Photofrin II photosensitization is mutagenic at the tk locus in mouse L5178Y cells

Genotoxic and mutagenic studies of teratogens in developing rat and mouse

In this review, genotoxic and mutagenic effects of teratogenic chemical agents in both rat and mouse have been reviewed. Of these chemicals, 97 are drugs and 33 are pesticides or belong to other groups. Large literature searches were conducted to determine the effects of chemicals on chromosome abnormalities, sister chromatid exchanges, and micronucleus formation in experimental animals such as rats and mice. In addition, studies that include unscheduled DNA synthesis, DNA adduct formations, and gene mutations, which help to determine the genotoxicity or mutagenicity of chemicals, have been reviewed. It has been estimated that 46.87% of teratogenic drugs and 48.48% of teratogenic pesticides are positive in all tests. So, all of the teratogens involved in this group have genotoxic and mutagenic effects. On the other hand, 36.45% of the drugs and 21.21% of the pesticides have been found to give negative results in at least one test, with the majority of the tests giving positive results. However, only 4.16% of the drugs and 18.18% of the pesticides were determined to give negative results in the majority of the tests. Among tests with major negative results, 12.50% of the teratogenic drugs and 12.12% of the teratogenic pesticides were negative in all conducted tests.

Alterations in mitochondrial and apoptosis-regulating gene expression in photodynamic therapy-resistant variants of HT29 colon carcinoma cells

Photodynamic therapy (PDT) is a novel cancer therapy inducing irreversible photodamage to tumor tissue via photosensitizer-mediated oxidative cytotoxicity. The cellular and molecular responses associated with PDT are only partially understood. We have reported previously the generation of several photosensitizer-specific PDT-resistant cell variants of HT29 human colon adenocarcinoma cells by selecting cells from sequential PDT treatment using different photosensitizers. In this report, we describe the use of messenger RNA (mRNA) differential display to identify genes that were differentially expressed in the parental HT29 cells compared with their resistant variants. In comparison with parental HT29 cells, mRNA expression was increased in the PDT-resistant cell variants for BNIP3, estrogen receptor-binding fragment-associated gene 9, Myh-1c, cytoplasmic dynein light chain 1, small membrane protein I and differential dependent protein. In contrast, expression in the PDT-resistant variants was downregulated for NNX3, human HepG2 3' region Mbol complementary DNA, glutamate dehydrogenase, hepatoma-derived growth factor and the mitochondrial genes coding for 16S ribosomal RNA (rRNA) and nicotinamide adenine dinucleotide (NADH) dehydrogenase subunit 4. The reduction for mitochondrial 16S rRNA in the PDT-resistant variants was confirmed by Northern blotting, and the elevated expression of the proapoptotic BNIP3 in the PDT-resistant variants was confirmed by Northern and Western blotting analysis. We also examined the expression of some additional apoptosis-regulating genes using Western blotting. We show an increased expression of Bcl-2 and heat shock protein 27 and a downregulation of Bax in the PDT-resistant variants. In addition, the mutant p53 levels in the parental HT29 cells were reduced substantially in the PDT-resistant variants. We suggest that the altered expression in several mitochondrial and apoptosis-regulating genes contributes to PDT resistance.

Photomutagenicity of retinyl palmitate by ultraviolet a irradiation in mouse lymphoma cells

Retinyl palmitate (RP), a storage form of vitamin A, is frequently used as a cosmetic ingredient, with more than 700 RP-containing cosmetic products on the U.S. market in 2004. There are concerns for the possible genotoxicity and carcinogenicity of RP when it is exposed to sunlight. To evaluate the photomutagenicity of RP in cells when exposed to ultraviolet A (UVA) light, L5178Y/Tk+/- mouse lymphoma cells were treated with different doses of RP alone/or in the presence of UVA light. Treatment of the cells with RP alone at the dose range of 25-100 microg/ml did not increase mutant frequencies (MFs) over the negative control, whereas treatment of cells with 1-25 microg/ml RP under UVA light (82.8 mJ/cm2/min for 30 min) produced a dose-dependent mutation induction. The mean induced MF (392 x 10(-6)) for treatment with 25 microg/ml RP under UVA exposure was about threefold higher than that for UVA alone (122 x 10(-6)), a synergistic effect. To elucidate the underlying mechanism of action, we examined the mutants for loss of heterozygosity (LOH) at four microsatellite loci spanning the entire chromosome 11, on which the Tk gene is located. The mutational spectrum for the RP + UVA treatment was significantly different from the negative control, but not significantly different from UVA exposure alone. Ninety four percent of the mutants from RP + UVA treatment lost the Tk+ allele, and 91% of the deleted sequences extended more than 6 cM in chromosome length, indicating clastogenic events affecting a large segment of the chromosome. These results suggest that RP is photomutagenic in combination with UVA exposure in mouse lymphoma cells, with a clastogenic mode-of-action.

Photochemical genotoxicity: principles and test methods. Report of a GUM task force

In recent years, assessing the photogenotoxic potential of a compound became an issue for certain drugs and cosmetical products. Therefore, existing methods performed according to international guidelines (e.g. OECD guidelines) were adapted to the use of concurrent UV-visible (UV-Vis) light irradiation for the assessment of photomutagenicity/photogenotoxicity. In this review, photobiological bases of the processes occurring in the cell after irradiation with UV- and/or visible (vis)-light as well as a compilation of testing methods is presented. Methods comprise cell free investigations on naked DNA and in vitro methods, such as the photo-Ames test, the photo-HPRT/photo-mouse lymphoma assay (MLA), the photo-micronucleus test (MNT), the photo-chromosomal aberration test (CA) and the photo-Comet assay. A compilation of the currently available international literature of compounds tested on photogenotoxicity is given for each method. The state of the art of photogenotoxicity testing as well as the rational for testing are outlined in relation to the recommendations reached in expert working groups at different international meetings and to regulatory guidance papers. Finally, photogenotoxicity testing as predictor of photocarcinogenicity and in the light of risk assessment is discussed.

Squaraine dyes for photodynamic therapy: study of their cytotoxicity and genotoxicity in bacteria and mammalian cells

Halogenated squaraine dyes are characterized by long wavelength absorption (>600 nm) and high triplet yields and therefore represent new types of photosensitizers that could be useful for photodynamic therapy. We have analyzed the cytotoxicity and genotoxicity of the bromo derivative 1, the iodo derivative 2 and the corresponding nonhalogenated dye 3 in the absence and presence of visible light. At concentrations of 1-2 microM, 1 and 2 reduced the cloning efficiency of AS52 Chinese hamster ovary cells to less than 1% under conditions that were well tolerated in the dark. Similarly, the proliferation of L5178Y mouse lymphoma cells was inhibited by photoexcited 1 and 2 with high selectivity. The squaraine 3 was much less efficient. Both 1 and 2 induced only few mutations in the gpt locus of the AS52 cells in the presence of light and were not mutagenic in the dark. No mutagenicity with and without irradiation was observed in Salmonella typhimurium TA100 and TA2638. However, both 1 and 2 plus light increased the frequency of micronuclei in AS52 cells. The results indicate that halogenated squaraines exhibit photobiological properties in vitro that are favorable for photodynamic therapeutical applications.

Oxidative DNA damage and mutations induced by a polar photosensitizer, Ro19-8022

The oxidative DNA damage induced by the polar photosensitizer Ro19-8022 in the presence of light was studied and correlated with the associated mutagenicity. Both in isolated DNA and AS52 Chinese hamster ovary cells, photoexcited Ro19-8022 gave rise to a DNA damage profile that was similar to that caused by singlet oxygen: base modifications sensitive to the repair endonuclease Fpg protein, which according to high-performance liquid chromatography (HPLC) analysis were predominantly 8-hydroxyguanine (8-oxoG) residues, were generated in much higher yield than single-strand breaks, sites of base loss (AP sites) and oxidative pyrimidine modifications sensitive to endonuclease III. Fifty percent of the Fpg-sensitive modifications were repaired within 2 h. Under conditions that induced 10 Fpg-sensitive modifications per 10(6) bp (six 8-oxoG residues per 10(6) bp), approximately 60 mutations per 10(6) cells were induced in the gpt locus of the AS52 cells. A rather similar mutation frequency was observed when a plasmid carrying the gpt gene was exposed to Ro19-8022 plus light under cell-free conditions and subsequently replicated in bacteria. Sequence analysis revealed that GC-->TA and GC-->CG transversions accounted for 90% of the base substitutions. A significant generation of micronuclei was detectable in AS52 cells exposed to the photosensitizer plus light as well.

Mutagenicity of photodynamic therapy as compared to UVC and ionizing radiation in human and murine lymphoblast cell lines

The mutagenicity of photodynamic therapy (PDT) using red light and either Photofrin (porfimer sodium) (PF) or aluminum phthalocyanine (AlPc) as the photosensitizer was determined at the thymidine kinase (TK) locus in the human lymphoblastic cell lines, TK6 and WTK1, and was compared to the mutagenicity of UVC and X-radiation in these cells as well as the mutagenicity of PDT in murine L5178Y lymphoblastic cell lines. Photodynamic therapy was found not to be mutagenic in TK6 cells, which possess an active p53 gene and which are relatively deficient in recombination and repair of DNA double-strand breaks. In contrast, PDT with either sensitizer was significantly mutagenic in WTK1 cells, which harbor an inactivating mutation in the p53 gene and are relatively efficient in recombination and double-strand break repair as compared to TK6 cells. The induced mutant frequency in WTK1 cells with PF as the photosensitizer was similar to that induced by UVC radiation but lower than that induced by X-radiation at equitoxic fluences/doses. The mutant frequency induced by PDT in WTK1 cells with either photosensitizer was much lower than that induced in murine lymphoblasts at equitoxic fluences. The TK6 and WTK1 cells did not differ in their sensitivity to the cytotoxic effects of PDT, but the level of PDT-induced apoptosis was greater in TK6 than in WTK1 cells. These results indicate that the mutagenicity of PDT varies in different types of cells and may be related to the repair capabilities as well as the p53 status of the cells.

Enzymatic recognition and biological effects of photodynamic damage induced in DNA by 1,6-dioxapyrene plus UVA

The specific recognition of DNA modifications by repair endonucleases was used to characterize DNA damage induced by 1,6-dioxapyrene (1,6-DP) in the presence of ultraviolet light at 365 nm (UVA) in the plasmid YEplac181. Under cell free conditions, 1,6-DP plus UVA generated lesions are recognized by the UvrABC endonuclease, the proteins Nth, Nfo and Fpg. The number of UvrABC sensitive sites was at least ten-fold higher than that of Fpg or Nth sensitive sites. Moreover, 1,6-DP plus UVA generated single-strand breaks which are the second most frequent lesions. To investigate the biological effect of DNA damage, YEplac181 DNA was treated with 1,6-DP plus UVA and transformed into Escherichia coli or Saccharomyces cerevisiae. In Escherichia coli, the transformation efficiency of 1,6-DP plus UVA treated DNA was greatly reduced in the uvrA mutant compared to that in the wild-type strain. However, the transforming efficiency was not affected in Fpg-deficient strains. In Saccharomyces cerevisiae, the transformation efficiency of 1,6-DP plus UVA treated YEplac181 was greatly reduced in the rad14::URA3 strain. The photobiological effect of 1,6-DP plus UVA was also analysed in haploid yeast strains of various repair capacities. The results show that the yeast strain defective in the nucleotide excision repair pathway (rad14::URA3) is hypersensitive to 1,6-DP plus UVA treatment as compared to the parental wild-type strain. It is confirmed that the lethal effect of 1,6-DP plus UVA on wild-type yeast is strongly oxygen dependent, whereas the survival of the rad14::URA3 mutant only exhibits a minor oxygen dependence. To conclude, our data show that the photodynamic DNA lesions induced by 1,6-DP plus UVA can be recognized and repaired in pro- and eukaryotic cells by the nucleotide excision repair pathway.

The biology of photodynamic therapy

The subcellular, cellular and tissue/tumour interactions with non-toxic photosensitizing chemicals plus non-thermal visible light (photodynamic therapy (PDT) are reviewed. The extent to which endothelium/vasculature is the primary target is discussed, and the biochemical opportunities for manipulating outcome highlighted. The nature of tumour destruction by PDT lends itself to imaging outcome by MRI and PET.

Cross-resistance to photofrin-mediated photodynamic therapy and UV light and recovery from photodynamic therapy damage in Rif-8A mouse fibrosarcoma cells measured using viral capacity

Photodynamic therapy (PDT) utilizes the localized delivery of light to activate a photosensitizing drug (such as Photofrin) which is selectively retained by the tumour tissues. The intrinsic in vitro sensitivity of tumour cells to PDT is thought to be an important determinant of clinical tumour response to PDT. In this work we show the feasibility of using a viral capacity assay for adenovirus (Ad) DNA synthesis as an indicator of cellular sensitivity to and recovery from Photofrin-mediated PDT. Rif-1 mouse fibrosarcoma cells and a PDT resistant derivative, Rif-8A, as well as Chinese hamster ovary (CHO) cells and CHO-MDR multi-drug resistant mutant cells were studied. Consistent with the clonogenic survival of these cells, the capacity of PDT-treated cells for Ad DNA synthesis was greater for Rif-8A compared to Rif-1 cells and for CHO-MDR compared to CHO-N cells. Delaying infection of the Rif cells from immediately after, to 6 hours after PDT, resulted in an increased capacity for Ad DNA synthesis, which was greater for Rif-8A compared to Rif-1 cells, suggesting that the increased resistance of Rif-8A cells to PDT results from an elevated recovery and/or repair of PDT damage. The capacity of UV-irradiated cells for Ad DNA synthesis was also greater for Rif-8A compared to Rif-1 cells indicating a cross-resistance of Rif-8A cells to UV. These results suggest some overlap in the types of cellular damage induced by UV and PDT and/or overlap in the pathways for the repair of UV and PDT damage in Rif cells.

Photodynamic therapy in neurosurgery: a review

Photodynamic therapy (PDT) has been investigated extensively, both experimentally and clinically, as an adjunctive treatment in the neuro-oncological field. It is based on the more selective accumulation of a photosensitizer in malignant than normal tissue with low systemic toxicity. Subsequent light activation induces photo-oxidation, followed by selective tumour destruction via vascular and direct cellular mechanisms. Malignant brain tumours carry a lethal prognosis with a median survival of 15 months despite surgery, radiotherapy and chemotherapy. PDT is therefore a logical therapeutic concept for brain tumours infiltrating into normal brain. In this review, all the available data on patients treated with haematoporphyrin derivative-mediated PDT are critically analysed. Over 310 patients have been reported in the literature suffering from primary or recurrent malignant brain tumours which were treated with PDT following tumour resection in open clinical phase I/II trials. This number includes 58 patients treated at our own institution. Variations in the treatment protocols make evaluation scientifically difficult; however, there is a clear trend of increased median survival after surgical resection and one single photodynamic treatment. PDT is generally well tolerated and side effects consist of moderate increased intracranial pressure and prolonged skin sensitivity to direct sunlight. The current available data indicate that PDT is a safe treatment, which is well tolerated by the patients and yields an improvement in survival of those with malignant brain tumours. Conclusive information can be expected from controlled clinical trials which are currently being designed. The results raise the hope that PDT will be a valuable addition to the armamentarium for the treatment of cerebral malignancies.

Primary DNA damage, HPRT mutation and cell inactivation photoinduced with various sensitizers in V79 cells

DNA strand breaks and hypoxanthine guanine phosphoribosyl transferase (HPRT) mutants were measured in parallel in photochemically treated (PCT) cells and compared at the same level of cell survival. Chinese hamster fibroblasts (V79 cells) were either incubated with the lipophilic dyes tetra(3-hydroxyphenyl)porphyrin (3THPP) and Photofrin II (PII), the anionic dye meso-tetra(4-sulfonatophenyl)porphine (TPPS4) or the cationic dye meso-tetra(N-methyl-4-pyridyl)porphine (p-TMPyPH2) before light exposure. In the cells, the lipophilic dyes were localized in membranes, including the nuclear membrane, while the hydrophilic dyes were taken up primarily into spots in the cytoplasm. In addition, the hydrophilic TPPS4 was distributed homogeneously throughout the whole cytoplasm and nucleoplasm. According to the HPRT mutation test, the mutagenicity of light doses survived by 10% of the cells was a factor of six higher in the presence of 3THPP than of PII, whereas for X-rays it was a factor of three higher than for PCT with 3THPP. Light exposure in the presence of the hydrophilic dyes TPPS4 and p-TMPyPH2 was not significantly mutagenic. There was no correlation between the induced rates of HPRT mutants and of DNA strand breaks. Thus, TPPS4 was the most efficient sensitizer with regard to DNA strand breaks when compared at the same level of cell survival, followed by 3THPP, PII and p-TMPyPH2. Hence, the rate of DNA strand breaks cannot be used to predict the mutagenicity of PCT.

Large mutagenic lesions are induced by photodynamic therapy in murine L5178Y lymphoblasts

Mutagenic lesions at the thymidine kinase locus (tk) in mouse lymphoma L5178Y (LY) cells treated with red light and either Photofrin (PF) or chloroaluminum phthalocyanine (AlPc) as the photosensitizer were compared in the relatively photodynamic therapy (PDT)-sensitive strain LY-R16 and the relatively resistant strains LY-S1 and LY-SR1. Southern blot analysis revealed that 92% (36/39) of the PDT-induced thymidine kinase (TK-/-) mutants of strains LY-R16 and LY-SR1 lost the entire active tk allele. (Strain LY-S1 lacks a known tk polymorphism and has not been analyzed for loss of the active tk allele.) A decrease in galactokinase (GK) activity in the TK-/- mutants has been taken as an indication that the mutagenic lesion extends from the tk gene to the closely linked galactokinase gene (gk). Using PF as the photosensitizer, GK activity was decreased in 45% of the LY-R16 mutants and in 22% of the LY-S1 and LY-SR1 mutants. With photoactivated AlPc, 59% of the TK-/- mutants of strains LY-S1 and LY-SR1 showed GK inactivation. (LY-R16 mutants were not analyzed because of the low LY-R16 mutant frequency induced by PDT with AlPc) Thus, many of the TK-/- mutants of LY cells induced by PDT with either PF or A1Pc harbor multilocus lesions.

DNA damage induced by photosensitizers in cellular and cell-free systems

The specific recognition of DNA modifications by repair endonucleases was used to characterize the DNA damage induced by photosensitizers in the presence of visible light. Under cell-free conditions, chemically unrelated photosensitizers (methylene blue, acridine orange, proflavin, riboflavin, hematoporphyrin) induce the same type of DNA damage. It is characterized by a high number of base modifications sensitive to the repair endonuclease FPG protein (formamidopyrimidine-DNA glycosylase), while both the number of DNA strand breaks and the number of sites of base loss (sensitive to exonuclease III or endonuclease IV) is low. Therefore the damage is markedly different from that induced by hydroxyl radicals. Mechanistically, the generation of the base modifications sensitive to FPG protein involves singlet oxygen in some, but possibly not all cases, as substituting D2O for H2O increases the reaction yield six-fold in the case of methylene blue, but only 1.4-fold in the case of acridine orange. In plasmids from Salmonella typhimurium strains treated with methylene blue or acridine orange plus light and from Escherichia coli strains treated with acridine orange or proflavin plus light, the same type of damage was observed as under cell-free conditions. In L1210 mouse leukemia cells exposed to acridine orange plus light, the numbers of modifications sensitive to FPG protein and exonuclease III were quantified, in addition to strand breaks, by a modified alkaline elution assay. Again, the number of base modifications sensitive to FPG protein was found to be several-fold higher than the number of strand breaks and sites of base loss. It has to be concluded that the DNA damage in the intact cells is not mediated by hydroxyl radicals or cellular nucleases, but by the same mechanism as operates under cell-free conditions with these agents.

Protection by the fluoride ion against phthalocyanine-induced photodynamic killing of Chinese hamster cells

When a dilute F- solution was added to a culture of Chinese hamster cells that had been preincubated with an aluminium phthalocyanine sensitizer derived from AlPcCl, the photosensitivity of the cells was markedly reduced compared to control cells not treated with F-. Under the same treatment conditions, the reduction in [3H]thymidine incorporation into cellular DNA caused by light and this sensitizer and the production of DNA-protein crosslinks caused by light and this sensitizer were also inhibited by F-. In contrast, the killing of Chinese hamster cells, the reduction of thymidine incorporation by the cells, and the production of DNA-protein crosslinks in the cells caused by the combination of light and either Photofrin II or the silicon phthalocyanine HOSiPcOSi(CH3)2(CH2)3-N(CH3)2 were not inhibited by F-. We conclude that the aluminium phthalocyanine sensitizer used is largely or completely AlPc(OH)(H2O), that it is converted to a fluoro complex by F-, and that this compound probably is a less efficient generator of photochemical damage at a critical cellular target(s) than is AlPc(OH)(H2O). The inhibition of thymidine incorporation and DNA-protein crosslink formation indicates that the effects of F- can be expressed at intracellular sites. It is further concluded that the silicon phthalocyanine sensitizer and Photofrin II do not interact significantly with F-.