Kabanov V.V
Director, Chief of Laboratory B. I. Stepanov Institute of Physics of the National Academy of Sciences of Belarus 68 Nezavisimosti Ave., Minsk, 220072 Republic of Belarus

Abstract:

The purpose of this work – research by steady and time-resolved fluorescence spectroscopy the influence of medium pH on the ionic species, aggregation and photochemical activity of one of the most promising dye for photodynamic therapy of tumors – chlorin e6 – in a free state, in the presence of detergents, as well as in the complex with the key enzyme of the glycolysis system and the Krebs cycle. It is shown that in a buffer medium chlorin e6 is an anion both in the range of physiological values of pH, and in the acidic environment characteristic for tumor cells. At pH 5.5 chlorin e6 may exist in multiple spectrally distinguishable anionic forms, differing in the position and/or the number of protonated carboxyl groups in the molecule. Transition to the acidic area contributes to aggregation of the dye, but its interaction (complexation) of enzymes causes a complete disaggregation of the pigment. Enzymes, binding with high affinity molecule sensitizers, act as the most sensitive target for photodynamic treatment. Estimates show, however, that because of the short lifetime of the singlet oxygen molecule in the cell (30–180 nsec), its diffusion path does not exceed 10–20 nm (a distance commensurable with the size of the protein molecule). Therefore, the photodynamic effect can manifest itself only in the nearest neighborhood of the sensitizer and, first of all, it will apply to the molecules that enter into the complex with this sensitizer.