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British Journal of Cancer (2005) 92, 298-304.
doi:10.1038/sj.bjc.6602331 Published online 18 January 2005
Singlet oxygen luminescence as an in vivo photodynamic therapy dose metric: validation in normal mouse skin with topical amino-levulinic acid
M J Niedre1,2, C S Yu1,2, M S Patterson3,4 and B C Wilson1,2
1Department of Medical Biophysics, Ontario Cancer Institute/University Health Network Ontario, Canada
2University of Toronto, Toronto, Ontario, Canada
3Juravinski Cancer Center,Hamilton, Ontario, Canada
4McMaster University, Hamilton, Ontario, Canada
Correspondence to: BC Wilson, Department of Medical Biophysics, Ontario Cancer Institute/University Health Network, 610 University Avenue, Toronto, ON M5G 2M9, Canada. E-mail: wilson@uhnres.utoronto.ca
Received 28 June 2004; revised 25 October 2004; accepted 25 October 2004; published online 18 January 2005
Although singlet oxygen (1O2) has long been proposed as the primary reactive oxygen species in photodynamic therapy (PDT), it has only recently been possible to detect it in biological systems by its luminescence at 1270 nm. Having previously demonstrated this in vitro and in vivo, we showed that cell survival was strongly correlated to the 1O2 luminescence in cell suspensions over a wide range of treatment parameters. Here, we extend this to test the hypothesis that the photobiological response in vivo is also correlated with 1O2 generation, independent of individual treatment parameters. The normal skin of SKH1-HR hairless mice was sensitised with 20% amino-levulinic acid-induced protoporophyrin IX and exposed to 5, 11, 22 or 50 J cm-2 of pulsed 523 nm light at 50 mW cm-2, or to 50 J cm-2 at 15 or 150 mW cm-2. 1O2 luminescence was measured during treatment and the photodynamic response of the skin was scored daily for 2 weeks after treatment. As observed by other authors, a strong irradiance dependence of the PDT effect was observed. However, in all cases the responses increased with the 1O2 luminescence, independent of the irradiance, demonstrating for the first time in vivo an unequivocal mechanistic link between 1O2 generation and photobiological response.
Keywords: photodynamic therapy; singlet oxygen; luminescence; dosimetry
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