather than by photoexcited MTX. In conclusion, photoexcited MTX undergoes hydrolysis through intramolecular electron transfer, resulting in the formation of DHP, which exhibits a phototoxic effect caused by oxidation of biomacromolecules through photoinduced electron transfer.     

Single-cell gel/comet assay applied to the analysis of UV radiation-induced DNA damage in Rhodomonas sp. (Cryptophyta).

The single-cell gel/comet assay is an electrophoretic technique used to detect single-strand breaks in DNA. Damage is assessed examining individual cells under an epifluorescent microscope. UV-induced DNA damage consists mostly of the formation of pyrimidine dimers; therefore, most of the damage cannot be detected using a standard comet assay. The enzyme T4 endonuclease V breaks DNA strands at sites of pyrimidine dimers. The main objective of this work is to evaluate the comet assay to detect UV-induced damage in DNA after an initial treatment of cells with T4 endonuclease V. This work was conducted on Rhodomonas sp. (Cryptophyta), a marine unicellular flagellate. Cells of Rhodomonas sp. were exposed to 12 h visible + ultraviolet-A + ultraviolet-B (VIS + UVA + UVB) and VIS (control), with and without T4 endonuclease V. Cells exposed to VIS + UVA + UVB showed approximately 200% more damage than control if these were treated with T4 endonuclease V. Rhodomonas sp. were exposed to 3, 6, 9 and 12 h of VIS, VIS + UVA and VIS + UVA + UVB. Damage induced by VIS + UVA + UVB as detected by the comet assay increased along with exposure time. However, damage caused by VIS and VIS + UVA remained relatively constant at all times. Results of this study indicate that the comet assay is more sensitive to UV radiation damage when used in conjunction with T4 endonuclease V. This modification of the comet assay can be used as an alternative technique to detect DNA damage in single cells caused by UV radiation.     

Direct determination of four fluoroquinolones,enoxacin, norfloxacin,ofloxacin, and ciprofloxacin,in pharmaceuticals and blood serum by HPLC

A rapid, accurate and sensitive method has been developed for the quantitative determination of four fluoroquinolone antimicrobial agents, enoxacin, norfloxacin, ofloxacin and ciprofloxacin, with high in-vitro activity against a wide range of Gram-negative and Gram-positive organisms.A Kromasil 100 C(8) 250 mm x 4 mm, 5 microm analytical column was used with an eluting system consisting of a mixture of CH(3)CN-CH(3)OH-citric acid 0.4 mol L(-1) (7:15:78 %, v/v). Detection was performed with a variable wavelength UV-visible detector at 275 nm resulting in limits of detection: 0.02 ng per 20 microL injection for enoxacin and 0.01 ng for ofloxacin, norfloxacin and ciprofloxacin. Hydrochlorothiazide (HCT) was used as internal standard at a concentration of 2 ng microL(-1). A rectilinear relationship was observed up to 2 ng microL(-1) for enoxacin, 12 ng microL(-1) for ofloxacin, 3 ng microL(-1) for norfloxacin, and 5 ng microL(-1) for ciprofloxacin. Separation was achieved within 10 min. The statistical evaluation of the method was examined by performing intra-day (n=8) and inter-day precision assays (n=8) and was found to be satisfactory with high accuracy and precision. The method was applied to the direct determination of the four fluoroquinolones in human blood serum. Sample pretreatment involved only protein precipitation with acetonitrile. Recovery of analytes in spiked samples was 97+/-6% over the range 0.1-0.5 ng microL(-1).     

Ion-pairing and reversed phase liquid chromatography for the determination of three different quinolones: Enrofloxacin,lomefloxacin and ofloxacin

Two simple and sensitive high performance liquid chromatographic (HPLC) methods have been developed for the simultaneous determination of three different quinolones: enrofloxacin, lomefloxacin and ofloxacin in their pure and dosage forms, one with reversed phase HPLC and the other with ion-pair HPLC. In reversed phase HPLC, method (A), the mobile phase consists of 2.18% aqueous solution of KH₂PO₄ with pH adjusted to 2.4 ± 0.2 with acetonitrile (80:20; v/v), the mobile phase pumped at flow rate of 1.2 ml min^?1. A Neucleosil C₁₈ column (10 μm, 100 Å), 250 mm length × 4.6 mm diameter was utilized as stationary phase. Detection was affected spectrophotometrically at 294 nm. While in ion-pair HPLC, method (B), the mobile phase was aqueous solution of 0.65% sodium perchlorate and 0.31% ammonium acetate adjusted to pH 2.2 ± 0.2 with orthophosphoric acid: acetonitrile (81:19; v/v), the mobile phase pumped at flow rate of 1.5 ml min^?1. A μ bondapack C₁₈ column (10 μm, 100 Å), 250 mm length × 4.6 mm diameter was utilized as stationary phase. Detection was affected spectrophotometrically at 294 nm. Linearity ranges for enrofloxacin, lomefloxacin and ofloxacin were 4.0–108, 7.0–112 and 8.0–113 μg ml^?1, respectively using method A and 8.0–112, 7.0–112 and 5.0–105 μg ml^?1, respectively applying method B. Minimum detection limits obtained were 0.013, 0.023 and 0.035 μg ml^?1 for enrofloxacin, lomefloxacin and ofloxacin, respectively using method A, and 0.028, 0.023 and 0.011 μg ml^?1 using method B. The proposed methods were further applied to the analysis of enrofloxacin in injection and tablets containing the ofloxacin and lomefloxacin drugs, and the results were satisfied.     

Bromoacetophenone-based photonucleases: photoinduced cleavage of DNA by 4'-bromoacetophenone-pyrrolecarboxamide conjugates

[formula: see text] 4'-Bromoacetophenone derivatives which upon excitation can generate monophenyl radicals capable of hydrogen atom abstraction were investigated as photoinducible DNA cleaving agents. Pyrrolecarboxamide-conjugated 4'-bromoacetophenones were synthesized, and their DNA cleaving activities and sequence selectivities were determined.     

Electronic structure and specroscopic properties of norfloxacin,enoxacin, and nalidixic acid

The X-ray photoelectron spectra (XPS) of the core electrons of the carbon, oxygen, nitrogen, and fluorine atoms of antibiotics from the class of quinolones (nalidixic acid, norfloxacin, and enoxacin), having different antibacterial activities, were measured and interpreted. The integrated intensities of the π-π* and n-π* transition bands in the absorption spectra of the compounds were analyzed. The maxima of the luminescence spectral bands are given along with the lifetimes of the excited states and quantum yields of the protolytic forms of the compounds in aqueous media. The XPS data were compared with the Mulliken charges on heteroatoms obtained by quantum-chemical calculations.     

Nickel, copper, and zinc centered ruthenium-substituted porphyrins: effect of transition metals on photoinduced DNA cleavage and photoinduced melanoma cell toxicity

Coordination of two [Ru(bipy)(2)Cl](+) moieties (where bipy = 2,2'-bipyridine) to the pyridyl nitrogens in the 5,10-positions of meso-5,10,15-(4-pyridyl)-20-(pentafluorophenyl)porphyrin gives the diruthenium porphyrin complex I. Insertion of nickel(II), copper(II), and zinc(II) into the porphyrin center gives the complexes II-IV, respectively. Electronic transitions associated with the ruthenium porphyrin include an intense Soret band and four less intense Q-bands in the visible region of the spectrum. An intense π-π* transition in the UV region associated with the bipyridyl groups and a metal-to-ligand charge transfer (MLCT) band appearing as a shoulder to the Soret band are also observed. A shift of the Soret band and collapse of the Q-bands into one band is observed upon insertion of the metal ions into the porphyrin center. Electrochemical properties associated with the complexes include a redox couple in the cathodic region attributed to the porphyrin and a redox couple in the anodic region due to the Ru(III/II) couple. DNA titrations of the complexes indicate that they interact strongly with DNA potentially through an intercalation mechanism. Irradiation of aqueous solutions of the complexes and supercoiled DNA at a 5:1 base pair to complex ratio with visible light above 400 nm shows nicking of DNA for the nickel(II) and copper(II) complexes and photocleavage of DNA for the zinc(II) complex. Cell studies with dermal skin (normal) fibroblast and melanoma cells indicate that the free base porphyrin(I) is toxic to both normal and melanoma cells, while the nickel(II) and copper(II) complexes, II and III, are non-toxic to both cell lines when irradiated with a tungsten lamp. The zinc(II) complex, IV, is non-toxic to normal cells but toxic to melanoma cells when irradiated under the same conditions.