Cyanine dyes as protectors of K562 cells from photosensitized cell damage

Several cyanine dyes were found to protect K562 leukemia cells against toxi city mediated by cis -di(4-sulfonatophenyl)diphenylporphine (TPPS2) and lig ht. Most cyanine dyes derived from dimethylindole were better photoprotecto rs than cyanine dyes with other structures. This correlated with the fact t hat cyanine dyes derived from dimethylindole were predominately monomeric a t millimolar concentrations within K562 cells, while other cyanine dyes for med aggregates. For cyanine dyes that are derived from dimethylindole and h ave absorption band wavelengths greater than 700 nm, fluorescence-energy tr ansfer from TPPS2 to the cyanine dye was the most important mechanism for p hotoprotection, There was no spectroscopic evidence for complex formation b etween the cyanine dyes and TPPS2, The dimethylindole derivative, 1,1',3,3, 3',3'-hexamethylindodicarbocyanine, was an excellent photoprotector, but a poor quencher of TPPS2 fluorescence and a relatively poor singlet-oxygen qu encher. This cyanine dye may act by quenching excited triplet TPPS2. Single t-oxygen quenching may contribute to the photoprotection provided by cyanin e dyes not derived from dimethylindole. Differences in the subcellular dist ribution of the various cyanine dyes studied may have contributed to the di fferent apparent mechanisms of photoprotection.