Cross-link formation of phage lambda DNA in situ photochemically induced by the furocoumarin derivative angelicin

Thio and Seleno Derivatives of Angelicin as Efficient Triplet Harvesting Photosensitizers: Implications in Photodynamic Therapy

Photodynamic therapy (PDT) is widely accepted in medical practice for its targeted induction of apoptosis in cancerous cells. Angelicin (Ang) has traditionally been known for its efficacy in cancer treatment and its capability to enter a photoexcited triplet state. This study has comprehensively assessed the effects of substituting individual chalcogen atoms at three specific positions in Angelicin, with the objective of facilitating access to this elusive triplet state to enhance its role as a photosensitizer in PDT. The study scrutinizes various enhancements and factors that are crucial for efficient triplet harvesting. The decrease in singlet-triplet energy gap (ΔEST) and increased spin-orbit coupling (SOC) values present numerous viable pathways for intersystem crossing (ISC), leading to the triplet manifold. The lifetime of ISC, thus, decreases from 10-5 s-1 in Ang to 10-8 s-1 in thioangelicin (TAng) and finally to 10-9 s-1 in selenoangelicin (SeAng). Additionally, this study investigates the two-photon absorption properties of thio and seleno-substituted Angelicin for their potentialities as non-UV photosensitizers. The interplay between electron-withdrawing and electron-donating substitutions in these derivatives significantly enhances the two-photon absorption cross-sections (σ) to as high as 49.3 GM while shifting the absorption wavelengths towards the infrared region enabling them as efficient PDT photosensitizers.

Cho Endonuclease Functions during DNA Interstrand Cross-Link Repair in Escherichia coli

DNA interstrand cross-links are complex lesions that covalently link both strands of the duplex DNA. Lesion removal is proposed to be initiated via the UvrABC nucleotide excision repair complex; however, less is known about the subsequent steps of this complex repair pathway. In this study, we characterized the contribution of nucleotide excision repair mutants to survival in the presence of psoralen-induced damage. Unexpectedly, we observed that the nucleotide excision repair mutants exhibit differential sensitivity to psoralen-induced damage, with uvrC mutants being less sensitive than either uvrA or uvrB We show that Cho, an alternative endonuclease, acts with UvrAB and is responsible for the reduced hypersensitivity of uvrC mutants. We find that Cho's contribution to survival correlates with the presence of DNA interstrand cross-links, rather than monoadducts, and operates at a step after, or independently from, the initial incision during the global repair of psoralen DNA adducts from the genome.

IMPORTANCE

DNA interstrand cross-links are complex lesions that covalently bind to both strands of the duplex DNA and whose mechanism of repair remains poorly understood. In this study, we show that Cho, an alternative endonuclease, acts with UvrAB and participates in the repair of DNA interstrand cross-links formed in the presence of photoactivated psoralens. Cho's contribution to survival correlates with the presence of DNA interstrand cross-links and operates at a step after, or independently from, the initial incision during the repair process.

Synthesis, reactions and biological activities of furochromones: a review

Furochromone derivatives are important synthetic targets which showed a myriad of interesting biological activities. Ammi visnaga (Umbelliferae) is the most famous source of these derivatives, which has been used in folk medicine for millennia targeting different ailments. Since the isolation of furochromone derivatives, different synthetic methodologies were developed for their preparation. Despite the recent interesting findings on this class of compounds, the chemical literatures lack a comprehensive summary on the synthetic methodologies and biological activities of furochromone derivatives. This review highlights recent advances in furochromones chemistry by discussing different synthetic procedures developed for the preparation of naturally occurring derivatives as well as other unique derivatives which showed promising biological activities. It also sheds light on the most common reactions of furochromone derivatives and the utilization of these derivatives as the blocks for many biologically active compounds.

Quantification and repair of psoralen-induced interstrand crosslinks in human cells

Bi-functional alkylating agents that cause crosslinks are commonly used in chemotherapy. However, there is no conclusive knowledge for human cells regarding the number of induced interstrand crosslinks (ICLs) and the unhooking rate when the lesion is removed from one of the DNA strand. Using a newly developed method, we quantified the number of induced ICLs for the five furocoumarins; psoralen, 5-methoxypsoralen, 8-methoxypsoralen, tri-methoxypsoralen and angelicin. In quantitative terms, the results were in agreement with the values found by others. In kinetic studies using mammalian cells, we found that half of the psoralen-induced ICLs were unhooked within 2.5h. The rate in normal human diploid fibroblasts was found to be 20,000 ICLs/h/cell. In comparison to survival, 2500 ICLs per cell led to 50% toxicity, indicating that the unhooking of the ICLs is not the crucial step for ICL tolerance. Surprisingly, only 3500 ICLs per cell corresponded to a significant delay in the replication fork elongation. The results indicate involvements of additional pathway(s) for the delay since the effect on replication elongation could be monitored when only 10% of the replication forks encounter an ICL.

Synthesis of new visnagen and khellin furochromone pyrimidine derivatives and their anti-inflammatory and analgesic activity

6-[(4-Methoxy/4,9-dimethoxy)-7-methylfurochromen-5-ylideneamino]-2-thioxo-2,3-dihydropyrimidin-4-ones 1a,b were prepared by reaction of 6-amino-2-thiouracil with visnagen or khellin, respectively. Reaction of 1a,b with methyl iodide afforded furochromenylideneaminomethylsulfanylpyrimidin-4-ones 2a,b. Compounds 2a,b were reacted with secondary aliphatic amines to give the corresponding furochromen-ylideneamino-2-substituted pyrimidin-4-ones 3a-d. Reaction of 3a-d with phosphorus oxychloride yielded 6-chlorofurochromenylidenepyrimidinamines 4a-d, which were reacted with secondary amines to afford furochromenylideneamino-2,6-disubstituted pyrimidin-4-ones 5a-d. In addition, reaction of 5a-d with 3-chloropentane-2,4-dione gave 3-chloro-furochromenylpyrimidopyrimidines 6a-d. The latter were reacted with piperazine and morpholine to give 1-(furochromenyl)-pyrimidopyrimidine-3,6,8-triylpiperazines or-3,6,8-triylmorpholines 7a-d. The chemical structures of the newly synthesized compound ware characterized by IR, ¹H-NMR, ¹³C-NMR and mass spectral analysis. These compounds were also screened for their analgesic and anti-inflammatory activities. Some of them, particularly 3-7, exhibited promising activities.

Quantitative determination of psoralen and angelicin from some medicinal herbs by high performance liquid chromatography

A reversed-phase high performance liquid chromatographic method was developed to determine the contents of psoralen and angelicin from some medicinal herbs. The optimum eluent for chromatography was 20 v/v% acetonitrile in water on a Zorbax 300SB C18 column. The identification was carried out by comparing the retention time and mass spectra of the relevant peaks with their standards. The variation of the concentration of psoralen and angelicin was wide between different species. The seeds of Psoralea corylifolia showed the highest contents of psoralen (7.8 mg/g) and angelicin (2.3 mg/g) among the tested herbs.

Decreased survival of UV-irradiated Staphylococcus aureus in the presence of 8-methoxypsoralen in the post-irradiation plating medium

For Staphylococcus aureus, the presence of 8-methoxypsoralen (8-MOP) in the post-irradiation plating medium increased the lethal effect of far-UV light (FUV; approximately 254 nm) and of 8-MOP plus near-UV light (8-MOP+NUV; approximately 365 nm), an effect similar to that caused by acriflavine which inhibits DNA repair. In the repair-proficient strain, the presence of 8-MOP in the plating medium was almost as effective in inhibiting the repair of damage caused by FUV as that caused by 8-MOP photoadditions. Survival data obtained with Rec(-)-like and Uvr(-)-like strains suggest that 8-MOP in the plating medium, although possibly inhibiting recombination repair, was much more effective in inhibiting excision repair of FUV damage. Regarding 8-MOP+NUV treatment, 8-MOP in the plating medium had a lesser effect in the repair-deficient strains, differing from that observed after FUV treatment, which is consistent with the notion that different types of damage are caused by the two treatments.

Interstrand cross-links induce DNA synthesis in damaged and undamaged plasmids in mammalian cell extracts

Mammalian cell extracts have been shown to carry out damage-specific DNA repair synthesis induced by a variety of lesions, including those created by UV and cisplatin. Here, we show that a single psoralen interstrand cross-link induces DNA synthesis in both the damaged plasmid and a second homologous unmodified plasmid coincubated in the extract. The presence of the second plasmid strongly stimulates repair synthesis in the cross-linked plasmid. Heterologous DNAs also stimulate repair synthesis to variable extents. Psoralen monoadducts and double-strand breaks do not induce repair synthesis in the unmodified plasmid, indicating that such incorporation is specific to interstrand cross-links. This induced repair synthesis is consistent with previous evidence indicating a recombinational mode of repair for interstrand cross-links. DNA synthesis is compromised in extracts from mutants (deficient in ERCC1, XPF, XRCC2, and XRCC3) which are all sensitive to DNA cross-linking agents but is normal in extracts from mutants (XP-A, XP-C, and XP-G) which are much less sensitive. Extracts from Fanconi anemia cells exhibit an intermediate to wild-type level of activity dependent upon the complementation group. The DNA synthesis deficit in ERCC1- and XPF-deficient extracts is restored by addition of purified ERCC1-XPF heterodimer. This system provides a biochemical assay for investigating mechanisms of interstrand cross-link repair and should also facilitate the identification and functional characterization of cellular proteins involved in repair of these lesions.

Transformation of Escherichia coli cells by pH 2.3 plasmid DNA treated with psoralens plus near-UV light

The effect of two psoralens, 8-methoxypsoralen (8MOP) and angelicin (ANG), plus near-UV (PUVA) on the transformation capacity of pH 2.3 plasmid DNA on Escherichia coli was studied. Under identical experimental conditions the 8MOP linking to plasmid DNA drastically decreased its transformation capacity compared with the ANG linking. In the case of 8MOP, the decrease depends on the UV dose, as well as on the molar ratios of psoralen and DNA nucleotides. When the effect of short-wavelength UV (UVB) was tested, the higher the molar ratios, the more the combined effects of PUVA and UVB were negative.

Photosensitized cleavage and cross-linking of pBR322 DNA with khellin and visnagin

The naturally occurring furanochromones khellin and visnagin have received considerable attention, largely because of their vasodilatory properties and of their ability (particularly that of khellin) to induce skin pigmentation upon ultraviolet light treatment of patients suffering from vitiligo. There are conflicting statements in the literature on whether or not they are capable of cross-linking DNA photochemically. Supercoiled and linear pBR322 DNA was used to probe this reaction. The results showed that both khellin and, to a greater extent, visnagin photosensitized DNA cross-linking. In addition, both photosensitizers induced extensive DNA cleavage.

Light-activated plant defence

Sunlight provides the energy required for all biochemical, physiological and developmental processes necessary for plant growth, reproduction and survival. The role of light in photosynthesis and photomorphogenesis has been appreciated for some time; however, the role of light in plant defence is a comparatively recent realization. Between 75-100 photosensitizers or phototoxins, molecules that become toxic in the presence of light, have been extracted from higher plant tissues. These biologically-active compounds have diverse biosynthetic origins and belong to at least 15 different phytochemical classes (i.e. acetophenones, acetylenes, benzophenanthrenes, β-carbolines, coumarins, extended quinones, furanochromones, furanocoumarins, furanoquinolines, isoquinolines, lignans, pterocarpans, quinolines, sesquiterpenes and thiophenes). Of more than 100 angiosperm families assayed, phototoxins and/or phototoxic activity have been reported in c. 40 families representing 32 orders and 8 subclasses of the Magnoliophyta. Most of these allelochemicals are acute toxins with little organism-specificity. As such, they are effective biocides capable of killing a wide-range of potentially harmful organisms including: viruses, pathogenic bacteria and fungi, nematodes and herbivorous insects, as well as competing plant species. This review focuses on the phytochemistry, taxonomic occurrence and toxicological consequences of phototoxic metabolites in flowering plants. The available information suggests that phototoxic phytochemicals: (i) are broad-spectrum allelochemicals capable of protecting plants against a variety of detrimental organisms in nature, (ii) represent a successful defensive strategy in both primitive and advanced plant taxa, and (iii) may be an effective defence under a variety of photoenvironmental conditions. CONTENTS Summary 401 I. Introduction 401 II. Chemistry/biochemistry of plant photosensitizers 402 III. Botanical distribution of photosensitizers 403 IV. Toxicology 405 V. Biological activity/defensive role of photosensitizers 408 VI. Concluding remarks 413 References 415.

Phage nucleoprotein-psoralen interaction: quantitative characterization of dark and photoreactions

The irradiation of the phage T7 system containing psoralen as photosensitizer causes many processes, each of them leading to phage inactivation. These processes include the UV-induced photoreactions in the phage nucleic acid, and photoreactions in the nucleic acid sensitized by either psoralen or psoralen photobreakdown products. In addition the intercalation of the psoralen molecule itself in the phage nucleic acid as well as the psoralen photobreakdown products cause phage inactivation. Under appropriate experimental conditions these reactions can be studied and characterized separately. The quantitative characteristics (e.g. inactivation cross-section, action spectra and index for dark genotoxicity) are demonstrated for different linear and angular psoralens. Some theoretical and practical consequences of the results obtained are discussed.

Angelicins, angular analogs of psoralens: chemistry, photochemical, photobiological and phototherapeutic properties

Angelicin and some of its derivatives are naturally occuring compounds which show interesting photobiological properties. In this review various aspects of angelicin and its derivatives have been reported. The natural occurrence and the chemical synthesis both of naturally occurring and synthetic angelicins have been reviewed. Photochemical and photophysical properties of angelicins have been considered with particular reference to the capacity to generate active forms of oxygen, photoreactions with nucleic acids, proteins and unsaturated fatty acids. Photobiological effects have been considered: skin phototoxicity, antiproliferative effects, genotoxicity, ability to induce hemolysis in erythrocytes, inactivation of prokaryotic and eukaryotic microorganism and of viruses. The ability of some angelicins to induce photocarcinogenesis has been reviewed as well as in the activity as photochemotherapeutic agents.

Therapeutic potential of plant photosensitizers

Many bioactive phytochemicals have been shown in recent years to be photosensitizers, i.e. their toxic activities against viruses, micro-organisms, insects or cells are dependent on or are augmented by light of certain wavelengths. These activities are often selective, and this has led to the concept of therapeutic prospects in the control of infectious diseases, pests and cancer. Reaction mechanisms commonly involve singlet oxygen and radicals, which are thought to cause photodamage to membranes or macromolecules. The main classes of plant photosensitizers reviewed here are polyyines (acetylenes, thiophenes and related compounds); furanyl compounds; beta-carbolines and other alkaloids; and complex quinones. We propose that within each group of phytochemicals there are several representatives that merit further study for therapeutic abilities in appropriate animal models.

Action spectra for photoinduced inactivation of bacteriophage T7 sensitized by 8-methoxypsoralen and angelicin

The action spectrum (240-300 nm) for photoinactivation of unsensitized phage T7 and the action spectra (310-380 nm) for photoinactivation of phage T7 sensitized with 8-methoxypsoralen (8-MOP) and angelicin were measured by an automated method. For unsensitized phage T7 the action spectrum is in good agreement with the absorption spectrum. For sensitization with angelicin the action spectrum is similar to the absorption spectrum, but for sensitization with 8-MOP the spectra are different. The agreement between the T7 absorption and action spectra in the far-UV region is due to photodamage of DNA, leading to phage inactivation. The similarity in the action and absorption spectra in the near-UV region for sensitization with angelicin seems to be in accordance with the monofunctional photobinding of angelicin to DNA. The action spectrum for sensitization with 8-MOP has a maximum at about 320 nm and this suggests that, in addition to the monoadducts, the biadducts play a role in the inactivation of phage T7. Taking the number of bound furocoumarin molecules into consideration, the quantum efficiencies were estimated. Furocoumarin increases the quantum efficiency in the near-UV region and the values are similar to those obtained in far-UV light without psoralens.

Two DNA endonuclease activities from normal human and xeroderma pigmentosum chromatin active on psoralen plus ultraviolet light treated DNA

DNA endonuclease activities from the chromatin of normal human and xeroderma pigmentosum, complementation group A (XPA), lymphoblastoid cells were examined on DNA treated with 8-methoxypsoralen (8-MOP) or 4,5',8-trimethylpsoralen (TMP) plus long wavelength ultraviolet (UVA) light, which produce monoadducts and DNA interstrand cross-links, and angelicin plus UVA light, which produces mainly monoadducts. 9 chromatin-associated DNA endonuclease activities were isolated from normal and XPA cells and assayed for activity on PM2 bacteriophage DNA that had been treated with 8-MOP or TMP in the dark and then exposed to UVA light. Unbound psoralen was removed by dialysis and a second dose of UVA light was given. Cross-linking of DNA molecules was confirmed by alkaline gel electrophoresis. In both normal and XPA cells, two DNA endonuclease activities were found which were active on 8-MOP and TMP plus UVA light treated DNA. One of these endonuclease activities, pI 4.6, is also active on intercalated DNA and a second one, pI 7.6, is also active on UVC (254 nm) light irradiated DNA. The major activity against angelicin plus UVA light treated DNA in both normal and XPA cells was found in the fraction, pI 7.6. The levels of activity of both of these fractions on all 3 psoralen-damaged DNAs were similar between normal and XPA cells. These results indicate that in both normal and XPA cells there are at least two different DNA endonucleases which act on both 8-MOP and TMP plus UVA light treated DNA.

Effects of recB, recF and uvrA mutations on Weigle reactivation of lambda phages in Escherichia coli K12 treated with 8-methoxypsoralen or angelicin and 365-nm light

The extent of Weigle reactivation (W-R) of lambda c+ phages treated with bifunctional 8-methoxypsoralen and 365-nm light (8-MOP + UVA) and with monofunctional angelicin and 365-nm light (ANG + UVA) were compared in Escherichia coli strains with different excision repair and recombinational capacities. In uvrA6 host cells, irradiation of the cells with 254-nm radiation only decreased the survival of phages treated with 8-MOP + UVA. The extent of W-R of ANG + UVA-treated phages in uvrA6 cells, however, was much larger than that obtained in other host cells. These results indicate that monoadducts produced by ANG + UVA treatment can be repaired effectively by the repair induced without uvrA gene products, but lesions produced by 8-MOP + UVA treatment cannot be repaired by the repair. The small W-R of ANG + UVA-treated phages in wild-type cells may be due to the high repairability of the lesions by constitutive excision repair in the cells. recB21 reduced only a little of the W-R of 8-MOP + UVA- or ANG + UVA-treated phages obtained in wild-type cells. Although recF143 cells have an almost comparable host-cell repair capacity of 8-MOP + UVA- or ANG + UVA-treated phages to that of the wild-type cells, recF143 mutation reduced not only the extent of W-R of 8-MOP + UVA-treated phages to 17% of that obtained in wild-type cells but also the extent of W-R of ANG + UVA-treated phages to 12% of that obtained in uvrA6 cells.

Repair of interstrand cross-links in DNA of Saccharomyces cerevisiae requires two systems for DNA repair: the RAD3 system and the RAD51 system

We have studied the role of the excision-repair system and the recombination-repair system in the removal of cross-links and monoadducts caused by furocoumarins plus 360 nm radiation in yeast DNA by neutral and alkaline sucrose gradients and by a fluorometric procedure which detects cross-linked DNA molecules. We found that the excision-repair system, represented by the rad3 mutations, is required both for the removal of monoadducts, causing single-strand break formation, and for the removal of cross-links, causing double-strand break formation. The recombination-repair system, represented by the rad51 mutation, is necessary for double-strand break repair following cross-link removal, but it has no role in the repair of monoadducts. It can be concluded, that at least some of the same enzymes are used in yeast for both the excision of pyrimidine dimers and the excision of cross-links or monoadducts caused by furocoumarins plus light. The RAD3 and RAD51 repair systems, which act independently in the repair of UV-induced lesions, are part of a single system for the repair of cross-links.

Interaction of bacteriophage O2 with strains of the genus Oerskovia

Bacteriophage O2 multiplies normally on Oerskovia turbata IMET 47 153. It has a burst size of about 100 p.f.u. per infected cell and a latent period of 100 min at 30 degrees C. On Oerskovia xanthineolytica IMET 47 383 clear spots were formed after addition of high phage concentrations onto agar top layers. By phase contrast observation, and measurement of the optical density of infected cultures, it was found that the clearing effect on strain IMET 47 383 was due to lysis-from-without. Phage O2 adsorbs and injects its DNA into cells of strain IMET 47 383 but phage multiplication does not occur, and the phage DNA becomes degraded. Inhibition of phage DNA injection by the combined action of xanthotoxin -- u.v. irradiation abolished the clearing activity of phage lysates. Therefore, both adsorption and DNA injection seem to be prerequisites for the release of a lytic activity out of the phage particle, which is responsible for the clearing effect on strain IMET 47 383.