Generation of superoxide and singlet oxygen from α-tocopherolquinone and analogues.

Three potential routes to generation of reactive oxygen species from a tocopherolquinone have been identified. The quinone of the water-soluble vitamin E analogue Trolox C (Trol-Q) is reduced by hydrated electron and isopropanol a hydroxyalkyl radical, and the resulting semiquinone reacts with molecular oxygen to form superoxide with a second order rate constant of 1.3 x 108 dm3 mol-1 s-1, illustrating the potential for redox cycling. Illumination (UV-A, 355 nm) of the quinone of 2,2,5,7,8-pentamethyl-6-hydroxychromanol (PMHC-Q) leads to a reactive short-lived (ca 10-6 s) triplet state, able to oxidise tryptophan with a second order rate constant greater than 109 dm3 mol-1 s-1. The triplet states of these quinones sensitize singlet oxygen formation with quantum yields of about 0.8. Such potentially damaging reactions of a tocopherolquinone may in part account for the recent findings that high levels of dietary vitamin E supplementation lack any beneficial effect and may lead to slightly enhanced levels of overall mortality

New Approaches to Photodynamic Therapy from Type I, II and III to Type IV Using One or More Photons

Photodynamic therapy (PDT) is an alternative cancer treatment to conventional surgery, radiotherapy and chemotherapy. It is based on activating a drug with light that triggers the generation of cytotoxic species that promote tumour cell killing. At present, PDT is mainly used in the treatment of wet age-related macular degeneration, for precancerous conditions of the skin (e.g. actinic keratosis) and in the palliative care of advanced cancers, for instance of the bladder or the oesophagus. PDT is still not used as a first line cancer treatment, which is surprising given the first clinical trials by Dougherty’s group dating back to the 1970’s. PDT has significant advantages over surgery or radiation therapy for low lying tumours due to better cosmetic outcome and localised treatment for the patients. However, despite these advantages and significant developments in optical technology that has enabled light penetration to deeper lying tumours, in excess of 5 cm, a lack of phase III clinical trials has slowed down the uptake of PDT by the healthcare sector as a frontline treatment in cancer. However research continues to demonstrate the potential benefits of PDT and the need to stimulate funding and uptake of clinical studies using next generation photosensitizers offering advanced targeted delivery, improved photodynamic dose combined with modern light delivery technologies. This review surveys the available PDT treatments and emerging novel developments in the field with a particular focus on two-photon techniques that are anticipated to improve the effectiveness of PDT in tissues at depth and on next generation drugs that work without the need of the presence of oxygen for photosensitization making them effective where hypoxia has taken hold

Photoreactivity of biologically active compounds. XIX: Excited states and free radicals from the antimalarial drug primaquine

The formation and reactivity of excited states and free radicals from primaquine was studied in order to evaluate the primary photochemical reaction mechanisms. The excited primaquine triplet was not detected, but is likely to be formed with a short lifetime (< 50 ns) and with a triplet energy < 250 kJ/mol as the drug is an efficient quencher of the fenbufen triplet and the biphenyl triplet, and forms 1O2 by laser flash photolysis (PQΦΔ = 0.025). Primaquine photoionises by a biphotonic process and also forms the monoprotonated cation radical (PQH2+•) by one electron oxidation by OH• (kq = 6.6•109 M-1s-1) and Br2•- (kq = 4.7•109 M-1s-1) at physiological pH, detected as a long-lived transient decaying essentially by a second order process (k2 = 7.4•108 M-1s-1). PQH2+• is scavenged by O2, although at a limited rate (kq = 1.0•106 M-1s-1). The reduction potential (E°) of PQH2+• / PQH+ is < +1015 mV. Primaquine also forms PQH2+• at pH 2.4, by one electron oxidation by Br2•- and proton loss (kq = 2.7•109 M-1s-1). The non-protonated cation radical (PQ+•) is formed during one electron oxidation with Br2•- at alkaline conditions (kq = 4.2•109 M-1s-1 at pH 10.8). The estimated pKa-value of PQH2+•/ PQ+• is pKa ~ 7-8. Primaquine is not a scavenger of O2•- at physiological pH. Thus self-sensitization by O2•- is eliminated as a degradation pathway in the photochemical reactions. Impurities in the raw material and photochemical degradation products initiate photosensitized degradation of primaquine in deuterium oxide, prevented by addition of the 1O2 quencher sodium azide. Photosensitized degradation by formation of 1O2 is thus important for the initial photochemical decomposition of primaquine, which also proceeds by free radical reactions. Formation of PQH2+• is expected to play an essential part in the photochemical degradation process in a neutral, aqueous medium

Time-resolved nanosecond fluorescence lifetime imaging and picosecond infrared spectroscopy of combretastatin A-4 in solution and in cellular systems

Fluorescence lifetime images of intrinsic fluorescence obtained with two-photon excitation at 630 nm are shown following uptake of a series of E-combretastatins into live cells, including human umbilical vein endothelial cells (HUVECs) that are the target for the anticancer activity of combretastatins. Images show distribution of the compounds within the cell cytoplasm and in structures identified as lipid droplets by comparison with images obtained following Nile red staining of the same cells. The intracellular fluorescent lifetimes are generally longer than in fluid solution as a consequence of the high viscosity of the cellular environment. Following incubation the intracellular concentrations of a fluorinated derivative of E combretastatin A4 in HUVECs are up to between 2 and 3 orders of magnitude higher than the concentration in the surrounding medium. Evidence is presented to indicate that at moderate laser powers (up to 6 mW) it is possible to isomerize up to 25% of the combretastatin within the femtolitre focal volume of the femtosecond laser beam. This suggests that it may be possible to activate the E-combretastatin (with low cellular toxicity) to the Z-isomer with high anticancer drug activity using two-photon irradiation. The isomerization of Z- and E-combretastatins by 266 nm irradiation has been probed by ultrafast time-resolved infrared spectroscopy. Results for the E-isomer show a rapid loss of excess vibrational energy in the excited state with a lifetime of 7 ps, followed by a slower process with a lifetime of 500 ps corresponding to the return to the ground state as also determined from the fluorescence lifetime. In contrast the Z-isomer, whilst also appearing to undergo a rapid cooling of the initial excited state, has a much shorter overall excited state lifetime of 14 ps

Nanoscale hydroxyl radical generation from multiphoton ionization of tryptophan

Exposure of solutions containing both tryptophan and hydrogen peroxide to a pulsed (~180 fs) laser beam at 750 nm induces luminescence characteristic of 5 hydroxytryptophan. The results indicate that 3-photon excitation of tryptophan results in photoionization within the focal volume of the laser beam. The resulting hydrated electron is scavenged by the hydrogen peroxide to produce the hydroxyl radical. The latter subsequently reacts with tryptophan to form 5-hydroxytryptophan. The involvement of hydroxyl radicals is confirmed by use of ethanol and nitrous oxide as scavengers and their effects on the fluorescence yield in this system. It is postulated that such multiphoton ionization of tryptophanyl residues in cellular proteins may contribute to the photodamage observed during imaging of cells and tissues using multiphoton microscopy

Three-dimensional imaging and uptake of the anticancer drug combretastatin in cell spheroids and photoisomerization in gels with multiphoton excitation

The uptake of E-combretastatins, potential pro-drugs of the anticancer Z-isomers, into multicellular spheroids has been imaged by intrinsic fluorescence in three dimensions using two-photon excited fluorescence lifetime imaging with 625 nm ultrafast femtosecond laser pulses. Uptake is initially observed at the spheroid periphery but extends to the spheroid core within 30 minutes. Using agarose gels as a three-dimensional model, the conversion of Z(trans) E(cis) via two-photon photoisomerization is demonstrated and the location of this photochemical process may be selected precisely within the micron scale in all three dimensions at depths up to almost 2 mm. We discuss these results for enhanced tissue penetration at longer near-infrared wavelengths for cancer therapy and up to three-photon excitation and imaging using 930 nm laser pulses with suitable combretastatin analogues

Design and Synthesis of Potent in Vitro and in Vivo Anticancer Agents Based on 1-(3′,4′,5′-Trimethoxyphenyl)-2-Aryl-1H-Imidazole

A novel series of tubulin polymerization inhibitors, based on the 1-(3',4',5'-trimethoxyphenyl)-2-aryl-1H-imidazole scaffold and designed as cis-restricted combretastatin A-4 analogues, was synthesized with the goal of evaluating the effects of various patterns of substitution on the phenyl at the 2-position of the imidazole ring on biological activity. A chloro and ethoxy group at the meta- and para-positions, respectively, produced the most active compound in the series (4o), with IC50 values of 0.4-3.8 nM against a panel of seven cancer cell lines. Except in HL-60 cells, 4o had greater antiproliferative than CA-4, indicating that the 3'-chloro-4'-ethoxyphenyl moiety was a good surrogate for the CA-4 B-ring. Experiments carried out in a mouse syngenic model demonstrated high antitumor activity of 4o, which significantly reduced the tumor mass at a dose thirty times lower than that required for CA-4P, which was used as a reference compound. Altogether, our findings suggest that 4o is a promising anticancer drug candidate that warrants further preclinical evaluation

Global Diversity of Ascidiacea

The class Ascidiacea presents fundamental opportunities for research in the fields of development, evolution, ecology, natural products and more. This review provides a comprehensive overview of the current knowledge regarding the global biodiversity of the class Ascidiacea, focusing in their taxonomy, main regions of biodiversity, and distribution patterns. Based on analysis of the literature and the species registered in the online World Register of Marine Species, we assembled a list of 2815 described species. The highest number of species and families is found in the order Aplousobranchia. Didemnidae and Styelidae families have the highest number of species with more than 500 within each group. Sixty percent of described species are colonial. Species richness is highest in tropical regions, where colonial species predominate. In higher latitudes solitary species gradually contribute more to the total species richness. We emphasize the strong association between species richness and sampling efforts, and discuss the risks of invasive species. Our inventory is certainly incomplete as the ascidian fauna in many areas around the world is relatively poorly known, and many new species continue to be discovered and described each year

Digital engagement methods for earthquake and fire preparedness:a review

Natural or human-made hazards may occur at any time. Although one might assume that individuals plan in advance for such potentially damaging events, the existing literature indicates that most communities remain inadequately prepared. In the past, research in this area has focused on identifying the most effective ways to communicate risk and elicit preparedness by means of public hazard education campaigns and risk communication programmes. Today, web- and mobile-based technologies are offering new and far-reaching means to inform communities on how to prepare for or cope with extreme events, thus significantly contributing to community preparedness. Nonetheless, their practical efficacy in encouraging proactive hazard preparedness behaviours is not yet proven. Building on behaviour change interventions in the health field and looking in particular at earthquakes and fire hazards, the challenging RISK team has reviewed the currently active websites, Web, and mobile applications that provide information about earthquake and home fire preparedness. The review investigates the type of information provided, the modality of delivery, and the presence of behaviour change techniques in their design. The study proves that most of the digital resources focus on a single hazard and fail to provide context-sensitive information that targets specific groups of users. Furthermore, behaviour change techniques are rarely implemented in the design of these applications and their efficacy is rarely systematically evaluated. Recommendations for improving the design of Web- and mobile-based technologies are made so as to increase their effectiveness and uptake for a multi-hazard approach to earthquake and home fire preparedness