Induction of breaks in deoxyribonucleic acid by photoexcited promazine derivatives

Phenothiazine electrophores immobilized on periodic mesoporous organosilicas by ion exchange

Two different phenothiazines carrying quaternary ammonium groups in the side chain have been synthesized and fully characterized.

First synthesis and electronic properties of diphenothiazine dumbbells bridged by heterocycles

According to cyclic voltammetry, symmetrical dumbbell-shaped phenothiazine dyads bridged by heterocycles show intense electronic coupling between the redox-active phenothiazine moieties. Furthermore, the fluorescence of the pyridyl-bridged derivatives can be controlled by pH change giving reversibly switchable redox-active biselectrophore dyads.

Synthesis and electronic properties of sterically demanding N-arylphenothiazines and unexpected Buchwald-Hartwig aminations

Phenothiazine is coupled under Buchwald-Hartwig conditions with bromo anthracenes and perylene as substrates to give phenothiazine-anthracene and phenothiazine-perylene dyads and triads. Investigation of the electronic properties of these sterically demanding N-aryl phenothiazines by absorption and emission spectroscopy, cyclic voltammetry, and DFT calculations revealed that the individual chromophores are decoupled in the electronic ground state but show unique electronic communication in the excited state. For the anthracenyl-bridged diphenothiazine an intense electronic coupling of the phenothiazinyl units is detected upon oxidation. Besides, attempts to synthesize phenothiazine compounds with even more sterically demanding aryl substituents in the 10-position under N-arylation conditions gave rise to the formation of quite unexpected products of arylation and/or oxidative coupling. The folding angle of the phenothiazine in a consanguineous series correlates well with the first oxidation potential.

DNA cleavage induced by photoexcited antimalarial drugs: a photophysical and photobiological study

The interactions and the photosensitizing activity of three antimalarial drugs quinine (Q), mefloquine (MQ) and quinacrine (QC) toward DNA was studied. Evidences obtained by absorption and emission spectroscopy and by linear dichroism measurements indicate that these derivatives bind the macromolecule with a high affinity (binding constants Ka approximately 10(5) M(-1)). The absorption characteristics of the drugs changed markedly by addition of DNA and their fluorescence was quenched with rate constants higher than that of diffusion. The geometry of binding involves predominantly the intercalation into the double helix. The DNA photocleavage properties of antimalarials was investigated using plasmid DNA as a model, at different [drug]/ [DNA] ratios. The results indicate that mainly MQ and Q are able to induce significant photodamage to DNA. In particular the marked effect of the former drug is evidenced after treatment of photosensitized DNA by two base excision repair enzymes, formamydo-pyrimidine glycosilase (Fpg) and Endonuclease III (Endo III). From a mechanistic point of view, experiments carried out in different experimental conditions indicate that these drugs photoinduce DNA damage through singlet oxygen and/or radical cation production. These findings are further supported by the determination of two photoproducts of 2'-deoxyguanosine, which are diagnostic for Type I and Type II pathways, namely 2,2-diamino(2-deoxy-beta-D-erythro-pentofuranosyl)-4-amino-5(2H)-oxazolone and (R,S)4-hydroxy-8-oxo-4,8-dihydro-2'-deoxyguanosine (4-OH-8-oxo-dGuo). Laser flash photolysis experiments carried out in the presence of DNA indicates that the excitation produces mainly the triplet state for Q and the triplet and radical cation for QC. Moreover the singlet and triplet states and radical cations of the drugs are quenched by 2'-deoxyguanosine monophosphate. The absorbances of these transients decrease with increasing DNA concentration.

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.

Excited-state properties and in vitro phototoxicity studies of three phenothiazine derivatives

This work concerns a combined photophysical, photochemical and photobiological study of three drugs (psychotherapeutic agents) of the phenothiazine series: perphenazine, fluphenazine hydrochloride and thioridazine hydrochloride. The excited-state properties were first investigated by stationary and time-resolved fluorimetry and by laser flash photolysis. The spectral description was assisted by quantum-mechanical calculations with the INDO/1-CI method. In organic media the lowest excited singlet state was found to decay by fluorescence (small quantum yield) and mainly by intersystem crossing to the lowest triplet state, which is responsible for oxygen photosensitization (high yields of singlet oxygen production) and photodegradation. A further decay pathway in aqueous solutions was the photoionization process, which led to the formation of the phenothiazine radical cations and the solvated electron. After the preliminary study of the photobehavior in organic solvents and in water, the phototoxicity of the three drugs was investigated on various biological substrates through a series of in vitro assays under UVA irradiation. Photohemolysis of mouse erythrocytes and phototoxicity on cultured murine fibroblasts were observed for all three compounds. Lipid photoperoxidation was then investigated using linoleic acid as the unsaturated lipid model and isolated red blood cell membranes. The drug-induced photodamage was also evaluated on proteins by measuring the photosensitizing cross-linking in erythrocyte ghosts. The combined approach proved to be useful in understanding the mechanism by which these phenothiazine derivatives induce skin photosensitization. In particular, the photophysical properties of the compounds under investigation and the results of the study on their phototoxicity are in agreement with a mechanism that involves the radical cation of the drugs as a main intermediate.

Synthesis of functionalized ethynylphenothiazine fluorophores

Alkynylated and butadiynyl-bridged phenothiazines with variable functionalization can be synthesized in good yields by cross-coupling and condensation approaches. In addition, the structure of the diethynylated phenothiazine (7a) has been corroborated by an X-ray structure analysis. These oligofunctional heterocycles are fluorescent with modest quantum yields (Phi(f) = 20-35%) and represent suitable building blocks for novel photoexcitable molecular wires.

Generation of electronically excited triplet species at the cellular level: a potential source of genotoxicity

Selected enzymatic systems can efficiently produce a product in the electronically excited triplet state. Earlier, only the formation of electronically excited singlet species was known. The formation of triplet species has been demonstrated with both normal substrates/metabolites and with xenobiotics, even at the cellular level. Triplet excited species have intrinsically much longer lifetimes than excited singlets, whereby they can be potentially important agents for normal and/or deleterious processes, including mutagenesis. Enzymically generated triplet species can damage DNA, even when protein coated, as in the case of the lambda-phage of Escherichia coli. Some evidence of damage by triplet species has also been reported for intact cells. Triplet excited species may produce their effects through type I and/or type II dark photosensitization, that is, the events may be started by H abstraction and/or singlet oxygen/superoxide ion production. The induction of lipid peroxidation, with concomitant clastogenic effects, appears to be of special importance.

Mechanism of DNA cleavage mediated by photoexcited non-steroidal antiinflammatory drugs

DNA damage photoinduced by four nonsteroidal antiinflammatory drugs (NSAID) have been investigated by neutral agarose gel electrophoresis. Upon irradiation at 300 nm, in phosphate buffered solution, benoxaprofen, naproxen, ketoprofen, tiaprofenic acid photosensitized the formation of single-strand breaks (SSB) in double stranded supercoiled phi X174 DNA. The efficiency of the cleavage is higher in argon saturated solutions than in aerated solutions and it is not correlated with the quantum yield of photodegradation of the drugs. Simultaneously with the DNA strand breaks, NSAID promote a weak reduction of the electrophoretic mobility of the supercoiled form that may be attributed to the formation of pyrimidine dimers or other DNA unwinding products. These photodimerization processes suggest the involvement of a triplet-triplet energy transfer between NSAID and DNA. Addition of mannitol and superoxide dismutase decreases the efficiency of the cleavage suggesting that HO. and O2.- are involved in the DNA cleavage. Unexpectedly, addition of sodium azide quenches the cleavage both in aerated or in deaerated solutions. Substituting H2O by D2O does not change the number of SSB thus suggesting that 1O2 does not take an important place in the cleavage of DNA. From our data we tentatively assume that the cleavage occurs through a radical mechanism that may involve in a first step an energy or an electron transfer. Gel sequencing on NSAID-photoinduced DNA breakage exhibits no particular specificity except in the case of benoxaprofen where a slight selectivity for cytosine is observed.

DNA strand breaks photosensitized by benoxaprofen and other non steroidal antiinflammatory agents

Benoxaprofen, a non steroidal antiinflammatory drug is known to be highly phototoxic. Upon irradiation at 300 nm, benoxaprofen is shown to enhance the cleavage of phi X 174 DNA in buffered aqueous solution (pH 7.4). A linear relationship between the number of single strand breaks and the irradiation time is found. In deaerated solutions, these breaks are three times greater in the presence than in the absence of benoxaprofen. In both cases the rate of cleavage decreases in the presence of air. The rate of DNA damage increases with the drug per base pair ratio up to approximatively 0.2 and then decreases at higher ratios. Other NSAIDs, naproxen, ketoprofen, diflunisal, sulindac and indomethacin have been tested as photocleavers of DNA by using the same experimental conditions. A comparison of the efficiency of cleavage of all these drugs (including BNP) was obtained at drug concentrations such that the light absorbance was the same. Benoxaprofen, naproxen, ketoprofen and diflunisal induce single strand breaks. Sulindac and indomethacin do not cause breaks, and they can in some conditions even act as screening agents. The most efficient of the series are naproxen and ketoprofen. In the presence of oxygen, at the same concentrations as above, the efficiency of benoxaprofen, ketoprofen and diflunisal is decreased while that of naproxen is increased. This suggests that all these compounds do not interact with DNA by the same mechanism. In the case of BNP, the mechanism of photoinduced DNA cleavage is discussed in detail. It is shown that the photoactive agent is the decarboxylated derivative of benoxaprofen, as the photodecarboxylation of benoxaprofen is much faster than the photocleavage of DNA.

In vivo photodegradation of chlorpromazine

The in vivo photodegradation of chlorpromazine (CPZ) in the skin was investigated after systemic administration of 3H-CPZ to shaven Wistar rats and exposure to UV-A. Promazine (PZ) and 2-hydroxy-promazine (2-OH-PZ) appeared to be formed in irradiated rats, but not in the skin of rats kept in the dark. This indicates that upon irradiation with UV-A the PZ-radical is formed which can be held responsible for the photobinding to eye and skin constituents as observed earlier [Schoonderwoerd and Beijersbergen von Henegouwen (1987) Photochem. Photobiol. 46, 501-505]. Chlorpromazine-sulfoxide (CPZSO) is a major metabolite of CPZ. Less CPZSO was found in the skin of irradiated rats compared to those kept in the dark. As this appeared not to be caused by photobinding or photodegradation of CPZSO it can be concluded that CPZSO is not a photoproduct of CPZ under these experimental conditions. This study shows that the in vivo photodegradation of CPZ proceeds via the promazinyl radical rather than via the radical cation.

Characterization of free radicals produced during oxidation of etoposide (VP-16) and its catechol and quinone derivatives. An ESR Study

Spectroscopic evidence for the radical-mediated metabolism of VP-16, VP-16 catechol, and VP-16 quinone during enzymatic oxidation and autoxidation has been obtained. Autoxidation of the catechol yields the primary semiquinone together with the primary molecular product VP-16 quinone, which subsequently undergoes hydrolytic oxidation to form secondary quinones and semiquinones. Both primary and secondary phenoxyl radicals were detected during peroxidatic oxidation of VP-16. Neither the primary nor the secondary radicals react with DNA at a detectable rate. Evidence for the production of hydroxyl radical during iron-catalyzed oxidation of VP-16 catechol was obtained. These free radical reactions may have implications for the mechanism of antitumor action of VP-16.

UV-A induced DNA nicking activities of skin photosensitive drugs: phenothiazines, benzothiadiazines and afloqualone

Plasmid pBR 322 was subjected to UV-A irradiation in the presence of photosensitive drugs, i.e., phenothiazines [chlorpromazine hydrochloride (CPZ), promethazine hydrochloride (PMZ) and mequitazine (MQZ)], benzothiadiazines [penflutizide (PFZ), hydrochlorothiazide (HCT) and methyclothiazide (MCT)] and afloqualone (AQ). The distribution of the closed-circular and the open-circular form of the plasmid DNA was analyzed by means of neutral agarose gel electrophoresis. All the drugs used induced more or less DNA nicking to yield the open-circular form. The nicking activities of the phenothiazines were in the order: CPZ greater than PMZ greater than MQZ. CPZ elicited extensive degradation of the DNA by photosensitization. The nicking activities of the benzothiadiazines and AQ were much weaker than CPZ and PMZ.

Antioxidant action and photosensitizing effects of three different chlorpromazines

Chlorpromazine inhibits by about 60% the lipid peroxidation stimulated by Fe2+/ascorbate in liposomes and the lipid peroxidation stimulated by cumene hydroperoxide in microsomes. Under the same conditions, two new synthetic derivatives of chlorpromazine, i.e., a N-benzoyloxymethylchlorpromazine and a N-pivaloyloxymethylchlorpromazine, induce no more than a 20% inhibition. On the other hand, when the different chlorpromazines are entrapped in liposomes and subsequently irradiated with near-UV light, they act as photosensitizing agents giving rise to lipid peroxidation. The latter is quite extensive in the presence of chlorpromazine or N-pivaloyloxymethylchlorpromazine, whereas it is drastically lower in the presence of N-benzoyloxymethylchlopromazine. The N-benzoyloxymethylchlorpromazine molecule, despite its low photodynamic effect, retains its neuroleptic properties. The possible mechanisms of the antioxidant and prooxidant actions of these compounds are discussed.

Dopamine receptors: molecular structure and function

Two distinct categories of dopamine receptors, termed D1 and D2, have been identified on the basis of pharmacological and biochemical criteria. Some of the progress made in our understanding of the subunit structure, function and signal transduction properties of these important membrane proteins are reviewed.

Alkaline labilization of DNA photosensitized by promazine derivatives

Superhelical pBR322 DNA has been photosensitized in the presence of various promazine derivatives. Agarose gel electrophoresis of the photosensitized DNA reveals that true single-strand breaks are induced during irradiation. Alkaline treatment of the photosensitized DNA with a subsequent alkaline agarose gel electrophoresis demonstrates that in addition to true single-strand breaks, these drugs can induce alkali-labile lesions. Although true single-strand breaks are induced randomly into a 5'-[32P]-end labeled pBR322 DNA fragments, the alkaline-labile alterations are located specifically at the level of guanine residues. A strong correlation seems to exist between the visualization of this labilization and the induction of a covalent photoadduct on guanine by the photosensitization mediated by PZ.

Photosensitization of SV 40 DNA mediated by promazine derivatives and 4'-hydroxymethyl-4,5',8-trimethylpsoralen. Inhibition of the in vitro transcription

In vitro transcription by E. coli RNA polymerase was carried out on SV40 DNA photoreacted with various promazine derivatives. Inhibition of the template activity was recorded with increasing irradiation times in the presence of promazine derivatives. Promazine covalent adducts on guanine did not terminate RNA synthesis and seemed to be bypassed by the enzyme. HMT (4'-hydroxymethyl-4,5',8-trimethylpsoralen) photoreaction with DNA was carried out under two conditions: irradiation with lambda greater than 395 nm favouring monoadduction on pyrimidine residues and irradiation at 360 nm inducing a maximum of interstrand diadducts. Both adducts were able to terminate RNA synthesis on the phototreated SV40 DNA and using the O-methyl-nucleotide sequencing procedure, the termination sites were precisely mapped. Monoadducts on the coding strand and cross-links induced termination two bases away from the covalent adduct, but monoadducts on the noncoding strand did not half RNA polymerase.

Spin trapping: ESR parameters of spin adducts

Spin trapping has become a valuable tool for the study of free radicals in biology and medicine. The electron spin resonance hyperfine splitting constants of spin adducts of interest in this area are tabulated. The entries also contain a brief comment on the source of the radical trapped.

Interaction between enzyme-generated triplet carbonyls and molecules intercalated into DNA

The phosphorescence from enzyme-generated and -protected triplet acetone is very efficiently quenched by dyes intercalated into DNA. The process is unlikely to be due to energy transfer and is tentatively ascribed to electron transfer occurring within the DNA helix complex with the acting enzyme. This quenching markedly protects DNA from breaks induced by triplet acetone. In the case of some barely emissive enzyme-generated triplet carbonyl species, it is possible to detect a weak emission resulting from the interaction with dye X DNA; this emission may be associated with back electron transfer.

Phototoxic potential of mequitazine, a phenothiazine derivative, as determined by the photosensitized action on microbiological systems

In order to determine phototoxic potential of mequitazine (MQZ), a phenothiazine derivative, in vitro tests were attempted using microbiological systems. When Escherichia coli was irradiated with ultraviolet-A light in the presence of MQZ, the surviving fraction was decreased with increasing fluence. Irradiation of bacteriophage lambda in the presence of the drug decreased the surviving fraction as well. Possible targets for the photosensitized action in these systems were discussed.

DNA alterations photosensitized by tetracycline and some of its derivatives

Bacteriophage M13 mp10 DNA were irradiated with near-UV light in the presence of tetracycline derivatives and primed with synthetic oligonucleotide to be used for DNA synthesis using Escherichia coli DNA polymerase. Chain terminations were observed by denaturing polyacrylamide gel electrophoresis and mapped precisely. All the synthesis stops occurred before or at the level of guanine residues, showing that the photoreaction mediated by tetracycline derivatives led to a preferential alteration of guanine residues. These lesions were demonstrated to be induced in DNA through a pathway involving singlet oxygen. Tetracycline derivatives also photoinduced the breakage of the DNA sugar-phosphate backbone monitored by the conversion of supercoiled phi X174 DNA to a relaxed form. This lesion was shown to be initiated by hydroxyl radicals. The production of this free radical has been confirmed by electron paramagnetic resonance (EPR) spin trapping experiments using 5,5-dimethyl-1-pyrroline-N-oxide as spin trap. In addition to the EPR signal due to OH radicals trapping another unassigned signal has been detected.

Biomolecular photoalterations mediated by phenothiazine derivatives

This survey focuses on recent developments in the field of the ultraviolet photochemistry and photobiology of phenothiazine derivatives. One of the major alterations introduced by this kind of photosensitized reaction is a covalent addition of the photosensitizer or one of its photoproducts onto the macromolecular target. This reaction has been observed with soluble and membrane proteins, lipids and DNA. In the latter case, the addition occurs at the level of guanine residues and leads to inhibition of DNA replication.

Termini generated at the site of the DNA breakage mediated by photoexcited promazines

Promazine derivatives are known to be able to photoinduce, in vitro, direct single-strand breaks into DNA (Decuyper et al., Biochem. Pharmac. 33, 4025-4031 (1984]. Using [32P]end labeled DNA fragments, it is demonstrated that this DNA breakage occurs almost regardless of the nucleotide sequence of the DNA. Using 3'-[32P]end or 5'-[32P]end labeled oligonucleotide and enzymatic digestion of the fragments generated, it is demonstrated that the termini generated at the site of the breakage are 5'-phosphate, 3'-phosphate and 3'-termini which are presumed to be 3'-phosphoglycolate. This is consistent with an attack of the sugar moeity of the sugar-phosphate backbone of the DNA by the reactives species generated upon near-u.v. irradiation of promazine derivatives.