22 February 2013 Effects of oxygenation on PDT efficacy as a function of reactive oxygen species formation
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Using two agents that preferentially target lysosomes for photodamage but produce different reactive oxygen species (ROS) upon irradiation, we examined effects of the degree of oxygenation on photokilling. Irradiation of the chlorin NPe6 results in a high yield of singlet oxygen but the bacteriopheophorbide WST11 forms only oxygen radicals. We found that PDT efficacy of WST11 was impaired when the ambient oxygen concentration was reduced to 1%, while that of NPe6 was essentially unaffected. These result were correlated with photobleaching effects. Use of fluorescent probes for singlet oxygen vs. OH radical revealed that photobleaching was correlated with 1O2 but not .OH formation during irradiation of solutions containing NPe6. Photoproduct formation could be followed by changes in absorbance spectra. In the presence of mercaptoethanol, different photoproducts were formed, showing that environmental factors could influence photochemical reactions.
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David Kessel, David Kessel, Michael Price, Michael Price, } "Effects of oxygenation on PDT efficacy as a function of reactive oxygen species formation", Proc. SPIE 8568, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XXII, 856802 (22 February 2013); doi: 10.1117/12.2004560; https://doi.org/10.1117/12.2004560

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