Singlet Oxygen and Hydroxyl Radicals in Photodynamic Therapy (PDT)

Principle

Method

• EPR serves as a tool to identify the generated reactive oxygen species (ROS), singlet oxygen as a non radical and the hydroxyl radical
• The activity of the photosensitizer can be quantified by the amount of generated ROS
• Schemes of irradiation can be developed to keep the ROS level constant with time
• Reactions can be followed online
• Samples can be irradiated directly in the cavity through an irradiation window

Spin Trap

• DMPO and DEPMPO for hydroxyl radicals and secondary alkyl radicals
• TMPone (2,2,6,6-tetramethyl-4-piperidone) for singlet oxygen

Irradiation of an oxygen saturated solution of methylene blue with multiple laser light flashes

ESR spectrum of DMPO hydroxyl radical adduct after 100 laser light flashes of 50 mJ, 10 Hz (MiniScope MS100).

ESR spectrum of DMPO secondary alkyl radical adduct after 1000 laser light flashes of 50 mJ, 10 Hz (MiniScope MS100).

Amount of hydroxyl radical adduct (OH) and alkyl radical adduct of DMPO dependent on the number of laser light flashes

Detailed information about EPR and photodynamic therapy (PDT)

• Hydroxyl radical generation caused by the reaction of singlet oxygen with a spin trap, DMPO, increases significantly in the presence of biological reductants.
  Nishizawa, C., Takeshita, K., Ueda, J., Mizuno, M., Suzuki, K. T., Ozawa, T., Free Radic. Res. 38(4), 385-392 (2004)
• EPR studies of the photodynamic properties of a novel potential photodynamic therapeutic agent: photogeneration of semiquinone radical anion and active oxygen species (O2o-, oOH, H2O2 and 1O2).
  Xu, S., Zhang, X., Chen, S., Zhang, M., Shen, T., Photochem. Photobiol. Sci. 2(8), 871-876 (2003).

Detailed information about photodynamic therapy (PDT)

• The present and future role of photodynamic therapy in cancer treatment.
  Brown, S. B., Brown, E. A., Walker, I., Lancet Oncol. 5(8), 497-508 (2004).
• Photodynamische Therapie. (german)
  Hirth, A., Michelsen, u., Wöhrle, D., Chemie in unserer Zeit 2/99, 84-94 (1999).

Irradiation of an oxygen saturated solution of the porphyrine Photosan® with laser light

EPR spectrum of DMPO secondary alkyl radical, which appears directly after irradiation with laser light (MiniScope MS100).

EPR spectrometers suitable for this method

	MiniScope MS300, high sensitivity
	MiniScope MS100

Accessories required for this method

• Flat cell
• Special holder SH-P which allows an always equal position of the flat cell in the cavity and therefore high reproducibility of the measurements
• Holder with fitting for mounting on the flat cell matching special holder SH-P