DNA Photobinding Research Articles

Ruthenium(ii) arene complexes showing DNA photobinding: the role of the basicity of the monodentate ligand

With a decrease in the basicity of the monodentate ligand X, the ligand photodissociation efficiencies of the complexes increase gradually.

A novel azopyridine-based Ru(II) complex with GSH-responsive DNA photobinding ability.

A novel azopyridine-based Ru(II) complex [Ru(bpy)2(L1)2](2+) (bpy = 2,2'-bipyridine, L1 = 4,4'-azopyridine) was designed and synthesized as a potential glutathione (GSH)-responsive photoactivated chemotherapy (PACT) agent, the DNA covalent binding capability of which can only be activated after GSH reduction and visible light irradiation.

A new, bioactive structural motif: Visible light induced DNA photobinding and oxygen independent photocleavage by RuII, RhIII bimetallics

The Ru,Rh bimetallic complexes, [(bpy)2Ru(dpp)RhCl2(phen)]3+ and [(bpy)2Ru(bpm)RhCl2(phen)]3+ (bpy=2,2′-bipyridine, dpp=2,3-bis(2-pyridyl)pyrazine, phen=1,10-phenanthroline, and bpm=2,2′-bipyrimidine), couple one ruthenium polyazine light absorber to a cis-RhIIICl2 center through a dpp or bpm bridging ligand in contrast to the previously studied Ru,Rh,Ru trimetallics. This motif provides a sterically accessible Rh reactive site. These bimetallics are efficient visible light absorbers possessing many advantages compared to the previously reported trimetallics: lower cationic charges, reduced stereoisomerization, and independent variation of terminal ligands at each metal center to modulate properties. The bimetallic systems display efficient visible light induced bioreactivities with DNA. In addition to the known DNA photocleavage in related Ru,Rh,Ru trimetallics, these Ru,Rh bimetallic systems display visible light induced DNA binding. Low lying triplet metal to metal charge transfer (3MMCT) excited states provide oxygen independent photoreactivity. This previously unexplored structural motif for DNA modification holds promises in photodynamic therapy and DNA modification schemes.

Metal to ligand charge transfer induced DNA photobinding in a Ru(ii)–Pt(ii) supramolecule using red light in the therapeutic window: a new mechanism for DNA modification

The Ru(II)-Pt(II) supramolecular complex, [(Ph(2)phen)(2)Ru(dpp)PtCl(2)](2+), displays a new mechanism for DNA modification: photobinding through a (3)MLCT excited state. Gel shift analysis, selective DNA precipitation, and DNA melting point experiments support efficient covalent DNA binding following visible light excitation.

A new Os,Rh bimetallic with O2 independent DNA cleavage and DNA photobinding with red therapeutic light excitation

Many Ru and Os systems display photoactive (3)MLCT states. Systems activated by therapeutic window light in the absence of O(2) remain elusive. [(bpy)(2)Os(dpp)RhCl(2)(phen)](3+) photobinds and photocleaves DNA under red light in an oxygen independent manner, due to molecular design involving one Os chromophore coupled to a photoactive cis-Rh(III)Cl(2) moiety.

A method for genome-wide analysis of DNA helical tension by means of psoralen–DNA photobinding

The helical tension of chromosomal DNA is one of the epigenetic landmarks most difficult to examine experimentally. The occurrence of DNA crosslinks mediated by psoralen photobinding (PB) stands as the only suitable probe for assessing this problem. PB is affected by chromatin structure when is done to saturation; but it is mainly determined by DNA helical tension when it is done to very low hit conditions. Hence, we developed a method for genome-wide analysis of DNA helical tension based on PB. We adjusted in vitro PB conditions that discern DNA helical tension and applied them to Saccharomyces cerevisiae cells. We selected the in vivo cross-linked DNA sequences and identified them on DNA arrays. The entire procedure was robust. Comparison of PB obtained in vivo with that obtained in vitro with naked DNA revealed that numerous chromosomal regions had deviated PB values. Similar analyses in yeast topoisomerase mutants uncovered further PB alterations across specific chromosomal domains. These results suggest that distinct chromosome compartments might confine different levels of DNA helical tension in yeast. Genome-wide analysis of psoralen–DNA PB can be, therefore, a useful approach to uncover a trait of the chromosome architecture not amenable to other techniques.

ChemInform Abstract: Difurocoumarins, Psoralen Analogues: Synthesis and DNA Photobinding.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Difurocoumarins, Psoralen Analogs: Synthesis and DNA Photobinding

A new tetracyclic derivative, difurocoumarin, was synthesized and studied in order to ascertain its possible use as a photochemotherapeutic agent alternative to psoralens. The compound proved able to photobind monofunctionally to DNA on irradiation with UV-A. A photocycloadduct with thymine was isolated and characterized spectroscopically.

Molecular mechanics and dynamics study of DNA-furocoumarins complexes: Effect of methylation of the angular derivatives on the intercalation geometry

Results of molecular mechanics calculations on intercalation complexes between DNA and angelicin derivatives: angelicin, 4′-methylangelicin, 5′-methylangllicin, 4,4′-dimethylangelicin, 4,5′-dimethylangelicin, 4,6,4′-trimethylangelicin and 4,6,5′-trimethylangelicin, are presented. The correlation between the presence of methyl groups and an increase in DNA photobinding affinity is discussed on the basis of the molecular structures. The influence of the orientation of the angelicins within the intercalation cavity is also discussed. Finally, the consequences of the dynamical behaviour of angelicin in the intercalation cite are studied.

Benzoangelicins: New monofunctional DNA photobinding agents

4,6-Dimethylbenzoangelicin, obtained by fusing a benzene ring at the furan side of 4,6-dimethylangelicin, was studied in terms of crystal structure and interactions with DNA in both ground and excited states. 4,6-Dimethylbenzoangelicin has a planar structure and forms a molecular complex with DNA, undergoing intercalation inside the double helix. Under UVA irradiation, it photoconjugates covalently with the macromolecule, showing a DNA photobinding rate slightly lower than that of 8-methoxypsoralen, involving however only its 3,4 double bond, i.e. behaving as a pure monofunctional agent. The parameters of dark binding and photobinding were determined, and two C 4 cycloadducts with thymine were isolated and characterized.

Synergism between aflatoxins in covalent binding to DNA and in mutagenesis in the photoactivation system

Aflatoxins (AFs) produce singlet oxygen upon their exposure to UV (365-nm) light. Singlet oxygen in turn activates them to mutagens and DNA-binding species. DNA binding and mutagenesis by AFs were enhanced in D 2O as compared to reactions in H 2O, and a singlet oxygen scavenger inhibited mutagenesis. DNA photobinding of 3H-AFB 1 increased in the presence of unlabeled AFB 2, and the addition of AFB 2 enhanced mutagenesis by AFB 1 in a synergistic manner. These results are compatible with the notion that singlet oxygen, formed by one aflatoxin molecule, can readily activate another aflation molecule. This may bear an environmental implication in that the weakly carcinogenic AFB 2, which is often produced in nature together with AFB 1, may be important in enhancing the activation of AFB 1 by sunlight.

Photosensitization of DNA of defined sequence by furochromones, khellin and visnagin

The sequence specificity in the in vitro DNA photobinding of khellin and visnagin, two naturally occurring furochromones proposed for chemotherapy of vitiligo, was investigated by using DNA sequencing methodology. The 3′–5′ exonuclease associated with the T4 DNA polymerase served as a tool for determining photoadducts distribution on DNA fragments of the lac I gene of Escherihia coli. The photoadduct distribution of psoralen is also studied for comparison. Upon UVA irradiation, visnagin mainly forms monoadducts with thymine and to a lower extent with cytosine. Alternating (A—T) n sequences are hot spots for visnagin photoaddition. This is a property shared with furocoumarins. TTT sites are also quite reactive to visnagin, as they are to methylated angelicins. In contrast, with psoralen derivatives, there is no preferential photobinding in 5′-TpA sites, and 5′-ApT sites react as well. Furthermore, many sites such as T in the GC context, and C in any context, react, although weakly. The visnagin photoadduct distribution resembles very much the photoadduct distribution of methylated angelicins as described by Miolo et al. The photoreaction of these two series of compounds is less sequence dependent than the photobinding of psoralen derivatives as described by Sage and Moustacchi and by Boyer et al. The sequence specificity in khellin-DNA photobinding is the same as for visnagin, even though it forms much fewer photoadducts. The absence of photo-oxidation of DNA after treatment with visnagin or khellin plus UVA suggests that furochromones do not present any photodynamic effect on DNA.

Photobiological effects in Saccharomyces cerevisiae induced by the monofunctional furocoumarin 4,4′,6-trimethylangelicin (TMA) and the bifunctional furocoumarin 8-methoxypsoralen (8-MOP)

Recently, the monofunctional furocoumarin 4,4′,6-trimethylangelicin (TMA) has been proposed for photochemotherapeutic use. In order to assess its genotoxic potential, the photobiological (genetic) effects of TMA were studied in a diploid strain of Saccharomyces cerevisiae (D7) and compared to those of the bifunctional furocoumarin 8-methoxypsoralen (8-MOP). At equimolar concentrations, the induction of lethal effects by TMA in the presence of equal 365-nm radiation was higher than that exerted by 8-MOP. TMA was also more active than 8-MOP in inducing nuclear events such as nuclear reverse mutation and mitotic recombination (crossing-overs and gene conversion) per unit dose of 365-nm radiation.At equal survival, however, TMA was less efficient in inducing reverse mutation and crossing-over, showing the same activity as 8-MOP in the induction of gene conversion. TMA was more active than 8-MOP in the induction of cytoplasmic ‘petite’ mutations per unit dose of 365-nm radiation and per viable cell.The high photobiological activity of this monofunctional furocoumarin is mainly related to its strong DNA photobinding but also to the type of monoaddition induced, to the sequential distribution in DNA and to the generation of active forms of oxygen.

Monofunctional angular furocoumarins: sequence specificity in DNA photobinding of 6,4,4'-trimethylangelicin and other angelicins.

The sequence specificity in the photoreaction (365 nm) of 6,4,4'-trimethylangelicin (TMA) with DNA fragments of the lac I gene of Escherichia coli was studied by using DNA sequencing methodology. In order to map the sites of TMA photoaddition, we took advantage of the (3'-5') exonuclease activity associated with T4 DNA polymerase, which is blocked by bulky adducts, such as furocoumarin photoadducts. A quantitative analysis of the sites of photoaddition is reported. TMA was demonstrated to photoreact with thymine and, to a lower extent, to cytosine. AT-rich sequences and TTT sites in a GC context are the most reactive sites towards TMA whereas TA, AT, CA, AC sites are weaker sites with similar reactivity. Cytosines in alternated CG sequences are also targets of TMA photobinding. We observed a less pronounced sequence specificity of TMA than that of other psoralen derivatives already studied (Sage and Moustacchi, 1987; Boyer et al., 1988). A comparison with other furocoumarins 4,4'-dimethylangelicin (4,4'-DMA), 4'-methylangelicin (4'-MA), angelicin, 4,5',8-trimethylpsoralen (TMP) and 8-methoxypsoralen (8-MOP) is also reported. The role of flanking sequence and consequently of the local conformation at the various sites of photoaddition is discussed. A preferential orientation of the TMA molecule during the intercalation in the dark is suggested. Hot alkali treatment of TMA-modified DNA did not reveal any DNA strand breakage due to photooxidized bases.

Photophysical, photochemical and photobiological properties of pyrrolocoumarins; A new class of photoactive compounds

With the aim of finding new photoactive compounds that may reduce the side effects of 8-methoxypsoralen photochemotherapy we report on some photophysical, photochemical and photobiological properties of recently synthesized pyrrolocoumarins, in particular 4-methyl- N-ethyl- pyrrolo[3,2- g]coumarin (PCNEt) which has an absorption maximum in the UV-A (320 – 400 nm). Laser (347 nm) flash photolysis studies showed triplet transients that were quenched by O 2 and by ground state PCNEt. Singlet minus triplet spectra were broad (350 – 550 nm) and, at 700 nm, indicated solvated electron and radical production. PCNEt complexes with DNA in the dark and photobinds to thymine but does not form DNA cross-links. PCNEt was phototoxic in yeast with an action spectrum similar to its absorption spectrum. PCNEt showed photohaemolytic activity but was not phototoxic on guinea pig skin. These data suggest that PCNEt may photosensitize via several mechanisms: direct DNA photobinding, photodynamic action, or photoproduction of radicals.

Photochemical, photophysical and photobiological properties of some methylallopsoralens which are potential agents for photochemotherapy

Two new trimethylallopsoralens, 4,7,4′- and 4,7,5′-trimethylallopsoralen, form molecular complexes with DNA and by successive UVA (320–400 nm) irradiation photobind monofunctionally to the macromolecule. The DNA photobinding rates at 365 nm and photobinding quantum yields at 330 nm are markedly higher for 4,7,4′-trimethylallopsoralen than for 4,7,5′-trimethylallopsoralen. Their capacities to generate singlet oxygen in water and benzene are low, particularly for 4,7,4′-trimethylallopsoralen, and the two trimethylallopsoralens completely lack skin phototoxicity on guinea-pig skin. Both compounds show antiproliferative activity in terms of DNA synthesis inhibition in Ehrlich cells and T 2 phage infectivity higher than that displayed by angelicin. In view of its monofunctional character, lack of skin phototoxicity, low singlet oxygen yield and antiproliferative activity, 4,7,4′-trimethylallopsoralen deserves further clinical studies as a potential photochemotherapeutic agent.

Sequence context effects on 8-methoxypsoralen photobinding to defined DNA fragments.

The photoreaction of 8-methoxypsoralen (8-MOP) with DNA fragments of defined sequence was studied. We took advantage of the blockage by bulky adducts of the 3'-5'-exonuclease activity associated with the T4 DNA polymerase. The action of the exonuclease is stopped by biadducts as well as by monoadducts. The termination products were analyzed on sequencing gels. A strong sequence specificity was observed in the DNA photobinding of 8-MOP. The exonuclease terminates its digestion near thymine residues, mainly at potentially cross-linkable sites. There is an increasing reactivity of thymine residues in the order T less than TT much less than TTT in a GC environment. For thymine residues in cross-linkable sites, the reactivity follows the order AT much less than TA approximately TAT much less than ATA less than ATAT less than ATATAA. Repeated A-T sequences are hot spots for the photochemical reaction of 8-MOP with DNA. Both monoadducts and interstrand cross-links are formed preferentially in 5'-TpA sites. Our results highlight the role of the sequence and consequently of the conformation around a potential site in the photobinding of 8-MOP to DNA.

Effect of molecular structure on the photophysical properties, the photoreactivity with DNA and the photobiological activity of monofunctional pyridopsoralens.

Abstract— 7‐Methyl‐pyrido[4,3‐c]psoralen (2N‐MePyPs) has been synthesized in order to investigate the possible effect of the position of the pyridine‐nitrogen atom on the photoreactivity towards DNA and the photobiological activity of pyridopsoralens, a new family of psoralen derivatives. In comparison to its isomer, 7‐methyl‐pyrido[3,4‐c]psoralen (MePyPs), 2N‐MePyPs shows a 2.5 times lower DNA photobinding capacity. Photobiological experiments with diploid yeast (Saccharomyces cerevisiae) reveal that this compound differs strikingly from its isomer MePyPs. It has only a weak antiproliferative potential and, per unit dose, a lower capacity than MePyPs for the induction of nuclear genotoxic effects. With respect to these latter features, 2N‐MePyPs resembles the monofunctional furocoumarin 3‐CPs.

Photobinding of psoralens to bacterial macromolecules in situ and induction of genetic effects in a bacterial test system. Effects of singlet oxygen diagnostic aids D2O and DABCO.

AbstractThe photobinding of radiolabeled psoralen and 8‐methoxypsoralen (8‐MOP) to biological macromolecules under conditions that affect the lifetime of singlet oxygen (1O2) is reported. These conditions are: increase of 1O2 lifetime in D2O and 1O2 quenching with DABCO. The photobinding to calf thymus DNA was studied in vitro and the covalent photobinding to DNA and other biological macromolecules (RNA, proteins) was also studied in intact bacteria. The results of the DNA photobinding experiments have been related to the induction of genetic damage in a bacterial test system. In addition, laser flash photolysis has been used to measure the effect of D2O and DABCO on the psoralen and 8‐MOP triplet lifetimes. In general D2O increases the triplet lifetimes and DABCO quenches the triplet states with the probable formation of radicals. The results suggest that the covalent photobinding of 8‐MOP to various biological macromolecules in situ is a basis for cell damage occurring at various cellular targets. Analysis of the results of the mutagenicity test suggests that in the presence of D2O the mechanism of induction of genetic lesions is not changed and therefore largely seems to be independent of singlet oxygen.

DNA photobinding of 7-methylpyrido[3,4- c]psoralen and 8-methoxypsoralen Effects on macromolecular synthesis, repair and survival in cultured human cells

The photobinding to DNA of tritiated 7-methylpyridol[3,4- c]psoralen (MPP), a recently synthesized monofunctional compound of therapeutical interest, and of 8-methoxypsoralen (8-MOP) was determined in cultured normal human fibroblasts. Employing compounds at 10 −6 M, MPP photobinds approximately 11 times more efficiently than 8-MOP: one molecule is fixed respectively per 7.5 × 10 4 or 8.1 × 10 5 base pairs/kJ · m −2 of 365-nm radiation (UVA). Removal of bound material from DNA is slow and limited in 48–72 h of post-treatment incubation to 30–40% of initial adducts formed by MPP and to 50–60% of those of 8-MOP. For equivalent photobinding MPP and 8-MOP induce similar inhibitions of DNA synthesis. However, the recovery of DNA synthesis during post-treatment incubation is lower after photoaddition of MPP than after that of 8-MOP. MPP also exerts a much higher lethal effect than 8-MOP: one lethal hit corresponds to about 4400 and to 19 900 adducts per cell respectively. Alkaline elution experiments confirmed the monofunctional nature of MPP and indicated that in MPP-damaged cells DNA breaks accumulate with time of post-treatment incubation. In contrast, after photoaddition of 3-carbethoxypsoralen (3-CPs), another monofunctional furocoumarin, or irradiation with 254-nm UV, DNA breaks are induced only transiently. In 8-MOP-treated cells, DNA cross-links appear to be partially repaired. In conclusion, MPP monoadducts turn out to constitute more cytotoxic lesions than 8-MOP mono- and bi-adducts.