Molecular mechanisms of photosensitization

Oxygen-independent organic photosensitizer with ultralow-power NIR photoexcitation for tumor-specific photodynamic therapy

Photodynamic therapy (PDT) is a promising cancer treatment but has limitations due to its dependence on oxygen and high-power-density photoexcitation. Here, we report polymer-based organic photosensitizers (PSs) through rational PS skeleton design and precise side-chain engineering to generate •O2- and •OH under oxygen-free conditions using ultralow-power 808 nm photoexcitation for tumor-specific photodynamic ablation. The designed organic PS skeletons can generate electron-hole pairs to sensitize H2O into •O2- and •OH under oxygen-free conditions with 808 nm photoexcitation, achieving NIR-photoexcited and oxygen-independent •O2- and •OH production. Further, compared with commonly used alkyl side chains, glycol oligomer as the PS side chain mitigates electron-hole recombination and offers more H2O molecules around the electron-hole pairs generated from the hydrophobic PS skeletons, which can yield 4-fold stronger •O2- and •OH production, thus allowing an ultralow-power photoexcitation to yield high PDT effect. Finally, the feasibility of developing activatable PSs for tumor-specific photodynamic therapy in female mice is further demonstrated under 808 nm irradiation with an ultralow-power of 15 mW cm-2. The study not only provides further insights into the PDT mechanism but also offers a general design guideline to develop an oxygen-independent organic PS using ultralow-power NIR photoexcitation for tumor-specific PDT.

Increasing the Selectivity of Light-Active Antimicrobial Agents - Or How To Get a Photosensitizer to the Desired Target

Photosensitizers combine the inherent reactivity of reactive oxygen species with the sophisticated reaction control of light. Through selective targeting, these light-active molecules have the potential to overcome certain limitations in drug discovery. Ongoing advances in the synthesis and evaluation of photosensitizer conjugates with biomolecules such as antibodies, peptides, or small-molecule drugs are leading to increasingly powerful agents for the eradication of a growing number of microbial species. This review article, therefore, summarizes challenges and opportunities in the development of selective photosensitizers and their conjugates described in recent literature. This provides adequate insight for newcomers and those interested in this field.

Chemiexcitation: Mammalian Photochemistry in the Dark†

Light is one way to excite an electron in biology. Another is chemiexcitation, birthing a reaction product in an electronically excited state rather than exciting from the ground state. Chemiexcited molecules, as in bioluminescence, can release more energy than ATP. Excited states also allow bond rearrangements forbidden in ground states. Molecules with low-lying unoccupied orbitals, abundant in biology, are particularly susceptible. In mammals, chemiexcitation was discovered to transfer energy from excited melanin, neurotransmitters, or hormones to DNA, creating the lethal and carcinogenic cyclobutane pyrimidine dimer. That process was initiated by nitric oxide and superoxide, radicals triggered by ultraviolet light or inflammation. Several poorly understood chronic diseases share two properties: inflammation generates those radicals across the tissue, and cells that die are those containing melanin or neuromelanin. Chemiexcitation may therefore be a pathogenic event in noise- and drug-induced deafness, Parkinson's disease, and Alzheimer's; it may prevent macular degeneration early in life but turn pathogenic later. Beneficial evolutionary selection for excitable biomolecules may thus have conferred an Achilles heel. This review of recent findings on chemiexcitation in mammalian cells also describes the underlying physics, biochemistry, and potential pathogenesis, with the goal of making this interdisciplinary phenomenon accessible to researchers within each field.

Benchmarking DFT functionals for photophysics of pyranoflavylium cations

An intense absorption, phosphorescence, a long triplet excited state lifetime and singlet oxygen generation capabilities are characteristics of pyranoflavylium cations, analogues to pyranoanthocyanidins originated in the maturation process of red wine. Such properties make these compounds potential photosensitizers to be applied in photodynamic therapy. In this context, the photophysical processes underlying that treatment critically depend on the electronic structure of the pyranoflavylium molecules. When employing density functional theory to describe the electronic structure of molecules, the choice of the most suitable functional is not trivial, and benchmark studies are needed to orient practitioners in the field. In this work, a benchmark of seven of the most commonly used density functionals in addressing the photophysical properties of a set of eight pyranoflavylium cations is reported. Ground and excited state geometries, molecular orbitals, and absorption, fluorescence and phosphorescence transition energies were calculated using density functional theory approaches, and evaluated and compared to experimental data and monoreferential wave function-based methodologies. Statistical analysis of the results indicates that global-hybrid functionals allow an excellent description of absorption and emission energies, with errors around 0.05 eV, while range-separated variants led to somewhat larger errors in the range 0.1-0.2 eV. In contrast, range-separated functionals display excellent phosphorescence energies with errors close to 0.05 eV, in this case global-hybrids showing increased discrepancies around 0.5-0.1 eV.

Interrogating biological systems using visible-light-powered catalysis

Light-powered catalysis has found broad utility as a chemical transformation strategy, with widespread impact on energy, environment, drug discovery and human health. A noteworthy application impacting human health is light-induced sensitization of cofactors for photodynamic therapy in cancer treatment. The clinical adoption of this photosensitization approach has inspired the search for other photochemical methods, such as photoredox catalysis, to influence biological discovery. Over the past decade, light-mediated catalysis has enabled the discovery of valuable synthetic transformations, propelling it to become a highly utilized chemical synthesis strategy. The reaction components required to achieve a photoredox reaction are identical to photosensitization (catalyst, light source and substrate), making it ideally suited for probing biological environments. In this Review, we discuss the therapeutic application of photosensitization and advancements made in developing next-generation catalysts. We then highlight emerging uses of photoredox catalytic methods for protein bioconjugation and probing complex cellular environments in living cells.

Genetically Encoded Photosensitizer for Destruction of Protein or Cell Function

There are several paths when excited molecules return to the ground state. In the case of fluorescent molecules, the dominant path is fluorescence emission that is greatly contributing to bioimaging. Meanwhile, photosensitizers transfer electron or energy from chromophore to the surrounding molecules, including molecular oxygen. Generated reactive oxygen species has potency to attack other molecules by oxidation. In this chapter, we introduce the chromophore-assisted light inactivation (CALI) method using a photosensitizer to inactivate proteins in a spatiotemporal manner and development of CALI tools, which is useful for investigation of protein functions and dynamics, by inactivation of the target molecules. Moreover, photosensitizers with high efficiency make it possible optogenetic control of cell ablation in living organisms and photodynamic therapy. Further development of photosensitizers with different excitation wavelengths will contribute to the investigation of multiple proteins or cell functions through inactivation in the different positions and timings.

In Vitro Alternatives and Phototoxicity Testing. II. Effects of Reactive Oxygen Species in In Vitro Phototoxicity Assays

The effects of reactive oxygen species (including singlet oxygen) in two in vitro phototoxicity assays — the 3T3 cell neutral red uptake phototoxicity (3T3 NRU PT) assay and the photohaemolysis assay — were assessed by using scavengers. Fifteen test substances, which had previously been shown to be phototoxic in vitro, were assessed. Eleven of these produced singlet oxygen. The major factor in the photodynamic reaction of bithionol was thought to be a Type I reaction, because bithionol did not produce singlet oxygen and did not react to histidine. Acridine was regarded as a Type II substance, because of the evident effect of histidine as a scavenger. 8-Methoxypsoralen and 5-methoxypsoralen produced singlet oxygen, but their actions were not affected by the scavengers. In this study, we confirmed that reactive oxygen species have great effects in in vitro phototoxicity, and that the 3T3 NRU PT assay can be used to detect effects which are thought to be the direct reaction of an excited photosensitiser to biological substrates (Type III reaction), for example, 8-methoxypsoralen. Therefore, we suggest that photohaemolysis and phototoxicity could be used to evaluate the photodynamic mechanisms of photosensitising chemicals.

Mechanism of coralyne-mediated DNA photo-nicking process

Previously, we reported that coralyne and UVA combination sensitized a wide range of human carcinoma cells regardless of their p53 status. The coralyne induced photosensitization of cancer cells may be clinically attractive, as mutation in the p53 gene is prevalent in many types of tumors. Coralyne mediated photosensitization of cancer cells is attributable to its ability to cause extensive DNA single strand breaks (SSB). However, the precise mechanism of coralyne induced DNA photo-damage is not yet known. The present study was aimed to understand the hitherto unknown mechanism of the coralyne-induced DNA photo-cleavage process. To this end, we compared the DNA photo-nicking properties of berberine, jatrorrhizine and coralyne, and deciphered involvement of the photochemical processes in the photo-nuclease action of coralyne using absorption and electron spin resonance spectroscopy, high performance liquid chromatography and mass spectroscopy (MS) techniques in conjunction with relevant in vitro studies with plasmid DNA. In association with UVA, coralyne, but not berberine and jatrorrhizine induced significant nicking of plasmid DNA via an O₂-independent photo-chemical process. The Job's plot of our spectrophotometric data suggested that one coralyne molecule remains intercalated with two DNA base pairs (i. e., 1:2) and starts forming aggregates beyond this molar ratio. The DNA photo-nicking by the combination of coralyne and UVA (designated as CUVA) was primarily caused by the coralyne aggregates without any significant contribution from the DNA-intercalated coralyne monomer.

The aetiology, prevalence and morbidity of outbreaks of photosensitisation in livestock: A review

BACKGROUND

Photosensitisation is a clinical condition occurring in both humans and animals that causes significant injury to affected individuals. In livestock, outbreaks of photosensitisation caused by ingestion of toxic plants are relatively common and can be associated with significant economic loss.

OBJECTIVES

The agents that are most commonly implicated in outbreaks of photosensitisation have not been formally investigated on a global scale. To address this question, a systematic review of the literature was undertaken to determine the most common causative agents implicated in outbreaks of photosensitisation in livestock in Australia and globally, as well as the prevalence and morbidity of such outbreaks.

METHODS

A systematic database search was conducted to identify peer-reviewed case reports of photosensitisation in livestock published worldwide between 1900 and April 2018. Only case reports with a full abstract in English were included. Non peer-reviewed reports from Australia were also investigated. Case reports were then sorted by plant and animal species, type of photosensitisation by diagnosis, location, morbidity and mortality rate and tabulated for further analysis.

RESULTS

One hundred and sixty-six reports qualified for inclusion in this study. Outbreaks were reported in 20 countries. Australia (20), Brazil (20) and the United States (11) showed the highest number of peer-reviewed photosensitisation case reports from this analysis. Hepatogenous (Type III) photosensitisation was the most frequently reported diagnosis (68.5%) and resulted in higher morbidity. Panicum spp., Brachiaria spp. and Tribulus terrestris were identified as the most common causes of hepatogenous photosensitisation globally.

CONCLUSIONS

Hepatogenous photosensitisation in livestock represents a significant risk to livestock production, particularly in Australia, Brazil, and the United States. Management of toxic pastures and common pasture weeds may reduce the economic impact of photosensitisation both at a national and global level.

Photocyclization of diarylethenes: the effect of imidazole on the oxidative photodegradation process

It was found that imidazole prevents the side process of diarylethenes photocyclization and the photodegradation of photochromic compounds.

The development of ruthenium(ii) polypyridyl complexes and conjugates for in vitro cellular and in vivo applications

Ruthenium(ii) [Ru(ii)] polypyridyl complexes have been the focus of intense investigations since work began exploring their supramolecular interactions with DNA. In recent years, there have been considerable efforts to translate this solution-based research into a biological environment with the intention of developing new classes of probes, luminescent imaging agents, therapeutics and theranostics. In only 10 years the field has expanded with diverse applications for these complexes as imaging agents and promising candidates for therapeutics. In light of these efforts this review exclusively focuses on the developments of these complexes in biological systems, both in cells and in vivo, and hopes to communicate to readers the diversity of applications within which these complexes have found use, as well as new insights gained along the way and challenges that researchers in this field still face.

Type I and Type II Photosensitized Oxidation Reactions: Guidelines and Mechanistic Pathways

Here, 10 guidelines are presented for a standardized definition of type I and type II photosensitized oxidation reactions. Because of varied notions of reactions mediated by photosensitizers, a checklist of recommendations is provided for their definitions. Type I and type II photoreactions are oxygen-dependent and involve unstable species such as the initial formation of radical cation or neutral radicals from the substrates and/or singlet oxygen (¹ O₂¹ ∆_g ) by energy transfer to molecular oxygen. In addition, superoxide anion radical (O2·-) can be generated by a charge-transfer reaction involving O₂ or more likely indirectly as the result of O₂ -mediated oxidation of the radical anion of type I photosensitizers. In subsequent reactions, O2·- may add and/or reduce a few highly oxidizing radicals that arise from the deprotonation of the radical cations of key biological targets. O2·- can also undergo dismutation into H₂ O₂ , the precursor of the highly reactive hydroxyl radical (·OH) that may induce delayed oxidation reactions in cells. In the second part, several examples of type I and type II photosensitized oxidation reactions are provided to illustrate the complexity and the diversity of the degradation pathways of mostly relevant biomolecules upon one-electron oxidation and singlet oxygen reactions.

In vitro studies of different irradiation conditions for Photodynamic inactivation of Helicobacter pylori

Helicobacter pylori (HP) infections are considered to be the main cause for chronic gastritis and gastric ulcers, whereby more than half of the world's population is nowadays infected. The increased use of antibiotics is leading to an enhanced resistance. Photodynamic inactivation of bacteria seems to be a potential alternative for antibiotic therapies. In our study we used the photosensitizer Chlorin e6 (Ce6) in combination with red light-emitting diodes to inactivate HP in vitro. Ce6 uptake is determined by spectroscopy. Furthermore diverse experiments of different concentrations in the range of 0-100 μM of the photosensitizer and exposure times up to 300 s are carried out in order to find optimal irradiation parameters (wavelength: 660 nm, power density: 9 mW/cm(2), absorbed dose: up to 2.7 J/cm(2)). The data show a significant reduction after already a few seconds of illumination, even with a low Ce6 concentration in the sub-μM-region. At a concentration of 100 μM a nearly total inactivation (6-log10-reduction) of HP was achieved within 60s of irradiation.

Photodynamic therapy involves an antiangiogenic mechanism and is enhanced by ferrochelatase inhibitor in urothelial carcinoma

The purpose of the present study was to investigate the mechanism of photodynamic therapy (PDT) supplemented with exogenously added 5-aminolevulinic acid (ALA) on human urothelial cancer (UC). Moreover, we aimed to determine whether the therapeutic effects of ALA-based PDT (ALA-PDT) for UC could be enhanced by deferoxamine (DFX), an inhibitor of ferrochelatase. The efficiency of ALA-PDT on these cells was analyzed using flow cytometry and the type of cell death was also assessed. The ALA-PDT promoting effect of DFX was examined on both UC cells and human umbilical vein endothelial cells (HUVEC). The ALA-PDT decreased levels of mitochondrial membrane potential and induced cell death mainly via apoptosis in these cells. Moreover, inhibition of ferrochelatase by DFX led to an increase of protoporphyrin IX (PpIX) accumulation and enhanced the effect of ALA-PDT on UC cells. We further investigated the effect of DFX on in vivo PDT with a tumor-bearing animal model and found that DFX efficiently enhanced tumor cell apoptosis. ALA-PDT induced death of neovascular endothelial cells in tumors but did not affect small vessel endothelial cells in normal tissues surrounding the tumor. Furthermore, DFX enhanced inhibition of neovascularization. These results demonstrated ALA-PDT dominantly induced apoptosis over necrosis by direct action on UC as well as via antiangiogenic action on neovacular endothelial cells, suggesting that the therapeutic damage by ALA-PDT could be kept to a minimum in the surrounding normal tissues. In addition, increased accumulation of PpIX by DFX could enhance this effectiveness of ALA-PDT.

Photochemical activation of TRPA1 channels in neurons and animals

Optogenetics is a powerful research tool because it enables high-resolution optical control of neuronal activity. However, current optogenetic approaches are limited to transgenic systems expressing microbial opsins and other exogenous photoreceptors. Here, we identify optovin, a small molecule that enables repeated photoactivation of motor behaviors in wild-type zebrafish and mice. To our surprise, optovin's behavioral effects are not visually mediated. Rather, photodetection is performed by sensory neurons expressing the cation channel TRPA1. TRPA1 is both necessary and sufficient for the optovin response. Optovin activates human TRPA1 via structure-dependent photochemical reactions with redox-sensitive cysteine residues. In animals with severed spinal cords, optovin treatment enables control of motor activity in the paralyzed extremities by localized illumination. These studies identify a light-based strategy for controlling endogenous TRPA1 receptors in vivo, with potential clinical and research applications in nontransgenic animals, including humans.

Adenosine-triggered elimination of methylene blue noncovalently bound to immobilized functional dsDNA-aptamer constructs

Immobilization and electrochemical characterization of specially designed functional DNA-aptamer constructs are of great importance for the development of versatile biosensors (not limited to gene analysis) and the investigation of molecular interactions between DNA and other molecules. We have constructed a "DNA conformational switch" by incorporating the antiadenosine aptamer sequence in the middle of an otherwise cDNA double helix, as its structural change responds to the presence of small molecule ligands (e.g., adenosine). In particular, methylene blue (MB) was used as a model system to probe the rather complex interaction modes between small redox molecules and the dsDNA-aptamer construct. Besides intercalating with the double-stranded DNA stem, MB can stack with a single guanine base in the relatively unstructured aptamer domain or electrostatically bind to the DNA backbone. The decreased surface density of MB after adenosine binding indicated that the ligand-gated structural change of the dsDNA-aptamer construct can eliminate MB molecules that were originally bound to the aptamer domain but not those in the complementary stem.

Alkyl-substituted magnesium phthalocyanine: phototoxicity after excitation of higher electronic states in cells in vitro

Photodynamic tumour therapy (PDT) on the basis of a sequential two-photon excitation of suitable sensitizers is expected 1) to prevent skin phototoxicity caused by day-light and 2) may occur via an oxygen-independent mechanism of photosensitization. Here we investigated cellular uptake, localization and phototoxicity of ( t-butyl )4- PcMg , a promising dye for a sequential two-step activation, in Jurkat cells (human T cell line) and murine hybridoma cells (B cells) in vitro. Pheophorbide a (pheo) was used as a classical Type II reference sensitizer. Excitation of higher singlet states was performed both by direct UV-excitation and by sequential two-step laser excitation in the Q-band with maximum photon flux densities of about 1026 phot.cm−2.s−1. Irradiation of ( t-butyl )4- PcMg in cells in vitro is accompanied by a rapid destruction of the dye, as was proved by confocal fluorescence microscopy. Irradiated cells exhibit a less pronounced decrease of viability and a transient cell cycle arrest of about 24 h. Pheo incubated cells are characterized by a complete stop of proliferation. In contrast, no long-lasting phototoxicity was observed with ( t-butyl )4- PcMg . Low fluorescence levels and rapid photobleaching prevented the identification of intracellular dye-localization. Our data indicate the presence of a radical mechanism as origin of an irreversible dye destruction that accounts for the low phototoxicity of ( t-butyl )4- PcMg .

Spectroscopic studies on the thermodynamic and thermal denaturation of the ct-DNA binding of methylene blue

The ct-DNA binding properties of methylene blue (MB) including binding constant, thermodynamic parameter and thermal denaturation (T(m)) have been systematically studied by spectrophotometric method. The binding of MB to ct-DNA is quite strong as indicated by remarkable hypochromicity, red shift and equilibrium binding constant (K(b)). Van't Hoff plot of 1/T versus lnK(b) suggests that the MB dye binds exothermically to ct-DNA which is characterized by large negative enthalpy and entropy changes. According to polyelectrolyte theory, the charge release (Z) when ct-DNA interacts with MB is +1.09 which corresponds very well to the one positive charge carried by the MB dye. The K(b) at a low concentration of salt is dominated by electrostatic interaction (90%) while that at a high concentration of salt is mostly controlled by non-electrostatic process (85%). However, the stabilization of the DNA binding event in both cases is governed by non-electrostatic process. A moderate stabilization of double helix ct-DNA occurs when the MB dye binds to ct-DNA as indicated by the increase in T(m) of ct-DNA of about 5.5 degrees C in the presence of MB. This suggests that MB dye possibly binds to ct-DNA via electrostatic and intercalation modes.

Mechanism of cell death by 5-aminolevulinic acid-based photodynamic action and its enhancement by ferrochelatase inhibitors in human histiocytic lymphoma cell line U937

Photodynamic therapy (PDT) for tumors is based on the tumor-selective accumulation of a photosensitizer, protoporphyrin IX (PpIX), followed by irradiation with visible light. However, the molecular mechanism of cell death caused by PDT has not been fully elucidated. The 5-aminolevulinic acid (ALA)-based photodynamic action (PDA) was dependent on the accumulation of PpIX, the level of which decreased rapidly by eliminating ALA from the incubation medium in human histiocytic lymphoma U937 cells. PDA induced apoptosis characterized by lipid peroxidation, increase in Bak and Bax/Bcl-xL, decrease in Bid, membrane depolarization, cytochrome c release, caspase-3 activation, phosphatidylserine (PS) externalization. PDT-induced cell death seemed to occur predominantly via apoptosis through distribution of PpIX in mitochondria. These cell death events were enhanced by ferrochelatase inhibitors. These results indicated that ALA-based-PDA induced apoptotic cell death through a mitochondrial pathway and that ferrochelatase inhibitors might enhanced the effect of PDT for tumors even at low concentrations of ALA.

Photoinduced unfolding of beta-lactoglobulin mediated by a water-soluble porphyrin

We investigated the effects that the irradiation of a tetra-anionic porphyrin (mesotetrakis(sulfonatophenyl)porphyrin) noncovalently bound to beta-lactoglobulin (BLG) produces on the conformation of the protein. Although BLG is not a potential target for the biomedical applications of porphyrins, it is a useful model for investigating the effects of photoactive ligands on small globular proteins. We show in this paper that irradiation causes a large unfolding of the protein and that the conformational change is not mediated by the formation of reactive oxygen species. Instead, our data are consistent with an electron-transfer mechanism that is capable of triggering structural changes in the protein and causes the Trp19 residue to undergo chemical modifications to form a derivative of kynurenine. This demonstrates that protein unfolding is prompted by a type-III photosensitizing mechanisms. Type-III mechanisms have been suggested previously, but they have been largely neglected as useful mediators of biomolecular damage. Our study demonstrates that porphyrins can be used as mediators of localized protein conformational changes and that the biomedical applications as well as the mechanistic details of electron transfer between exogenous ligands and proteins merit further investigation.

Photodynamic inhibition of acetylcholinesterase after two-photon excitation of copper tetrasulfophthalocyanine

Sequential two-photon (2-gamma) activated copper tetrasulfophthalocyanine (CuPcS(4)) was shown capable of inactivating acetylcholinesterase (ACE). ACE activity was measured photometrically by the Ellman method. Simultaneous irradiation of ACE in the presence of CuPcS(4) with 514 nm (183 mW/cm(2)) and 670 nm (86 mW/cm(2)) continuous wave (CW) light induced a 20-50% increase in enzyme inhibition as compared to one-photon (1-gamma) irradiation, using either 514- or 670-nm (CW) light at the same fluences. The enzyme activity was not affected by CuPcS(4) or light alone, decreased linearly with the irradiation time, and was shown to be oxygen-dependent. We conclude that the photoinactivation of ACE with sequential 2-gamma irradiation involves reactive oxygen species produced by the interaction of the upper excited T(n) state of CuPcS(4) with molecular oxygen. As CuPcS(4) shows little activity as a conventional 1-gamma photosensitizer, unwanted side effects such as prolonged skin sensitivity are eliminated rendering 2-gamma photodynamic therapy advantageous for the treatment of selected medical applications.

Photosensitized degradation of losartan potassium in an extemporaneous suspension formulation

During development of an extemporaneous suspension formulation for losartan potassium, previously unknown degradation products were observed in experimental suspensions prepared in a commercial cherry syrup vehicle. These degradates increased rapidly when analytical solutions prepared from that suspension were exposed to ambient light. The structures of the degradates were determined using a combination of preparative HPLC, LC/MS, (13)C and (1)H NMR (1D and 2D), and mechanistic chemistry. Each degradate results from destruction of the imidazole ring of losartan. Formation of the two major degradates required exposure to light (UV or visible) and the presence of oxygen. Experiments using Rose Bengal (a singlet oxygen photosensitizer) and 1,4-diazabicyclooctane (DABCO; a singlet oxygen quencher) established that the major photodegradates are formed via the intermediacy of singlet oxygen. The identity of the photosensitizer in the formulation was not unequivocally determined; however, the experiments implicated the artificial flavoring in fulfilling this role.

Photodynamic treatment (ALA-PDT) suppresses the expression of the oncogenic Bcr-Abl kinase and affects the cytoskeleton organization in K562 cells

K562 is the chronic myelogenous leukemia (CML)-derived cell line that expresses high levels of chimeric oncoprotein Bcr-Abl. The deregulated (permanent) kinase activity of Bcr-Abl leads to continuous proliferation of K562 cells and their resistance to the apoptosis promotion by conventional drugs. The photodynamic treatment (PDT) based on the application of 5-aminolevulinic acid (ALA) and irradiation with blue light (ALA-PDT) resulted in the suppression of K562 cells proliferation. It was followed by a necrosis-like cell death [K. Kuzelová, D. Grebenová, M. Pluskalová, I. Marinov, Z. Hrkal, J. Photochem. Photobiol. B 73 (2004) 67-78]. ALA-PDT led to the perturbation of the Hsp90/p23 multichaperone complex of which the Bcr-Abl is the client protein. Bcr-Abl protein was suppressed whereas the bcr-abl mRNA level was not affected. Further on, we observed several changes in the cytoskeleton organization. We detected ALA-PDT-mediated disruption of filamental actin structure using FITC-Phalloidin staining. In connection with this we uncovered certain cytoskeleton organizing proteins involved in the cell response to the treatment. Among these proteins, Septin2, which plays a role in maintaining actin bundles, was suppressed. Another one, PDZ-LIM domain protein 1 (CLP36) was altered. This protein acts as an adaptor molecule for LIM-kinase which phosphorylates and thus inactivates cofilin. Cofilin was indeed dephosphorylated and could thus be activated and operate as an actin-depolymerizing factor. We propose the scheme of molecular response of K562 cells to ALA-PDT.

Two-photon absorption of copper tetrasulfophthalocyanine induces phototoxicity towards Jurkat cells in vitro

The feasibility to induce oxygen-independent tumour cell kill by two-photon excitation of copper tetrasulfophthalocyanine (CuPcS4) was studied in Jurkat cells in vitro. Following incubation with CuPcS4 cells were transferred to a closed cuvette and irradiated with 532 nm pulsed-laser or 680 nm continuous-laser light to evaluate the effect of either two- or one-photon excitation, respectively. Cell survival was measured using MTT and Trypan Blue exclusion tests. Cell viability decreased 10-20% following two-photon excitation while one-photon illumination did not affect cell survival. These data confirm that two-photon excitation of CuPcS4 to the upper excited triplet state results in the formation of toxic species suggesting its potential use as a sensitizer for the photodynamic treatment of poorly oxygenated tumours.

Early apoptotic features of K562 cell death induced by 5-aminolaevulinic acid-based photodynamic therapy

5-Aminolaevulinic acid-based photodynamic therapy (ALA-PDT) is used to eliminate cancerous cells through photoactivation of endogenously formed protoporphyrin IX (PPIX) following the administration of PPIX precursor, 5-aminolaevulinic acid (ALA). We report on the kinetics of PPIX accumulation and the mechanism of cytotoxic effects of ALA-PDT studied in the chronic myelogenous leukaemia derived cell line K562. The PPIX distribution and, consequently, cytotoxic effects were found to be heterogenous. A subpopulation of K562 cells accumulating PPIX to a lesser extent exhibits only transient cell cycle arrest. A fraction of cells, probably those with higher PPIX accumulation, are irreversibly damaged by ALA-PDT. We detected several signs of an early apoptosis: lowering of Bcl-xL expression, decrease of the mitochondrial and plasma membrane potential, the cytochrome c release into the cytoplasm, and the unmasking of the mitochondrial antigen 7A6. However, late apoptotic events were lacking: neither caspase-3 activation nor DNA fragmentation occurred. Instead, rapidly progressing cell necrosis resulting from plasma membrane damage was observed. We suggest that the high level of the antiapoptotic heat-shock proteins HSP70 and HSP27 found by us in the K562 cells is responsible for the inhibition of the apoptotic process upstream of caspases activation.

In vitro evaluation of the cytotoxic and mutagenic potential of the 5-aminolevulinic acid hexylester-mediated photodynamic therapy

Photodynamic therapy (PDT) of tumors with 5-aminolevulinic acid hexylester (h-ALA) causes photo-oxidative reactions in treated tissues. In order to study cytotoxic and/or mutagenic effects, cells of the tumor cell line RPMI 2650 as well as fibroblasts of the cell line WS 1 were given photodynamic treatment in vitro. The cells were photosensitized with a 1mM h-ALA-medium solution for 5h and illuminated with different light doses (0.5, 1.0, 1.5 and 2.0 J/cm2) using red light (633+/-20 nm). PDT-induced cytotoxic effects were determined by measurement of the mitotic index (MI) and the nuclear division index (NDI). Chromosome aberrations (CA) and micronuclei (MN) were recorded to study mutagenicity. After treatment of the photosensitized RPMI 2650 cells with a light dose of 2.0 J/cm2, the MI was significantly decreased to 16.9 per thousand in comparison with that of the h-ALA control (33.8 per thousand ). In photosensitized WS 1 cells, light doses up to 2.0 J/cm2 showed no significant effect. The NDI of photosensitized RPMI 2650 cells was significantly decreased by light doses from 1.0 to 2.0 J/cm2, whereas no significant effect was seen in WS 1 cultures. Thus, h-ALA-PDT only induced desirable cytotoxic effects in tumor cells, but not in the fibroblasts. After application of light doses from 0.5 to 2.0 J/cm2, photosensitized RPMI 2650 cultures showed CA in 7.0-7.5% of the metaphases, which was not a significant increase (h-ALA control: 5.5%). In WS 1 cultures metaphases containing CA varied non-significantly from 5.0 to 7.5%. The MN rates were approximately the same in illuminated RPMI 2650 cultures and in the corresponding h-ALA control (4.4-4.9 per thousand ). The MN rates of the illuminated WS 1 cultures also varied non-significantly from 4.5 to 5.0 per thousand in comparison with the h-ALA control (5.5 per thousand ). In the mutagenicity tests the h-ALA-PDT had no significant effect, neither on the tumor cells nor on the fibroblasts. In addition to the cytogenetic analysis, spectral karyotyping (SKY) was used to characterize the cell lines and gain more detailed information on possibly PDT-induced CA. The SKY evaluation also showed no significant increase of the CA rate, but confirmed the result of the CA test. Thus, within the scope of the experiments performed, a mutagenic potential of the h-ALA-PDT can be excluded.

Methylene Blue Binding to DNA with Alternating AT Base Sequence: Minor Groove Binding is Favored over Intercalation

The results presented in this paper on methylene blue (MB) binding to DNA with AT alternating base sequence complement the data obtained in two former modeling studies of MB binding to GC alternating DNA. In the light of the large amount of experimental data for both systems, this theoretical study is focused on a detailed energetic analysis and comparison in order to understand their different behavior. Since experimental high-resolution structures of the complexes are not available, the analysis is based on energy minimized structural models of the complexes in different binding modes. For both sequences, four different intercalation structures and two models for MB binding in the minor and major groove have been proposed. Solvent electrostatic effects were included in the energetic analysis by using electrostatic continuum theory, and the dependence of MB binding on salt concentration was investigated by solving the non-linear Poisson-Boltzmann equation. We find that the relative stability of the different complexes is similar for the two sequences, in agreement with the interpretation of spectroscopic data. Subtle differences, however, are seen in energy decompositions and can be attributed to the change from symmetric 5'-YpR-3' intercalation to minor groove binding with increasing salt concentration, which is experimentally observed for the AT sequence at lower salt concentration than for the GC sequence. According to our results, this difference is due to the significantly lower non-electrostatic energy for the minor groove complex with AT alternating DNA, whereas the slightly lower binding energy to this sequence is caused by a higher deformation energy of DNA. The energetic data are in agreement with the conclusions derived from different spectroscopic studies and can also be structurally interpreted on the basis of the modeled complexes. The simple static modeling technique and the neglect of entropy terms and of non-electrostatic solute-solvent interactions, which are assumed to be nearly constant for the compared complexes of MB with DNA, seem to be justified by the results.

Rheological Characterization of Photochemical Changes of Ethyl(hydroxyethyl)cellulose Dissolved in Water in the Presence of an Ionic Surfactant and a Photosensitizer

The effects of addition of the photosensitizer riboflavin (RF) to semidilute solutions of the systems ethyl(hydroxyethyl)cellulose (EHEC)/water, EHEC/sodium dodecyl sulfate (SDS), and EHEC/cetyltrimethylammonium bromide (CTAB) on the turbidity and the linear viscoelasticity are studied. The turbidity behavior and the cloud point (CP) are influenced by the addition of RF to the EHEC/SDS system, whereas no discernible change is observed for the other systems. The rheological features of all systems are affected by the presence of RF at lower temperatures, whereas at temperatures close to the CP, only a slight effect is detected. Both the EHEC/SDS and EHEC/CTAB systems evolve thermoreversible gels at the same temperature (37.5 degrees C), but in the presence of RF, the EHEC/CTAB system does not form a gel, whereas the gel temperature for the EHEC/SDS system is depressed (32.5 degrees C). Light irradiation of RF in the EHEC/SDS/RF system causes fragmentation of the network and a higher temperature is required to re-form the incipient gel network. The photochemical degradation of EHEC gives rise to a decrease in the dynamic moduli and the complex viscosity for all of the three systems. The effect is strengthened at higher temperatures and it is most pronounced for the EHEC/SDS system.

A light in multidrug resistance: photodynamic treatment of multidrug-resistant tumors

The major drawback of cancer chemotherapy is the development of multidrug-resistant (MDR) tumor cells, which are cross-resistant to a broad range of structurally and functionally unrelated agents, making it difficult to treat these tumors. In the last decade, a number of authors have studied the effects of photodynamic therapy (PDT), a combination of visible light with photosensitizing agents, on MDR cells. The results, although still inconclusive, have raised the possibility of treating MDR tumors by PDT. This review examines the growing literature concerning the responses of MDR cells to PDT, while stressing the need for the development of new photosensitizers that possess the necessary characteristics for the photodynamic treatment of this class of tumor.

Riboflavin-photosensitized changes in aqueous solutions of alginate. Rheological studies

Interactions between photoexcited riboflavin (RF), promoted by irradiation in the range of 310-800 nm, and alginate have been studied in air equilibrated aqueous solutions with the aid of rheological methods. Light irradiation of RF causes under aerobic conditions fragmentation of alginate and a decrease in the shear viscosity and other rheological parameters of its solutions. The decrease is most pronounced in concentrated polymer solutions. The photochemical degradation of alginate is inhibited in the presence of the quenchers/scavengers d-mannitol, glutathione, potassium iodide, and sodium azide and in excess oxygen. The addition of thiourea to alginate-RF solutions leads to enhanced degradation of the polymer. Significant shear-thinning effects and deviations from the Cox-Merz rule are observed at higher polymer concentrations.

Mitochondrial and endoplasmic reticulum stress-induced apoptotic pathways are activated by 5-aminolevulinic acid-based photodynamic therapy in HL60 leukemia cells

We studied the mechanism of the cytotoxic effects of 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT; induction with 1 mM ALA for 4 h followed by a blue light dose of 18 J/cm(2)) on the human promyelocytic leukemia cell line HL60 using biochemical and electron microscopy methods. The disruption of mitochondrial membrane potential, deltapsi(m), was paralleled by a decrease in ATP level, unmasking of the mitochondrial antigen 7A6, release of cytochrome c into the cytoplasm, activation of caspases 9 and 3 and cleavage of poly(ADP-ribose) polymerase (PARP). This was followed by DNA fragmentation. These data suggest that ALA-PDT activates the mitochondrial apoptotic pathway. The level of endoplasmic reticulum Ca(2+)-binding chaperones ERp57 and ERp72 and of anti-apoptotic proteins Bcl-2 and Bcl-x(L) was decreased whereas that of Ca(2+)-binding protein calmodulin and the stress protein HSP60 was elevated following ALA-PDT. Inhibition of the initiator caspase 9, execution caspase 3 and Ca(2+)-dependent protease m-calpain, did not prevent DNA fragmentation. We conclude that, in our in vitro model, ALA-based photodynamic treatment initiates several signaling processes in HL60 cells that lead to rapidly progressing apoptosis, which is followed by slow necrosis. Two apoptotic processes proceed in parallel, one representing the mitochondrial pathway, the other involving disruption of calcium homeostasis and activation of the endoplasmic reticulum stress-mediated pathway.

Photosensitizer initiated attacks on DNA under dry conditions and their inhibition: a DNA archiving issue

Long-term aging of dry DNA is thought to be due to the attack of diverse cascades of reactive species with probably, no one single initiator of the cascades explaining all circumstances. Photosensitizer-initiated reactions from methylene blue and riboflavin were used to generate two model systems of reactive species around dry DNA in order to understand such systems and how to block them. Damage was assessed using plasmid DNA as a substrate with an in-situ microgel electrophoretic technique. Photodynamic methylene blue damage to DNA was very oxygen dependent but not that of riboflavin. This indicates that indirect type II pathways, probably via singlet oxygen were important for methylene blue but not for riboflavin. In both the absence and presence of oxygen, the DNA protection offered by dry caffeine and urate to both photodynamic agents indicated that most DNA attack was via electrophilic species. Overall, protection of dry archived DNA from spontaneously reactive species such as free radicals appears to be a real issue and, as expected, the predominant species in air appear to involve oxygen but not exclusively or necessarily so.

Photodynamic therapy: a new concept in medical treatment

A new concept in the therapy of both neoplastic and non-neoplastic diseases is discussed in this article. Photodynamic therapy (PDT) involves light activation, in the presence of molecular oxygen, of certain dyes that are taken up by the target tissue. These dyes are termed photosensitizers. The mechanism of interaction of the photosensitizers and light is discussed, along with the effects produced in the target tissue. The present status of clinical PDT is discussed along with the newer photosensitizers being used and their clinical roles. Despite the promising results from earlier clinical trials of PDT, considerable additional work is needed to bring this new modality of treatment into modern clinical practice. Improvements in the area of light source delivery, light dosimetry and the computation of models of treatment are necessary to standardize treatments and ensure proper treatment delivery. Finally, quality assurance issues in the treatment process should be introduced.

ESR studies of a series of phthalocyanines. Mechanism of phototoxicity. Comparative quantitation of O2-. using ESR spin-trapping and cytochrome c reduction techniques

ESR experiments with 2,2,6,6-tetramethyl-4-piperidone (4-oxo-TEMP) and the spin-trap 5,5-dimethyl pyrroline-N-oxide (DMPO) have been performed on a series of new phthalocyanines: the bis(tri-n-hexylsiloxy) silicon phthalocyanine ([(nhex)3SiO]2SiPc), the hexadecachloro zinc phthalocyanine (ZnPcCl16), the hexadecachloro aluminum phthalocyanine (AlPcCl16), the hexadecachloro aluminum phthalocyanine sulfate (HSO4AlPcCl16), whose photocytotoxicity has been studied against various leukemic and melanotic cell lines. Type I and Type II pathways occur simultaneously in DMF although the Type II seems to be prevalent. These results are not changed when the bis(tri-n-hexylsiloxy) silicon phthalocyanine is entrapped into liposomes. By contrast, the Type I process is favored in membrane models for all the perchlorinated phthalocyanines. This modified behavior may be accounted on a possible stacking of phthalocyanines in membranes and a preventing effect of axial ligands against aggregation in the case of the bis(tri-n-hexylsiloxy) silicon phthalocyanine. The photodynamic action of zinc perchlorinated phthalocyanine is not dependent on singlet oxygen, phototoxicity of this molecule being essentially mediated by oxygen free radicals. Quantitation of the superoxide radical was accomplished, with good agreement, by two techniques: the cytochrome c reduction and the ESR quantitation based on the double integration of the first derivative of the ESR signal. The disproportionation of the superoxide radical or degradation of the spin-trap seem to be avoided in aprotic solvents such as DMF.

Sensitized photomodification of single-stranded DNA by a binary system of oligonucleotide conjugates

A photoactivatable binary system of oligonucleotide conjugates that form reactive species when assembling on a target nucleotide sequence has been developed. The binary system consists of two oligonucleotides. One contains a photosensitizing group, and the second contains a photoreactive group. Binding of the oligonucleotides to adjacent sequences in the target nucleic acid brings the groups in contact, which allows transfer of the absorbed energy from the sensitizer to the reagent and triggers crosslinking of the reagent to the target. One advantage of the binary system is the improved specificity, which is determined by independent binding of two oligonucleotides to the target sequence. Another advantage is the very high efficiency of the reaction achieved because each molecule of the target-bound sensitizing conjugate can activate many photoreactive oligonucleotide conjugate molecules bound to the target sequence.

Light induces peroxidation in retina by activating prostaglandin G/H synthase

Prostaglandin G/H synthase (PGHS) has been shown to generate peroxides to a significant extent in the retina and absorbs light at the lower end of the visible spectrum. We postulated that PGHS could be an important initial source of peroxidation in the retina exposed to light, which would in turn alter retinal function. Exposure of pig eyes (in vivo) to light (350 fc/3770 lx) caused after 3 h a 50% increase and by 5 h a 30% decrease in a- and b-wave amplitudes of the electroretinogram (ERG) which were comparable at 380-650 nm and 380-440 nm but were not observed at wavelengths > 450 nm. These effects of light were prevented by free radical scavengers (dimethylthiourea and high-dose allopurinol) and PGHS inhibitors (naproxen and diclofenac), but stable analogs of prostaglandins did not affect the ERG. Both increases and subsequent decreases in ERG wave amplitudes following light exposure in vivo were associated with increases in retinal prostaglandin and malondialdehyde (peroxidation product) levels, which were inhibited by the nonselective PGHS blockers, naproxen and diclofenac. Similar observations were made in vitro on isolated porcine eyecups as well as on retinal membranes exposed to light (250 fc/ 2700 lx) 380-650 nm and 380-440 nm but not at > 500 nm. Both PGHS-1 and PGHS-2 contributed equivalently to light-induced prostaglandin synthesis, as shown after selective PGHS-2 blockers, but mRNA expression of PGHS-1 and 2 was not affected by light. Finally, light stimulated activities of pure PGHS-1 and PGHS-2 isozymes, and these were also shown to produce superoxide radical (detected with fluorogenic spin trap, proxyl fluorescamine). Taken together, data suggest that PGHS- (1 and 2) is activated by short wavelength visible light, and in the retina is an important source of reactive oxygen species which in turn alter retinal electrophysiological function. PGHS thus seems a likely chromophore in setting forth photic-induced retinal injury. Findings provide an explanation for increased sensitivity of the retina to visible light predominantly at the far blue range of its spectrum.

Saccharomyces cerevisiae mutants defective in heme biosynthesis as a tool for studying the mechanism of phototoxicity of porphyrins

Mutants of Saccharomyces cerevisiae accumulating uroporphyrin (UP) or protoporphyrin (PP) were used as a model for the in vivo phototoxic effect of porphyrins observed in the human skin photosensitivity associated with porphyrias (porphyria cutanea tarda and erythropoietic protoporphyria). We have found that UP is localized in vacuoles and PP is present in all compartments except vacuoles in yeast cells. Endogenous PP is much more effective as a photosensitizer of yeast cells than UP. Protoporphyrin action is strictly dependent on the presence of oxygen. In contrast, UP displays a phototoxic effect even if oxygen is not present in the suspension, implicating a free radical mechanism that operates in anaerobiosis upon photosensitization by UP. Catalase or superoxide dismutase deficiency affects photosensitization by UP. A possible mechanism of UP photosensitizing activity is discussed.