Spectroscopic studies of photobleaching and photoproduct formation of meta(tetrahydroxyphenyl)chlorin (m-THPC) used in photodynamic therapy. The production of singlet oxygen by m-THPC
✍ Scribed by Christophe Hadjur; Norbert Lange; Julia Rebstein; Philippe Monnier; Hubert van den Bergh; Georges Wagnières
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 902 KB
- Volume
- 45
- Category
- Article
- ISSN
- 1011-1344
No coin nor oath required. For personal study only.
✦ Synopsis
Meta(tetrahydroxyphenyl)chlorin (m-THPC) is a new photosensitizer currently undergoing clinical trials at Lausanne's CHUV hospital for photodynamic therapy (PDT) of early cancer in the upper aerodigestive tract. The illumination of m-THPC with light at 650 nm in aqueous solution containing 10% foetal calf serum (FCS) causes two simultaneously occurring processes: its photodegradation and the formation of a more stable photoproduct absorbing at 320 nm. The photodegradation quantum yield (~p6) of m-THPC is found to be of the order of 1.5 × 10-~ in 10% FCS. A strong dependence on oxygen concentration of the photodegradation and the formation of photoproducts has been observed. Indeed, the m-THPC presents rather low qbpb under N2-saturated conditions: 6.9 × 10-6. In aerobic conditions, the photodegradation as well as the formation of photoproducts, have been competitively inhibited by known singlet oxygen (~O2) quenchers. The addition of superoxide dismutase (SOD), catalase or desferal, known quenching agents of type I mechanisms, has little or no effect on the rate of photobleaching and photoproduct formation of m-THPC, m-THPC generates IO 2 with a quantum yield of 0.3 in ethanol solution as determined by photo-oxidation experiments using 1,3-diphenylisobenzofuran (DPBF) as substrate. The rate and quantum yield of DPBF photo-oxidation are found to increase with increasing substrate concentration and decrease in phosphate buffer solution (~a = 0.01), due to the partially hydrophilic character of m-THPC. In addition, the reaction of IO2 with TEMP (2,2,6,6-tetramethyl-4-piperidone) in combination with electron paramagnetic resonance (EPR) detection has been used to determine the formation of tO2 by m-THPC in ethanol solution.