CHED 272 |
| Photodynamic therapy (PDT) is a cancer treatment that uses a combination of red laser light, a photosensitizing agent and molecular oxygen to bring about a therapeutic effect. Porphyrins (POR), phthalocyanines (PC), chlorins (CHL) and others are currently being used in photodynamic treatment (PDT) of tumors due to their large absorption coefficients in the 500-800 nm range. In the presence of air these will photosensitize the production of singlet oxygen and superoxide. Singlet oxygen production, the so-called Type II pathway, is claimed as the most important process which kills tumor cells. However, Type I pathways, those involving photoreduction or photooxidation of substrates, have also been proposed as photocytotoxic events in PDT, especially in hypoxic environments. Since hypoxic tissues have a reductive environment and as example of Type I pathway, in this work we show that addition of a biologically relevant reducing agent, hypoxanthine (HX), to an anaerobic mixture of the dye aluminum phthalocyanine tetrasulfonate (AlPcS4) and the quinone 2,5-dicloro-diaziridinyl-1,4-benzoquinone, DClAZQ, generates larger amounts of semiquinone upon irradiation at 680 nm. In addition, it was found that HX was photooxidized by AlPcS4 to xanthine and uric acid in the presence of DClAZQ. Furthermore, larger amounts of DClAZQ-DNA covalent adducts are formed, after irradiation at 680 nm, upon addition of hypoxanthine (HX) + AlPcS4 than in the absence of any of these two reagents. Thus, it is expected that PDT through this form of Type 1 reaction will improve its efficiency, especially for solid tumors, where hypoxic regions are abundant. |
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Undergraduate Research Poster Session
2:30 PM-4:30 PM, Monday, August 20, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Chemical Education |