How promising is phototherapy for cancer?

Oncological phototherapy, including current photodynamic therapy (PDT), developmental photoactivated chemotherapy (PACT) and photothermal therapy (PTT), shows promising photo-efficacy for superficial and internal tumours. The dual application of light and photochemotherapeutic agents allows accurate cancer targeting, low invasiveness and novel mechanisms of action. Current advances in new light sources and photoactive agents are encouraging for future development

Porphyrin-Melanins interaction: effect on fluorescence and nonradiative relaxations

Optical techniques and pulsed-laser, time-resolved photoacoustics (PA) were employed to obtain information on the mechanism of interaction between cationic zinc tetrabenzilpyridilporphyrin (ZnTBzPyP) and synthetic l-Dopa melanins. Synthetic eumelanin and pheomelanin strongly quench the fluorescence of ZnTBzPyP, but Stern-Volmer plots suggest a mechanism of interaction quite different for the two pigments. This diversity was confirmed by PA: for eumelanin no thermal relaxation was observed other than prompt heat, whereas for the complexed form of ZnTBzPyP with pheomelanin we were able to detect a heat-emitting species with a non-radiative lifetime in the microsecond range. The involvement of oxygen in the photophysics of the complexes formed between the cationic porphyrin and the two pigments was demonstrated, but its role has yet to be described

Irradiation of the porphyrin causes unfolding of the protein in yhe protoporhyrin IX/Beta-Lactoglobulin noncovalent complex.

Porphyrins such as protoporphyrin IX (PPIX) are known to occasionally cause conformational changes in proteins for which they are specific ligands. It has also been established that irradiation of porphyrins noncovalently intercalated between bases or bound to one of the grooves can cause conformational effects on DNA. Conversely, there is no evidence reported in the literature of conformational changes caused by noncovalently bound PPIX to globular proteins for which the porphyrin is not a specific ligand. This study shows that the irradiation of the porphyrin in the PPIX/lactoglobulin noncovalent complex indeed causes a local and limited (similar to 7%) unfolding of the protein near the location of Trp19. This event causes the intrinsic fluorescence spectrum of the protein to shift to the red by 2 nm and the average decay lifetime to lengthen by approximately 0.5 ns. The unfolding of lactoglobulin occurs only at pH > 7 because of the increased instability of the protein at alkaline pH. The photoinduced unfolding does not depend on the presence Of 02 in solution; therefore, it is not mediated by formation of singlet oxygen and is likely the result of electron transfer between the porphyrin and amino acid residue

Photoinduced Electron Transfer Reactions within Zeolites : Detection of Radical Cations and Dimerization of Arylalkenes

Photosensitized electron transfer reactions between excited singlet acceptors and arylalkenes included within NaX zeolites have been studied using a combination of product studies, fluorescence spectroscopy, and diffuse reflectance laser flash photolysis. Steady-state and time-resolved fluorescence quenching of cyanoaromatic and ionic sensitizers by arylalkenes demonstrates that singlet quenching occurs predominantly by a static process. Diffuse reflectance flash photolysis studies indicate that quenching of singlet cyanoaromatic sensitizers by trans-anethole and 4-vinylanisole occurs via electron transfer and yields relatively long-lived radical cations. Signals due to trapped electrons (Na43+) are also observed, suggesting that photoionization of the cyanoaromatic sensitizer occurs in competition with electron transfer quenching of the excited singlet by the alkene. The long lifetimes of the radical cations indicate the utility of the zeolite environment for controlling the energy-wasting back electron transfer step. Photosensitized electron transfer reactions of five alkenes (trans-anethole, 4-vinylanisole, phenyl vinyl ether, and two indenes), using both ionic and cyanoaromatic sensitizers, lead to predominantly dimeric cyclobutane products as in solution. However, the dimer ratios are substantially different with the cis/syn cyclobutanes formed preferentially in the zeolite reactions, presumably as a result of constraints imposed by the restricted space of the zeolite supercage. In fact the zeolite environment is more important in determining the geometry of the dimeric products than is the method (direct or sensitized photocycloaddition vs radical ion initiation) for their generation.NRC publication: Ye