A comparative study of the photosensitizing characteristics of some cyanine dyes

The present work has been carried out to explore the potential application of cyanines in photodynamic therapy. After photosensitization, the in vitro cytotoxic and antiproliferative activity on HeLa cells of a total of 35 cy anines belonging to several chemical subgroups is explored. Most of these c yanines have never been used before in similar experimental work. From a fi rst set of experiments, it is found that none of the krypto-, oxa- and imid acyanines is photobiologically active on HeLa cells. Conversely, five thiac yanines (Thiacl-5), one rhodacyanine (Rhodac) and four indocyanines (Indoc2 , Indoc4, Indoc5, Indoc7) show photodependent cytotoxicity or antiprolifera tive effects. A more detailed study shows that out of the ten selected comp ounds, eight cyanines feature significant photodependent cytotoxic and anti proliferative effects. All possess maximum absorption ranges between 545 an d 824 nm. In particular, Rhodac, a tetramethinemeromonomethine rhodacyanine dye with an absorption maximum of 655 nm (ethanol) and a molar absorption coefficient epsilon = 108 000 shows very promising photodependent biologica l activity. In general, the measured singlet oxygen quantum yield of the se lected cyanines is low ( < 0.08) and does not correlate with the degree of photosensitization. Furthermore, the present study shows that cyanines with a partition coefficient close to 1.5 accumulate to the highest extent in H eLa cells, while the more hydrophobic compounds (e.g., indocyanines) concen trate less intracellularly. (C) 2000 Elsevier Science S.A. All rights reser ved.