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pH‐Dependent Spectral Properties of HpIX, TPPS 2a , m THPP and m THPC ¶
Author(s) -
Čunderlíková Beata,
Bjørklund Eva G.,
Pettersen Erik O.,
Moan Johan
Publication year - 2001
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2001)0740246pdspoh2.0.co2
Subject(s) - chemistry
Lower extracellular pH in tumors as compared to normal tissues has been proposed to be a factor contributing to the tumor selective uptake of several photosensitizers. Therefore, the pH dependence of absorption and fluorescence spectral properties of four different drugs relevant for photodynamic therapy (hematoporphyrin IX [HpIX], disulfonated meso ‐tetraphenylporphine [TPPS 2a ], meso ‐tetra(3‐hydroxyphenyl)porphine [ m THPP] and meso ‐tetra(3‐hydroxyphenyl)chlorin [ m THPC]) has been examined. Spectral analysis of the dyes dissolved in phosphate buffered saline (PBS) indicates pH‐dependent modification in the physiologically important region (6.0–8.0) only in the case of HpIX. This modification is probably related to the protonation of carboxylic groups. Spectral changes of HpIX in PBS observed at acidic pH values <5, as well as those of the rest of the drugs (inflection points of titration curves occurred at about 5.1, 3.8 and 2.4 for TPPS 2a , m THPP and m THPC, respectively), are likely to be due to the protonation of imino nitrogens. The tumor localizing properties of m THPP and m THPC reported in the literature appear to be due to factors other than pH‐dependent changes in the lipophilicity of the drugs.