Physicochemical modeling of the role of free radicals in photodynamic therapy

Mitochondria-Targeted Two-Photon Fluorescent Photosensitizers for Cancer Cell Apoptosis via Spatial Selectability

Organelle-targeted photosensitizers have been reported to be effective cell apoptosis agents. Mitochondria is recognized as an ideal target for cancer treatment due to its central role in oxidative metabolism and apoptosis. Meanwhile, two-photon (TP) fluorescence microscopy has become a powerful tool for fluorescence imaging in biological events based on its minimizing photodamage/photobleaching and intrinsic 3D resolution in deep tissues and in vivo. In this study, a series of novel mitochondrial-targeted TP fluorescent photosensitizers (TP-tracers) are designed, synthesized, and systematically investigated. These TP-tracers exhibit extraordinary anti-interference capability among different cations, anions, and amino acids as well as the insensitivity to the changes of pH and complex biological environments. TP-tracers are further used in fluorescence living cells, Drosophila brains, and zebrafish imaging with low cytotoxicity, excellent mitochondria-targeting, and TP properties. The results demonstrate efficient mitochondria-targeting cell selective apoptosis based on TP-activated cancer cells with highly single cell selectivity, and the pharmacokinetic study reveals that MitoY2 does not have accumulation in rats. It is believed that these molecules hold great potential in TP-related smart phototherapy.

Effect of tetrapyrrole-based photosensitizers on spin trapping by 5,5-dymethyl-1-pyrroline N-oxide

Kinetics of the effect of three different tetrapyrrole-based photosenzitizers, pheophorbide a, meso-tetrahydroxyphenyl chlorin, and 3,7-bis(2-carboxyethyl)-2,8,12,17-tetramethyl-13,18-bis[(5-propoxycarbonyl-3-4-dihidroxy-phenyloxy) ethyl] porphyrin, on spin trapping with of 5,5-dymethyl-1-pyrroline N -oxide (DMPO) – a method widely applied in photodynamic therapy research – was investigated in the chemical model system of initiated oxidation of ethylbenzene. Spin adducts were measured by ESR spectroscopy, and kinetics of the consumption of the spin trap and accumulation of main products of oxidation (acetophenon, 1-phenyl-ethanol and 1-phenyl-ethyl-hydroperoxide) were followed using high performance liquid chromatography. The ESR spectrum of the non-illuminated system corresponded to an adduct formed between the spin trap and α–phenylethyl peroxyl radical, while under illumination, the spectrum indicated competitive formation of another adduct. Based on analysis of the corresponding g factor and hyperfine coupling constant values of the latter adduct ( g = 2.00587, αN = 13.57 G , αH = 2.27 G ), the nitrone ring has presumably been split up and an adduct was formed between α-phenylethyl radical and 4-methyl-4-nitrosopentanoic acid – a product of the oxidation of the parent spin trap by singlet oxygen. Computer modeling based on detailed reaction mechanism and fitted to the measured data confirmed this assumption. The rate constants gave values of 2.3 × 105 M −1. s −1 for the formation of the adduct and 1.0 × 104 M −1. s −1 for its decay by interaction with free radicals offering a more detailed quantitative understanding of spin trapping in the presence of tetrapyrrole photosensitizers under illumination.

Comparative investigation of superoxide trapping by cyclic nitrone spin traps: the use of singular value decomposition and multiple linear regression analysis

The kinetics of the reaction between superoxide and the spin trapping agents 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO), and 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide (BMPO) were re-examined in the superoxide-generating xanthine/xanthine oxidase system, by competition with spontaneous dismutation. The approach used singular value decomposition (SVD), multiple linear regression, and spectral simulation. The experiments were carried out using a two-syringe mixing arrangement with fast scan acquisition of 100 consecutive EPR spectra. Using SVD analysis, the extraction of both temporal and spectral information could be obtained from in a single run. The superoxide spin adduct was the exclusive EPR active species in the case of DEPMPO and BMPO, and the major component when DMPO was used. In the latter case a very low concentration of hydroxyl adduct was also observed, which did not change during the decay of the DMPO-superoxide adduct. This indicates that the hydroxyl radical adduct is not formed from the spontaneous decay of the superoxide radical adduct, as has been previously suggested [correction]. It was established that in short-term studies (up to 100 s) DMPO was the superior spin trapping agent, but for reaction times longer than 100 s the other two spin traps were more advantageous. The second order rate constants for the spin trapping reaction were found to be DMPO (2.4 M(-1)s(-1)), DEPMPO (0.53 M(-1)s(-1)), and BMPO (0.24 M(-1)s(-1)) determined through competition with spontaneous dismutation of superoxide, at pH 7.4 and 20 degrees C.

Encapsulation of p-THPP into nanoparticles: cellular uptake, subcellular localization and effect of serum on photodynamic activity

The cellular uptake, localization and efflux of meso-tetra-(4-hydroxyphenyl)porphyrin (p-THPP)-loaded nanoparticles have been studied in EMT-6 tumor cells. The effect of blood serum on photocytotoxicity has also been evaluated. Sub-130 nm nanoparticles based on poly(D,L-lactide-co-glycolide) (PLGA) (50:50 PLGA and 75:25 PLGA) and poly(D,L-lactide) (PLA) have been examined in comparison with free p-THPP. For all formulations tested, uptake of photosensitizer into cells was dependent on concentration, time and temperature. All nanoparticulate formulations accumulated within the cells to a greater extent relative to free drug. Indeed, the fluorescence intensities measured on EMT-6 cells treated with p-THPP-loaded nanoparticulate formulations were at least two-fold higher than those obtained with free dye. Furthermore, the highest accumulation level was found with PLGA nanoparticles. Fluorescence microscopy revealed that endocytosis is a major intracellular sequestration mechanism of these p-THPP formulations and that these were localized into early and late endosomes. The efflux study performed on both nonirradiated and irradiated cells indicated that free and p-THPP-loaded nanoparticles gradually escaped from EMT-6 cells as a function of time. This was more pronounced when cells were treated with nanoparticles and irradiated, reflecting important photodamage. It was also found that regardless of the nanoparticulate formulations tested, p-THPP photocytotoxicity was influenced by the concentration of the serum.

Quantitative spin trapping and triplet quenching by radicals for in vivo studies. I. The chemical model

In order to determine quantitatively the free radical content and its changes affected by additives using spin trapping under in vivo conditions, an approach is suggested carrying out experiments in a completely mixed open system (CMOS). Measurements have been carried out for a chemical oxidation process as a model system, and analysis of products and of the spin trap was extended by kinetic ESR spectrometry of the spin adducts. Since in a CMOS differential equations of accumulation of all species can be transformed into algebraic expressions using available rate constants for the formation of the spin adducts, corresponding concentrations of free radicals have been calculated. In addition, it has been established that triplet excited photosensitizers have a double effect: increasing the rate of initiation by decomposing hydroperoxide-type compounds and inhibiting the overall process by interactions with free radicals. Results indicate that by changing the "reaction vessel" the method can be applied for ex vivo and in vivo systems.