Selection of proper sensitizers for photodynamic therapy on the basis of time-resolved and steady-state photothermal study

Abstract

ABSTRACT The possibility of application of natural photosynthetic pigments and their derivatives in photodynamic therapy and photodynamic diagnosis has been investigated. The triplet states of dyes are highl y photochemically active, therefore, the dyes exhibiting high efficiency of triplet states generation are usually efficient photosensitizers in photodynamic therapy. Generation of triplet states has been estimated by means of the laser induced optoacoustic spectroscopy. The type of the photoreaction was established by comparing the yield of triplet generation with and without the oxygen presence. The intersystem crossing transition from excited singlet state S 1 to triplet state T 1 is competing with fluorescence emission, therefore, the dyes with efficient triplet generation usually are not suitable for diagnosis whi ch requires a high yield of fluorescence.The chlorophyll-like pigments of prospective applications in medicine have been studied. Prelim inary selection of dye-sensitizers has been made on the basis of investigation of the same dyes in model systems (solutions) and their complexes with macromolecules. The final study has been performed for resting (healthy) and stimulated (cancerous cells models) lymphocytes. Of course, the properties of sensitizers in cells and in models are not the same, but the measurements have enabled a selection (from a set of similar molecules) of the most promising dyes, tested later in the cells. The results obtained for chlorophyll-like pigments are compared with those obtained for the synthetic dyes (porphyrins, stilbazolium merocyanines and phthalocyanines) earlier investigated in our laboratory and with literature data. Keywords: Laser Induced Optoacousic Spectroscopy, Phot odynamic Diagnosis, Photodynam ic Therapy, photosynthetic pigments, singlet stat es, steady-state photoacoustic spectroscopy, triplet states