Phototransformations of porphyrins in aqueous and micellar media

Sulfonated Phthalocyanines: Photophysical Properties, in vitro Cell Uptake and Structure-activity Relationships

Aluminium phthalocyanines sulfonated to a different degree ( AlPcS n) and consisting of various isomeric species were studied by spectroscopic techniques to determine their tendencies to form dimers and aggregates. These characteristics were compared with the cell-penetrating properties of the species, using the Ehrlich ascites mouse tumor cell line, to arrive at structure-activity relationships. AlPcS n preparations consisting of the least number of isomeric species exhibited the highest tendency to form dimers and aggregates, whereas the more complex preparations, consisting of many isomeric products, showed more consistent monomeric features in aqueous environments. Uptake in cells was shown to correlate well with the overall hydrophobicity of the preparation and inversely with its degree of aggregation in the extracellular environment. Among the purified, single isomeric AlPcS n the amphiphilic disulfonated AlPcS 2a , enriched in positional isomers featuring sulfonate groups on adjacent phthalic subunits, showed the best membrane-penetrating properties. Even higher cell uptake was observed for the AlPcS 2mix reflecting a combination of optimal lipophilicity and a low degree of aggregation. Similarly, in the case of AlPcS 4, the pure isomeric compound showed less cell uptake than the mixed isomeric preparation of similar hydrophobicity, reflecting the higher degree of aggregation invoked by its symmetrical structure. Our data indicate that mixed sulfonated phthalocyanine preparations may exert higher photodynamic efficacy in biological applications as compared to the pure isomeric constituents.

Photobleaching studies on azabenzoporphyrins and related systems: a comparison of the photobleaching of the zinc(II) complexes of the tetrabenzoporphyrin, 5-azadibenzo[b,g]porphyrin and phthalocyanine systems

The kinetics of photobleaching of zinc(II) tetra-t-butyltetrabenzoporphyrin 1, zinc(II) 13,17-diethyl-12,18-dimethyl-5-azadibenzo[b,g]porphyrin 2 and zinc(II) tetra-t-butylphthalocyanine 3 are studied. In methanol containing ca 0.1% pyridine, complex 1 undergoes photoaggregation, 2 is relatively photostable, while 3 undergoes a smooth true photobleaching process with loss of intensity across the visible region. Where appropriate, apparent first-order rate constants for the photodiminution of the α band in the spectra are reported, and the effects of solvent variation and of additives are measured. It has not been possible to provide an overall rationalization of the solvent effects, but the effects of additives support the view that the photo-oxidative processes involve singlet oxygen. Experiments with potassium superoxide do not support superoxide involvement. Preparative experiments in methanol have been carried out with 1 and 3. 1 leads to a large recovery of the starting material, indicating that the photoaggregation does not involve the formation of new covalent bonds. 3 gives rise to at least five products (besides the starting material). Two of these, isolated in low yields (<5%), are identified as a fragmentation (depolymerization) product, 4-t-butylphthalonitrile, and the expected oxidative product, 4-t-butylphthalimide. The results are discussed and conclusions drawn.

Silicon nanoparticles produced by femtosecond laser ablation in water as novel contamination-free photosensitizers

We report the synthesis of novel inorganic contamination-free photosensitizers based on colloidal silicon nanoparticles prepared by laser ablation in pure deionized water. We show that such nanoparticles are capable of generating singlet oxygen ((1)O(2)) under laser irradiation with a yield estimated at 10% of that of photofrin, which makes them a potential candidate for therapeutics, antiseptics, or disinfectants. We also discuss a model of (1)O(2) generation and the possibility for optimizing its release. Potential advantages of such novel inorganic photosensitizers include stable and nonphotobleaching (1)O(2) release, easy removal, and low dark toxicity.

Milestones in the development of photodynamic therapy and fluorescence diagnosis

Many reviews on PDT have been published. This field is now so large, and embraces so many sub-specialties, from laser technology and optical penetration through diffusing media to a number of medical fields including dermatology, gastroenterology, ophthalmology, blood sterilization and treatment of microbial-viral diseases, that it is impossible to cover all aspects in a single review. Here, we will concentrate on a few basic aspects, all important for the route of development leading PDT to its present state: early work on hematoporphyrin and hematoporphyrin derivative, second and third generation photosensitizers, 5-aminolevulinic acid and its derivatives, oxygen and singlet oxygen, PDT effects on cell organelles, mutagenic potential, the basis for tumour selectivity, cell cooperativity, photochemical internalization, light penetration into tissue and the significance of oxygen depletion, photobleaching of photosensitizers, optimal light sources, effects on the immune system, and, finally, future trends.

Experimental and theoretical investigation of fluorescence photobleaching and recovery in human breast tissue and tissue phantoms

Photobleaching and recovery of 488-nm excited fluorescence from resected human breast tissue samples have been studied. Profiles of photobleaching decay were seen to be faster in cancerous tissue than in those of the normal tissue. The reverse behavior was observed in profiles of recovery after photobleaching. A theoretical model based on one-dimensional diffusion theory has been developed to provide insight into the phenomena of fluorescence during photobleaching and recovery in a multiply scattering medium such as tissue. To understand photobleaching and recovery with the help of this theoretical model, we carried out experiments with model media that were prepared with authentic fluorophores, scatterers, and absorbers. The results of these studies suggest that the fluorescence photobleaching profiles are affected more by the absorption than by the scattering properties of a turbid medium such as tissue. In contrast, the scattering properties of the medium are found to affect the fluorescence recovery profiles to a greater extent. These observations could be related to the observed difference in fluorescence photobleaching and recovery profiles of normal and cancerous breast tissues.

Spectroscopic and biological testing of photobleaching of porphyrins in solutions

The photobleaching of protoporhyrin IX (PP IX) and hematoporphyrin derivative (HpD) solutions was followed using three different methods: spectrophotometry, fluorometry and photodynamically induced cytotoxicity. The latter entails photoirradiation of HT29 human colon adenocarcinoma cells in the presence of preirradiated solutions of HpD and PP IX (lambda < or = 415 nm). The highest cytotoxicity was observed in the presence of unirradiated dye and decreased with the time of preirradiation. This decay in photocytotoxicity was further used to determine the porphyrin photobleaching kinetics in solution. For both sensitizers, quantum yields of photobleaching obtained by matching fluorescence were higher than that obtained from absorbance measurements (10 and 11 times for HpD and PP IX, respectively). This difference reflects preferential photobleaching of photolabile monomeric forms compared to aggregated. The highest quantum yield was obtained in the biological test (decay in cytotoxicity) which was 14 times higher for HpD and 30 times higher for PP IX than the quantum yield obtained from absorbance measurements. The absence of correlation between biological and fluorescence measurements has to be taken into account in the in vivo situation. Dark storage of preirradiated sensitizers (37 degrees C, 24 h) completely restored photocytotoxity for PP IX but only partially for HpD, whereas fluorescence patterns were partially restored for both sensitizers.

Spectroscopic studies of photobleaching and photoproduct formation of porphyrins used in tumour therapy

The illumination of haematoporphyrin, meso-tetraphenylporphyrin tetrasulphonate and haematoporphyrin derivative in aqueous solution causes two simultaneously occurring processes: photodegradation and the formation of stable photoproducts absorbing in the red spectral region. In the case of haematoporphyrin and its derivatives, these photoproducts have an absorption maximum around 640 nm (photoproduct 640). The former process, which is detected as the bleaching of the porphyrin absorption spectrum as well as a decrease in the fluorescence intensity, is slightly dependent on the solution pH and becomes dominant when the formation of the photoproduct reaches saturation. For the most part, the photodegradation can be explained as the opening of the porphyrin ring, leading to an increase in light absorbance in the UV region. The formation of photoproduct 640 is closely related to the aggregation state of the porphyrins, and shows a distinct dependence on the medium pH. The effectiveness of photoproduct 640 formation strongly increases in neutral and alkaline solutions, whereas the porphyrins are photostable below pH 5. The spectroscopic features of the photoproducts of haematoporphyrin and haematoporphyrin derivative, with absorption bands in the visible region, are similar to those of chlorin and/or porphyrin-chlorin linked systems. On the basis of these spectroscopic studies, it is suggested that photoproduct 640 is a chlorin-type molecule formed predominantly from the aggregates of porphyrins when photo-oxidation and photoreduction are in competition.

Singlet oxygen generation by Photofrin in homogeneous and light-scattering media

The singlet oxygen quantum yield (phi delta) for Photofrin solubilized by Triton X-100 was measured in homogeneous and light-scattering media using the photosensitized inactivation of lysozyme as an internal actinometer. Higher values of phi delta at 630 nm than at 514 nm are attributed to the formation of a far-red-absorbing photosensitizing photoproduct.