Photosensitization of Biomolecules by Phenothiazine Derivatives

A Trojan horse approach for enhancing the cellular uptake of a ruthenium nitrosyl complex

Ruthenium nitrosyl (RuNO) complexes continue to attract significant research interest due to several appealing features that make these photoactivatable nitric oxide (NO˙) donors attractive for applications in photoactivated chemotherapy. Interesting examples of molecular candidates capable of delivering cytotoxic concentrations of NO˙ in aqueous media have been discussed. Nevertheless, the question of whether most of these highly polar and relatively large molecules are efficiently incorporated by cells remains largely unanswered. In this paper, we present the synthesis and the chemical, photophysical and photochemical characterization of RuNO complexes functionalized with 17α-ethinylestradiol (EE), a semisynthetic steroidal hormone intended to act as a molecular Trojan horse for the targeted delivery of RuNO complexes. The discussion is centered around two main molecular targets, one containing EE (EE-Phtpy-RuNO) and a reference compound lacking this biological recognition fragment (Phtpy-RuNO). While both complexes displayed similar optical absorption profiles and NO˙ release efficiencies in aqueous media, important differences were found regarding their cellular uptake towards dermal fibroblasts, with EE-Phtpy-RuNO gratifyingly displaying a remarkable 10-fold increase in cellular uptake when compared to Phtpy-RuNO, thus demonstrating the potential drug-targeting capabilities of this biomimetic steroidal conjugate.

Trends and targets in antiviral phototherapy

Photodynamic therapy (PDT) is a well-established treatment option in the treatment of certain cancerous and pre-cancerous lesions. Though best-known for its application in tumor therapy, historically the photodynamic effect was first demonstrated against bacteria at the beginning of the 20^th century. Today, in light of spreading antibiotic resistance and the rise of new infections, this photodynamic inactivation (PDI) of microbes, such as bacteria, fungi, and viruses, is gaining considerable attention. This review focuses on the PDI of viruses as an alternative treatment in antiviral therapy, but also as a means of viral decontamination, covering mainly the literature of the last decade. The PDI of viruses shares the general action mechanism of photodynamic applications: the irradiation of a dye with light and the subsequent generation of reactive oxygen species (ROS) which are the effective phototoxic agents damaging virus targets by reacting with viral nucleic acids, lipids and proteins. Interestingly, a light-independent antiviral activity has also been found for some of these dyes. This review covers the compound classes employed in the PDI of viruses and their various areas of use. In the medical area, currently two fields stand out in which the PDI of viruses has found broader application: the purification of blood products and the treatment of human papilloma virus manifestations. However, the PDI of viruses has also found interest in such diverse areas as water and surface decontamination, and biosafety.

Light-enhanced antibiotic activity of Brazilian medical plants (Croton campestris A, Ocimum gratissimum L and Cordia verbenaceae DC)

Background: Although broad-band ultraviolet (UV)-A has been described as a therapeutic option for various skin diseases, there are few studies investigating the efficacy of UV-A irradiation in treating diseases related to infectious agents. Objective: Evaluate the light-enhanced antibacterial activity of Brazilian medical plants, Croton campestris A (Euphorbiaceae), Ocimum gratissimum L. (Lamiaceae), and Cordia verbenaceae DC (Boraginaceae). Methods: Hexane extracts of Croton campestris A., Ocimum gratissimum L., and Cordia verbenaceae DC were assayed using a UV-A exposure method against strains of Staphylococcus aureus and Escherichia coli. Assays were performed in triplicate with and without exposure to UV-A radiation to test for light-activated or lightenhanced antibacterial activity. Results: All extracts showed activity against the S. aureus strain. Extracts of O. gratissimum and C. verbenaceae were the most active after exposure to UV-A light, with an increase in antibacterial activity of 140 and 100%, respectively. No extract showed light-activated antibacterial activity against E. coli. Conclusion: C. campestris, O. gravissimum and C. verbenaceae showed light-enhanced antibiotic activity. This suggests that phytochemical investigations may be warranted.

Fate of the drug chlorpromazine in river water according to laboratory assays. Identification and evolution over time of degradation products. Sorption to sediment

Toxic effects of the non-biodegradable drug chlorpromazine and its degradation products have been reported on microorganisms in aqueous media. Here, chlorpromazine degradation assays in forced and non-forced conditions have been done to know its persistence and degradation products in river water. Sunlight irradiation promotes the complete degradation of chlorpromazine (2 μg L(-1)) in less than 4 h, but if the exposure to sunlight is limited chlorpromazine is detected during 4 weeks in river water. Sixteen degradation products in surface water are described for first time after solid-phase extraction and analysis by ultra-pressure liquid chromatography/quadrupole time-of-flight/mass spectrometry; their structures are proposed from the molecular formulae of the fragment-ions observed in high-resolution tandem mass spectra. Hydroxylation and oxidation products such as chlorpromazine sulfoxide, 2-hydroxypromazine and 2-hydroxypromazine sulfoxide were predominant degradation products in the early stages; some benzo[1,4]thiazin-6-ol derivatives resulting from the breakdown of the phenothiazine core were the major and relatively stable products after 20 weeks under non-forced conditions. A degradation pathway of chlorpromazine in water is outlined. Moreover, it is shown that chlorpromazine is very strongly adsorbed on sediment while the degradation products that kept the promazine core have a notable capacity of sorption, too; sorption coefficients are calculated. Finally, a prediction about the toxicity of the degradation products in aquatic ecosystems suggests that some of them have toxicities similar, or even higher, than chlorpromazine.

DNA photo-cleaving agents in the far-red to near-infrared range – a review

Ideal photonucleases for clinical applications cleave DNA upon activation with deeply penetrating far-red to near-infrared light.

An insight on bacterial cellular targets of photodynamic inactivation

The emergence of microbial resistance is becoming a global problem in clinical and environmental areas. As such, the development of drugs with novel modes of action will be vital to meet the threats created by the rise in microbial resistance. Microbial photodynamic inactivation is receiving considerable attention for its potentialities as a new antimicrobial treatment. This review addresses the interactions between photosensitizers and bacterial cells (binding site and cellular localization), the ultrastructural, morphological and functional changes observed at initial stages and during the course of photodynamic inactivation, the oxidative alterations in specific molecular targets, and a possible development of resistance.

The photoinduced transformation of fluorescent DNA base analogue tC triggers DNA melting

While fluorescent analogues of the canonical nucleobases have proven to be highly valuable in a large number of applications, up until today, fluorescent DNA base analogues remain virtually inapplicable for single-molecule fluorescence experiments which require extremely bright and photostable dyes. Insight into the photodegradation processes of these fluorophores is thus a key step in the continuous development towards dyes with improved performances. Here, we show that the commercially available fluorescent nucleobase analogue tC under intense long-term illumination and in the presence of O2 is degraded to form a single photoreaction product which we suggest to be the sulfoxide form of tC. The photoproduct is characterized by a blue-shifted absorption and a less intense fluorescence compared to that of tC. Interestingly, when tC is positioned inside double-stranded DNA this photodriven conversion of tC to its photoproduct greatly reduces the duplex stability of the overall double helix in which the probe is positioned. Since tC can be excited selectively at 400 nm, well outside the absorption band of the natural DNA bases, this observation points towards the application of tC as a general light-triggered switch of DNA duplex stability.

Ready biodegradability of trifluoromethylated phenothiazine drugs, structural elucidation of their aquatic transformation products, and identification of environmental risks studied by LC-MS( n ) and QSAR

The environmental fate of transformation products from organic pollutants such as drugs has become a new research area of increasing interest over the last few years. Whereas in the past mainly parent compounds or their major human metabolites were studied, new questions have arisen what compounds could be formed during incomplete degradation in the aquatic environment and what effects the resulting transformation products might have on nature and mankind. Psychiatric drugs are among the most important prescription drugs worldwide, but so far only little data is provided upon their degradation behavior. This especially accounts for tricyclic antipsychotic drugs of the phenothiazine class. Therefore, the degradation of such drugs was investigated in this study. In this study the aerobic Closed Bottle test (The Organisation for Economic Co-operation and Development (OECD) 301D) was used to assess the ready biodegradability of three trifluoromethylated phenothiazine drugs: fluphenazine, triflupromazine, and trifluoperazine. As it is known from literature that phenothiazine drugs can easily form various photolytic transformation products under light exposure, photochemical transformation was also investigated. Since transformation products are usually not available commercially, the calculation of environmental parameters with the aid of quantitative structure activity relationship (QSAR) software was used for first evaluation of these compounds. According to the OECD test guideline, all trifluoromethylated phenothiazines had to be classified as not readily biodegradable. Chromatographic data revealed the formation of some transformation products. Comparing retention time and mass spectrometric data with the analytical results of the light exposure experiments, we found peaks with the same retention time and mass spectra. So these transformation products were not of bacterial, but photolytic, origin and are formed very quickly even under low light doses. A special chromatographic column and solvent gradient along with multiple stage mass spectrometric fragmentation experiments uncovered the presence of, in total, nine photolytic transformation products and allowed for their structural elucidation. Typical modifications of the molecules were sulfoxidation, exocyclic N-oxidation, and transformation of the trifluoromethyl to a carboxylic moiety. The obtained results of the QSAR calculations show that all transformation products are highly mobile in the aquatic environment and elimination through biotic or abiotic pathways cannot be expected. Transformation products of trifluoromethylated phenothiazine drugs have to be expected in the aquatic environment, yet nothing is known about their toxicological properties. Therefore, further risk assessment upon these drugs and their fate is strongly recommended.

Pitavastatin, a new HMG-CoA reductase inhibitor, induces phototoxicity in human keratinocytes NCTC-2544 through the formation of benzophenanthridine-like photoproducts

This study reports the results of an investigation of the phototoxicity mechanism induced by pitavastatin and its photoproducts, namely 6-cyclopropyl-10-fluoro-7,8-dihydrobenzo[k]phenanthridine (PP3) and 6-cyclopropyl-10-fluorobenzo[k]phenanthridine (PP4). The phototoxicity was tested in human keratinocytes cell lines NCTC-2544, and the results proved that under the same conditions, all three compounds exhibited phototoxic effects in the model tested. The reduction in cell viability was found to be both concentration- and UVA dose-dependent. A point of note is that both the photoproducts produced a dramatic decrease in cell viability with GI(50) values one order of magnitude lower compared to the parent compound. In particular, the fully aromatic derivative (PP4) showed the highest antiproliferative activity. Flow cytometric analysis indicated that pitavastatin and the photoproduct PP4 principally induced necrosis, as revealed by the large appearance of propidium iodide-positive cells and also confirmed by the rapid drop in cellular ATP levels. Further studies committed to better understanding of photoinduced cell death mechanism(s) revealed that neither pitavastatin nor PP4 induced mitochondrial depolarization or lysosomal damage, but, interestingly, extensive cell lipid membrane peroxidation along with a significant oxidation of model proteins occurred, suggesting that pitavastatin and PP4 exert their phototoxic effect mainly in the cellular membranes. The present results suggest that the phototoxicity of pitavastatin may be mediated by the formation of benzophenanthridine-like photoproducts that appear to have high potential as photosensitizers.

Potential phototoxicity of rosuvastatin mediated by its dihydrophenanthrene-like photoproduct

In this work, rosuvastatin has been used to gain insight into the molecular basis of statin photosensitization. This lipid-lowering drug, also known as "superstatin", contains a 2-vinylbiphenyl-like moiety and has been previously described to decompose under solar irradiation, yielding stable dihydrophenanthrene analogues. During photophysical characterization of rosuvastatin, only a long-lived transient at ca. 550 nm was observed and assigned to the primary photocyclization intermediate. Thus, the absence of detectable triplet-triplet absorption and the low yield of fluorescence rules out the role of the parent drug as an efficient sensitizer. In this context, the attention has been placed on the rosuvastatin main photoproduct (ppRSV). Indeed, the photobehavior of this dihydrophenanthrene-like compound presents the essential components needed for an efficient biomolecule photosensitizer i.e. (i) a high intersystem crossing quantum yield (Φ(ISC) = 0.8), (ii) a triplet excited state energy of ca. 67 kcal mol(-1), and (iii) a quantum yield of singlet oxygen formation (Φ(Δ)) of 0.3. Furthermore, laser flash photolysis studies revealed a triplet-triplet energy transfer from the triplet excited state of ppRSV to thymidine, leading to the formation of cyclobutane thymidine dimers, an important type of DNA lesion. Finally, tryptophan has been used as a probe to investigate the type I and/or type II character of ppRSV-mediated oxidation. In this way, both an electron transfer process giving rise to the tryptophanyl radical and a singlet oxygen mediated oxidation were observed. On the basis of the obtained results, rosuvastatin, through its major photoproduct ppRSV, should be considered as a potential sensitizer.

Photodynamic therapy based on 5-aminolevulinic acid and its use as an antimicrobial agent

Exogenous 5-aminolevulinic acid (ALA) is taken up directly by bacteria, yeasts, fungi, and some parasites, which then induces the accumulation of protoporphyrin IX (PPIX). Subsequent light irradiation of PPIX leads to the inactivation of these organisms via photodamage to their cellular structures. ALA uptake and light irradiation of PPIX produced by host cells leads to the inactivation of other parasites, along with some viruses, via the induction of an immune response. ALA-mediated PPIX production by host cells and light irradiation result in the inactivation of other viruses via either the induction of a host cell response or direct photodynamic attack on viral particles. This ALA-mediated production of light-activated PPIX has been extensively used as a form of photodynamic therapy (PDT) and has shown varying levels of efficacy in treating conditions that are associated with microbial infection, ranging from acne and verrucae to leishmaniasis and onychomycosis. However, for the treatment of some of these conditions by ALA-based PDT, the role of an antimicrobial effect has been disputed and in general, the mechanisms by which the technique inactivates microbes are not well understood. In this study, we review current understanding of the antimicrobial mechanisms used by ALA-based PDT and its role in the treatment of microbial infections along with its potential medical and nonmedical applications.

Influence of photosensitizer solvent on the mechanisms of photoactivated killing of Enterococcus faecalis

This study evaluated the mechanisms involved and the influence of photosensitizer solvent in the killing of Enterococcus faecalis using photodynamic therapy (PDT). Enterococcus faecalis cells incubated with 100 microm methylene blue dissolved in water and in MIX (a mixture of glycerol:ethanol:water) were irradiated with 664 nm diode laser (63.69 J cm(-2)). The effect of PDT on the viability of bacteria, and the functional integrity of cell wall, chromosomal DNA and membrane proteins were analyzed. The bactericidal action of PDT was significantly higher when a MIX-based photosensitizer solvent was used (P<0.001). Fluorimetric and fluorescence microscopy-based analysis showed the functional impairment of E. faecalis cell wall which was significantly higher when a MIX-based photosensitizer solvent was used (P<0.001). PDT with MIX-based photosensitizer solvent showed extensive damage to chromosomal DNA. However, both PDT conditions showed similar trend in the degradation of membrane proteins, although cross-linked proteins were evident only in PDT conducted with MIX-based photosensitizer solvent. The findings from our study showed that PDT destroyed the functional integrity of cell wall, DNA and membrane proteins of E. faecalis. The degrees of damage on these targets were influenced by the photosensitizer solvent used during PDT.

SPECTROSCOPIC AND ELECTROCHEMICAL PROPERTIES OF 2-AMINOPHENOTHIAZINE

Phenothiazines derivatives are versatile compounds that are used in many fields, depending on the type and position of the substitution on the parent molecule. The photochemical, photophysical and electrochemical properties of several phenothiazine derivatives have been previously reported in detail. However, no reports have been presented for 2-aminophenothiazine (APH), a candidate that provides for the further chemical modification and the introduction of specific substituents. In this work, the photophysical and electrochemical properties of APH were measured in acetonitrile. The APH ground state absorption and fluorescence spectrum (phi(f) < 0.01) are similar to the corresponding that of PH parent molecule. A mono exponential decay fluorescence lifetime of 0.65 ns was determined for APH in acetonitrile. Characterization of the 355 nm nanosecond laser flash photolysis transient species reveals the presence of the triplet-triplet transient intermediate with a high intersystem crossing quantum yield (phi(T) = 0.72 +/- 0.07), indicating that the APH main excited state deactivation channel is intersystem crossing. The oxidation potential of APH is lower than phenothiazine parent molecule ((0.38 V vs 0.69 V vs Ag/AgCl(sat)). Altogether, these results show that APH has photochemical and photophysical properties similar to the phenothiazine parent molecule, but with the possibility of providing an amino functionality at 2-position for further chemical modification.